Enantiotropic Nematic Phase Research Articles

Synthesis and liquid crystalline properties of novel series containing 5H-thiazolo[3,4-b][1, 3, 4]thiadiazole unit with schiff base and azo linkage

Two series were synthesized containing a 5H-thiazolo[3,4-b][1, 3, 4]thiadiazole unit with a Schiff base and an azo linkage. Polarized optical microscope (POM) and differential scanning calorimetry (DSC) were used to examine the mesomorphic behavior. Enantiotropic nematic phases were present in compounds with alkoxy terminal groups of n = 1–4 methylene units for both series. While enantiotropic smectic A (SmA) is also present in molecules with n = 6–8 carbon atoms in addition to nematic phases for a series of azo linkage. The molecules in the Schiff base linkage series with n = 6–8 exhibited pure smectogenic liquid crystalline behavior.

Liquid Crystal Dimers and the Twist-Bend Phases: Non-Symmetric Dimers Consisting of Mesogenic Units of Differing Lengths.

The syntheses and characterisation of the 4-[{[4-({n-[4-(4-cyanophenyl)phenyl]-n-yl}oxy)phenyl]-methylidene}amino]phenyl-4-alkoxybenzoates (CBnOIBeOm) are reported with n=8 and 10 and m=1-10. The two series display fascinating liquid crystal polymorphism. All twenty reported homologues display an enantiotropic nematic (N) phase at high temperature. When the length of the spacer (n) is greater than that of the terminal chain (m), the twist-bend nematic (NTB) phase is observed at temperatures below the N phase. As the length of the terminal chain is increased and extends beyond the length of the spacer up to three smectic phases are observed on cooling the N phase. One of these smectic phases has been assigned as the rare twist-bend smectic C subphase, the SmCTB-α phase. In all the smectic phases, a monolayer packing arrangement is seen, and this is attributed to the anti-parallel associations of the like mesogenic units.

Biphenyl based schiff base derivatives of 6-aminocoumarin: Design, synthesis, mesomorphic properties and DFT studies

The study focused on synthesizing two series of coumarin Schiff base liquid crystals. These series involved molecules with variations in alkoxy chains at aldehyde ends: one being the Schiff base with 4′‑hydroxy-[1,1′]-biphenyl-4-carbaldehyde (ASBP series) and the other being alkyl 4-formyl-[1,1′]-biphenyl-4-carboxylate (AEBP series). The compounds were characterized using FTIR, NMR, and Mass spectral analyses. All the compounds were studied for their mesomorphic properties, differential scanning calorimetry (DSC) and polarized optical microscopy (POM). In both the homologous series, variation of alkyl chain length showed intriguing phase transitions. In the first homologous series ASBP, compound with hexyloxy chain displayed an enantiotropic nematic (N) phase, while those with chain lengths n = 8–16 exhibited enantiotropic smectic A (SmA) mesophase. Similarly, in the AEBP series, compounds with n = 6,8 chain length showed an enantiotropic nematic (N) phase, while those with higher chain lengths n = 10–16 exhibited enantiotropic smectic A (SmA) phases. SmA mesophase was further confirmed by powdered XRD analysis. The study included DFT theoretical calculations to comprehend the compounds' mesomorphic behavior, comparing them with analogous reported compounds. Additionally, the investigation correlated experimental findings of individual compounds with calculated parameters like polarizability, dipole moment, and aspect ratio. Molecular electrostatic potential projections and analysis of frontier molecular orbitals were also employed to elucidate how polarity variations in terminal chains and mesogenic cores influenced the energy gap of FMOs and the distribution of electrostatic charges on these compounds. It has been found that the ASBP series has lower energy gap and higher dipole moment than the AEBP series.

Unsymmetrical mesogenic dimers containing azo and azomethine naphthalenes: Synthesis, characterization, mesomorphic properties and DFT studies

The synthesis and properties of two new mesogenic homologous series comprising of sixteen unsymmetrical dimers of cyanoazobenzene and azo/azomethine naphthalene are described. Their right structure was confirmed by FT-IR, 1HNMR , 13CNMR , and elemental analysis. On the polarising optical microscope (POM), their thermotropic properties were examined and further confirmed using differential scanning calorimetry (DSC). All sixteen dimers exhibit an enantiotropic nematic phase. The relationship between the nematic-isotropic transition temperature and the structures of dimers was discussed. A view of their photochromic behaviour was gained by UV–visible spectroscopy. The 6–31 g (d, p) basis set is combined with the B3LYP functional, which is used for computational studies of all the dimers. The examination of Electrostatic Potential (ESP) and optical characteristics also yielded important information about the electronic structure.

