Spectroscopy and dynamics of excited-state intramolecular proton-transfer reaction in 5-hydroxyflavone

Spectroscopy and dynamics of excited-state intramolecular proton-transfer (ESIPT) in 5-hydroxyflavone (5HF) have been investigated. In cyclohexane dual fluorescence maxima at ∼420 and 700 nm were observed. The time scale for both proton and deuterium transfer in the excited state cannot be resolved under the response time of ca. 160 fs of our femtosecond fluorescence upconversion system. Following ESIPT the excited keto-tautomer undergoes an unusually fast relaxation rate of ∼1.2 ps−1. Fast internal conversion is concluded to play a major role to account for the dominant radiationless deactivation.