Are Redox‐active Centers Bridged by Saturated Flexible Linkers Systematically Electrochemically Independent?

Abstract

The extent to which electrophores covalently bridged by a saturated linker are electrochemically independent was investigated considering the charge/spin duality of the electron and functionality of the electrophore as a spin carrier upon reduction. By combining computational modeling with electrochemical experiments, we investigated the mechanism by which tethered electrophores react together within 4,4'‐oligo[n]methylene‐bipyridinium assemblies (with n = 2 to 5). We show that native dicationic electrophores (redox state Z = +2) are folded prior to electron injection into the system, allowing the emergence of supra‐molecular orbitals (supra‐MOs) likely to support the process of the reductive s bond formation giving cyclomers. Indeed, for Z = +2, London Dispersion (LD) forces contribute to flatten the potential energy surface such that all‐trans and folded conformers are approximately isoenergetic. Then, upon one‐electron injection, for radical cations (Z = +1), LD forces significantly stabilize the folded conformers, except for the ethylene derivative deprived of supra‐MOs. For radical cations equipped with supra‐MOs, the unpaired electron is delocalized over both heterocycles through space. Cyclomer completion (Z = 0) upon the second electron transfer occurs according to the inversion of redox potentials. This mechanism explains why intramolecular reactivity is favored and why pyridinium electrophores are not independent.