Formation of spontaneous charge-transfer salt in the molecular system of EDT-TTF and long alkyl-chained sulfonic acid

Conducting Langmuir-Blodgett (LB) films were obtained from a mixture of EDT-TTF, octadecanesulfonic acid (OS), and stearic acid. A spontaneous formation of mixed valence state (MVS) of EDT-TTF molecules occurs during the film preparation, which is the first observation for non-oxygen substituted TTF derivative. Physical properties of the LB films were investigated by the measurements of surface pressure-area isotherms, x-ray diffraction profiles, infrared absorption spectra, and dc conductivity. It was found that OS is a key molecule to induce the MVS formation. Other TTF derivatives may give conducting LB films when they are mixed with suitable long alkyl chained acid molecules.