Conductive gold nanoparticle assembly linked through interactions between the radical cations of ethylene- and propylene-3,4-dioxythiophene mixed tetramer thiolate

Abstract

A conjugated mixed tetramer consisting of ethylenedioxythiophene (EDOT (E)) and propylenedioxythiophene (ProDOT (P)) dimers (E₂P₂) with a methylthio end-capping group at the EDOT side was directly introduced via a thiolate linker on a gold nanoparticle (AuNP) surface covered with dodecylamine by a ligand exchange reaction. The molar fraction of the thiolate of E₂P₂ in the dodecylamine protecting group of AuNPs reached up to 0.35. Cyclic voltammetry of the AuNPs showed two couples of anodic and cathodic peaks due to the E₂P₂ moiety, suggesting that the radical cation of the E₂P₂ unit could be generated on the AuNPs. In practice, the formation of stable radical cations of E₂P₂ on the AuNPs was observed in dichloromethane by chemical oxidation with AgSbF₆. The conductivity of the drop-cast film of the neutral AuNPs was moderate (∼10⁻⁴ S cm⁻¹), while the conductivity after doping with iodine vapor was increased to ∼10⁻² S cm⁻¹. Similarly, the drop-cast film of the dichloromethane solution of the chemically oxidized AuNPs having an E₂P₂ radical cation moiety showed better conductivity than the iodine-doped film. Accordingly, the π-dimer between the E₂P₂ radical cation moieties on the neighboring AuNPs was considered to form an effective conduction path in the AuNP assembly.