Spectroscopic and theoretical investigations of donor–π–acceptor–donor architectured cyclometalated iridium(III) and ruthenium(II) complexes in photocatalytic hydrogen generation

Unlocking the full potential of solar-driven hydrogen production hinges on the development of next-generation photosensitizers that combine efficiency, stability, and environmental compatibility. Here, we introduce a new class of cyclometalated iridium(III) and ruthenium(II) complex-es, meticulously engineered with a donor–π–acceptor–donor (D–π–A–D) molecular framework. By integrating triphenylamine-based donor motifs and extended π-conjugation, alongside strategically tailored anchoring groups, these complexes transcend conventional photosensitizer de-sign—enabling high light-harvesting capabilities, robust interfacial coupling with TiO₂, and accelerated charge separation dynamics. Advanced spectroscopic, electrochemical, and DFT investigations reveal that the D–π–A–D architecture not only amplifies visible-light absorption but also facilitates efficient electron injection into semiconductor interfaces. Notably, iridium(III) complexes equipped with phosphonate anchors achieve a maximum turnover number (TON) of 19,182 for photocatalytic hydrogen evolution under blue LED illumination. Beyond efficiency, these photosensitizers exhibit remarkable operational durability and minimal ecological impact, charting a path toward scalable, sustainable hydrogen generation. These findings underscore the considerable potential of D–π–A–D cyclometalated metal complexes, equipped with optimized anchoring groups, to function as robust photosensitizers for sustainable solar-driven hydrogen production.