Formation of hexagonal columnar phases by heterocyclic pyrimidine derivatives

The synthesis, characterization, and mesomorphic properties of a new type of heteronuclear compounds derived from pyrimidine as core group are reported. These compounds were prepared by condensation reactions of appropriate acetophenones and benzonitriles in the presence of trifluoromethanesulphonic anhydride. They were characterized by 1 H and 13 C NMR spectroscopy and elemental analysis, and their phase transitions characterized and studied by thermal analysis and polarizating microscopy. These compounds exhibit hexagonal columnar (Col h ) phases, as expected for disk-like molecules; the formation of columnar phases was found to be dependent on the numbers of alkoxy side chains attached. For those compounds having the same numbers of flexible side chains attached, the one with a preferred unsymmetric structure exhibited better mesomorphic properties. The observed improved mesomorphic behaviour of these compounds over other similar all-carbon heterocyclic compounds is attributed to the greater polarization of nitrogen atoms in the core ring.     

Photoluminescent nickel(II)-metallomesogens derived from salphen ligands: influence of halogens at the spacer on mesomorphism and emission properties

Three new series of photoluminescent nickel(II) metallomesogens, [NiL]; H₂L = N,N′-Bis(4-n-alkoxysalicylidene)-4-fluoro/bromo/chloro-1,2-diaminobenzene (n = 12, 14, 16) based on ‘salphen’ ligands have been synthesised and their mesomorphic and photophysical properties explored. The complexes, isolated as orange microcrystalline solids were characterised by elemental analyses, FT-IR, ¹H NMR and UV-visible spectroscopy. Thermal studies show all the compounds to be enantiotropic liquid crystals displaying columnar mesophase over a wide temperature range. Electronegativity and steric requirement of the halogen substituent at the ligand’s spacer remarkably influence the 2-D packing of the columns in the lattice in these complexes controlling the supramolecular mesomorphic order and photoluminescence. The mesophase behaviour of the fluoro-substituted complex is characterised by a transition from a columnar oblique (p1) to columnar rectangular (p2mm) phase, former stable till ambient temperature. The chloro and bromo analogues, on the other hand, displayed exclusively columnar rectangular (p2mm) mesophase with the former transforming into a glassy state and latter into a crystalline phase during cooling to ambient temperature. Molecular model based on interdigitated anti-parallel and back to back arrangements in the different columnar mesophase are proposed on the basis of X-ray diffraction (XRD) studies. The complexes emit in the blue region when excited with near UV wavelength.     

Formation of hexagonal columnar phases by heterocyclic pyrimidine derivatives

The synthesis, characterization, and mesomorphic properties of a new type of heteronuclear compounds derived from pyrimidine as core group are reported. These compounds were prepared by condensation reactions of appropriate acetophenones and benzonitriles in the presence of trifluoromethanesulphonic anhydride. They were characterized by ¹H and ¹³C NMR spectroscopy and elemental analysis, and their phase transitions characterized and studied by thermal analysis and polarizating microscopy. These compounds exhibit hexagonal columnar (Col_h) phases, as expected for disk-like molecules; the formation of columnar phases was found to be dependent on the numbers of alkoxy side chains attached. For those compounds having the same numbers of flexible side chains attached, the one with a preferred unsymmetric structure exhibited better mesomorphic properties. The observed improved mesomorphic behaviour of these compounds over other similar all-carbon heterocyclic compounds is attributed to the greater polarization of nitrogen atoms in the core ring.     

Heterocyclic 1,3,4-oxadiazole as columnar core

The synthesis, characterization and mesomorphic properties of a new type of liquid crystalline compound, the 2,5-bis(3,4,5-trialkoxyphenyl)-1,3,4-oxadiazoles, 3a-3h, are reported. These heterocyclic compounds are derived from unsaturated 1,3,4-oxadiazole as the core group, and obtained by the condensation reaction of 3,4,5-trialkoxybenzoic acid N-(3,4,5-trialkoxybenzoyl)-hydrazides and phosphorus oxychloride in toluene under reflux. All compounds were characterized by ¹H and ¹³C NMR spectroscopy, and elemental analysis. The mesomorphic properties of these and the related compounds 1, 2 were characterized and studied by differential scanning calorimetry and polarizing optical microscopy. The formation of columnar mesophases was found to be dependent on the numbers of alkoxy sidechains. The compounds 3 exhibited hexagonal columnar (Col_h) phases, however compounds 1, 2 formed crystalline phases. Compounds 3b-3e with shorter carbon chains were room temperature liquid crystals. Polar induction by nitrogen and/or oxygen atoms on the heterocyclic core ring might be responsible for the formation and better observed mesomorphic properties in this type of compound.     

