Measurements of the Complete Solvation Response in Ionic Liquid

Sergei Arzhantsev, Hui Jin, Gary A. Baker, and Mark MaroncelliJ. phys. Chem. B 2007,111, 4978-4989

Miyasaka laboratory Satoe Morishima

2

Contents

Introduction -Ionic liquid as a solvent - Photo-induced solvation dynamics Femtosecond~nanosecond - Dynamic Stokes shift

Results and Discussion -Kerr-gated emission (KGE) -Time-correlated single photon counting (TCSPC) -Results of time-resolved spectroscopy -Solvation “Mechanism”

Conclusion -Bi-phasic solvation dynamics was observed.

3

N NCH3CH2

1-ethyl-3-methylimidazolium（ emim+ ）

NS S CF3

O

OF3C

O

Obis(trifluoromethylsulfonyl)imide

（ TFSI- ）

NaCl (m.p. 800 )℃

A molten salt at room temperature constituted from anion and cation.

Ionic liquid is spotlighted as a new type of solvent.

IntroductionExperimentResults &Discussion

ConclusionIonic Liquid

Example

emimTFSI (m.p. -16 )℃

S. Hayashi & h.Hamaguchi, Chem. Lett. 33, 1590-1591 (2004)

4

: dipole

rotation diffusion

Solvent Influence IntroductionExperimentResults &Discussion

Conclusion

The solvation ( 溶媒和 ) structure and molecular dynamics of ILs can be different from that of ordinary solvent.

Electric conductivity

Vapor pressure nearly 0

Hard to burn

High viscosity

Biochemistry

Energy device

material

Green chemistry

application

5

IntroductionExperimentResults &Discussion

Conclusion

X-rays

UltravioletRays

visible

infrared

Microwaves

Wavelength(m)

10-10

10-8

10-6

10-5

10-2

vibration

Rotation

electronic excitation

Photo-Excitation at UV-Vis Region

IR spectroscopy

Electro magnetic spectrum

HOMO

LUMO

Ground state Excited state

6

Detection of Dynamic Stokes Shift

Time-resolved spectroscopy can

directly observe solvation 　 dynamics !

Excited state

h

Ground state

time

IntroductionExperimentResults &Discussion

Conclusion

Energy relaxation

timeBlue Red

Time-scale of solvation in IL:

Femtosecond~nanosecond

7

Time-correlated single photon counting (TCSPC) : >20 ps

Femtosecond:

Roughly 50% of the solvation responseis too rapid to be observed by TCSPC 　･･･

Picosecond:

TCSPCKGE

10 100 100010.1 (ps)

KGE + TCSPC technique may give us complete solvation

Instrumental Time-Resoluton

IntroductionExperimentResults &Discussion

Conclusion

Kerr-gated emission (KEG) ~450 fs

8

Time-correlated single photon counting

TCSPCExperimentIntroduction

Results &Discussion

Conclusion

Light source: Ti: Sapphire laser (SHG)

Exciting λ: 　 390 nm 　　　　　　　　　　　　　　　　　　　　

System response time ： ~36 ps （ FWHM ）

Step size: 4 ps

temperature ： 295K 　

t t’

photon

Laser pulse

125 ns time

Co

un

ts

9

Kerr-gated emission KGE ExperimentIntroductionResults &Discussion

Conclusion

KGE set up

10

Kerr-gated emission KGE 2

ExperimentIntroductionResults &Discussion

Conclusion

benzene

Kerr-Gate

benzene

11

Sample ExperimentIntroductionResults &Discussion

Conclusion

Solvatochromic probe :Trans-4-dimethylamino-4’-cyanostilbene

12

Results of KGE+TCSP

CIntroduction ConclusionExperiment

Results &discussion

htime

Time-resolved emission spectra of DCS in [Im41

+] [BF4-]

Peak shift solvation☞Fast (fs) and slow (ps~ns)

time

13

Emission peak shift

Introduction ConclusionExperimentResults &discussion

Sub-ps component:

1 ： 100 ~ 700 fs (~20 %)

Dominant slower component

2 ： 80 ps ~ 3.0 ns (~80 %)

： 0.3~0.5

Bi-phasic Solvation Function

14

Sub-picosecond component

Introduction ConclusionExperimentResults &discussion

Reduced mass( 換算質量 )(R+ + R- ) : Sum of van der Waals radii

There is a reasonable correlation of both f1 and 1 with 1/{±(R++ R-)}1/2

15

pico~nanosecond component

Introduction ConclusionExperimentResults &discussion

Time scale of slower component is not directly proportional to viscosity but rather to p (p≈1.2 – 1.3)

D=kT / 6r

Slow components associate with diff

usion??

16

Author have presented KGE+TCSPC measurements of the complete solvation response in six ionic liquids using the probe DCS

Observed response functions were found to be biphasic, consisting ofa sub-picosecond component associated with inertial solvent motion And

a dominant “slow” component which is correlated to the solvent viscosity.

Conclusion Introduction ExperimentResults &Discussion

conclusion