Microwave-assisted synthesis, structure, and tunable liquid-crystal properties of 2,5-diaryl-1,3,4-thiadiazole derivatives through peripheral n-alkoxy chains

Abstract

A series of substituted 2,5-diaryl-1,3,4-thiadiazole derivatives are prepared by microwave-assisted synthesis in the absence of an organic solvent. All derivatives are well characterized by 1H and 13C NMR, MS, and elemental analyses. The X-ray crystal structure of 2,5-di-(4-decyloxyphenyl)-1,3,4-thiadiazole reveals the tilt lamellar arrangement of rod-shaped molecules, which are stabilized by a variety of weak non-covalent interactions. The liquid crystalline properties are studied by polarized-light optical microscopy (POM), differential scanning calorimetry (DSC), and in situ variable temperature X-ray diffraction (VTXRD). By variations in the peripheral n-alkoxy chains, the calamitic mesogens exhibit enantiotropic smectic (SmC and/or SmA) mesophases with wide mesomorphic temperature ranges, whilst the disc-like mesogens form hexagonal columnar mesophase (Col h) at room temperature. The bulk electrical conductivity values of the smectic mesophases of 1-3 are in the range of 10-3-10-4Scm-1, which are slightly higher than that of their solid films. In contrast, the solid film made from 2,5-di-(3,4,5-tri-ACHTUNGTRENUNGoctyloxyphenyl)-1,3,4-thiadiazole shows poor conductivity (2×10-7Scm-1). ©2009 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim.