29th winter inter-american photochemical society conferencebreakfast bagels and danishes will be...

I N T E R - A M E R I C A N P H O T O C H E M I C A L S O C I E T Y

29th Winter Inter-American Photochemical Society Conference

January 2-5, 2020

Lido Beach Resort, Sarasota FL

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We thank all our sponsors for their generous support of this conference,

which has allowed for an exciting and rewarding program. Look for

more sponsor information at the end of this program booklet!

Diamond

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Platinum

Gold

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Silver

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THURSDAY, JANUARY 2, 2020 Registration (Pre Function Area) 4:00 – 7:00 pm

All Talks will be held in the Royal Palm and Banyan Room Opening Comments from the Organizers, 7:00 – 7:10 pm

Gary Moore & Liz Young

SESSION 1. 7:10 – 9:00 pm

Session Chair: Linda Shimizu, University of South Carolina Amanda Morris, Virginia Tech 7:10 – 7:50 pm The Role of Spin-Orbit Coupling in Long Range Energy Transfer

through Metal Organic Frameworks

2019 I-APS Presidential Award Lecture (introduction by James McCusker) 7:50 – 7:55 pm

Leif Hammarström, Uppsala University 7:55 – 8:55 pm Molecular Mechanisms of Artificial Photosynthesis

Reception and poster session, Cypress Room, Lido Beach Resort 9:00 – 11:00 pm

FRIDAY, JANUARY 3, 2020 Breakfast bagels and Danishes will be served in the lecture hall 7:30 – 8:30 am

SESSION 2. 8:30 – 12:20 pm

Session Chair: Joel Rosenthal, University of Delaware

Paul King, National Renewable Energy Laboratory 8:30 – 9:10 am Photochemical N2 Reduction by Nanocrystal Nitrogenase Complexes

Petra Fromme, Arizona State University 9:10 – 9:50 am Investigation of the Dynamics of Light-Driven Reactions in Biology with X-ray Free Electron Lasers Coffee Break 9:50 – 10:10 am

Daniel Nocera, Harvard University 10:10 – 10:50 am Artificial Leaf and Bionic Leaf–Food and Fuel from Sunlight, Air and Water

Kristin Wustholz, William and Mary 10:50 – 11:30 am Harnessing Single-Molecule Dynamics for Photocatalysis and Multicolor Imaging

A. Jean-Luc Ayitou, Illinois Institute of Technology 11:30 – 12:10 pm Navigating the Photophysics of Non-Classical Aromatic Triplet Chromophores: Application in Light Harvesting & Triplet Sensitization

Juan (Tito) C. Scaiano, Founder of LuzChem 12:10 – 12:20 pm

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Lunch 12:20 – 2:00 pm

SESSION 3. 2:00 – 5:25 pm

Session Chair: Sarah Schmidtke Sobeck, College of Wooster

Carsten Milsmann, West Virginia University 2:00 – 2:40 pm Thermally Activated Delayed Fluorescence in Complexes of Earth-Abundant Group 4 and 14 Elements

Sergei Vinogradov, University of Pennsylvania 2:40 – 3:20 pm Magnetic Control of Phosphorescence in Multichromophoric Systems Coffee Break 3:20 – 3:40 pm

2019 I-APS Gerhard Closs Student Award Lecture 3:40 – 3:45 pm

(introduction by James McCusker)

Yishu Jiang, Northwestern University 3:45 – 4:05 pm Regio- and Diastereoselective [2+2] Photocycloaddition Photocatalysed by Quantum Dots

Julio de Paula, Lewis and Clark College 4:05 – 4:45 pm Chemistry + Archaeology + Art History

Curtis Berlinguette, University of British Columbia 4:45 – 5:25 pm Ada: A Self-Driving Lab for Accelerating the Discovery of Photovoltaic Materials Dinner 5:25 – 7:00 pm

SESSION 4. 7:15 – 9:00 pm

Session Chair: Gerald Meyer, University of North Carolina

Charles Schmuttenmaer, Yale University 7:15 – 7:55 pm THz Spectroscopy: Studying Carrier Dynamics in Nanostructured Materials for Solar Energy Conversion

2019 I-APS Award in Photochemistry Lecture (introduction by James McCusker) 7:55 – 8:00 pm

Felix Castellano, North Carolina State University 8:00 – 9:00 pm From Molecules to Materials: Triplets are Everywhere

Poster Session, Cypress Room, Lido Beach Resort 9:00 – 11:00 pm

SATURDAY, JANUARY 4, 2020 Breakfast bagels and Danishes will be served in the lecture hall 7:30 – 8:30 am

SESSION 5. 8:30 – 12:15 pm

Session Chair: Kathryn Knowles, Rochester University

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Anna Gudmundsdottir, University of Cincinnati 8:30 – 9:10 am Photomechanical Organic Crystals Produced by Molecular Gas Extrusion BGSU Distinguished Woman in Science Sponsored by the Center for Pure & Applied Photosciences at BGSU

Pravas Deria, Southern Illinois University 9:10 – 9:50 am

Excited-State Properties and Energy Transduction in Metal−Organic

Frameworks Towards Low-Density Molecular Light-Harvesting Assemblies

Coffee Break 9:50 – 10:10 am

Stephen Bradforth, University of Southern California 10:10 – 10:50 am Symmetry Breaking Charge Transfer for Rapid, Long-Lived Charge Separation

David Zigler, Cal Poly 10:50 – 11:30 am Disentangling Electron Transfer at the Dye-Semiconductor Interface to Guide Strategies in Dye Design

2019 I-APS Young Investigator Award (introduction by James McCusker) 11:30 – 11:35 am

Josh Vura-Weis, University of Illinois 11:35 – 12:15 pm What Did The Metals Know, and When Did They Know It? Femtosecond M-edge XANES Reveals Short-Lived States in Transition Metal Complexes Sponsored by Elsevier/Journal of Photochemistry and Photobiology A: Chemistry Lunch 12:20 – 2:00 pm

I-APS Business Meeting 1:30 – 1:55 pm

SESSION 6. 2:00 – 5:55 pm

Session Chair: John Swierk, Binghamton University

K. V. Lakshmi, Rensselaer Polytechnic Institute 2:00 – 2:40 pm Understanding the Mechanism of Solar Water Oxidation in Photosystem II

Rodrigo Palacios, University of Rio Cuarto 2:40 – 3:20 pm Understanding and Designing Conjugated Polymer Nanoparticles for Practical Applications Sponsored by Energy & Environmental Science Coffee Break 3:20 – 3:40 pm

Announcement and Presentation of 29th Winter Conference Poster Award Winners 3:40 – 4:00 pm

Gary Moore & Liz Young

Ksenija D. Glusac, University of Illinois at Chicago 4:00 – 4:40 pm Catalyst-Grafted Graphene Nanostructures

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2020 Nicholas J. Turro Award (introduction by James McCusker) 4:40 – 4:45 pm

Juan (Tito) C. Scaiano, University of Ottawa 4:45 – 5:55 pm The Benzyl Radical, One of Nick’s Favorites, Learns New Tricks

Banquet at Tommy Bahama's 6:30 – 10:30 pm

The banquet site is located at 300 John Ringling Blvd. It is a fifteen-minute walk from the hotel and is adjacent to St. Armand's Circle. The menu is Caribbean-style buffet and there will be vegetarian options available.

SUNDAY, JANUARY 5, 2020 Breakfast bagels and Danishes will be served in the lecture hall 7:30 – 8:30 am

SESSION 7. 8:30 – 12:10 pm

Session Chair: Valentine Vullev, University of California, Riverside

Joseph Furgal, Bowling Green State University 8:30 – 9:10 am Silsesquioxane/Siloxane Hybrid Network Polymers from Static to Photo-Active Materials

Malcolm D. E. Forbes, Bowling Green State University 9:10 – 9:50 am

Radical–Triplet Pair Interactions: New Tools for Mechanistic Photochemistry

Jean-Hubert Olivier, University of Miami 9:50 – 10:30 am Molecular Strategies to Regulate the Electronic Properties of π-Conjugated

Superstructures Coffee Break 10:30 – 10:50 am

Linda Shimizu, University of South Carolina 10:50 – 11:30 am Urea Tethered Triphenylamines and Their Formation of Regenerable Radicals

Ana Moore, Arizona State University 11:30 – 12:10 pm Grotthuss-Type Proton Wires Powered by PCET

Closing Remarks

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Abstracts

of Oral Presentations

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The Role of Spin-Orbit Coupling in Long

Range Energy Transfer through Metal Organic Frameworks

Arnab Chakraborty, William Maza, and Amanda J. Morris* Virginia Tech

Metal-organic frameworks (MOFs) are a diverse class of highly ordered and tunable nanoscale materials that are increasingly employed in several solar energy conversion schemes.

Investigation of light-harvesting and energy transfer processes within the three-dimensional framework of such nanoscopic materials results in more efficient design of biomimetic

chromophore arrays for artificial photosynthesis. Here, we present synthesis and photophysical investigation of Ru(II), Os(II), and Ir(III) polypyridyl complexes doped into 3D framework of UiO-67

MOF. MOFs were synthesized by following well established one-pot solvothermal synthetic protocol, and the powders were structurally characterized with the help of X-ray powdered diffraction (PXRD) patterns and scanning electron microscopy (SEM) images. Steady-state and

time-resolved spectroscopic techniques aided in exploring the photophysical behavior in MOFs as a function of dopant concentration. The MOFs exhibited unmatched stability under photo-

excitation. As an extension of our previously reported study of dipole-dipole energy transfer in RuDCBPY doped UiO-67 MOF, here we further explore the energy transfer process with systematic variation of MOF-incorporated chromophore as a function of spin-orbit coupling. Our recent

study reveals a substantial increase of Förster distance (R0 = 88±12Å) in OsDCBPY doped UiO-67 MOF in comparison to our previously reported RuDCBPY doped UiO-67 MOF (R0 = 22±5Å).

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Molecular Mechanisms of Artificial

Photosynthesis

Leif Hammarström* Uppsala University

Conversion of solar energy to a fuel requires a series of photo-induced charge separation steps that lead up to proton-coupled electron transfer (PCET) reactions at the catalysts for water oxidation and fuel formation. In natural photosynthesis and respiration, PCET is involved in a similar

manner. PCET is required for levelling the potentials of the sequential catalyst redox steps. It also has substantial impact on the reaction rate, due to modulations of the reaction energy barrier

as well as the strong dependence on the distance the proton has to tunnel during the reaction. For the design of efficient solar fuels production, and understanding of biological PCET, it is

therefore necessary to understand and control PCET reactions.

The introduction of proton relays in the secondary coordination sphere of molecular solar fuels catalysts has become a popular strategy to accelerate catalysis. The exact mechanism behind

the effects is often unclear, but assumed to be enhanced proton-tunneling probability in a PCET reaction. However, our work on some catalysts show that the supposed proton relay has no such

function. Instead, we use a metal-hydride catalyst model system and direct time-resolved observations to show that its proton-coupled oxidation could be accelerated by several orders

of magnitude by an internal base that facilitates proton transfer.

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Photochemical N2 Reduction by

Nanocrystal Nitrogenase Complexes

Paul King*, Katherine A. Brown, Bryant Chica, David W.

Mulder, Hayden Kallas, Jesse Ruzicka, Lance C. Seefeldt, John W. Peters, and Gordon Dukovic

National Renewable Energy Laboratory, Utah State University, University of Colorado Boulder, Washington State University

The activation and reduction of dinitrogen (N2) to ammonia (NH3) is one of the most energy

demanding and difficult chemical reactions. Nitrogenase catalyzes this chemical transformation by coupling ATP hydrolysis by the Fe protein to drive the sequential delivery of electrons to the

MoFe protein for N2 reduction. We have shown that the Fe protein can be replaced by semiconducting nanocrystals to accomplish light-driven N2 reduction by MoFe protein. The light-harvesting properties and tunability of nanocrystal photochemistry are being combined with

photochemical and biophysical approaches to study the energetic requirements for photoexcited electron injection into MoFe protein, and electron transfer and substrate reduction

chemistry at the catalytic site FeMo-cofactor. Approaches include light-driven electron paramagnetic resonance spectroscopy, and transient absorption spectroscopy to identify and

define interfacial electron transfer mechanisms and MoFe protein intermediates for the photocatalytic reduction of N2 to ammonia. Recent progress and results from these studies will be presented.

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Investigation of the Dynamics of Light-Driven Reactions in Biology with X-ray Free

Electron Lasers

Petra Fromme* Arizona State University

X-ray Free Electron Lasers (XFELs) have opened a new avenue for structural discovery of the function and dynamics of biomolecules. Processes in biology are highly dynamic and the study of their dynamics is one of the grand challenges of Structural Biology as most structures

determined so far only provide a static picture of the molecule. Serial Femtosecond Crystallography (SFX) provides a novel concept for structure determination, where X-ray

diffraction “snapshots” are collected from a fully hydrated stream of nanocrystals, using femtosecond pulses from high energy X-ray free-electron lasers (XFELs).(1-4) The XFEL pulses are

so strong that they destroy any solid material, but a femtosecond is so short (1 fs =10-15 s) that X-ray damage is diminished and diffraction from the crystals is observed before destruction takes effect.(3) Structural Biology with X-ray Free electron lasers allows data collection at near

physiological conditions at room temperature thereby opening new avenues for the study of the dynamics of light driven biomolecular reactions, where molecular snapshots of biomolecules “in

action” are recorded.(6-10) In this talk results are presented from recent experiments to study the dynamic processes in light-driven systems that includes photoreceptors as well as the key proteins

in oxygenic photosynthesis Photosystem I and II. The talk will close with a prospective of the development of compact femto and attosecond X-ray Sources at ASU (CXLS and CXFEL)(11) and at DESY (AXSIS) (12), which are highly synergistic to large XFELs and will in the future provide

new opportunities to study the ultrafast dynamics of reactions with a combination of X-ray diffraction, X-ray spectroscopy and ultrafast optical spectroscopy.

References: (1) Chapman,HN et al 2011, Nature, 470, 73-77; (2) Fromme P and Spence JC 2011 Curr Opin Struct Biol 2011, 21: 509-516; (3) Barty,A et al. 2012 Nature Photonics 6, 35–40; (4) Boutet S et al

2012, Science, 337: 362-364; (5) Liu W et al 2013, Science 342: 1521-1524; (6) Aquila,A et al 2012, Optics Express, 20 (3), 2706-16; (7) Kupitz C et al 2014, Nature 513, 261-5; (8) Young ID et al. 2016,

Nature 543, 131-135 ; (9), Suga M et al.2017, Nature 543, 131-135 ; (10) Ayyer, K. et al. Nature 2016, 530, 202-206; (11) Zhang, C et al, 9th International Particle Accelerator Conference IPAC2018,

Vancouver, BC, Canada JACoW Publishing ISBN: 978-3-95450-184-7, (12) Kartner, F.X. et al. 2016, Nuclear Instruments & Methods in Physics Research Section A -Accelerators Spectrometers Detectors and Associated Equipment, 829, 24-29.

