Helical polymer brushes with a preferred-handed helix-sense triggered by a terminal optically active group in the pendant

Helical polymer brushes with a preferred-handed helix-sense composed of a poly(phenylacetylene) backbone and poly(phenyl isocyanate) pendants are synthesized. The helix-sense of the backbone is effectively controlled by the helical chirality of the pendants, which is triggered by an optically active group introduced at the pendant terminal.     

Two- and three-dimensional smectic ordering of single-handed helical polymers

Rodlike polymers with precisely defined architectures are ideal building blocks for self-assembled structures leading to novel nanometer-scale devices. We found that the living polymerization of a single isocyanide enantiomer bearing an l-alanine pendant with a long n-decyl chain simultaneously produced diastereomeric right- and left-handed helices with different molecular weights and narrow molecular weight distributions. Each single-handed, rodlike helical polymer with a controlled length and handedness isolated by a facile solvent fractionation method with acetone self-assembled to form well-defined two- and three-dimensional smectic ordering on the nanometer scale on a substrate and in a liquid crystalline state as evidenced by direct atomic force microscopic observations and X-ray diffraction measurements, respectively.     

Dual memory of enantiomeric helices in a polyacetylene induced by a single enantiomer

We report the dual memory of both the enantiomeric right- and left-handed helical conformations induced in a polyacetylene based on the temperature-stimulated helicity inversion of the polymer. The polyacetylene folds into a one-handed helix induced by noncovalent bonding interactions with a single enantiomeric amine. The induced helix underwent a reversible inversion of the helicity by temperature. The diastereomeric right- and left-handed helices obtained at different temperatures could be further memorized when the optically active amine was replaced by an achiral diamine, generating right- and left-handed helices of the mirror images of each other. Consequently, both enantiomeric helices can be produced with a high efficiency from dynamically diastereomeric helical polyacetylenes induced by a single enantiomer.     

Chiroptical transcription of helical information through supramolecular harmonization with dynamic helices

With biologically important "peptide bundling" as the motif, new chromophoric cyclic host 1 was designed, which consists of two zinc porphyrin units that are connected by dynamic peptide helices of nonameric aminoisobutyric acid (Aib) units. Upon inclusion of pyridine-anchored helical peptides between the zinc porphyrin units, 1 displayed an intense exciton-coupled circular dichroism (CD) band at 410-450 nm, whose sign reflected the helical sense of the guest peptides. Studies with conformationally defined dehydrophenylalanine-containing analogues indicated that the dynamic helical chains in the host are stereochemically harmonized with right- or left-handed helices of the guest peptides in a confined nano space, leading to either clockwise- or anticlockwise-twisted geometry (chiroptical output) of the connecting zinc porphyrin chromophores.     

Discontinuous change in the helical pitch of cholesteric liquid crystals by photoisomerization of a chiral azobenzene molecule

This paper describes the discontinuous change in the helical pitch of a cholesteric liquid crystal (ChLC) by means of the photoisomerization of chiral azobenzene molecules under homogenous alignment conditions. A mixture of E44, R811 and Azo was prepared in the ratio 68/28/4, respectively. R811 and Azo have opposite twisting abilities such that they induce right- and left-handed helices, respectively when added to E44. The mixture was injected into a glass cell having a 2 or 5 µm cell gap, and treated for homogeneous molecular orientation. The wavelength of selective reflection from the ChLC was shifted to shorter wavelengths by the trans-cis photoisomerization of Azo. The change in the helical pitch was not only discontinuous, but also dependent on the cell thickness. The discontinuous change in the helical pitch was estimated to be almost the same as the half turn of the helical pitch in each cell gap, and was dependent on the number of helical half pitches in the glass cell. The homogeneous alignment condition affects the photochemical change in the helical structure of the ChLC system.     

Helical heterojunctions originating from helical inversion of conducting polymer nanofibers

The helical sense of conducting polyaniline nanofibers was induced using chiral acid as dopant, which can be inversed through a copolymerization of aniline with N-methyl aniline. By delicately controlling the inversion driving force of steric hindrance, we successfully obtained "helical heterojunctions" composed of right- and left-handed helical structures in one helical nanofiber.     

