Design Changes That Lead to Large Effects in Photocatalysis: A Ruthenium-Terpyridine Complex Stable and Active Enough to Outperform [Ru(bpy)3]2.

We report here the synthesis of a new heteroleptic ruthenium-terpyridine complex that exhibits both high stability and enhanced photocatalytic activity with an increase of approximately one order of magnitude for the hydrogen evolution reaction coming from a strong push-pull effect. The complex demonstrates high performance under blue light (445 nm), achieving a turnover number (TON) above 3500 molH2 molPS-1 with sustained hydrogen production for over 6 days. That TON value is more than twice as high as that of the reference [Ru(bpy)3]2+ complex under the same conditions. Under red light (630 nm), this complex also shows high efficiency and stability with no significant decrease in the turnover frequency over 6 days, achieving a TON over 960 molH2 molPS-1, a value competitive with reference [Ru(bpy)3]2+ complex under blue light (this last showing no hydrogen evolution under red-light). We identified a kinetic competition between the main H2 production process and degradation reactions from the reduced complex species and could further enhance the sustainability of the system (under blue light) by increasing the cobalt catalyst concentration. A TON above 4100 molH2 molPS-1 could be reached after 8 days.