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Takeuchi Eisukle Miyasaka Lab.

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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Takeuchi Eisukle Miyasaka Lab.

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  1. Photo-induced Ultrafast Intramolecular Charge Separation Process of 10-Cyano-9, 9’-Bianthryl in Polar Solvents Takeuchi Eisukle Miyasaka Lab.

  2. 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

  3. 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

  4. 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.

  5. Solvation Dynamics（溶媒和ダイナミクス） in polar organic solvent in Ionic Liquid δ+ δ- CH3CN : anion : cation hυ hυ

  6. Charge Separation (CS) of bianthryl derivatives Photo-induced Ultrafast Intramolecular Charge Separation Process hυ 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

  7. Motivation in Ionic Liquid : anion : cation BA CBA 5.12 Debye 0 Debye dipole moment : (calculation) hυ Purpose of my work : To reveal the difference of solvation dynamics from pre-solvation : polar and non-polar solute

  8. 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)

  9. 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.

  10. 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

  11. TA spectrum of CBA / Deme BF4 Delay time : 0.1 ps ~ Spectrum are broadening - δ- + δ+ Structural relaxation : Delocalization

  12. 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

  13. 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.

  14. 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

  15. Beat signal of CBA / Deme BF4 420 ~ 500 nm: LEstate Emission 550 ~ 720 nm: CSstate Absorption FFT (fast Fourier transform)

  16. Beat signal of BA / Deme BF4 400 ~ 450 nm: LEstate Emission 550 ~ 600 nm: CSstate Absorption FFT

  17. 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.

  18. 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

  19. 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

  20. 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

  21. 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

  22. Time-resolved fluorescence spectrum CBA / ACN CBA / Deme BF4

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