Chiral Polymers Research Articles

Competition between Circularly Polarized Light and Molecular Chirality in the Assembly of Main-chain Liquid Crystalline Polymers

Abstract Polymeric systems responding to chiral information are actively pursued for applications in optoelectronics and photonics. Here we report on the diastereomeric relationship between chiral liquid crystal polymers and circularly polarized light (CPL). We synthesize a chiral copolymer incorporating photoisomerizable diazobenzene moieties as well as isosorbide-based monomers. The circular dichroism of the film can be inverted by irradiation with CPL indicating that the influence of the chiral subunits on the helicity of the cholesteric arrangement can be overruled by the action of CPL. By following the out-of-equilibrium photo-switching process over time, we demonstrate that the formation of helical ordering in the chiral liquid crystal phases is much faster by CPL irradiation than by heat.

34‐5: Invited Paper: C‐PS‐VA — Innovative LC Materials Enabling Super‐High Transmittance for High‐Resolution Displays

In recent years, and for the next generation of TVs and monitors, increasing resolution is a key trend. One challenge is keeping the transmittance while pixel density increases. Chiral Polymer Stabilized Vertical Alignment (C‐PS‐VA) technology uses LC mixtures with higher birefringence and a chiral dopant and increases transmittance by more than 10% compared to conventional Polymer Stabilized Vertical Alignment (PS‐VA). This paper summarizes the recent developments of liquid crystal mixtures for C‐PS‐VA.

A 1D Cd-coordination polymer containing serine derivative and its application in luminescence sensor for Tb(Ⅲ)

A novel chiral Cd-coordination polymer (CP1) was synthesized by solvothermal reaction with chiral ligand 1,4-bis((L‑serine)methyl)benzene (L-H2bsmb) and cadmium oxide, and the structure of CP1 was characterized by single-crystal X-ray diffraction, fourier transform infrared spectoscopy (FT-IR), powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), elemental analysis (EAs), solid circular dichroism (CD) and fluorescence spectroscopy. One dimensional chain for CP1 was constructed to a chiral 3D structure by intermolecular hydrogen bonds between carboxyl group and coordination water molecules and weak interaction of C‒H•••π. In aqueous system, the fluorescence of CP1 shows excellent stability. Through the detection experiments towards 32 different ions, it was found that CP1 has specific selection for Tb(Ⅲ) ions with the fast response time (within 1 min), low detection limit (11.4 nM), strong anti-interference ability and good recyclability. Fluorescent test strips based on CP1 allow to sense Tb(Ⅲ) ion quickly and easily by naked eyes, which provides an excellent method for monitoring Tb(Ⅲ) in human body and water systems.

Single-chain chiral Ru-Cu star polymers for highly efficient catalytic aqueous asymmetric transfer hydrogenation

It is of great research value to design simulated enzyme catalysts with high catalytic activity, high selectivity and that are reusable in water. In this work, a star-shaped thermal responsive polymer-Ru/diamine functional intelligent chiral catalyst was synthesized by controlled atom transfer radical polymerization (ATRP). Polymerization can be controlled through self-catalysis of chiral monomers and polymers. Because of the complex that forms between the chiral polymer and Cu2+, the synthesized star polymer experiences a chiral amplification effect. At the same time, the star Ru-Cu catalyst can be assembled into single-chain polymers in water, which showed better catalytic activity and selectivity than the Ru catalyst for aqueous asymmetric reactions, and can be recycled up to six times. Our work provides a new method for controllable synthesis of chiral polymers without additional ligands and the need to remove Cu2+ at the end of the reaction, making the method green and more cost-effective. In summary, bimetallic nanocatalysts were controllably constructed by star chiral polymers through the ATRP pathway. This method significantly aids the development of helical chiral polymers and the preparation of high-efficiency enzyme catalysts.

