Heavy-Atom-Free Photosensitizers for High-Yield CO2-to-CO Conversion

Heavy-Atom-Free photosensitizers (HAFPs) with abundant resources show great potential to construct noble metal-free and high-yield CO2 photoreduction systems, but have rarely been achieved due to their poor intersystem crossing (ISC) efficiency. Herein, a library of HAFPs (B-1-B-8) were rationally designed by coupling various anthracene donors and boron dipyrromethene acceptors to break the short-lived excited state limitation of pure organic chromophores. The special orthogonal geometry between electron donor and acceptor contributes to triggering spin-orbit charge transfer-induced ISCs to achieve long-lived triplet and reduced states, which can facilitate consecutive intermolecular electron transfers to further boost CO2 reduction. Impressively, the reduced HAFP B-8 can efficiently sensitize iron catalysts to construct noble metal-free photocatalytic systems for highly efficient and selective CO2 -to-CO conversion with 1311 mu mol yield. Experimental and theoretical investigations clearly illustrate the structure-activity relationship, highlighting a new avenue to develop highly efficient organic photosensitizers to boost CO2 photoreduction.