Electronic conduction in biphenyl liquid crystals

A series of 4-alkyl-4'-alkoxylbiphenyls, which are one of the representative calamitic liquid crystals having a small aromatic core moiety, has been synthesized and their charge carrier transport properties are characterized in order to examine how small the core size can be for a high mobility. The biphenyls exhibit both smectic B and E phases and the hole transport characterized by a high mobility of 10(-3) cm(2) V-1 s(-1) in the smectic mesophases. The mobility depends on temperature in both smectic phases, and furthermore it depends on the electric field in the smectic E phase. The fact that such a small molecule of biphenyl exhibits the mobility comparable to those of triphenylenes and TPD (N,N'-diphenyl-N,N'-bis(3-methyl-phenyl)[1,1'-biphenyl]-4,4'-diamine) gives an insight into the molecular design of high mobility liquid crystalline materials.