Conducting Langmuir–Blodgett films of an amphiphilic unsymmetrical ethylenedithiotetrathiafulvalene derivative: EDT–TTF–CH2OC(O)C17H35

Abstract

Langmuir-Blodgett (LB) films of the novel amphiphilic ethylenedithiotetrathiafulvalene derivative [EDT–TTF–CH₂OC(O)C₁₇H₃₅, 5] assembled on a range of solid substrates have room temperature in-plane do conductivity values as high σ_rt= 10^–2–10^–3 S cm^–1 as deposited; iodine doping results in an immediate decrease in conductivity to values of σ_rt=ca. 10^–6 S cm^–1, which subsequently increases over a few hours to σ_rt=ca. 10^–3 S cm^–1, as a stable mixed-valence state is attained. The LB films have been characterized by ellipsometry, UV–VIS spectroscopy and cyclic voltammetry. By comparison with analogous long-chain TTF and BEDT–TTF derivatives, it appears that the carbonyl group in the side chain of 5 facilitates LB film formation, and the ethylenedithio bridge of 5 contributes to the unusually high conductivity of the as-deposited films, possibly due to the presence of non-bonded, intermolecular S—S interactions. Analogous derivatives of trimethyl-TTF and ethylenediseleno-TTF substituted with the same side-chain, i.e., triMe–TTF–CH₂OC(O)C₁₇H₃₅, 10, and EDS–TTF–CH₂OC(O)C₁₇H₃₅, 11, respectively, form LB films with significantly lower conductivity values than 5, both before and after iodine doping.