Chiral Polymers Research Articles

Side-chain chiral fluorescent liquid crystal polymers with highly efficient circularly polarized luminescence emission in a glassy-state SmC* film

A series of high-efficiency CPL-active homopolymer materials in solid films with modulated properties were fabricated.

The pH-Triggered Amphiphilic Polycarbodiimides as Nanovesicles

The pH-triggered polymers are a sub-class of stimuli-responsive macromolecules. These smart polymers can experience physical or chemical transition due to small pH responses. pH-dependent materials gain great demand within a short period, by considering their potential applications. pH-triggered macromolecules typically possess weak basic or weak acidic functional groups. The functional groups often used include tertiary amines, pyridines, phosphate, and carboxylic acids. These stimuli-dependent materials are ideal candidates for the biomedical field. Herein, report pH-dependent chiral amphiphilic carbodiimide polymers. Helical polycarbodiimides consist of alternating imine and amine backbone, attached to different pendant groups. Substituting the pendant groups, enable to change of the properties of polycarbodiimides. Thus, we invented polar functional groups such as dimethylamine and piperazine to the side chains to enhance the solubility in an aqueous medium. Moreover, each unit of these polymers consists of hydrophobic methyl functionality and hydrophilic dimethyl and piperazine side groups. Thus, these carbodiimide polymers were self-assembled in aqueous solutions as well as buffer solutions due to the hydrophilic and hydrophobic moieties of the polymer. The micelles can be used as nanocarriers. Furthermore, the pH-dependent swelling properties were observed in these polymeric nanoparticles in different time intervals. Thus, the pH-triggered volume change of the micelles can be used as a controlled release, targeted site drug delivery applications.

First example of Ugi's amine as a platform for the construction of chiral coordination polymers: synthesis and properties

Here, the first example of phosphinic acid containing Ugi's amine (HL) is presented.

Chiral porous CN-bridged coordination polymer mimicking MOF-74 and showing magnetization photoswitching.

A chiral porous cyanide-bridged framework {[MnII(L)]2[WIV(CN)8]·10H2O}n (1; L = 2,6-bis[1-(2-(N-methylamino)ethylimino)ethyl]-pyridine) showing a strong structural similarity to MOF-74 has been prepared and characterised. The crystallised water molecules can be easily removed below 60 °C, leading to a distinct crystal colour change and the activation of its photomagnetic properties - constituting the so called photomagnetic sponge behaviour of this system. The complete dehydration of 1 proceeds through a single-crystal-to-single-crystal transformation and the resulting anhydrous framework {[MnII(L)]2[WIV(CN)8]}n (1anh) was studied using single-crystal X-ray diffraction.

Chiral polymer hosts for circularly polarized electroluminescence devices

Polymer electroluminescence devices producing circularly polarized luminescence (CP PLEDs) have valuable photonic applications. The fabrication of a CP PLED requires a polymer host that provides the appropriate chiral environment around the emitting dopant. However, chemical strategies for the design of chiral polymer hosts remain underdeveloped. We have developed new polymer hosts for CP PLED applications. These polymers were prepared through a free-radical polymerization of 3-vinylcarbazole with a chiral N-alkyl unit. This chiral unit forces the carbazole repeat units to form mutually helical half-sandwich conformers with preferred (P)-helical sense along the polymer main chain. Electronic circular dichroism measurements demonstrate the occurrence of chirality transfer from chiral monomers to achiral monomers during chain growth. The (P)-helical-sense-enriched polymer interacts diastereoselectively with an enantiomeric pair of new phosphorescent (R)- and (S)-dopants. The magnitude of the Kuhn dissymmetry factor (gabs) for the (P)-helically-enriched polymer film doped with the (R)-dopant was found to be one order of magnitude higher than that of the film doped with the (S)-dopant. Photoluminescence dissymmetry factors (gPL) of the order of 10−3 were recorded for the doped films, but the magnitude of diastereomeric enhancement decreased to that of gabs. The chiral polymer host permits faster energy transfer to the phosphorescent dopants than the achiral polymer host. Our photophysical and morphological investigations indicate that the acceleration in the chiral polymer host is due to its longer Förster radius and improved compatibility with the dopants. Finally, multilayer CP PLEDs were fabricated and evaluated. Devices based on the chiral polymer host with the (R)- and (S)-dopants exhibit electroluminescence dissymmetry factors (gEL) of 1.09 × 10−4 and −1.02 × 10−4 at a wavelength of 540 nm, respectively. Although challenges remain in the development of polymer hosts for CP PLEDs, our research demonstrates that chiroptical performances can be amplified by using chiral polymer hosts.

