eisuke takeuchi miyasaka lab. photoinduced electron transfer in bianthryl and derivatives in ionic...

Eisuke Takeuchi Miyasaka Lab.

Photoinduced Electron Transfer in Bianthryl and derivatives in Ionic Liquid

Contents

I. IntroductionWhat is ionic liquid (IL)?Charge transfer (CT) of bianthryl derivatives.

II. MotivationEffect of pre-solvation on CT dynamics.

III.Experimental methodFemtosecond transient absorption (TA) spectroscopy.

IV. My workComparison of symmetric and asymmetric bianthryl derivatives.

V. Summary

What is ionic liquid (IL)?

Ionic Liquid Inorganic salt

ex. NaClDeme BF4

CH3

NC2H5 C2H4OCH3

C2H5

F

B

F F

F

m.p 9℃ m.p 800℃

N NH3C C4H9

NS S

F3C CF3

O

O O

O

Bmim TFSI m.p -4℃

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

Science 302, 792 (2003)

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

SEM image of IL.IL does not vaporize even in vacuum.

What is ionic liquid (IL)?

Electric conductivityVapor pressure: nearly 0Hard to burn (fire resistant)Heat-resistantHigh viscosity etc…

Application in various fields.Safe and sustainable solvent

（ Green solvent ）Electrochemical

device （ Electrolyte ）Lubricant

Organic solventIonic Liquid

hυ

: cation: anion

CH3CN

hυ

δ+ δ-

Solvation Dynamics 　（溶媒和ダイナミクス）

Charge transfer (CT) of bianthryl derivatives

hυ

Locally Excited (LE) state Charge Transfer (CT) state9,9’-Bianthryl (BA)

*

LE emission

CN

10-Cyano-9,9’-Bianthryl (CNBA)

Solute of this experiment

Electron withdrawing group

According to quantum chemical calculationslowering CT state 0.25eV in comparison with BA

M. Jurczok et al. Chemical Physics. . 256, (2000) 137-

LE state

hυCT emission

CT state

ener

gy

solvation coordinate

CNBA

Charge transfer (CT) of bianthryl derivatives

BA

0.25eV

MotivationPeculiarity of solvation coordinate and dynamics effect reactivity of solute

CN

polar molecule nonpolar molecule with a symmetric

Pre - solvation different ?

: cation: anion

Femtosecond transient absorption (TA) spectroscopyTransient Absorption ( 過渡吸収 ) 　

D t

SampleDetector

　 delay time

pulse2

pulse1

delay time D t : several fs ~

1 fs = 10-15 s = 0.000 000 000 000 001 seconds

distance that light travels in1s 30 fs

globe7.5 times( 300,000 km )

pylori bacteria3 times( 9 μm )

pulse-duration : 30 fs

CN * CN

+

-

My work

Delay tim

e

Time constant: 0.063ps

672nm

My work

Delay tim

e-

+

CN

δ-

δ+

CN

720nm

Time constant : 60ps

Compare BA

BA

680nm

Time constant CNBA : 0.063ps BA : 1.25ps

Time constant : 60ps

Time constant: 0.063ps

hυ

*

δ-

δ+

-

+

My work

CN

CN

CN

CN

LE state

Grand state

CT state

Solvation (1.5ns)

Summary

Charge transfer in CNBA / Deme BF4 is more faster than charge transfer by solvation and unaffected by solvation

The ultrafast CT kinetics could be arising from the pre-solvation state caused by the polar nature of asymmetric CNBA, while for nonpolar symmetric BA, much drastic solvent reorganization is required.

LE stateCT state

LE state

CT state

CNBABA

0.5 kcal / mol

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

≈ 0