Phase behavior of a new class of anthraquinone-based discotic liquid crystals.

Abstract

Five novel columnar liquid crystalline compounds (4.1 - 4.5) consisting of a central anthraquinone core carrying four alkoxy chains (R = n-C6H13, n-C8H17, n-C10H21, n-C12H25, and 3,7-dimethyl octyl) with two diagonally opposite 1-ethynyl-4-pentylbenzene units were synthesized and their phase transitions were investigated between changes in the molecular structure & their self-assembly into the columnar mesophases. Small and wide angle X-ray scattering (SAXS/WAXS) studies were performed to deduce the exact nature of the mesophases and their corresponding electron density maps were derived from the intensities of the peaks observed in the diffraction patterns. A comparison of compounds with different alkoxy chains indicated that columnar rectangular (Colr) phase was stable at lower temperature for shortest peripheral alkoxy chain (4.1; R = n-C6H13) and found to exhibit columnar hexagonal (Colh) phase and then discotic nematic (ND) phase with increasing temperature. In contrast, increasing the peripheral chain length to n-C8H17 or branched one (4.2 and 4.5) stabilized the Colh phase at lower temperature and showed ND phase at higher temperature. Further increase in chain length (4.3 and 4.4; n-C10H21, n-C12H25) demonstrated the formation of ND phase. Conductivity measurement in Colh mesophase was found almost ten times higher in magnitude than corresponding Colr phase. HOMO-LUMO band gap of all the compounds was found to be in the range of 2.79 eV to 2.82 eV which is quiet less and comparable with optical energy band gap.

DOI: 10.1021/acs.langmuir.7b03031

Cite this paper

@article{De2017PhaseBO, title={Phase behavior of a new class of anthraquinone-based discotic liquid crystals.}, author={Joydip De and Santosh Prasad Gupta and Indu Bala and Sandeep Kumar and Santanu Kumar Pal}, journal={Langmuir : the ACS journal of surfaces and colloids}, year={2017} }