Chiral magnetic hybrid materials constructed from macromolecules and their chiral applications.

Chirality is a fundamental and ubiquitous feature of living organisms in nature. Magnetic materials, in particular magnetic nanoparticles (MNPs), show some interesting properties such as large specific surface area, easy surface modification, magnetic responsivity and separation ability. Integrating MNPs with chirality in a single material will undoubtedly create a large number of advanced multi-functional materials. Despite the great advancements made in this area, there have been no review articles to summarize the relevant studies. The present work reviews the major progress recently made in constructing chiral magnetic hybrid materials (CMHMs) using macromolecules, which are classified based on the primary chiral macromolecular organic components, namely, biological polymers and synthetic polymers, and the applications of the resulting chiral hybrids in chiral research fields, including asymmetric catalysis, enzymatic resolution, chromatographic separation, enantioselective crystallization and enantioselective adsorption, are also summarized. The challenges and prospects of related research fields are proposed in the last section.

Chiral polymers based on thiophenes functionalized at the 3-position with a pendant containing a stereogenic sulfur atom. Synthetic and structural aspects

The first synthesis of new, chiral polythiophenes functionalized at the 3-position of the thiophene ring with a pendant containing a stereogenic sulfur atom of sulfoxides, sulfoximines or sulfinates was developed.

On the Optical Activity of Poly(l-lactic acid) (PLLA) Oligomers and Polymer: Detection of Multiple Cotton Effect on Thin PLLA Solid Film Loaded with Two Dyes

Optical rotatory dispersion (ORD) is a beautiful analytical technique for the study of chiral molecules and polymers. In this study, ORD was applied successfully to follow the degree of polycondensation of l-(+)-lactic acid toward the formation of poly(lactic acid) oligomers (PLAO) and high molecular weight poly(l-lactic acid) (PLLA) in a simple esterification reaction equipment. PLLA is a biodegradable polymer obtainable from renewable raw materials. The racemization of the intrinsically isotactic PLLA through thermal treatment can be easily followed through the use of ORD spectroscopy. Organic or molecular electronics is a hot topic dealing with the combination of π-conjugated organic compounds and polymers with specific properties (e.g., chirality) which can be exploited to construct optoelectronic devices, such as organic light-emitting diodes (OLEDs), organic photovoltaic (OPV) high efficiency cells, switchable chirality devices, organic field-effect transistors (OFETs), and so on. ORD spectroscopy was applied to study either the gigantic optical rotation of PLLA films, as well as to detect successfully the excitonic coupling, occurring in thin solid PLLA green film loaded with a combination of two dyes: SY96 (a pyrazolone dye) and PB16 (the metal-free phthalocyanine pigment). The latter compound PLLA loaded with SY96 and PB16 shows a really gigantic optical activity in addition to typical ORD signal due to exciton coupling and may be considered as a simple and easily accessible model composite of a chiral polymer matrix combined with π-conjugated dyes for molecular electronics studies.

