Photo-induced excitation enhances intramolecular hydrogen bonding interactions for CHPHI compound. Enhanced hydrogen bond OH⋯N facilitates ESIPT tendency. ICT further promotes the occurrence of ESIPT reaction for CHPHI system. Nonpolar solvent environment is more favorable for ESIPT behavior of CHPHI fluorophore.

Abstract

Excited-state intramolecular proton transfer (ESIPT) reaction, as one of the most fundamental photochemical behaviors, plays a crucial role in the design of novel optical materials. This study investigates the photo-induced hydrogen bonding behaviors and related ESIPT process of 3-(1H-phenanthro[9,10-d]imidazol-2-yl)-9-phenyl-9H-carbazol-4-ol (CHPHI) in solvents with varying polarities. Based on analyses of the core-valence bifurcation (CVB) index, geometrical structure parameters, topological analysis, and infrared (IR) vibrational spectra, we infer that light excitation facilitates the enhancement of intramolecular hydrogen bonding. This phenomenon can promote the ESIPT process. In particular, we have observed that the enhancement of hydrogen bonding becomes more pronounced as solvent polarity weakens. To further investigate the relationship between solvent polarity and ESIPT behavior, we conduct an exploration of the frontier molecular orbitals (MOs) in CHPHI. Finally, by comparing the magnitudes of excited-state barriers in different solvents, we claim that nonpolar solvents drive the ESIPT reaction for CHPHI fluorophore.