Liquid Crystalline Behavior Research Articles

Synthesis and characterisation of asymmetrical mesogenic materials based on 2,5-disubstituted-1,3,4-oxadiazole

ABSTRACTNew mesogenic homologous series bearing 1,3,4-oxadiazole ring with a nitro terminal group, 4-(5-(4-nitrophenyl)-1,3,4-oxadiazol-2-yl)phenyl 4-((4-methoxybenzylidene)amino)benzoate (G1–G11), were synthesised. Their chemical structures are identified by fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance (1H-NMR) and elemental analysis. The liquid crystalline properties of the series Gn and their precursory Fn were screened by differential scanning calorimetry and optical polarising microscopy (OPM). The compounds of the series Gn were screened by thermogravimetric analysis to observe their thermal stability. The target compounds (Gn) in this study, were displayed different liquid crystalline mesophase, the first two homologous (G1 and G2) did not show any liquid crystalline behaviour, the homologous (G3–G10) which have an alkoxy terminal group (n = 3–10) exhibited nematic phase, whilst the last derivative of the series (G11), n = 12, displayed SmA phase. The mesomorphic properties of these derivatives were affected by the presence of the nitro group at the end of the molecules which was classified as a strong polar group. Also, the role of alkoxy terminal chain and the bent heterocyclic ring (1,3,4-oxadiazole) in the liquid crystalline properties of these molecules were debated.

The smectic order of wrinkles

A thin elastic sheet lying on a soft substrate develops wrinkled patterns when subject to an external forcing or as a result of geometric incompatibility. Thin sheet elasticity and substrate response equip such wrinkles with a global preferred wrinkle spacing length and with resistance to wrinkle curvature. These features are responsible for the liquid crystalline smectic-like behaviour of such systems at intermediate length scales. This insight allows better understanding of the wrinkling patterns seen in such systems, with which we explain pattern breaking into domains, the properties of domain walls and wrinkle undulation. We compare our predictions with numerical simulations and with experimental observations.

Efficient and practical method for the synthesis of hydrophobic azines as liquid crystalline materials

ABSTRACTA series of hydrophobic symmetrical azines: 1,2-bis[4-(n-alkoxy)benzylidene]hydrazine (where, n-alkoxy: O(CH2)nH, n = 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 16, or 18) have been prepared following an efficient and practical method. These compounds have been synthesized via the condensation reaction of hydrazine hydrate and appropriately 4-(n-alkoxy) benzaldehydes in acidic medium under ambient conditions. The prepared organic compounds have been characterized and their structures were elucidated depending upon micro-elemental analysis and spectral data (IR, UV-Vis, 1HNMR, 13C{1H}NMR, 2D 1H-1H-cozy, 2D 1H-13C-HSQC, and mass spectra). Liquid crystalline behavior of the prepared compounds was studied using polarized light optical microscopy and differential scanning calorimetry techniques. This study revealed that all the compounds displayed enantiotropic liquid crystal properties, exhibiting smectic and nematic mesophases.

Synthesis of vinyl-functionalized azobenzene mesogens and study of their liquid-crystalline behavior

ABSTRACTFour vinyl-functionalized azobenzene-based liquid crystals (LCs) were synthesized and characterized by 1H and 13C nuclear magnetic resonance, and Fourier transform infrared spectroscopies. Their thermal stability was measured by thermogravimetric analysis and their thermotropic liquid-crystalline properties were determined by differential scanning calorimetry (DSC), polarized optical microscopy (POM), and X-ray diffraction (XRD). The azobenzene-based LCs displayed a nematic phase whereas those mesogens having an extra phenyl group developed lamellar mesophases of the SmA and SmC types. Combined with non-photoactive monomers, these vinyl-functionalized azobenzene-based mesogens can be used to prepare photo-active side-chain liquid crystal elastomers having potential use in optical actuators.