Synthesis and Characterization of Bimetallic Nanoclusters Stabilized by Chiral and Achiral Polyvinylpyrrolidinones. Catalytic C(sp3)–H Oxidation

Second-generation chiral-substituted poly-N-vinylpyrrolidinones (CSPVPs) (-)-1R and (+)-1S were synthesized by free-radical polymerization of (3aR,6aR)- and (3aS,6aS)-5-ethenyl-tetrahydro-2,2-dimethyl-4H-1,3-dioxolo[4,5-c]pyrrol-4-one, respectively, using thermal and photochemical reactions. They were produced from respective d-isoascorbic acid and d-ribose. In addition, chiral polymer (-)-2 was also synthesized from the polymerization of (S)-3-(methoxymethoxy)-1-vinylpyrrolidin-2-one. Molecular weights of these chiral polymers were measured using HRMS, and the polymer chain tacticity was studied using 13C NMR spectroscopy. Chiral polymers (-)-1R, (+)-1S, and (-)-2 along with poly-N-vinylpyrrolidinone (PVP, MW 40K) were separately used in the stabilization of Cu/Au or Pd/Au nanoclusters. CD spectra of the bimetallic nanoclusters stabilized by (-)-1R and (+)-1S showed close to mirror-imaged CD absorption bands at wavelengths 200-300 nm, revealing that bimetallic nanoclusters' chiroptical responses are derived from chiral polymer-encapsulated nanomaterials. Chemo-, regio-, and stereo-selectivity was found in the catalytic C-H group oxidation reactions of complex bioactive natural products, such as ambroxide, menthofuran, boldine, estrone, dehydroabietylamine, 9-allogibberic acid, and sclareolide, and substituted adamantane molecules, when catalyst Cu/Au (3:1) or Pd/Au (3:1) stabilized by CSPVPs or PVP and oxidant H2O2 or t-BuOOH were applied. Oxidation of (+)-boldine N-oxide 23 using NMO as an oxidant yielded 4,5-dehydroboldine 27, and oxidation of (-)-9-allogibberic acid yielded C6,15 lactone 47 and C6-ketone 48.

Taking chiral polymers toward immune regulation

AbstractThe implanted materials and devices can be recognized by the immune system, which in turn mediate the immune microenvironment of tissues. The immune system in mammals is composed of diverse components such as immune cells, cytokines, radicals and antibodies etc. Chiral polymers with good biocompatibility, tailorable ability and ease of fabrication are excellent candidates for diverse biomedical applications. Different chiral biomaterials have been investigated to study the interactions of immune cells and the resulted immune responses, but the effects of chiral polymers on immune regulation are less tackled. Tailoring the chemical and physical properties of chiral polymers can lead to beneficial immune responses. This review focuses on the different fabrication strategies of chiral polymers and interactions of chiral polymers with immune cells and other biological components. The adhesion and interaction patterns of chiral polymers with immune cells, changes in shapes and characteristics of cells, release or inhibition of cytokines, and resulting response are discussed in the review.

Reduction of solar infrared heating by using highly transparent thin films based on organic chiral nematic liquid crystal polymer.

This paper demonstrates a thin and transparent reflector film for the near infrared, based on chiral nematic liquid crystal (CLC) polymers. Two films reflect almost 50% of unpolarized incident light from 730 to 820 nm and from 880 to 1030 nm, while remaining completely transparent in the visible region with transmittance >90%. An efficient window uses the combination of two reflectors. After exposing two window-cubes for 2 h to direct sunlight, the temperature inside the cube with reflector windows was 4°C lower than in cube with plain windows. This reveals that the infrared (IR) reflectors can effectively control the indoor temperature. These films, which are 8 µm in thickness, can be detached from the glass substrates and used as a free-standing film, or be attached to a flexible optical foil or a solid window. The foils can be applied in buildings, offices, and automobiles to statically reduce the energy consumption required for air conditioning or lighting. The free-standing foils show acceptable resistance to polar protic solvents and are thermally stable up to 100°C.

Amplified Circularly Polarized Electroluminescence Behavior Triggered by Helical Nanofibers from Chiral Co-assembly Polymers.

