Liquid Crystalline Temperature Research Articles

Controllable Circularly Polarized Luminescence with High Dissymmetry Factor via Co-Assembly of Achiral Dyes in Liquid Crystal Polymer Films.

Circularly polarized luminescence (CPL) materials are highly demanded due to their great potential in optoelectronic and chiroptical elements. However, the preparation of CPL films with high luminescence dissymmetry factors (glum ) remains a formidable task, which impedes their practical application in film-based devices. Herein, a facile strategy to prepare solid CPL film with a high glum through exogenous chiral induction and amplification of liquid crystal polymers is proposed. Amplification and reversion of the CPL appear when the films are annealed at the chiral nematic liquid crystalline temperature and the maximal glum up to 0.30 due to the enhancement of selective reflection. Thermal annealing treatment at different liquid crystalline states facilitates the formation of the chiral liquid phase and adjusts the circularly polarized emission. This work not only provides a straightforward and versatile platform to construct organic films capable of exhibiting strong circularly polarized emission but also is helpful in understanding the exact mechanism for the liquid crystal enhancement of CPL performance.

Synthesis, Structural and Theoretical Analyses of C≡N···I Halogen-Bonded Liquid Crystalline Complexes of 4-Cyano-4′-alkoxy Biphenyl Systems

A series of 4-cyano-4′-alkoxybiphenyl compounds were synthesized by varying the spacer chain lengths (−CH2−)n, where n = 3–10, for the systematic study of a halogen-bonded (XB) complex with 1,4-diiodotetrafluoro benzene. The XB liquid crystalline complexes obtained from the liquid-assisted grinding method were characterized by FTIR, Raman, DSC, and PXRD studies. Further, C≡N···I XB interaction was established by single-crystal X-ray diffraction analysis. The odd-even analysis has suggested that the even carbon chain length containing XB liquid crystalline complexes shows slightly higher alteration in their isotropic temperature compared to the odd carbon chain lengths of such complexes. Furthermore, it is interesting to note that the higher alkyl chain complexes (n = 6–10) showed liquid crystalline temperature at lower values with respect to their ligands. The Hirshfeld and energy framework analyses have also been carried out to assess the stability and percentage contribution of XB noncovalent interaction. The frontier molecular orbital, noncovalent interaction, molecular electrostatic potential, and QTAIM analysis were performed using DFT to evaluate the nature of XB in these halogen-bonded liquid crystalline systems.

Effect of Different Polar Groups on the Mesomorphic and Physical Properties of Synthesized Schiff Base Liquid Crystalline Compounds

Five compounds of calamitic Schiff base with liquid crystalline behavior were synthesized and characterized. The terminal of compounds were substituted with different types of polar groups are - OCH3, -COCH3, - Br, and -COOC2H5, -CF3. The chemical structures of all compounds were characterized by FTIR spectroscopy while the phase transitions and optical textures of the samples were observed by polarized optical microscope. Furthermore, the transition temperatures of the compounds and their liquid crystalline temperature range were determined by using differential scanning coulometer. All compounds showed a higher tendency to exhibit an antiotropic nematic mesophases with different transition temperature range. Moreover, the dielectric and electrical conductivity were investigated. Using different polar groups in the synthesized liquid crystalline compounds is accompanied by significant changes in mesophase thermal stabilities as well as physical properties and all samples are with positive dielectric anisotropy.

Thermally stable birefringent films from a liquid crystalline polymer having side groups containing N-benzylideneaniline

Polymethacrylate liquid crystalline polymer having side groups containing N-benzylideneaniline moiety was synthesized, and its photoinduced reorientation behavior was investigated using linearly polarized UV light. Films of these polymer exhibited axis-selective trans-cis-trans photoreorientation of the side groups upon irradiation. Annealing the film in the liquid crystalline temperature range of the polymer after irradiation greatly amplified their otherwise minimal photo-induced optical anisotropy. Due to the extended mesogenic structure of the side groups, the polymer showed significant thermal stability and a high degree of optical anisotropy after annealing.

