Using Polylactide As Chiral Source For Constructing Circularly Polarized Luminescent Materials

Chirality is an essential property of nature.Chirality transfer in hierarchical assembly structures at the molecular,macromolecular and supramolecular levels plays a crucial role in the evolution and information exchange of organisms.Exploring the generation and transfer of chirality at different hierarchical levels has always been a challenging and significant research topic.However,at present,the chirality transfer system is mainly limited to supramolecular self-assembly system and conducted in solution or liquid crystals.There are few reports on the study of chirality transfer between different types of macromolecules in solid state.The explorations under this research topic are anticipated to afford some new chirality associated findings and open up new advanced functional architectures and materials that combine the advantages of diverse macromolecules;furthermore,the studies also may update our understanding about natural homochirality.Chiral crystallization and chiral crystals have constituted a flourishing area spanning multiple hierarchical scales from molecules to nano-and micro-dimensions because of the significant and extensive implications for pharmaceutics,nanoscience and technologies,photoelectric industries,among others.Realizing chiral crystals from achiral compounds is an important but challenging issue.From the perspective of practical applications,synthetic chiral polymers are anticipated to demonstrate some incomparable advantages when used as chiral templates toward chiral crystallization.Synthetic chiral helical polymers are of special interest because of the relatively easy processibility,definite chirality and its tunability,the well-known chiral amplification effect,and so forth.Circularly polarized luminescence（CPL）materials have become a new research hotspot in the field of chiral and fluorescent materials because of their important potential applications in the fields of organic light-emitting diodes（OLEDs）,information storage and encryption,biological probes,and so on.The synthesized helical polymer-based CPL materials have attracted more and more attention because of their relatively high stability,good processability and unique helical chirality of the polymer skeleton,which are more conducive to the realization of high luminescent asymmetry factor(g_lum).Thin film devices as solid state luminescent materials have more potential in practical applications.Considering the importance of solid-state CPL materials,a method of constructing CPL composite films by simply casting was established in this thesis.Full-color and white CPL films,handedness-tunable and asymmetric intensity adjustable nonreciprocal CPL films were prepared,and the universality of the preparation method was verified.In this thesis,the chiral polylactide was used as the chiral source and chiral substrate,and the CPL composite films were prepared by the casting method.The main content is described as follows:1.Firstly,the chirality transfer of chiral polylactide（PLA）to racemic helical substituted polyacetylene（P1）was realized in the solid casting film,which led to the strong optical activity of the initial racemic helical polyacetylene.In this process,chiral PLA acted as both a film-forming matrix and chiral source,and hydrogen bond is the main driving force of chirality transfer.Secondly,the induced helical chirality can be further transferred to achiral fluorescent molecules,resulting in full-color and white CPL emission.In addition,the potential applications of the obtained CPL active films in circularly polarized organic light-emitting diodes（CP-OLEDs）are also demonstrated.This thesis not only provides a new insight for understanding the chirality transfer between different macromolecules,but also establishes a simple and general strategy for the construction of advanced chiral functional materials.2.The chiral crystallization of achiral fluorescent compound（1,8-naphthalene dicarboxylic anhydride,NA）was realized by using chiral polymer PLA as chiral template and film-forming substrate.In the process of crystallization,chiral super-crystallization complex with"kebab"structure were formed,which effectively realized the chirality transfer from PLA to NA,and showed excellent CPL properties.The prepared composite films exhibited an asymmetry factor up to 10^-2.More interestingly,because of the polarization mechanism,handedness switchable and asymmetric intensity adjustable nonreciprocal CPL emission can be easily realized in a sample by simply flipping or rotating the film.The thesis not only provides a new idea for the study of chiral supra-crystals,but also establishes a simple and flexible method for the construction of nonreciprocal CPL active materials.