As eries of heteroleptic iridium(III) complexes functionalized with two phosphonic acid (ÀPO 3 H 2 )g roups ( dfppy IrP, ppy IrP, btp IrP,a nd piq IrP)w ere prepared and anchored onto rhenium(I) catalyst( ReP)-loadedT iO 2 particles (TiO 2 / ReP) to build up an ew IrP-sensitized TiO 2 photocatalyst system (IrP/TiO 2 /ReP). The photosensitizing behavior of the IrP series was examined within the IrP/TiO 2 /ReP platform for the photocatalytic conversion of CO 2 into CO. The four IrPbased ternary hybridss howed increased conversion activity and durability than that of the corresponding homo-(IrP + ReP) and heterogeneous (IrP + TiO 2 /ReP) mixed systems.Amongt he four IrP/TiO 2 /ReP photocatalysts, the lowenergy-light (> 500 nm) activated piq IrP immobilized ternary system ( piq IrP/TiO 2 /ReP) exhibitedt he most durable conversion activity,g iving at urnover number of ! 730 for 170 h. A similark inetic feature observed through time-resolved photoluminescence measurements of both btp IrP/TiO 2 and TiO 2free btp IrP films suggestst hat the net electron flow in the ternary hybrid proceeds dominantly through ar eductive quenching mechanism,u nlike the oxidative quenching route of typical dye/TiO 2 -based photolysis.[a] P.Scheme1.Schematicrepresentation of the photocatalytic IrP/TiO 2 /ReP ternary system and components used in this study.TON = turnovern umber, NP = nanoparticle.