Ultrafast proton transfer in the S1 state of 1-chloroacetylaminoanthraquinone

Abstract

Excited state intramolecular proton transfer (ESIPT) in 1-chloroacetylaminoanthraquinone (CAAQ) and 1,8-dihydroxyanthraquinone (DHAQ) in solution is investigated at room temperature by means of femtosecond transient absorption spectroscopy. While ESIPT is practically instantaneous in DHAQ, in CAAQ the same process occurs with measurable kinetics, with a time constant of 100 fs. The energy diagrams for the ground and excited states of the proton-transferred and non-proton-transferred species, compatible with these observations, are discussed and an estimate is given for the activation energy of the process.