We report the design, synthesis, and characterization of four N-annulated perylene diimide (NPDI) functionalized rhenium bipyridine [Re(bpy)] supramolecular dyads. The Re(bpy) scaffold was connected to the NPDI chromophore either directly [Re(py-C0-NPDI)] or via an ethyl [Re(bpy-C2-NPDI)], butyl [Re(bpy-C4-NPDI)], or hexyl [Re(bpy-C6-NPDI)] alkyl-chain spacer. Upon electrochemical reduction in the presence of CO2 and a proton source, Re(bpy-C2/4/6-NPDI) all exhibited significant current enhancement effects, while Re(py-C0-NPDI) did not. During controlled potential electrolysis (CPE) experiments at Eappl = -1.8 V vs Fc+/0, Re(bpy-C2/4/6-NPDI) all achieved comparable activity (TONco ∼25) and Faradaic efficiency (FEco ∼94%). Under identical CPE conditions, the standard catalyst Re(dmbpy) was inactive for electrocatalytic CO2 reduction; only at Eappl = -2.1 V vs Fc+/0 could Re(dmbpy) achieve the same catalytic performance, representing a 300 mV lowering in overpotential for Re(bpy-C2/4/6-NPDI). At higher overpotentials, Re(bpy-C4/6-NPDI) both outperformed Re(bpy-C2-NPDI), indicating the possibility of coinciding electrocatalytic CO2 reduction mechanisms that are dictated by tether-length and overpotential. Using UV-vis-nearIR spectroelectrochemistry (SEC), FTIR SEC, and chemical reduction experiments, it was shown that the NPDI-moiety served as an electron-reservoir for Re(bpy), thereby allowing catalytic activity at lower overpotentials. Density functional theory studies probing the optimized geometries and frontier molecular orbitals of various catalytic intermediates revealed that the geometric configuration of NPDI relative to the Re(bpy)-moiety plays a critical role in accessing electrons from the electron-reservoir. The improved performance of Re(bpy-C2/4/6-NPDI)dyads at lower overpotentials, relative to Re(dmbpy), highlights the utility of chromophore electron-reservoirs as a method for lowering the overpotential for CO2 conversion.
|Number of pages||16|
|Journal||Journal of the American Chemical Society|
|State||Published - Oct 13 2021|
Bibliographical noteFunding Information:
G. C. W. acknowledges the Canada Research Chairs Program, CFI JELF (34102), NSERC DG (2019-04392), and the University of Calgary. W. E. P. acknowledges the Canada Research Chairs Program. J. K. acknowledges Alberta Graduate Excellence Scholarship (AGES) and NSERC CGS-D scholarship programs. This research was undertaken thanks in part to funding from the Canada First Research Excellence Fund (CFREF). C. R. and K. R. acknowledge funding by the Research Corporation for Science Advancement (RCSA) Cottrell Scholars program (Award No. 24432); computing resources on the Lipscomb High Performance Computing Cluster were provided by the University of Kentucky Information Technology Department and the Center for Computational Sciences (CCS).
© 2021 American Chemical Society.
ASJC Scopus subject areas
- Chemistry (all)
- Colloid and Surface Chemistry