Effects of Desymmetrization on Thiophene-Based Bent-Rod Mesogens.

The synthesis and characterization of various thiophene-based bent-rod liq. crystals are reported, and the effects of varying lateral dipole and core desymmetrization upon mesophase behavior are described. Incorporation of desymmetrized core 7 into the mol. framework has very different consequences depending upon whether n-alkoxy or tetracatenar-type end groups were used. Tetracatenar-type mesogens 8-11 are significantly less mesogenic than the previously reported sym. series 3. When sym. straight-chain compds. 13-17 and unsym. straight-chain compds. 18-21 were studied, however, the desymmetrized core gave rise to mesophases with much broader temp. ranges. Variable temp. x-ray diffraction of these compds. suggests the formation of antiparallel dimers of mols. within the liq. crystal phase, and this may explain the relatively stable mesophases formed by these compds. and their incompatibility with chiral induction. The effects of altering the lateral substituents were also explored, and 3,4-difluorothiophene-based compds. 24-27 exhibit broad nematic mesophases. [on SciFinder(R)]