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

A conjugated mixed tetramer consisting of ethylenedioxythiophene (EDOT (E)) and propylenedioxythiophene (ProDOT (P)) dimers (E 2 P 2 ) 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 E 2 P 2 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 E 2 P 2 moiety, suggesting that the radical cation of the E 2 P 2 unit could be generated on the AuNPs. In practice, the formation of stable radical cations of E 2 P 2 on the AuNPs was observed in dichloromethane by chemical oxidation with AgSbF 6 . 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 E 2 P 2 radical cation moiety showed better conductivity than the iodine-doped film. Accordingly, the π-dimer between the E 2 P 2 radical cation moieties on the neighboring AuNPs was considered to form an effective conduction path in the AuNP assembly. Drop-casting of gold nanoparticle (AuNP) with radical cation moiety of a quaterthiophene derivative provided a conductive film. The interparticle π-dimer was considered to act as effective conduction paths in the AuNP assembly.