Abstract
We have prepared four new Cu(II) complexes containing valine moieties with imidazole ligands at the fourth coordination sites and examined their photo-induced reactions with TiO2 in order of understanding the reaction mechanisms. Under a nitrogen atmosphere, the intermolecular electron transfer reactions (essentially supramolecular interactions) of these systems, which resulted in the reduction of Cu(II) species to Cu(I) ones, occurred after UV light irradiation. In this study, we have investigated the conditions of the redox reactions in view of substituent effects of aldehyde moieties. The results of cyclic voltammetry (CV) on an rotating ring-disk electrode (RRDE) suggested that the substitution effects and redox potentials were correlated. Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations were also performed to simulate the UV–Vis and circular dichroism (CD) spectra; the results revealed a reasonably good correlation between the substituent effects and the highest occupied molecular orbitals and the lowest unoccupied molecular orbitals (HOMO-LUMO) gaps associated with the most intense transition bands. In addition, we summarized the substitution effects of Cu(II) complexes for their corresponding UV light-induced reactions.
Highlights
Inorganic nanoparticles such as TiO2 have been used in cosmetics for a long time because their optical absorption and scattering of UV light are remarkable
We have previously reported that some copper(II) complexes, especially Schiff base complexes with L-amino acid moieties, showed photo-induced electron transfer reactions with
Complexes alone showed no changes after UV light irradiation
Summary
Inorganic nanoparticles such as TiO2 have been used in cosmetics for a long time because their optical absorption and scattering of UV light are remarkable. To take advantage of these inorganic nanoparticles and metal complexes such as UV absorbers, it is possible to control their absorption wavelengths and strongly absorbed UV light to react with TiO2 by compositing the metal complexes. It is possible to develop UV protection dye complexes to improve conventional sunscreen material. In this manner, we have previously reported that some copper(II) complexes, especially Schiff base complexes with L-amino acid moieties, showed photo-induced electron transfer reactions with. We prepared four new related Cu(II) complexes containing valine moieties (Figure 1) with imidazole ligands at the fourth coordination sites and examined their photo-induced reactions with TiO2 to understand their reaction mechanism
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