Boosting CO2 Photoreduction by π-π-Induced Preassembly between a Cu(I) Photosensitizer and a Pyrene-Appended Co(II) Catalyst

The design of a highly efficient system for CO2 photoreduction fully based on earth-abundant elements presents a challenge, which may be realized by installing suitable interactions between photosensitizer and catalyst to expedite the intermolecular electron transfer. Herein we have designed a pyrene-decorated Cu(I) complex with a rare dual-emission behavior, aiming at additional π-interaction with a pyrene-appended Co(II) catalyst for visible-light-driven CO2-to-CO conversion. The results of 1H NMR titration, time-resolved fluorescence/absorption spectroscopies, quantum chemical simulations and photocatalytic experiments clearly demonstrate that the dynamic π-π interaction between sensitizer and catalyst is highly advantageous in photocatalysis by accelerating the intermolecular electron transfer rate up to 6.9 × 105 s-1, thus achieving a notable apparent quantum efficiency of 19% at 425 nm with near-unity selectivity. While comparable to most earth-abundant molecular systems, this value is over three-times of the pyrene-free system (6.0%) and far surpassing the benchmarking Ru(II) tris(bipyridine) (0.3%) and Ir(III) tris(2-phenylpyridine) (1.4%) photosensitizers under parallel conditions.