Heterocyclic 1,3,4-oxadiazole as columnar core

The synthesis, characterization and mesomorphic properties of a new type of liquid crystalline compound, the 2,5-bis(3,4,5-trialkoxyphenyl)-1,3,4-oxadiazoles, 3a-3h, are reported. These heterocyclic compounds are derived from unsaturated 1,3,4-oxadiazole as the core group, and obtained by the condensation reaction of 3,4,5-trialkoxybenzoic acid N-(3,4,5-trialkoxybenzoyl)-hydrazides and phosphorus oxychloride in toluene under reflux. All compounds were characterized by ¹H and ¹³C NMR spectroscopy, and elemental analysis. The mesomorphic properties of these and the related compounds 1, 2 were characterized and studied by differential scanning calorimetry and polarizing optical microscopy. The formation of columnar mesophases was found to be dependent on the numbers of alkoxy sidechains. The compounds 3 exhibited hexagonal columnar (Col_h) phases, however compounds 1, 2 formed crystalline phases. Compounds 3b-3e with shorter carbon chains were room temperature liquid crystals. Polar induction by nitrogen and/or oxygen atoms on the heterocyclic core ring might be responsible for the formation and better observed mesomorphic properties in this type of compound.     

Light emitting,star-shaped tris(N-salicylideneaniline) discotic liquid crystals bearing trans-stilbene fluorophores: synthesis and characterization

Star-shaped tris(N-salicylideneaniline) discotics possessing trans-stilbene fluorophores have been synthesized by condensing 1,3,5-triformylphloroglucinol with 4-(alkoxystyryl)benzen-amines, and characterized. ¹H and 2D ¹H–¹H COSY NMR experiments reveal their occurrence in two inseparable keto-enamine tautomeric forms featuring C_3h and C_s rotational symmetries. Their columnar liquid crystal behavior has been ascertained unequivocally with the aid of a polarizing optical microscope and a differential scanning calorimeter. Photoluminescence property has been examined both in solution and columnar states. Green light emission observed in the solution state is especially noteworthy. Thus, intrinsic self-assembly into a fluid columnar state exhibiting light emission property clearly illustrates their significance in technological applications.     

Control over Nanostructures and Associated Mesomorphic Properties of Doped Self‐Assembled Triarylamine Liquid Crystals

We have synthesized a series of triarylamine‐cored molecules equipped with an adjacent amide moiety and dendritic peripheral tails in a variety of modes. We show by ¹H NMR and UV/Vis spectroscopy that their supramolecular self‐assembly can be promoted in solution upon light stimulation and radical initiation. In addition, we have probed their molecular arrangements and mesomorphic properties in the bulk by integrated studies on their film state by using differential scanning calorimetry (DSC), variable‐temperature polarizing optical microscopy (VT‐POM), variable‐temperature X‐ray diffraction (VT‐XRD), and atomic force microscopy (AFM). Differences in the number and the disposition of the peripheral tails significantly affect their mesomorphic properties associated with their lamellar‐ or columnar‐packed nanostructures, which are based on segregated stacks of the triphenylamine cores and the lipophilic/lipophobic periphery. Such structural tuning is of interest for implementation of these soft self‐assemblies as electroactive materials from solution to mesophases.     

Wide-line 1H NMR and DSC study of mesomorphic transformations of p-(alkoxybenzylidene)-p′-toluidines

p-(Alkoxybenzylidene)-p′-toluidines (ABTs) with 7, 8, and 10 carbon atoms in the alkyl moiety have been studied by wide-line ¹H NMR and DSC. The thermotropic properties of these compounds have been studied in the temperature range 20–80°C, including main mesomorphic transformations of ABTs. The 1H NMR line shapes, widths, and second moments, as well as specific features of their temperature-induced changes, are discussed. The DSC data are compared with the character of mesomorphic transformations and ¹H NMR data. The formation limits and ranges and stabilities of liquid-crystalline states of the ABT structure emerging on heating are determined.     