Two chiral binaphthyl polymers (R/S-P1 and R/S-P2) with different dihedral angles of the binaphthyl moiety were chosen as chiral inducers to construct chiral co-assemblies with an achiral pyrene-naphthalimide dye (NPy) and then acted as the emitting layer (EML) of circularly polarized electroluminescence (CP-EL) devices. The anchored dihedral angle of R/S-P2 not only exhibited the enhanced chirality signal, but also had a strong chirality-inducing effect on the achiral NPy dye in the chiral co-assembly (R/S-P2)0.6 -(NPy)0.4 . After annealing at 120 °C, the CPL signal (|gem |) of ordered helical nano-fibers (R/S-P2)0.6 -(NPy)0.4 was amplified to 5.6×10-2 , which was about 6-fold larger than that of (R/S-P1)0.6 -(NPy)0.4 . The amplified gem value of (R/S-P2)0.6 -(NPy)0.4 was due to the formation of a helical co-assembly through the strong π-π stacking interaction between the R/S-P2 and the achiral NPy. This kind of ordered helical nano-fibers (R/S-P2)0.6 -(NPy)0.4 acted as the EML of CP-OLEDs, and achieved an excellent CP-EL performance (|gEL |=4.8×10-2 ).

Amplified Circularly Polarized Electroluminescence Behavior Triggered by Helical Nanofibers from Chiral Co‐assembly Polymers

AbstractTwo chiral binaphthyl polymers (R/S‐P1 and R/S‐P2) with different dihedral angles of the binaphthyl moiety were chosen as chiral inducers to construct chiral co‐assemblies with an achiral pyrene‐naphthalimide dye (NPy) and then acted as the emitting layer (EML) of circularly polarized electroluminescence (CP‐EL) devices. The anchored dihedral angle of R/S‐P2 not only exhibited the enhanced chirality signal, but also had a strong chirality‐inducing effect on the achiral NPy dye in the chiral co‐assembly (R/S‐P2)0.6‐(NPy)0.4. After annealing at 120 °C, the CPL signal (|gem|) of ordered helical nano‐fibers (R/S‐P2)0.6‐(NPy)0.4 was amplified to 5.6×10−2, which was about 6‐fold larger than that of (R/S‐P1)0.6‐(NPy)0.4. The amplified gem value of (R/S‐P2)0.6‐(NPy)0.4 was due to the formation of a helical co‐assembly through the strong π–π stacking interaction between the R/S‐P2 and the achiral NPy. This kind of ordered helical nano‐fibers (R/S‐P2)0.6‐(NPy)0.4 acted as the EML of CP‐OLEDs, and achieved an excellent CP‐EL performance (|gEL|=4.8×10−2).

Strategies to synthesize a chiral helical polymer accompanying with two stereogenic centers for chiral electroanalysis

In most cases, the recognition efficiency of chiral electroanalysis relies on the chiral carbon center, whereas its medium is just used to transfer the electron. Differently, in this study, an ionic helical polymer with right- or left-handed configuration was prepared via an acid-base interaction between the ionic polymer and enantiopure 1,2-diphenylethane-1,2-diamine. The structure and absolute handedness of the helical polymers were well characterized by the circular dichroism spectrum, gel permeation chromatography, and Fourier transform infrared spectroscopy. The pyridinium moiety of the helical polymer contributes to the electron transfer when it was directly modified on the surface of the glassy carbon electrode as an electrochemical enantioselector for chiral electroanalysis. Results indicated that different configurations of amino acids can be recognized in the responses of different electric signals, namely peak current or peak potential. The peak current ratio between L- and d-isomer can be up to 7.5 and 23.2 for tryptophan and tyrosine, respectively. Most importantly, the reversal of the electric signal can be observed toward L- and d-isomer under the different testing conditions such as pH and metal ion content, because of two stereogenic centers (the chiral inducer and the stereogenic axis) in the helical polymer. Overall, we believe that the present study offers a great promise for the synthesis and application of the ionic helical polymers accompanying with multiple stereogenic centers.

White‐Light Emission and Circularly Polarized Luminescence from a Chiral Copper(I) Coordination Polymer through Symmetry‐Breaking Crystallization

AbstractAchieving white‐light emission, especially white circularly polarized luminescence (CPL) from a single‐phase material is challenging. Herein, a pair of chiral CuI coordination polymers (1‐M and 1‐P) have been prepared by the asymmetrical assembly of achiral ligands and Cu2I2 clusters. The compounds display dual emission bands and can be used as single‐phase white‐light phosphors, achieving a “warm”‐white‐light‐emitting diode with an ultra‐high color rendering index (CRI) of 93.4 and an appropriate correlated color temperature (CCT) of 3632 K. Meanwhile, corresponding CPL signals with maximum dissymmetry factor |glum|=8×10−3 have been observed. Hence, intrinsic white‐light emission and CPL have been realized simultaneously in coordination polymers for the first time. This work gains insight into the nature of chiral assembly from achiral units and offers a prospect for the development of single‐phase white‐CPL materials.

