Second-harmonic generation and the influence of flexoelectricity in the nematic phases of bent-core oxadiazoles
Second-harmonic generation and the influence of flexoelectricity in the nematic phases of bent-core oxadiazoles
复制标题
DOI：
10.1080/02678292.2016.1172355
复制
发表时间：
2016-04
期刊：
影响因子：
2.2
通讯作者：
J. Addis;S. Kaur;D. Binks;M. Dickinson;C. Greco;A. Ferrarini;V. Görtz;J. Goodby;H. Gleeson
中科院分区：
文献类型：
--
作者：
J. Addis;S. Kaur;D. Binks;M. Dickinson;C. Greco;A. Ferrarini;V. Görtz;J. Goodby;H. Gleeson
研究了弯核恶二唑基液晶（lc）向列相的二次谐波生成（SHG），并与棒状化合物4-氰基-4′-正辛基联苯（8CB）进行了比较。在所有材料中都观察到弱的、各向同性散射的二次谐波（SH）光，与向列指示子波动的二次谐波相一致。弯芯材料产生的SH强度是8CB材料的3.4倍。我们从温度、弹性常数和挠曲电系数对SH强度的依赖性的角度讨论了这一结果。我们通过使用原子模型的分子场方法计算了后者，从而展示了分子参数如何影响挠曲电系数，并说明了该方法在预测弯核lc挠曲电行为方面的潜力。我们发现弯核化合物中SH信号的增加部分是由于它们的向列相处于更高的温度，也可能是由于它们具有更大的挠曲电系数，高达8CB的1.5倍。与棒状化合物相比，弯核化合物的挠曲电系数增加的报告与这些估计是一致的。图形抽象
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. GRAPHICAL ABSTRACT