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Self-Assembly of a Functional Oligo(Aniline)-Based Amphiphile into Helical Conductive Nanowires

Bell, O. Alexander, Wu, Guanglu, Haataja, Johannes S., Brömmel, Felicitas, Fey, Natalie, Seddon, Annela M., Harniman, Robert L., Richardson, Robert M., Ikkala, Olli, Zhang, Xi, Faul, Charl F. J.
Journal of the American Chemical Society 2015 v.137 no.45 pp. 14288-14294
aniline, aqueous solutions, circular dichroism spectroscopy, electrical conductivity, electronics, models, nanowires, stereoisomerism, water solubility
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.