Insights into the different mechanistic stages of light-induced hydrogen evolution of a 5,5′-bisphenanthroline linked RuPt complex

Herein, the synthesis in conjunction with the structural, electrochemical, and photophysical characterization of a 5,5′-bisphenanthroline ( phenphen ) linked heterodinuclear RuPt complex ( Ru(phenphen)Pt ) and its light-driven hydrogen formation activity are reported. A single crystal X-ray diffraction (SC-XRD) analysis identified a perpendicular orientation of the two directly linked 1,10-phenanthroline moieties. The disruption of π-conjugation blocks intramolecular electron transfer as evidenced by a comparative time-resolved optical spectroscopy study of Ru(phenphen)Pt and the reference complexes Ru(phenphen) and Ru(phenphen)Ru . However, reductive quenching is observed in the presence of an external electron donor such as triethylamine. Irradiating Ru(phenphen)Pt with visible light (470 nm) leads to H 2 formation. We discuss a potential mechanism that mainly proceeds via Pt colloids and provide indications that initial hydrogen generation may also proceed via a molecular pathway. As previous reports on related heterodinuclear RuPt-based photocatalysts revealed purely molecular hydrogen evolution, the present work thus highlights the role of the bridging ligand in stabilizing the catalytic center and consequently determining the mechanism of light-induced hydrogen evolution in these systems. The fate of a catalyst: a dinuclear photocatalyst containing orthogonally oriented binding sites for chromophoric and catalytic metal centres changes the mechanism of light-driven hydrogen evolution from a molecular to a colloid-driven process.