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Precisely Tuning Helical Twisting Power via Photoisomerization Kinetics of Dopants in Chiral Nematic Liquid Crystals
Langmuir ( IF 3.9 ) Pub Date : 2018-01-03 00:00:00 , DOI: 10.1021/acs.langmuir.7b03786
Dongxu Zhao , Yuan Qiu , Weinan Cheng , Shuguang Bi 1 , Hong Wang , Qin Wang , Yonggui Liao , Haiyan Peng , Xiaolin Xie
Affiliation  

It has been paid much attention to improve the helical twisting power (β) of dopants in chiral nematic liquid crystals (CLCs); however, the correlations between the β value and the molecular structures as well as the interaction with nematic LCs are far from clear. In this work, a series of reversibly photo-switchable axially chiral dopants with different lengths of alkyl or alkoxyl substituent groups have been successfully synthesized through nucleophilic substitution and the thiol–ene click reaction. Then, the effect of miscibility between these dopants and nematic LCs on the β values, as well as the time-dependent decay/growth of the β values upon irradiations, has been investigated. The theoretical Teas solubility parameter shows that the miscibility between dopants and nematic LCs decreases with increasing of the length of substituent groups from dopant 1 to dopant 4. The β value of chiral dopants in nematic LCs decreases from dopant 1 to dopant 4 both at the visible light photostationary state (PSS) and at the UV PSS after UV irradiation. With increasing of the length of substituent groups, the photoisomerization rate constant of dopants increases for trans–cis transformation upon UV irradiation and decreases for the reverse process upon visible light irradiation either in isotropic ethyl acetate or in anisotropic LCs, although the constant in ethyl acetate is several times larger than the corresponding value in LCs. Also, the color of the CLCs could be tuned upon light irradiations. These results enable the precise tuning of the pitch and selective reflection wavelength/color of CLCs, which paves the way to the applications in electro-optic devices, information storage, high-tech anticounterfeit, and so forth.

中文翻译:

通过手性向列型液晶中掺杂剂的光异构化动力学精确调节螺旋扭曲力

改善手性向列液晶(CLC)中掺杂剂的螺旋扭曲能力(β)已引起人们的广泛关注。然而,β值与分子结构之间的相关性以及与向列LC的相互作用尚不清楚。在这项工作中,已经通过亲核取代和硫醇-烯点击反应成功地合成了一系列具有不同长度的烷基或烷氧基取代基的可逆光开关轴向手性掺杂剂。然后,研究了这些掺杂剂和向列型液晶之间的可混溶性对β值的影响,以及随着时间的推移,β值随时间的衰减/增长。1至掺杂剂4。向列LC中手性掺杂剂的β值从掺杂剂1降低到掺杂剂4在可见光静止状态(PSS)和紫外线照射后的紫外线PSS上均如此。随着各取代基长度的增加,在各向同性乙酸乙酯或各向异性LC中,掺杂剂的光异构化速率常数在UV辐射下反式-顺式转变时增加,而在可见光辐射下的逆过程中则下降,而在乙酸乙酯中则为常数。是LC中对应值的几倍。而且,CLC的颜色可以根据光照射来调整。这些结果使得能够精确调节CLC的间距和选择性反射波长/颜色,从而为电光设备,信息存储,高科技防伪等方面的应用铺平了道路。
更新日期:2018-01-03
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