Discontinuous change in the helical pitch of cholesteric liquid crystals by photoisomerization of a chiral azobenzene molecule

This paper describes the discontinuous change in the helical pitch of a cholesteric liquid crystal (ChLC) by means of the photoisomerization of chiral azobenzene molecules under homogenous alignment conditions. A mixture of E44, R811 and Azo was prepared in the ratio 68/28/4, respectively. R811 and Azo have opposite twisting abilities such that they induce right- and left-handed helices, respectively when added to E44. The mixture was injected into a glass cell having a 2 or 5?µm cell gap, and treated for homogeneous molecular orientation. The wavelength of selective reflection from the ChLC was shifted to shorter wavelengths by the trans-cis photoisomerization of Azo. The change in the helical pitch was not only discontinuous, but also dependent on the cell thickness. The discontinuous change in the helical pitch was estimated to be almost the same as the half turn of the helical pitch in each cell gap, and was dependent on the number of helical half pitches in the glass cell. The homogeneous alignment condition affects the photochemical change in the helical structure of the ChLC system.     

Helical structures of conjugate polymers created by oxidative polymerization using synthetic lipid assemblies as templates

The morphology of conjugate polymers (such as poly(ethylenedioxythiophene), poly(pyrrole), and poly(aniline)) can be controlled in their polymerization processes, by applying the concept of the templating method to oxidative polymerization. As oxidative polymerization of these monomers produces cationic intermediates, the anionic assemblies can act as potential templates due to the mutual electrostatic attractive force. Oxidative polymerization of ethylenedioxythiophene (EDOT), pyrrole, and aniline was carried out using helical superstructures of synthetic lipid assemblies as templates. Interestingly, we have found that oxidative polymerization of these monomers results in novel polymeric aggregates, such as a helical-tape structure and an intertwined helical structure, and that both the right-handed and left-handed helical structures can be created by a change in the hydrophilic head groups. This is the first example of helical superstructures composed of conjugate polymers that have been designed utilizing a convenient templating method.     

Synthesis and property of helical poly(phenylacetylene)s bearing chiral ruthenium complexes and real space imaging of meso- and nanoscopic structures by atomic force microscopy

Novel sets of helical poly(phenylacetylene)s bearing a chiral ruthenium (Ru) complex with opposite chirality (Δ and Λ forms) as a bulky pendant (poly- 1 and poly- 2 ) were synthesized through the polymerization of the corresponding optically pure phenylacetylenes with a rhodium catalyst, and their structures in solution and morphology on solid substrates were investigated with NMR, ultraviolet–visible, and circular dichroism (CD) spectroscopies and with atomic force microscopy (AFM), respectively. The obtained cis–transoidal polymers (poly- 1 and poly- 2 ) showed characteristic Cotton effects in the region of metal-to-ligand charge transfer of the chiral Ru pendants. Poly- 1 and poly- 2 were thought to have a predominantly one-handed helical conformation induced by the chiral pendants. However, the apparent Cotton effects derived from the helically twisted π-conjugated polymer backbone could not be observed, probably because of the strong chiral chromophoric pendants. However, in the AFM images, the helical polymers adsorbed on mica could be easily discerned as isolated strands, and the visualization and discrimination of the right- and left-handed helical structures of the chiral polymers were achieved by high-resolution AFM imaging. On the basis of the AFM observations together with the CD measurements and computational calculation results, possible structures of poly- 1 and poly- 2 were examined. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4621–4640, 2004     

Asymmetrically tilted alignment of rigid-rod helical polysilanes on a rubbed polyimide surface

The homogeneous alignments of helical rod-like polysilanes on a rubbed polyimide alignment layer were investigated by polarized optical microscopy (POM) and atomic force microscopy (AFM) analyses. The POM and AFM observations determined that polysilanes with a series of aliphatic side chains helically arranged around the main chains were tilted to the right and left by 33° from the rubbing direction when the handedness of the side-chain helical array is left and right, respectively. It is interesting to note that the side-chain arrays run perpendicular to the rubbing direction on the polyimide surface, which is different from intuitive "knob and hole" packing of the extended polyimide chain and the helical grooves between the side-chain arrays surrounding the polysilane backbone. More surprisingly, both right- and left-tilting smectic domains were simultaneously observed with an equal probability for an achiral polysilane, which apparently has the interconverting right- and left-handed helical segments separated by helical reversals. This might be the first observation of the chiral segregation of dynamic helical polymers.     

