Synthesis and liquid crystal properties of a novel family of oligothiophene derivatives

In order to develop novel oligothiophene-based liquid crystals capable of hydrogen bonding, new terthiophene derivatives containing an alkylamide group, N,N'-dialkyl-5,5"-dichloro-2,2:5',2"-terthiophene-4,4"-dicarboxamide (DNC(n)DCl3T, n=8, 18), N,N"-dialkyl-5,5"-dibromo-2,2':5',2"-terthiophene-4,4"-dicarboxamide (DNC(n)DBr3T, n=5, 8, 16, 18), or N,N'-dialkyl-5,5"-diiodo-2,2:5',2"-terthiophene-4,4"-dica-rboxamide (DNC(n)DI3T, n=8, 18), were designed and synthesized, and their thermal behaviour was examined. It was found that DNC(18)DC13T, DNC(n)DBr3T and DNC(n)DBr3T (n=8, 16, 18) form a smectic A phase and that the alkyl chain length greatly affects liquid crystal phase formation. The absence of liquid crystallinity in the corresponding ester derivatives suggests that intermolecular hydrogen bonding also plays a role in the formation of a liquid crystal phases in the DNC(n)DBr3T system. (C) 2004 Elsevier Ltd. All rights reserved.