Design,Preparation And Properties Of Circularly Polarized Luminescence Materials Based On Polyacetylene

Chiral functional materials generating circularly polarized luminescence(CPL)have aroused considerable attention,not only for better understanding the inherent chirality of excited states but also owing to the prospective applications of CPL-active materials in 3D displays,optical encryption,biological probes,data storage and asymmetric synthetic.Chirality and fluorescence are two indispensable elements in the construction of CPL materials.During the past several years,numerous CPL materials have been designed and prepared using diverse chiral species.In spite of the striking advancement,it still remains a big challenge to construct CPL-active materials with high luminescence asymmetry factor(glum)values,tunable handedness and full-color emission.Polyacetylene,as one of the important branches of helical polymers,is well known for its chirality amplification effect and dynamic helical structure.This study is intended to design and prepare CPL material with high glum values,tunable handedness and full-color emission based on helical substituted polyacetylene,which may provide a universal platform for future construction of CPL-active smart materials and devices with promising potentials.The specific content is described as follows.(1)Pyrene-functionalized chiral helical polyacetylenes with interesting CPL properties were synthesized by copolymerization with a chiral monomer and a fluorescent monomer.The dynamic helical conformation of substitute polyacetylenes is sensitive to external stimuli such as solvent and temperature.Moreover,combining the fact that polymer main-chains have strong absorption ability to fluorescence,the fluorescence intensity of the obtained polyacetylene can be simply adjusted by temperature,solvent and copolymerization ratio.More noticeably,CPL signal inversion was observed in the copolymers solution and the mixed solutions of homopolymers of two monomers due to the entirely different CPL generation mechanisms(chirality transfer and "matching rule").(2)Chiral fluorescent thin films generating CPL were prepared by dissolving polyacetylene into polymethyl methacrylate(PMMA)or polyvinyl butyral(PVB)used as matrix.The handedness of CPL of the polymers could be simply inverted by regulating the state of as-prepared polymer from solution to thin film because of the presence of two different CPL generation mechanisms.Besides,over 100-fold intensity amplification of CPL signal was obtained during the state-change process.Moreover,the dissymmetry factor could be conveniently tuned from 10-1 to 10-3 order of magnitude by changing the filmforming solvents due to the "helix-to-coil" conformation transition occurring to the polyacetylene backbone.More importantly,a series of CPL thin films with high glum values and full-color emission could be simply prepared by coassembly of achiral fluorescent dye and as-prepared polyacetylene.(3)Cyclodextrin-functionalized alkyne monomers and alkene monomers emitting blue fluorescence were prepared.After polymerization,the cyclodextrin-functionalized polyacetylene emitted almost no fluorescence emission because of the strong absorption ability to fluorescence of the polyacetylene main chain.Fortunately,the as-prepared polyacetylene possessed optical activity due to chirality transfer occurring between cyclodextrin and polyacetylene main chain.Surprisingly,the handedness of CD of the polyacetylene could be simply inverted by regulating the proportion of solvent(DMSO/H2O)due to the unique hydrophilic and hydrophobic structure of cyclodextrins.More noticeably,bio-based CPL materials were successfully prepared by adding anthracic acid into the polyacetylene solution,and the glum values reached up to 10-3 order.The handedness of CPL also could be easily inverted by changing the solvent ratio.