Theoretical Investigation Into Excited State Dual Hydrogen Bonding Effects and the Proton‐Transfer Behaviors for HDBE Fluorophore: Solvent Polarity

Given the potential bioimaging prospect as a fluorescent chemosensor and biomarker, the novel 3‐ethoxysalicyladimine‐based azine (HDBE) fluorophore has been theoretically explored in this work. Since solvent environment could change the luminescent properties of organic molecular materials to a certain extent, thus, we mainly focus on revealing solvent polarity‐driven effects on excited‐state processes for the HDBE fluorophore. Symmetrical structure of HDBE itself endow the symmetrical variations of intramolecular dual hydrogen bonds (O1─H2···N3 and O4─H5···N6). By paying attention to geometrical alterations, infrared (IR) spectral shifts, hydrogen bonding core‐valence bifurcation (CVB) descriptors alongside recombined frontier molecular orbitals (MOs), we confirm that polar solvents could facilitate hydrogen‐bonding‐enhancing behaviors by photoexcitation. Dependent on the restriction optimization manner, the constructed potential energy surfaces (PESs), coupled with the identified transition state (TS) forms along with the reaction pathway, further clarify the solvent‐polarity‐controlled excited state intramolecular single proton transfer (ESIPT) mechanism, despite the dual hydrogen bonds HDBE possesses.