λ-Shaped liquid crystal trimers with dual terminal cholesteryl moieties: synthesis and concomitant of N*, SmA and cholesteric glassy phases

ABSTRACTTwo homologous series of λ-shaped chiral liquid crystal trimers composed of a laterally substituted benzylidene-aniline as the central core armed by two cholestryl ester moieties via odd-even alkyl spacer are synthesised. All the compounds are mesogenic exhibiting both chiral nematic (N*) and SmA phases except for trimers bearing long spacers (n = 9–10). A pronounced odd-even effect is observed on the phase transition temperatures and clearing enthalpies when the spacer length is varied in which the even-parity members show higher value. The widening of N* phase upon elongation of the alkyl spacer can be interpreted as a result of the destabilisation of SmA phase. Full recrystallisation from the cholesteric phase upon cooling is not observed for all the compounds bearing long spacer, especially oxydecanoyl spacer. Instead, the anisotropic fluid vitrified to form the cholesteric glassy state characteristic of polymer at low temperature. This finding is also evident from the polarising optical microscope whereby non-crystalline texture which resembles the Grandjean texture with various reflection colours is observed upon cooling to low temperature. The effect of the lateral substituents on the liquid-crystalline behaviour is also discussed.

Discotic Liquid Crystals with Graphene: Supramolecular Self‐assembly to Applications

In past decades many breakthroughs have been witnessed in research on liquid crystals (LCs) and the application of LCs has spread. On another side graphene is considered as a rapidly rising star on the horizon of materials science, soft condensed matter physics and promising applications. Supramolecular chemistry of LCs and graphene together is described as “chemistry beyond the molecule”. A new class of 2D colloidal graphene oxide liquid crystalline material consisting discotic liquid crystallinity and their interactions with LCs present a platform for number of versatile properties and applications. This review focuses on discotic liquid crystalline (DLC) behavior of graphene oxide/reduced graphene oxide in various solvents, their characterization and application for energy storage, wet‐spinning fibers, electro‐optical devices, and displays etc. In the first part of this review, a brief introduction of discotic graphene oxide liquid crystals (GOLCs), their fundamental, synthesis process, supramolecular structures of graphene‐DLC composites is highlighted. In the second part, some important physical studies and application of this largest polycyclic aromatic core of DLCs are discussed. Finally, an outlook on this emerging two dimensional material in liquid crystal field with relevant scientific application background is presented.

Synthesis and characterisation of biodegradable liquid crystal elastomer with the property of shape recovery

ABSTRACTNovel shape recovery biodegradable liquid crystal (LC) elastomer is reported here for the first time. The method of synthesis of the shape memory biodegradable LC elastomer has been explored. During the reaction, the LC molecules are added to form LC polymers, and then cross-linking agent is added to form a cross-linked LC elastomer. The LC elastomer in this work is hydrophilic. In vitro degradation of the LC elastomer films in a buffer of pH 7.4 at 37°C shows that the LC elastomer has good degradability. The biodegradable LC elastomer exhibits liquid crystalline behaviour and has shape memory ability. Its shape memory and actuating properties also have been studied. The reversible transition from liquid crystalline phase to isotropic phase is utilised as the switching mechanism for these stimuli-responsive materials. When reheating the LC elastomer to 120°C, the shape will recover.

Synthesis and mesomorphic properties of calix[4]resorcinarene–triphenylene oligomers

ABSTRACTBy controlling the mol ratios of reactants, novel calix[4]resorcinarene–triphenylene monomer, dimer and tetramer were designed and synthesised in yields of 50–60% via Click chemistry. Their structures were characterised by NMR and MS. Their liquid crystalline behaviours were studied by differential scanning calorimetry, polarising optical microscopy and X-ray diffraction analysis. The more triphenylene units on calix[4]resorcinarene resulted in the wider temperature scopes of mesophase and higher phase transition temperatures. The monomer 6 and dimer 7 showed the mixed columnar mesophase with hexagonal columnar structure and disordered lamellar columnar structure, and compound 8 possessed only disordered lamellar columnar mesophase. These research results suggest that calix[4]resorcinarene was a good platform to construct columnar liquid crystal and the mesomorphic properties were greatly influenced by the substituted numbers of mesogen units on calix skeleton.