Photoluminescent columnar zinc(II) bimetallomesogen of tridentate [ONO]-donor Schiff base ligand

A new zinc(II) bimetallomesogenic complex, [Zn₂L₂], of tridentate [ONO]-donor Schiff base ligand (L = N-(2-hydroxyethyl)-4-hexadecyloxysalicylaldimines) was synthesised and their mesomorphic and photoluminescence properties were investigated. The compounds were characterised by Fourier transform infrared spectroscopy (FTIR), ¹H and ¹³C nuclear magnetic resonance (NMR), ultraviolet-visible spectroscopy (UV-Vis) spectroscopy, elemental analyses and fast atom bombardment (FAB) mass spectrometry. The mesomorphic behaviour of the complex was investigated by polarised optical microscopy, differential scanning calorimetry and X-ray diffraction (XRD) study. A rectangular or oblique columnar mesophase is conjectured on the basis of powder X-ray diffraction (PXRD) study. The complex is found to be blue light emitter in solution, in solid and in condensed states with broad emission maxima at ～427–464 nm. The density functional theory (DFT) calculations revealed a distorted square planar structure around each zinc(II) centre in the dinuclear framework. Time-dependent DFT spectral correlative study was undertaken to account for the electronic transition.     

Columnar liquid crystalline tris-(ether)triazines with pendant 1,3,4-thiadiazole groups: synthesis,mesomorphic, luminescence,solvatofluorochromic and electrochemical properties

Novel columnar liquid crystals whose molecular structures consist of a C₃ star-shaped 1,3,5-triazine unit as a central core, and three pendant 2-phenyl-5-(di-, and/or tri-n-alkoxyphenyl)-1,3,4-thiadiazole arms, containing ether connecting groups, variable number and positions of linear alkoxy chains were synthesised and their mesomorphic properties were studied by differential scanning calorimetry, polarised optical microscopy and X-ray diffraction. The mesomorphic properties were found to be dependent on the length, position and number of the peripheral alkoxy chains. Most compounds form enantiotropic hexagonal columnar phases. These compounds also show photoluminescent properties in the visible region with good quantum yields. Photophysical studies were realised in solution and in solid state. Also, solvatofluorochromism and cyclic voltammetry studies were performed.     

Technologically promising,room temperature luminescent columnar liquid crystals derived from s-triazine core: molecular design,synthesis and characterization

Three fold Horner-Wadsworth-Emmons (HWS) reaction of triphosphonate with achiral/chiral 3,4,5-tris(alkoxy)benzaldehydes yield novel achiral/chiral star-shaped liquid crystals (LCs), in which three fluorophore arms such as 1,2,3-tris(alkoxy)-5-styrylbenzenes are tethered to a central s-triazine core. These LCs, the first of their kind, display a columnar liquid crystalline phase over a wide temperature range existing between well below and above the room temperature, which is evidenced by optical and calorimetric studies. Besides, they show photoluminescence both in solution and mesomorphic states. Thus, given their self-organization into fluid one-dimensional columnar array coupled with light generating capability, these organic ordered-fluids can be regarded as novel media for advanced technological applications.     

Supermolecular Columnar Liquid‐Crystalline Phosphorus Dendrimers Decorated with Sulfonamide Derivatives

A series of supermolecular liquid crystals has been synthesized by combining phosphorus dendrimers of the zero, first, and fourth generations with sulfonamide derivatives, thus generating dendromesogens bearing 6, 12, and 96 mesogenic units on their surfaces. The relevant reactions could be monitored by ¹H, ¹⁹F, and ³¹P{¹H} NMR spectroscopies. The thermal and mesomorphic properties of the products have been studied by optical microscopy, differential scanning calorimetry, and X‐ray diffraction. All of the new macromolecules prepared in this work have been found to show mesomorphic properties over a wide temperature range; moreover, for all of the compounds, the columnar mesophases observed were maintained or vitrified at room temperature. On increasing the generation of these dendromesogens, mesophases appear at lower temperatures and remain stable over a wider temperature interval. In all cases, on the basis of X‐ray analysis, a cylindrical symmetry of the molecules can be proposed to promote the supramolecular columnar arrangement observed in the mesophases. In this type of model, the height of the dendrimer clearly increases with increasing dendrimer generation, whereas its cross‐ sectional area increases only slightly, probably due to compression of the highly hyperbranched structures as a consequence of their progressive steric constraints. The mesomorphic arrangement is governed by the peripheral sulfonamide units.     

