用于液晶盒偶氮染料光致取向层的合成和性质

Synthesis and Properties of Azo Dye Aligning Layers for Liquid Crystal Cell

我们研究了可用于光致取向液晶(LCs)偶氮染料的合成和性质,提出了偶氮染料的结构与合成过程。偶氮染料光致取向完全是因为分子吸收振子垂直于UV光偏振方向的再取向。讨论了在偏振光场中,偶氮染料分子旋转扩散现象的定性模型。测量了波长为372nm时,偏振吸收光谱的有序参数S=-0.4(80%的最大绝对值Sm=-0.5)。对一个偶氮染料膜,利用在正常的正入射偏振光之后,紧跟一个斜入射的非偏振光两步曝光,可以获得温度稳定的5.3°预倾角。光致取向基片的方位角锚定能为Aφ≈10-4Jm-2,这与摩擦聚酰亚胺(PI)层的锚定能相同。我们发现,光致取向液晶盒的电压保持率甚至比摩擦PI层取向的还高,因此,偶氮染料完全可以用作有源矩阵液晶显示器的取向层。光致取向偶氮染料层的热稳定性很高,但UV稳定性需通过诸如聚合等来改良。于是,我们设想了一种新的基于聚合偶氮染料层的LCD取向技术。

The synthesis and properties of azo dyes that can be used for photoaligning liquid crystals (LCs) have been investigated. The structures and t he synthetic procedure for the azo dyes are presented. The photoaligning of azo dyes takes place purely due to the reorientation of the molccular absorption osc illators perpendicular to the UV light polarization. The qualitative model for t he phenomenon in terms of the rotational diffusion of the azo dye molccules in t he field of the polarized light is discussed. The order parameters S = - 0.4 ( 8 0% of the maximum absolute value Sm = - 0.5 ) were measured from the polarized a bsorption spectra at the wavelength 372nm.A temperature stable pretilt angle of 5.3°was obtained by a two-step exposure of the azo dye film using normally inci dent polarized light followed by oblique nonpolarized light. The azimuthal ancho ring energy of the photoaligned substrate was Aφ≈10-4Jm-2, which is the same a s the anchoring of the rubbed polyimide(PI) layer. The voltage holding ratio val ue of a photoaligned LC cell was found to be even higher than for a rubber PI layer,which enables the applications of azo dyes as aligning layers in active ma trix liquid crystal displays. The thermal stability of the photoaligned azo dye layer is sufficiently high,but UV stability has to be improved, e.g. by polymer ization. A new LCD aligning technology based on polymerized azo dye layer is env isaged.