Electronic Coupling in Cofacial Heterobimetallic AgCu‐Porphyrin Dimers: Bioinspired Analogs of Chlorophyll Special Pairs

ABSTRACT

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.