Mechanism of a one-photon two-electron process in photocatalytic hydrogen evolution from ascorbic acid with a cobalt chlorin complex.

A one-photon two-electron process was made possible in photocatalytic H2 evolution from ascorbic acid with a cobalt(II) chlorin complex [Co(II)(Ch)] via electron transfer from ascorbate to the excited state of [Ru(bpy)3](2+) followed by electron transfer from [Ru(bpy)3](+) to Co(II)(Ch) with proton to give the hydride complex, which reacts with proton to produce H2. [Co(III)(Ch)](+) was reduced by ascorbate to reproduce Co(II)(Ch).