Mesogenic heterocycles formed by bis-pyrazoles and bis-1,3,4-oxadiazoles

Three new series of compounds 1a-c containing multiple heterocyclic 2,5-pyrazoles, 1,3,4-oxadiazole and thiophene exhibiting mesophases were reported. Crystallographic data showed that the crystal 1a (n=8) is a linear-shaped molecule with a molecular length of ca. 40.57 Å. However, three heterocyclic rings were not coplanar. All compounds 1a formed smectic A/C phases, and all compounds 1c exhibited columnar phases, which were confirmed by powder X-ray diffractometer (XRD). A N_cell and R_ar value equal to 3.91 and 18.29 Å within a slice of 9.0 Å thick were obtained for derivatives 1c (n=8), indicating that two molecule was correlated within columns in Col_h phases. All derivatives showed good stabilities at temperature below T=383-426°C on thermogravimetric analysis (TGA). The PL spectra of all compounds 1b-c (n=8) showed one intense peak at λ_max=428-496 nm, and these photoluminescent emissions (PL) originated from 1,3,4-oxadiazole moiety.