Chiral Polymers Research Articles

Influence of molecular weight on helical twisting power of oligomer chiral dopants

Chiral mesogenic monomers have been widely used in applications based on chiral liquid crystals, where polymerization is normally required to fulfill the device function. The change of molecular weight has a notable impact on the properties of the formed polymers. Herein, we systematically investigate the influence of molecular weight on the helical twisting power (HTP) of chiral oligomers when used as chiral dopants. Two series of side-chain and main-chain liquid crystal oligomers are synthesized and examined in terms of phase behavior, HTP value and dependence on temperature. The relationship between the HTP value and molecular weight of the oligomer is established, which is markedly dependent on the molecular structure. The insights obtained from the current study could help develop methods to in-situ analyze functional devices based on chiral liquid crystal polymers.

Chirality in polythiophenes: A review.

Chiroptical polythiophene (PTh), as one of the most important chiral conductive polymers, is an emerging and hot topic in chiral materials, which shows great application potentials in fields as diverse as chiral sensing and separation, asymmetry catalysis, chiroptoelectronics, and even chiro-spintronics. This review summarizes progress in chiral polythiophenes (PThs) in the past 10 years, including the synthesis, properties and applications. Main focus is placed on the manner in which chirality is implemented and the optical activity of the chiral PThs. We showcase examples in which the chirality of PThs is induced by side chain substituents with point, planar, and axial chirality or arises from external chiral media. Application of chiral PThs is also included. Finally, perspectives for further development are offered.

Inside Cover: Hydrogen‐Bond‐Driven Synergistically Enhanced Hyperpolarizability: Chiral Coordination Polymers with Nonpolar Structures Exhibiting Unusually Strong Second‐Harmonic Generation (Angew. Chem. Int. Ed. 38/2021)

Systematically synthesized new noncentrosymmetric nonpolar chiral coordination polymers exhibit unusually strong second-harmonic generation efficiencies attributable to the synergistic effect of polarizable metal cations and increased hyperpolarizability in the donor–acceptor system originating from the robust hydrogen bonding in the coordinated linkers. Details can be found in the Communication by Joonhyuk Kee and Kang Min Ok on page 20656.

One-Pot Synthesis of Supertough, Sustainable Polyester Thermoplastic Elastomers Using Block-Like, Gradient Copolymer as Soft Midblock

It remains challenging to synthesize supertough thermoplastic elastomers (TPEs) since the stretchability and tensile strength are mutually exclusive. Here, we report a one-pot strategy for the prep...

Toward Efficient Synthesis of Porous All-Carbon-Based Nanocomposites for Enantiospecific Separation.

Chiral separation and asymmetric synthesis and catalysis are crucial processes for obtaining enantiopure compounds, which are especially important in the pharmaceutical industry. The efficiency of the separation processes is readily increased by using porous materials as the active material can interact with a larger surface area. Silica, metal–organic frameworks, or chiral polymers are versatile porous materials that are established in chiral applications, but their instability under certain conditions in some cases requires the use of more stable porous materials such as carbons. In addition to their stability, porous carbon materials can be tailored for their ability to adsorb and catalytically activate different chemical compounds from the liquid and the gas phase. The difficulties imposed by the functionalization of carbons with chiral species were tackled in the past by carbonizing chiral ionic liquids (CILs) together with a template to create pores, which results in the entire body of a material that is built up from the precursor. To increase the atomic efficiency of ionic liquids for better economic utilization of CILs, the approach presented here is based on the formation of a composite between CIL-derived chiral carbon and a pristine carbon material obtained from carbohydrate precursors. Two novel enantioselective carbon composite materials are applied for the chiral recognition of molecules in the gas phase, as well as in solution. The enantiomeric ratio of the l-composite for phenylalanine from the solution was (L/D) = 8.4, and for 2-butanol from the gas phase, it was (S/R) = 1.3. The d-composite showed an opposite behavior, where the enantiomeric ratio for phenylalanine was (D/L) = 2.7, and for 2-butanol from the gas phase, it was (R/S) = 1.3.

