Study of Fluorescent Dichroic Liquid Crystal Dyes for Wearable and Flexible Device
Authors: Li Xiaolian , Wang Zhaofen 
Published: February 2020

There is growing attention and rapid development on flexible electronic devices with electronic materials and sensing technology innovations. In particular, strain sensors with high elasticity and stretchability are needed for several potential applications including human entertainment technology, human–machine interface, personal healthcare, and sports performance monitoring, etc. Significant advancements in wearable and flexible electronic and photonic technologies, are materials science of new and alternative materials and methods of coating and deposition, characterization of flexible and transparent or display electronic devices, the electronics behind new sensor development for wearables and flexible technology, and new device design concepts.The anisotropic properties of a system comprising a guest dye dissolved in an aligned liquid-crystalline host were reported, arising from the combination of the bulk liquid crystal host alignment and the anisotropic shape and absorption characteristics of the dye molecules.
For many applications, it is also desirable for a guest–host mixture to exhibit a long useable lifetime in addition to the optical properties described above. Many of the proposed applications involve exposure of the systems to wearable and flexible device, polarisers, smart windows and lasers. The stability of a dye molecule may be strongly dependent on its chemical environment, so the stabilityof a guest–host system may depend on the nature of the host mixture as well as that of the dye.
A series of new fluorescent dichroic dyes which included phenylacetylene substituent group to 4-site of the 1,8-dicyanonaphthene were synthesized. All dyes were characterized by nuclear magnetism and high resolution mass spectrum. The dicyanonaphthene fluorescent dichroic dyes meet the application conditions of ‘Guest-host’ display.
Phenylacetylene bridge bond is often used for liquid crystal molecular design and synthesis to improve the liquid crystal birefringence because of its excellence stability, optical anisotropy.On the one hand, the addition of the phenylacetylene bond increases the molecular linearity and the aspect ratio, which is more favorable for the arrangement of the dye molecules in the main liquid crystal, thereby increasing the ordered parameters of the dye molecules in the liquid crystal; On the other hand, phenylacetylene bonds can increase the molecular conjugation system and optimize the optical properties of dye molecules.
Ester groups as a class of important linking groups have been widely used in the synthesis of diamodal dyes4.The 1,8-naphthalene dinitrile is regarded as the precursor, introduced p-ethynylbenzoic acid at its 4-position and then through the acylation reaction to introduce the alkoxy chain, in order to obtain a greater degree of conjugation, in the main liquid crystal has good solubility and high dichroic dye.

Acknowledgements

We are grateful to the National Natural Science Foundation of China (21576043), supported by the Fundamental Research Funds for the Central Universities.