Preparation Of AIE Fluorescent Compounds Cholesterol And Study On Their Circularly Polarized Luminescence

Chirality are ubiquitous in nature.Due to the Circular dichroism and circular polarized luminescence,chiral materials show potential prospects in 3D imaging,liquid crystalline display,optoelectronic devices,nonlinear optics,anti-counterfeiting materials and so on.Consequently,circularly polarized luminescence material has been drawn great attention by scientists and has become a hot topic in recent years.Cholesterol is a kind of organic molecules with multiple chiral centers,which can be made into different kinds of circularly polarized luminescence materials by reasonable molecular modification and design.The main study of this paper are as follows:Three AIE circularly polarized luminescence compounds?TPE-?Ph Chol?_n??n=1,2and 4?with different substituents were synthesized by Suzuki coupling reaction with using tetraphenylethylene?TPE?,a typical aggregation-induced emission?AIE?molecule,as fluorescence chromophores and cholesterol derivatives as chiral centers.The compounds are characterized by ¹H NMR and ¹³C NMR to confirm chemical structure.Through the study of UV-vis,PL and CPL,it is found that all compounds have obvious AIE phenomenon and circularly polarized luminescence properties.TPE-?Ph Chol?has exhibited the strongest circularly polarized luminescence?CPL?emission signals,with CPL dissymmetry factors of 4.99×10^-2.When increasing the substituent number of cholesterol groups,it changes molecules stacking way in space,causing circularly polarized luminescence signal to and CPL dissymmetry factor to be significantly reduced.TPE-?Ph Chol?and TPE-?Ph Chol?₂have good compatibility with nematic liquid crystals host?5CB?.Chiral liquid crystals are prepared by mixing compounds with 5CB as chiral dopants.Typical fingerprint textures planar Grandjean texture is observed in homeotropic cell and planar cell by polarizing microscope respectively.?-Cyanostilbene and its derivatives are widely used for preparing luminescent liquid crystal materials.Here,a simple synthetic method to prepare a luminescence liquid crystal with CPL performance is developed by connecting cyanostilbene with cholesterol groups.PL spectrums proves that all compounds have aggregation induced enhanced luminescence,and CPL spectrums indicate chiral optical property of C_n-CN-Chol ware successfully obtained due to rational molecular designing.C_n-CN-Chol emit negative circularly polarized luminescence signal with a dissymmetry factor of3.79×10^-3 and-1.14×10^-2.The compound shows a wide temperature range in the LC phase,with liquid crystal phases changed during the cooling process.The schlieren texture is observed by polarizaing microscope.Liquid crystal texture change into fingerprint textures after cooling to the crystallization process.