Luminescent palladium(II) metallomesogens based on cyclometalated Schiff bases and N-benzoyl thiourea derivatives as co-ligands

Luminescent cyclometalated palladium(II) complexes based on Schiff bases and N-benzoylthiourea (BTU) ligands with different numbers of alkoxy groups at their periphery were designed and prepared. The BTU ligands coordinate through the O and S atoms in a deprotonated bidentate fashion as confirmed by IR and NMR spectroscopy data. Additionally, giving the asymmetrical structure of BTU ligands, the 1H-NMR showed the presence of only one of the two possible isomers. The liquid crystalline behavior of these palladium(II) complexes was investigated by a combination of polarized optical microscopy (POM) and differential scanning calorimetry (DSC) while their thermal stability was studied by thermogravimetric analysis (TGA). The mesomorphic behavior of palladium(II) complexes depends on the number and chain length of alkoxy groups grafted on BTU derivatives (monotropic smectic A and C phases). The palladium(II) complexes are thermally stable on a broad temperature range up to about 220 °C. Interestingly, when the number of alkoxy groups on the BTU ancillary ligands was increased, the corresponding palladium(II) complexes lost their mesogenicity and only melting to the isotropic state was observed. The solid-state emission spectra of palladium(II) complexes show two maxima around 580 and 650 nm, respectively, with a shoulder around 710 nm when the samples are irradiated in the 330–380 nm range.

Lyotropic Liquid-crystalline Pseudo-polymer Particles with an Iron Oxide Monodispersed Core Controlled in Size and Shapes in Ionic Liquids

Spindle- and disk-shaped pseudo-poly(methyl methacrylate) particles obtained by the surface-initiated atom transfer radical polymerization on α-Fe2O3 or Fe3O4 monodispersed fine particles exhibited lyotropic liquid-crystalline behavior in ionic liquids for a wide range of the mixing ratio. Effects of the size and shape of the particles on the lyotropic liquid-crystalline properties and the nanolevel self-organized structures have also been investigated.

Cyclometalated palladium(II) metallomesogens with Schiff bases and N-benzoyl thiourea derivatives as co-ligands

Two series of cyclometalated palladium(II) complexes based on Schiff bases and N-benzoylthiourea (BTU) ligands having four alkoxy groups at their periphery, with different number of carbon atoms, have been designed and prepared. The liquid crystalline behavior of these palladium(II) complexes was investigated by a combination of polarized optical microscopy (POM), differential scanning calorimetry (DSC) and powder X-ray diffraction while their thermal stability was studied by thermogravimetric analysis (TGA). The palladium(II) complexes are thermally stable on a broad temperature range up to 230°C showing, depending on the alkoxy chain length, either monotropic or, for longest alkyl chain, enantiotropic smectic A and C phases. The luminescent properties of palladium(II) complexes were reported. These complexes show a yellow-orange solid-state emission at room temperature with two emission maxima at λmax around 580 and 650nm, respectively, with a shoulder around 710nm, when the samples are irradiated in the 330–380nm range.

Liquid Crystals of Graphene Oxide: A Route Towards Solution‐Based Processing and Applications

The liquid crystalline behavior of graphene oxide (GO) has enabled the design of facile and effective solution processing methods for assembling highly ordered macroscopic graphene structures, further expanding the development of novel graphene‐based devices. In this progress report, first the preparation of liquid crystalline graphene oxide (LCGO) with a particular emphasis on different approaches to improve the oxidation efficiency and to control the GO sheet size is discussed. Then the use of LCGO dispersions in the solution processing of 1D, 2D and 3D architectures with highly tailored microstructures is covered. The LCGO composites are also reviewed as an important part of novel graphene‐based multi‐functional materials. Finally, various applications of LCGO are discussed to highlight the critical role of LCGO in expanding the applications of graphene. Based on these systematic discussions, an outlook on the future directions, challenges, and opportunities in this field is provided.

