Time-resolved resonance Raman scattering of the excited singlet state of 2-(2′-hydroxyphenyl)benzoxazole after excited state intramolecular proton transfer

Picosecond time-resolved resonance Raman spectra after excited state intramolecular proton transfer in 2-(2′-hydroxyphenyl)benzoxazole have been investigated. The two most intense resonance Raman lines belonging to the S1-keto tautomer are assigned to vibrations with strong ν(CO) and δ(NH) components, respectively. The intensities of corresponding anti-Stokes resonance Raman spectra indicate that the high-frequency modes are not directly vibrationally excited by the reaction. For modes below 1000 cm−1 substantial excess populations were observed. The S1-keto tautomer is already close to thermal equilibrium after 2 ps and it cools down within about 8 ps.