Strong impacts of inter-π-chain charge transfer accelerating CO2 reduction photocatalysis of carbazole–diimine-based linear conjugated polymer/Ru complex hybrids

Conjugated polymers are promising candidates for photocatalyst materials owing to the molecular design flexibility in tuning their properties, including visible light responsiveness. The rational introduction of a molecular metal complex acting as a catalyst at a specific location is an effective approach to activate conjugated polymer photocatalysts for the selective conversion of small molecules, such as carbon dioxide. However, the photocatalytic activity of the conjugated polymer/metal complex hybrids has not been satisfactory. In particular, there is still much room for improvement in polymer structure engineering to maximise the activation of a molecular complex catalyst centre by photoexcited electrons. This work demonstrates the strong impact of side chains and ligand structures, which do not significantly affect the optical properties of the polymers, on their photocatalytic performance for CO2 reduction. The relatively rigid aromatic side chains and condensed aromatic ligand moieties enable effective inter-π-chain charge transfer to activate the isolated (i.e. low-concentration) Ru(II) complex catalyst. The manipulation of photoexcited charge transfer by structural modulation resulted in a significantly improved photocatalytic activity (quantum efficiency of 2.2% at 450 nm) compared to the counterpart photocatalysts containing the alkyl side chain and bipyridine ligand moieties.