Synthesis and mesogenic properties of a novel family of oligothiophene derivatives

With the aim of developing new oligothiophene-based liquid crystals involvi ng hydrogen bonding, new terthiophene derivatives containing an alkylamide group, N,N'-distearyl-2,2':5', 2"-terthiophene-5,5"-dicarboxamide (DNC(18)3 T) and N,N'-dialkyl-5,5"-dibromo-2,2':5',2"-terthiophene-4,4"-dicarboxamide s (DNC(n)DBr3T, n = 5, 8, 16, 18), were designed and synthesized, and their thermal behaviour examined. While DNC(18)3T did not exhibit liquid crystal linity DNC(n)DBr3T compounds with n = 8, 16, 18 were found to form smectic A phases. In addition to liquid crystal behaviour, crystal polymorphism was also observed for DNC(16)DBr3T. It is shown that both the position of the amido group and the alkyl chain length greatly affect liquid crystal phase formation. The absence of liquid crystallinity in the corresponding ester d erivatives suggests that intermolecular hydrogen bonding also plays a role in the formation of liquid crystal phases in the DNC(n)DBr3T system.