Mesomorphic behaviors and charge carrier transport in terthiophene derivatives

We synthesized dialkylterthiophene derivatives omega-substituted with cyclohexylethyl moiety, which exhibit smectic mesophases at room temperature, and investigated their charge carrier transport properties. In particular, transpentylcyclohexylethyl-propylterthiophene (3-TTP-C2CH-5) held SmB phase at room temperature. Furthermore, a 3:1 mixture of 3-TTP-C2CH-5 and (2-methylbutyl)-dodecylterthiophene (5*-TTP-12) showed the SmB phase between 101degreesC and -15degreesC, and the highly ordered smectic phase below -15degreesC. In the SmB phase of the mixture, hole and electron mobility was 10(-3) cm(2)/Vs, and independent of temperature and electric field over room temperature. However, below room temperature, the mobility depended on both temperature and electric field, as is often observed in organic amorphous solids and formarized by Gaussian disorder model, suggesting that the carrier transport in the smectic mesophase can be explained by the hopping conduction in disordered molecular sites.