Liquid Crystalline Polyacetylene Research Articles

Phase Behaviors of Side-Chain Liquid Crystalline Polyacetylenes with Different Length of Spacer: Where Will the Decoupling Effect Appear?

Phase structures and transitions of a series of biphenyl containing side-chain liquid crystalline polyacetylenes (SCLCPAs) with different length of spacer and alkyl tail, poly((m + 2)-{[(4′-alkyloxy-4-biphenylyl)carbonyl]oxy}-1-yne) [P-m,7 (m = 4, 5, 8), P-m,5 (m = 9), P-m,5L (m = 3, 9), m is the number of methylene units in the spacer], were studied by differential scanning calorimeter, polarized light microscopy, one- and two-dimensional wide-angle X-ray diffraction. It is revealed that phase structures of the samples are strongly dependent on the lengths of spacer and alkyl tail. The samples with short spacer (m ≤ 4) render the molecular shape of sheet-like due to the strong coupling between the backbone and the biphenyl groups on side-chains. They form highly ordered smectic phase with an additional ordering on the subnanometer scale (SmXo) at low temperatures. For m > 5, P-m,7 exhibits the low-temperature phase of smectic B (SmB), while P-9,5 and P-9,5L form smectic E (SmE). As the long spacers adopt...

Self-Organized Columnar Phase of Side-Chain Liquid Crystalline Polymers: To Precisely Control the Number of Chains Bundled in a Supramolecular Column

Self-organization of liquid crystalline (LC) polyacetylene derivatives (PAs) bearing hemiphasmid side-chains was investigated. The synthesized PAs can form smectic and columnar phases, depending on the constitutions of side chains. With a nanosegregation structure, the columnar phase of PAs takes a bundle of chains as its building block, of which the chain number is precisely determined by the volume fraction of the rigid component in PAs. The "precise multi-chain column" can be understood using a mean field theory, from which the deduced number of chains in the supramolecular column agrees well with the experimental result. This study reveals that the volume fraction of the rigid component plays a significant role in the self-organization of side-chain LC polymers, which is valuable for the rational design of macromolecules with precisely ordered structures.

Dynamic switching of the circularly polarized luminescence of disubstituted polyacetylene by selective transmission through a thermotropic chiral nematic liquid crystal.

The circularly polarized luminescence (CPL) of chiral disubstituted liquid-crystalline polyacetylene (di-LCPA) can be dynamically switched and amplified from left- to right-handed CPL and vice versa through the selective transmission of CPL across a thermotropic chiral nematic liquid crystal (N*-LC) phase. By combining a chiral di-LCPA CPL-emitting film with an N*-LC cell and tuning the selective reflection band of the N*-LC phase to coincide with the CPL emission band, a CPL-switchable cell was constructed. The phase change induced by the thermotropic N*-LC cell by varying the temperature leads to a change in the selective transmission of CPL, which enables the dynamic switching and amplification of CPL. It is anticipated that CPL-switchable devices might find applications in switchable low-threshold lasers and optical memory devices.

Side-Chain Liquid Crystalline Polyacetylenes with Increasing Length of Alkyl Tails: From Highly Ordered Smectic to Smectic C Phase

Phase structures and transitions of a series of side-chain liquid crystalline polyacetylene (SCLCPA) with a short spacer of three methylene units and different lengths of alkyl tails, namely, poly(5-{[(4′-alkyl-4-biphenylyl)carbonyl]oxy}-1-pentyne) (P-3,m, m is the number of the carbon atoms in the alkyl tail, m = 5, 7, 9, 11), were investigated using differential scanning calorimeter, polarized light microscopy, and one- and two-dimensional wide-angle X-ray diffraction. With the short spacer, P-3,m possesses the mesogenic groups on the side chain and polyacetylene backbone coupled together and thus renders sheetlike shape with the width nearly twice of the extended side-chain length. Experimental results reveal that the liquid crystalline (LC) structure of P-3,m is strongly dependent on the side-chain tail length, different from that of other SCLCPAs. For m < 11, several layers of the sheetlike P-3,m molecules stack together to form a smectic A (SmA) block, and the number of molecular layers increases with increasing m. The adjacent SmA blocks slide halfway to each other, leading to a highly ordered smectic phase with frustrated molecular packing at low temperatures. The enantiotropic phase transition sequence of P-3,m (m < 11) follows: highly ordered smectic with additional ordering on the subnanometer scale ↔ highly ordered smectic ↔ semctic C (SmC) ↔ isotropic. However, when m is increased to 11, the packing of sheetlike P-3,11 gives the SmC phase, with the transition sequence of SmC with additional ordering on the subnanometer scale ↔ SmC ↔ isotropic. The phase structures of P-3,m were studied by computer modeling. The phase changing from the highly ordered one to SmC with increasing m may be ascribed to that the P-3,11 molecules intend to maximize the interaction between the biphenyl moieties in neighboring chains. We also investigated the orientation behavior of the highly ordered smectic phase under electric field, wherein a unique striplike texture was well developed, with the side chain and main chain parallel and perpendicular to the electric field, respectively.