Synthesis, mesomorphic and magnetic properties at room temperature of biphenyl ester-aromatic imine with terminal alkoxy chains and methoxy substituent

ABSTRACT A series of calamitic biphenyl ester-aromatic imine derived from the reaction of 4-formylphenyl-4’-(alkyloxy)-[1,1’-biphenyl]-4-carboxylate and p-anisidine have been successfully synthesised and characterised. The general molecular structures of ultimate compounds show the central fragment made up by a hybrid core of biphenyl ester-aromatic imine in which the terminal alkoxy chains, CnH2n + 1 in which n = 7–12 were connected to biphenyl while the other end consists of methoxy moiety attached to a phenyl ring. All the target compounds under polarised lights exhibit enantiotropic nematic phase of which the temperature range was further supported by DSC analysis. It can be summarised that the lengthening of terminal alkoxy chains has contributed to the lowering of melting and clearing temperatures as well as the thermal stability of nematic phase. A dedicated magnetic characterisation analysis disclosed that apart from a dominant diamagnetic character these compounds possess a noticeable magnetic interaction despite knowing that the compounds belong to the non-metal and non-radical containing species.

Unsymmetrical coumarin-biphenyl hybrids: Self-assembling behaviour and DFT investigations

A series of new unsymmetrical coumarin-biphenyl hybrid [1,1′-biphenyl]-4-yl (E)-4-(((7-alkyloxy-2-oxo-2H-chromen-3-yl)imino)methyl)benzoates, BPCE-(2–18) self-assembling molecules have been designed and synthesized. Biphenyl end group at one end of molecules have been linked to the substituted coumarin core through imine and ester mesogenic linking units. Initial members of the series exhibited enantiotropic nematic phase, middle members showed nematic as well as smectogenic behaviour (smectic A) whereas the last member showed only smectogenic behaviour with disappearance of nematic mesophase. In addition, a comparative study has been done with structurally similar mesogens. The study incorporated Density Functional Theory calculations to determine the aspect ratio, dipole moment, and polarizability. These factors influence the terminal and lateral interactions of the compounds. Moreover, computation of molecular electrostatic potential was conducted to examine reactivity concerning both nucleophilic and electrophilic attacks. The theoretical findings were then discussed to validate the experimental data and elucidate the mesomorphic behaviour of the compounds. Additionally, calculations for the energy gap of frontier molecular orbitals, global softness, and chemical hardness were performed to assess the potential suitability of the liquid crystalline compounds for various applications.

A cinnamate liquid crystal for rapid optical recording

ABSTRACT Photorecording materials have been applied for information recording. Herein, a cinnamate liquid crystal with an enantiotropic nematic phase was synthesised, which can be isomerised and polymerised under the irradiation of the 365-nm UV light. Cholesteric liquid crystal polymer network (CLCN) films were prepared using the mixtures of it, LC242, a chiral dopant and a photoinitiator. The CLCN films possess a slight gradient helical pitch which increases from the bottom to the top of the films. The formation of this structure should be driven by the photoisomerisation of the cinnamate. Under the irradiation of 365-nm UV light with a low intensity, the CLC mixtures show a photochromic behaviour which is proposed to be driven by the formation of oligomers. Based on this, the CLC mixtures can be applied for optical recording.

Mesomorphic, magnetic and DFT studies of biphenyl-based molecule with various substituted anilines

ABSTRACT A new series of liquid crystals consisting of biphenyl unit connected to phenyl core system have been successfully prepared wherein various substituents X= OCH3, F, Cl, Br and I were introduced in the para position of the imine fragment while the length of terminal alkoxy chain of seven carbon atoms was intact. The mesomorphic and thermal studies by POM and DSC exhibit dominant enantiotropic nematic (N) phase. A relatively weak magnetism was detected with vibrating sample magnetometer (VSM) for compounds 3F and 3I at room temperature, wherein the magnetic strength of fluoro-substituted compound appeared stronger than the iodo-substituted compound. The connectivity between the substituents X and their kinetic stability associated with the changes in HOMO-LUMO energy gap value (ΔEgap) supports that the terminal substituents X have great influence on the ΔEgap which can be ascribed to the chemical activity of the compounds. Present study shows an increase in the ΔEgap from OCH 3 < I < Br < Cl < F, where the largest ΔEgap indicates high molecular kinetic stability and low chemical reactivity because adding electrons to high-lying LUMO is energetically unfavourable, resulting in disruption of the molecular packing and reduction of nematogenic, which were validated by DSC and POM.

