Charge Accumulation and Multi-Electron Photoredox Chemistry with a Sensitizer-Catalyst-Sensitizer Triad.

Photoinduced electron transfer in donor-sensitizer-acceptor compounds usually leads to simple electron-hole pairs, and photoredox catalysis typically relies on single-electron transfer (SET) events. This work reports on a molecular triad able to accumulate two electrons on a central dibenzo[1,2]dithiin moiety flanked by two peripheral RuII photosensitizers. Under continuous illumination, the doubly reduced form of the dibenzo[1,2]dithiin undergoes thiolate-disulfide exchange with an aliphatic disulfide substrate, thereby acting as a two-electron catalyst after two initial SET events with triethylamine at the RuII sensitizers. The use of a relatively simple triad for coupling two separate SET processes to a subsequent two-electron reduction is an important conceptual advance from photoinduced SET and light-driven charge accumulation towards multi-electron photoredox catalysis. This is relevant for artificial photosynthesis and light-driven multi-electron chemistry in general.