Charge Carrier Transport Properties of Biphenyl Liquid Crystals with a Dimer Structure

In order to have better understanding design of liquid crystalline molecules as organic semiconductors, we synthesized a series of biphenyl liquid crystals with a dimer structure such as 1,8-bis[4-(4'-butylbiphenyl)]octane (4BP8BP4) and 1,8-bis[4-(4'-octylbiphenyl)]octane (8BP8BP8) as a model material, and characterized their phase-transition behaviors and charge-transport properties. These biphenyl dimers exhibited smectic B (SmBhex) phase at higher temperatures and higher mobility, i.e., 5-6 x 10(-3) cm(2) V-1 s(-1) that does not depend on temperature, compared with that of a corresponding monomer, 4-octyl-4'-butylbiphenyl (8BP4). We discuss the present result in a framework of disorder in the liquid crystal phase for an organic semiconductor.