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advances.sciencemag.org/cgi/content/full/6/41/eaba7855/DC1
Supplementary Materials for
Acceptor plane expansion enhances horizontal orientation of thermally activated
delayed fluorescence emitters
Yepeng Xiang, Pan Li, Shaolong Gong*, Yu-Hsin Huang, Chun-Yu Wang, Cheng Zhong, Weixuan Zeng, Zhanxiang Chen, Wei-Kai Lee, Xiaojun Yin, Chung-Chih Wu*, Chuluo Yang*
*Corresponding author. Email: [email protected] (S.G.); [email protected] (C.-C.W.); [email protected] (C.Y.)
Published 9 October 2020, Sci. Adv. 6, eaba7855 (2020)
DOI: 10.1126/sciadv.aba7855
This PDF file includes:
General Information Photophysical Characterization The Fitting of Transient Photoluminescence Decay Curves and Analyses of Rate Constants X-Ray Structural Analysis of PXZPyPM Determination of the Emitting Dipole Orientation of an Emitting Layer Calculation of Thin-Film Emission Characteristics, OLED Optical Out-Coupling Efficiency and Theoretical External Quantum Efficiency Synthesis and Characterization of PXZPyPM and PXZTAZPM Figs. S1 to S10 Tables S1 to S4
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General Information:
All the reagents and solvents used for the synthesis or measurements were
commercially available, and used as received unless otherwise stated. The 1H NMR
and 13
C NMR spectra were recorded on Bruker Advanced II (400 MHz) spectrometer
with CDCl3 CD2Cl2 or DMSO-d6 as the solvent and tetramethylsilane (TMS) as an
internal reference. Elemental analysis of carbon, hydrogen, and nitrogen was
performed on a Vario EL III microanalyzer. Molecular masses were determined by a
Thermo Trace DSQ II GC/MS. Thermogravimetric analysis (TGA) and differential
scanning calorimetry (DSC) were performed on NETZSCH STA 449C instrument
and NETZSCH DSC 200 PC unit under a nitrogen atmosphere, respectively. The
thermal stability of the samples was determined by measuring their weight loss,
heated at a rate of 10 oC min
-1 from room temperature to 600
oC. The decomposition
temperature (Td) was determined as the temperature that corresponds to 5% weight
loss of the initial weight of the compounds. The glass transition temperature (Tg) was
determined from the second heating scan at a heating rate of 10 oC min
-1 from -60 to
200 oC. Cyclic voltammetric (CV) studies of the compounds were carried out in
nitrogen-purged dichloromethane (CH2Cl2) at room temperature with a CHI
voltammetric analyzer. n-Bu4PF6 (0.1 M) was used as the supporting electrolyte. The
conventional three-electrode configuration consists of a platinum working electrode, a
platinum wire auxiliary electrode, and an Ag wire pseudo-reference electrode with
ferrocene (Fc/Fc+) as the external standard. The HOMO energy levels (eV) of the
compounds were calculated according to the formula: -[4.8+(E1/2(ox/red)-E1/2(Fc/Fc+))]eV.
The LUMO energy levels (eV) of the compounds were calculated by using HOMO
levels and energy gap. The energy levels of S1 and T1 were calculated based on the
onset wavelengths of fluorescence (300 K), fluorescence (77 K) and phosphorescence
(77 K) spectra of three emitters in the mCPCN host (6.0 wt.%). Then the ΔEST values
were obtained on the basis of the equation of ΔEST = S1 (77 K) - T1 (77 K).
Photophysical Characterization:
Synthesized compounds were subjected to purification by temperature-gradient
sublimation in high vacuum before use in subsequent studies. Thin films for
photophysical characterization were prepared by thermal evaporation on quartz
substrates at 1-2 Å/sec in a vacuum chamber with a base pressure of
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The integration time window used for phosphorescence measurements was 1 ms.
Photoluminescence quantum efficiency (PL) was characterized by a
spectrofluorimeter (FluoroMax-P, Horiba Jobin Yvon Inc.). PLs of thin films were
determined using the spectrofluorimeter equipped with a calibrated integrating sphere.
During the PL measurements, the integrating sphere was purged with pure and dry
nitrogen to keep the environment inert. The selected monochromatic excitation light
of 325 nm was used to excite samples placed in the calibrated integrating sphere.
There were at least five independent samples for the PL measurements of each
emitter/host system.
