Theoretical study on the ESIPT processes and fluorescence properties of 2-(1H-Benzimidazol-2-yl)phenol-based derivatives

Abstract

The molecules based on the excited state intramolecular proton transfer (ESIPT) process are widely used in the fluorescent probes, organic light-emitting diodes and other fields due to their unique optical properties. However, the relationship between the structures and optical properties of ESIPT-based molecules still needs to be further explored. Herein, the effects of different functional groups embedded with the benzene ring on the ESIPT properties and electronic spectra of 2-(1H-Benzimidazol-2-yl)phenol (HBYP)-based derivatives (DPYP, HAYP and HIYP) were explored by using the density functional theory and time-dependent density functional theory methods. Utilizing theoretical calculations, the geometric parameters, including bond lengths and bond angles, infrared vibration spectra, frontier molecular orbitals, potential energy curves as well as topological analysis of the bond critical point of the molecules in the ground and excited states were acquired. The results manifest that the ESIPT process is facile to occur for HBYP and its three derivatives upon the photo-excitation, which can be confirmed by comparing the crucial geometric parameters, IR stretching vibration peaks and energy barriers between the S0 and S1 states. It is worth noting that the molecule HAYP exhibits the largest proton transfer barrier at the S1 state among the studied molecules, and the fluorescence peaks corresponding to its enol and keto forms show the most obvious Stokes shifts of 260 nm and 284 nm, respectively. Therefore, we can deduce that the fluorescence properties can be further affected by regulating the ESIPT characteristics of molecules via the functional group substitution.