Electrically modulated large range tuning of self-assembled photonic bandgaps in polymer-stabilised blue phases

ABSTRACT Developing 3D photonic nanostructures with stimuli-directed controllability has been a burgeoning but challenging area in the field of optical materials as there are numerous opportunities in next-generation communication systems. In this study, polymer-stabilised blue phase I material systems with self-assembled 3D tunable photonic bandgap (PBG) were prepared by using different acrylate monomers. From the comparison of the electric responsive behaviours, the electrical tunability of the material system was noteworthyly improved by using chiral acrylate monomers. And a reversible electrically modulated large range red shifting of the PBG was achieved through the fabrication of the chiral polymer network. Besides, the optical quality and response time can be improved by increasing the polymerisable chiral monomer concentration.

Synthesis and the crystal structure of a new chiral metal-organic coordination polymer based on l-proline-substituted 2-aminobenzene-1,4-dicarboxylic acid derivative

Synthesis and the crystal structure of a new chiral metal-organic coordination polymer based on l-proline-substituted 2-aminobenzene-1,4-dicarboxylic acid derivative

Gold Nanohelices for Chiral Plasmonic Films by Templated Electroless Plating (Advanced Optical Materials 10/2021)

As shown in article number 2002133 by Rong-Ming Ho and co-workers, gold nanohelices for chiral plasmonic polymer films can be fabricated by using self-assembled chiral block copolymers as templates for templated electroless plating. The gold nanohelix can serve as absorber and scatterer in the polymeric films for manipulating circular-polarized light based on its chirality. This bottom-up approach suggests a facile method for fabrication of plasmonic nanohelices.

Synthesis of cinchona squaramide polymers by Yamamoto coupling polymerization and their application in asymmetric Michael reaction

Yamamoto coupling polymerization has been used for the synthesis of polymeric chiral organocatalysts. Cinchona squaramide derivatives with dibromophenyl moiety were polymerized under the Yamamoto coupling conditions to afford the corresponding chiral polymers in good yields. Using this technique, novel cinchona alkaloid polymers containing the squaramide moiety were designed and successfully synthesized. In addition to the homopolymerization of cinchona squaramide monomers with a dibromophenyl group, achiral comonomers such as dibromobenzene were copolymerized with the cinchona monomers to yield chiral copolymers. These chiral polymers were successfully utilized as polymeric catalysts in asymmetric Michael addition reactions. Good to excellent enantioselectivities were observed for different types of asymmetric Michael reactions. Using the chiral homopolymer catalyst P4, almost perfect diastereoselectivity (>100:1) with 99% ee was obtained for the reaction between methyl 2-oxocyclopentanecarboxylate 25 and trans-β-nitrostyrene 17. The polymer catalysts developed in this study have robust structures and can be reused several times without a loss in their catalytic activities.

Light‐Responsive Circularly Polarized Luminescence Polymers with INHIBIT Logic Function

AbstractDynamically tuning the emission of circularly polarized luminescence (CPL) materials through external stimuli is fascinating because of their fundamental and application interests. In this work, light‐responsive and luminescence‐tunable CPL‐active materials are synthesized by mixing achiral helical polymer containing vibration‐induced emission (VIE) molecules and spiropyran (SP) with a chiral helical polymer. Through regulating the distinct emission of VIE molecules and the reversible photoisomerization of SP, the dynamic Förster resonance energy transfer (FRET) can be explored to reversibly control the emission color of CPL in different states after light‐controlled isomerization. This project is the first comprehensive investigation of CPL‐active materials with VIE properties. Finally, taking the advantage of the multistimuli responsive CPL signal in different states, an “INHIBIT” logic gate with CPL signal output based on the combination of control of UV/vis light irradiation time and state alternation is constructed.

Chiral Detection with Coordination Polymers

Coordination polymers and metal-organic frameworks are prime candidates for general chemical sensing, but the use of these porous materials as chiral probes is still an emerging field. In the last decade, they have found application in a range of chiral analysis methods, including liquid- and gas-phase chromatography, circular dichroism spectroscopy, fluorescence sensing, and NMR spectroscopy. In this minireview, we examine recent works on coordination polymers as chiral sensors and their enantioselective host-guest chemistry, while highlighting their potential for application in different settings.