Structure and thermal transitions in a biomedically relevant liquid crystalline poly(ester amide).

There is still a need to develop bioresorbable polymers with high strength and high modulus for load-bearing biomedical applications. Here we investigate the liquid crystalline structural features of poly(desaminotyrosyl-tyrosine dodecyl dodecanedioate), poly(DTD DD), a new bioresorbable poly(ester amide) that is currently studied in vivo as a slow-degrading implantable biomaterial for load bearing applications. Thermally induced structural changes in poly(DTD DD) were studied using simultaneously differential scanning calorimetry (DSC) and X-ray scattering. The hexatic SmB organization of the polymer chains that exists at room temperature becomes progressively disordered upon heating, changing into a SmF phase and then into a smectic C phase at 60°C before turning into a free flowing melt at 130°C. X-ray scattering data and thermal analysis indicate the presence of a 2D ordered structure in the polymer melt. A structural model with an interesting 3-fold symmetry in the packing of the side chains around the rigid aromatic main chain, and the packing of these chains into fibrils is proposed. The liquid crystalline behavior of poly(DTD DD) makes it possible to melt process it at low temperatures without thermal degradation. This is a noteworthy advantage for the use of poly(DTD DD) as a high strength, readily processable, yet biodegradable polymer.

Liquid crystalline supramolecular crosslinked polymer complexes of ditopic rylenebisimides and P4VP

ABSTRACTPerylenebisimide and naphthalenebisimide (PBI‐PDP and NBI‐PDP) end functionalized with pentadecyl phenol is designed as ditopic hydrogen bonding acceptors to form supramolecular crosslinked network with poly(4‐vinyl pyridine) (P4VP). The pristine PBI‐PDP has been grown as single crystals from DCM‐MeOH (dichloromethane‐methanol) mixture at room temperature, which revealed a P21 space group. Noticeably, the pentadecyl alkyl chain shields the aromatic perylene core on both sides resulting in the absence of π–π interaction in single‐crystal assembly. The naphthalenebisimide derivative exhibits thermotropic liquid crystalline behavior, while both the molecules exhibits lyotropic liquid crystalline phases in tetrahydrofuran (THF), which were characterized using a combination of differential scanning calorimeter, X‐ray diffraction, and polarized light microscopy. The hydrogen‐bonded complex of both the rylenebisimides with P4VP preserves the mesomorphic properties in THF. The electron transport mobility measured by space charge limited current measurements reveals a two orders of magnitude increase in the charge transport in the P4VP complex compared to that of the pristine molecule. The average electron mobility obtained is μe,avg: 10−3 cm2/Vs for P4VP‐PBI compared to μe,avg: 10−5 cm2/Vs for pristine PBI derivative. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 951–959

Study of Cr → SmA phase transition and hydrogen bonding in four-ring bent-core liquid crystal

A newly designed asymmetrical four-ring bent-core compound (4′-n-decyloxyphenylazo)-phenyl-4-yl-3-[N-(4′-n-octadecyloxy-2-hydroxybenzylidene) amino]-2-methyl benzoate exhibiting liquid crystalline behavior was synthesized and characterized. The thermal and textural morphology were studied using differential scanning calorimetry and polarizing optical microscopy, respectively. The study of hydrogen bonding and dynamics of the phase transition has been performed at the molecular level using temperature dependent Fourier transform infrared (FTIR) spectroscopy. The spectral analysis of OH, CH2/CH3, CO, and CN stretching vibrational bands revealed clear signatures of Cr→SmA phase transition at 125°C. Density functional theory has been adopted for the geometry optimization and conformational study of the monomer using the B3LYP/6-31G(d) method. The conformational analysis has been performed to predict the most stable conformer along with the possible conformers using one-dimensional potential energy scan employing the same level of theory. The combination of experimental findings and theoretical analysis helped to understand the mechanism of phase transitions at the molecular level.