Self-assembly and ionic conductivity of phthalocyanine-containing liquid-crystalline compound films

A series of phthalocyanine-containing liquid-crystalline compounds (LCCs) are prepared by use of polystyrene sulfonic acid, copper phthalocyanine and an isonicotinate compound via self-assembly. The liquid crystal behavior of LCCs is identified using a polarizing microscope, differential scanning calorimetry, and X-ray diffraction measurements. The LCCs exhibit a helical columnar phase structure, and the liquid crystal behavior of the LCCs is adjusted by changing the composition of the compounds. A series of oriented LCC films are fabricated under different applied electric field intensity at liquid-crystalline temperature. The ionic conductivity is investigated by use of a Li solution passing through the orientated LCC films. Compared with the non-orientated samples, the samples orientated by 25 V/m of electric field show nearly 2-fold increase of conductivity, which is up to 4.0 × 10−4 S cm−1.

Synthesis and characterization of hexamethylenetetramine-based ionic liquid crystals

A series of hexamethylenetetramine-based ionic liquid crystals (ILCs) containing cholesterol derivatives and different anions including Br−1, BF4−1, PF6−1, H2PO4−, CF3COO−, TsO−, and CSA-SO3- were synthesized, and the characterization, possible applications and self-assembly behavior were discussed. The ILCs were synthesized from bromine-containing precursor liquid crystal, which was made of cholesterol and 4-bromobutyryl chloride. The ILCs showed smectic A (SmA) mesophase. For these hexamethylenetetramine-containing ILCs, Tg, Ti and liquid-crystalline temperature range reduced slightly in sequence of Br−1, BF4−1, PF6−1, H2PO4−, CF3COO−, TsO−, and CSA-SO3- anions. But the d-spacing of the lamellar structure in SmA phase increased in this sequence of these anions. Because of microphase separation and ionic electrostatic attraction, the SmA layers and self-assembly were formed in these ILCs. The ionic conductivities of the ILCs significantly increased in SmA phase due to unique facilitated ion transport pathways of lamellar ionic channels.

Terminal Effect of the Semi-fluorocarbon Chain on the Liquid Crystalline Behaviors of Some Compounds

Two series of chiral compounds with semi-perfluorocarbon chains and alkoxy ones, nBP4F and nBP6F, are synthesized. Enantiotropic SmA phase is identified in all of these compounds. When the alkoxy chain length is short, enantiotropic SmB is also identified. When the alkoxy chain length is longer than 6 carbons, enantiotropic SmC* phase is formed. Their clearing points increase with increasing the perfluorocarbon chain length. Comparison of compounds with -CF3, -CHF2 and -CF2Cl groups at the terminals of the fluorocarbon chains, the clearing point sequence is -CHF2 < -CF2Cl < -CF3; and the melting point sequence is -CF3 < -CHF2 < -CF2Cl. Therefore, the compounds with semi-perfluorocarbon chains show the widest liquid crystalline temperature range. Moreover, the SmC* phase of the compounds with -CF3 at the terminals shows the highest thermostability.

Synthesis and characterisation of two homologous series of LC acrylic monomers based on phenolic and resorcinic azobenzene groups

ABSTRACTThe synthesis and phase characterisation of two homologous series of monomers of acrylic azo-compounds has been presented. The characterisation comprises polarising optical microscopy (POM), differential scanning calorimetry (DSC) and powder X-ray diffractometry (PXRD). All studied monomers exhibit a narrow nematic phase with decrease in temperature range while increasing the alkoxy tail length. For the resorcinic azo benzenes at higher tail lengths, SmA and SmC phases are present. Phenolic azo compounds show only SmA phase. The resorcinic family showed more stable phases, with broader liquid crystalline temperature range than its phenolic equivalent.

The effect of thermal annealing on the layered structure of smectic liquid crystalline organic semiconductor on polyimide gate insulator and its OFET performance

The electrical performance of organic field-effect transistors (OFETs) depends on the quality of thin-film organic semiconductors, which is significantly affected by solution-processing conditions and additional processes. We investigated the effects of post-thermal annealing on the thin-film morphologies of liquid crystalline organic semiconductors on polyimide gate insulator surface and the FET performances of the films. The active material selected for the OFETs was 2-decyl-7-phenyl-[1]benzothieno[3,2-b][1]benzothiophene (Ph-BTBT-C10), which shows a highly ordered smectic E (SmE) mesophase and polycrystalline thin films feature very high mobility. We aimed to produce well defined molecular orientation and crystal structure in thin-film Ph-BTBT-C10 on polyimide gate insulator not typical SiO2 gate insulator via thermal annealing process. Uniform bilayer- or monolayer-structured polycrystalline thin films were obtained on polymer gate insulator after thermal annealing at a SmE (over 148°C) and SmA (over 213°C) liquid crystalline phase temperature, respectively. The OFET using bilayer-structured thin film showed high performance with a mobility of 2.27cm2/Vs.

