Co-facial pi-pi Interaction Expedites Sensitizer-to-Catalyst Electron Transfer for High-Performance CO2 Photoreduction

The sunlight-driven reduction of CO2 into carbonaceous fuels can lower the atmospheric CO2, concentration and provide renewable energy simultaneously, attracting scientists to design photocatalytic systems for facilitating this process. Significant progress has been made in designing high-performance photosensitizers and catalysts in this regard, and further improvement can be realized by installing additional interactions between the abovementioned two components, however, the design strategies and mechanistic investigations on such interactions remain challenging. Here, we present the construction of molecular models for intermolecular pi-pi interactions between the photosensitizer and the catalyst, via the introduction of pyrene groups into both molecular components. The presence, types, and strengths of diverse pi-pi interactions, as well as their roles in the photocatalytic mechanism, have been examined by H-1 NMR titration, fluorescence quenching measurements, transient absorption spectroscopy, and quantum chemical simulations. We have also explored the rare dual emission behavior of the pyrene-appended iridium photosensitizer, of which the excited state can deliver the photo-excited electron to the pyrene-decorated cobalt catalyst at a fast rate of 2.60 x 10(6) s(-1) via co-facial pi-pi interaction, enabling a remarkable apparent quantum efficiency of 14.3 +/- 0.8% at 425 run and a high selectivity of 98% for the photocatalytic CO2-to-CO conversion. This research demonstrates non-covalent interaction construction as an effective strategy to achieve rapid CO2 photoreduction besides a conventional photosensitizer/catalyst design.