Can Hydrated Electrons be Produced from Water with Visible Light?

Ab initio computational methods are employed to explore whether hydrated electrons can be produced by the photodetachment of the excess hydrogen atom of the heptazinyl radical (HzH) in finite-size HzH⋅⋅⋅(H₂O)_n clusters. The HzH radical is an intermediate species in the photocatalytic oxidation of water with the heptazine (Hz) chromophore. Hz (heptaazaphenalene) is the monomer of the ubiquitous polymeric water-oxidation photocatalyst graphitic carbon nitride (g-C₃N₄). The energy profiles of minimum-energy excited-state reaction paths for proton-coupled electron transfer from HzH to water molecules were computed for the HzH⋅⋅⋅H₂O and HzH⋅⋅⋅(H₂O)₄ complexes with the CASPT2 method. The results reveal that the photodetachment of the excess H-atom from the HzH radical is a barrierless reaction in these hydrogen-bonded complexes, resulting in the formation of H₃O and H₃O(H₂O)₃ radicals, respectively, which are finite-size models of the hydrated electron. The computational results suggest that the photocatalytic formation of hydrated electrons from water with visible light could be possible in principle.