Molecular catalyst coordinatively bonded to organic semiconductors for selective light-driven CO₂ reduction in water

The selective photoreduction of CO₂ in aqueous media based on earth-abundant elements only, is today a challenging topic. Here we present the anchoring of discrete molecular catalysts on organic polymeric semiconductors via covalent bonding, generating molecular hybrid materials with well-defined active sites for CO₂ photoreduction, exclusively to CO in purely aqueous media. The molecular catalysts are based on aryl substituted Co phthalocyanines that can be coordinated by dangling pyridyl attached to a polymeric covalent triazine framework that acts as a light absorber. This generates a molecular hybrid material that efficiently and selectively achieves the photoreduction of CO₂ to CO in KHCO₃ aqueous buffer, giving high yields in the range of 22 mmol g^-1 (458 μmol g^-1 h^-1) and turnover numbers above 550 in 48 h, with no deactivation and no detectable H₂. The electron transfer mechanism for the activation of the catalyst is proposed based on the combined results from time-resolved fluorescence spectroscopy, in situ spectroscopies and quantum chemical calculations.