This work is supported by the National Science Foundation BIOXFEL STC (NSF-1231306), the Biodesign Institute at Arizona State University, the Chemical Biology consortium of the National Cancer Institute, the

US National Institutes of Health (NIH), National Institute of General Medical Sciences grants R01 GM095583 and the European Research Council, “Frontiers in Attosecond X-ray Science: Imaging and Spectroscopy

(AXSIS)”, ERC-2013-SyG 609920.

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Artificial Leaf and Bionic Leaf–Food and

Fuel from Sunlight, Air and Water

Daniel Nocera* Harvard University

Hybrid biological | inorganic (HBI) constructs have been created to use sunlight, air and water (as the only starting materials) to accomplish carbon fixation and nitrogen fixation, thus providing a path to a sustainable nitrogen and carbon cycle for distributed and renewable fuels and crop

production.

The carbon and nitrogen fixation cycles begin with the Artificial Leaf, which was invented to

accomplish the solar fuels process of natural photosynthesis – the splitting of water to hydrogen and oxygen using sunlight – under ambient conditions. To create the Artificial Leaf, the oxygen

evolving complex of Photosystem II was mimicked, the most important property of which was the self-healing nature of the catalyst. Self-healing catalysts of the Artificial Leaf permit water splitting to be accomplished using any water source—which is the critical development for: (1) the

Artificial Leaf, as it allows for the facile interfacing of water splitting catalysis to materials such as silicon and (2) the Bionic Leaf, as it allows for the facile interfacing of water splitting catalysis to

bioorganisms. For the latter, a bio-engineered bacterium has been developed to convert carbon dioxide from air, along with the hydrogen produced from the catalysts of the Artificial Leaf, into

biomass and liquid fuels, thus closing an entire artificial photosynthetic cycle. The Bionic Leaf operates at unprecedented solar-to-biomass (10.7%) and solar-to-liquid fuels (6.2%) yields, greatly exceeding the 1% yield of natural photosynthesis.

Extending this approach, a renewable and distributed synthesis of ammonia (and fertilizer) at ambient conditions has been created by coupling solar-based water splitting to a carbon and

nitrogen fixing bioorganism. Nitrogen is fixed to ammonia by using the hydrogen (via carbon fixation to a polyhydroxybutyrate) produced from water splitting to power a nitrogenase in the bioorganism. When introduced into soil, the bioorganisms act as living biofertilizer, and they

increase crop yields by >150-300%. By interfacing energy with agriculture via the Bionic Leaf, we show that for a 400-acre farm there is a carbon dioxide budget saving of 125,000 lbs of CO2.

The science that will be presented will show that using only sunlight, air and water, distributed and renewable systems may be designed to produce fuel (carbon neutral) and food (carbon

negative) within sustainable cycles for the biogenic elements. Such science will be particularly useful to the poor of the world, where large infrastructures for fuel and food production are not tenable.

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Harnessing Single-Molecule Dynamics for

Photocatalysis and Multicolor Imaging

Kelly Kopera, John Li, Harrison Tuckman, and

Kristin L. Wustholz* William and Mary

The conversion of solar energy into renewable fuels using a dye-sensitized photoelectrosynthetic

cell (DSPEC) requires the efficient utilization of absorbed photons in charge transfer events as well as the minimization of unwanted losses. To minimize charge recombination losses and kinetic

redundancy in these systems, the lifetime of charge carriers can be prolonged by using dye sensitizers like Eosin Y (EY) that undergo intersystem crossing to a long-lived triplet state prior to

electron injection. However, minimizing kinetic redundancy requires understanding of the extent and origin of kinetic dispersion in the electron injection, recombination, and intersystem crossing dynamics – information that is not accessible at the ensemble-averaged level. Here, the

heterogeneous excited-state dynamics of EY photosensitizers in complex, condensed phase environments is probed using single-molecule spectroscopy (SMS). Using a combination of SMS

measurements, robust statistical analysis, and Monte Carlo simulations, we demonstrate that both triplet state decay and dispersive electron transfer consistent with the Albery model are operative. In the process of these investigations, we discovered that EY exhibits striking single-

molecule emission dynamics that can be differentiated from the dynamics of other xanthene dyes, revealing new opportunities in single-molecule-based sensing and imaging.

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Navigating the Photophysics of Non-

Classical Aromatic Triplet Chromophores: Application in Light Harvesting & Triplet

Sensitization

Guang Yang, Young Ju Yun, Nareshbabu Kamatham, and

A. Jean-Luc Ayitou* Illinois Institute of Technology

Polyaromatic chromophores are actively researched for their attractive light-harvesting and

optoelectronic properties. These chromophores constitute the main building blocks of most organic electronics and photonics devices. It is well-known that in the absence of any internal or external factor that would effectively influence spin-orbit couplings within these chromophores,

a Singlet-to-Triplet (S-T) ISC cannot occur. To promote rapid S-T ISC in heavy-atom-free -* type

polyaromatic chromophores, our group has recently introduced a novel strategy allowing to truncate the ground state intrinsic aromaticity of polyaromatics which, upon photo-excitation,

can undergo rapid ISC thanks to aromaticity reversal. Using advanced spectroscopy tools, we successfully deciphered the behavior and nature of the corresponding triplet species. Interestingly, our studies revealed that subtle changes viz. electron affinity, C-hybridization, and

additional -conjugation could be used to modulate the behavior and kinetic of the metastable

triplet species. Furthermore, we successfully employed these chromophores in light-harvesting, triplet sensitization, and photonic amplification.

My presentation will discuss the photophysical characterization and excited behaviors of the chromophores of interest. In addition, I will describe potential applications with these chromophores including our ongoing triplet-sensitization and photonic amplification research.

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Thermally Activated Delayed Fluorescence

in Complexes of Earth-Abundant Group 4 and 14 Elements

Carsten Milsmann* West Virginia University

In recent years, there has been increasing interest in the fundamental photophysics of complexes based on earth-abundant metals and their applications in photocatalysis. Matching or even

surpassing the remarkable properties of well-established precious metal photosensitizers based on ruthenium or iridium has proven a major challenge due to the distinct electronic structures of

precious versus base metals. The potential benefits of using earth-abundant metals are far-reaching and include significantly reduced cost of photochemical processes, resource

availability for large scale applications, and often reduced toxicity or improved biocompatibility due to their presence (or even essential role) in the biosphere.

The first part of this presentation will highlight the Milsmann group’s efforts to elucidate the

photophysical properties of ligand-to-metal charge transfer (LMCT) excited states in photoluminescent group 4 complexes. These molecules exhibit exceptionally long-lived triplet

LMCT excited states with lifetimes of several hundred microseconds, featuring highly efficient photoluminescence emission owing to thermally activated delayed fluorescence (TADF) emanating from the higher-lying singlet LMCT configuration. Due to their rich redox chemistry,

these complexes engage in numerous photoredox catalytic processes through excited state electron transfer.

The second part of the talk will report our efforts to enable TADF in molecular main group chromophores M(MePDPPh)2 (M = Si, Ge, Sn and MePDPPh = [2,6-bis(5-methyl-3-phenyl-1H-

pyrrol-2-yl)pyridine). These compounds readily access triplet excited states upon excitation with visible light at room temperature in solution and exhibit emission due to delayed fluorescence.

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Magnetic Control of Phosphorescence in

Multichromophoric Systems

Dmitry Andrianov, Thomas Troxler, and Sergei Vinogradov* University of Pennsylvania

The possibility to magnetically control molecular emissivity presents interests for various fields of technology and medicine. Here we present experiments exploring magnetic field effects (MFE) on phosphorescence in donor-acceptor dyads and triads based on Pt porphyrins (PtP). Our

systems were designed to undergo reversible electron transfer (ET) upon photoexcitation, generating radical pairs (RP), existing in equilibrium phosphorescent triplet states. The RPs decay

either via recombination to the ground state (singlet channel) or by forming the PtP triplet state (triplet channel) and emitting phosphorescence. The net distribution of the decay rate over the

recombination channels, and hence the phosphorescence decay lifetime and intensity, are governed by the spin dynamics in the RPs and, therefore, are sensitive to external magnetic fields. One of the designed systems was found to exhibit a particularly strong and positive MFE with the

magnitude reaching up to ~12% in the fields as low as 200 mT. The field dependence and the sign of the MFE is characteristic of the hyperfine mechanism, although at higher fields

participation of the Δg mechanism was also detected. A kinetic model has been developed that allows us to accurately reproduce the observed charge and energy dynamics in the

phosphorescent MFE-sensitive systems. Overall, this work constitutes a step towards the design of magnetically sensitive luminescent materials, which in the future may be explored in construction of biological imaging probes.

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Regio- and Diastereoselective [2+2]

Photocycloaddition Photocatalysed by Quantum Dots

Yishu Jiang*, Chen Wang, Cameron R. Rogers, Mohamad S. Kodaimati, and Emily A. Weiss

Northwestern University

Light-driven [2+2] cycloaddition is the most direct strategy to build tetrasubstituted cyclobutanes, core components of many lead compounds for drug development. Significant advances in the

chemoselectivity and enantioselectivity of [2+2] photocycloadditions have been made, but exceptional and tunable diastereoselectivity and regioselectivity (head-to-head versus head-to-tail adducts) is required for the synthesis of bioactive molecules. Here we show that colloidal

quantum dots serve as visible-light chromophores, photocatalysts and reusable scaffolds for homo- and hetero-intermolecular [2+2] photocycloadditions of 4-vinylbenzoic acid derivatives,

including aryl-conjugated alkenes, with up to 98% switchable regioselectivity and 98% diastereoselectivity for the previously minor syn-cyclobutane products. Transient absorption

spectroscopy confirms that our system demonstrates catalysis triggered by triplet–triplet energy transfer from the quantum dot. The precisely controlled triplet energy levels of the quantum dot photocatalysts facilitate efficient and selective heterocoupling, a major challenge in direct

cyclobutane synthesis.

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Chemistry + Archaeology + Art History

Julio de Paula*, Valerie A. Walters, Eugenia Rose,

and Bryan Hunter Lewis and Clark College

Atomic and molecular spectroscopy techniques familiar to physicists and chemists can be deployed in the field to provide useful information about objects recovered from archaeological

sites or manuscripts and paintings housed in churches and museums. The first part of this presentation will be a brief tutorial on archaeometry, in which physical, chemical, and biological

approaches merge with traditional archaeological methods to uncover details of ancient history and culture. The second part will describe investigations of a 16th century Book of Hours housed

at Lewis & Clark College and several 15th century paintings housed in the museum of the Church of Sant Jaume in Alcudia, Spain. The focus is on the analysis by X-ray fluorescence and Raman spectroscopy of pigments used in the paintings and the manuscript’s illustrations. We found

evidence of undocumented restoration of some of the paintings, whereas the manuscript appears to be in its original condition. The third and final part of the presentation will describe an

educational project related to our research activities: a free suite of online resources on analytical spectroscopy consisting of a textbook, video tutorials, and an inexpensive laboratory

program in English, Portuguese, and Spanish. The research and educational efforts to be described are funded in part by a grant from the Research Corporation for Science Advancement.

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Ada: A Self-Driving Lab for Accelerating the

Discovery of Photovoltaic Materials

Curtis Berlinguette* University of British Columbia

Clean energy technologies are notoriously slow to commercialize because discovering and optimizing new materials for applications typically takes over a decade. Self-driving laboratories that iteratively design, execute, and learn from experiments in a fully autonomous loop present

an opportunity to accelerate the materials discovery and optimization process. I will present here a self-driving modular robotic platform capable of optimizing thin films common to energy

conversion, storage, and conservation technologies. This materials acceleration platform (MAP) is capable of autonomously modulating the optical and electronic properties of thin films by

modifying the film composition, deposition parameters, and annealing conditions. The platform is driven by a machine learning (ML) algorithm suitable for high-dimensional optimization. We demonstrate this MAP by using it to maximize the hole mobility of organic hole transport materials

(HTMs) for use in perovskite solar cells (PSCs). An unexpected outcome of this optimization process was the finding that highly-doped HTM compositions can enhance the thermal stability

of HTM films. These results demonstrate the possibilities of using autonomous laboratories to discover organic and inorganic materials relevant to clean energy technologies.

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THz Spectroscopy: Studying Carrier

Dynamics in Nanostructured Materials for Solar Energy Conversion

Coleen T. Nemes, Brian Pattengale, and

Charles Schmuttenmaer* Yale University

Terahertz spectroscopy has proven itself to be an excellent non-contact probe of charge injection and conductivity with sub-picosecond time resolution. One may exploit this capability

to study a variety of materials, and here we choose to probe the transient photoconductivity of dye-sensitized nanostructured wide band gap semiconductors as well as lower band gap metal oxides such as WO3. These systems are of interest in the area of renewable energy research and

artificial photosynthesis.

In addition, we have recently shown that it is possible to probe a fully functioning dye-sensitized

solar cell by using patterned transparent conductive oxide (TCO) electrodes. The standard TCO electrodes transmit visible light, but reflect THz light, and are in fact often used as dichroic mirrors

in THz experiments. Our results show that it is possible to probe a DSSC while applying a bias voltage and/or under steady-state illumination. Recent results demonstrate a full 3-electrode THz-transparent spectroelectrochemical cell.

Time permitting, I will discuss recent results of THz probes of conductivity in conductive MOFs.

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From Molecules to Materials: Triples are Everywhere

Felix Castellano* North Carolina State University

The generation and transfer of triplet excitons across semiconductor nanomaterial-molecular interfaces will play an important role in emerging photonic and optoelectronic technologies and

understanding the rules that govern such phenomena is essential.(1) The ability to cooperatively merge the photophysical properties of semiconductor quantum dots, with those of well-

understood molecular chromophores is therefore paramount. CdSe semiconductor nanocrystals, selectively excited by green light, engage in interfacial Dexter-like triplet-triplet

energy transfer with surface-anchored polyaromatic carboxylic acid acceptors, thereby extending its excited state lifetime by 5 orders-of-magnitude.(2) Net triplet energy transfer also occurs from surface anchored

molecular acceptors to freely diffusing molecular solutes, further extending the triplet exciton lifetime while sensitizing singlet

oxygen in aerated solution. The successful translation of triplet excitons from semiconductor nanoparticles to bulk solution implies a general paradigm that such materials are effective

surrogates for molecular triplets.

Inspired by the notion that semiconductor nanocrystals present molecular-like photophysical

and photochemical properties, 1-pyrenecarboxylic acid (PCA)-functionalized CdSe quantum dots are shown to undergo thermally activated delayed photoluminescence.(3) This

phenomenon results from a near quantitative triplet-triplet energy transfer from the nanocrystals to PCA, producing a molecular triplet-state ‘reservoir’ that thermally repopulates the photoluminescent state of CdSe through endothermic reverse triplet-triplet energy transfer. The

resultant photoluminescence properties are systematically and predictably tuned through variation of the quantum dot–molecule energy gap, temperature, and the triplet-excited-state

lifetime of the molecular adsorbate. The concepts developed here appear to be generally applicable to semiconductor nanocrystals interfaced with molecular chromophores enabling

potential applications of their combined excited states.

