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 [CoII(Ch)] via electron transfer from ascorbate to the excited state of [Ru(bpy)3]2+ followed by electron transfer from [Ru(bpy)3]+ to CoII(Ch) with proton to give the hydride complex, which reacts with proton to produce H2. [CoIII(Ch)]+ was reduced by ascorbate to reproduce CoII(Ch).