Measurements of the Complete Solvation Response in Ionic Liquid Sergei Arzhantsev, Hui Jin, Gary A. Baker, and Mark Maroncelli J. phys. Chem. B 2007,111, 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 1-ethyl-3-methylimidazolium （ emim + ） bis(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. Introduction Experiment Results & Discussion Conclusion Ionic Liquid Example emimTFSI (m.p. -16 ℃ ) S. Hayashi & h.Hamaguchi, Chem. Lett. 33, (2004)

4 : dipole rotation diffusion Solvent Influence Introduction Experiment Results & 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 Introduction Experiment Results & Discussion Conclusion X-rays Ultraviolet Rays visible infrared Micro waves Wavelength (m) vibration Rotation electronic excitation Photo-Excitation at UV-Vis Region IR spectroscopy Electro magnetic spectrum HOMO LUMO Ground stateExcited state

6 Detection of Dynamic Stokes Shift Time-resolved spectroscopy can directly observe solvation dynamics ! Excited state h Ground state time Introduction Experiment Results & Discussion Conclusion Energy relaxation time BlueRed Time-scale of solvation in IL: Femtosecond~nanosecond

7 Time-correlated single photon counting (TCSPC) : >20 ps Femtosecond: Roughly 50% of the solvation response is too rapid to be observed by TCSPC ･･･ Picosecond: TCSPC KGE (ps) KGE + TCSPC technique may give us complete solvation Instrumental Time-Resoluton Introduction Experiment Results & Discussion Conclusion Kerr-gated emission (KEG) ~450 fs

8 T ime- c orrelated s ingle p hoton c ounting TCSPC Experiment Introduction 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 tt’ photon Laser pulse 125 ns time Counts

9 K err- g ated e mission KGE Experiment Introduction Results & Discussion Conclusion KGE set up

10 K err- g ated e mission KGE 2 Experiment Introduction Results & Discussion Conclusion benzene Kerr-Gate benzene

11 Sample Experiment Introduction Results & Discussion Conclusion Solvatochromic probe : Trans-4-dimethylamino-4’-cyanostilbene

12 Results of KGE+TCSPC IntroductionConclusionExperiment Results & discussion h time Time-resolved emission spectra of DCS in [Im 41 + ] [BF 4 - ] Peak shift ☞ solvation Fast (fs) and slow (ps~ns) time

13 Emission peak shift IntroductionConclusionExperiment Results & 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 IntroductionConclusionExperiment Results & discussion    Reduced mass( 換算質量 ) (R + + R - ) : Sum of van der Waals radii There is a reasonable correlation of both f 1 and  1 with 1/{  ± (R + + R-)} 1/2

15 pico~nanosecond component IntroductionConclusionExperiment Results & discussion Time scale of slower component is not directly proportional to viscosity  but rather to  p (p≈1.2 – 1.3) D=kT / 6  r Slow components associate with diffusion??

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 of a sub-picosecond component associated with inertial solvent motion And a dominant “slow” component which is correlated to the solvent viscosity. Conclusion IntroductionExperiment Results & Discussion conclusion