ヒドロキシプロピルセルロースへの置換基の導入による液晶材料化&lt;br/&gt;&amp;mdash;熱的性質および配向挙動&amp;mdash;

Novel thermotropic liquid-crystalline cellulose derivatives were synthesized by the addition reaction of hydroxypropylcellulose with isocyanate. The liquid-crystalline cellulose derivatives exhibited columnar mesophases on heating and cooling. The cellulose derivatives formed a water-absorbing resin and their resinous gel films showed water-absorbency and stability with time. The resin plates of the cellulose derivatives were obtained by a hot press process at liquid-crystalline temperatures. They showed a tensile strength that was stronger than that of polypropylene.

Columnar liquid-crystalline metallomacrocycles.

We report synthesis of novel macrocyclic molecules and their metal complexes as well as their thermotropic columnar liquid-crystalline behavior. The macrocyclic ligands were prepared size-selectively based on dynamic covalent chemistry. X-ray study of a model macrocycle with short alkyl chains revealed that they were discrete and highly symmetric, with an inner vacant cavity of 9 Å diameter enclosed by a 56π planar ring composed of four bis(salicylidene)-o-phenylenediamine (salphen) moieties alternating with four carbazoles. Ni(2+) and Cu(2+) ions were incorporated into the four salphen ligands and formed square-planar metal complexes inside the macrocycles. From the structural and thermal analyses via X-ray diffraction measurements, differential scanning calorimetry, and polarized optical-microscopic observations, it was revealed that the macrocyclic ligand and its metal complexes self-assembled into columnar liquid-crystalline phases depending on the temperature and displayed a highly fluid character over a wide range of temperatures. The peripheral alkyl chains were influential in controlling the temperature range and flowability of the liquid-crystalline phases, and the range of the liquid-crystalline temperature of the metallo-macrocycles was significantly higher than those of the metal-free macrocycles. To the best of our knowledge, these are the first examples of thermotropic columnar liquid crystals of macrocyclic metal complexes with a large hollow area.

Molecular Reorientation Behavior of Photocrosslinkable Liquid Crystalline Copolymer Films Composed of 4-(4-Methoxycinnamoyloxy)biphenyl and Phenylester Side Groups

The cooperative molecular reorientation in methacrylate copolymer films comprising photoreactive 4-(4-methoxycinnamoyloxy)biphenyl and phenylester in their side chains was investigated by irradiation with linearly polarized ultraviolet light and subsequent annealing. Both cinnamate and phenylester side groups were miscible in the copolymer composition, and axis-selective photoreaction of the cinnamate groups was observed. Thermally enhanced cooperative in-plane orientation of both side groups was obtained when the irradiated films were annealed in the liquid crystalline temperature range of the copolymers.

Photoinduced Orientation of Photoresponsive Polymers with N-Benzylideneaniline Derivative Side Groups

Axis-selective photoreaction, photoinduced orientation, and formation of surface relief (SR) gratings of liquid crystalline polymethacrylates comprised of N-benzylideneaniline (NBA) derivative side groups are explored. Irradiating with linearly polarized (LP) 313 nm light generates molecular reorientation of the NBA side groups based on the axis-selective trans–cis–trans photoisomerization and photocleavage of the NBA groups. The in-plane order parameter (S) and birefringence (Δn) are ∼0.53 and ∼0.16, respectively. Furthermore, thermally stimulated amplification of the photoinduced optical anisotropy occurs upon exposing films to LP 313 nm light and subsequently annealing in the liquid crystalline temperature range of the material. The amplified S and Δn values are ∼0.71 and ∼0.21, respectively. Finally, polarization holography using 325 nm He–Cd laser beams with various interferometric polarization conditions demonstrates the formation of SR gratings with a molecularly oriented structure based on the per...

