Molecular-fastener effects on transport property of TTCn–TTF field-effect transistors

We have studied the electrical conduction of tetrakis(alkylthio)–tetrathiafulvalene (TTCn–TTF) on thin-film field-effect transistors (FET). The field-effect mobility of 10−6–10−5 cm2/Vs was obtained for TTCn–TTF with n = 8, 14, and 18. The mobility increased with increase in the length of alkyl chains. The origin of the increase in mobility is attributed to the reduction in intermolecular distance between adjacent TTF moieties caused by the intermolecular interaction through alkyl chains. Consistently, the X-ray diffraction (XRD) experiments showed that the longer alkyl chain gives the shorter distance between the adjacent TTF moieties. The temperature dependence of the mobility for TTCn–TTF shows a change in activation energy at around 220 K, which is attributable to the phase transition of TTCn–TTF.