Ultrafast Heterogeneous Electron Transfer:

The Perylene TiO System2

V. May and L. WangInstitut für Physik

Humboldt-Universität zu Berlinand

S. Ramakrishna and F. WilligHMI, Berlin

Perylene on TiO2

t = 75fs ET -1 -1

w = 357cm , 421cmvib

TiO colloids2

0.5 nm

dye

hw

hw

e

TiO2

Perylen

C(CH )3 3

Cl

Cl

C(CH )3 3

-

- current interest in photoinduced heterogeneous ET V. Sundström (Lund) M. Grätzel (Laussanne)

- besides TiO use of ZnO- and 2

SnO -systems2

- transport and relaxation in the semiconductor conduction band

- back-reactions

- charge injection time of 6 fs for the system alizarin / TiO l2

- study of charge injection after internal conversion, from triplet states, from different conformations,

- theory of nonadiabatic ET well established (Marcus, Jortner)

- ultrafst ET transfer times below 1 ps since 15 eyars search for vibrational coherences

- hetrogeneous ET (perylene / TiO )2

outside a solvent (high vacuum) injection times below 100 fs

Energy level scheme and PES(perylene / TiO )2

Eg

Econ

Ee

Eval

Eg

Econ

Ee

Eval

Eg

Econ

Ee

Eval

diabatic states

|D*>|A> |D>|A>+ -

|D >|A >

Uk

Ue

Ug

2eV

3eVhw=0.1eV

l=0.1-0.3eV

t =75fsET

Uk

Ue

Ug

Ur=0

Ue

Ug

Ur=1

Ur=2

after polynomial expansion

with conduction band continuum

PES

0 20 40 60 80 100time (fs)

0.0

0.2

0.4

0.6

0.8

1.0

leve

l po

pula

tion

0 20 40 60 80 100time (fs)

0.0

0.2

0.4

0.6

0.8

1.0

leve

l po

pula

tion

Change of the Injection Time

V = 0.02 eV V = 0.2 eV

PgPg

Pe

Pe

Pcont

Pcont

Charge injection into the band continuum

Uk

Ue

Ug

Uk

Ue

Ug

l= 0.01eV

l= 0.1eV

l= 0.025 eV

Uk

Uf

Ug

Ue

l= 0.01eV

l= 0.025 eV

l= 0.1eV

Transient Absorption Spectra

t= 10 fs

Laser pulse control of the charge injection process

Uk

Ue

Ug

Uk

Ue

Ug

target state:

displaced vibrational

ground-statein Ug

length of the control pulse:

100f

Bridge Mediated Heterogeneous Electron Transfer

2eV

3eV

hw=0.1eV, l=0.1-0.3eV

Uk

Ue

Ug

U2

U1

0 20 40 60 80 100time (fs)

0.0

0.2

0.4

0.6

0.8

1.0

leve

l po

pula

tion

Pe

P1,2

Pcont

Laser Pulse Control of Bridge Mediated Heterogeneous ET

0 20 40 60 80 100time (fs)

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

leve

l po

pula

tion

0 20 40 60 80 100time (fs)

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

leve

l po

pula

tion

40 60 80 100 120 140time (fs)

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

leve

l po

pula

tion

Pg

P1,2

Pcont

Pcont

Pcont

Pe

Pe

P1,2

P1,2

Pe

Pg

Pg

E(t)

E(t)

E(t)

V =V =V =V =0.05 eVe,1 1,cont e,2 2,cont

V =V =0.05 eVe,1 1,cont

V =V =0.07 eVe,2 2,cont