References: (1) Garakyaraghi, S.; Castellano, F. N. Nanocrystals for triplet sensitization: Molecular behavior

from quantum-confined materials. Inorg. Chem. 2018, 57, 2351-2359. (2) Mongin, C.; Garakyaraghi, S.; Razgoniaeva, N.; Zamkov, M.; Castellano, F. N. Direct

observation of triplet energy transfer from semiconductor nanocrystals. Science 2016, 351, 369-372.

(3) Mongin, C.; Moroz, P.; Zamkov, M.; Castellano, F. N. Thermally activated delayed

photoluminescence from pyrenyl-functionalized CdSe quantum dots. Nat. Chem. 2018, 10, 225-230.

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Photomechanical Organic Crystals Produced

by Molecular Gas Extrusion

Anna Gudmundsdottir* University of Cincinnati

Converting external stimuli, such as light and heat, into mechanical motions has recently gone from fantasy to reality as researchers have manufactured smart materials to perform functions for sensing, molecular machinery, and medical devices. Reforming notions of fragility, single crystals have been able to replicate the hopping, expansion, and jumping seen in previously studied polymer analogues. One drawback for many mechanically responsive crystals is motions are caused by shifts between polymorphs or strains created by reactions in the crystal, which are difficult to predict reliably. This work describes crystal motions induced by nitrogen release from organic azido molecular crystals. Gas release offers a predictability advantage over other types of photomechanical crystals and these crystals could find use in medicine or in nanoscale propulsion applications. The crystalline motions have been characterized using optical microscopy and correlated to X-ray structures. The reaction mechanism was probed using laser flash photolysis with support from calculations.

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Excited-State Properties and Energy

Transduction in Metal−Organic Frameworks towards Low-Density Molecular Light-

Harvesting Assemblies

Pravas Deria*, Jierui Yu, Xinlin Li, and Karan Maindan Southern Illinois University

The light-energy conversion system in photosystem I and II defines exquisite pigment assembly

that is responsible for its unique photophysical and photochemical behaviors. Some of its unique properties include large spatial dispersion of the photo-exited state (or delocalized exciton) and

ultrafast directional energy migration to special pigment-pair (i.e. reaction center, RC) for work producing charge separation. Unlike any other solid molecular compositions, MOFs provide a unique platform within its precisely organized chromophore/linker to engineer energy

transducing functionality. The excited-state properties of MOFs, established through various steady-state and time-resolved spectroscopic experiments as well as computational

investigations, are reminiscent of the natural light-harvesting complex (LHC) antenna assembly. For example, the optically active excited states in MOFs are delocalized over multiple

chromophores, where the exciton size, energy, and dynamics are modulated by their underlying topological structures. High-density pigment assemblies in MOF also facilitate efficient energy transfer, where a molecular and topologically tuned strategy can be implemented to improve

its efficiency. Finally, the excited state energy can be transferred to complementary redox-active units, installed at the predetermined positions, driving charge-separation process like the RC of

the natural LHC.

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Symmetry Breaking Charge Transfer for

Rapid, Long-Lived Charge Separation

Stephen Bradforth*, Mark E Thompson, Laura Estergreen, Mike Kellogg, and Ali Akil University of Southern California

The approach we have taken is to couple strongly absorbing chromophores into orthogonal

dimers to drive Symmetry Breaking Charge Transfer (SBCT) and form charge-separated excited states from the initially localized excited (LE) state. A key design criterion for the SBCT studies is

that they are capable of chelating to a metal center or being fused into a dimer by linking two dyes at their meso carbons. We have found that for both Zn(dipyrrin)2 and meso-bridged BODIPY

and DIPYR compounds excitation initially gives an inter-chromophore charge separated state on the ps time scale, and that the charge-separated state lives for 0.5-2 ns.

Both BODIPY and DIPYR dimers involve an intermediate partial charge transfer state where charge density is pushed onto the meso-bridge of the dimer complex as observed in 9,9’-

bianthryl. The partial charge transfer state is facilitated by the positive overlap of the LUMO and HOMO orbitals, respectively, at the meso carbons. The HOMO orbital of the BODIPY dimer has a node at the meso carbon, so no such interaction exists, thus the BODIPY dimer is expected to

transfer an electron to form the SBCT; for the DIPYR dimers it is the LUMO that has a node and therefore a hole should be transferred to form the SBCT state in this case. Polarized pump-probe

measurements are being used investigate the directionality of the electron transfer reactions in the three types of dimer studied here.

26


What Did the Metals Know, and When Did

They Know It? Femtosecond M-edge XANES Reveals Short-Lived States in Transition

Metal Complexes

Josh Vura-Weis*

University of Illinois

X-ray absorption near edge spectroscopy (XANES or NEXAFS) is a powerful technique for electronic structure determination. Recent developments in extreme ultraviolet (XUV) light

sources using the laser-based technique of high-harmonic generation have enabled core-level spectroscopy to be performed on femtosecond to attosecond timescales. We have extended the scope of tabletop XUV spectroscopy and demonstrated that M2,3-edge XANES,

corresponding to 3p→3d transitions, can reliably measure the electronic structure of first-row transition metal coordination complexes with femtosecond time resolution. We use this ability to

track the excited-state relaxation pathways of photocatalysts and spin crossover complexes. The spin selectivity of M-edge XANES is an especially good diagnostic of intermediate states in Fe(II)N6

dynamics. This work establishes extreme ultraviolet spectroscopy as a useful tool for mainstream research in inorganic, organometallic, and materials chemistry.

27


Understanding the Mechanism of Solar

Water Oxidation in Photosystem II

K. V. Lakshmi* Rensselaer Polytechnic Institute

The solar water-splitting protein complex, photosystem II (PSII), catalyzes one of the most energetically demanding reactions in Nature by using light energy to drive a catalyst capable of oxidizing water. The water oxidation reaction is catalyzed by the tetramanganese-calcium-

oxo (Mn4Ca-oxo) cluster in the oxygen-evolving complex (OEC) of PSII which cycles through five light-driven charge-storage or S-state intermediates (S0-S4). However, a detailed mechanism of

the reaction remains elusive as it requires knowledge of the binding and activation of substrate water molecules in the higher S-state intermediates of the OEC. We are developing state-of-the-

art two-dimensional (2D) hyperfine sublevel correlation spectroscopy methods to probe the S state intermediates of the water oxidation reaction. In this presentation, I will describe ongoing studies in our laboratory to elucidate the mechanism of the delivery and binding of substrate

water at the Mn4Ca-oxo cluster in the S2 and S3 states that the OEC that has important implications on the mechanistic models for water oxidation in PSII.

This study is supported by the Photosynthetic Systems Program, Office of Basic Energy Sciences, United States Department of Energy (DE-FG02-07ER15903).

28


Understanding and Designing Conjugated Polymer Nanoparticles for Practical

Applications

Rodrigo Palacios* University of Rio Cuarto

Conjugated polymers (CPs) are organic semiconductors of great relevance due to their application in organic-electronic devices, such as solar cells, light emitting diodes, and field effect transistors, among others. It is generally accepted that electronic excitations in CPs are

localized in relatively short segments (5-12 monomers) called quasi-chromophores that act largely independently, so that a polymer chain can be considered as a multicromophoric

system. Thus, the performance of CP-based devices depends to a large extent on elementary photoinduced energy transfer (ET) processes that occur between these quasi-chromophores

and dopants or impurities present in the polymer matrix. In particular, the efficiency of ET from CP to dopant is associated with a benchmark parameter named Antenna Effect (AE). Conjugated polymer nanoparticles (CNP) are nanostructured systems that can be manufactured controlling

particle size as well as the amount and spatial distribution of dopant dyes. This allows their use as model systems for the study of confined ET processes and also for their use in a series of practical

applications that critically depend on AE.

In this talk I will describe our work in the development of doped CNP and in the characterization

of intraparticle ET processes using conventional spectroscopic techniques, measurements of single particle fluorescence and computational modeling. Through the modeling of experimental measurements, the influence of several parameters on the ET process and on the

AE was determined, such as: quantity and location of dopants and traps, exciton diffusion length and particle size.(1) The knowledge obtained allowed the optimization of CNP for applications

where efficient photoexcitation of "photoactive" molecules is required. To discuss some applications of these materials I will summarize our work in the development of CNP as efficient photosensitizers of reactive oxygen species (2) and their successful use in photodynamic therapy

protocols against brain and colorectal cancer cells (3) and in photodynamic inactivation of antibiotic-resistant bacteria of clinical relevance (4). Finally, I will describe our recent work using

CNP as efficient macro-photoinitiators of vinyl polymerization to form biocompatible macro and nano hydrogels in aqueous media in the absence of co-initiators.

References: (1) Ponzio, R.A. et al. J. Phys. Chem. C. To be submitted (2019). (2) Spada, R. M. et al. Dyes Pigments 149, 212–223 (2018).

(3) Ibarra, L. E. et al. Nanomed. 13, 605–624 (2018). (4 )Martinez, S.R. et al. ACS Infectious Diseases. To be submitted (2019).

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Catalyst-Grafted Graphene Nanostructures

Ksenija D. Glusac* University of Illinois at Chicago

Combining efficient molecular catalysts with photochemically active nanocarbon structures

prepared via bottom-up synthetic approaches represents a new class of materials for artificial photosynthesis. Here, we present a study of photoinduced energy and electron transfer in

molecular assemblies composed of graphene quantum dots (GQDs) and Co-coordinated graphene quantum dots. First, the exciton size and dynamics of two GQD assemblies of varying sizes were investigated using time-resolved laser spectroscopy and computational methods. The

results of this study show that the molecular assemblies exhibit exciton coherence lengths of only 1-2 monomeric units, indicating that the ballistic energy transport is not likely to take place. The

exciton-exciton annihilation studies have shown that the excitons have high mobilities along the aggregate. However, fast trapping of excitons limits the diffusion lengths to 16 and 3 nm. The results are discussed in terms of resonance energy transfer model. The photophysical behavior of

GQDs that contain Co-based hydrogen-evolving catalysts was also investigated. The Co-GQD structures preserved the electrocatalytic behavior of Co-based models, while the

photochemical behavior is consistent with the efficient photoinduced electron transfer from GQD to the Co-center. The results of this study are expected to be relevant to the scientific

community studying solar energy conversion.

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The Benzyl Radical, One of Nick’s Favorites,

Learns New Tricks

Juan (Tito) Scaiano* University of Ottawa

For many years the benzyl radical was Nick Turro’s work horse. From photochemistry, to decarbonylations, cage effects, EPR studies and magnetic fields, the versatile benzyl radical could do no wrong. I was fortunate to overlap with Nick in some of these studies and share the

excitement. By the time our teenage book was finally published, Nick had conveyed his contagious interest on the rich chemistry of this innocent-looking free radical.

The Norrish Type I reaction provides the conventional, predictable and reliable source for many radicals, formed in pairs, benzyl included. Now, can you find a free radical source to make just

one organic free radical? Transition metal complexes provide a redox route to do just that, but at the expense of abundant precursor-derived debris. In contrast, semiconductors (e.g., TiO2) can be tamed to do the job, making a desirable radical, with just H2 as the debris. What is more,

photogenerated holes can be strongly electrophilic and capable of making benzyl radicals efficiently from otherwise unreactive sources such as toluene, xylenes and mesitylene. These are

good radical precursors for this semiconductor-initiated chemistry.

The recombination of benzyl radicals to give 1,2-diphenylethane may look as boring as free

radical chemistry could possibly be. But have another look, give benzyl something to bite on, tell it to be persistent, and suddenly it will only settle for unusual unpredictable chemistry, making sp3-sp2 bonds that were not in the repertoire before.

Surely Nick would approve of his favorite radical coming out of retirement to do new tricks and showing us that even innocent-looking species can give us surprises and keep us entertained for

a long time.

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Silsesquioxane/Siloxane Hybrid Network

Polymers from Static to Photo-Active Materials

Joseph C. Furgal*, Nai-hsuan Hu, Buddhima Rupasinghe, Herenia Espitia Armenta, Chamika Lenora, Shahrea

Mahbub, and Mahmud Rashed Bowling Green State University

High surface area materials are of considerable interest for gas storage/capture, molecular sieving, catalyst supports, slow release drug delivery systems and as scaffolds for photo re- arrangeable/healable materials. We have developed a simple and fast route to very high

surface area, mechanically robust, hydrophobic polymer networks prepared by fluoride catalyzed hydrolysis of mixtures of RSi(OEt)3 and bis-triethoxysilylalkanes (i.e. BTSE) at room

temperature. These materials offer specific surface areas up to 1300 m2/g, tunable pore sizes and thermal stabilities above 200 °C. The polymerization times and surface areas can be controlled

by adjusting the solvent (type and volume), catalyst (as nBu4NF) and the various cross-linking components. We have also synthesized and characterized a series of photo-responsive materials with “active” cross-linkers in place of BTSE and R-group fillers based on hexaarylbisimidazole

(HABI), metal ion coordination, and photo-isomerizable structures. With these cross-linkable groups we are able to change pore geometries to expel fluids or other analytes, and/or

decompose the material on-demand to reform it later. These materials can find use in healable polymers, capture and release systems and for molecular separations.

32


Radical–Triplet Pair Interactions: New Tools

for Mechanistic Photochemistry

Malcolm D. E. Forbes*, and Fengdan Zhao Bowling Green State University

The utility and importance of time-resolved magnetic resonance methods for the investigation of photochemical reaction mechanisms cannot be overstated. Both organic and inorganic photoexcited states often lead to free radicals that have strong chemically induced electron

spin polarization (CIDEP), easily detected on the sub-microsecond time scale using time–resolved (CW) electron paramagnetic resonance spectroscopy (TREPR). Of the four known CIDEP

mechanisms (radical pair mechanism (RPM), spin–correlated radical pair mechanism (SCRPM), triplet mechanism (TM), and radical–triplet pair mechanism (RTPM), the latter is by far the least

understood theoretically but may, in the end, prove to be the most useful of all of them. Radical-triplet pairs involve electron spin state mixing and sometimes quenching of triplet states by stable doublet state free radicals such as nitroxides. The RTPM is attractive for investigation of excited-

state and radical dynamics for reasons: 1) the process is overall non-destructive, i.e., the triplet and the nitroxide eventually return to their electronic ground states with Boltzmann spin state

populations, and 2) the resulting spectrum reports spin state information from the unobserved excited triplet state through the nitroxide, the intensity of which can be related to encounters

between the two, driven by translational motion. Simultaneously, the recorded TREPR spectrum of the nitroxide contains line shape information related to rotational motion. The ability to observe and record both types of motion, especially in heterogeneous systems such as micelles, vesicles,

bubbles, and emulsions is highly advantageous, particularly when one notes that polarity and order parameters can also be extracted by spectral simulation. In this talk I will give an overview

of all four CIDEP mechanisms and introduce the intricate features of the RTPM, with examples from my laboratory and others to show how structural, dynamic and kinetic information can be obtained in both organic and inorganic systems. I will use this overview as a platform to suggest

new pathways that can exploit the RTPM for the investigation of more complex systems such as dye-sensitized solar cells, structured fluids, and the physiochemical properties of commercially

important polymers.

