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Second-harmonic generation and the influence of flexoelectricity in the nematic phases of bent-core oxadiazoles

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JournalLIQUID CRYSTALS
DateAccepted/In press - 27 Mar 2016
DatePublished (current) - 24 Apr 2016
Number of pages18
Pages (from-to)1-18
Original languageEnglish

Abstract

Second-harmonic generation (SHG) in the nematic phase of bent-core oxadiazole-based liquid crystals (LCs) was studied and compared to that for the rod-like compound 4-cyano-4ʹ-n-octylbiphenyl (8CB). Weak, isotropically scattered second-harmonic (SH) light was observed for all materials, consistent with SHG by nematic director fluctuations. The SH intensity produced by the bent-core materials was found to be up to ~ 3.4 times that of 8CB. We discuss this result in terms of the dependence of SH intensity on temperature, elastic constants and flexoelectric coefficients. We have calculated the latter by using a molecular field approach with atomistic modelling, thus demonstrating how molecular parameters contribute to the flexoelectric coefficients and illustrating the potential of this method for predicting the flexoelectric behaviour of bent-core LCs. We show that the increased SH signal in the bent-core compounds is partly due to their nematic phases being at a much higher temperature, and also potentially due to them having greater flexoelectric coefficients, up to ~1.5 times those of 8CB. These estimates are consistent with reports of increased flexoelectric coefficients in bent-core compounds in comparison to rod-like compounds.

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© 2016, The Authors.

    Research areas

  • bent-core liquid crystals, flexoelectric coefficients, Nematic liquid crystals, non-linear optics, second-harmonic generation

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