Ancillary Ligand Effects on Heteroleptic Ir Dye in Dye-Sensitized Photocatalytic CO Reduction: Photoaccumulation of Charges on Arylated Bipyridine Ligand and Its Control on Catalytic Performance.

Herein, we report the synthesis, and photochemical and -physical properties, as well as the catalytic performance, of a series of heteroleptic Ir photosensitizers (IrPSs), [Ir(C^N) (N^N )] , possessing ancillary ligands that are varied with aryl-substituents on bipyridyl unit [C^N=(2-pyridyl)benzo[b]thiophen-3-yl (btp); N^N =4,4'-Y -bpy (Y=-Ph or -PhSi(Ph) ]. We found that the π-extension of bipyridyl ligand by aryl-substitution put bipyridyl ligand in use as an electron relay unit that performed charge accumulation before delivering to the catalytic center, greatly improving the overall CO -to-CO conversion activities. In a typical run, the aryl-substituted IrPS ( IrP-Ph )-sensitized homogeneous systems (IrPS+Re catalyst) gave a turnover number of 1340 (Φ =24.2 %) at the early stage of photolysis (<5 h). This study demonstrates that the π-character modulation on the ancillary bipyridyl ligand is critical for forthcoming catalytic performance.