Tracking Charge Accumulation in a Functional Triazole-Linked Ruthenium-Rhenium Dyad Towards Photocatalytic Carbon Dioxide Reduction

The [Re(bpy)(CO)(2)Cl] catalyst pioneered by Lehn for the two-electron reduction of CO2 has constantly revealed unique facets in the mechanistic understanding of the selective transformation of CO2 A novel triazole-linked ruthenium photosensitizer and a rhenium catalyst dyad was synthesized and investigated for photo-induced charge accumulation using time-resolved absorption spectroscopy. The triazole bridging ligand promoted weak electronic communication between the two units, resulting in an anodic shift of the reduction potentials of the Re moiety. Upon excitation of the photosensitizer, the first reduction of the catalyst occurred with a fast apparent rate of 5x10(7) s(-1). Using a double-excitation nanosecond pumppump-probe setup to track the second electron accumulation on the catalytic unit was not conclusive as no observable absorption changes occurred upon the second excitation, suggesting a pathway for an efficient intramolecular reverse electron transfer preventing the two-electron accumulation at the catalyst under our experimental conditions. Nevertheless, under continuous irradiation and with the use of sacrificial electron donors, photocatalytic CO2 reduction assays showed good turnover numbers, hinting at the non-innocent role of byproducts in solution.

Automated summary

The catalyst pioneered by Lehn for the two-electron reduction of CO2 has unique features in selective transformation. A novel ruthenium photosensitizer and rhenium catalyst dyad showed efficient charge accumulation under photo-induced conditions, although second electron accumulation was not observed in the experiment.