A detailed theoretical simulation about the excited state dynamical process for the novel (benzo[d]thiazol-2-yl)-5-(9H-carbazol-9-yl)phenol molecule

Given that molecular excited state dynamical process plays important roles in designing and developing novel applications in recent years. In this work, based on density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods, we theoretically explored the novel (benzo[d]thiazol-2-yl)-5-(9H-carbazol-9-yl)phenol (HBT-Cz) system about its excited state behaviors. Via simulating the electrostatic potential surface (EPS) of HBT-Cz structure, we confirm the formation of intramolecular hydrogen bond O2-H3 center dot center dot center dot N4 in the S-0 state. Our theoretical dominating bond lengths, bond angles, and the infrared (IR) vibrational spectra involved in hydrogen bond demonstrate that O2-H3 center dot center dot center dot N4 should be strengthened in the S-1 state. Upon the photoexcitation, we find the charge transfer characteristics around hydrogen bonding moieties play important roles in facilitating excited state intramolecular proton transfer (ESIPT) process. Via constructing potential energy curves, we confirm the ESIPT reaction that further explains previous experimental phenomenon. Moreover, we also search the S-1-state transition state (TS) structure along with ESIPT path, based on which we simulate the intrinsic reaction coordinate (IRC) path. Combing with the atom-centered density matrix propagation (ADMP) molecular dynamics simulation, we further confirm the ESIPT mechanism presented in this work. We sincerely hope that our theoretical work could guide novel applications based on HBT-Cz system in future.