Photoinduced polymer-stabilised chiral nematic liquid crystal films reflecting both right- and left-circularly polarised light

A phototunable polymer-stabilised liquid crystal film reflecting both right- and left-circularly polarised light has been successfully fabricated by a washout/refill method. The film was obtained by prefabricating the polymer network with a left-handed helical structure and then refilling a light-driven chiral nematic liquid crystal with a right-handed helical structure into the network. Interestingly, the reflection wavelength and the reflectivity properties can be precisely tuned by UV-light irradiation. A hyper-reflective notch, the reflectivity of which approaches 100%, was achieved in a layer when the pitch lengths of the two opposite helical structures are almost the same. Moreover, their original state can be properly returned by visible-light irradiation.     

Synthesis of chiral azobenzene-based compounds for use in the photochemical tuning of the helical structure of liquid crystals

We have synthesized azobenzene-based molecules containing either one or two chiral groups. A cholesteric phase can be induced by adding the chiral azobenzene compounds to a host nematic liquid crystal. We investigated the effects of the trans - cis photoisomerization of the chiral azobenzene compounds on the properties of the cholesteric phase, such as the helical pitch length. This can be increased or decreased by the photoisomerization of the chiral azobenzene compounds. We discuss the photochemically driven change in the helical pitch of the cholesteric phase with respect to structural effects involving the chiral groups.     

Induction of Helical Structure by Sesamin,and Production of Oriented Helical Polymer with Liquid Crystal Magneto‐Electrochemical Polymerization

Sesamin was employed as a chiral dopant for preparing cholesteric liquid crystals with right‐handed helical architecture. Helical twisting power of sesamin is to be 13.4 μm^?1. Electrochemical polymerizations were carried out with sesamin‐induced cholesteric liquid crystal electrolyte solution for obtaining conjugated polymer films with helical structure. The film was transcribed the helical order from the liquid crystal electrolyte solution with helical structure produced by sesamin during the polymerization process. The helical axes of the macromolecular superstructure of the polymer films were oriented in a magnetic field of 4.5 T. This results demonstrated liquid crystal magneto‐electrochemical polymerization with helical structure induced by sesamin as a natural chiral compound. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 1894–1899     

Origin of strong chiroptical activities in films of nonafluorenes with a varying extent of pendant chirality

Novel nonafluorenes with a varying extent of pendant chirality were synthesized for an investigation of the origins of chiroptical activities in neat films. Thermal annealing of 4-microm-thick sandwiched films and of 90-nm-thick spin-cast films, all on surface-treated substrates, produced monodomain glassy films characterized as a right-handed cholesteric stack with a helical pitch length ranging from 180 to 534 nm and from 252 to 1151 nm, respectively. The observed strong circular dichroism (CD) and g(e) as functions of helical pitch length in single-substrate monodomain glassy cholesteric films were quantitatively interpreted with a circularly polarized fluorescence theory accounting for light absorption, emission, and propagation in a cholesteric stack. Although intertwined molecular helices were likely to be present, cholesteric stacking of rodlike molecules seemed to be the predominant contributor to the strong chiroptical activities. All the cholesteric stacks comprising a polydomain glassy film on an untreated substrate were found to contribute to CD and g(e) largely to the same extent as in a monodomain film. A circularly polarized blue organic light-emitting diode containing a nonafluorene film resulted in a g(e) of 0.35 with a luminance yield of 0.94 cd/A at 20 mA/cm(2), the best performance to date.     

Synthesis of chiral azobenzene-based compounds for use in the photochemical tuning of the helical structure of liquid crystals

We have synthesized azobenzene-based molecules containing either one or two chiral groups. A cholesteric phase can be induced by adding the chiral azobenzene compounds to a host nematic liquid crystal. We investigated the effects of the trans-cis photoisomerization of the chiral azobenzene compounds on the properties of the cholesteric phase, such as the helical pitch length. This can be increased or decreased by the photoisomerization of the chiral azobenzene compounds. We discuss the photochemically driven change in the helical pitch of the cholesteric phase with respect to structural effects involving the chiral groups.     