Synthesis and characterization of ferroelectric liquid crystalline organosiloxanes containing 4-(4-undecanyloxy bi-phenyl-1-carboxyloxy)phenyl (2S,3S)-2-chloro-3-methylvalerate and 4-(4-undecanyloxybenzoyloxy)biphenyl (2S,3S)-2-chloro-3-methylvalerate.

A series of new organosiloxane ferroelectric liquid crystalline (FLC) materials have been synthesized, and their mesomorphic and physical properties have been characterized. Four new disiloxanes and trisiloxanes, containing biphenyl 4-hydroxybenzoate and phenyl 4-hydroxybiphenylcarboxylate as mesogenic units and eleven methylene unit as spacers and (2S,3S)-2-chloro-3-methylvalerate unit as chiral end groups. The molecule, using three phenyl ring as a mesogenic unit, formulates much wider liquid crystalline phase temperature ranges than that of a two phenyl ring unit. The phenyl arrangement differences of mesogenic unit result in the greater differences of the liquid crystal phase formation. The siloxane molecule induction is helpful to the more regular smectic phase formation and smectic phase stabilization, such as chiral SC (SC*) and SB phases. The siloxane molecule is helpful to reduce the phase transition temperature and broaden the liquid crystal temperature range of the SC* phase and, simultaneously, it will not induce chain crystallization phenomenon and dilute the Ps value. The synthesis and characterization of the new FLCs materials, which exhibit a room temperature SC* phase and higher spontaneous polarization are presented.

Molecular reorientation behavior of photocrosslinkable liquid-crystalline polymer films containing phenylamide side chains

The cooperative molecular reorientation in methacrylate copolymer films comprising photoreactive 4-(4-methoxycinnamoyloxy)biphenyl and phenylamide in their side chains was investigated by irradiation with linearly polarized ultraviolet light and subsequent annealing. Both cinnamate and phenylamide side groups were miscible in the copolymer composition, and axis-selective photoreaction of the cinnamate groups was observed. Thermally enhanced cooperative in-plane orientation of both side groups was obtained when the irradiated films were annealed in the liquid-crystalline temperature range of the copolymers.

Main-chain liquid crystalline copolyesters with a phosphorus-containing non-coplanar moiety

A series of phosphorus-containing main-chain thermotropic liquid crystalline copolyesters named poly(4,4′-biphenylene decanedioate-co-4,4′-(phenylphosphoryl)dibenzoate) (PBPDP) were synthesized by random polycondensation from mesogenic diol 4,4′-biphenol (BP), decanedioic acid (DA) and phosphorus-containing non-coplanar diacid named 4,4′-(phenylphosphoryl)dibenzoic acid (PPDBA). Chemical structures and physical properties of PBPDPs were characterized by Fourier-transform infrared spectroscopy (FTIR), proton and 31P nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC) and X-ray diffraction (WAXD). Thermal stability of the copolyesters was determined via thermogravimetric analysis (TGA), and the liquid crystalline behaviours were observed using polarizing optical microscopy (POM). Results showed that the introduction of PPDBA into the copolyester could decrease the liquid crystalline temperature (Tlc) and the isotropic temperature (Ti) as a result of both copolymerization and the non-coplanar structure of PPDBA; furthermore, when the molar ratio of PPDBA reached 15%, the copolyester turned into a semi-crystalline polymer and lost its liquid crystallinity. Thermal stability of the copolyester increased with increasing the content of PPDBA, due to the positive contribution of the phosphorus-containing structure.

38.1: Highly Thermally‐Stable OFETs Fabricated with Liquid Crystalline Organic Semiconductors

AbstractWe have developed a new soluble FET material having a highly ordered smectic liquid crystal phase of a phenyl and alkyl‐substituted benzothienobenzothiophene derivative, Ph‐BTBT‐10. This BTBT derivative had high processability for solution processes and highly thermal stability thanks to the solid‐like nature of the highly ordered smectic phase. Polycrystalline thin films of ph‐BTBT‐10 spin‐coated at a liquid crystalline temperature of 110 °C were uniform in macroscale and molecularly flat in microscale, and FETs fabricated with the thin films showed high FET mobility of 5.7 cm2/Vs, kept high mobility of 3 cm2/Vs after the thermal stress for 5 minutes up to 150 °C, and still operated even after thermal stress at 170°C.

