Abstract
The development of CO(2) conversion catalysts has become paramount in the effort to close the carbon loop. Herein, we report the synthesis, characterization, and photocatalytic CO(2) reduction performance for a series of N-annulated perylene diimide (NPDI) tethered Re(bpy) supramolecular dyads [Re(bpy-C2-NPDI-R)], where R = -H, -Br, -CN, -NO(2), -OPh, -NH(2), or pyrrolidine (-NR(2)). The optoelectronic properties of these Re(bpy-C2-NPDI-R) dyads were heavily influenced by the nature of the R-group, resulting in significant differences in photocatalytic CO(2) reduction performance. Although some R-groups (i.e. -Br and -OPh) did not influence the performance of CO(2) photocatalysis (relative to -H; TON(co) ∼60), the use of an electron-withdrawing -CN was found to completely deactivate the catalyst (TON(co) < 1) while the use of an electron-donating -NH(2) improved CO(2) photocatalysis four-fold (TON(co) = 234). Despite being the strongest EWG, the -NO(2) derivative exhibited good photocatalytic CO(2) reduction abilities (TON(co) = 137). Using a combination of CV and UV-vis-nIR SEC, it was elucidated that the -NO(2) derivative undergoes an in situ transformation to -NH(2) under reducing conditions, thereby generating a more active catalyst that would account for the unexpected activity. A photocatalytic CO(2) mechanism was proposed for these Re(bpy-C2-NPDI-R) dyads (based on molecular orbital descriptions), where it is rationalized that the photoexcitation pathway, as well as the electronic driving-force for NPDI(2-) to Re(bpy) electron-transfer both significantly influence photocatalytic CO(2) reduction. These results help provide rational design principles for the future development of related supramolecular dyads.