O-H vibrational motions promote sub-50 fs nonadiabatic dynamics in 3-hydroxypyran-4-one: interplay between internal conversion and ESIPT

A theoretical study is used to explore the involvement of O-H vibrational motions in the S 0 → S 2 photoinduced dynamics of 3-hydroxypyran-4-one (3-HOX). Two transitions, S 0 → S 1 and S 0 → S 2 , are attributed to the experimentally observed electronic absorption spectral features in the range of 3.5-5.5 eV. We compute model potential energy surfaces of vibronically coupled S 1 (nπ*) and S 2 (ππ*) states with the aid of extensive electronic structure calculations. The S 1 -S 2 conical intersection is characterized in the O-H bend and O-H stretch vibrational coordinate space. Quantum wavepacket dynamics simulations reveal an ultrafast S 2 → S 1 internal conversion decay, where about 90% of the S 2 population disappears within the first 50 fs of the propagation time. The participation of O-H vibrational motions in the early events of nonadiabatic dynamics is analyzed based on the time evolution of nuclear densities on S 2 . We discuss the implications of these observations to provide fundamental insights into the nonadiabatic excited-state intramolecular proton transfer in 3-HOX and its derivatives. The OH out-of-plane bend vibration induces an extremely rapid S 2 to S 1 internal conversion in 3-hydroxypyran-4-one.