The Fitting of Transient Photoluminescence Decay Curves and Analyses of Rate
Constants:
The lifetimes of transient photoluminescence decay curves of emitters were fitted
based on the following equations:
Bi-exponential Fitting N (t) = Ae-t τp⁄ +Be-
tτd⁄ +C I
chi-square = ∑(Nfitting-Nexperiment)
2
Nexperiment
X = A+B
a = A/X, b = B/X
Y = aτp + bτd
Фp = (aτp/Y) ФPL, Фd = (bτd1/Y) ФPL
The rate constants were calculated by assuming knr, S 90%). The rate constants of
radiation (kr), ISC (kISC) and RISC (kRISC) of the emitters were obtained based on the
following equations:
kp= 1
τp II
kd=
1
τd III
kr = Φpkp + Φdkd ≈ Φpkp IV
kISC=
Φd
Φd+Φp*kp ≈(1-Φp)kp V
kRISC≈ Φd
Φp*kp*kd
kISC VI
X-Ray Structural Analysis:
The single crystal of PXZPyPM was achieved from solvent evaporation method from
chlorobenzene. Single-crystal X-ray-diffraction data were obtained from a Bruker
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APEX2 Smart CCD diffractometer through using MoKα radiation (λ = 0.71073 Å)
with a ω/2θ scan mode at 296 K. Structures of the crystals were solved by direct
methods using the APEX2 software. None-hydrogen atoms were refined
anisotropically by full-matrix least-squares calculations on F2
using APEX2, while the
hydrogen atoms were directly introduced at calculated position and refined in the
riding mode. Drawings were produced using Mercury-3.3. CCDC-1860254
(PXZPyPM) contains supplementary crystallographic data. These data can be
obtained free of charge from the Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
Determination of the Emitting Dipole Orientation of an Emitting Layer:
To determine the emitting dipole orientation in a molecular emitting film,
angle-resolved and polarization-resolved photoluminescence measurements were
performed. The sample consisted of a fused silica substrate with the 30-nm-thick
mCPCN film doped with emitters. The sample was attached to a fused silica half
cylinder prism by index matching liquid. The excitation of the samples was performed
with the 325-nm line of the continuous-wave He:Cd laser with a fixed excitation
angle of 45o. The emission angle was changed by use of an automatic rotation stage.
The spectra were resolved by using a p-polarizing filter and were measured by a fiber
optical spectrometer. The angle-dependent p-polarized emission intensity at the peak
wavelength of the PL spectrum of the emitting layer was detected. The emitting
dipole orientation (the horizontal dipole ratio Θ//) was then determined by least square
fitting of the measured angle-dependent p-polarized emission intensity with calculated
results.
Calculation of Thin-Film Emission Characteristics, OLED Optical Out-Coupling
Efficiency and Theoretical External Quantum Efficiency:
The simulation tool used for optical simulation of organic layer structures and OLEDs
is developed by ourselves and is based on the equivalence between molecular
emission through electronic dipole transitions and radiation from classical electrical
dipole antenna. With plane-wave expansion of a dipole field (with each plane-wave
mode being characterized by an in-plane wave vector kt), electromagnetic fields
generated by a radiation dipole embedded in a layered structure is calculated, from
which the distribution of the radiation power into different plane-wave modes and the
far-field radiation can be obtained. Emission characteristics of an emitting layer or an
OLED are calculated by assuming that the emitting layer contains an ensemble of
mutually incoherent dipole radiators with distributions in orientations, locations, and
frequencies. The overall emission characteristics and optical out-coupling efficiencies
of internally generated radiation into air were calculated by locating emitting dipoles
in the emitting layer and by considering the orientational distribution [using the
emitting dipole orientation measured] and the full spectral distribution [using the
photoluminescence spectra of emitting layers] of radiating dipoles. When calculating
the pure optical out-coupling efficiency (ηout), the emitters are assumed to have 100%
emission quantum efficiency. In addition, the refractive indexes (n) and extinction
http://www.ccdc.cam.ac.uk/data_request/cif
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coefficient (k) of each material in our device structure are used for calculating ηout (fig.
S1).
fig. S1. Optical parameters. (a) The refractive indexes (n) and (b) extinction
coefficient (k) of each material used in the devices.
The theoretical external quantum efficiency (EQEtheoretical) is estimated using the
following equation:
EQE
theoretical = η
rΦPLγηout VII
where ηr refers to a fraction of radiative excitons, γ represents the charge balance
factor, andФPL is the photoluminescence quantum yield of the emitter doped into the mCPCN host (the doping concentration is 6 wt.%). Assuming the perfect charge
balance (γ = 1) and full harvesting of singlet and triplet excitons (ηr = 1), combined
with the ФPL values of 100% for both PXZPM and PXZPyPM and 93% for PXZTAZPM, as well as the simulated ηout values (34.0%, 39.1%, and 39.7% for the
PXZPM-, PXZPyPM-, and PXZTAZPM-based devices, respectively), the theoretical
EQEs calculated with ФPL ηout are 34.0%, 39.1%, and 36.9% for PXZPM-, PXZPyPM-, and PXZTAZPM-based devices, respectively.
