Performance of new cyclotriphosphazene derivatives in photocatalytic reactions

Abstract

Photosensitizers that are good producers of singlet oxygen, and the photocatalytic reactions promoted by these photosensitizers, have always been of great interest. In this study, we aimed to develop new photosensitizers based on cyclotriphosphazene and evaluate their performance in photocatalytic reactions. In this context, three new cyclotriphosphazene derivatives, each bearing BODIPY and thiophene units, were synthesized, and their molecular structures were characterized using spectroscopic techniques. Both the BODIPY derivatives and their cyclotriphosphazene derivatives had absorption in the visible region, and also, the resulting cyclotriphosphazene compounds exhibited significantly better molar absorption coefficients compared to the precursor BODIPY units. Incorporation of the halogen atom into the molecules resulted in the redshift of absorption and emission maxima, as well as decrease in the fluorescence characteristics of these molecules. The singlet oxygen-producing abilities of the molecules were evaluated by the chemical trapping method using DPBF as the singlet oxygen scavenger molecule, and the change was monitored by UV-vis absorption spectroscopy. Cyclotriphosphazene compounds 7 and 8 performed significantly better than both methylene blue and their precursor units, with singlet oxygen quantum yield values of 0.85 and 0.91. Finally, the ability of these compounds to convert 1,3-cyclohexadiene into peroxides (2,3-dioxabicyclo[2.2.2]oct-5-ene and 3-hydroperoxycyclohexa-1,4-diene) was evaluated. The compounds displayed notable photocatalytic activity toward the oxidation of 1,3-cyclohexadiene compared to tetraphenyl porphyrin (TPP), a known photocatalyst.