Analytical Chemistry and Spectroscopy
Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
Resonance Raman spectra of the three isoelectronic proton transfer systems 2-(2′-hydroxy-5′-methylphenyl)-benzotriazole (TIN), 2-(2′-hydroxyphenyl)benzothiazole (HBT) and 2-(2′-hydroxyphenyl)benzoxazole (HBO) were measured with excitation in the range of the S0-S1 absorption band of the enol tautomers. In each compound, about 15 modes in the wavenumber range between 120 and 1650 cm-1 show a strong coupling to the electronic transition. In TIN and HBT, combination tones of the strongest mode below 500 cm-1 and the vibrations at higher wavenumbers point to the strong anharmonicity of the low wavenumber motion. The experimental results are analysed by normal-mode calculations, which provide insight into the microscopic elongations in the molecules. The coupling strengths derived from the spectra are used to calculate the envelope of the S0-S1 absorption bands of TIN and HBT, reproducing the measured spectra very well. Theoretical simulations of the combination tone spectra give information on the vibrational modes involved in excited-state proton transfer.
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