33


Molecular Strategies to Regulate the

Electronic Properties of π-Conjugated Superstructures

Kaixuan Liu, Victor Paulino, Arindam Mukhopadhyay, Brianna Bernard, Chuan Liu, and Jean-Hubert Olivier*

University of Miami

As a product of the dynamic equilibrium between solubilized building blocks and self-assembled

structures, supramolecular architectures are fragile compositions where minor changes in temperature, solvent dielectric, and building-block concentration can trigger the dismantlement of superstructures and a concomitant loss of the emergent properties associated with them.

Undeniably, developing molecular strategies to covalently polymerize superstructures can provide entirely new nanoscale platforms with which to elucidate structure-function properties

that remain elusive by current supramolecular methodologies. We will introduce the design

principles to tether 1-dimensional supramolecular polymers built from -conjugated subunits

using molecular lockers that differ in length and structural rigidity. Confirmed by atomic force microscopy and transmission electron microscopy, organic nanomaterials created in this manner

are best characterized by a nanowire morphology than span the nano-to-mesoscale dimensions suggesting that conformation of supramolecular 1D assemblies can be captured. We will show

that modifying the structure of molecular locks provides new avenues to regulate excitonic coupling between neighboring units by design. Furthermore, investigation of the electronic

properties of length-sorted nanowires exploiting spectroelectrochemical measurement methods reveals a non-negligible stabilization of the energy of the conduction band with respect to that of the parent, non-polymerized self-assembly. It is important to note that the presented strategy

delivers a new tool to not only capture conformation of supramolecular assemblies but also to enforce the formation of emergent electronic properties not accessible in pristine, non-covalent

assemblies.

34


Urea Tethered Triphenylamines and Their

Formation of Regenerable Radicals

Ammon J. Sindt, Baillie A. DeHaven, Dustin W. Goodlett,

and Linda S. Shimizu* University of South Carolina

Stable organic radicals have important applications as molecular magnets, probes in biological systems, polarizing agents and radical initiators for polymerization; however, they are rare and

limited to specific structural families. Self-assembly potentially affords an easy strategy for stabilizing organic radicals outside the known structural classes.

Herein, we examine the effect of assembly on the stability of photogenerated radicals of urea tethered triphenylamines. Triphenylamine containing bis-urea macrocycles and urea tethered

linear analogues were synthesized and their crystal structures determined. These crystalline materials control the distinct microenvironments around the photoactive groups. Upon excitation in solution, triphenylamines with unsubstituted para-positions form radical cations that rapidly

degrade through pathways such as benzidine formation. Upon UV-irradiation of the crystalline assemblies, both linear and macrocyclic systems display remarkably persistent and regenerable

radicals. Advantageously, the triphenylamine bis-urea macrocycles assemble into columnar structures affording porous organic materials. Upon activation these crystals undergo guest exchange in single-crystal-to-single-crystal transformations generating a series of isoskeletal host-

guest complexes that can be directly compared. We are investigating the factors that influence the quantity of radicals formed and are evaluating the stability of these radicals. In particular,

we probe the microenvironment around the chromophores, compare their rigid supramolecular network and evaluate their structures using EPR, magic angle spinning (MAS) C-13 and Xe-129

NMR.

35


Grotthuss-Type Proton Wires Powered by PCET

Ana L. Moore*, Thomas A. Moore, Gary F. Moore, Devens Gust, Emmanuel Odella, S. Jimena Mora, and Brian L.

Wadsworth Arizona State University

Inspired by an iconic PCET process in photosynthesis, a benzimidazole-phenol(BIP) system illustrates an E1PT process (one-electron oxidation results in the transfer of one proton), which has

been described theoretically by a concerted mechanism.(1) We have shown that PCET can also drive a one-electron two-proton PCET reaction, known as an E2PT process, in amino- or imino-

substituted BIPs upon electrochemical oxidation of the phenol and that strategic substitutions at ~12 Å from the phenol can control the process (E1PT or E2PT).(2-3) Aiming at long-range proton translocation, we designed and synthesized constructs consisting of a phenol, a Grotthuss-type

hydrogen-bonded network based on a polybenzimidazole covalent framework, and a terminal proton acceptor. Translocation of protons up to ∼16 Å was observed to occur by an E4PT process

in this construct.(3) In all cases, infrared spectroelectrochemistry was used to demonstrate that upon oxidation of the phenol, protons translocate across a well-defined hydrogen-bonded

network to the terminal proton acceptor. The objectives of this study include determining how many proton transfers can be associated with a simple oxidation in a PCET process and how to manage the thermodynamic consequences of such processes. In the long term, we are planning

the construction of molecular proton wires where proton transport across lipid bilayers (~30Å) would generate proton-motive force (PMF) in conjunction with photochemically induced PCET.

These constructs provide a path towards artificial photosynthesis in which PCET-based proton management plays a role in efficient catalysis in both oxidative and reductive processes.

References:

(1) Mora, S. J.; Odella, E.; Moore, G. F.; Gust, D.; Moore, T. A.; Moore, A. L., Proton-Coupled Electron Transfer in Artificial Photosynthetic Systems. Acc. Chem. Res. 2018, 51, 445-453.

(2) Huynh, M. T.; Mora, S. J.; Villalba, M.; Tejeda-Ferrari, M. E.; Liddell, P. A.; Cherry, B. R.; Teillout, A.-L.; Machan, C. W.; Kubiak, C. P.; Gust, D.; Moore, T. A.; Hammes-Schiffer, S.; Moore, A. L.,

Concerted One-Electron Two-Proton Transfer Processes in Models Inspired by the Tyr-His Couple of Photosystem II. ACS Cent. Sci. 2017, 3, 372-380.

(3) Odella, E.; Mora, S. J.; Wadsworth, B. L.; Huynh, M. T.; Goings, J. J.; Liddell, P. A.; Groy, T. L.;

Gervaldo, M.; Sereno, L. E.; Gust, D.; Moore, T. A.; Moore, G. F.; Hammes-Schiffer, S.; Moore, A. L., Controlling Proton-Coupled Electron Transfer in Bioinspired Artificial Photosynthetic Relays.

J. Am. Chem. Soc. 2018, 140, 15450-15460. (4) Odella, E.; Wadsworth, B. L.; Mora, S. J.; Goings, J. J.; Huynh, M. T.; Gust, D.; Moore, T. A.; Moore,

G. F.; Hammes-Schiffer, S.; Moore, A. L., Proton-Coupled Electron Transfer Drives Long-Range Proton Translocation in Bioinspired Systems. J. Am. Chem. Soc. 2019, 141, 14057-14061.


36

Abstracts

of Posters presentations

1 Supramolecular Assay for Carbonic Anhydrase Enzymes Inhibitors

Petr Koutnik Elena G. Shcherbakova, Tsuyoshi Minami, Tsukuru Minamiki, Yui Sasaki,

Shizuo Tokito, and Pavel Anzenbacher – Department of Chemistry, Bowling Green State University; Research Center for Organic Electronics, Yamagata University

Supramolecular chemistry with its emphasis on molecular association and ligand binding is an ideal tool to investigate enzyme-ligand interactions. Carbonic anhydrases (CAs) are a family of enzymes, which catalyze conversion of carbon dioxide and water to bicarbonate and protons while maintaining acid-base balance in blood and tissues. CAs are metalloenzymes comprising Zn(II) in their active center. This

Zn(II) center coordinates sulfonamide moiety, a feature utilized in the design of CA inhibitors. The clinical application of CA inhibitors include the treatment of a wide spectrum of diseases such as glaucoma, epilepsy, stroke, cancer, etc. In this poster presentation we will describe how sulfonamide inhibitors associate with CA and how this feature is utilized in the design of fluorescent supramolecular sensing ensembles useful in evaluation of the efficacy of the enzyme inhibitors.

2 Bridging Concepts Between Heterogeneous-, Homogeneous-, and Bio-Catalysis to Model Photoelectrosynthetic Reactions

Brian L. Wadsworth, Edgar A. Reyes Cruz, Nghi Nguyen, Daiki Nishiori, Anna M. Beiler, and Gary F. Moore – Arizona State University, School of Molecular Sciences and the Biodesign Institute

Although the benchmarking and modeling of molecular electrocatalysts and enzymes are well

developed, such efforts have not been as rigorously extended to describe photoelectrochemical assemblies featuring molecular catalysts immobilized on light-absorbing semiconductor surfaces. In this poster presentation, I will highlight kinetic models describing the interplay between light absorption, charge transfer, and catalytic activity in molecular-modified semiconductors [1-4] where, in addition to

37

chemical substrates, both electrons and photons are required reagents (Figure 1). The kinetics associated with these hybrid materials are modeled using pre-equilibrium or steady-state approximations, yielding analytical expressions that are similar in form to those applied in studies involving classic enzymatic reactions and Michaelis−Menten-type kinetic analyses. This work forges a link between kinetic models used to describe heterogeneous-, homogeneous-, and bio-catalytic systems.

(1) Beiler, A. M.; Khusnutdinova, D.; Wadsworth, B. L.; Moore, G. F. Cobalt Porphyrin-polypyridyl Surface Coatings for Photoelectrosynthetic Hydrogen Production. Inorg. Chem. 2017, 56, 12178–12185.

(2) Wadsworth, B. L.; Khusnutdinova, D.; Moore, G. F. Polymeric Coatings for Applications in Electrocatalytic and Photoelectrosynthetic Fuel Production. J. Mater. Chem. A. 2018, 6, 21654–21665.

(3) Khusnutdinova, D.; Wadsworth, B. L.; Flores, M.; Beiler, A. M.; Reyes Cruz, E. A.; Zenkov, Y.; Moore, G. F.

Electrocatalytic Properties of Binuclear Cu(II) Fused Porphyrins for Hydrogen Evolution. ACS Catal. 2018, 8, 9888–9898.

(4) Wadsworth, B. L.; Beiler, A. M.; Khusnutdinova, D.; Reyes Cruz, E. A.; Moore, G. F. Interplay between Light Flux, Quantum Efficiency, and Turnover Frequency in Molecular-Modified Photoelectrosynthetic Assemblies. J. Am. Chem. Soc. 2019, 141, 15932–15941.

3 The Effect of the Trifluoropropynyl Ligand on Emissive Platinum Complexes

Mary Jo McCormick, Rhodes Hambrick, and Paul S. Wagenknecht – Department of Chemistry, Furman University

Alkynyl PtII complexes of the type Pt(tbbpy)(C2R)2 have been investigated as phosphors for organic light emitting diodes (OLEDs). The design of blue emitters with high emission quantum yields is an active area of research. In order to observe the effects of the trifluoropropynyl ligand (C2CF3) on the photoluminescence of platinum complexes, Pt(tbbpy)( C2CF3)2 (tbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine) was synthesized in two steps via a dichloro- precursor. Photophysical properties of the complex were studied using steady-state fluorescence and UV/Vis spectroscopy. The emission of Pt(tbbpy)( C2CF3)2 is

blue-shifted (max = 488 nm) relative to a widely studied analog, Pt(tbbpy)(CCPh)2 (max = 536 nm). The

strong electron-withdrawing properties of the trifluoropropynyl ligand are thought to be responsible for this shift in emission. Self-quenching of the emission is observed; emission intensity does not increase

linearly with concentration. At higher concentrations, an excimer emission (max = 613 nm) is also observed in dichloromethane. Consequently, a saturated solution of the chromophore in

dichloromethane exhibits white emission due to the combination of the luminescence of the excimer and the observed complex.

4 Self-Regulating Photochemical Rayleigh-Bénard Convection Using a Highly-Absorbing Organic Photoswitch

Serena Seshadri, Luke F. Gockowski, Jaejun Lee, Miranda Sroda, Matthew E. Helgeson, Javier Read de Alaniz, and Megan T. Valentine – Department of Chemistry, Department of Mechanical Engineering and Department of Chemical Engineering, University of California Santa Barbara

Autonomous control of liquid motion is vital to the development of new actuators and pumps in fluid systems. Recently, light has been recognized as a formidable tool for non-invasive, wavelength-selective, remote control over liquid motion with high spatial and temporal resolution. In this work, we identify unique features of a donor acceptor Stenhouse adduct (DASA), a highly-absorbing negatively

38

photochromic molecular switch, that enable its use for the control of fluid velocity. The balance between convective mass transport and the tunable rate of the back reaction of DASA offers a unique handle by which we can control the self-regulatory properties of the system. For solvents in which DASA 3.0 has a fast back reaction, the dynamic steady state achieved in solution produces a self-regulating thermal gradient that can drive fluid flow at a constant velocity. In solvents in which DASA bleaches rapidly and has a slow back reaction, it operates as an effective “off-switch” after the solution has entirely bleached and the thermal gradient dissipates. Leveraging features of DASA’s chemical properties and solvent-dependent reaction kinetics, we demonstrate its use for photo-controlled Rayleigh-Bénard convection

to generate dynamic, self-regulating flows with unparalleled fluid velocities (~mm s-1) simply by illuminating the fluid with visible light. The exceptional absorbance of DASAs in solution, uniquely controllable reaction kinetics and resulting spatially-confined photothermal flows present exciting opportunities for optofluidics applications requiring tunable flow behavior.

5 Investigating the Concentration Dependence and Charge-Separation of Donor –Acceptor Stenhouse Adducts

Miranda M. Sroda, Friedrich Stricker, Alexandria Bernal, and Javier Read de Alaniz – Department of Chemistry, University of California Santa Barbara

Negative T-type photochromism is a powerful concept for designing optimized molecular photoswitches

for soft materials applications, allowing enhanced light penetration. Donor-acceptor Stenhouse adducts (DASAs) are a novel class of easily accessible photochromic molecules exhibiting promising properties such as high molecular contraction, visible light absorption and negative photochromism. In collaboration with the Bardeen group, we recently reported the unusual concentration dependence of a third generation DASA. Understanding and overcoming the concentration of DASAs will be essential for incorporating DASAs into materials. For example, the development of organic photomechanical materials requires high photochrome concentrations because the work density should be highly influenced by the photochrome density. In this work, we continue to investigate the driving force behind the increasing thermal back reaction and reveal the varying degree of concentration dependence within DASAs. Based on these studies, we hypothesize the concentration dependence of DASAs is correlated to the ionic character of the open ground state structure and is likely due to ionic character interference with the ground state electrocyclization stage of the isomerization. The effects of solution-state dielectric and intermolecular interactions on the degree of charge separation provides insight into the switching properties, specifically the solvatochromatic shifts which correlate with concentration dependence of DASAs in solution. Furthermore, using external dopants such as ionic liquids or water we can control the back reaction kinetics, in order to either mimic (increase rate of thermal back reaction) or overcome the concentration dependence (decrease rate of thermal back reaction). This work sets a foundation for better understanding the important factors that govern DASA switching kinetics. As well as setting design considerations for DASAs able to switch at high concentrations making them a viable candidate for photomechanical actuation.