Effortless Extraction of Structural and Orientational Information from 13C-1H Dipolar Couplings for Thiophene Mesogens.

Five molecular mesogens containing phenyl rings and thiophene are subjected to a detailed 13C NMR investigation. The first mesogen contains only phenyl rings, while the other four have thiophene with substitution at position 2 or 3. Two of these also have a spacer inserted between the thiophene and the rest of the core unit. The mesophase properties evaluated by complementary techniques reveal an enantiotropic nematic phase for all the cases and smectic C as well as Crystal J for a few mesogens. In addition to solution 13C NMR, the samples were studied using 1D and 2D solid-state 13C NMR experiments in the liquid crystalline phase. The chemical shifts and 13C-1H dipolar couplings obtained in the mesophase provided cutting-edge information about the molecular structure and orientation of the thiophene mesogens. Accordingly, dramatic differences in these parameters are noted for the mesogens, and consequently, the identification of 2- and 3-substituted thiophene mesogens is accomplished by a simple visual examination of the 2D spectra. Furthermore, for mesogens with a spacer between thiophene and the rest of the core, 13C chemical shifts and 13C-1H dipolar couplings showed remarkable variation, which was directly reflected in the order parameters. For instance, the order parameter (Szz) of thiophene in 2- and 3-substituted mesogens in which the spacer is absent is ∼0.63 whereas for those with spacer, it is reduced to ∼0.14-0.18. In comparison, the mesogen in which the core unit is made up of phenyl rings alone that is used to benchmark the characteristics of thiophene ordering showed an order parameter of ∼0.85. The study unambiguously demonstrates the supremacy of 13C NMR in extracting the structural and orientational information on mesogens in which thiophene is a constituent of the core unit.

“Novel Magneson-I derived λ-shaped tris azo liquid crystalline trimers”

One new homologous series of liquid crystalline λ-shaped tris azo trimers containing azobenzene moiety as a rigid core and ether linkages were synthesized by the reaction of various n-butylazobenzene having bromoalkoxy tail with magneson-I dye respectively. Their right structure was confirmed by FT-IR, 1H NMR, 13C NMR spectroscopy, mass spectrometry and elemental analysis. On the polarising optical microscope (POM), their thermotropic properties were examined, and additional studies were conducted using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). All the trimers with an even number of flexible spacers (n = 2 and 4) show excellent liquid crystalline properties as an enantiotropic nematic phase with greater mesophase length and good thermal stability. The introduction of odd-membered methylene disrupts the orderly stacking of layers and results in a change in mesogenic behaviour. Their structure-property relationships, the influence of different flexible spacers, the mesophase ranges and the photo-isomerisation of liquid crystalline trimers were described. A view of their photochromic behaviour was gained by UV–Visible spectroscopy. The 6-31G (d, p) basis set is combined with the B3LYP functional, which is used for computational studies of λ-shaped tris azo trimers. This approach allows for the determination of various quantum mechanical descriptors that can help us comprehend the mesogenic nature of molecules in computational studies. The results of the Gaussian calculation showed that the target compounds have low energy differences between HOMO-LUMO levels and good chemical reactivity. The examination of ESP and optical characteristics also yielded important information about the electronic structure and potential uses of these compounds.

