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Photo-induced Ultrafast Intramolecular Charge Separation Process of 10-Cyano-9, 9’-Bianthryl in Polar Solvents. Takeuchi Eisukle Miyasaka Lab. Contents. Introduction What is Ionic L iquid (IL)? Solvation Dynamics. Charge Separation (CS) of bianthryl derivatives.

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slide1

Photo-induced Ultrafast Intramolecular Charge Separation Process of 10-Cyano-9, 9’-Bianthryl in Polar Solvents

Takeuchi Eisukle

Miyasaka Lab.

slide2

Contents

IntroductionWhat is Ionic Liquid (IL)?Solvation Dynamics.Charge Separation (CS) of bianthrylderivatives.

MotivationEffect of pre-solvation on CS dynamics.

Experimental method Femtosecond transient absorption (TA) spectroscopy.

My workComparison of CBA in Deme BF4 and in ACN.Comparison of symmetric and asymmetric bianthryl derivatives.

Summary

slide3

What is Ionic Liquid (IL)?

Molten organic salt at room temperature, which consists of organic cations and inorganic anions

Ionic Liquid :

Ionic Liquid

Inorganic salt

Bmim TFSI

m.p -4℃

Deme BF4

m.p 9℃

m.p 800℃

ex. NaCl

slide4

What is ionic liquid (IL)?

  • Electric conductivity
  • Vapor pressure: nearly 0
  • Hard to burn (fire resistant)
  • Heat-resistant
  • High viscosity
  • etc…

Application in various fields.

Safe and sustainable solvent

(Green solvent)

Electrochemical device(Electrolyte)

Lubricant

S. Kuwabata, et al., Chem. Lett. 35, 600 (2006)

Science 302, 792 (2003)

SEMimage of IL.

IL does not vaporize even in vacuum.

slide5

Solvation Dynamics(溶媒和ダイナミクス)

in polar organic solvent

in Ionic Liquid

δ+

δ-

CH3CN

: anion

: cation

slide6

Charge Separation (CS) of bianthryl derivatives

Photo-induced Ultrafast Intramolecular Charge Separation Process

9,9’-Bianthryl (BA)

Locally Excited (LE) state

Charge Separate (CS) state

Solute

BA

10-Cyano-9,9’-Bianthryl (CBA)

dipole moment :

(calculation)

5.12 Debye

0 Debye

slide7

Motivation

in Ionic Liquid

: anion

: cation

BA

CBA

5.12 Debye

0 Debye

dipole moment :

(calculation)

Purpose of my work :

To reveal the difference of solvation dynamics from pre-solvation : polar and non-polar solute

slide8

delay time

D t

Detector

Sample

Femtosecond transient absorption (TA) spectroscopy

Transient Absorption (過渡吸収)

pulse2

pulse1

pulse-duration : 30 fs

delay time D t : several fs~

  • Advantages of Femtosecond TA
  • Gain informations of excitation state, grand state, ionic radical, and radical of solute
  • High time-resolution(about 10-15 s)
slide9

Stady state spectrum of samples

  • CBA and BA have fluorescence solvatochromism.
  • Polarity of Deme BF4 (IL) is comparable to Acetonitrile(ACN)
  • Stokes shift of CBA is stronger than that of BA.
  • There is the LE state of BA in polar solvents.
slide10

TA spectrum of CBA / Deme BF4

Delay time : ~ 100 fs

CS state Absorption

LE state Absorption

Form Charge Separate state faster than solvation

I.G. Voigt-Martin, D.H. Yana, R. Wortmann, and K. Elich, Ultramicroscopy, 57 (1995) 29-43

slide11

TA spectrum of CBA / Deme BF4

Delay time : 0.1 ps ~

Spectrum are broadening

-

δ-

+

δ+

Structural relaxation : Delocalization

slide12

TA spectrum of CBA / Acetonitrile (ACN)

Spectrum are broadening at 0.5 ps

-

δ-

Form Charge Separate state faster than solvation

+

δ+

Structural relaxation (Delocalization) occurs on faster than in Deme BF4

LE state Absorption

CS state Absorption

slide13

Time-resolved spectrum of CBA / Deme BF4 and CBA / ACN

CS state

Rise time constant

Deme BF4 : 59 fs

ACN : 49 fs

Formation the CS state is independent of solvents.

Structural relaxation

Rise time constant

Deme BF4 : 130 fs (62 %)

69 ps (38 %)

ACN 4 : 370 fs

Structural relaxation is dependent of solvents.

slide14

TA spectrum of BA / Deme BF4

CS state Absorption

Time-resolved spectrum of CS state

CSof CBAoccurs in much faster than BA

LE state Absorption

stimulated emission

slide15

Beat signal of CBA / Deme BF4

420 ~ 500 nm: LEstate Emission

550 ~ 720 nm: CSstate Absorption

FFT (fast Fourier transform)

slide16

Beat signal of BA / Deme BF4

400 ~ 450 nm: LEstate Emission

550 ~ 600 nm: CSstate Absorption

FFT

slide17

Summary

  • Intramolecular CS reaction of CBA occurs in an ultrafast timescale of ca. 50 fs in a IL and also in a polar organic solvent, because of the solvation structure of grand state.
  • Structure relaxation of CBA is dependent of solvents : viscosity of solvent
  • CBA / Deme BF4 and BA / Deme BF4 occur coherent vibration(685cm-1) of LE state.
slide18

Charge Separation (CS) of bianthryl derivatives

CBA

BA

CBA

LE

CT

CT

LE

CT

BA

LE

CT

Reaction Rates in the Phenomenological Adiabatic Excited-State Electron-Transfer Theory

K. Tominagaet al. J. Phys. Chem. 95, 10485 (1991)

No activation energy.

Activation energy: 0.5 kcal / mol

slide19

TA spectrum of CBA / Acetonitrile (ACN)

Spectrum are broadening at 0.5 ps

fs TA spectrum (delay time : 3 ps~ )

LE state Absorption

CS state Absorption

slide20

Time-resolved spectrum of CBA / Deme BF4 and CBA / ACN

CS state

Rise time constant

Deme BF4 : 59 fs

ACN : 49 fs

Structural relaxation

Rise time constant

Deme BF4 : 130 fs (62 %)

69 ps (38 %)

ACN 4 : 370 fs

slide21

Time-resolved spectrum of CBA / Deme BF4 and CBA / ACN

Structural relaxation

Rise time constant

Deme BF4 : 130 fs (62 %)

69 ps (38 %)

ACN 4 : 370 fs

Structural relaxation is dependent of solvents.

Viscosity (at room temperature)

Deme BF4 : 590cP

ACN 4 : 0.035 cP

H2O(ref.) : 1.002 cP