Synthesis and Characterization of Bent-shaped Liquid Crystals with Thiophenic Central Core

ABSTRACT
New bent shaped mesogenic compounds based on 2,5-disubstituted thiophene central core were successfully synthesized. Lengths of rigid centers as well as degree of conjugation were varied by coupling benzene, naphthalene and biphenyl systems to the thiophene through Sonogashira cross-coupling reaction. Effects of these structural variations on optical, thermal and mesomorphic properties of the liquid crystals were determined. All the final compounds showed good thermal stabilities. Some compounds display liquid crystalline properties forming smectic and nematic mesophases. Results showed a general pattern that increasing the length of rigid part of the molecule increased the tendency to form a mesophase. All of the synthesized compounds showed UV–vis absorption in the 342–373 nm range with high molar extinction coefficients. Choloroform solutions of all compounds showed strong blue fluorescence emitting between 404-411nm region with reasonably large Stokes shifts (39-59 nm) and moderately high emission efficiencies of 26-56 % (Φf = 0.26–0.56).