Ultrafast dynamics of gas-phase excited-state intramolecular proton transfer in 1-hydroxy-2-acetonaphthone

The excited-state dynamics of 1-hydroxy-2-acetonaphthone (HAN) was studied in the gas phase using femtosecond time-resolved multiphoton ionization spectroscopy. Following femtosecond excitation to its S1 state, HAN was found to exhibit a biexponential decay behavior which can be consistently interpreted in terms of rapid excited-state intramolecular proton transfer (ESIPT) followed by other slower decay channels. The results revealed that ESIPT in HAN (S1) occurs in ∼60–85 ps in the energy range studied and suggested the existence of an energy barrier to tautomerization.