Trinuclear Re(I)-Coordinated Organic Cage as the Supramolecular Photocatalyst for Visible-Light-Driven CO 2 Reduction.

Photocatalytic reduction of excess CO 2 in the atmosphere to value-added chemicals by visible light can be an effective solution to fuel shortage and global warming. Considering these issues, we designed and successfully synthesized a trinuclear Re(I)-coordinated organic cage (Re-C 4 R ) as the supramolecular photocatalyst. Photophysical, electrochemical properties, and photocatalytic performance comparison of Re-C 4 R and its mononuclear analogue Re-bpy are discussed in detail. Notably, the covalent linkage of three Re(I) subunits in Re-C 4 R leads to TON CO = 691 (per Re(I) site in 4 h) more than three times as much as TON CO = 208 of Re-bpy. Compared to Re-bpy, higher current enhancement in the control CV experiments under CO 2 was observed for Re-C 4 R . CO 2 adsorption process can be promoted because of the cryptand structure and multiple amine groups of Re-C 4 R . Moreover, decay lifetimes of Re-C 4 R are shorter than those of Re-bpy in the ultrafast transient absorption (TA) and photoluminescence (PL) decay spectra, indicating that the trinuclear cryptate structure of Re-C 4 R could facilitate electron transfer efficiency during CO 2 reduction.