A one-dimensional chiral gadolinium complex based on a tartaric acid derivative: crystal structure, thermal behavior and magnetic properties

A new chiral one-dimensional gadolinium coordination polymer [Gd(HDTTA)3(CH3OH)3]n (1) (D-H2DTTA = (+)-Di-p-toluoyl-D-tartaric acid) was synthesized at room temperature, and fully structurally characterized by Infrared (IR), elemental analysis (EA), single-crystal and powder X-ray diffraction (PXRD). The structure analysis shows that complex 1 belongs to the trigonal system with R3 space group and displays an infinite chain structure along the c axis. In 1, each Gd3+ cation is in the tri-capped trigonal prism geometry, and neighboring Gd3+ cations are connected by three partly deprotonated HDTTA− ligands with the Gd···Gd distance of 7.686(1) Å. The circular dichroism (CD) spectrum demonstrates the chirality of the complex. Magnetic studies reveal that complex 1 displays weak antiferromagnetic interactions between Gd3+ cations and it exhibits a small magnetic entropy change (−ΔS m = 7.26 J kg−1 K−1 with ΔH = 7 T and T = 2.5 K) because of long Gd···Gd distance and relatively low magnetic density.

In Situ Polymerization of Chiral Poly(fluorene-alt-benzothiadiazole) Nanocomposites with Enhanced Chirality

Poly(fluorene-alt-benzothiadiazole) (PFBT) is a promising chiral polymer for use in metamaterials and other photonic applications, due to its large chiral optical activity at visible wavelengths. However, its usages are very limited, since it is not readily patternable into microstructures and challenging to apply to applications. In this paper, we demonstrate photo patterning of chiral PFBT/Achiral SU-8 photoresist to produce high quality structures while retaining the extraordinary chiral optical activity of our previously-reported PFBT/SU8 nanocomposite films. The ability to produce cleanly patterned microfeatures with high chirality may enable wider use of PFBT in chiral metamaterials and other photonic applications.

Enantiomeric Switching of the Circularly Polarized Luminescence Processes in a Hierarchical Biomimetic System by Film Tilting.

Circularly polarized luminescence (CPL) switching has attracted great attention due to the potential applications in chiral photonics and electronics. However, the lack of examples to achieve switchable CPL within a single material in the dry solid state hampers the scope of applications. Herein, we demonstrate a crystalline chiral polymer film as a polarizing medium consisting of radially assembled twisted crystallites, where achiral aggregation-induced emissive luminogens (AIEgens) are confined between the twisted crystalline stacks, eventually yielding handedness-switchable CPL by simple film tilting. Hierarchically organized twisted crystallites create the selective reflection activity of the polarizing medium. Upon film tilting, enantiomeric switching is realized by selectively collecting transmitted and reflected CPL components. The confined AIEgens in the crystalline polarizing system show a great enhancement of the luminescence efficiency. Moreover, the approach is general with broadband activity, and various AIEgens could be applied to generate full-color-tunable CPL. Additionally, the rigid and continuous nature of this polarizing system affords enhanced optical stability and facile modulation, developing a general route for designing chiroptical materials.

Consequences of Chirality in Directing the Pathway of Cholesteric Helix Inversion of π-Conjugated Polymers by Light.

Control over main-chain motion of chiral π-conjugated polymers can lead to unexpected new functionalities.Here, it is shown that by combining photoswitchable azobenzene units in conjugation with chiral fluorene comonomers and appropriate plasticizers, the polymer organization and chiroptical properties of these alternating copolymers steered by light and its state of polarization can be dynamically controlled. The configuration of the stereogenic centers in the side chains of the fluorene units determines the handedness of the cholesteric organization in thermally annealed films, indicating cooperative behavior. The polymer alignment and helicity of the supramolecular arrangement can be switched by irradiating with linearly and circularly polarized light, respectively.Intriguingly, when switching the handedness of thermally induced cholesteric organizations by illuminating with circularly polarized light that is opposite to the handedness of the cholesteric phases, a nematic-like intermediate state is observed during helix interconversion. By the sequence of irradiation with left and right circularly polarized light followed by thermal annealing, an asymmetric motion, reminiscent of that seen in molecular motors is observed. These findings suggest that functional conjugated polymers can exhibit emergent properties at mesoscopic scale.

