Highly Robust Rhenium(I) Bipyridyl Complexes Containing Dipyrromethene-BF2 Chromophores for Visible Light-Driven CO2 Reduction

New rhenium bipyridyl complexes with dipyrromethene-BF2 chromophores (A-ReBDP-CZ, A-ReBDP2, ReBDP-CZ, and ReBDP2) were developed for highly efficient photocatalytic carbon dioxide (CO2) reduction to carbon monoxide (CO). These catalysts consisted of two moderate electron-deficient groups (dipyrromethene-BF2, BDP) as the visible-light-harvesting antenna as well as both electron donor (N-phenylcarbazole, CZ) and acceptor (BDP) on Re bipyridyl framework. Among ReBDP-CZ and ReBDP2 complexes, the ReBDP2 incorporating two electron-deficient BDP chromophores had a longer-lived photoexcited state (182.4 mu s) and a twofold enhanced molar absorption coefficient (epsilon=157000 m(-1) cm(-1)) compared with ReBDP-CZ. Thus, ReBDP2 achieved the superior photocatalytic reactivity and stability with a CO turnover number (TONCO) value as high as 1323 and quantum yield (phi(CO)) up to 55 %, which was the most excellent photocatalysis efficiency among the single-active-site Re catalysts without additional photosensitizer. Furthermore, the acetylene-bridged linker was detrimental to the photoactivity and durability of the catalyst. In brief, two BDP-based Re bipyridyl systems with outstanding catalytic performance and significant visible-light-harvesting capabilities in the solar spectrum offer a promising strategy for solar-to-fuel conversion schemes.