Construction Of Dye-doped Cholesteric Liquid Crystal Composites And Regulation Of Multicolor Fluorescence Behavior

Cholesteric liquid crystals have periodic helical molecular structure and exhibit unique optical properties.Selective reflection is one of the most typical characteristics of cholesteric liquid crystals.Selective reflection means that cholesteric liquid crystals selectively reflect certain wavelengths of light,thus showing different colors in white light.By changing the content of chiral additives or doping optical isomers,the reflective wavelength of liquid crystals can be changed.Fluorescent materials are widely used in color display,anti-counterfeiting printing,fluorescent patterns and other fields because of their high sensitivity and selectivity.In recent years,remarkable progress has been made in the study of fluorescence enhancement of dyes,most of which are based on changes in luminescence intensity caused by external stimuli,such as plasma resonance fluorescence enhancement,metal fluorescence enhancement,light-induced luminescence enhancement,etc.The preparation process of most fluorescence enhancement techniques is strict and can not be dynamically adjusted.In this paper,two methods are studied to change the reflection wavelength of the cholesteric liquid crystal,thereby adjusting the fluorescence intensity of the dye and preparing dual-mode multicolor patterns.The main research contents are as follows:(1)In-situ fluorescence enhancement:The central reflection wavelength of cholesteric liquid crystal can be changed by adjusting the content of chiral additives in the system.The dye molecules(BBOT,Coumarin 6 and Rhodamine B)are added to the liquid crystal system.When the reflection wavelength of the liquid crystal matches the fluorescence emission peak of the dye,the fluorescence enhancement effect can be achieved and the fluorescence behavior of dye can be regulated.A liquid crystal fluorescent array was obtained by a partial exposure method,and liquid crystal particles were obtained.The reflective and fluorescent dual mode multicolor pattern was prepared by screen printing.(2)Dynamic fluorescence enhancement:By adjusting the degree of photoisomerization of azobenzene molecules,the central reflection wavelength of cholesteric liquid crystals can be changed.The isomerization of the azo molecule can be achieved by illumination or heating,which disturbs the liquid crystal system and changes the reflection wavelength,further affecting the fluorescence intensity of the dye.In this way,dynamic adjustment of the reflection wavelength can be achieved on the same liquid crystal film.A multicolor pattern was prepared by transfer printing and partial exposure,and different colors were exhibited in the reflective mode and the fluorescent mode.