Theoretical insights into photoinduced excited-state behaviors for the novel CHPPhl fluorophore: Effects of solvent polarity

Inspired by the distinguished photochemical and photophysical properties of novel hydroxyl-substituted tetraphenylimidazole (HPI) derivatives that could be potentially applied across various disciplines, in this work, effects of solvent polarity on excited-state hydrogen bond effects and excited-state intramolecular proton transfer (ESIPT) reaction of 3-(6,9-Diphenyl-1H-phenanthro[9,10-d]imidazole-2-yl)-9-phenyl-9H-carbazol-4-ol (CHPPhl) are focused. By comparing the structural changes and infrared (IR) vibrational spectra of the E-HBT fluorophore in polar acetone, moderate polar tetrahydrofuran and non-polar hexane solvents, 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 (PECs) based on restrictive optimization and searching transition state (TS) form, we confirm change of surrounding solvent polarity has a regulatory effect on the ESIPT behavior for CHPPhl; that is, the lower the solvent polarity is more conducive to the ESIPT reaction. Solvent polarity associated photo-induced hydrogen bonding interactions and ESIPT behaviors for CHPPhl fluorphore.image