The influence of the imine bond direction on the phase behaviour of symmetric and non-symmetric liquid crystal dimers

The synthesis and characterisation of two series of liquid crystal dimers are reported: the symmetric 1,5-bis(4′-oxyanilinebenzylidene-4-alkane)pentanes (m-O5O-m), and the non-symmetric 1-(4-cyanobiphenyl-4′-yloxy)-5-(4′-oxyanilinebenzylidene-4-alkane)pentanes (CBO5O-m). In the acronyms for each series m refers to the terminal chain length. The m-O5O-m series showed monotropic nematic phases for m = 1-7. Smectic behaviour emerged at m = 7 and nematic behaviour extinguished at m = 8. For the CBO5O-m series, an enantiotropic nematic phase is seen for m = 1-10. In addition, m = 1 shows a twist-bend nematic phase, and m = 9 and 10 an interdigitated smectic A phase. These series are compared to the corresponding dimers in which the imine link in the benzylideneaniline fragments is reversed, the m.O5O.m and CBO5O.m series. For the symmetric dimers, reversing the imine link has a small effect on the nematic-isotropic transition temperatures, TNI, but a much larger effect on the smectic-isotropic transition temperatures, TSmI. In both cases, the m.OnO.m series shows the higher values. The values of TNI are also slightly higher for the CBO5O.m series than the CBO5O-m series. Surprisingly, the values of TSmI are higher for the CBO5O-m than for the CBO5O.m series. These differences are discussed in terms of the changes in shape and electronic distributions arising from reversing the imine link.

Preparation of Laterally Chloro-Substituted Schiff Base Ester Liquid Crystals: Mesomorphic and Optical Properties

A new class of Schiff base/ester compounds: ICln, 4-((2′-chlorophenylimino)methyl)phenyl-4″-alkoxy benzoates, were synthesized and their mesophase characteristics and thermal behavior were evaluated. Differential scanning calorimetry (DSC) was used to study mesophase transitions, and polarized optical microscopy was carried out to identify the phases (POM). The results show that all compounds are monomorphic, and enantiotropic nematic (N) phases were seen at all side chains. It was found that lateral Cl atoms in the terminal benzene ring influence both conformation and mesomorphic properties. Comparisons between the present investigated lateral Cl derivatives and their laterally neat, as well as their isomeric, compounds have been briefly discussed. Results revealed that the insertion of lateral Cl substituent in the molecular structure impacts the type and stability of the formed mesophases. The exchanges of the ester-connecting moiety improve their thermal nematic stability than their previously prepared structurally isomeric derivatives. These compounds exhibit a broad absorption in the UV-Visible region, including a peak in UV region and a tail around 550 nm, and there were observed to be absorption tail increases and energy band gap decreases with the increase of the alkoxy side chain length. The photoluminescence (PL) intensity was noted to be quenched for the bulky alkoxy group ascribed to non-radiative recombination through the defect states. Moreover, time resolved fluorescence decay spectra reveal that both the radiative and non-radiative recombination lifetime increases with the increase of alkoxy side chain length.

Design of New V Shaped Thermotropic Liquid Crystals containing Heterocyclic

The characterization and design of this study of new liquid crystals with a V shape compounds containing thiazolidine-2,4-dione and 1,3-phenylene as a core unite with mesophase properties were reported. Preparation and characterization of chloroacetic acid, water, and thiourea to produce thiazolidine-2,4-dione [I] in the presence of strong hydrochloric acid. The 4-hydreoxybenzaldehyde and n-alkyl bromide were reacted with potassium hydroxide to create the n-alkoxy benzaldehyde., then the compound [I] reacted with [II]n in presence of piperidine to produce compounds [III]n. Also, converted resorcinol to a corresponding compound [IV] by refluxing pyridine and DMF with two moles of chloracetyl chloride, after that interacted the compounds [III]n and compound [IV] with sodium acetate to form compounds [V]n. FT-IR and 1HNMR spectroscopy were really used to determine the structures of the produced substances. Using polarized optical microscopy, these mesogens' mesomorphic characteristics were studied (POM).The synthesized molecules exhibited enantiotropic liquid crystal phases, the substances [V]1-4 exhibited an only the enantiotropic nematic phase.

