Extended conjugated mesogens: synthesis and mesomorphic properties of H-shaped mesogens based on 3,3ʹ,5,5ʹ-tetrasubstituted 2,2ʹ-bithiophene with oligo(1,4-phenyleneethynylene) arms

Tetraalkyl, tetraalkoxy and dialkyldialkoxy derivatives, [R 1 C 6 H 4 CCC 6 H 2 (C 2 H 5 ) 2 CC] 2 [R 2 C 6 H 4 CCC 6 H 2 (C 2 H 5 ) 2 CC] 2 C 8 H 2 S 2 where R 1 and R 2 = alkyl and alkoxy chains of different lengths, exhibit nematic phases.

The length, number and position of the terminal chains strongly affect the mesomorphic properties. The tetraalkyl derivatives in which R 1 = R 2 = pentyl to heptyl exhibit enantiotropic mesophases, whereas the derivatives with octyl or nonyl chains exhibit monotropic mesophases. The tetraalkoxy derivatives in which R 1 = R 2 = pentyloxy to nonyloxy all exhibit enantiotropic nematic phases.