Liquid crystalline polyacetylene derivatives with advanced electrical and optical properties

Herein, we review the recent progress in advanced functionalities of liquid crystalline polyacetylenes (LCPAs). We focus on properties and functionalities that include (i) electrical anisotropy, (ii) linearly polarised luminescence (LPL), and (iii) circularly polarised luminescence (CPL). In Section 2, mono-substituted LCPAs are macroscopically aligned by magnetic force, which results in enhancement of the electrical conductivity by two orders of magnitude. In Section 3, di-substituted LCPAs are macroscopically aligned using a rubbing technique to exhibit LPL with notable dichroic ratios. In Section 4, lyotropic di-substituted LCPAs are induced with chiral moieties or chiral dopants, leading to the formation of a N*-LC phase. The high degree of helical ordering in the N*-LC phase is indispensable for the generation of CPL with a large value of the dissymmetry factor in emission (gem).

Mesogen jacketed liquid crystalline polyacetylene containing triphenylene discogen: synthesis and phase structure

Triphenylene-containing acetylenes with one or three methylene units as spacers and the corresponding mesogen-jacketed liquid crystalline polyacetylenes (MJLCPAs) were designed and synthesized, the mesomorphic properties and phase behaviors of the monomers and novel side-chain liquid crystalline polymers were investigated. The monomers [HCC(CH2)mC18H6(OC6H13)5; m = 1, 3] are prepared by consecutive etherization, coupling, and etherization reactions, and the chemical structures were confirmed by mass spectroscopy and 1H/13C-NMR. The phase behaviors of the monomers were investigated by differential scanning calorimetry (DSC), polarized light microscopy (PLM), and wide-angle X-ray diffraction (WAXD). The results show that both of the monomers form a hexagonal columnar liquid crystal phase at room temperature. The monomers are polymerized using [Rh(nbd)Cl]2 as catalyst and producing soluble polymers in the yields of 55% and 52%, respectively. The chemical structures and phase behaviors of the two polymers are characterized and evaluated by IR, NMR, TGA, DSC, and WAXD analyses. Both of the two polymers show enhanced thermal and chemical stability with thermal decomposition temperatures up to higher than 340 °C due to the protection of the “jacketed effect” of the side-chain triphenylenes wrapped around the rigid polyacetylene main-chain. The polymers adopt a columnar shaped structure and self-organized into hexagonally packed columnar phase. The relative electron density maps of the columnar structure are also reconstructed.

Lyotropic Chiral Nematic Liquid Crystalline Aliphatic Conjugated Polymers Based on Disubstituted Polyacetylene Derivatives That Exhibit High Dissymmetry Factors in Circularly Polarized Luminescence

We synthesized disubstituted liquid crystalline polyacetylene (diLCPA) derivatives bearing 4-nonyloxy phenyl groups with lyotropic and thermotropic LC behavior. The poly(diphenylacetylene) main chain structure of the diLCPAs and the chirality induced with either chiral moieties or chiral dopants allow the formation of a highly ordered lyotropic N*-LC phase. Circular dichroism (CD) spectra of the diLCPAs imply that one-handed intrachain helical structures are formed in solution, while interchain helical π-stacking between the polymer main chains are formed in cast film and in the N*-LC state. Absorption dissymmetry factors (g(abs)) in the N*-LC state show values on the order of 10(-1). The N*-LC state facilitates the formation of helically π-stacked structures with a high degree of helical ordering of the diLCPA and is indispensable for the generation of circularly polarized luminescence (CPL) with high emission dissymmetry factors (g(em)) on the order of 10(-1). To the best of our knowledge, this is the highest reported value of CPL achieved for aliphatic, conjugated polymers. As an alternative to the thermotropic N*-LC phase, we have found that the lyotropic N*-LC phase of diLCPA could be promising materials possessing CPL functionality for use in next-generation π-conjugated organic optoelectronic devices, displays, and sensors.

