New mesogenic thiophene and furan derivatives

The synthesis of novel liquid-crystalline heteroaromatic compounds incorporating the five membered thiophene and furan rings is described. The objective of the present work is to substitute the mesogenic units styrylthiophene, styrylfuran, phenylthiophene and phenylfuran for the aromatic structural units styrylbenzene and biphenyl in known mesomorphic compounds, thereby permitting a comparison of the effect of heterocyclic units on mesomorphic properties. The compounds synthesized with the mesogenic units styrylthiophene and phenylthiophene exhibited liquid-crystalline properties while compounds with the units styrylfuran and phenylfuran did not. The existence of mesophases in these compounds is closely associated with the configuration (linearity) of the molecule. The heterocyclic rings thiophene and furan are pentagonal and 2,5-disubstitution leads to non-collinear bonds which produce a deviation from linearity of the order of 32° and 54°, respectively.