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. The selective CO₂ photoreduction in water mediated by earth-abundant photocatalysts remains highly challenging. Here the authors present the coordinative anchorage of molecular catalysts on a pyridine-armed covalent triazine framework for CO₂ photoreduction to CO in fully aqueous solutions. [ABSTRACT FROM AUTHOR]