Construction And Regulation Of Chiral Supramolecular Structures In Heterogeneous Azobenzene Polymer Systems

Nowadays,the efficient construction and precise regulation of novel chiral supramolecular materials has received extensive attention due to the rapid development of chiral supramolecular chemistry and molecular self-assembly strategies.On the one hand,chiral supramolecules have been widely introduced into azobenzene-containing(Azo)polymers to greatly broaden the potential applications of chiral polymers.On the other hand,the regulation of the polymeric chiral supramolecular structures can be achieved by tuning the non-covalent weak interactions between Azo units and the reversibility of isomerization.However,the traditional self-assembly strategy for constructing chiral supramolecular structures usually requires the synthesis of polymers followed by self-assembly either by solvent change,pH switch,dialysis,or film rehydration.Such strategy involves multiple steps and is typically conducted at highly diluted concentration in mixed solvents.Hence,it is necessary to explore a more efficient and powerful synthetic methodology for the in-situ controlled construction and precise regulation of supramolecular assemblies.Focused on the key scientific issues(such as the regulation of chiral supramolecular structures,chirality transfer,chirality switch and the relationship between chirality and structures),the construction and regulation of chiral supramolecular structures in heterogeneous Azo-polymers were systematically studied.Based on the supramolecular assembly,internal liquid-crystalline(LC)ordering and solvophobic self-assembly,this dissertation developed a novel strategy for the in-situ preparation of polymeric chiral supramolecular structures in a mono-solvent system.Furthermore,the possibility of construction and regulation of chiral supramolecular structures in completely achiral Azo-polymer systems were also explored.This study not only realized the in-situ construction and precise regulation of the chiral supramolecular structures in Azo-polymer systems,but also demonstrated the internal stacking mode and chirality regulation mechanism,and finally revealed the chirality transfer,amplification and control from molecular level to supramolecular level.The detailed results are summarized as follows:(1)The construction of photoresponsive polymer particles with supramolecular helicity from achiral monomers by helix-sense-selective polymerization.So far,most reports of helix-sense-selective polymerization(HSSP)have focused on the construction of macromolecular chirality of the main-chain helical polymers;however,the study on the in-situ preparation of polymeric chiral supramolecular structures has not been reported.In this chapter,Azo-polymer particles with supramolecular chirality were successfully prepared from achiral Azo-containing monomers for the first time by helix-sense-selective dispersion polymerization(HSSDP)in the presence of chiral octanols.The effects of solid content,chiral octanols and polymerization time on the chiral expression,morphological transition,chiral responsiveness and chiral memory were systematically investigated.(2)In-situ controlled construction of hierarchical Azo-polymeric supramolecular chiral assemblies by polymerization-induced chiral self-assembly.The traditional self-assembly strategy for constructing polymeric supramolecular chiral assemblies exhibits many disadvantages.The limited characterization techniques and stacking mechanisms seriously hindered development and application of polymeric supramolecular chiral materials.In addition,the precise regulation of the growth and expression of polymeric supramolecular chiral structures is still challenging.Furthermore,the efficient and universal strategies to obtain single-handed structures are also lacking.If a novel in-situ strategy for constructing polymeric supramolecular assemblies with multi-level chirality and multi-dimensional morphology can be developed,the internal supramolecular chiral stacking mechanism can be tracked and deeply investigated.Based on the supramolecular assembly,internal LC ordering and solvophobic self-assembly,for the first time,we proposed a new method and general platform for the construction of hierarchical chiral supramolecular structures in heterogeneous polymer systems:polymerization-induced chiral self-assembly(PICSA).The PICSA processes of chiral Azo building units with the spacer lengths of 2,3,4,5,6,11,12 and 16 methylene were investigated in detail.Furthermore,the effects of polymerization parameters,Azo types,the lengths of core-forming blocks and isomerization on the chiral supramolecular structures were also systematically studied.The PICSA strategy provides a new platform for the precise construction and controllable regulation of hierarchical supramolecular chiral assemblies.(3)Polymerization-induced helicity inversion in Azo-polymeric supramolecular systems.The dynamic regulation of the helical structures and the in-situ control of hierarchical chirality will bring the study of Azo-polymeric chirality to a higher level.Herein,structurally similar chiral Azo monomers were designed in this chapter,in which the alkyl chains comprised the chiral stereocenter with different achiral tail-lengths(isobutyl,isopentyl,isohexyl and isooctyl).The supramolecular chiral assemblies of Azo-polymers containing different terminal structures were constructed through PICSA strategy,and we successfully achieved stacking mode-driven multiple helicity inversion by controlling the degree of polymerization(DP)in PICSA process.Besides,the effects of DP,UV light,temperature,aging time on chiroptical and LC properties were systematically studied.The mechanisms of chiral regulation and multiple inversions were also characterized,providing theoretical foundations for the chirality regulation of polymeric supramolecules.The results show that the polymerization-induced helicity inversion with chiroptical and morphological transitions is dependent on the tail-length.In addition,the LC phase behavior allowed the transcription of stacking modes,thereby controlling the dynamic reversal of supramolecular chirality.(4)Site-specific "Domino Effect" in Azo-polymeric supramolecular systems.How to construct hierarchical chiral supramolecular structures efficiently in achiral polymer systems is one of important scientific issues.In this chapter,we used the chiral dominos to precisely construct multi-level and multi-dimensional supramolecular structures in achiral polymer systems by PICSA strategy.In order to explore the "Domino Effect",a small amount of chiral Azo units(chiral seed)was used to induce achiral Azo units,and the mechanism of chirality induction,transfer,amplification and control was studied in detail.The construction and regulation of chiral supramolecular structures in achiral Azo-polymer systems under the guidance of PICS A strategy and "Domino Effect" were further clarified.It was found that the position of the chiral domino seed(covalently attached to the initial,middle and end of the polymer chain and non-covalently attached to the side chain)and the type of achiral Azo units(Azo6MA-OCH3,Azo6MA-CH3,Azo6MA-F and Azo6MA-CN)could significantly influence the "Domino Effect" and the higher-order morphological transitions.The efficient construction and precise regulation of hierarchical chiral supramolecular structures in the achiral polymer systems were realized.(5)Abnormal "Sergeants-and-Soldiers Principle" in Azo-polymeric supramolecular systems.The chiral amplification of supramolecular structures can only be regulated linearly,but difficult to be reversed in traditional "Sergeants-and-Soldiers Principle"(SaS).Based on the multiple chiroptical inversion,introducing SaS to PICSA system will be able to modulate the supramolecular chiral structures precisely.This chapter concentrated on using the opposite forces between the chiral-chiral and achiral-chiral molecules to enable the entire supramolecular structures with regulated helical ordered orientation.An achiral soldier was first synthesized,and then co-polymerized and co-assembled with chiral sergeants in PICSA process.Our previous work demonstrated that the stacking mode transition could drive the multiple chiroptical inversion.If we introduce chiral sergeants and achiral soldiers simultaneously into this system,the stacking mode transition would result in normal and abnormal SaS and high-order morphologies.It was found that there were two abnormal SaS effects and higher-order morphologies with the increase of the chiral sergeant contents.As a result,there are five correlations between chiral expression and the DP of the core-forming Azo blocks,which have never occurred in the SaS type of chiral amplification systems in previous reports.