6 Addressing the Origin of Photocurrents in Photoelectrosynthetic Assemblies Containing Light-absorbing Catalysts

39

Nghi Nguyen, Brian L. Wadsworth, Daiki Nishiori, Anna M. Beiler, and Gary F. Moore – Arizona State University, School of Molecular Sciences and the Biodesign Institute

Direct integration of electrocatalysts with photovoltaics provides a strategy for photoelectrochemically powering endergonic chemical transformations and storing intermittent solar energy as fuels. [1-4] However, many electrocatalytic components used in such hybrid assemblies also absorb visible light. This raises the questions: to what extent do electrocatalytic coatings screen photons from reaching the underlying photovoltaic, do excited-state species associated with coating layers contribute to photocurrent production via mechanisms involving dye-sensitization processes, and are relatively high or low loadings of catalytic sites preferred? In this poster presentation, I will highlight how surface-characterization methods coupled with optical and electrochemical techniques can address the origin of photocurrents in photoelectrosynthetic assemblies composed of cobalt porphyrin catalysts interfaced with gallium phosphide semiconductors featuring polypyridyl surface coatings (Figure 1). This approach highlights a general yet useful strategy for better understanding the fuel-production activity of photoelectrosynthetic assemblies containing molecular catalyst that absorb visible light.

(1) Moore, G. F.; Brudvig, G. W. Energy Conversion in Photosynthesis: A Paradigm for Solar Fuel Production. Annu. Rev. Condens. Matter Phys. 2011, 2, 303−327.

(2) Beiler, A. M.; Khusnutdinova, D.; Wadsworth, B. L.; Moore, G. F. Cobalt Porphyrin-polypyridyl Surface Coatings for Photoelectrosynthetic Hydrogen Production. Inorg. Chem. 2017, 56, 12178–12185.

(3) Wadsworth, B. L.; Beiler, A. M.; Khusnutdinova, D.; Reyes Cruz, E. A.; Moore, G. F. Interplay between

Light Flux, Quantum Efficiency, and Turnover Frequency in Molecular-Modified Photoelectrosynthetic Assemblies. J. Am. Chem. Soc. 2019, 141, 15932–15941.

(4) Wadsworth, B. L.; Khusnutdinova, D.; Urbine, J. M.; Reyes, A. S.; Moore, G. F. Expanding the Redox Range of Surface-immobilized Metallocomplexes using Molecular Interfaces. Appl. Mater. Interfaces, 2019, Accepted. DOI: 10.1021/acsami.9b15286.

7 Excited-State Chemistry and Photostability of Anthraquinone-Based Dyes

Yukin Jin, Leah Bowers, Meg Heller, Elliott Detrich, and Sarah J. Schmidtke Sobeck – Department of

Chemistry, The College of Wooster

The light stability of anthraquinone-based dyes and pigments can vary significantly across this class of dyes and depending upon the dye preparation or environment. Our studies focus on the impact of structural variations and local environment on the photo-stability and degradation mechanisms for anthraquinone-based dyes. Two case studies are presented. First the excited state energetics and photochemistry are compared for purpurin and alizarin. Secondly the long-term photodegradation of carminic acid is assessed under different pH conditions to assess the lightfastness for different hues. In the first case study, alizarin and purpurin provide a model set to evaluate how substituents on the anthraquinone core impact photostability. The color loss, traced spectroscopically throughout UV-irradiation, is fit to unique kinetic models for alizarin and purpurin indicating that the dyes follow different degradation mechanisms and rates vary with pH. The experimentally determined fluorescence lifetimes and computationally modeled excited state energetics for alizarin are consistent with an excited state proton transfer process, but not for purpurin. This process is thought to provide an efficient means for

alizarin to return to its stable ground state following UV-excitation and results in better lightfastness relative to purpurin. The results provide context for our investigations of the photo-degradation of carminic acid including assessment of the degradation mechanism and products. The degradation of carminic acid

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and formation of photoproducts are traced using HPLC, and combined with LC-MS and NMR characterization to propose a breakdown mechanism. The investigations allow a broader understanding of the impact of structural modifications and environment on the photochemistry of anthraquinone dyes. This can inform preservation methods, analysis of objects for original composition, and potential new applications for this class of dye materials.

8 Photoinitiated PCET in Ir(III) Hydroamination Photocatalysts

Robert R. Knowles, Ana L. Moore, Thomas A. Moore, Emmanuel Odella, Hunter Ripberger, Hannah J.

Sayre, and Gregory D. Scholes – Department of Chemistry, Princeton University; School of Molecular Sciences, Arizona State University

Proton coupled electron transfer (PCET) is a critical step in photocatalytic hydroamidation reactions. A hydrogen atom donor, benzimidazole phenol (BIP) was tethered to an Ir(III) photocatalyst to accelerate

the rate of PCET. The rate of PCET, monitored with time-resolved IR spectroscopy, occurs on the picosecond timescale. The long-lived charge separated state was observed with visible transient absorption spectroscopy. Increasing the rate of PCET has improved hydroamidation yields.

9 Investigating the Binding Sites for Small Molecules in the Sodium Deoxycholate Hydrogel using Fluorescence Quenching

Ankur A. Awasthi and Cornelia Bohne – Department of Chemistry, University of Victoria

Our objective is to determine how many microenvironments are accessible to hydrophobic guests in sodium deoxycholate (NaDC) hydrogels. We assumed that hydrogels have two regions for guests to

reside in, an entrapped water phase and a gel network. We used pyrene as a polarity sensitive probe. The ratio between I and III peaks (I/III) in the pyrene emission spectrum reveals the polarity of the microenvironment around this probe. Steady-state and time-resolved fluorescence experiments helped us determine the accessibility of quenchers to excited pyrene in various sites of the gel. All experiments were done at constant ionic strength as an ionic quencher, iodide, was used. Steady-state data show that pyrene was quenched more efficiently in hydrophilic sites, as the I/III ratio decreases with increasing quencher concentrations. Time-resolved data revealed three different lifetimes for pyrene located in NaDC hydrogels. The shortest lifetime was assigned to pyrene in the aqueous region of the gel where excited pyrene is quenched most efficiently. The longest unquenched lifetime was assigned to pyrene in the gel network, with hindered access to iodide. Pyrene with the intermediate lifetime was assigned to a third location in the gel as it was quenched with a lower efficiency than for pyrene in the entrapped aqueous phase. Our results show that the NaDC hydrogel is comprised of at least three microenvironments to accommodate guests and each microenvironment has varying accessibility for an ionic species. These results have relevance when incorporating hydrophobic drugs in gels because the presence of various environments may influence the release kinetics of the drug from the gel.

10 Interfacing Perovskite Nanocrystals for Efficient Charge Transfer

Jesse Tamayo, Cambria Bennett, Pauline Do, Tori Do, Karen El-Maraghy, and Valentine Vullev – Department of Chemistry and Department of Bioengineering, University of California-Riverside

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Perovskite nanocrystals have garnered much attention in the past decade for their ability to harvest solar energy. In fact, solar cell efficiencies of perovskite films have increased at an unprecedented rate from 3.8% in 2009 to 22.7% in 2017. Even with these advances, perovskites are known for their instability in polar media making solution-based experiments challenging. Much is to be discovered in regard to interfacing the perovskite surface and improving their stability in colloidal solutions.

In this work we focus on the all-inorganic CsPbBr3 perovskite nanocrystals. Their large surface-to-volume

ratios are beneficial for investigating interfacial charge transfer (CT) between the nanocrystals (as electron acceptor) and small organic conjugates (as electron donors). Aliphatic amines have propensity for binding to surfaces of perovskite materials. Therefore, we select ethyleneamine derivatives of phenothiazine (PTZ), along with their analogues lacking the amines, for electron donors. Phenothiazines have sufficient driving force for hole transfer at 300 meV. We observe photoluminesce quenching only when the amine derivatized PTZ is present in solution. Trap passivation is also observed only in the amine functionalized PTZ. Slow charge transfer rates lead us to believe the ethylene linker greatly slows CT regardless of binding affinity. These results demonstrate that the binding affinity to the inorganic surface decisively affects the interfacial charge transfer. Using the ethyleneamine derivatives of the same donors further confirms the importance of binding affinity. To preserve the integrity of the perovskite nanocrystals, we employ hydrocarbon solvents. Nevertheless, we observe charge-transfer quantum efficiency of about 90% even in such non-polar media.

Additionally, the concentration of the donor plays a significant role in maintaining both colloidal stability

and structural integrity of the perovskite nanocrystals. Aggregation is found to occur when the nanocrystals are subjected to excessive donor concentration.

These findings provide important paradigms for interfacing perovskites with organic conjugates.

11 Photophysics and Electronic Structure of Solution-Processed Nanostructured Thin Films of Hematite

Jacob L. Shelton and Kathryn E. Knowles – Department of Chemistry, University of Rochester

Hematite (Fe2O3) has been studied extensively as a photoanode for water oxidation; however, the literature contains many conflicting descriptions of its photophysics. This poster presents recent data that identify spectral signatures of indirect transitions in transient absorption spectra of solution-processed nanostructured thin films of hematite. Comparison of transient absorption spectra to thermal difference spectra generated by taking the difference between a steady-state absorption spectrum collected at elevated temperature and one collected at room temperature enables distinction of spectral features associated with increased thermal energy (i.e. phonons) in the semiconductor lattice from features associated with purely electronic transitions of photoexcited carriers. A resonance Raman excitation profile confirms strong phonon coupling to absorption features near the band-edge. Electronic structure calculations indicate that these data are consistent with direct formation of an electron small polaron upon photoexcitation of hematite. Identification of the spectral signatures of the polaron state not only enables accurate assignment of transient absorption spectra of hematite films, but also has significant implications for the interpretation of photoelectrochemical and spectroelectrochemical experiments on hematite. Further characterization of the polaron state will provide important insights into the function of hematite thin films as photoelectrodes for solar fuels generation.

12 Dielectric-Loss Spectroscopy’s Contribution to Photoredox Mechanistic Studies

Justin Earley, Anna Zieleniewska, Obadiah Reid, and Garry Rumbles – Department of Chemistry, University of Colorado; National Renewable Energy Laboratory

Photoredox catalysts harvest light to drive thermodynamically unfavorable reactions by oxidizing or reducing a substrate species. It is key for these molecules to have a long-lived excited state and/or

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sufficient charge separation for the charge transfer processes to occur. Additionally, the separated charge’s spatial character, or delocalization, provides useful mechanistic insight into how the intermediate charge transfer state of a photoredox catalyst evolves.

Dielectric-loss (DL) spectroscopy is a technique sensitive to changes in the charge distribution of molecules in solution. Given a charge separated lifetime greater than a few tens of nanoseconds, DL spectroscopy can measure the strength and lifetime of a dipole as well as how a charge is delocalized over a molecule. This study utilizes time-resolved DL spectroscopy and steady-state DL spectroscopy to map the charge kinetics of the photoredox catalyst Ir[dF(CF3)ppy]2(dtbpy)·PF6 as a starting point for understanding a full catalytic cycle. Additionally, we show how the DL spectroscopy technique fits in with other photophysical measurements to provide a larger breadth of understanding of a photoredox cycle.

13 Nanoshell Quantum Dot Structure for Sustained Biexciton Populations

James Cassidy, Dmitry Porotnikov, and Mikhail Zamkov – Center for Photochemical Sciences, Bowling Green State University

Multiple-exciton (MX) generation is beneficial to many applications of semiconductors, including photoinduced energy conversion, stimulated emission, and carrier multiplication. Here, we demonstrate that such Auger recombination of biexcitons could be suppressed through the use of a quantum-well (QW) nanoshell architecture. The reported nanoscale geometry effectively reduces Coulomb interactions between photoinduced charges underlying Auger decay. This leads to increased biexciton lifetimes, as was demonstrated in this work through ultrafast spectroscopy methods. In particular, we observed that the biexciton lifetime of CdSe-based QW nanoshells (CdS/CdSe/CdS) was increased more than 30 times relative to that of zero-dimensional CdSe NCs. The slower biexciton decay in QW nanoshells was attributed to a large confinement volume, which compared favorably to other existing MX

architectures.

14 Delayed Photoluminescence in Metal-Conjugated Fluorophores

Mingrui Yang and Mikahil Zamkov – Center for Photochemical Sciences, Bowling Green State University

Assemblies of metal nanostructures and fluorescent molecules represent a promising platform for the

development of biosensing and near-field imaging applications. Typically, the interaction of molecular fluorophores with surface plasmons in metals results in either quenching or enhancement of the dye excitation energy. Here, we demonstrate that fluorescent molecules can also engage in a reversible energy transfer (ET) with proximal metal surfaces, during which quenching of the dye emission via the energy transfer to localized surface plasmons can trigger delayed ET from metal back to the fluorescent molecule. The resulting two-step process leads to the sustained delayed photoluminescence (PL) in metal-conjugated fluorophores, as was demonstrated here through the observation of increased PL lifetime in assemblies of Au nanoparticles and organic dyes (Alexa 488, Cy3.5, and Cy5). The observed enhancement of the PL lifetime in metal-conjugated fluorophores was corroborated by theoretical calculations based on the reverse ET model, suggesting that these processes could be ubiquitous in many other dye-metal assemblies.

15 Assignment of Electronic Transitions of Dithiocarboxylates

Abraham K. Newman, Jose M. Madriaga, Monica G. Aichouri, J. Michael Sieffert, Ava M. Henry, Shannon E. Heinrich, Vincent M. Swift, Alicia Y.Y. Cheong, M. Taylor Haynes, and David F. Zigler – Department of Chemistry and Biochemistry, California Polytechnic State University

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The combination of experimental and computational methods reveals differences in the electronic states of dithiocarboxylates, RCS2-, compared to thiocarbonyls, R2C=S. Dithiocarboxylates are a class of

compounds that find frequent use as RAFT-polymerization transfer agents and excellent ligands for electro-active metal complexes. Features in the electronic absorption spectra of dithiocarboxylates are typically assigned based on well-studied thiocarbonyl compounds which seems to be a questionable proxy for those of dithiocarboxylates. Some of the lowest electronic states consists of charge transfer between the substituent groups and the CS2 which are represented by the electronic states nπ*, ππ*, and σπ*. These studies further reveal the important role of substituents to influence the order and energy of the assorted excited states.

16 Structural Dependence of Electron Transfer in Conjugated Polymer

Nanoparticles

Jaclyn Rebstock and Elizabeth J. Harbron – Department of Chemistry, William & Mary

Conjugated polymer nanoparticles (CPNs or Pdots) have become popular fluorophores for a variety of

fluorescence imaging applications due to their brightness, photostability, and aqueous compatibility. Recently, their ability to generate charged species has begun to be exploited in applications ranging from photocatalysis to photodynamic therapy. Upon excitation, CPNs can eject an electron via photoinduced electron transfer (PET) to oxygen or other acceptors. PET generates a hole in the CPN, which quenches its fluorescence. These processes are thus undesirable for fluorescence-based applications due to the reduction in fluorescence intensity. However, for redox-based applications such as photodynamic therapy and solar cells, PET becomes desirable regardless of fluorescence quenching. We seek to determine the dependence of PET on conjugated polymer structure and irradiation dosage. We will present studies of PET and the concomitant fluorescence quenching in the most widely-used CPNs. These results will ultimately aid in the selection of polymers and irradiation conditions for CPN-based applications.

