Innovative molecular design of bridged biphenyls for calamitic nematic liquid crystals with extensive π-conjugated mesogens†

To develop advanced materials based on calamitic nematic liquid crystals, it is essential to design functional optoelectronic mesogens that can form nematic phases at low temperatures. This study proposes a new molecular design strategy for low-temperature nematic liquid crystals using large π-conjugated mesogens with optical/electrical functions. Bridged biphenyls were synthesized by bridging the two phenyl rings with propylene. This bridging structure reduced the molecular planarity and prevented the molecules from aligning neatly in one direction, resulting in lowering the temperature range of the nematic phases. Terphenyl and phenyltolane derivatives exhibited supercooled nematic phases at room temperature, while quarterphenyl and bis(phenylethynyl)-biphenyl derivates exhibited nematic phases below 100 °C. The proposed design is more effective for rigid mesogens compared to conventional calamitic nematic liquid crystal design.