Synthesis of Liquid Crystalline Polyacetylene Containing Chiral Terphenyl and&amp;amp;nbsp;Its &amp;ldquo;Jacket Effect&amp;rdquo;

Synthesis of Liquid Crystalline Polyacetylene Containing Chiral Terphenyl and&amp;amp;nbsp;Its &amp;ldquo;Jacket Effect&amp;rdquo;

Disubstituted Liquid Crystalline Polyacetylene Derivatives That Exhibit Linearly Polarized Blue and Green Emissions

We synthesized disubstituted liquid crystalline polyacetylene (di-LCPA) derivatives by polymerizing acetylene derivatives consisting of LC moieties either directly or indirectly attached to the main chain through flexible alkyl spacers. The di-LCPA derivatives show either enantiotropically thermotropic LC or lyotropic LC behavior. The origin of emission of substituted PAs, with respect to their substituents and structure, was elucidated. Depending on the substituents of the side chains, the polymers exhibit blue (470–485 nm) and green (500–540 nm) photoluminescence (PL) in chloroform and in cast film. The di-LCPA derivatives were macroscopically aligned using rubbing technique, and the aligned structures of the polymers are characterized in terms of main chain and side chain type alignments through XRD measurements. The emission color and alignment direction toward an external force in the di-LCPA derivatives are crucially determined by both the linkage forms (direct or indirect attachment) between the main chain and side chains and the molecular moieties (alkyl or aromatic moiety) of the side chains. The macroscopically aligned films of the polymers exhibit linearly polarized photoluminescence (LPL) with notable dichroic ratios. We fabricate multilayer electroluminescence (EL) devices using the polymers as the emissive polymer layer that emit 480 nm light with promising EL properties. We emphasize that although substituted PA derivatives are usually nonluminescent, the di-LCPA derivatives emit intense fluorescence with notable linear dichroism, and they could be promising for optically anisotropic luminescent materials.

Synthesis and properties of novel ferroelectric liquid crystalline polyacetylenes containing terphenyl mesogens with chiral groups

Novel ferroelectric liquid crystalline (FLC) polyacetylenes, namely, “side-end-fixed” type of PAM 6 OTPhOR* and “side-on-fixed” type of PAM 3 OCO(TPh)OR* were designed and synthesized in high yields (89.3 and 62.0%), respectively, where the terphenyl was linked at the different positions. The thermal stability of PAM 3 OCO(TPh)OR* is better than PAM 6 OTPhOR* owing to the “jacket effect” from terphenyl pendant linked at the waist position well protecting the main chain from the perturbations. The PAM 3 OCO(TPh)OR* shows enantiotropic chiral smectic A phase (SmA*), but it is noteworthy that the PAM 6 OTPhOR* exhibits enantiotropic chiral smectic C phase (SmC*) responsible for ferroelectric liquid crystallinity. Compared to “side-end-fixed” type of polymer, the “side-on-fixed” type shows better light emitting property, ascribed to the mesogen linked at the waist position has stronger tendency to enhance the main-chain coplanarity. Furthermore, the circular dichroism (CD) spectra demonstrate that the asymmetric force field generated by the chiral center affects the secondary structure of PAM 3 OCO(TPh)OR*. Novel ferroelectric liquid crystalline polyacetylenes (PAM 6 OTPhOR* and PAM 3 OCO(TPh)OR*) containing terphenyl pendants with chiral end groups were synthesized. The “side-on-fixed” type of PAM 3 OCO(TPh)OR* showed enantiotropic SmA*, but it is noteworthy that the “side-end-fixed” type of PAM 6 OTPhOR* showed enantiotropic SmC* responsible for ferroelectric liquid crystallinity. Compared to “side-end-fixed” type of polymer, the “side-on-fixed” type shows better light emitting property ascribed to the mesogen linked at the waist position have stronger tendency to enhance the main-chain coplanarity.

Smectic Aggregates of Sheet-Like Side-Chain Liquid Crystalline Polyacetylenes Directly Formed During Solution Polymerization

We have successfully synthesized two side-chain liquid crystalline polyacetylenes (denoted as P3-5 and P2-5) with the mesogenic units based on a “phenyl−ester−phenyl” motif directly linked to the semirigid polyacetylene backbone in a terminal-on mode without flexible spacer. During the polymerization catalyzed by Rh(nbd)[B(C6H5)4] in toluene, the resultant polymers (or oligomers) automatically precipitate out of the polymerization solution as red solids, which cannot be dissolved in common organic solvents. Wide-angle X-ray diffraction results confirm that the polymer precipitates possess a smectic (or sanidic) structure, suggesting that the molecules without flexible spacers are sheet-like and can stack parallel to each other during polymerization. We in situ monitored the solution polymerization and the aggregation processes using UV−visible and 1H NMR spectroscopy methods. The experimental results indicate that after reaching a critical molecular weight the P3-5 and P2-5 molecules self-aggregate in sol...

