Selenoxanthylium Salts─Organic Photocatalysts for Low-Energy Photoredox Catalysis.

The design of low energy organic photoredox catalysts relies predominantly on π-extended frameworks. Incorporation of selenium into the xanthylium core shifts absorption toward the red region relative to lighter chalcogens (O and S), enabling catalysis with 650 nm light-sources. Selenoxanthylium salts are low-energy-absorbing organic photocatalysts with defined excited-state topology, distinguishing locally excited and charge-transfer states. Incorporation of a heavier chalcogen constitutes a design principle complementary to extended π-frameworks commonly used in organic photocatalysts. Under red-light irradiation, the catalysts engage in reductive quenching and operate on up to 5.0 mmol scale. Catalytic activity is demonstrated across multiple transformations, including [4 + 2] and [2 + 2] cycloadditions, C-H aminations, boronic acid oxidations, aza-Henry reactions, and trifluoromethylations.