Effects of atomic electronegativity of halogen on excited state reactional behaviors for 4-chloro-2-[1-(4-methoxy-phenyl)-4,5-diphenyl-1H-imidazol-2-yl]-phenol compound: a theoretical study

Inspired by the brilliant photochemical and photophysical properties of organic molecule containing the halide substitution that could be potentially applied across various disciplines, in this work, effects of atomic electronegativity of halogen (F, Cl, and Br) on excited state hydrogen bond effects and excited state intramolecular proton transfer (ESIPT) reaction. We present the characteristic 4-chloro-2-[1-(4-methoxy-phenyl)-4,5-diphenyl-1H-imidazol-2-yl]-phenol (CMDIP) that is the main objective of this study to explore in detail the influence of the change of atomic electronegativity by photoexcitation. By comparing the structural changes and infrared (IR) vibrational spectra of the CMDIP derivatives (CMDIP-F, CMDIP-Cl, and CMDIP-Br) fluorophores in S0 and S1 states, combined with the preliminary detection of hydrogen bond interaction by core-valence bifurcation (CVB) index, we can conclude that the hydrogen bond could be strengthened in S1 state, which is favorable for the occurrence of ESIPT reactions. The charge recombination behavior of hydrogen bond induced by photoexcitation also further illustrates this point. Via constructing potential energy curves (PESs) based on restrictive optimization and searching transition state (TS) form, we confirm the change of atomic electronegativity has a regulatory effect on the ESIPT behavior for CMDIP derivatives, that is, the higher the atomic electronegativity is more conducive to the ESIPT reaction.