Rigid axially symmetrical C60-BODIPY triplet photosensitizers: effect of bridge length on singlet oxygen generation

Abstract

The effect of bridge length on singlet oxygen generation has been studied by designing two rigid axially symmetrical C₆₀-BODIPY triplet photosensitizers: C₆₀-B1 and C₆₀-B2, with different bridge lengths. Rigid phenyl and diphenylacetylene are selected as linkers in C₆₀-B1 and C₆₀-B2, respectively, and the bridge length of C₆₀-B2 is about 6.9 Å longer than that of C₆₀-B1. The photochemical and photophysical properties of the dyads are investigated using steady-state and transient spectroscopies, as well as theoretical calculations. Higher efficiency of energy transfer and higher yield of the triplet C₆₀ in C₆₀-B1 are detected. To investigate the effect of bridge length on singlet oxygen generation, the photooxidation reactions of 1,5-dihydroxynaphthalene (DHN) have been carried out with C₆₀-B1, C₆₀-B2, and the reference compounds as photosensitizers. Higher quantum yield of singlet oxygen is generated in C₆₀-B1 (0.82) with a shorter bridge compared to that in C₆₀-B2 (0.59). The photooxidation rate constant of C₆₀-B1 is 1.4 times as that of C₆₀-B2 and 1.3 times as that of MB. The results obtained here are helpful for designing novel donor–bridge–acceptor triplet photosensitizers.