Liquid-crystalline Janus-type fullerodendrimers displaying tunable smectic-columnar mesomorphism

Janus-type liquid-crystalline fullerodendrimers were synthesized via the 1,3-dipolar cycloaddtition of two mesomorphic dendrons and C60. By assembling poly(aryl ester) dendrons functionalized with cyanobiphenyl groups, displaying lamellar mesomorphism, with poly(benzyl ether) dendrons carrying alkyl chains, which display columnar mesomorphism, we could tailor by design the liquid-crystalline properties of the title compounds as a function of each dendron size. The liquid-crystalline properties were examined by polarized optical microscopy, differential scanning calorimetry, and X-ray diffraction. Depending on the dendrimer generations, smectic (SmC and/or SmA phases) or columnar (Colr-c2mm or Colr-p2gg phases) mesomorphism was obtained. The supramolecular organization is governed by (1) the adequacy of the cross-sectional area of the dendrons, (2) the microsegregation of the dendrimer, (3) the deformation of the dendritic core, and (4) the dipolar interactions between the cyanobiphenyl groups. Comparison of the mesomorphic properties of two fullerodendrimers with those of model compounds (fullerene-free analogues) indicated that the C60 unit does not influence the type of mesophase that is formed. Molecular properties determined in solution (permanent dipole moment, specific dielectric polarization, molar Kerr constant) confirm that microsegregation persists in solution and strengthen the models proposed for the structure of the mesophases.     

Novel room-temperature perylene liquid crystals: synthesis of 1,7-dibrominated cholesterol–perylene bisimides with different ester-bridging chains and their mesomorphic properties

Three novel 1,7-dibrominated cholesterol–perylene liquid crystals 6a, 6b and 6c with different ester-bridging chains were designed and synthesised in yields of 30–40%. Their structures were characterised by FT-IR, ¹H NMR and HR-MS spectra. Their mesomorphic behaviours were studied by differential scanning calorimetry (DSC), polarising optical microscopy (POM) and X-ray diffraction (XRD). Compounds 6a, 6b and 6c exhibit hexagonal columnar liquid crystalline phase at room temperature. Their mesomorphic temperature ranges are as wide as 140–162°C. Their fluorescence spectra suggested that they possess good fluorescence properties in solution. The soft ester-bridging chains are more favourable for room-temperature mesophase and high fluorescence than the rigid ester-bridging chain.     

Amphiphilic N-benzoyl-1-amino-1-deoxy-D-glucitol derivatives forming thermotropic lamellar, columnar and different types of cubic mesophases

Novel amphiphilic glucamine derivatives have been synthesized. These are N-benzoyl-1-deoxy1-methylamino-D-glucitols and N-benzoyl-1-amino-1-deoxy-D-glucitols carrying one, two or three aliphatic chains (CnH2n 1O- with n 3, 6 and 12) grafted to the benzamido group. The thermotropic mesophases of these compounds were studied by thermal polarizing optical microscopy and differential scanning calorimetry, and some also by X-ray scattering. Depending on the number and the length of the alkyl chains lamellar, bicontinuous cubic, hexagonal columnar or inverted micellar cubic mesophases were detected by analogy with lyotropic systems. In the contact region between lamellar phases of the single chain amphiphiles and micellar cubic phases of the mesomorphic triple chain compounds, hexagonal columnar phases can be induced. A hexagonal columnar phase was also induced in the contact region between a bicontinuous and a micellar cubic mesophase. The lyotropic liquid crystalline behaviour of the dodecyloxy substituted N-benzoyl-1-deoxy-1-methylamino-D-glucitols was investigated by the solvent penetration method using ethylene glycol as protic solvent. On increasing the solvent content, the double chain compound forms a cubic and a lamellar mesophase and the triple chain compound forms a hexagonal columnar lyomesophase. The dodecyloxy substituted compounds were also investigated with respect to their behaviour as thin films at the air-water interface using a Langmuir film-balance. Different types of pi/Aisotherms were observed whereby the molecular areas at collapse were determined either by the size of the carbohydrate head group (single chain compounds) or by the number of alkyl chains (double and triple chain compound).     

Stabilization and induction of discotic mesophases by trifluoroacetic acid

It is shown that trifluoroacetic acid (TFA) can form 1 1 molar complexes with alkyloxy discotic compounds, thereby enhancing their mesomorphic properties. In particular, when hexaalkyloxytriphenylenes (THEn) (n being the number of carbons per side chain) are crystallized from, or mixed with, TFA, complexes are formed which exhibit the Dho(Colho) mesophase, as do the neat THEn's, but with a broader range of thermal stability and a higher degree of order. The mesophases of these complexes are completely miscible with those of the neat compounds. Likewise, 1 1 mixtures of hexa-alkyloxytribenzocyclononene (TBCEn) and TFA yield complexes showing enhanced mesomorphic properties for the mesogenic homologues of this series and induced mesomorphism for the lower homologues, which in the neat form are not mesogenic. The mesomorphic properties of these TFA complexes with THEn (n=3-6) and with TBCEn (n=4-6) are investigated by means of optical microscopy, differential scanning calorimetry, X-ray diffraction and NMR spectroscopy. It is suggested that the enhancement of the mesomorphic properties is due to formation of oxonium ion complexes.     

