Keisuke Tominaga

PHOTO-INDUCED REACTIONS OF CH2I2 IN SOLUTION STUDIED BY THE ULTRAFAST TRANSIENT ABSORPTION SPECTROSCOPY

Abstract We have studied the photo-induced reactions of CH 2 I 2 upon excitation at 268 nm in CH 3 CN by femtosecond transient absorption spectroscopy. The time profile of transients observed at 400 nm consists of three components: fast rise (200 fs), fast decay (500 fs), and slow rise (7–13 ps). The first two components are independent of the solute concentration and are assigned to the photofragment CH 2 I radical. The slow rise becomes faster by increasing concentration and is assigned to the formation of a charge-transfer complex between the photofragment I and CH 2 I 2 in solute aggregate. This is followed by full electron transfer from CH 2 I 2 to I forming CH 2 I 2 + .

Ultrafast intermolecular electron transfer from orthomethoxyaniline to excited coumarin dyes

Ultrafast intermolecular electron transfer (ET) from orthomethoxyaniline (orthoanisidine, ANS) to a number of excited (S1) 4-trifluoromethyl-1,2-benzopyrones (coumarins) having differently substituted 7-amino group has been investigated by femtosecond fluorescence up-conversion technique. The ET dynamics in the present systems are nonsingle-exponential and occur faster than the diffusive solvation dynamics. The ET rates are largely dependent on the nature of the substituents at the 7-amino group of the coumarins. This dependence is well correlated with the free energy changes (ΔG0) for the ET reactions. The ET dynamics become slower on using deuterated ANS as the donor, where the amino group hydrogens of ANS are substituted by deuterium. The deuterium isotope effect, however, gradually reduces as the ET dynamics becomes faster. Conventional ET theories can not explain all the observations. The results are explained on the basis of the two-dimensional ET model, which considers the solvent coordinate and th...

Ultrafast intermolecular electron transfer in coumarin–hydrazine system

Abstract Ultrafast intermolecular electron transfer (ET) from electron-donating solvents to excited coumarin dyes has been investigated by the femtosecond fluorescence up-conversion technique. In this work we have used hydrazine derivatives as an electron-donating solvent to investigate the effects of very low oxidation potentials of electron-donating solvents on the ET dynamics. The ET rate with the aromatic hydrazines is much faster (sub-picoseconds) than that with the aliphatic hydrazine (a few tens of picoseconds), although the oxidation potential of the aliphatic hydrazine is lower than that of the aromatic hydrazine. However, the coumarin–hydrazine systems used in this study are not in the so-called Marcus inverted region. The results are discussed in light of the theoretical prediction from the two-dimensional ET model. We find that the electronic matrix element should be largely different between the aromatic and aliphatic hydrazine cases, which may result from the different molecular orbitals of these molecules.

Ultrafast dynamics of photoexcited trans-1,3,5-hexatriene in solution by femtosecond transient absorption spectroscopy

Abstract We have investigated the ultrafast dynamics of trans-1,3,5-hexatriene in cyclohexane and acetonitrile solutions following photoexcitation to the 1 1 B u state. The transient absorption in the visible region consists of an instantaneous rise (

Deuterium isotope effect on the solvation dynamics

Deuterium isotope effect on the solvation dynamics is observed in the system of aniline (AN) as a solvent for the first time by the dynamic Stokes shift method. Perdeuterated AN (AN–d7) or amino deuterated AN (AN–d2) shows slower solvation dynamics than normal AN. Deuterium effect on the solvation of N,N–dimethylaniline (DMA) is also studied and there is no isotope effect on the solvation process. The differences between AN and DMA are proposed to be related to the presence and absence of the intermolecular hydrogen bondings.

Development of two-dimensional Raman spectroscopy by higher-order optical nonlinear spectroscopy

Recent development of the optical two-dimensional spectroscopy is reviewed. This is an optical analogue of the two-dimensional magnetic resonance technique. We especially focus on the spectroscopy on the vibrational state in condensed phases and discuss about correlation of the vibrational modes which are anharmonically coupled.

Vibrational Dynamics of the OH Stretching Mode of Water in Reverse Micelles Studied by Infrared Nonlinear Spectroscopy

Vibrational dynamics of the OH stretching mode of water in the water pool of reverse micelles (H 2 O/Aerosol OT (AOT)/isooctane) are studied by nonlinear infrared spectroscopy such as transient grating method and three-pulse photon echo peak shift measurements. The W 0 value (W 0 =[H 2 O]/[AOT]) is changed from 2 to 40, which corresponds to a water pool diameter of a few nm to about 20 nm. Polarization dependent transient grating experiments show rapid anisotropy decay of the OH stretching mode, which could be due to resonant intra and intermolecular energy transfer. From the three-pulse photon echo peak shift experiments, the spectral diffusion is found to be dependent on W 0 .

Recent developments of optical two-dimensional spectroscopy in liquids

Recent development of optical two-dimensional spectroscopy is reviewed. This is an optical analogue of the two-dimensional magnetic resonance technique. We especially focus on the spectroscopy on the vibrational state in condensed phases and discuss about correlation of the vibrational modes which are anharmonically coupled.

Electron transfer dynamics in the excited state studied by stochastic-Liouville equation

Abstract Electron transfer dynamics in the excited state is theoretically investigated by means of the stoschastic-Liouville equation. We evaluate time dependence of the density matrix for the three electronic states, the ground state, locally excited state, and the charge transfer state by solving the equation numerically. We treat the optical transition and electronic interaction in the excited states quantum mechanically to investigate these effects on the reaction dynamics.

Stochastic-Liouville approach to optically induced electron transfer: electronic coherence in the reaction dynamics

Electron transfer (ET) dynamics in the excited state were investigated theoretically by means of the stochastic-Liouville equation. Time dependences of both the diagonal and off-diagonal elements of the density matrix of the three electronic states, the ground state, locally excited (LE) state and the charge-transfer (CT) state, were evaluated by solving the equation numerically. The formalism includes three major effects in the ET dynamics simultaneously: optical transition, electronic interaction between the LE and CT states and solvation dynamics. From results of the numerical calculation, roles of the electronic coupling and solvation dynamics in ET and effects of the electronic coherence created by the optical excitation on ET are discussed. Application of the present method to non-linear optical spectroscopy in briefly considered. Copyright