17 Exploring the Microwave-Assisted, Non-aqueous Synthesis of Metal Oxide Photocatalysts for Alcohol Oxidations

Kori D. McDonald, and Bart M. Bartlett – Department of Chemistry, University of Michigan

Utilization of sunlight irradiation has become one of the most useful and economic avenues for exploring the reactivity of organic compounds. As organic compounds are mainly excited by UV light, the strong visible irradiation from the sun causes no reaction. Binary semiconductors, like CdS or TiO2, have shown preliminary exploration into this reactivity, though their instability in aqueous systems and UV light excitation, respectively, raise the need for more complex materials to offer improved reactivity. Visible light active metal oxides present themselves as strong candidates for these, though common synthetic methods are harsh and offer little control over particle formation. With the aid of direct heating through microwave irradiation in non-aqueous media, nanocrystalline tungsten (VI) oxide is achievable in 30 minutes at 200 °C, faster and lower temperatures than conventional synthesis methods. Forming in a platelet morphology, these particles are as small as 20 nm with a BET surface area of 37 m2•g–1 WO3. These nanoplatelets are active for the photocatalytic oxidation of the 1° alcohols benzyl alcohol (rate constant of 0.26 h–1g–1 WO3) and 5-(hydroxymethyl)-2-furfural (rate constant of 1.00 h–1g–1 WO3) using a 150 mW/cm2 460 nm blue LED source. As expected, these rate constants are larger than those observed for commercially prepared, micron-sized WO3. The nanoplatelet WO3 catalysts are stable under these reaction conditions, as the overall morphology and size of the particles are retained through the reactions. Moreover, the nanoplatelets are recyclable—showing no loss in activity for 5 reaction cycles.

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18 Photoelectrochemical Nitrate Oxidation for Indirect Alcohol Oxidation on Bismuth Vanadate in Acetonitrile

Bradley D. Terry, John L. DiMeglio, and John Cousineau – Department of Chemistry, University of Michigan

Biomass valorization through the selective oxidation of bio-derived alcohols offers a viable route of

obtaining polymer precursors free from petrochemical feedstocks. Recently, using light-absorbing cadmium sulfide nanowires, the selective oxidation of bio-renewable 5-hydroxymethylfurfural (5-HMF) to polymer precursor diformylfuran (DFF) was reported by the Bartlett group. Introducing nitrate salts vastly increased the rate of aldehyde product formation, leading to the discovery that nitrate anion served as a mediator for photocatalytic alcohol oxidation. To explore the generality and mode of nitrate-mediated alcohol oxidation, we performed photoelectrochemical measurements on bismuth vanadate to track essential mechanistic features. The overpotential for nitrate oxidation was found to decrease significantly in the presence of alcohol substrate. Solution-based UV-vis spectroscopic analysis revealed no change in the electronic structure of nitrate. Together, these results are suggestive of a chemical step facilitating nitrate oxidation that enables selective indirect alcohol oxidation. The stoichiometric generation of nitric acid, a weak electrolyte in acetonitrile, and a competing background reaction with acetonitrile solvent remain significant challenges in enabling selective nitrate mediation. Nevertheless, this mechanistic insight points to strategies that will enable redox mediators to improve yield and efficiency for catalytic primary alcohol oxidation reactions using semiconductor photoelectrodes.

19 Studying the Reactivity of Ester-Nitrenes in Solid State

Noha A. Ahmed and Anna D. Gudmundsdottir – Department of Chemistry, University of Cincinnati

Although solid state chemistry reactions are more efficient and selective, most of the organic reactions still being performed and studied in solution. Aside from promising with a clean way for doing the reactions, solid state chemistry is selective in the type of products one can get as the reactants are arranged in an ordered and tight crystals. Nitrenes are highly reactive electron deficient uncharged intermediates. They can be formed in two different spin states—singlet and triplet. The physical and chemical properties of both states are different as well as their lifetime and energy. Depending on which state contributed in the product formation the product can be different. Our goal in this project is to study the photolysis in a triplet sensitized alkoxycarbonyl azide 1 in the solid state and in solution, and to

characterize the resulting products, and to figure out the mechanism of the reaction in each case.

20 Photochemistry of Octaacid Encapsulated Azide complexes

Rajkumar Merugu, Sujan K. Sarkar, Shipra Gupta, Breyinn Loftin, Rohith Anand Varikoti, Jeanette A. Krause, V. Ramamurthy and Anna D. Gudmundsdottir – Department of Chemistry, University of Cincinnati

The photoreactivity of octa acid (OA) encapsulated 2-azido-(4ˈ-methoxy)-acetophenone was investigated. The photoexcitation of OA-encapsulated 2-azido-(4ˈ-methoxy)-acetophenone leads to photoinduced electron transfer from OA to the triplet excited state of 2-azido-(4ˈ-methoxy)-acetophenone. In order to understand the electron transfer properties of 2-azido-(4ˈ-methoxy)-acetophenone in its triplet excited state, it was selectively excited in the presence of N,N-dimethyl-1-naphthalenamine and DABCO, well-known electron donors. The photoinduced electron transfer mechanism involving an anion intermediate derived from 2-azido-(4ˈ-methoxy)-acetophenone was

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proposed based on product studies and laser flash photolysis.

21 Investigating the Electron-Transfer Dynamics of Eosin Y Photosensitizers Using Single-Molecule Spectroscopy and Monte Carlo Simulations

Kelly M. Kopera, Harrison G. Tuckman, and Kristin L. Wustholz – Department of Chemistry, William & Mary

Growing global energy demands have necessitated the search for alternative sources of renewable fuels. Dye-sensitized photocatalysis (DSP) is a promising low cost, sustainable method that directly converts solar energy to readily usable forms of energy such as hydrogen fuel. While DSP is a promising technology, its efficiency is limited by back electron transfer and kinetic redundancy. In order to fully understand these processes, single-molecule spectroscopy (SMS) is used to probe the electron transfer (ET) dynamics of photosensitizers. In particular, eosin Y (EY), a brominated fluorescein derivative that undergoes intersystem crossing prior to injection, is investigated using SMS. In this approach, blinking dynamics - stochastic fluctuations in emissive and nonemissive intensities under continuous photoexcitation - are measured for single molecules of EY on glass, TiO2, and in oxic and anoxic environments. The emission dynamics are parsed into emissive (“on”) and nonemissive (“off”) events and fit to cumulative probability distributions using a maximum likelihood estimation and Kolmogorov-Smirnov test approach. In the absence of TiO2, the data are lognormally distributed, consistent with triplet state

decay and dispersive electron transfer. However, for EY-sensitized TiO2, the on- and off-time distributions are not well described by any tested functional form, motivating us to implement new modeling approaches (e.g., finite mixture model, Monte Carlo simulations). Our results show that back-to-back events, temporal binning, and thresholding obscure the functional form and are thus important considerations for understanding the underlying ET dynamics.

22 Pulse Radiolysis Study of Short-Lived Redox Intermediates in Photocatalysis

Seokjoon Oh, and Matthew J. Bird – Chemistry Division, Brookhaven National Laboratory

Light-harvesting reactions are ubiquitous in nature and are crucial in transforming low- energy or -value materials into higher energy products. Such reactions are often mediated by photocatalysts that harness the energy of light to oxidize or reduce compounds. This work demonstrates the utility of pulse radiolysis for investigating photocatalytic reaction mechanisms with short-lived redox intermediates. We present two catalytic systems in this work. First, we examine the kinetics and thermodynamics of Ni cross-coupling catalysts that operate in tandem with Ir-based photocatalysts. Pulse radiolysis allows oxidation of the Ni complex without a redox mediator or Ir photocatalyst, allowing examination of the Ni(II/III) couple in isolation on a nanosecond timescale. Second, we study the thermodynamics of chloroamides, which undergo stereoselective radical cyclizations in the presence of ‘ene’-reductase and light. We estimate the redox potential of an α-chloroamide, which undergoes rapid mesolytic cleavage (<10 ps lifetime) upon reduction, by comparing measured electron transfer rates to those predicted by Marcus theory. Together, these results show that pulse radiolysis is a powerful tool for investigating both kinetics and thermodynamics of photocatalytic reactions. These results will be used to further elucidate photocatalytic mechanisms in these systems.

23 Ultrafast Transient Absorption Studies of Conjugated Polyelectrolytes and Cationic Electron Acceptors Complexes

Pradeepkumar Jagadesan and Kirk Schanze – Department of Chemistry, University of Texas San Antonio

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A series of poly(phenylene ethynylene) (PPE)-type conjugated polyelectrolytes (CPEs) that feature alkyl sulfonate (−R-SO3–)-solubilizing groups were synthesized via chain- and step-growth polymerization methods. CPEs synthesized by chain-growth method display higher fluorescence quantum yields and better-resolved spectra, suggesting that the chains are comparatively defect-free and do not aggregate in solution. Titrations with cationic acceptors in water and MeOH display amplified fluorescence quenching effect with Stern-Volmer constants (Ksv) >106 M−1. Ultrafast transient absorption measurements were carried out to gain insight concerning the quenching mechanism. Femtosecond−picosecond transient absorption spectra of CPEs and methyl viologen complex revealed

the presence of CPEs+• charge transfer (CT) state that confirms the quenching mechanism involves photoinduced electron transfer from CPEs to the acceptor. Similar observations made with other cationic acceptors, and modulation of electron transfer kinetics using supramolecules will also be discussed.

24 Controlling Excited State Mixing in Rhenium(I) Tricarbonyl Chromophores through Ancillary Ligands

Cory E. Hauke, and Felix N. Castellano – Department of Chemistry, North Carolina State University

Knowledge of the nature of excited states is important to the design and synthesis of molecules for a wide range of applications from OLEDs to photocatalysts to sensing. When the character of the excited

state is a mix of two or more characters, unexpected and beneficial photophysical properties can result. A series of rhenium(I) diimine tricarbonyl complexes were synthesized where the diimine is 3,4,7,8-tetramethyl-1,10-phenanthroline. By varying the ancillary ligand across the ligand field series from isonitrile to chloride, seven molecules were synthesized which contain excited states ranging from a π→π* state of the diimine ligand to metal-to-diimine metal-to-ligand charge transfer (MLCT). In some instances, the excited states are a mixture of both ligand-centered and MLCT triplet excited states; this had a profound impact on photophysical properties such as photoluminescence quantum yield and excited state lifetime of these chromophores. The nature and extent of excited state triplet mixing was studied using both static and transient photoluminescence kinetics as well as through electronic structure calculations. Ultrafast transient absorption spectroscopy was used to glean insight into the excited state evolution processes occurring in this series of Re(I) MLCT complexes.

25 Photochemical Upconversion Induced Polymerization

Nancy Awwad, Anh Thy Bui, and Felix N. Castellano – Department of Chemistry, North Carolina State University

The revolutionary technology of 3D printing is quickly pervading many industries, predominantly

employing photopolymerization as its commonly used technique. The present work reports the study of photochemical upconversion through triplet-triplet annihilation (TTA) in pre-polymer systems to initiate electron transfer in radical chain polymerization. First, homomolecular TTA was investigated in zinc(II) tetra-phenylporphyrin (ZnTPP) in a variety of solvents following Q-band excitation at 514.5 nm. ZnTPP acts as both the sensitizer and upconverting emitter as the TTA process ultimately yields an S2 excited porphyrin as evidenced through the observation of its characteristic fluorescence at 435 nm. Upon addition of the liquid-based monomer trimethylolpropane triacrylate (TMPTA), we propose that green excitation at 514.5 nm promotes an electron transfer from the TTA-produced ZnTPP S2 excited state that induces free radical polymerization. Fluorescence upconversion experiments following direct excitation

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of the Soret band at 400 nm illustrated that TMPTA dynamically quenched the ZnTPP S2 fluorescence whose lifetime reduced from 1.51 ps in pure toluene to 0.26 ps in a 15:1 TMPTA/toluene mixture ([TMPTA]= 3.47 M). Using methyl acrylate (MA) as a surrogate for TMPTA in model quenching studies avoiding polymerization, dynamic excited state quenching of the S2 fluorescence was also observed (kq = 7.8 × 1011 M-1 s-1), whereas the respective S1 and T1 excited states remained completely unaffected in the presence of MA. The utility of our approach was finally illustrated by producing micron-sized structures in a confocal fluorescence microscope, utilizing a variety of low-power visible light sources.

26 Understanding Conformational Dynamics of Trans-N-heterocyclic Carbenes Platinum(II) Acetylides: A Femtosecond Transient Absorption Spectroscopy Study

Silvano R. Valandro, Ru He, and Kirk S. Schanze – Department of Chemistry, University of Texas at San

Antonio

N-heterocyclic carbenes (NHCs) based platinum (II) complexes have been the subject of intense research in the last decade owing to their potential applications in organic light-emitting devices (OLED). Understanding the excited state properties of these platinum-based triplet emitters is essential for their potential application in molecular optoelectronics.[1] As the main goal of this study, we would like to understand the effect of steric hindrance on the interconversion dynamics between the twisted and planar conformations of these Pt(II) complexes. For that, four NHCs based Pt(II) complexes containing different ligands were synthesized. The fsTA kinetics were fit using multi-exponential functions, with two components and a constant representing the long-lived triplet-triplet absorption. Given this, it is likely that these components are due to singlet-triplet intersystem crossing and the following triplet conformation relaxation associated with the twisting of the phenyl acetylide ligands. It is seen that tert-butyl substituents on the phenyl rings lead to a decrease in the lifetime constants, as well as the relative amplitudes, indications a torsional restriction caused by tert-butyl groups. The substituents on the carbene ligand also play an important role, where carbenes containing cyclohexyl groups showed a relaxation lifetime

around 4x smaller than the carbenes with butyl groups.

(1) Zhong, F.F., et al.. Inorg Chem, 2019. 58, 1850-1861.

27 Synthesis of Urea-Tethered, Halogenated Triphenylamines for the Study Halide

Influence on the Generation and Persistence of Photogenerated Radicals

Muhammad S. Hossain, Ammon J. Sindt, Dustin G. Goodlett, Mark D. Smith, and Linda S. Shimizu – Department of Chemistry and Biochemistry, University of South Carolina

Persistent organic radicals are important functional building blocks for materials with magnetic, optical, and electronic properties. In particular, para substituted triphenylamines (TPAs) have applications in organic magnetic materials and photoconductors, due to the formation of stable radical cations compared with partially substituted TPA counterparts. Our group employs self-assembly which provides

further stabilization of TPA radical cations. Specifically, urea-tethered TPAs (X = Cl, Br) afford persistent and regenerable radicals upon UV-irradiation, even though the TPA units are not fully substituted at their para sites. In solution, these compounds quickly degrade once radicals are generated. However, in solid state these compounds can make regenerable radicals which can persist even after 30 days with half-life of one week without any significant change in the single crystal structure. Herein, we investigate how halogen substituents affect the assembly of urea-tethered TPAs and how halides substitution modulates

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their photophysical properties including on absorption and emission. Our goal is to probe how the heavy atom alters the stability of photogenerated radicals in solution and the solid-state.