Synthesis of Polymers Bearing a Chiral Backbone via Stereospecific Ionic Ring-Opening Polymerization of Chiral Donor-Acceptor Cyclopropanes.

The stereospecific ionic ring-opening polymerization of various donor-acceptor cyclopropanes is reported. The chiral cyclopropane monomers are readily prepared with established methodology and stereospecific polymerization is best conducted with a catalytic amount of MgBr2 serving as a Lewis acid and as an initiator. Polymers with molecular masses of up to 7800g mol-1 containing a stereocenter in every repeating unit are obtained and the substituents of the monomers can be readily varied to access a novel class of chiral polymers.

Enantiomeric Separation of Semiconducting Single-Walled Carbon Nanotubes by Acid Cleavable Chiral Polyfluorene.

Helical wrapping by conjugated polymer has been demonstrated as a powerful tool for the sorting of single-walled carbon nanotubes (SWCNTs) according to their electronic type, chiral index, and even handedness. However, a method of one-step extraction of left-handed (M) and right-handed (P) semiconducting SWCNTs (s-SWCNTs) with subsequent cleavage of the polymer has not yet been published. In this work, we designed and synthesized one pair of acid cleavable polyfluorenes with defined chirality for handedness separation of s-SWCNTs from as-produced nanotubes. Each monomer contains a chiral center on the fluorene backbone in the 9-position, and the amino and carbonyl groups in the 2- and 7-positions maintain the head-to-tail regioselective polymerization resulting in polyimines with strictly all-(R) or all-(S) configuration. The obtained chiral polymers exhibit a strong recognition ability toward left- or right-handed s-SWCNTs from commercially available CoMoCAT SWCNTs with a sorting process requiring only bath sonication and centrifugation. Interestingly, the remaining polymer on each single nanotube, which helps to prevent aggregation, does not interfere with the circular dichroism signals from the nanotube at all. Therefore, we observed all four interband transition peaks (E11, E22, E33, E44) in the circular dichroism (CD) spectra of the still wrapped optically enriched left-handed and right-handed (6,5) SWCNTs in toluene. Binding energies obtained from molecular dynamics simulations were consistent with our experimental results and showed a significant preference for one specific handedness from each chiral polymer. Moreover, the imine bonds along the polymer chains enable the release of the nanotubes upon acid treatment. After s-SWNT separation, the polymer can be decomposed into monomers and be cleanly removed under mild acidic conditions, yielding dispersant-free handedness sorted s-SWNTs. The monomers can be almost quantitatively recovered to resynthesize the chiral polymer. This approach enables high selective isolation of polymer-free s-SWNT enantiomers for their further applications in carbon nanotube (CNT) devices.

Synthetic strategies towards chiral coordination polymers

• Chiral coordination polymers can be synthesised via direct or indirect methods. • Indirect methods include spontaneous resolution, chiral templating and induction. • Ligands with point chirality can be derived from various chiral pool molecules. • Other coordination polymers are built from ligands with axial or planar chirality. • Post-synthetic modification can be used to impart or unveil chirality in frameworks. Chiral coordination polymers and porous chiral MOFs have great potential as agents for enantioselective separations, sensing, and catalysis due to their well-structured internal chiral cavities. They also have physical properties that may be exploited, such as non-linear optical activity, ferroelectrics, magnetochiral dichroism, and use as chemical shift reagents. There are many ways in which chiral coordination polymers can be synthesised and the file has grown tremendously over the past two decades. In this review, we will discuss some of the main synthetic approaches that have been taken towards this fascinating class of materials. The main focus will be placed on synthetic approaches using enantiopure ligands, the route that is most likely to yield homochiral network solids. We will highlight the applications of many examples, noting how the design of the frameworks influences their application. Whilst this is a mature field, there still lies huge potential for functional chiral materials, and we aim to demonstrate areas that are ripe for exploration.