Synthesis and molecular structure of V-shaped liquid crystalline compounds: Spectroscopic, mesomorphic, DFT investigations, electrochemical and fluorescence studies

A series of V-shaped compounds consisting of a central phenyl core connected by two identical mesogenic units which possess the imine (C=N) and ester (COO) bonds along with the terminal alkoxy chain (-OCnH2n+1) where n = 6-12. The ultimate compounds were synthesised and characterized by CHN elemental analysis, Fourier-Transform Infrared (FT-IR), nuclear magnetic resonance (1H-NMR), and UV-Visible (UV-Vis) spectroscopic techniques. The mesomorphic properties, thermal behaviour and conformation of compounds were studied by using polarised optical microscopy (POM), and differential scanning calorimetry (DSC). It can be generalized from present study that the V-shaped compounds with odd n carbon number in alkoxy chains were non-mesogenic. Whilst the compounds with shorter alkoxy chains of n = 6 and 8 were monotropic nematic, the compounds which possess longer alkoxy chains (n = 10 and 12) exhibited enantiotropic nematic phase. The computational method Chem3D Pro suggests the molecular structures of all the compounds with even n carbon number in the alkoxy chain. The Gaussian calculation with B3LYP/6-31G+(d,p) condition was employed to further demonstrate the chemical reactivity for all target compounds based on HOMO-LUMO analysis, the energy difference between HOMO-LUMO and surface charges. The target molecules of which the member containing the even n parity along the mesogenic arms have shown the same trend of electrocatalytic behaviour particularly toward the detection of hydrogen peroxide via the cyclic voltammetry study. Furthermore, the member with n=12 has been validated as a remarkable fluorogenic probe for the detection of Zn2+ ion.

Heterocyclic compounds-based liquid crystals

A series of liquid crystals comprising a heterocyclics dihydro pyrrole and 1,2,3-triazole rings [VII]-[X] were synthesized by many steps starting from a reaction of 3,3'-dimethyl-[1,1'-biphenyl]-4,4'-diamine with chloroacetyl chloride in a mixture of solutions DMF and TEA to synthesise the compounds [I], then the compounds [I] reacted with malononitrile in 1,4-dioxane and TEA solutions to produce compounds [II], then the first step is repeated with compound [II] where it reacted with chloroacetyl chloride in mixture of DMF and TEA to give compound [III], this compound reacted with sodium azide in the presence of sodium chloride and DMF as solvent to produce the compound [IV], which reacted with acrylic acid by a 1.3 dipolar reaction in solvent THF to give compound [V], this compound which reacted with thionyl chloride to gave carbonyl chlorides compound [VI], finally the last compound reacted with a variety of amines to product compounds [VII]a-d. The structures of the synthesized compounds were actually determined by Fourier-transform infrared spectroscopy FT-IR and Proton nuclear magnetic resonance 1H-NMR, The properties of liquid crystalline were characterized by hot stage Polarising Optical Microscope POM. The synthesized molecules exhibited enantiotropic liquid crystal phases, and the compounds [VII]a-d exhibited an enantiotropic nematic phase only.liquid crystal

Synthesis and characterization of novel swallow-tailed Schiff base liquid crystals

A series of swallow-tailed Schiff base liquid crystals with different end groups were synthesized and characterized. 4-chlorobenzoic acid, 4-methylbenzoic acid and 4-methoxybenzoic acid were connected with three hydroxyl groups of cholic acid by acyl chloride method to obtain intermediates SB-R1, SB-R2 and SB-R3. Schiff base phenol S-X1, S-X2 and S-X3 were linked with carboxyl groups of intermediate cholic acid to obtain the target compounds through esterification reaction. The structures of five kinds of swallow-tailed Schiff base liquid crystal compounds (SSB-RX1∼SSB-RX5) were characterized by IR、1H-NMR、13C-NMR and elemental analysis and liquid crystal performance was analysed by POM and DSC. The results showed that the five target products had good mesomorphic property and they all exhibited enantiotropic nematic phase which had schlieren texture and droplet texture.

Effects of terminal substituents on mesomorphic properties of Schiff base – ester mesogens and DFT calculations

ABSTRACT Two new groups of rod-like molecules with benzothiazole-aromatic systems: one group (B1Y) and the other (B2Z) having a Schiff and ester linkages with different terminal groups were synthesised. The structures of synthesised compounds were confirmed by using physicochemical techniques such as 1H-NMR, mass spectra and FT-IR spectra. Differential scanning calorimeter (DSC) and polarising optical microscopy have been employed to verify their liquid crystalline behaviours and transition temperatures. All the synthesised compounds (groups B1Y and B2Z) showed enantiotropic nematic phase except the compound B2 H. The thermal range of nematic phase for the compounds was greatly affected by the type of terminal groups. The change of the type of terminal groups in the compounds (B2Z) was theoretically studied to investigate if the theoretical calculations possess an agreement with the practical results.

