Synthesis and characterisation of novel isoxazole-based banana liquid crystals from naturally occurring curcumin

Abstract

Isoxazole-based bent-core liquid crystals (LCs) derived from naturally occurring curcumin were synthesised and their LC properties were investigated by polarising optical microscopy, differential scanning calorimetry and X-ray diffraction techniques. Five compounds, including a branched alkyl chain derivative, were prepared and characterised. These derivatives exhibit enantiotropic mesophases. While lower homologues display widetemperature-range nematic phase, a longer-chain derivative 3d shows smectic C phase in addition to the nematic phase. The bent angle in these compounds is in between calamitic LCs and banana LCs. Therefore, the molecules escape from polar order packing observed in typical bent-core LCs. Increasing the length of alkyl chain reduces both melting and isotropic temperatures in the series. However, the compound with branched alkyl chains exhibits significant reduction in the nematic-isotropic temperature only. Detailed XRD experiments confirm the presence of the N phase in the lower homologues and SmC phase in a higher homologue.

Iron-Mediated Synthesis of Isoxazoles from Alkynes: Using Iron(III) Nitrate as a Nitration and Cyclization Reagent

“…N, 5.09. M-2 : yellow solid, mp 106.2–107.5 °C (lit . mp 105–107 °C); 1 H NMR (400 MHz, DMSO, 25 °C) δ 8.01–7.89 (m, 2H), 7.82–7.70 (m, 1H), 7.61 (t, J = 7.8 Hz, 2H), 6.55 (s, 2H); 13 C­{ 1 H} NMR (100 MHz, DMSO, 25 °C) δ 188.9, 135.3, 133.9, 129.5, 128.9, 83.3; ESI-MS [M – H] − m / z 164.22.…”

“…Isoxazoles are core components of numerous pharmaceutically active molecules such as mofezolac, acivicin, zonisamide, broxaterol, and leflunomide . Furthermore, they can serve as efficient building blocks in diverse functional materials . Therefore, various methods for the synthesis of isoxazoles have been developed .…”

Ethylenedioxythiophene as a novel central unit for bent-core liquid crystals

“…The presence of heteroatoms such as N, O and S causes significant effects on lateral or longitudinal dipoles. Incorporation of five-member heterocyclic compounds widens the bent angle and show extensive mesomorphic behaviour [4]. A number of 2,5-disubstituted thiophene-based liquid crystal compounds have been synthesised and investigated their structural properties [5][6][7][8][9][10][11][12][13][14][15].…”