Phase Transitions and Structures of 5-{[(4’-Pentyloxy-4-biphenylyl)carbonyl]oxy}-1-pentyne

Phase transitions and structures of the monomer of side-chain liquid crystalline polyacetylene containing biphenyl mesogen,namely,5-{[(4'-pentyloxy-4-biphenylyl)carbonyl]oxy}-1-pentyne (A3EO5) were investigated by differential scanning calorimetry (DSC),one dimensional (1D) wide angle X-ray diffraction (WAXD),and polarized light microscopy equipped with hot-stage (PLM-hot stage).DSC and 1D-WAXD results show that A3EO5 forms an enantiotropic liquid crystal and displays four transitions during the cooling and subsequent heating processes.Upon cooling from isotropic phase to room temperature,the sample forms smectic A phase and then leads to smectic B phase with pseudo long-range orientation within the layer structure,further lowering the temperature,A3EO5 forms smectic E phase with orthorhombic packing within the smectic layer and enters crystal phase.PLM results show that the sample forms spherulitic texture,focal conic texture and concentric arcs texture during the cooling process.

Fluorescence Behavior of Biphenyl Containing Side-Chain Liquid Crystalline Polyacetylene with Various Lengths of Spacers

Steady state fluorescence and fluorescence decay of a series of monosubstituted biphenyl containing side-chain liquid crystalline polyacetylenes with different lengths of spacers were investigated. For comparison, a monomer was selected as a model compound. Steady state fluorescence spectra elucidated that the polymers and the monomer showed single fluorescence emission arising from the biphenyl group on the side chain. With decreasing the length of the spacer, the fluorescence intensity of the polymer decreased accordingly. The fluorescence decay showed that the decay of the monomer could be fitted to be a single-exponential decay, while that of the polymers should be fitted to be a triple-exponential decay, which may be originated from the local high concentration induced quenching and the rotational restriction of the side-chain biphenyl groups. Solvent effects illustrated that the interaction between the solvents and the biphenyl groups strengthened with increasing the polarity of the solvents.

Synthesis and hierarchical superstructures of side‐chain liquid crystal polyacetylenes containing galactopyranoside end‐groups

AbstractThree kinds of chiral saccharide‐containing liquid crystalline (LC) acetylenic monomers were prepared by click reaction between 2‐azidoethyl‐2,3,4,6‐tetraacetyl‐β‐D‐galactopyranoside and 1‐biphenylacetylene 4‐alkynyloxybenzoate. The obtained monomers were polymerized by WCl6‐Ph4Sn to form three side‐chain LC polyacetylenes containing 1‐[2‐(2,3,4,6‐tetraacetyl‐β‐D‐galactopyranos‐1‐yl)‐ethyl]‐1H‐[1,2,3]‐triazol‐4′‐biphenyl 4‐alkynyloxybenzoate side groups. All monomers and polymers show a chiral smectic A phase. Self‐assembled hiearchical superstructures of the chiral saccharide‐containing LCs and LCPs in solution state were studied by field‐emission scanning electron microscopy. Because of the LC behavior, the LC molecules exhibit a high segregation strength for phase separation in dilute solution (THF/H2O = 1:9 v/v). The self‐assembled morphology of LC monomers was dependent upon the alkynyloxy chain length. Increasing the alkynyloxy chain length caused the self‐assembled morphology to change from a platelet‐like texture (LC‐6) to helical twists morphology (LC‐11 and LC‐12). Furthermore, the helical twist morphological structure can be aligned on the polyimide rubbed glass substrate to form two‐dimensional ordered helical patterns. In contrast to LC monomers, the LCP‐11 self‐assembled into much more complicate morphologies, including nanospheres and helical nanofibers. These nanofibers are evolved from the helical cables ornamented with entwining nanofibers upon natural evaporation of the solution in a mixture with a THF/methanol ratio of 3:7. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6596–6611, 2009

Micropatterning of liquid crystalline polyacetylene derivative by using self-organization processes

Side-chain type liquid crystalline polyacetylene, which has mesogenic moieties as side chains, is one of the promising materials for practical applications in the electronics. Micropatterning of the conductive polymer is a significant issue in this field. We show a simple method to fabricate micropatterns of side-chain type liquid crystalline polyacetylene derivative. Under dry condition, stripes patterns and lattice pattern were formed based on the fingering instability and stick-slip motion of the receding meniscus. Honeycomb-patterned polymer film was obtained by casting polymer solution under humid condition. The micropatterns drastically changed by changing solution concentration and preparation conditions.

