Polymer Chromophore–Catalyst Assembly for Photocatalytic CO₂ Reduction

A polystyrene-based chromophore–catalyst assembly (PS-RuC/RuCat) was synthesized and applied for photocatalytic CO2 reduction in an organic solution in the presence of a sacrificial donor. The polymer assembly contains Ru(bpy)32+ (RuC, bpy = 2,2′-bipyridine) as the chromophore and a derivative of [Ru(tpy)(6-mbpy)(CH3CN)]2+ (RuCat, tpy = 4′-phenyl-2,2′:6′,2″-terpyridine and 6-mbpy = 6-methyl-2,2′-dipyridyl) as the CO2 reduction catalyst. The photophysical and electrochemical properties of the polymer assembly were investigated. Picosecond transient absorption and time-resolved emission reveal that the RuC chromophores are quenched by energy transfer to the RuCat units in the polymer assembly. Cyclic voltammetry shows that PS-RuC/RuCat effects electrocatalytic reduction of CO2 with an onset of approximately −1.25 V versus Ag/AgCl. Photocatalytic studies were conducted separately for the PS-RuC/RuCat polymer assembly and a mixture of monomers RuC and RuCat in a mixture of dimethylformamide and triethanolamine with 1-benzyl-1,4-dihydronicotinamide as a sacrificial reductant. The primary CO2 reduction products CO and H2 were detected in both photocatalytic systems. Formic acid was detected at low levels by nuclear magnetic resonance and is a very minor product. The polymer assembly system shows a lower photocatalytic CO2 reduction quantum yield (6.7%) but exhibits improved stability compared with a mixed molecular chromophore/catalyst system.