Ab initio investigation of excited state dual hydrogen bonding interactions and proton transfer mechanism for novel oxazoline compound*

Abstract

Owing to the importance of excited state dynamical relaxation, the excited state intramolecular proton transfer (ESIPT) mechanism for a novel compound containing dual hydrogen bond (abbreviated as “1-enol”) is studied in this work. Using density functional theory (DFT) and time-dependent density functional theory (TDDFT) method, the experimental electronic spectra can be reproduced for 1-enol compound. We first verify the formation of dual intramolecular hydrogen bonds, and then confirm that the dual hydrogen bond should be strengthened in the first excited state. The photo-excitation process is analyzed by using frontier molecular orbital (HOMO and LUMO) for 1-enol compound. The obvious intramolecular charge transfer (ICT) provides the driving force to effectively facilitate the ESIPT process in the S1 state. Exploration of the constructed S0-state and S1-state potential energy surface (PES) reveals that only the excited state intramolecular single proton transfer occurs for 1-enol system, which makes up for the deficiencies in previous experiment.