Mesogen induced self-assembly for hybrid bulk heterojunction solar cells based on a liquid crystal D–A copolymer and ZnO nanocrystals

A new donor–acceptor type liquid-crystalline copolymer, poly[3-(6-(cyanobiphenyoxy)thiophene)-alt-4,7-(benzothiadiazole)], P3HbpT-BTD, was designed via copolymerization of liquid-crystalline electron-donating thiophene units and electron-accepting benzothiadiazole (BTD) units. The nanostructure and photoelectric properties of the copolymer under different thermal treatment conditions were systematically investigated. Studies of the relationship between the annealing conditions and the nanostructures of the copolymer revealed that the cyano-biphenyl mesogenic units could induce the copolymer chains into a well ordered lamella structure upon annealing at the liquid crystalline state temperature. When the hybrid films of P3HbpT-BTD/ZnO nanoparticles (NPs) were annealed at a temperature below or above the mesophase temperature region, less ordered copolymer chains resulted in an undeveloped interpenetrating network and caused great aggregation of ZnO NPs. Most strikingly, the hybrid film annealed at the liquid-crystalline state temperature (180 °C) achieved a well-dispersed and highly oriented nanoscale assembled nanoparticle region. The spontaneous self-organization of P3HbpT-BTD enhanced the crystallinity and orientation of the ZnO NPs. Therefore, the resulting nanoscale phase separation of the hybrid films led to well-ordered percolated networks. Hybrid bulk heterojunction photovoltaic devices based on the copolymer P3HbpT-BTD and ZnO NPs were fabricated under different annealing treatments. A maximum power conversion efficiency of 1.98% was achieved upon annealing at the mesophase temperature (180 °C).

Axis-Selective Photo-Fries Rearrangement and Photoinduced Molecular Reorientation in Liquid Crystalline Polymer Films

The thermally enhanced photoinduced molecular reorientation based on an axis-selective photo-Fries rearrangement was explored for the first time using three liquid crystalline polymethacrylates with 4-(2′-(4″-methoxyphenyl)ethynyl)phenyl benzoate side groups (1a), 4-methoxybiphenyl benzoate side groups (1b), and 4-methoxyphenyl benzoate side groups (1c). All the polymeric films exhibited an axis-selective formation of the photo-Fries products at the phenyl benzoate derivatives side groups by irradiating with linearly polarized (LP) UV light. Annealing the films in the liquid crystalline temperature range of the material greatly amplified the photoinduced small optical anisotropy of the irradiated films. For 1a and 1b, the photoinduced small anisotropy was amplified in a direction parallel to the polarization (E) of LPUV light and the reorientational order (S) was greater than 0.7. In contrast, the orientation direction was perpendicular to E for 1c (S ∼ 0.57). Finally, a simple double-exposure method usin...

Diethynylbenzene-Based Liquid Crystalline Semiconductor for Solution-Processable Organic Thin-Film Transistors

We report here the synthesis and characterization of novel diethynylbenzene-based liquid crystalline semiconductor (P1) for organic thin-film transistors (OTFTs). Compound P1 was synthesized by the Sonogashira coupling reaction between 2-bromo-5-(4-hexylthiophen-2-yl)thieno[3,2-b]thiophene and 1,4-bis(dodecyloxy)-2,5-diethynylbenzene. Top contact OTFTs were fabricated by spin casting with 2 wt% solution of P1 in chloroform and their best performance, which exhibited a hole mobility of 4.5 x 10(-5) cm2/Vs, was showed after annealing of the films at liquid crystalline temperature. Time-of-flight (TOF) mobility measured at liquid crystalline phase was observed to be 1.5 x 10(-6) cm2/Vs for both positive and negative carriers. These results indicate that the liquid crystallinity helps to improve the molecular packing and enhance charge mobility for P1. These advantages can be applicable to design and construct solution-processable OTFT materials for electronic applications.