White-Light Emission and Circularly Polarized Luminescence from a Chiral Copper(I) Coordination Polymer through Symmetry-Breaking Crystallization.

Achieving white-light emission, especially white circularly polarized luminescence (CPL) from a single-phase material is challenging. Herein, a pair of chiral CuI coordination polymers (1-M and 1-P) have been prepared by the asymmetrical assembly of achiral ligands and Cu2 I2 clusters. The compounds display dual emission bands and can be used as single-phase white-light phosphors, achieving a "warm"-white-light-emitting diode with an ultra-high color rendering index (CRI) of 93.4 and an appropriate correlated color temperature (CCT) of 3632 K. Meanwhile, corresponding CPL signals with maximum dissymmetry factor |glum |=8×10-3 have been observed. Hence, intrinsic white-light emission and CPL have been realized simultaneously in coordination polymers for the first time. This work gains insight into the nature of chiral assembly from achiral units and offers a prospect for the development of single-phase white-CPL materials.

Intramolecular Partners in Asymmetric Catalysis Copolymerization: Highly Enantioselective and Controllable at Enhanced Temperatures and Low Loadings.

Asymmetric copolymerization of meso-epoxide and anhydride is a powerful strategy for preparing various isotactic polyesters with two contiguous stereogenic centers. However, the previous binary systems suffered from slow rates at low loadings, poor enantioselectivities and transesterification reactions at enhanced temperatures. Herein, we report novel dinuclear aluminium complexes with multiple chiralities and ammonium salts anchored on ligand frameworks. These bifunctional catalysts exhibit high activities and enantioselectivities for epoxides/anhydrides copolymerizations at harsh conditions via intramolecularly synergistic catalysis, affording polyesters with unprecedented molecular weights and narrow distributions. Notably, no transesterification reactions were observed, significantly different from the binary catalyst/cocatalyst pairs. This study represents a rare example regarding temperature-independent asymmetric induction for preparing chiral polymers from achiral monomers.

Intramolecular Partners in Asymmetric Catalysis Copolymerization: Highly Enantioselective and Controllable at Enhanced Temperatures and Low Loadings

AbstractAsymmetric copolymerization of meso‐epoxide and anhydride is a powerful strategy for preparing various isotactic polyesters with two contiguous stereogenic centers. However, the previous binary systems suffered from slow rates at low loadings, poor enantioselectivities and transesterification reactions at enhanced temperatures. Herein, we report novel dinuclear aluminium complexes with multiple chiralities and ammonium salts anchored on ligand frameworks. These bifunctional catalysts exhibit high activities and enantioselectivities for epoxides/anhydrides copolymerizations at harsh conditions via intramolecularly synergistic catalysis, affording polyesters with unprecedented molecular weights and narrow distributions. Notably, no transesterification reactions were observed, significantly different from the binary catalyst/cocatalyst pairs. This study represents a rare example regarding temperature‐independent asymmetric induction for preparing chiral polymers from achiral monomers.

A structural study into halogenated derivatives of mandelic acid as building blocks of chiral coordination polymers

Mandelic acid and its derivatives are an excellent source of chirality for the construction of chiral coordination polymers (CPs) and metal-organic frameworks (MOFs) for enantioselective applications. To date, limited reports exist for the incorporation of mandelic acid derivatives with halogen substituents such as fluorine and chlorine despite the extra intermolecular interactions possible. The extra sites for hydrogen and halogen bonding in these mandelic acid derivatives may afford interesting modes of coordination and packing in 3 D space. Six CPs containing mandelic acid and its halogenated analogues, (R)-2-chloromandelic acid, 3,5-difluoromandelic acid, 4-trifluoromethylmandelic acid, together with linear dipyridyl co-ligands are reported. These structures consist of three 2 D sql sheets and three 1 D chains with a range of packing motifs influenced by the differing intermolecular interactions present.

