Exploring substituents and solvent effects on the reduction potential and molecular properties of five derivatives of hydroxybenzophenone (HBP) with their possible conformations and isomers

Abstract

Hydroxybenzophenone (HBP) molecules have their applications in commercial sunscreens as an UV chromophore because of their photostability and lack of reactivity after several hours of irradiation. They are usually photoexcited from the ground state chelated enol form to excited state where it undergoes proton transfer to chelated keto form and undergoes dihedral twisting to the ground state twisted keto form before going back to enol form. In this research, the three proposed isomers of five substituted 2-hydroxybenzophenones were modelled with additional three conformational changes in the ground state chelated enol and the results are related to the available experimental observations in solvents acetonitrile, n-dimethylformamide and dimethylsulfoxide. A significant difference in reduction potential, electron affinity and molecular properties was observed within the four ground state conformations and also the two excited-state proton transfer geometries for each of the five derivatives. The nature of the solvents also had significant effects on the electron affinity, HOMO, LUMO and energy bandgap of the molecules. The best possible conformation from the theoretical models that better described the experimental observations is the ground state trans chelated enol (named M1d) because of the close range of its reduction potential values and their strong level of correlation to that of the experiment and also a close range of its λmax values to that of the experiment.