Visible and infrared spectroscopy of intramolecular proton transfer using picosecond laser pulses

Abstract Intramolecular proton transfer in the excited electronic state of 2-(2-hydroxyphenyl)-benzothiazole (HBT) is investigated on the picosecond time scale. A Stokes shift of approximately 10000 cm−1 between the absorption and the fluorescence maximum and a fluorescence quantum yield of 1.5% are found for HBT in C2Cl4. A fluorescent state S' is formed within 6 ps after excitation. In the excited molecule two new infrared bands are detected which correspond to NH and C=O stretching vibrations. These data give direct proof of proton transfer. The spectroscopic data suggest that the potential energy surface of the transferred proton is very anharmonic.

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