Krzysztof A. Zaklika

Ultrafast studies on proton transfer in photostabilizers

Abstract Excited-state intramolecular proton transfer (ESIPT) is currently of considerable experimental theoretical interest and practical industrial interest, e.g. in polymer stabilizers. The vast majority of ESIPT systems involve transfer of a proton from an oxygen donor. 1,5-dihydroxyanthraquinone is typical, with ESIPT leading to dual fluorescence emission. The emission is conveniently discussed in terms of a four-state diagram, where N, N*, T and T* correspond to the normal 9,10-keto ground state, the normal 9,10-keto excited state, the 1,9-keto ground tautomeric state and the 1,9-keto excited tautomeric state respectively. The short-wavelength emission has been assigned to the normal excited state and the long-wavelength emission to the excited tautomer. ESIPT with nitrogen as the proton donor is rare and is often complicated by dimerization. Previous studies of 1-aminoanthraquinone and 1-(acetylamino)anthraquinone have found no evidence for ESIPT. We now report compelling evidence for ESIPT in 1-(acylamino)anthraquinones.