Sheetlike Side-Chain Liquid Crystalline Polyacetylenes Forming Monolayer Lamellae in Dilute Solutions

Self-assembly behaviors of a series of hydrophobic side-chain liquid crystalline (LC) polyacetylenes, namely, poly(5-{[(4‘-alkoxy-4-biphenylyl)carbonyl]oxy}-1-pentyne)s [P-3,m (m = 5, 7, 9)], were studied in dilute solutions. The assembly was induced by tuning the solvent property to be selective for the alkyl tails on the side chains, with the processes characterized by turbidity, dynamic light scattering, 1H NMR, and excitation fluorescence anisotropy measurements. The morphology and structure of the P-3,m aggregates formed in the solutions were investigated using atomic force microscopy and wide-angle X-ray diffraction. The experimental results indicate that the P-3,m polymers can form monolayer lamellae in selective solvents. In the lamella, the P-3,m molecules are sheetlike and pack parallel to each other with their backbones located in the lamellar center and their alkyl tails covering the top and bottom lamellar surfaces. The lamellar thickness is largely determined by the width of the molecular sheet. When the solvent becomes selective for the tails, the P-3,m chains may undergo shape stiffening to become more sheetlike.

Synthesis and properties of mono-substituted liquid crystalline polyacetylene derivatives—doping, magnetic orientation, and photo-isomerization

Mono-substituted acetylene monomers with a liquid crystalline (LC) group are polymerized using rhodium, iron or molybdenum complex catalysts. LC polyacetylene derivatives with number-averaged molecular weights of 4000–330000 were obtained in 5–92% yield. The LC behavior is examined by X-ray diffraction, differential scanning calorimetry, and polarizing optical microscopy. The polymers prepared using rhodium or iron catalyst are confirmed to assume a cis form and to undergo an irreversible isomerization to the trans form upon heating. Photo-responsive polyacetylene derivatives are successfully synthesized through the introduction of an azobenzene moiety as a mesogenic core into the side-chain, and these forms exhibit a reversible photochemical cis-to- trans isomerization of the azobenzene moiety.

Synthesis and Properties of Polymers from Monosubstituted Acetylene Derivatives Bearing Ferroelectric Liquid Crystalline Groups

Novel liquid crystalline polyacetylene derivatives were developed as advanced LC conjugated polymers with quick response to an electric field used as external force. In practice, we synthesized ferroelectric LC conjugated polymers by introducing fluorine-containing chiral LC groups into side chains of polyacetylenes. Phase-transition behaviors of these polymers were examined by differential scanning calorimetry and polarizing optical microscopy. Mesophases as well as higher order structures were evaluated with X-ray diffraction measurements. The polymers synthesized showed chiral nematic (N*), twist grain boundary smectic A (TGBA*), and chiral smectic (SmC*) phases in the heating and cooling processes. Observation of the SmC* phase allows us to expect that the polymer should exhibit ferroelectricity.

Shear induced molecular alignments of a side-chain liquid crystalline polyacetylene containing biphenyl mesogens

Mesomorphic properties of a side chain liquid crystalline polyacetylene, poly(11-{[(4′-heptyloxy-4-biphenylyl)carbonyl]oxy}-1-undecyne) (PA9EO7), are investigated using polarized optical microscope, X-ray diffraction, and transmission electron microscope. Polymer PA9EO7 forms enantiotropic smectic A and smectic B phases. It also exhibits an additional high order smectic phase, a sandwich structure consisting of different molecular packing of biphenyl mesogenic moieties from that of alkyl spacers and terminals, when it is prepared from its toluene solution. Shearing the polymer film at its smectic A phase generates banded texture with the alignment of the backbones parallel to the direction of shear force. While at its high order smectic phase, the mesogen pendants of the polymer are arranged parallel to the direction of shear. The different mesomorphic behaviors arise from different molecular alignments influenced by the fluidity.

Polyacetylenes bearing mesogenic side groups: synthesis and properties. Part 3. Influence of flexible spacer length and tail functionality

We report on the synthesis of some novel liquid crystalline polyacetylenes derived from monosubstituted acetylenic monomers where the acetylenic moiety is linked through a short spacer (one or three methylene units and an ether bridge) to a biphenyl mesogenic core. The influence of length and functionality of the terminal groups on the thermal behaviour and on the nature of the mesophases is discussed. All the monomers show liquid crystalline behaviour. Polymerisations are carried out in solution with typical metathesis catalysts based on Mo and W and yield polyacetylenes with fairly high MW soluble in common organic solvents. Polymers are fully characterised by GPC, FT-IR, and 1H NMR techniques; their thermal and morphological behaviour has been studied by TGA, DSC, POM and X-ray diffraction experiments.