Simpson S H, Richardson R M, Hanna S
H. H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL, United Kingdom.
J Chem Phys. 2007 Sep 14;127(10):104901. doi: 10.1063/1.2767257.
The optical properties of nematic liquid crystals have been extensively exploited in the production of devices working in the visible range of the spectrum. These same properties can be employed to make devices that function in the near infrared as required for telecommunications applications. However, it is generally observed that the birefringence of liquid crystal mixtures decreases with increasing wavelength, making it important to identify new materials, optimized for use in the near infrared region. One route to high birefringence is to operate close to an absorption band edge, which in the present context implies choosing highly conjugated materials which are potentially colored and, thus, not suited to traditional display applications. In this paper we explore the usefulness of dye molecules as birefringence enhancers in mixtures with conventional nematic liquid crystals. The optical properties, in particular, the absorption edge, polarizability, and birefringence, of families of known dyes are calculated at optical (589 nm) and infrared (1550 nm) wavelengths, using electronic density functional theory. We demonstrate the expected correlation between the proximity of the absorption edge and the magnitude of the birefringence, and estimate the birefringence enhancement occurring when each dye is incorporated in a guest-host system.
向列型液晶的光学特性已在光谱可见范围内工作的器件生产中得到广泛应用。这些相同的特性可用于制造电信应用所需的近红外功能器件。然而，通常观察到液晶混合物的双折射随着波长增加而降低，因此识别适用于近红外区域的新型材料非常重要。实现高双折射的一种方法是在吸收带边缘附近工作，在当前情况下这意味着选择高度共轭的材料，这些材料可能有颜色，因此不适用于传统显示应用。在本文中，我们探讨了染料分子作为双折射增强剂与传统向列型液晶混合使用的有效性。使用电子密度泛函理论，计算了已知染料家族在光学（589纳米）和红外（1550纳米）波长下的光学特性，特别是吸收边缘、极化率和双折射。我们证明了吸收边缘的接近程度与双折射大小之间的预期相关性，并估计了每种染料掺入客体 - 主体系统时双折射的增强情况。