Natural optical activity as the origin of the large chiroptical properties in \u03c0-conjugated polymer thin films

Polymer thin films that emit and absorb circularly polarised light have been demonstrated with the promise of achieving important technological advances; from efficient, high-performance displays, to 3D imaging and all-organic spintronic devices. However, the origin of the large chiroptical effects in such films has, until now, remained elusive. We investigate the emergence of such phenomena in achiral polymers blended with a chiral small-molecule additive (1-aza[6]helicene) and intrinsically chiral-sidechain polymers using a combination of spectroscopic methods and structural probes. We show that – under conditions relevant for device fabrication – the large chiroptical effects are caused by magneto-electric coupling (natural optical activity), not structural chirality as previously assumed, and may occur because of local order in a cylinder blue phase-type organisation. This disruptive mechanistic insight into chiral polymer thin films will offer new approaches towards chiroptical materials development after almost three decades of research in this area.

DNA Origami Guided Self-Assembly of Plasmonic Polymers with Robust Long-Range Plasmonic Resonance.

Plasmonic polymers consisting of metallic nanoparticles (NPs) are able to squeeze light into the deep-subwavelength space and transfer along a highly confined nanoscale path in long range. DNA nanotechnology, particularly benefiting from the molecular programmability of DNA origami, has provided otherwise nearly impossible platforms for constructing plasmonic nanoparticle polymers with designer configurations and nanoscale gaps. Here, we design and assemble a DNA origami hashtag tile that is able to polymerize into one-dimensional chains with high rigidity. The DNA origami hashtag chains are used as frames to enable robust, versatile, and precise arrangement of metallic NPs into micrometer-long chiral and magnetic plasmonic polymers, which are capable of efficiently transporting plasmonic angular momentum and magnetic surface plasmonic polaritons at the deep-subwavelength scale. Our work provides a molecular platform for the fabrication of long, straight, and structurally complex nanoparticle polymers with emerging plasmonic properties that are appealing to a variety of fields.

Optically Active Polymers with Cationic Units Connected through Neutral Spacers: Helical Conformation and Chirality Transfer to External Molecules

Cationic chiral polymers consisting of a chiral “Arg monomeric unit” consisting of two l-arginine moieties joined together through an oxyhexane-1,6-diyloxy spacer unit and achiral “Sp monomeric unit” based on the spermine moiety where the two units are connected through a 1,4-dioxobutane-1,4-diyl spacer unit (“C2 monomeric unit”) were prepared in the cationic form as a salt of p-toluenesulfonic acid. Polymer conformation could not be directly deduced from circular dichroism (CD) spectra based on the amide group bands (200–240 nm), which are generally used to quantify α-helical, β-sheet, and random coil residues because of spectral overlapping with the p-toluenesulfonate bands. On the other hand, a helical conformation was proposed on the basis of the relation between CD intensity and Arg monomeric unit ratio of polymers, while the proposed conformation may not be highly ordered but rather fragmented and partial. The helix-forming propensity of a polymer consisting of a higher Arg monomeric unit ratio was supported by MD simulations in water and in vacuum. The copolymer consisting of 100% Arg monomeric units [poly(Arg100-C2)], the one consisting of 42% Arg monomeric units and 58% Sp monomeric units [poly(Arg50-C2–Sp50-C2)], and the one consisting of 20% Arg monomeric units and 80% Sp monomeric units [poly(Arg25-C2–Sp75-C2)] exhibited chirality transfer to methyl orange (MO), where transfer was most efficient with poly(Arg50-C2–Sp50-C2). Chirality transfer efficiency also remarkably varied depending on the standing time of polymer solution in H2O before it is mixed with MO, the time after mixing, and the concentration of the polymer. Theoretical calculations of absorbance and CD spectra of polymer–MO complexes suggested that the induced CD spectra mostly having bisignet spectral patterns are not based on exciton coupling between two MO molecules bound to the polymer chain but are composed of independent excitation bands. The design of chiral macromolecules introduced in this work based on a chain composed of charged chiral and achiral units separated by neutral achiral linker (spacer) units has not been studied from a view of chiral polymeric materials. Such a design of polymer chain may be applicable to a wider variety of chemical structures and will largely widen the scope of optically active polymers with helical conformation.

