Tracking the early nonadiabatic events of ESIPT process in 2-acetylindan-1,3-dione by quantum wavepacket dynamics

Abstract

Spectroscopy and dynamics associated with the three low-lying singlet excited electronic states of 2-acetylindan-1,3-dione (AID) are studied theoretically to interpret the early events of the excited-state intramolecular proton transfer process (ESIPT). Upon populating “bright” S3, AID decays to “dark” lower electronic states (S2 and S1) on a timescale of about 100 fs. Nuclear densities associated with the OH vibrations obtained from wavepacket calculations reveal their participation in the S3→ S2/S1 internal conversion. We show that AID requires very minimal distortions along these vibrations to access the conical intersections located near to the Franck–Condon (FC) point. Our findings demonstrate that the ultrafast nonadiabatic dynamics taking place within the FC zone make the assignment of ESIPT pathways and associated timescales in AID a challenging task.