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Synthesis and Characterization of PXZPyPM and PXZTAZPM:
fig. S2. Synthetic route of PXZPyPM and PXZTAZPM.
The corresponding halogen precursor of ClPPM and borate precursors were prepared
according to literature precedence (26).
2-(4-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)pyridine (1): To a
mixture of 2-(4-bromophenyl)pyridine (702 mg, 3.0 mmol), bis(pinacolato)diboron
(1.14 g, 4.5 mmol), potassium acetate (1.18 g, 12 mmol) and Pd(dppf)Cl2 (110 mg,
0.15 mmol) was added 50 mL of degassed dioxane. After stirring at 90 oC under an
argon atmosphere for 24 h, the mixture was cooled down to room temperature and
extracted with 3 × 40 mL of dichloromethane. The collected organic phase was
washed with brine and dried with anhydrous Na2SO4. After removal of the solvent,
the residue was purified by column chromatography on silica gel (eluent: petroleum /
ethyl acetate = 5:1, v/v) to afford the product as white solid (400 mg, yield: 47%). 1H
NMR (400 MHz, DMSO-d6 + TMS, 298K) δ [ppm]: δ 8.69 (d, J = 7.3 Hz, 1H), 8.12
(d, J = 8.2 Hz, 2H), 8.00 (d, J = 8.0 Hz, 1H), 7.90 (td, J = 7.8, 1.6 Hz, 1H), 7.80 (d, J
= 8.3 Hz, 2H), 7.39 (dd, J = 7.3, 4.8 Hz, 1H), 1.32 (s, 12H).
2,4-Diphenyl-6-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)-1,3,5-tria
zine (2): Prepared according to the same procedure as Compound 1 but using
2-(4-bromophenyl)-4,6-diphenyl-1,3,5-triazine. The residue was purified by column
chromatography on silica gel (eluent: petroleum / ethyl acetate = 5:1, v/v) to afford
the product as white solid (220 mg, yield: 52%). 1
H NMR (400 MHz, DMSO-d6 +
TMS, 298K) δ 8.76 (d, J = 7.9 Hz, 6H), 7.96 (d, J = 8.0 Hz, 2H), 7.76-7.66 (m, 6H),
1.36 (s, 12H).
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10,10'-((2-(4-(Pyridin-2-yl)phenyl)pyrimidine-4,6-diyl)bis(4,1-phenylene))bis(10
H-phenoxazine) (PXZPyPM): To a mixture of
10,10'-((2-chloropyrimidine-4,6-diyl)bis(4,1-phenylene))bis(10H-phenoxazine)
(ClPPM) (628 mg, 1.0 mmol),
2-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)pyridine (Compound 1)
(422 mg, 1.5 mmol), potassium carbonate (2.76 g, 20 mmol) and Pd(PPh3)4 (35 mg,
0.03 mmol) was added 20 mL of degassed tetrahydrofuran and 10 mL of degassed
water. After stirring at 80 oC under an argon atmosphere for 24 h, the mixture was
cooled down to room temperature and extracted with 3 × 40 mL of chloroform. The
collected organic phase was washed with brine and dried with anhydrous Na2SO4.
After removal of the solvent, the residue was purified by column chromatography on
silica gel (eluent: petroleum/dichloromethane = 1:2, v/v) to afford the product as a
yellow powder (470 mg, yield: 63%). 1H NMR (400 MHz, CD2Cl2-d2 + TMS, 298 K)
δ [ppm]: 8.80 (d, J = 8.6 Hz, 2H), 8.66 (d, J = 6.5 Hz, 1H), 8.53 (d, J = 8.5 Hz, 4H),
8.18 (d, J = 8.6 Hz, 2H), 8.14 (s, 1H), 7.83 (d, J = 8.0 Hz, 1H), 7.75 (td, J = 7.8, 1.6
Hz, 1H), 7.53 (d, J = 8.5 Hz, 4H), 7.23 (ddd, J = 7.3, 4.8, 1.0 Hz, 1H), 6.66-6.54 (m,
12H), 6.00 (dd, J = 7.8, 1.5 Hz, 4H). 13
C NMR (100 MHz, CDCl3-d) δ[ppm]: 164.5,
164.2, 156.7, 149.6, 144.0, 141.6, 138.3, 137.4, 137.2, 134.0, 131.5, 130.1, 129.0,
127.2, 123.3, 122.6, 121.7, 121.1, 115.6, 113.3, 110.7. EI-MS m/z: 747.7 [M+] (calcd:
747.3). Elemental analysis for C51H33N5O2: C, 81.91; N, 9.36; H, 4.45. Found: C,
81.78; N, 9.29; H 4.37.
