Whether the excited state intramolecular proton transfer of 1-hydroxy-2-acetonaphthone will happen?

The excited-state intramolecular proton transfers of 1-hydroxy-2-acetonaphthone (HAN) has been investigated via the time-dependent density functional theory (TDDFT) method and adiabatic molecular dynamics simulation. Four different tautomer forms (enol, enol rotamer, keto, keto mtamer) structures of HAN in the gas phase were fully optimized at the ground state (S-0) and the first excited state (S-1). The enol form, as the most stable structure in the S-0, was chosen as target structure for the excited state dynamics simulations. By the classical molecular dynamics of adiabatic approximation, we analyzed the bond lengths associated with proton transfer, which verified the existence of proton transfer in the excited state. And the result gives a more direct and reasonable explanation to the controversy about whether the ESIPT process in HAN will happen or not. Our results show that the proton-transfer process is completed within 37.0 fs, with the bond length O17-H18 change from 0.989 angstrom to 1.473 angstrom, and O24-H18 change from 1.656 angstrom to 1.047 angstrom in the S-1.