Supramolecular Nanoassemblies Harness Radical Excited-State Cascade Electron Transfer for Selective CO2 Photoreduction.

Mimicking the efficiency of natural photosynthesis for multielectron CO2 photoreduction remains a central challenge in solar fuel research. Toward this goal, we developed herein a noble metal free supramolecular ion-pair assembly comprising rhodamine B (RB), an underexplored organic photosensitizer, and a cobalt(II) tris(2-pyridylmethyl)amine complex (1Co), which self-assembles into core-shell nano/micro-assembly via counterion-mediated contact ion pairing. This confined ion pair architecture promotes counterion mediated, light-driven hopping electron transfer, suppressing geminate recombination and enabling efficient charge migration, as demonstrated by optical spectroscopy, femtosecond-nanosecond transient absorption, electrochemical impedance spectroscopy, and 2D mass spectrometry studies. Orthogonal dual-light excitation activates radical anion excited states (RB•-*) within the assembly, enabling a diffusion-independent cascade electron transfer pathway. This unique approach achieves selective CO2 photoreduction to syngas under single-light irradiation and switches product distribution toward methane generation under dual-light conditions- a rare feat for photocatalytic CO2 reduction systems. This work introduces a generalizable supramolecular ion-pairing strategy for engineering spatially preorganized donor-acceptor architectures that harness high-energy radical excited states for sustainable solar fuel generation.