New thiophene chalcones with ester and Schiff base mesogenic Cores: Synthesis, mesomorphic behaviour and DFT investigation

• Thiophene chalcones possessing Schiff base and ester mesogenic core have been synthesized. • Enantiotropic nematic (N) and Smectic A (SmA) phases were observed. • The impact of various connecting units, phenyl rings and of alkoxy chain length has been investigated. • Comparison with structurally similar compounds has been studied. • The DFT calculations of the thermodynamic and dimension parameters were conducted and correlated to mesomorphic behaviour. A new homologous series of thiophene-based mesogens, 4-((E)-((4-((E)-3-(thiophen-2-yl)acryloyl)phenyl)imino)methyl)phenyl-4-(alkyloxy)benzoate, TE- ( 2 – 18 ) in which thiophene heterocyclic unit at one end and long terminal alkoxy chains (C2-C18) at the other end were synthesized, characterized and studied for their mesomorphic and thermal behaviour. Differential scanning calorimetry (DSC) was used to investigate the phase transitions whereas types of mesophase were confirmed by polarized optical microscopy (POM). The mesomorphic investigation revealed that all new derivatives TE-(2 – 14) displayed an enantiotropic nematic phase (N) except the longer alkoxy chain ( n = 16 and 18) which are dimorphic in nature exhibited enantiotropic smectic A phase (SmA) in addition to enantiotropic nematic (N) phase. The mesomorphic behaviours of the new mesogens were investigated and discussed thoroughly and further compared with structurally similar compounds. Further, the optimised geometry of thiophene mesogens has been theoretically derived by the density functional theory (DFT) and the results revealed none co-planar structures for all compounds. The relationships between the calculated parameters, the polarizability, dimension parameters, have been used to illustrate the mesomorphic properties either the type of the texture or the mesomorphic range and stability.

Wide Nematogenic Azomethine/Ester Liquid Crystals Based on New Biphenyl Derivatives: Mesomorphic and Computational Studies.

The thermal stability and mesomorphic behavior of a new biphenyl azomethine liquid crystal homologues series, (E)-4-(([1,1′-biphenyl]-4-ylmethylene)amino)phenyl 4-(alkoxy)benzoate, In, were investigated. The chemical structures of the synthesized compounds were characterized using FT-IR, NMR, and elemental analyses. Differential scanning calorimetry (DSC) and polarized optical microscopy were employed to evaluate the mesomorphic characteristics of the designed homologues. The examined homologues possessed high thermal stability and broad nematogenic temperature ranges. Furthermore, the homologues were covered by enantiotropic nematic phases. The experimental measurements of the mesomorphic behavior were substantiated by computational studies using the density functional theory (DFT) approach. The reactivity parameters, dipole moments, and polarizability of the studied molecules are discussed. The theoretical calculations demonstrated that as the chain length increased, the polarizability of the studied series increased; while it did not significantly affect the HOMO–LUMO energy gap and other reactivity descriptors, the biphenyl moiety had an essential impact on the stability of the possible geometries and their thermal as well as physical parameters.

Coumarin derivatives containing schiff base and ester mesogenic core: Synthesis, mesomorphic behaviour and DFT calculations

New coumarin esters, (E)-4-(((7-(octyloxy)-2-oxo-2H-chromen-3-yl)imino)methyl)phenyl-4-alkyloxybenzoate, CE-(2-18) containing Schiff base linkage in which octyloxy chain at one end and different long terminal alkoxy chains (C2-C18) at the other end have been synthesized and studied for their mesomorphic behaviour. New compounds were characterized using different analytical techniques such as FT-IR, 1H NMR, 13C NMR, and Mass spectral analysis. The transitions of phase and mesophase investigation were carried out using differential scanning calorimetry and Polarised Optical Microscope. The mesomorphic investigation revealed that all new derivatives CE-(2-14) exhibited an enantiotropic nematic phase whereas except CE-2 and CE-3 all other members have also displayed enantiotropic smectic C phase in addition to enantiotropic nematic phase. The new mesogens mesomorphic behaviour of all synthesized compounds were thoroughly studied and discussed, as well as compared with structurally comparable substances. Finally, the DFT theoretical calculations were studied and compared with the experimental to explain the relationship between the structural parameters and the mesomorphic behaviour.