Synthesis of Chiral Porous Organic Polymers Through Nucleophilic Substitution for Chiral Separation

A chiral porous organic polymer (cPOP) was synthesized from chiral 1,2-bis(3,4-dichloromaleimide)cyclohexane and 1,3,5-tri(4-aminophenyl)benzene through facile and catalyst-free nucleophilic substi...

Diamond B23 CD Imaging of Thin Films of Chiral Materials or Achiral Polymers Coated with Chiral Molecules

The novel vertical sample chamber, developed at the B23 beamline for synchrotron radiation circular dichroism (SRCD), has enabled the Diamond User community to conduct different types of experiments from high throughput CD of protein and DNA folding using 96-well multiplates to CD imaging at high spatial resolution. Here, we present the application of CD imaging to large areas of achiral polymer PVA films doped with D-dopa to assess the chiral homogeneity of the film preparation with potential antimicrobial property. Synopsis: CDi application of Diamond B23 SRCD beamline.

Relation between Morphology and Chiroptical Properties in Chiral Conducting Polymer Films: A Case Study in Chiral PEDOT.

The electronic properties of conducting polymers are influenced by their micro- and macrostructural orders, which can be tailored by substituent modification. However, while the effect of substituents on conducting polymers is extensively investigated, chiral substituents are far less studied. Furthermore, many chiral conducting polymers have regioirregular structures, which result in polymer films with inferior properties. In this work, we apply electronic circular dichroism (ECD) spectroscopy to study the morphological changes to the chiral polymers under different polymerization conditions. For this purpose, we investigated 3,4-ethylenedioxythiophene (EDOT) derivatives having two stereogenic centers on each monomer and bearing methyl or phenyl side groups (dimethyl-EDOT and diphenyl-EDOT, respectively). Polymerizing the enantiomerically pure monomers produces regioregular and stereoregular dimethyl-PEDOT and diphenyl-PEDOT, respectively. The effect of the electrolyte and solvent on polymer film morphology was studied using scanning electron microscopy (SEM) and ECD, showing a correlation between the polymer’s morphology and the chiroptical properties of its films. We found that, for diphenyl-PEDOT, the combination of perchlorate anion electrolyte and acetonitrile solvent resulted in a unique morphology characterized by significant intermolecular interactions. These interactions were clearly observable in the ECD spectra in the form of exciton couplings, whose presence was supported by TD-DFT calculations. A small enantiomeric excess was sufficient to induce very intense ECD signals, demonstrating chiral amplification in electropolymerized films.

Exchange Interactions Drive Supramolecular Chiral Induction in Polyaniline (Small Methods 10/2020)

In article number 2000617, Claudio Fontanesi and co-workers study the camphor sulfonic acid induction of chirality on the supermolecular structure of electropolymerized aniline. The emergence of chirality is also associated to spin filtering properties of the chiral polymer, revealed by conducting probe atomic force microscopy in the presence of a magnetic field. Theoretical results suggest that the chiral induction is due to exchange interaction energy.

Supramolecular polymerization of chiral molecules devoid of chiral centers

AbstractThe iterative association of monomer units through noncovalent interactions often leads to chiral supramolecular polymers. Monomers comprising these materials can be further divided into those with chiral centers and those without. The latter class is often less studied but attractive since it features monomer designs with chirality at the core rather than the periphery of the molecules. In this mini‐review, we summarize the existing strategies to construct supramolecular polymers from chiral molecules with no chiral centers and offer perspectives on fundamental trends and differences between them and their counterparts with chiral centers. © 2020 Society of Industrial Chemistry