Self-assembly of a functional oligo(aniline)-based amphiphile into helical conductive nanowires

A tetra(aniline)-based cationic amphiphile, TANI-NHC(O)C₅H₁₀N(CH₃)₃⁺Br^– (TANI-PTAB) was synthesized, and its emeraldine base (EB) state was found to self-assemble into nanowires in aqueous solution. The observed self-assembly is described by an isodesmic model, as shown by temperature-dependent UV–vis investigations. Linear dichroism (LD) studies, combined with computational modeling using time-dependent density functional theory (TD-DFT), suggests that TANI-PTAB molecules are ordered in an antiparallel arrangement within nanowires, with the long axis of TANI-PTAB arranged perpendicular to the nanowire long axis. Addition of either S- or R- camphorsulfonic acid (CSA) to TANI-PTAB converted TANI to the emeraldine salt (ES), which retained the ability to form nanowires. Acid doping of TANI-PTAB had a profound effect on the nanowire morphology, as the CSA counterions’ chirality translated into helical twisting of the nanowires, as observed by circular dichroism (CD). Finally, the electrical conductivity of CSA-doped helical nanowire thin films processed from aqueous solution was 2.7 mS cm^–1. The conductivity, control over self-assembled 1D structure and water-solubility demonstrate these materials’ promise as processable and addressable functional materials for molecular electronics, redox-controlled materials and sensing.