Synthesis and Characterization of Mesogenic Compounds Possessing Bithiophene and Benzoxazole Units

A series of bithiophene-based compounds, 2-(5′-alkyl-2,2′-bithiophene-5-yl)-benzoxazole derivatives (nTBx), bearing different substituents (H, CH3, Cl, NO2) at the 5-position, were prepared and characterized. They exhibit enantiotropic mesophases with temperature ranges of 3°C–61°C and 4°C–71°C during heating and cooling, and nTBx with electron-withdrawing substituents (NO2, Cl) display higher clearing temperatures and wider mesophase ranges than those of corresponding homologues with electron donating substituents. Compared to biphenyl-based analogs (nB-x), nTBx show much larger red-shifted absorption bands (374–388 nm) and photoluminescence emission peaks (453–458 nm), thereby illustrating the impact of the bithiophene core on electronic properties originating from the π-molecular orbitals.