Flavin derivatives (FLs) are the building blocks and functional groups within many enzymes that absorb strongly in the visible light region and are redox cofactors in a large number of biological processes. We directly attached Br atoms into the conjugated framework of FL to afford FL dibromide (DBFL) and expected the heavy atom effect of Br to facilitate the intersystem crossing of excited FLs to reach the triplet states for efficient sensitization of O₂. Compared with FL (ε = 1.01 × 10⁴ M^–1 cm^–1 at 441 nm), DBFL shows stronger absorption in the visible range (ε = 1.90 × 10⁴ M^–1 cm^–1 at 450 nm). The singlet oxygen quantum yield of DBFL is enhanced from 55.3% in FL to 92.2% at the expense of decreased luminance quantum yield from 37.7% in FL to 5.5%, confirming that a large portion of the excited DBFL molecules evolves into triplet excited states. Both FL and DBFL were used in photosensitized oxidation of various sulfides to afford corresponding sulfoxides. DBFL exhibits a two—fivefold performance enhancement with respect to FL in sensitizing O₂ for photocatalytic oxidation. In addition, the oxidation of sulfides with DBFL was found efficient and led exclusively to sulfoxides, with no secondary oxidation products observed. Mechanistic investigations showed that both singlet oxygen and superoxide anion radical are formed as reactive oxygen species. The findings pave the way for design and application of novel organic sensitizers for photocatalytic oxidation.

中文翻译：

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黄素二溴化物是一种有效的硫化物光氧化敏化剂

黄素衍生物（FLs）是许多酶中的构件和功能基团，它们在可见光区域吸收强，并且在许多生物过程中都是氧化还原辅助因子。我们将Br原子直接连接到FL的共轭骨架中，得到FL二溴化物（DBFL），并预期Br的重原子效应将促进激发的FL的系统间交叉，从而达到三重态，以实现O _2的有效敏化。与FL（在441 nm处ε= 1.01×10 ⁴ M ^–1 cm ^–1）相比，DBFL在可见光范围内显示出更强的吸收（ε= 1.90×10 ⁴ M ^–1 cm ^–1在450 nm）。DBFL的单重态氧量子产率从FL中的55.3％提高到92.2％，但代价是将亮度量子产率从FL中的37.7％降低到5.5％，这证实了大部分被激发的DBFL分子演变为三重激发态。FL和DBFL均用于各种硫化物的光敏氧化，以提供相应的亚砜。与FL相比，DBFL在O ₂增敏方面的性能提高了两倍。用于光催化氧化。另外，发现用DBFL氧化硫化物是有效的，并且仅导致亚砜，没有观察到二次氧化产物。机理研究表明，单线态氧和超氧阴离子自由基均作为活性氧形成。这些发现为光催化氧化的新型有机敏化剂的设计和应用铺平了道路。