Ultrafast Excited-State Isomerization Dynamics of 1,1‘-Diethyl-2,2‘-Cyanine Studied by Four-Wave...

Ultrafast Excited-State Isomerization Dynamics of 1,1‘-Diethyl-2,2‘-Cyanine Studied by Four-Wave Mixing Spectroscopy

Benjamin Dietzek, Niklas hristensson, Torbjörn Pascher, Tõnu Pullerits, and Arkady Yartsev

J. Phys. Chem. B, 2007, 111 (19), pp 5396–5404

Miyasaka Lab.Masayasu Muramatsu

Contents

　 Introduction Photoinduced Isomerization 1122C 　 Excited-State bond-twisting

motion

　 Experimental method Transient Absorption TransientGrating Three-pulse photon echo peak-shift

　 Results ＆ Discussion 　 Summary

Photoinduced Isomerization

h

11-cis retinal

all-trans retinal

200fs

trans-stilbene

cis-stilbene

h’254nm

h313nm

Control　 pathway　 rate 　 .etc

model system 　 vs 　 biological system　　　→ function of the protein matrix

eye sight

Excited-State bond-twisting motion

N+ N

C2H5 C2H5

N+

N

C2H5

C2H5

Methanol

500ps

538nm523nm

trans-1122Ccis-1122C

Transient Absorption

A →h

Pump

Sample

A

A

Reference

ProbeProbe

Transient species

A = -log II0

Pulse participation

StimulatedEmission（ SE ）

GroundState

Bleach（ GSB ）

ExcitedState

Absorption（ ESA ）

time

Hole spectrum

Transient Grating （ TG ）

１）　 Thermal change２）　 Volume change３）　 Spectrum change

2pulse interference

3pulse interferencen(t) ： refracture indexk(t) ： absorbance

Three-pulse photon echo peak-shift

τ 0≫ ： decoherent 　　　　　　　　 → 　 no echoT 0≫ ： vanish diffraction fringe 　 → 　 no echo

Three-pulse photon echo peak-shift

Signal ink3+k2-k1

direction100fs1ps10ps100ps

Transient Absorption

Stimulated emission

4.9psESA:excited-state population

405nm

405nm(filled triangle)573nm(open star)700nm(open triangle)850nm(open aquare)1000nm(filled circle)

Transient Grating 548nm

Rise:Stimulated Emission (dark state)Decay:Internal Conversion

Viscosity, large →Decay time, large

Transient Grating 530nm 495nm

495nm ： no emission　　→ no rise

530nm 495nm

3PEPS 548nm

Rise:Stimulated Emission (another state)

viscosity　 large　　↓inhomogeneity　 large

The osillation pattern is insensitive to solvent　 →　 It is not related to torsion

3PEPS

VibrationalRelaxation

5ps~ Rise: cis isomer formation ? or Ultrafast Internal Conversion ?

methanol propanol

548nm(red), 530nm(green), 495nm(blue)

Summary

Transient Absorption ESA(405nm): ~1ps(flat),τ=4.9ps(decay) SE(548nm):~1ps(decay)→dark state

Transient Grating wavelength dependent rise ← ESA solvent dependent decay ← internal conversion

3PEPS high viscosity

→high inhomogeneity rise(495nm) →cis isomer?

1ps

4.9ps

500ps

538nm523nm