Electronic Coupling in Cofacial Heterobimetallic AgCu-Porphyrin Dimers: Bioinspired Analogs of Chlorophyll Special...

Understanding how subtle structural changes control electronic communication is central to mimicking the function of natural photosynthetic special pairs. Here, we present a combined experimental and DFT study of ethane- and ethene-bridged cofacial heterobimetallic Ag(II)Cu(II)-octaethylporphyrin dimers as synthetic analogues of chlorophyll special pairs. X-ray crystallography reveals clear geometric differences: the ethane-bridged dimer adopts a more slipped arrangement with greater lateral displacement and longer Cu···Ag distance, whereas the ethene-bridged analogue is more cofacial. These variations strongly influence electronic structure and redox properties. The ethane-bridged system shows a lower-energy HOMO and reduced oxidation potentials. Upon one-electron oxidation, both dimers undergo Ag-centered oxidation to form Ag(III), accompanied by significant HOMO-LUMO gap reduction and enhanced cofaciality. Differences become pronounced during the second oxidation step. The ethane-bridged dimer undergoes Cu(II)-porphyrin-centered oxidation to yield Ag(III)-Cu(II)(por•⁺), producing a triplet state with coupling between Cu(II) and a π-cation radical. In contrast, the ethene-bridged analogue oxidizes exclusively at the Ag(III)-porphyrin, maintaining a closed-shell Cu(II) center. These distinct pathways are reflected in their NIR absorptions (1006 vs. 876 nm) and calculated SOMO-LUMO gaps (0.49 vs. 0.28 eV). Overall, minor bridge modifications significantly tune coupling, redox localization, and spin states in these systems.