10,10'-((2-(4-(4,6-Diphenyl-1,3,5-triazin-2-yl)phenyl)pyrimidine-4,6-diyl)bis(4,1-
phenylene))bis(10H-phenoxazine) (PXZTAZPM): Prepared according to the same
procedure as PXZPyPM but using
2,4-diphenyl-6-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)-1,3,5-triazine
(Compound 2). The residue was purified by column chromatography on silica gel
(eluent: dichloromethane) to afford the product as yellow solid (1.20 g, yield: 67%). 1H NMR (400 MHz, CDCl3-d + TMS, 298 K) δ [ppm]: 9.01-8.96 (m, 4H), 8.83 (dd, J
= 8.0, 1.6 Hz, 4H), 8.60 (d, J = 8.5 Hz, 4H), 8.20 (s, 1H), 7.65-7.60 (m, 10H),
6.76-6.63 (m, 12H), 6.07 (dd, J = 7.8, 1.5 Hz, 4H). 13
C NMR (100 MHz, CDCl3-d) δ
[ppm]: 171.8, 171.4, 164.2, 144.0, 141.7, 141.4, 137.3, 136.2, 134.0, 132.7, 131.6,
130.1, 129.2, 129.0, 128.8, 128.7, 123.3, 121.7, 115.7, 113.3, 111.1. EI-MS m/z:
901.8 [M+] (calcd: 901.3). Elemental analysis for C61H39N7O2:
C 81.22, N 10.78, H
4.36. found: C 81.12, N 10.68, H 4.24.
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fig. S3. The energy levels and frontier molecular orbitals. (a) Acceptor segments.
(b) PXZPM, PXZPyPM and PXZTAZPM.
table S1. The calculated key parameters of excited states of PXZPM, PXZPyPM
and PXZTAZPM.
Emitter Excite state D* (Å) Sr Orbital contributions
†
PXZPM S1 2.168 0.29498 H-L:0.63; H1-L1:0.207
T1 1.858 0.47834 H1-L:0.467; H-L1:0.187
PXZPyPM S1 3.839 0.21362 H-L:0.565; H-L2:0.088
T1 1.768 0.51693 H2-L1:0.288; H-L:0.161
PXZTAZPM S1 2.584 0.22417 H-L1:0.629; H1-L3:0.136
T1 2.106 0.47393 H1-L1:0.361; H4-L:0.145
*Distance between centroid of hole and electron. †The top two orbital contributions of
excite state.
fig. S4. Structure of PXZPyPM. (a) Single crystal structure (CCDC number:
1860254, Triclinic, P-1) and molecular packing diagram of PXZPyPM with hydrogen
atoms omitted (solvent molecules: chlorobenzene). (b) Comparison between the
single crystal structure (green) and the DFT optimized structure (red) of PXZPyPM.
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fig. S5. p-polarized photoluminescence intensity measurements. Different emitting
layers (at photoluminescence peak wavelength) as a function of the emission angle
and simulated curves (lines and dotted lines) with different horizontal dipole ratios Θ//
of (a) PXZPM, (b) PXZPyPM, (c) PXZTAZPM doped into the mCPCN host (3.0, 6.0
and 12.0 wt.%), and (d) PXZPM, PXZPyPM and PXZTAZPM doped into the CBP
host (6.0 wt.%).
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fig. S6. Thermal and electrical properties of PXZPyPM and PXZTAZPM. (a)
TGA curves of PXZPyPM and PXZTAZPM. (b) DSC curves of PXZPyPM and
PXZTAZPM. (c) Oxidation behavior of PXZPyPM and PXZTAZPM.
table S2. Thermal, electrochemical and TD-DFT calculation data of PXZPM,
PXZPyPM and PXZTAZPM.
