Symmetric quinoxaline–oxadiazole conjugates: mesogenic behavior via quinoxaline–CH interactions

Three series of new heterocyclic 1,3,4-oxadiazoles 1–3 was prepared and their mesomorphic behavior was investigated. All compounds 1 and their precursors 2–3 exhibited nematic or/and smectic phases, which were confirmed by powder XRD diffractometer. A single crystallographic structure of mesogenic precursor 3 (n=6) was determined by X-ray analysis in order to correlate the molecular structures with the formation of mesophases. Crystallographic data indicated that the formation of mesomorphic properties might be controlled by CH–π and H-bonds. All clearing temperatures of compounds 1 were relatively higher at T_cl=279.0–310.9 °C and the range of mesophases was narrow, at ΔT_meso=14.3–34.0 °C on cooling process. The PL emissions for three compounds 1–3 showed one intense peak at λ_max=432–433 nm, and these photoluminescent emissions originated from quinoxaline moiety.