Cocatalyst-free Photocatalytic Hydrogen Evolution with Simple Heteroleptic Iridium(III) Complexes

A simple heteroleptic iridium(III) photosensitizer, Ir-1, containing two ligands 5-(trifluoromethyl)-2-phenylpyridine (C-N-CF3) and bipyridine (N-N) has for the first time been studied for cocatalyst-free photocatalytic hydrogen evolution (PHE). The complex Ir-1 produces a hydrogen production rate (H2) of 3.2 mmol g-1 h-1, which is over 3.6-fold higher than that of the control complex Ir-2 (0.9 mmol g-1 h-1) containing bipyridine and 2-phenylpyridine ligands without CF3 groups. The higher H2 of Ir-1 could be ascribed to the high light-harvesting property, longer triplet electron lifetime, and more appropriate driving force for accepting electrons from the sacrificial donor, which enable efficient charge separation and transfer of electrons for hydrogen evolution. Additionally, the photostability issues of Ir-1 and Ir-2 are addressed by the selection of suitable organic solvent/water photocatalytic systems.