Synthesis and Evaluation of Naphthalene Anhydride Fluorescence Dichroic Liquid Crystal Dye
Authors: Li Xiaolian 
Published: February 2020

Liquid crystals are materials which has properties between those of conventional liquid those of solid crystals There are many different types of liquid-crystal phases, which can be distinguished by their different optical properties. When viewed under a microscope using a polarized light source, different liquid crystal phases will appear to have distinct textures.The contrasting areas in the textures correspond to domains where the liquid-crystal molecules are oriented in different directions.

Liquid crystal material is mainly used for liquid crystal displays, which rely on the optical properties of certain liquid crystalline substances in the presence or absence of anelectric field . In a typical device, a liquid crystal layer sits between two polarizers that are crossed oriented to one another. Color LCD systems use the same technique, with color filters used to generate red, green, and blue pixels. Due to the use of polarizer, the utilization rate of light is decreased obviously.

Guest-host liquid crystal displays have many advantages, such as displaying information in excellent colour, good contrast ratio, a large viewing angle, high brightness and the need for only one or no external polarizers at all, so they can’t lead to excessive energy loss of beaming light and low brightness.

A series of naphthalene anhydride fluorescence dichroic liquid crystal dye (Z) have been designed and synthesized. Some of them have wide liquid crystal phase and bright fluorescence. All the Z molecules are tested for spectral properties, including UV-Vis, fluorescence and polarization spectra. The liquid crystal molecules have been tested for threshold voltage. All the new molecules are tested nuclear magnetic resonance spectroscopy and mass spectrometry. The properties of all the synthesized molecules are studied and analyzed. The absorption wavelength of Z series of naphthalimide fluorescent liquid crystal dye are at around 390 nm and emission wavelength are at around 500 nm. Bright yellow-green fluorescence was observed and the maximum fluorescence quantum yield reaches up to 0.88. Stokes shift are more than 100 nm. The maximum absorption order parameter of Z, SA is 0.69 and SF is between 0.45-0.63 in liquid crystal E7. In the negative liquid crystal BHR28000-300, the order parameter of Z with the applied voltage of 10V is up to 0.84. DSC test showed that Z have wide phase transition temperature.

Acknowledgements

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

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