Calix[4]resorcinarene-cholesterol columnar liquid crystals: Synthesis, mesomorphism and the influence of spacers on liquid crystalline behaviors

Abstract Novel calix[4]resorcinarene derivatives with four cholesterol units bridging by soft spacers or rigid Schiff-base spacers were prepared in yields of 63–76%. The hexagonal columnar liquid crystalline behaviors were firstly observed for calix[4]resorcinarene derivatives. The mesomorphic properties were influenced greatly by the structures of spacers. The rigid spacers were favorable for enhancing the phase transition temperatures and enlarging the temperature scopes of mesophase.

Synthesis, characterization of new carboxylic acid derivatives bearing 1,3,4-thiadiazole moiety and study their liquid crystalline behaviors

ABSTRACTThirteen carboxylic acid derivatives containing 1,3,4-thiadiazole ring in their core and swinging alkoxy terminal were synthesized. They were characterized by 1H, 13C NMR spectroscopy, FTIR, and mass spectrometry. Their liquid crystalline behaviors have been studied by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The 1,3,4-thiadiazole compounds in this study were 2,5 di-substituted asymmetrical, alkoxy, and carboxy linkages. The compounds with alkoxy of long carbon chains (n > 7) displayed Smectic C phase. The liquid crystal properties were found to be affected by the length of alkoxy chain attached to the phenyl moiety and the two types of the dimeric form were resulted from the hydrogen bonding interaction between carboxylic acid molecules.

PB05 液晶分子と芳香族分子の混合系の液晶(化学・材料)

PB05 液晶分子と芳香族分子の混合系の液晶(化学・材料)

Liquid Crystal Organization of Calix[4]arene‐Appended Schiff Bases and Recognition towards Zn2+

AbstractThe synthesis and liquid crystalline behavior of new calixarene Schiff base derivatives are reported. The materials were obtained by reaction of a tetraaminocalix[4]arene derivative with three aldehydes as mesogenic promotor moieties: 4‐(4′‐decyloxybenzoyloxy)benzaldehyde (A), 4‐(4′‐decyloxybenzoyloxy)salicylaldehyde (B) and 4‐(3′,4′‐didecyloxybenzoyloxy)salicylaldehyde (C). All of the compounds exhibit liquid crystalline properties and these were studied by optical microscopy, DSC and X‐ray diffraction. The relationship between the structure and the mesomorphic behavior of the compounds is discussed. The binding recognition and selectivity towards cations have been studied by absorption and fluorescence spectroscopy

Liquid crystalline polyaniline and phthalocyanine-based polysiloxanes bearing lateral fluoro-substituted benzoic acid groups

ABSTRACTA series of novel liquid crystalline polymers (PI, PII, PIII and PIV) containing lateral fluoro-substituted benzoic acid groups was synthesised using cholesteryl 4-(2-propenyloxy)-benzoate, 4-(allyloxy)-3-fluorobenzoic acid and poly(methylhydrogeno)siloxane. PI and PII showed smectic phase, but PIII and PIV showed chiral nematic phase due to more lateral fluoro-substituted benzoic acid groups in the polymer systems. Liquid crystalline polyaniline (PAN) and phthalocyanine (Pc)-based polysiloxanes showing chiral nematic phase were prepared by use of Pc, PAN and these liquid-crystalline polymers via hydrogen bond. PAN-based polysiloxanes showed different liquid crystalline behaviours from Pc-based polysiloxanes due to the difference of molecular structure. PAN-based polysiloxanes showed greater d-spacings between the side mesogenic groups than Pc-based polysiloxanes due to long rod-like geometrical shapes. Hydrogen bond based on lateral fluoro-substituted benzoic acid groups was formed to different geometrical shapes (strip or roundness) between PAN and Pc-based polysiloxanes.