Molecular-Level Tailoring of Energy Structure in Ternary Conjugated Polymers with a Built-in Ru-Complex Catalyst for Efficient CO₂ Reduction Photocatalysis

Efficient catalytic CO₂ conversion by harnessing visible-light energy is a substantial challenge for sustainability. Photocatalytic materials consisting of light absorbers and catalysts have been extensively developed. However, efficient photocatalytic systems have so far relied on the use of precious metal-based compounds or materials as light-absorbing components, primarily because of their long-lived photoexcited states. Herein, we report the design principles of ternary conjugated polymers as a metal-free light absorber with a built-in metal complex catalyst for substantially activating CO₂ reduction photocatalysis. The ternary conjugated system enabled exceedingly flexible tuning of their energy structure, which is beneficial for long-range charge separation by manipulating the photoexcited electrons to the site-selectively introduced molecular catalyst center. The key cascade energy structure was tailored, and its impacts on photocatalysis were unveiled by using both spectroscopic experiments and theoretical calculations. The precise molecular design resulted in very active visible-light CO₂ reduction, even without the aid of a precious metal-based light absorber, recording an external quantum efficiency up to 32.2% and producing a concentrated formate (∼0.48 M).