Geminal bis-ureas as gelators for organic solvents: gelation properties and structural studies in solution and in the gel state

Several geminal bis-urea compounds were synthesised by means of an acid-catalysed condensation of various benzaldehydes with different monoalkylureas. Many of these compounds form thermoreversible gels with a number of organic solvents at very low concentrations (<3mM) and which are stable to temperatures higher than 100 degrees C. Electron microscopy revealed a three-dimensional (3D) network of intertwined fibres, which are several tens of micrometers long and have a width ranging from approximately 30 to 300 nm. The possible aggregate forms and aggregate symmetries were evaluated by means of molecular mechanics calculations. 1H NMR, 2D NMR, 13C NMR and 13C-CP/MAS NMR techniques were used to obtain information about the aggregation and possible aggregate symmetry of geminal bis-ureas in solution, in the gel state, and in the solid state.     

New mesomorphic benzothiazol derivatives：Synthesis and characterization

In this paper, the synthesis of new mesomorphic benzothiazolyl derivatives, 6-ethoxy-2-[4-(4-alkyloxybenzoyloxy)benzylidenamino]benzothiazoles, is presented. The structures of the title compounds were elucidated using spectroscopic techniques, such as FT-IR, NMR (1H and 13C), elemental analysis and EI-MS. The mesomorphic behaviours of these compounds were determined by differential scanning calorimetric and polarizing optical microscopic techniques. Compounds exhibited nematic and tilted smectic phases upon heating from crystal phase. An obvious odd-even effect was observed in this homologous series.     

New polycatenar Schiff bases derived from 1,3,4-thiadiazole: synthesis,mesomorphism and luminescence behaviour

Two new series of columnar liquid crystal materials based on tetra- and hexacatenar Schiff bases were synthesised by reaction of 4-aminophenyl-1,3,4-thiadiazole derivatives with terephthalaldehyde (series 2a–f) and with 2,5-thiophenedicarbaldehyde (series 3a–f). The mesomorphic properties of these compounds were studied by differential scanning calorimetry (DSC), polarised optical microscopy (POM) and X-ray diffraction (XRD). The mesomorphic behaviour was found to be dependent on the nature of the central ring (benzene in series 2a–f, thiophene in series 3a–f), on length and on number of alkoxy chains. Both tetra- and hexacatenar compounds in series 2a–f display an enantiotropic hexagonal columnar phase. Whereas, in the case of the series 3, only the tetracatenar Schiff bases (3a, 3c and 3e) display enantiotropic hexagonal columnar mesomorphism, hexacatenar Schiff bases (3b, 3d and 3f) do not show mesomorphic properties. Photophysical studies were realised in solution and in solid state. Also, a thermogravimetric analysis was performed. A fibre obtained from compound 3b was analysed by POM showing that the mesophase is maintained in the fibre.     

Heterocyclic columnar pyrimidines: synthesis, characterization and mesomorphic properties

The synthesis, characterization, and mesomorphic properties of two series of heterocyclic compounds derived from a pyrimidine core are reported. These series, 1a and 1b, are substituted with a variety of functional groups (X=NHSO₂CF₃, F, Cl, Br, I, OCH₃, CH₃, C₂H₅) at the C^3' (meta)- or C^4' (para)-position of the terminal phenyl ring, and the substituent effect on mesophase formation was studied. The compounds were characterized by ¹H and ¹³C NMR spectroscopy and elemental analysis, and the mesomorphic behavior of the compounds was characterized and studied by differential scanning calorimetry, polarizing optical microscopy and powder X-ray diffraction. Most of the compounds were mesogenic at room temperature, and the mesophases were assigned as lamellar columnar (Col_L) phases, as expected for disk-like molecules. The results also revealed that compounds with a para-substituent (1a; except for -OCH₃) at the C^4'-position, exhibited higher clearing temperatures and wider temperature mesophase ranges than those of compounds with a meta-substituent (1b) at the C^3'-position. The higher clearing temperatures may be attributed to stronger dipolar interactions resulting from a greater resonance effect with the central core for para-substitution than for meta-substitution. The results also indicated that the columnar mesophases observed show a correlation with the electronic properties of the substituents; compounds containing electron-withdrawing substituents (X=F, Cl, Br, I, NHSO₂CF₃) also have higher clearing temperatures than compounds containing electron-donating substituents (X=Me, Et, OMe).