Observation of Coherent molecular oscillation : Herzberg-Tell

er type Wave Packet Motion

in Porphyrin J-aggregates

MIYASAKA Lab.Tetsuro KATAYAMA

Contents

“Observation of Herzberg － Teller-type Wave Packet Motion

in Porphyrin J-Aggregates Studied by Sub-5-fs Spectroscopy”

H. Kano, T. Saito,and T. Kobayashi . J. Phys. Chem. A, 2002, 106, 3445

Coherent molecular oscillation

Franck-Condon typeWave Packet Motion

Herzberg-Teller typeWave Packet Motion

Introduction

N. F. Scherer, et al., JCP,1993, 99, 153

Coherent molecular oscillation observed 　　 by femtosecond transient spectroscopy

Coherent molecular oscillation ： コヒーレントな分子振動Iodine ： ヨウ素 (I2)

Coherent molecular oscillation

Probe

Pump

Detector

Delay TimeSample

0

0 t

t

A

⊿

A

⊿

τ

･ Photoinduced absorption

･ Photo-bleaching , stimulated emission

Pump-probe spectroscopy

Photoinduced (Transient) absorption 　：　過渡吸収Stimulated emission 　：　誘導放出

Photo-bleaching ： ブリーチ

Franck-Condon type wave packet motion Linear coupling assuming harmonic oscillator

En

erg

y

Nucleus separation

･ The curvature is the same.･ Equilibrium nuclear 　 position is different.･ Coherent oscillation of transient 　absorption and stimulated 　emission are observed

･ Raman transitions causes wave packet motion in the ground state which can be observed in the photo-bleaching

excitedstate

groundstate

Franck-Condon type wave packet motion ： フランクコンドン型波束運動Raman transitions ： ラマン遷移Equilibrium nuclear position ： 平衡核

間距離

oscillate

Overtone was observed at 526nm probe for iodine

580 nm pump580 nm probe

580 nm pump526 nm probe

211 cm-1

420 cm-1

Overtone ： 倍音 N. F. Scherer, et al., JCP,1993, 99, 153

Why was overtone observed ? Typical Franck-Condon type wave packet

motion

524 nm

Center

Turning point

580 nm ,480 nm 　　　　　　

I2 excited state energy surfaces

ground state

N. F. Scherer, et al., JCP,1993, 99, 153

Theory Herzberg-Teller type wave packet motion

En

erg

y

Nucleus separation

･ The curvature is the same. ･ No displacement between the equilibrium position.

･ Transition frequency do not depend on the wave packet position. ･ In Herzberg-Teller type model .

Transition dipole moment depends on the wave packet position

μ+δμ

μ

μ-δμ

Herzberg-Teller type wave packet motion ： ヘルツベルグテラー型波束運動

constant

Two types of wave packet motion

Wavelength Wavelength

⊿

Franck-Condon type

Herzberg-Teller type

A

Experimental Sample　 Tetraphenylporphine 　tetrasulfonic acid 　

( TPPS4 ) 　　　　　　　　　　　　　　　 　　　　　　　　　　　　　　

～ 2nm

J-aggregate

R. Rotomskis et al J. Phys. Chem.B, 2004, 108, 2833

J-aggregate ： Ｊ会合体

AFM image of Macroscopic TPPS4 J-aggregates

AFM ： 原子間力顕微鏡法

(AFM image) (Optical microscopy)

Optical microscopy ： 光学顕微鏡 R. Rotomskis et al J. Phys. Chem.B, 2004, 108, 2833

Stationary absorption and fluorescence

H.Kano.et at.Journal of the Chinese Chemical Society, 2000, 47, 859

Stokes shift is very small(>20meV)

Transient absorption spectrum

Photo-bleaching andstimulated emission

Transient absorption

320fs

Probe wavelength dependence of the coherent oscillation

Overtone wasn’t observed

AmplitudeReversed at ～ 1.78eV

Resonance Raman spectrum

ruffling mode

It is attributed to out-of-plane ruffling mode

Frequency dependence of the initial phase and amplitude

Initial phase is constant

Amplitude is reversed around 1.78eV(697nm)

It might not be Franck-Condon type

Oscillation was observed in the integrated signal

Oscillation was also observed in the integrated signal from 1.65 to 1.91eV(752nmto 649nm)

It might not be Franck-Condon type

247cm-1

Justification of Herzberg-Teller type

1 Stokes shift was small(>20meV)

2 Over tone wasn’t observed at any

wavelength

3Amplitude was reversed around 1.78eVbut phase was constant.

4Coherent oscillation was also observedfrom integrated signal

Summary

The wave packet observed in the present study can be classified as a Herzberg-Teller type in contrast with the frequently studied conventional Franck-Condon type.

vibration

: Window function

X-ray Crystallography Ⅰ

X-ray Crystallography Ⅱ

How know formation of j-aggregate?

J-band

Dynamic IntensityBorrowing

-Vibronic coupling

-Configration interaction

Vibronic coupling parity-forbidden

a 　 vibration of the molecule can destroy the　 Inversion symmetry

The removal of the centre of symmetry gives rise to a vibronically allowed transition.

Experimental Setup

Laser system

Introduction Pump-Probe Spectroscopy　

Probe

Pump

TransmittanceDetection

Delay TimeSample

　

･･ What is Window function ?What is Window function ?

J-aggregate

Why is Stokes shift small ? Frenkel exiciton

: TPPS

: Transition dipole moment

Frenkel exiciton make a mode strong

Atkins,D.L. et al ,J. Phys. Chem., 1996, 100, 14391

Problem Really was it observed ?

E.A.Carson,et al.,J.phys.Chem.A 2004,108,1489-1500

Theory Herzberg-Teller type

μ

μ+δμ

－ δμ+δμ

μμ

Why does a wave packet form?

Results ＆ Discussions Stationary absorption

T. Ogawa et al..Chemical Physics Letters ,2005,408 ,186

J-band

(J-aggregate) (Monomer)

The laser spectrum

Resonance Raman spectrum