Enhanced red-light-driven hydrogen evolution by a diplatinum photocatalyst by the larger wavefunction leakage of iodide coordinated to the platinum center

Abstract

The single-molecular photocatalyst Pt₂(bpia)Cl₃ (bpia = bis(2-pyridylimidoyl)amido), recently proven to promote red-light-driven hydrogen evolution reaction (HER) in water via singlet-to-triplet (S–T) transitions (Angew. Chem. Int. Ed., 2025, 64, e202418884), is shown to gain a significantly improved photocatalytic performance upon ligating iodide instead of chloride to give Pt₂(bpia)I₃. Upon iodide ligation, the absorption and emission energies both show a red shift basically due to destabilization of the HOMO by mixing of the iodide orbitals having essentially higher orbital energies compared to those of chloride. Consequently, the triplet lifetime and the luminescence quantum yield both decrease by obeying the energy gap law. The unique S–T transition features of Pt₂(bpia)Cl₃ are preserved in Pt₂(bpia)I₃ with the excited-state redox properties remaining unchanged. In spite of apparently disadvantageous photophysical features induced by the iodide ligation, Pt₂(bpia)I₃ is ascertained to promote the photocatalytic HER at a considerably higher rate in comparison with Pt₂(bpia)Cl₃, primarily attributed to the higher reductive quenching efficiency for the triplet excited state of Pt₂(bpia)I₃. The observations are rationalized due to the substantially more excellent acceptor characteristics of iodide, in which its larger wavefunction leakage significantly contributes to a larger electronic coupling factor in driving the outer-sphere electron transfer from the sacrificial electron donor.