The effect of different photoluminescent side-chain length on the phase behaviour of chiral liquid crystal polymer

ABSTRACT Fluorescent liquid crystal polymers have attracted much attention because of the combination of fluorescence, liquid crystallinity and processability. In this study, we designed and synthesised two series of photoluminescent cholesteric liquid crystal polysiloxanes, which contained cholesterol mesogens and fluorescein methyl ester with different side chain lengths. The chemical structures and liquid crystal properties of the polymers were investigated by the usual methods. The photoluminescent property were characterised by fluorescence spectroscopy. At the same time, the effects of the lengths of the fluorescent group chains on the liquid crystal and fluorescence properties of the polymers were studied. The results showed that the synthesised polymers possessing very good fluorescent and liquid crystal properties, which may has certain practical value and application prospect.

Modulating the Crystallinity of a Circular Plastic towards Packaging Material with Outstanding Barrier Properties.

Chemically recyclable polymers have attracted increasing attention since they are promising materials in a circular economy, but such polymers appropriate for packaging applications are scarce. Here a combined thermal, mechanical, and transport (permeability and sorption) study is presented of a circular polymer system based on biobased trans-hexahydrophthalide which, upon polymerization, can lead to amorphous, homochiral crystalline, and nanocrystalline stereocomplex materials. This study uncovers their largely different transport properties of the same polymer but with different stereochemical arrangements and synergistic or conflicting effects of crystallinity on transport properties versus thermal and mechanical properties. Overall, the homocrystalline chiral polymer shows the best performance with an outstanding barrier character to gases and vapors, outperforming commercial poly(ethylene terephthalate) and polyethylene. The results presented herein show that it is possible to modify the crystalline structure of the same polymer to tune the mechanical and transport properties and generate multiple materials of different barrier characters.

Chiral Supramolecular Polymer Formed via Host-Guest Complexation of an Octaphosphonate Biscavitand and a Chiral Diammonium Guest

Abstract Chiral supramolecular polymers were constructed through the host-guest complexation of an octaphosphonate biscavitand and a chiral diammonium guest. Isothermal titration calorimetry determined that host-guest complexation was enthalpy- and entropy-favored with high binding constants. Diffusion-ordered NMR spectroscopy and viscometry of the host-guest solution revealed that supramolecular polymerization occurred, which most likely followed a ring-chain mechanism. The cyclic oligomers and the supramolecular polymer chains were visualized by atomic force microscopy. Circular dichroism was observed when the octaphosphonate biscavitand and the chiral diammonium guest were mixed, which suggested that chirally twisted supramolecular polymers were formed.

Absolute asymmetric polymerizations in solution needing no physical chiral source

Absolute asymmetric polymerizations, which do not need chiral compounds, are very limited. In addition, they involve spontaneously formed supramolecular compounds, or they need circularly polarized light, and the resulting polymers are often insoluble showing no chiral information at the molecular level. Here we have achieved five kinds of real absolute asymmetric polymerizations of achiral acetylene monomers showing no CD in solution to yield soluble high MW chiral polymers showing CD peaks in solution. These polymerizations did not contain spontaneously formed chiral crystals of monomers or did not use circularly polarized light. A new mechanism we propose here for this new unusual polymerization will give us clues to a better understanding of the reason for the homochirality of our world.

Molecular Chirality and Morphological Structural Chirality of Exogenous Chirality-Induced Liquid Crystalline Block Copolymers

Chiral expression from the molecular to macromolecular level, as well as aggregates, plays an important role in natural physiological activity. Therefore, understanding the chirality transfer mechanism will provide guidance for the design of new functional chiral materials. Herein, we have systematically investigated the chiral assembly and transfer from the molecular to morphological level in liquid crystalline block copolymers (LC-BCPs) induced by enantiopure tartaric acid (TA) as a chiral source. Both the experimental and theoretical results indicate that the self-organization of the liquid crystal side chains and H-bonding interactions formed between the chiral additive and LC-BCPs are key factors for chiral expression in the self-assembly of LC-BCPs doped with TA. Furthermore, the various morphologies, including particles, spheres, worms, helical cylinders, and spirals, were observed in the LC-BCPs using transmission electron microscopy. The strength of the liquid crystal related to the azobenzene side chain structure has a crucial effect on the morphological transition. This work provides guidance for the design of diverse chiral nanostructures in a chiral molecule-induced achiral polymer system and may establish a fabrication platform for chiral cryptography, optical metamaterials, and other potential applications.