High performance of ultrasonic-assisted synthesis of two spherical polymers for enantioselective catalysis

Chiral polymers have aroused great attention in among chiral supramolecular materials based on their features. Herein, for the first time, the synthesis of chiral polymeric composites (CMNPs/1,4-Zbtb & 1,3-Zbtb) have been reported with entrapment through three strategies: ultrasonic irradiation, solvothermal, and mechanical stirring. According to the obtained results, it is found that ultrasound-assisted synthesis can be considered as an inexpensive and efficient method than the others, from the point ofviewof energy and time consuming. In this strategy, encapsulation of chiral magnetic nanoparticles (CMNPs) by using tetrazole-based polymers (Zbtbs) happens, in-situly. These chiral sphere-like inorganic–organic polymers can be considered as core and shell composites with catalytic activity due to their acidic (semi unsaturated Zn: open metal sites) and basic (abundant basic nitrogens) centers. In these structures, the unprecedented chirality induction can happen from the core to shell by non-covalent interaction, easily. They could catalyze symmetric oxidation and asymmetric henry condensation to give chiral β-nitroalkanol. Circular dichroism and chiral gas chromatography were used to characterize the produced enantiomers. These chiral polymeric materials can be considered as unique acid-base bifunctional catalysts with efficient properties such as high stability, enantiomeric excess, enantioselectivity to the main product, and protecting from CMNPs leaching.

Synthesis of a rod-based porous coordination polymer from a nucleotide as a sequential chiral inductor

We report the two-step synthesis of a novel chiral rod-based porous coordination polymer (PCP). The chemical approach consists of the use of a previously prepared bis(ethylenediamine) copper monomer [Cu(en)]2(NO3)2 [where en = ethylenediamine] reacting with the cytidine 5′-monophosphate (CMP) nucleotide. The bis(ethylenediamine) copper compound—stabilized by axial coordination of nitrate counter-anions—reacts in the presence of sodium salt of CMP to yield right-handed copper(II) chains of P helicity with formula [Cu2(en)2(CMP)2]·5H2O (1). The axial coordination of the CMP2- ligands through the N3 and O2 sites (free nitrogen and carbonyl groups) of the cytosine nucleobase and oxygen atoms of phosphate moieties, ensure stabilization of the neutral chiral polymer. The supramolecular organization involves strong hydrogen bonding interactions to build supramolecular chains of the same helicity. The resulting PCP constitutes one of the few examples of CMP compounds exhibiting coordination involving both nucleobase and phosphate moieties, where a highly stable metal complex is used as precursor for the rational construction of rod-based hydrogen metal-organic frameworks (HMOFs). Furthermore, it shows the intrinsic capability of biomolecules to act as chiral transfer systems.

Chiral Coordination Polymers of Mandelate and its Derivatives: Tuning Crystal Packing by Modulation of Hydrogen Bonding

Chiral coordination polymers constructed from mandelic acid have shown promise in enantioselective recognition and sensing, whereas its methoxy-protected derivative, α-methoxyphenyl acetic acid, is rarely used as a ligand in coordination polymers. In this study, mandelic acid, 3,5-difluoromandelic acid, and α-methoxyphenyl acetic acid were combined with divalent transition metals and bridging dipyridyl co-ligands to obtain a series of six 1D coordination polymers. The coordination polymers of mandelate and 3,5-difluoromandelate possessed densely packed structures stabilised by hydrogen bonding. In contrast, the use of (R)-α-methoxyphenyl acetic acid gave rise to zig-zag chains with significant solvent-accessible void space.

Multifunctional chiral cationic porous organic polymers: gas uptake and heterogeneous asymmetric organocatalysis

Chiral porous organic polymers are characterized by robust, non-toxic and recyclable properties. Therefore, compared with small molecular catalysts, they have attracted much attention in the field of heterogeneous asymmetric organic catalysis.

Circularly polarized electroluminescence from an achiral fluorophore induced by co-assembly with chiral polymers

In this paper, this chiral supramolecular co-assembly (R/S-P2-Bpy) can not only emit deep blue CPL (λem = 420 nm, |gem| = 0.042) in spin-coated films, but also act as an EML of a CP-EL device (λem = 418 nm, |gEL| = 0.021).

Pair of chiral molecular ladders and successive hydration in single-crystal-to-single-crystal mode

Self-assembly of Zn(NO3)2 with a pair of new tridentate chiral Ls produced a pair of chiral ladder-type 1D coordination polymers, where crystals were transformed into different hydrated products of zigzag 1Ds depending on chirality in the SCSC mode.