28 Single Crystal-to-Single Crystal Guest Exchange and Electron Transfer in Triphenylamine Bis-Urea Macrocycles

Md Faizul Islam, Ammon J. Sindt, Mark D. Smith, and Linda S. Shimizu – Department of Chemistry and Biochemistry, University of South Carolina

Triphenylamines (TPA) are excellent electron donor molecules which are used in organic magnetic materials and organic dyes due to their ability to form radical cations. Recently, supramolecular assembly of TPA has been shown to influence the photophysics and photogeneration of the TPA radical cations. Herein, we examine the incorporation of TPAs as covalent C-shaped spacers within bis-urea macrocycles. These macrocycles assemble into columnar structures that contain the solvent of crystallization bound within the channels. Heating the crystals leads to removal of the solvent and activates the crystal for guest exchange by single-crystal-to-single-crystal transformations. This system enables us to study how encapsulation of acceptors inside the channels of the activated host molecule modulate the process of transfer of electron from host (donor) to guest (acceptor). The photoinitiated electron transfer process is currently under study in crystals of bis-urea TPA macrocycles that contain

either benzothiadiazole or iodine loaded within the host channels. The absorption, emission and lifetimes of these complexes will be presented.

29 Photogenerated Persistent Radicals of Benzophenone Supramolecular Assemblies

Dustin W. Goodlett, Ammon J. Sindt, Muhammad S. Hossain, Mark D. Smith, and Linda S. Shimizu – Department of Chemistry and Biochemistry, University of South Carolina

Photogenerated radicals of the self-assembled 4, 4’-benzophenone bis-urea macrocycle have been reported to persist for a minimum of 26 days in ambient conditions in the solid-state while radicals are not detected in solution. The radicals in the solid-state are hypothesized to be the result of an abstraction of

a hydrogen atom from one macrocycle by a photogenerated ketyl radical of its neighboring macrocycle in the crystal lattice. This generates a ground state triplet radical pair, which is thought to revert slowly in the solid. A constitutional isomer of the original 4,4’-benzophenone bis-urea macrocycle and linear analogs of both macrocycles were synthesized and crystallized to test how connectivity, solid-state organization, and availability of abstractable hydrogens might influence the process of photogeneration and reversion. The three new benzophenone self-assemblies were irradiated with 365 nm LEDs and their maximum radical concentrations were monitored via X-band EPR spectroscopy. The self-assembly with persistent radicals possessing the shortest life-time was tested for and shown capable of regenerating similar maximum radical concentrations via re-irradiation with the LEDs.

30 Acridinium and Acridone Constructs with Red-Shifted Emission

Anastasiia A. Tikhomirova, Kerry M. Swift, Richard A. Haack, Stefan J. Hershberger, and Sergey Y. Tetin –

Applied Research and Technology, Abbott Diagnostics Division, Abbott Laboratories

Acridinium water-soluble esters have been extensively used as chemiluminescent labels in research and diagnostic assays. Triggering acridinium with basic hydrogen peroxide produces a highly strained dioxetanone intermediate which converts into an acridone in an electronically excited state, emitting a

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blue light. All currently utilized acridinium conjugates emit around 420-440 nm. Chemiluminescent compounds with red-shifted emission can reduce optical interferences caused by biological samples and find immediate applications for multicolor detection. Here, we introduce acridinium-fluorescein and acridone-fluorescein piperazine-linked constructs that emit at 530 nm. Both acridone and acridinium were tethered to either 5- or 6-carboxyfluorescein forming two structural isomers. Direct excitation of acridones, as well as chemiluminescent triggering of acridiniums, led to a nearly complete energy transfer to the respective fluorescein moieties. Using UV-Vis absorption and fluorescence fluctuation spectroscopy, we investigated and optimized the diluent composition to prevent luminophore

aggregation. As monomolecular species, the acridone and acridinium isomers demonstrated similar absorption, excitation and emission spectra, as well as the expected fluorescence lifetimes and brightness. Having observed a similar red-shifted emission effect for a rhodamine construct, we conclude that coupling acridinium esters with spectrally overlapping fluorophores will lead to a new family of colorful chemiluminescent labels useful for clinical diagnostics.

31 Redox Active Ligands for Wavelength Selective Cm and Am Separations

Jiaqi Chen, Sahan R. Salpage, Joseph M. Sperling, Thomas E. Albrecht-Schmitt, and Kenneth Hanson – Department of Chemistry and Biochemistry, Florida State University

Efficient and cost-effective methods for separating ions are critical for industrial, health, and environmental applications. This is particularly true for radioactive waste processing[1] where the similarities of charge density, size, and binding affinities of lanthanide and actinide ions makes separations by traditional means (i.e. affinity columns, ion exchange resins), difficult if not impossible.[2] Recently, our group introduced wavelength selective excitation of coordination complexes containing redox active ligands as a new separations strategy which was successfully applied to the separation of Fe(II) and Ru(II) mixtures.[3] Monochromatic excitation of the Fe(II) and Ru(II) coordination complex results in photoinduced electron transfer (PET) from metal center to the benzenediazonium containing ligand, whose irreversible electrochemistry results in the formation of a new, readily separable complex. With proof-of-concept in hand, we have now transitioned to the wavelength selective separation of Cm(III) and Am(III) using benzenediazonium functionalize diethylenetriaminepentaacetic acid (DTPA-N2+) as the high binding affinity, redox active ligand. Upon excitation of Cm(DTPA-N2+) with 395 nm light, there is an irreversible chemical reaction resulting in a dramatic decrease in the solubility of the Cm(III) complex. Preferential precipitation is enabled by the wavelength selective excitation and reaction of the Cm(III) complex while the Am(III) complex remains unperturbed.

(1) Turhanen, P. A.; Vepsäläinen, J. J.; Peräniemi, S. Scientific Reports 2015, 5, 8992.

(2) Reuben, B. Chem. Ind. (London, U. K.) 2005, 27. (3) Salpage, S. R.; Lanzetta, R. C.; Zhou, Y.; Wang, J.

C.; Albrecht-Schmitt, T. E.; Hanson, K. Chemical Communications 2018, 54, 7507.

32 FRET as a Structural Probe for Metal Ion Linked Multilayer Assemblies on Metal Oxide Surfaces

Ashley Arcidiacono, Suliman Ayad, and Kenneth Hanson – Department of Chemistry and Biochemistry, Florida State University

Metal ion linked multilayers on mesoporous, semiconducting surfaces have recently emerged as a simple and effective strategy to control energy and electron transfer events at organic-inorganic interfaces. These interfaces have shown promise for use in photocatalysis, as molecular charge separation junctions, in electrochromics, for multiphoton/electron events, and more. Unlike in solution where the molecules are free to rotate, the structure of these assemblies plays a critical role in dictating the efficiency of these events, but little to no structural information currently available about these interfaces. Here we introduce

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Förster resonance energy transfer (FRET) as a spectroscopic probe for determining orientation of metal ion linked molecules on ZrO2 substrates. The films are composed of ZrO2, an anthracene FRET donor, a Zn(II) linking ion, and a Pt(II) porphyrin acceptor molecule with varying numbers of phenyl spacers between the chromophoric core and the metal ion binding group. As anticipated, with increasing number of phenyl spacers (i.e. distance) we observe an increase in emission intensity and lifetime that correspond to decreased FRET efficiency. Given that the change in distance is controlled, fitting of this data allows us to determine the relative orientation between the donor and acceptor molecules in the assembly. This is a key step towards understanding and then controlling orientations at these interfaces

to enable advanced structural design strategies.

33 Optimal Crystal Packing for Singlet Fission

Alexandr Zaykov, Petr Felkel, Eric A. Buchanan, Milena Jovanovic, Remco W. A. Havenith, R. K. Kathir, Ria

Broer, Zdenĕk Havlas, and Josef Michl – Institute of Organic Chemistry and Biochemistry, Czech Academy of Science; Faculty of Electrical Engineering, Czech Technical University in Prague; Department of Physical Chemistry, University of Chemi

A procedure is described for identification of all π-electron chromophore pair geometry choices that locally maximize the rate of conversion of a singlet exciton into singlet biexciton (triplet pair), using a simplified version of the diabatic frontier orbital model of singlet fission (SF). The procedure is applied to a pair of ethylenes as the simplest model, and to pairs of several much larger pi-electron systems. The value of |TA|2, the square of the electronic matrix element for SF with initial excitation fully localized on partner A, on a grid of several billion geometries within the six-dimensional space of physically realizable possibilities, is examined first. The optimized pair geometries are found to follow the qualitative guidance proposed earlier. In the neighborhood of each local maximum of |TA|2, consideration of mixing with charge-separated configurations and of excitonic interaction between partners A and B determines the SF energy balance and yields squared matrix elements for singlet fission out of the lower and upper excitonic states. Assuming equilibrated populations of these states, the geometry is further optimized to maximize the sum of the SF rates obtained from Marcus theory, and at about a hundred pair geometries, the resulting values are compared with those obtained from high-level ab initio calculations and found to follow the same trend. Finally, the biexciton binding energy at the optimized geometries is also calculated. Significant local maxima of SF rate for a pair of molecules are identified in the physically relevant part of space that avoids molecular interpenetration in the hard spheres approximation.

34 Excited State Proton Transfer Sensors with Emission Quantum Yield Enhancements up to 60% Upon Zn(II) Coordination

Suliman Ayad, Tanmay Banjeree, Bryan Cassale, and Kenneth Hanson – Department of Chemistry and Biochemistry, Florida State University

Fluorometric sensors/probes for transition metal ions are important for a number of applications including bioimaging, toxicity screening, water analysis/treatment, and more. Of the classes of molecular fluorophores, excited state proton transfer dyes (ESIPT) are particularly appealing because of their large apparent Stokes shift, on-off fluorescence, and their strong sensitivity to their environment including solvent, pH, and the presence of metal ions. Regarding the latter, metal ion sensing is typically achieved by covalently linking a metal ion receptor to the ESPIT fluorophore. This strategy has the advantage of having two independently tunable moieties but typically requires multi-step synthetic schemes and has reduced sensitivity. Here we introduce 1,3-bis(2-pyridylimino)-4,7-dihydroxyisoindole (BPI-OH) as a metal

ion sensing ESIPT dye that can be prepare in one synthetic step and whose metal chelation site is intrinsic to the molecule and is directly adjacent to the ESIPT fluorophore. Metal ion coordination to BPI-OH results in dramatic changes in the photophysical properties of the dye. For example, NiII, CuII, CoII, and HgII

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completely quench emission but ZnII binding increases the emission quantum yield from 25% to 60%. 1H NMR spectroscopy was used to show that the chelation site for the metal ions is the tridentate binding motif of BPI-OH. The increase in emission quantum yield can be attributed to a decrease in the non-radiative decay rates due to the increased rigidity upon ZnII chelation. Furthermore, upon protection of the ESIPT OH group with bromobutyrate, this dye can serve as a multi-component sensor when hydrazine cleaves the protecting group, turning on ESIPT fluorescence.

35 Role of Metal Ion Linked Multilayer Film Thickness and Substrate Porosity on Surface Loading, Diffusion, and Solar Energy Conversion

Alex J. Robb, Dalton T. Miles, and Kenneth Hanson – Department of Chemistry and Biochemistry, Florida State University

Understanding and controlling electron/energy transfer events at molecule-semiconductor interfaces is critical for their application in organic and hybrid electronic devices. With this goal in mind, metal ion linked multilayer assemblies have emerged as a simple, modular, and effective means of controlling these interfacial events. Multilayer assemblies were first generated on planar surfaces, but more recently, due to their high surface area and increased absorption, these assemblies on mesoporous metal oxides have shown promise for use in photocatalysis, electrochromics, photon upconversion, energy cascade

solar cells, and more. However, in contrast to planar surfaces where an indefinite number of layers can be loaded, the mesoporous nature of the nanocrystalline films fundamentally limits the size of the multilayer. Additionally, the thickness of these multilayers reduces the films’ porosity and can ultimately hinder device performance. Here we perform the first systematic study to understand how both the multilayer thickness and the porosity of the metal oxide influence variables like dye surface coverage, diffusion through pores, and overall solar cell performance. These insights are key in understanding the limitations of current multilayer films as well as guiding the strategic design of new molecule-semiconductor interfaces.

36 Revealing Spontaneous Rupture of Single Protein Molecule under Piconewton

Compressive Force using Correlated AFM-FRET Nanoscopy and its Implications

Susovan Roy Chowdhury and H. Peter Lu – Center for Photochemical Sciences, Bowling Green State University

Mechanical force vector fluctuations in living cell can have a significant impact on protein behavior and

functions. Here we have observed abrupt and spontaneous HPPK protein ruptures under a compressive force ranging from ∼12 to ∼75 pN, at a biologically available force amplitude range in living cells, using single-molecule AFM-FRET spectroscopic nanoscopy. Our correlated force-FRET trajectories showed FRET efficiency decreases at the same time when the force abruptly drops, indicating that the HPPK molecule involves a sudden large conformational change under compressive force manipulation. The rupture behavior is dependent on the physiological level of presence of ions, such as Na+ and Ca2+. We also observed sudden and spontaneous structural rupture of apo-CaM under compressive force applied by the AFM tip, though no such events were recorded in the case of Ca2+-ligated activated CaM form. We have also demonstrated how these ruptured Apo-CaM molecules can be activated to bind to C28W peptide, which is a property that only the calcium activated CaM is known to have. This indicates a plausible alternative pathway for CaM signaling inside cell. We also found similar rupture events of Tau protein molecules. We further explored the entangled protein state formed following the events of the multiple and simultaneous tau protein ruptures under crowding. Crowded proteins simultaneously rupture and then spontaneously refold to an entangled folding state, different from either folded or unfolded states of the tau protein, which can be a plausible pathway for the tau protein aggregation that is related to a number of neurodegenerative diseases like Alzheimer’s disease and Parkinson’s disease.

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37 Mechanistic Investigation of Phototriggered Intramolecular Sulfoxide Ligand Substitution in Ruthenium Terpyridine Complexes

Maksim Y. Livshits, Lei Wang, Elena Jakubikova, and Jeffrey J. Rack – Department of Chemistry and Chemical Biology, University of New Mexico; Department of Chemistry and Biochemistry, Ohio University; Department of Chemistry, North Carolina State University

The role of metal centered (MC) states in photo-induced ligand substitution reactions in Ru(II)-polypyridine complexes is still an active area of research with applications in photochemotherapy therapy and photocaging. Herein, we present a mechanistic density functional theory study to determine a preferred pathway for the dimethyl-sulfoxide intramolecular ligand substitution in [RuII(tpy)(pic)(DMSO)]+ (where tpy is 2,2’:6’2” terpyridine and pic is picolinate). Different mechanistic models have been proposed for this process that invoke either dissociative or non-dissociative ligand substitution. The dissociative ligand substitution model invokes 3MC excited state quenching of the metal-to-ligand charge transfer (3MLCT) excited state from which Ru-DMSO ligand bond elongation releases the DMSO to form a 5-coordinate Ru(II) species, which is followed by subsequent coordination of a rearranged ligand. The non-dissociative ligand substitution model invokes η2 ligand slip coordination creating a 7-coordinate (19e-) transition state along a 3MLCT excited state surface connecting the excited state product and reactant surfaces. The final observed ground state photoproduct is formed from simple relaxation or non-adiabatic collapse of the excited state photoproduct to the ground state. Both our photochemical and computational results suggest that the lowest-energy triplet isomerizing surface for intramolecular ligand substitution in [RuII(tpy)(pic)(DMSO)]+ is 3MLCT in character, with the exception of the transition state which exhibits 3MC mixing into the 3MLCT transition state. Furthermore,

we find that the non-dissociative pathway is lower in energy compared to the dissociative pathway which is also consistent with photophysical studies of DMSO photo-isomerization reactions in Ru(II) polypyridine complexes.

