Diplatinum Single-Molecular Photocatalyst Capable of Driving Hydrogen Production from Water via Singlet-to-Triplet Transitions

Solar-driven hydrogen production is regarded as one of the most ideal methods to achieve a sustainable society. In order to artificially establish efficient photosynthetic systems, efforts have been made to develop single-molecular photocatalysts capable of serving both as a photosensitizer (PS) and a catalyst (Cat) in hydrogen evolution reaction (HER). Although examples of such hybrid molecular photocatalysts have been demonstrated in the literature, their solar energy conversion efficiencies still remain quite limited. Here we demonstrate that a new dinuclear platinum(II) complex Pt₂(bpia)Cl₃ (bpia=bis(2-pyridylimidoyl)amido) serves as a single-molecular photocatalyst for HER with its performance significantly higher than that of the PtCl(tpy)- and PtCl₂(bpy)-type photocatalysts developed in our group (tpy=2,2':6′,2''-terpyridine, bpy=2,2′-bipyridine). The outstanding feature is that Pt₂(bpia)Cl₃ can produce H₂ even by irradiating the lower-energy light above 500 nm, which is rationalized due to the direct population of triplet states via singlet-to-triplet transitions (i.e., S-T transitions) accelerated by the diplatinum core. To the best of our knowledge, Pt₂(bpia)Cl₃ is the first example of a single-molecular photocatalyst enabling hydrogen production from water via the S-T transitions using lower-energy light (>580 nm).