Kinetics of Multielectron Transfers and Redox-Induced Structural Changes in N-Aryl-Expanded Pyridiniums: Establishing Their Unusual, Versatile Electrophoric Activity

A combined electrochemical and theoretical study of a series of pyridinium-based electrophores, consisting of reference N-alkyl-2,4,6-triarylpyridiniums (1–3) and N-aryl-expanded pyridiniums (EPs), i.e. N-aryl-2,4,6-triarylpyridiniums (4–10), is presented with the aim of elucidating multifaceted mechanisms underpinning the complex electrophoric activity of fluxional EP systems. Series 1–10 constitutes a library of model electrophores showing an incremental variation of their composition, charge, and steric hindrance. By kinetic mapping of the first two heterogeneous electron transfers (ETs) of 1–10 and computational mapping, at the density functional theory level, of their electronic and geometrical features in various redox states, it is established that, depending on whether EPs are made of one (4, 5) or two “head-to-tail”-connected pyridinium rings (6–10), the nature of the redox-triggered distortions (when allowed) is different, namely, N-pyramidalization due to hybridization change in the former case...