Uncovering photo-induced hydrogen bonding interaction and proton transfer mechanism for the novel salicylaldehyde azine derivative with para-position electrophilic cyano group

Abstract

In this work, we mainly focus on exploring the excited state hydrogen bonding dynamics and excited state intramolecular proton transfer (ESIPT) mechanism for a SAA derivative with para-position electron-withdrawing cyano group (CN-SAA). Insight into the geometrical changes, infrared (IR) spectra, and atomic charge populations, we infer dual intramolecular hydrogen bonds of CN-SAA can be enhanced in S1 state. Adopting three manners to estimate hydrogen bonding energies, we further confirm S1-state hydrogen bonding strengthening, which triggers ESIPT reaction. In view of photo-induced excitation, we find charge reorganization plays important roles in promoting ESIPT behavior for CN-SAA. Combining core-valence bifurcation (CVB) index and energy gap between HOMO and LUMO orbitals in solvents with different polarities, we predict nonpolar solvents contribute to facilitate ESIPT process. To clarify detailed ESIPT mechanism, we construct potential energy surface (PES), search transition state (TS) form, perform intrinsic reaction coordinate (IRC) energetic profile calculations and Born-Oppenheimer molecular dynamics simulations. We not only clarify the excited state intramolecular single proton transfer (ESISPT) reaction mechanism for CN-SAA compound, but also present the ESISPT regulating mechanism via solvent polarity.