Revealing how Proton Transfer Process of 2-Hydroxylbenzophenones Affected by the Intermolecular Hydrogen Bond with Different Para-Substituted Groups

Abstract 2-hydroxylbezophenone (HB) and its para-substituted variants are β-diketone derived compounds that can undergo ultrafast deactivation via the proton transfer process after excited by UV light. Due to these unique characteristics, they are usually applied as UV sunscreen filters. Here, the kinetics of HB and its derivatives with the para-substituted group in the different ratios of MeCN/H2O solutions are explored by ultrafast time-resolved transient absorption spectroscopy. HB molecules with para-substituted either electron-donating or electron-withdrawing groups exhibit faster decay rates than para-substituted methyl group's HB in water solutions. In association with DFT theoretical calculations, the intermolecular hydrogen bonding between HB para-substituted variants with water is responsible for the charge redistribution in the donor and acceptor of the proton, resulting in a dramatic acceleration for the energy dissipation decay with the increase of the percentage of water versus acetonitrile. This work unambiguously provides new insight into the design of UV sunscreen molecules dependent on the solvent environment.