Photooxidation utilizing visible light, especially with naturally abundant O2 as the oxygen source, has been well-accepted as a sustainable and efficient procedure in organic synthesis. We prepared amidated alloxazines (AAs) and investigated their photophysical properties as well as performance as heavy-atom-free triplet photosensitizers. Because of the difference in the framework structure of AAs and flavin (FL) and the introduction of carbonyl moiety, the absorption of FL at ∼450 nm is blue-shifted and weakened (ε = 8.7 × 103 for FL to ∼6.8 × 103 M–1 cm–1), but the absorption at ∼340 nm is red-shifted and enhanced by ∼50% (from ε = 6.4 × 103 for FL to ∼9.9 × 103 M–1 cm–1) in AAs. The intersystem crossing rates from the S1 to T1 are also enhanced in these AAs derivatives, while the fluorescence quantum yield decreases from ∼30 to ∼7% for FL and AAs, respectively, making the triplet excited state lifetime and the singlet oxygen quantum yield of AAs at least comparable to those of FL. In accordance with the prolonged triplet excited state lifetime and enhanced triplet quantum yield, 2–5-fold performance enhancements were observed for AAs in the photooxidation of sulfides with respect to FL. Both singlet oxygen and superoxide radical anion were identified as the key reactive oxygen species.

Heavy atom free photooxidation of sulfides efficiently sensitized by amidated alloxazines

ACS Fall 2021

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