38 Excited State Dynamics in Ru Complex Unraveled by 2D Spectroscopy

Martha A. Hermosilla Palacios, Sofia E. Dominguez, Luis Baraldo-Victorica, and Valeria D. Kleiman

– Department of Chemistry, University of Florida; Facultad de Ciencias Exactas y Naturales, University Buenos Aires

Polypyridine ruthenium (II) complexes have been of great interest for fundamental understanding of

energy and electron transfer. Recently mixed valence and excited states mixing have been the focus of multiple studies aiming to design better materials for solar-harvesting applications. In this work, we look at the excited state dynamics of a compound based on substituted forms of Ru polypyridines (Ru(tpy)(L)NCS, Ru(tpm)(L)NCS). We examine this complex with ultrafast transient absorption and two-dimensional visible spectroscopy to unravel the multiple states giving rise to their complex dynamics following excitation in the visible. Two-dimensional spectroscopy gives the advantage to investigate the coupling between states thus helping in the aforementioned assignment.

39 Photochemical Upconversion in Water using Cu(I) MLCT Excited States

Remi Fayad, Anh Thy Bui, and Felix N. Castellano – Department of Chemistry, North Carolina State

University

Photochemical upconversion (UC) through triplet-triplet annihilation (TTA), which employs a visible absorbing triplet photosensitizer and an acceptor/annihilator, is a process that generates a high energy photon from two lower energy photons. UC-TTA has been so far largely limited to pure organic solvents

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and solid-state polymeric constructs while being tied to the near exclusive use of rare and expensive metals in the photosensitizer component. In this work, we demonstrate that UC-TTA from the earth abundant photosensitizer [Cu(dsbtmp)2](PF6) (dsbtmp = 2,9-di(sec-butyl)-3,4,7,8-tetramethyl-1,10-phenanthroline), abbreviated as Cu PS, operates in water through encapsulation within cationic-based assembly. Cetyltrimethylammonium bromide (CTAB) was the surfactant of choice here as it can electrostatically bind the negatively charged water-soluble 10-phenylanthracene-9-caboxylate (PAC) acceptor to facilitate energy transfer across the interface. Efficient and diffusion limited triplet-triplet energy transfer (TTET) from the Cu(I) complex to the PAC acceptor was achieved from this design. The

lack of mobility of the acceptors/annihilators ultimately hindered the annihilation process and this was reflected in attenuated TTA rates and efficiencies. The combined experimental data illustrates that the water soluble PAC acceptor was able to extract excited triplet energy from the Cu(I) photosensitizers contained within the assemblies, ultimately delivering it to the bulk aqueous solution engaging in excited state electron transfer with various acceptors. This is particularly important for remotely operating photoredox reactions in water while rendering the Cu(I) photosensitizer spatially confined in the hydrophobic core of the assemblies.

40 Towards the Use of Triplet-Triplet Annihilation for Photoredox Catalysis with Pyrene

Samuel G Shepard and Felix N. Castellano – Department of Chemistry, North Carolina State University

Over the past decade, the use of photoredox catalysis to generate reactive organic radical species

under mild conditions using visible light has become a powerful tool for chemical synthesis. Because the strength of a chromophore as an excited state oxidant or reductant depends in part on the amount of energy stored in its excited state, there is a desire for blue or near-UV absorbing photoredox catalysts, pushing the absorption spectrum of the catalyst out of the most intense regions of the solar spectrum. One means of generating these high energy excited states with visible light excitation is through triplet-triplet annihilation. Recently, near-infrared-to-blue upconversion has been used to drive a photoredox catalytic cycle for the cyclization of enones and dienyl azides (1). However, the principle obstacle for the usage of triplet-triplet annihilators as photoredox catalysts directly is that the lifetimes of the excited singlet states of many of the most frequently used annihilators are too short relative to the diffusional timescale needed for excited state electron transfer to a quencher species. As will be shown, pyrene derivatives are notable exceptions, with singlet lifetimes of around 250 ns. These systems are already known as efficient triplet-triplet annihilators, with singlet energies of 3.3 eV. Stern-Volmer analysis reveals that this excited state can be quenched by sacrificial electron donors. These results, though preliminary, establish pyrene as a promising candidate for photoredox catalysis through upconversion.

(1) Ravetz, B. D.; et al. Nature 2019, 565 (7739), 343–346.

41 Detection of Arsenate in Water by Luminescence Spectroscopy Using Lanthanide/Transition Metal Dyads

Sepideh Farshbaf and Pavel Anzenbacher, Jr. – Department of Chemistry, Bowling Green State University

Arsenate is a species known for its toxicity to living organisms. The International Agency for Research on Cancer (IARC) considers arsenic compounds highly toxic and classified them as group I (human carcinogens). For this reason, U.S. Environmental protection agency (EPA) sets an arsenic maximum contaminant level for public water supplies at 0.010 mg/L (0.010 ppm). Thus, a reliable and sensitive technique and portable detection tools are sought. In this work, the cryptand cage and its fluorescent Eu3+ complex have been used for the detection of arsenate in water. The detection method is based on switch OFF-to-ON of the Eu3+ luminescence in the presence of arsenate. A sensing ensemble comprising a nitrogen-based cryptand ligand and the Eu3+ / Zn2+ cocktail in MeOH is capable of sensing of aqueous

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arsenate anion (HAsO42-) with the attendant increase in luminescence while providing a clearly observable turn-On signal. The binding processes associated with the change of the luminescence signal have been investigated using luminescence spectroscopy. The proposed complex is promising to detect arsenate with high selectivity and sensitivity. Further plans include the incorporation of polymerizable cryptand receptors into hydrogels and polymerized colloidal crystal arrays. This leads us to an environmentally safe and easily portable arsenic detector.

42 Photo-Switchable Silicon-Based Networks with High Thermal Stabilities and Porous Structures

Nai-hsuan Hu and Joseph C. Furgal – Department of Chemistry and Photochemical Sciences, Bowling Green State University

A vast number of photo-switchable molecules have been discovered and thoroughly studied. In azobenzene, the excitation caused by UV light weakens the central azo-double bond enabling the conversion of cis/trans isomers. Since it has a relatively simple structure and electron-transfer-free mechanism, azobenzene is the most approachable photo-switch for cooperating with polymer systems. For applications such as artificial muscles or photo-activated pump, a network structured porous polymer system is desired. One of the many challenges that has plagued success in this area is locking or over cross-linking of the structure, which forbids isomerization in azobenzene at the macroscale. This is especially true for silicon-based hybrid materials. Our group has successfully synthesized a silsesquioxane based network polymer capable of executing isomerization at the macroscale through curving or

shrinking/swelling in films and gels. In addition, the silicon-based system raises the thermal stability of azobenzenes, which has historically been a major disadvantage. Compared to the more commonly used carbon-based polymer systems, we can achieve higher photo-stability, increasing life time. This progress can open opportunities to many future research areas and applications.

43 Excited-State Manipulation via Nitro-Derivatization of Iridium Complexes

Ryan M. O’Donnell, T.J. Rohrabaugh, Alexis R. Burnette, Shamya K. London, Peter Y. Zavalij, and William M. Shensky III – Army Research Laboratory, Arizona State University; University of Arkansas at Pine Bluff; University of Maryland X-Ray Crystallographic Center

Organometallic iridium(III) complexes have seen widespread use over the past two decades, particularly as phosphorescent dopants in organic light emitting diodes (OLEDs). Interest in the nonlinear optical (NLO) applications of these materials has increased recently with reports of both two-photon absorption (2PA) and reverse saturable absorption (RSA). In order to achieve panchromatic RSA materials, we investigated the effect of introducing a nitro functional group at different positions along the 2-phenylbenzothiazole (pbt) cyclometalating ligand. The synthesis and spectroscopic characterization of four new complexes of the form [IrIII(C^N)2(acac)]0 where C^N is the nitro-derivatized pbt ligand and acac is acetylacetonate, will be presented. Particular emphasis on the photoluminescence and transient absorption properties will be discussed with respect to their potential application as RSA materials.

44 Unified Theme for Investigating Diverse Hydrogen Bonding

Mohamed Ayoub – Department of Mathematics and Natural Sciences, University of Wisconsin-Milwaukee

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at Washington County

We present a unified theme for diverse hydrogen bonded dimers, using density functional level of theory

and aug-cc-pVTZ basis set followed by natural bond orbital (NBO) analysis. Our analysis for more than fifty dimers include: neutral-neutral, neutral-charged (±), isomeric and pi(π) confirms that the physical basis for hydrogen bonding is due to delocalization of electrons from Lewis-base monomer (B, QCT) to

antibonding of Lewis acid monomer (HA, *H⎯A) and there is no evidence for dipole-dipole interaction.

We show that there is a strong correlation between experimental hydrogen bonding descriptors -energetic and structural- such as: hydrogen bond energy (DEH…B), hydrogen bond distance (RB….H),

elongation and IR-red shift of Lewis-acid bond (RHA & ) with theoretical descriptors: charge-transfer

(QCT) with corresponding stabilization energy (EQCT→*H⎯A), hydrogen bond order (bB…H) and Lewis-acid

bond order (bHA), in addition to contour and surface plots for overlap orbitals.

45 Rational Design and Synthesis of Macrocycle-Based Optical Chemosensors for Detection of Environmentally Relevant Anions

Aco Radujevic and Pavel Anzenbacher, Jr. – Center for Photochemical Sciences, Bowling Green State University

Sensing of environmentally relevant anion species is of crucial importance in reducing and managing the negative effect of eutrophication phenomenon. In particular, phosphorus-induced eutrophication is global issue due to pervasive use of inorganic phosphorus containing species in industrial and agricultural

applications. Hence, the rational design of optical chemosensors to measure phosphate levels in run-offs and waste streams is of crucial importance. Here, we present two different sensing platforms for potentially highly selective and reliable sensing platforms for monitoring of phosphate species. From a synthetic perspective, the design of our sensing platforms is inspired by flexibility of sensor scaffolds exhibiting potential for a cross-reactive binding, while the necessary degree of selectivity will be brought about by the fluorescence response from the attached signaling subunit (fluorophore). In both sensor platforms, scaffolds are based on poly-azamacrocycles which provide several important aspects of sensing processes: flexibility, protonation of amine functional groups which allows for sensing application in an aqueous environment. Both sensors display the ability to preorganize, which will facilitate the anion binding. The first optical chemosensor is based on Intramolecular Indicator-Displacement approach (IIDS). The IIDSs are integrated into a single-molecule assembly composed of an anionic dye tethered to positively charged ammonium-based receptor moieties. This ensemble forms an intramolecular dye-receptor complex. In the presence of phosphate analytes, the intramolecular dye is displaced from the receptor and changes its photophysical properties (fluorescence). The second optical chemosensor comprises pyrrole hydrogen bond donors as well as ammoinium moieties for electrostatic binding of anions. This macrocyclic sensor is functionalized with Dansyl fluorophore as a signaling unit. The fluorescence of the Dansyl is modulated by the formation of the sensor-analyte complex.

46 Design, Synthesis, and Photophysical Investigation of Novel Iridium(III) Acetylacetonate Bisphenylquinoline Complexes

Thomas N. Rohrabaugh, Jr., Ryan M. O’Donnell, Trenton R. Ensley, Peter Y. Zavalij, and William M. Shensky III – U.S. Army Combat Capabilities Development Command Army Research Laboratory

Due to their tunable photoreactivity and light absorbing properties, organometallic iridium(III) complexes have a wide variety of applications such as phosphorescent dopants in organic light emitting diodes (OLEDs), chemical sensing, light harvesting for solar cells, and photodynamic therapy. Particularly, our team is interested in their non-linear optical (NLO) properties such as reverse saturable absorption (RSA) and two-photon absorption (2PA). A series of iridium(III) complexes of structure [IrIII(C^N)2(acac)]0

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(where acac = acetylacetonate and C^N = 2-phenylquinolin, 2,4-diphenylquinoline, 6-nitro-2-phenylquinoline, or 6-nitro-2,4-diphenylquinoline) were synthesized to investigate the structural and electronic effects on the photophysical properties of these complexes by the addition of a nitro and/or a phenyl group to the C^N ligand. The syntheses, chemical characterization, and photophysical properties of these iridium(III) complexes will be discussed in detail herein.

47 Real-Time Viscosity Monitoring in Adhesives Using Luminescent Coordination Complexes as Molecular Sensors

Ankit Dara, Derek M. Mast, Anton Razgoniaev, Felix N. Castellano, and Alexis D. Ostrowski – Department of Chemistry and Center for Photochemical Sciences, Bowling Green State University; Department of Chemistry, North Carolina State University

Due to their tunable photoreactivity and light absorbing properties, organometallic iridium(III) complexes have a wide variety of applications such as phosphorescent dopants in organic light emitting diodes (OLEDs), chemical sensing, light harvesting for solar cells, and photodynamic therapy. Particularly, our

team is interested in their non-linear optical (NLO) properties such as reverse saturable absorption (RSA) and two-photon absorption (2PA). A series of iridium(III) complexes of structure [IrIII(C^N)2(acac)]0 (where acac = acetylacetonate and C^N = 2-phenylquinolin, 2,4-diphenylquinoline, 6-nitro-2-phenylquinoline, or 6-nitro-2,4-diphenylquinoline) were synthesized to investigate the structural and electronic effects on the photophysical properties of these complexes by the addition of a nitro and/or a phenyl group to the C^N ligand. The syntheses, chemical characterization, and photophysical properties of these iridium(III) complexes will be discussed in detail herein.

48 Multiphoton Photochemistry of Cyclopropenones in Biomedical Applications

Vladimir Popik – Department of Chemistry, University of Georgia

Photochemical decarbonylation of cyclopropenones is a very efficient and robust reaction. In less than 100 ps upon excitation cyclopropenones lose carbon monoxide to produce corresponding acetylenes. This reaction proceeds smoothly in solution, polymer matrix, crystalline state, and in gas phase with quantum efficiency often approaching unity. The photodecarbonylation of cyclopropenones can be also induced by non-resonant two- and three-photon excitation. We have demonstrated the utility of multiphoton excitation of multiphoton photochemistry of cyclopropenones for: • in vitro and “in tissue” protein labelling (multiphoton photo-click ligation); • 3-D patterning of hydrogels and polymers; •

generation of carbon monoxide (an important gasotransmitter); • activation of enediyne antitumor antibiotics analogue.

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Map to Banquet Location:

Tommy Bahama Restaurant, 300 John Ringling Blvd, Sarasota, FL 34236

Banquet will take place on the 2nd floor, 6:30-10:30 pm

Saturday, January 4th, 2020

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29th winter inter-american photochemical society conferencebreakfast bagels and danishes will be...

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