Synthesis and spectroscopic properties of novel dipyrrole and tetrapyrrole-based photosensitizers with various biphenylyl substituents

Abstract

Two series of novel pyrrole-based photosensitizers - sulfanyl porphyrazines, and BODIPY derivatives with different biphenylyl substituents such as fluorine atoms, cyano, or alkyloxycarbonyl groups, were synthesized, characterized, and subjected to broad spectroscopic studies. All tested compounds showed intensive light absorption, but only BODYPY derivatives exhibited emission properties. Moreover, iodinated BODIPYs revealed a significant heavy atom effect manifested by a red-shift of the absorption band by about 30 nm, about a 20-fold reduction in fluorescence intensity, and singlet oxygen generation efficiency increased 30–60 times compared to non-iodinated analogs. There was no correlation between the presence of peripheral fluorine atoms, cyano, or alkyloxycarbonyl groups and the absorption or emission properties. However, in both porphyrazines and BODIPYs, singlet oxygen formation was influenced by the substituents in the biphenylyl group. The compounds with cyano groups had the highest singlet oxygen generation ability and fluorine-analogs the lowest. Photodegradation studies revealed low or moderate decomposition of porphyrazines and non-iodinated BODIPYs with 5.9–18.8% of dyes degraded after 20 min of irradiation. However, the iodinated BODIPYs decomposed much faster, with the percentage of degradation in the range of 40.5–65.5%.