Tahei Tahara

Excitation-wavelength dependence of the femtosecond fluorescence dynamics of 7-azaindole dimer: further evidence for the concerted double proton transfer in solution

Abstract Excitation-wavelength dependence of the ultraviolet fluorescence dynamics of 7-azaindole dimer was examined in solution by femtosecond up-conversion method. It was found that the fluorescence decay of the dimer excited state showed a significant wavelength dependence. It changes from a bi-exponential decay to a single-exponential decay, when we scanned the excitation wavelength from 280 toward 313 nm (the red-edge of the dimer absorption). This result demonstrates that the proton-transfer dynamics itself exhibits a single exponential behavior. The obtained fluorescence data deny the appearance of the intermediate species and strongly support the concerted mechanism of the double proton transfer reaction.

Ultrafast fluorescence of the chromophore of the green fluorescent protein in alcohol solutions

The ultrafast fluorescence dynamics of solutions of the chromophore responsible for emission from the green fluorescent protein are measured by fluorescence up-conversion. Decays are non-exponential but well fit by a sum of two-exponentials. All decays have a prompt rise time. The two decay times are approximately independent of wavelength, but their weights are wavelength dependent, in a manner consistent with a spectral narrowing with time. The longer decay time has a weak dependence on medium viscosity.

Femtosecond study of solvation dynamics of DCM in micelles

Solvation dynamics of 4-(dicyanomethylene)-2-methyl-6-(p-dimethylamino-styryl) 4H-pyran (DCM) has been studied in neutral (triton X-100, TX) and cationic (cetyl trimethyl ammonium bromide, CTAB) micelles using femtosecond upconversion. Since DCM is insoluble in bulk water the observed solvation dynamics reports the relaxation dynamics exclusively at the micellar interface. It is observed that the solvation dynamics in TX is slower than that in CTAB. The solvation dynamics is described by components of 2.1, 165 and 2050 ps for TX and 0.23, 6.5 (average 1.75 ps) and 350 ps for CTAB.

Photochemical bimolecular reaction between biphenyl and carbon tetrachloride : observed ultrafast kinetics and diffusion-controlled reaction model

Abstract Ultrafast bimolecular reaction kinetics between photoexcited biphenyl and carbon tetrachloride, observed by femtosecond time-resolved fluorescence spectroscopy, is successfully interpreted by theories of diffusion-controlled reactions. The obtained decay kinetics is well explained by Smoluchowskis theory of diffusion-controlled reactions when the parameter R, distance between the reactants, is 0.39 nm. A modified kinetic theory by Collins and Kimball also explains the results satisfactorily, when R is 0.40 nm and the bimolecular reaction rate constant kact is 3.4×10 11 dm 3 mol −1 s −1 . It is suggested that molecular motions in solution for a time period of a few picoseconds is described by diffusion.

Time-wavelength two-dimensional femtosecond fluorescence imaging.

We report a new femtosecond time-resolved fluorescence spectrometer that enables us to observe fluorescence intensity as a time-wavelength two-dimensional image in a single measurement. This method utilizes a time-to-space conversion technique and fluorescence sum-frequency mixing with a femtosecond gate pulse. It provides a fluorescence image covering temporal and spectral spans of approximately 2 ps and approximately 60 nm, respectively. Calibration of the time and intensity axes of the image is made by use of a long-lived dye fluorescence. The two-dimensional fluorescence image of beta-carotene obtained demonstrates the high potential of this method for quantitative studies of ultrafast excited-state dynamics.