Photophysical properties of BODIPYs with sterically-hindered nitrophenyls in meso-position

Abstract

During recent years, the BODIPY core became a popular scaffold for designing of dyes with desirable properties. In this paper, we extend the library of possible modification of BODIPYs, presenting experimental data for a new family meso-substituted with nitrophenyl groups. We also present quantum chemical calculations, which complement the experimental data and give additional insight in the underlying photochemical and photophysical processes. Optical properties of novel compounds are characterized. It is shown that the fluorescence quantum yield and the efficiency of singlet oxygen generation differs by two orders of magnitude across the family. In aqueous solution, red-shifted fluorescence emission band is detected, corresponding to aggregates. This band has shorter decay time and wide excitation spectrum. We show that photolysis is not accompanied by the release of nitric oxide (NO) which was observed earlier for some dyes with nitrophenyl substituents. The experimental data presented in this paper may be useful for further designing of BODIPY dyes and NO photodonors.