Photosensitization\nof Ir-Dye on TiO<sub>2</sub> for\nEnhanced Hydrogen Evolution:\nPresence of Ferrocene Matters

Dye-sensitized photochemical hydrogen evolution is potentially\npromising and ecofriendly but often suffers from low stability and\nphotocatalytic activities. The Ir(III) complex plays an important\nrole in photoinduced energy and electron transfer processes, along\nwith excellent luminescence properties, such as high emission intensities\nand long lifetimes. In this work, a heterobimetallic Fe<sup>∧</sup>Ir photosensitizer has been rationally designed and synthesized for\nsolar hydrogen evolution application. Harnessing visible light with\na significantly high lifetime of 592 ns of bimetallic boosts hydrogen\nevolution performance compared to a monometallic system, i.e., without\na ferrocene auxiliary (390 ns). The longer lifetime of Fe<sup>∧</sup>Ir-dye is attributed to the extension of π-conjugation achieved\nby the ferrocene moiety into the ancillary ligand. The investigated\nmaterials exhibited the highest rate of ∼8.04 mmol g<sup>–1</sup> h<sup>–1</sup> (AQY = 19.68%, TON = 14894) under visible\nlight, and at neutral pH. Fe<sup>∧</sup>Ir-dye demonstrates\nquasi-reversible redox processes for Ir<sup>III/IV</sup> alongside\na reversible reduction of bpy<sup>0</sup>/bpy<sup>–1</sup>.\nThe induction of redox-active ferrocene in Fe<sup>∧</sup>Ir-dye\naltered the overall electronic properties of the catalyst. The light-harvesting\nability, theoretical molecular orbital levels, and redox potential\nbehavior of the dye-sensitized photocatalysts are systematically investigated,\ncomplementing the superior activity of the designed material.