compounds HOMO
*/LUMO
†
(eV)
HOMO/LUMO‡
(eV)
ΔEST§ (eV)
Tg/Td||
(oC)
PXZPM -5.10/-2.42 -4.73/-2.15 0.18 115/488
PXZPyPM -5.08/-2.36 -4.70/-2.05 0.22 162/489
PXZTAZPM -5.10/-2.44 -4.74/-2.22 0.20 185/503
*Obtained from Cyclic voltammograms in CH2Cl2 solution at room temperature; †LUMO = HOMO
a + Eg;
‡Estimated from DFT calculations. §Estimated from the
excited state analysis of S1 and T1. ||Measured by DSC or TGA.
fig. S7. Solvatochromic measurements. Normalized photoluminescence spectra of
(a) PXZPM, (b) PXZPyPM, and (c) PXZTAZPM (10-5
M) in toluene, chlorobezene,
tetrahydrofuran, and chloroform at 300 K (Excitation wavelength: 400 nm).
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fig. S8. Transient photoluminescence decay curves in the mCPCN host. The
transient photoluminescence decay spectra and fitting curves of 6.0 wt.% (a) PXZPM,
(b) PXZPyPM, and (c) PXZTAZPM doped into the mCPCN host at 300 K, following
excitation at 377 nm, detected at 521, 524, and 528 nm (photoluminescence peak
wavelength), respectively. The time-resolved photoluminescence spectra (20 and 5000
ns) of 6.0 wt.% (d) PXZPM, (e) PXZPyPM, and (f) PXZTAZPM doped into the
mCPCN host at 300 K (Excitation wavelength: 377 nm). The transient
photoluminescence decay spectra of 6.0 wt.% (g) PXZPyPM and (h) PXZTAZPM
doped into the mCPCN host from 100 to 300 K, following excitation at 377 nm,
detected at 524 and 528 nm (photoluminescence peak wavelength), respectively.
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fig. S9. Photoluminescence properties of PXZPM, PXZPyPM, and PXZTAZPM
doped into the PMMA films. Normalized fluorescence (300 K) and phosphorescence
(77 K) spectra of 6.0 wt.% (a) PXZPM, (b) PXZPyPM, and (c) PXZTAZPM doped
into the PMMA films (Excitation wavelength: 365 nm). The transient
photoluminescence decay spectra and fitting curves of 6.0 wt.% (d) PXZPM, (e)
PXZPyPM, and (f) PXZTAZPM doped into the PMMA films at 300 K, following
excitation at 377 nm, detected at 516, 518, and 517 nm (photoluminescence peak
wavelength), respectively. The time-resolved photoluminescence spectra (20 and 5000
ns) of 6.0 wt.% (g) PXZPM, (h) PXZPyPM, and (i) PXZTAZPM doped into the
PMMA films at 300 K (Excitation wavelength: 377 nm).
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fig. S10. Electroluminescence performance of devices. (a) Current
density-voltage-luminance curves of the devices based on emitting layers with
different doping concentrations of PXZPyPM emitter in the mCPCN host (Inset:
Electroluminescence spectra of the devices). (b) Power efficiency and external
quantum efficiency versus luminance curves of the PXZPyPM-based devices. (c)
Current density-voltage-luminance curves of the devices based on emitting layers
with different doping concentrations of PXZTAZPM emitter in the mCPCN host
(Inset: Electroluminescence spectra of the devices). (d) Power efficiency and external
quantum efficiency versus luminance curves of the PXZTAZPM-based devices.
table S3. Summary of electroluminescence characteristics for the devices based
on PXZPyPM and PXZTAZPM.*
compounds Doping concentration (wt.%) ELpeak (nm) EQE (%) PE (lm W-1
)
PXZPyPM
3 521 30.3 101.0
6 528 32.2 119.6
12 534 31.4 118.2
PXZTAZPM
3 522 26.9 82.2
6 530 30.1 101.5
12 536 25.0 90.6
*The device structure is ITO/MoO3 (1 nm)/TAPC (50 nm)/mCP (10 nm)/mCPCN: x
wt.% PXZPyPM or PXZTAZPM (20 nm)/3TPYMB (50 nm)/LiF (0.5 nm)/Al.
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table S4. Summary of performances of green to yellow TADF emitters (500 nm <
ELmax < 580 nm) with high external quantum efficiency (EQEmax > 30%).
Compounds ELmax (nm) EQEmax (%) PEmax (lm W
-1) Ref.
CzDBA 528 37.8 121.6 15
tBuCzDBA 542 32.4 109.8 15
cis-BOX2 518 33.4 - 20
Pm2 526 31.3 117.2 27
Pm5 541 30.6 116.3 27
4CzIPN 512 31.2 - 28
PXZPyPM 528 33.9 118.9 This work
aba7855_coverpageaba7855_SupplementalMaterial_v8