Imine Reversal Mediates Charge Separation and CO2 Photoreduction in Covalent Organic Frameworks

Abstract We investigate the correlation between CO2 reduction performance in twin COFs with reversed imine connectivity and reveal that imine-linkage imparts intramolecular charge transfer (ICT) directionality – an effect we term an “ICT Tesla Valve.” This reversal also affects the coordination of Re molecular catalyst (MC) and leads to a slowdown in light driven CO2→CO photoreduction. ICT towards Re MC in Re-f-COF facilitates efficient CO2 photoreduction while performance is reduced when ICT is direct away from Re MC in Re-r-COF. Combining theory with experimental data shows that ICT directionality affects the charge separation mechanism which is particularly evident in the much longer-lived excited state of Re-f-COF compared to Re-r-COF. These findings are unprecedented, revealing not only that the linker chemistry should be recognized as a key factor to consider in the development of COF photocatalysts but also provides a unique approach to tailor photocatalysts by controlling the direction of ICT.