Synthesis and characterisation of novel imidazolium-based ionic liquid crystals with a p-nitroazobenzene moiety

ISSN： 0267-8292

Source： Liquid Crystals, Vol.35, Iss.6, 2008-06, pp. : 765-772

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Abstract

A novel series of compounds with different counter anions, i.e. 1-{[4-(4-nitrophenylazo)phenyloxy]}alkyl-3-methyl-1H-imidazol-3-ium bromide salts (Cn , n = 3, 6, 10) and tetrafluoroborate salts (Dn , n = 3, 6, 10), were synthesised by the incorporation of an imidazolium group into paraffin side chain-terminated 4-nitroazobenzene derivatives. Their chemical structures were determined by 1H NMR, 13C NMR, UV spectroscopy and elemental analysis. The thermotropic liquid crystalline properties of these materials were further studied by polarising optical microscopy, wide-angle X-ray diffraction and differential scanning calorimetry. The results show that Cn and Dn (n = 6, 10) exhibit smectic liquid crystalline phases. The ionic liquid groups play an important role in forming the smectic layer structure, via enhancement of the thermal stability of the smectic state.