On the Supra-LUMO Interaction: Case Study of a Sudden Change of Electronic Structure as a Functional Emergence

The synergistic functioning of redox-active components that emerges from prototypical 2,2'-di( N -methylpyrid-4-ylium)-1,1'-biphenyl is described. Interestingly, even if a  trans conformation of the native assembly is expected, due to electrostatic repulsion between cationic pyridinium units, we demonstrate that  cis conformation is equally energy-stabilized on account of a peculiar LUMO (SupLUMO) that develops through space, encompassing the two pyridiniums in a single, made-in-one-piece, electronic entity (superelectrophoric behavior). This SupLUMO emergence originates in a sudden change of electronic structure. This finding is substantiated by solid state (single-crystal X-ray diffraction) and solution (NOE-NMR and UV-vis-NIR spectroelectrochemistry) studies, combined with electronic structure computations. Electrochemistry shows that electron transfers are so strongly correlated that two-electron reduction manifests itself as a single-step process with a large potential inversion consistent with inner creation of a carbon-carbon bond (digital simulation). The redox-gated covalent bond, serving as electron reservoir, was studied via atropisomerism of the reduction product (VT-NMR).  Trans and  cis native species are worth considered as intrinsically different, that is, as doubly-electrophoric and singly-superelectrophoric assemblies, beyond conformational isomerism. Importantly, the through-space-mediated SupLUMO may come in complement of other weak interactions encountered in Supramolecular Chemistry as a tool for the design of electroactive architectures.