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

TY - JOUR

T1 - Second-harmonic generation and the influence of flexoelectricity in the nematic phases of bent-core oxadiazoles

AU - Addis, J.

AU - Kaur, S.

AU - Binks, D. J.

AU - Dickinson, M. R.

AU - Greco, C.

AU - Ferrarini, A.

AU - Görtz, V.

AU - Goodby, John William

AU - Gleeson, H. F.

N1 - © 2016, The Authors.

PY - 2016/4/24

Y1 - 2016/4/24

N2 - 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.

AB - 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.

KW - bent-core liquid crystals

KW - flexoelectric coefficients

KW - Nematic liquid crystals

KW - non-linear optics

KW - second-harmonic generation

UR - http://www.scopus.com/inward/record.url?scp=84964556149&partnerID=8YFLogxK

U2 - 10.1080/02678292.2016.1172355

DO - 10.1080/02678292.2016.1172355

M3 - Article

AN - SCOPUS:84964556149

SN - 0267-8292

SP - 1

EP - 18

JO - LIQUID CRYSTALS

JF - LIQUID CRYSTALS

ER -