Helical pitch of ferroelectric liquid-crystalline polymers and copolymers

Ferroelectric liquid-crystalline polymers and copolymers were synthesized from acrylate polymers with side chains consisting of a flexible spacer unit, a mesogenic unit and an optically active substituent. In the chiral smectic C (S*_c) phases typical fan-shaped textures with equidistant lines (caused by the helical structures) were observed. It was found that the helical pitch increased with increasing polymer molecular weight. The helical pitch also increased in copolymers containing mixtures of right- and left-handed chiral side chains.     

Thermotropic cellulose derivatives with flexible substituents. III. Temperature dependence of cholesteric pitches exhibiting a cholesteric sense inversion

For the thermotropic cholesteric mesophase of tri-o-(β-methoxyethoxy)ethyl cellulose (DP = 11), cholesteric pitches larger than 2 μm were precisely determined by microscopic observation and their temperature dependence was examined in the temperature range from 80°C to 140°C. In the initial temperature region of 80°C to 106°C, the pitch increases with increasing temperature. After the pitch diverges at 106°C, it decreases as temperature is raised further. This anomalous temperature dependence of pitch was associated with a thermally-induced inversion from right- to left-handed helicoidal structure which was first observed in this kind of cellulose derivatives.     

High-Reflective Templated Cholesteric Liquid Crystal Filters

Cholesteric liquid crystals (CLCs) have been widely applied in optical filters due to Bragg reflection caused by their helical structure. However, the reflectivity of CLC filters is relatively low, commonly less than 50%, as the filters can only reflect light polarized circularly either left- or right-handedly. Therefore, a high-reflective CLC filter with a single-layer template was proposed which may reflect both right- and left-handed polarized light. The CLC filters of the red, green, blue color were fabricated by the templating technology, which show good wavelength consistency. Additionally, a multi-phase liquid crystal filter with high reflectance was demonstrated by the single-layer templating technology. The templated CLC or multi-phase liquid crystal filters show great potential applications in the optical community, reflective display, and lasing.     

Poly(α-isobutyl-β-D,L-aspartate)s: Polymerization effects on configuration and crystal structure of the stereocopolymers

Different polymerization methods were used for the preparation of poly(α-isobutyl-β-D ,L -aspartate)s containing variable ratios of D - to L -aspartic units and the microstructure of the resulting stereocopolymers was examined by NMR spectroscopy. Anionic ring-opening polymerization in solution of enantiomeric mixtures of α-isobutyl-β-D - and L -aspartalactams was found to proceed stereoselectively rendering block copolymers composed of right- and left-handed helical sequences. Configurationally statistical copolymers were obtained instead when the enantiomeric lactam mixtures were polymerized in the bulk. Random stereocopolymers could be prepared also by polycondensation in solution of mixtures of pentachlorophenyl α-isobutyl-β-D and -L -aspartates. The conformation in solution and the crystal structure of the resulting copolymers were investigated in connection with their stereochemical configuration and these features compared with those displayed by optically pure poly(α-isobutyl-β-L -aspartate). © 1996 John Wiley & Sons, Inc.     

Temperature‐Induced Chiroptical Changes in a Helical Poly(phenylacetylene) Bearing N,N‐Diisopropylaminomethyl Groups with Chiral Acids in Water

A stereoregular poly(phenylacetylene) bearing an N,N‐diisopropylaminomethyl group as the pendant (poly‐ 1 ) changed its structure into the prevailing one‐handed helical conformation upon complexation with optically active acids in water. The complexes exhibited induced circular dichroism (ICD) in the UV/Vis region of the polymer backbone. Poly‐ 1 is highly sensitive to the chirality of chiral acids and can detect a small enantiomeric imbalance in these acids, in particular, phenyl lactic acid in water. For example, a 0.005 % enantiomeric excess of phenyl lactic acid can be detected by CD spectroscopy. The observed ICD intensity and pattern of poly‐ 1 were dependent on the temperature and concentration of poly‐ 1 , probably due to aggregations of the polymer at high temperature as revealed by dynamic light scattering and AFM. On the basis of the temperature‐dependent ICD changes, the preferred chiral helical sense of poly‐ 1 was found to be controlled by noncovalent bonding interactions by using structurally different enantiomeric acids.