Schiff Base Liquid Crystals Research Articles

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.

Novel star-shaped liquid crystal macromolecules based on conjugated structures of azo and Schiff bases: synthesis and properties

ABSTRACT In this paper, a series of novel liquid crystal units (ASE-n, n = 4, 6, 8) of azo Schiff bases with sulphonic acid (-SO3H) as terminal substituents and different alkyl chain lengths were designed and synthesised. Nine star-shaped liquid crystal macromolecules with different central groups (ASE-P-n, ASE-T-n, ASE-G-n, n = 4, 6, 8) were synthesised by esterification of three novel azo Schiff base liquid crystal units (ASE-n, n = 4, 6, 8) with phloroglucinol, pentaerythritol and glucose. The structure of the synthesised compounds were analysed by infrared spectroscopy and 1H NMR. The results showed that all the compounds were consistent with the molecular structure design. The properties of liquid crystal such as phase transition temperature and liquid crystal mesophase range were characterised by POM and DSC. The effects of alkyl chain length and branched degree on the properties of liquid crystal were studied. The maximum absorption spectrum of the compound was determined by UV-Vis spectrophotometry. The photoisomerisation reaction of the compound was also studied. Under ultraviolet light (λ = 365 nm) irradiation, the effect of different duration on the cis-absorption percentage of azo (-N=N-) bond in the compound was studied.

Synthesis of New Liquid-Crystalline Compounds Based on Terminal Benzyloxy Group: Characterization, DFT and Mesomorphic Properties.

The effect of the terminal benzyloxy group on the mesomorphic properties of liquid crystalline materials developed from rod-like Schiff base has been described. For this objective, a novel Schiff base liquid crystal family, specifically new series of Schiff base liquid crystals, namely, (E)-4-(alkyloxy)-N-(4-(benzyloxy)benzylidene)aniline, In, are prepared and investigated in detail. The length of the terminal alkyloxy chain (n) varies amongst the compounds in the series. Where n varies between 6, 8 and 16 carbons. At the other end of the compounds, benzyloxy moiety was attached. The molecular structures of all synthesized compounds were established using different spectroscopic techniques. The molecular self-assembly was explored using differential scanning calorimetry (DSC) and polarized optical microscope (POM). Depending on the length of the terminal alkyloxy chain, only one type of SmA phase with different stability was observed. The previously reported para-substituted systems and the present investigated compounds were compared and discussed. The calculated quantum chemical parameters were computationally correlated using the DFT method via the B3LYP 6-311G(d,p) basis set. The theoretical computations revealed that the length of the alkyl side chain influences the zero-point energy, reactivity and other estimated thermodynamic parameters of benzoyloxy/azomethine derivatives. Furthermore, the FMO energy analysis shows that molecule I16 have higher HOMO energies than the other compounds, and I6 has a much lower LUMO level than the rest.

The influence of core fluorination on the phase behaviour of rod-like mesogens

ABSTRACT The effect of core fluorination on the mesomorphic properties of rod-like Schiff base-derived liquid crystalline materials was reported. For this purpose, two new series of laterally fluorinated Schiff base liquid crystals are synthesised and investigated in detail. The two series differ from each other’s in the length of the terminal alkoxy chain attached to one end of the aromatic core, where in the first series an octyloxy chain is used and in the second series it is replaced by a longer dodecyloxy chain. At the other end in both series of compounds, in addition to the nonsubstituted end (X = H) four different substituents were used (X = CH3O, C6H13O, CH3 and F). The molecular structures of all synthesised compounds were confirmed using different spectroscopic techniques. The molecular self-assembly was investigated using differential scanning calorimetry (DSC) and polarised optical microscope (POM). Depending on the length of terminal alkoxy chain at one end and nature of the substituent X at the other end, different types of mesophases were observed, including nematic and two different types of smectic phases.

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.

Glassy nematogenic properties induced by six-membered ring’s trimeric fluorinated Schiff base liquid crystals

ABSTRACT New non-conventional Schiff base trimers composed of two fluorinated benzylideneaniline moieties connected to a halogen-substituted benzalideneaniline core at the ortho and para positions via octylene spacers were synthesized and characterized. The halogen X at the 4-position of the benzalideneaniline core includes F, Cl, Br and I. All the members exhibit enantiotropic nematic phase except for the compounds possessing fluorine and iodine substituents, which show only monotropic characteristics. A notable feature is that upon cooling the trimers vitrified to form the glassy state at low temperature. The Schlieren texture remains unchanged even it reaches the room temperature. This phenomenon resembles the one exhibited by glassy nematic liquid crystals and the enthalpy changes associated with the nematic to glass transition are unresolved due to the negligible value of heat change. The effect of different halogens towards the mesomorphic properties of the trimers was also described.

Polar Alkoxy Group and Pyridyl Effects on the Mesomorphic Behavior of New Non-Symmetrical Schiff Base Liquid Crystals

A series of non-symmetrical Schiff base liquid crystals were prepared and investigated. Schiff bases of p-alkyloxy aniline derivatives and 4-phenyl pyridine-4′-carbaldehyde were synthesized. The terminal alkoxy groups substituting aniline are of varied chain length, namely C6, C8, and C16. The structures of the compounds were confirmed via 1H NMR and 13C NMR spectroscopy. Different mesophases of the samples were thermally and optically characterized by differential thermal analysis (DSC) and polarized optical microscopy (POM). All samples revealed enantiotropic smectic B (SmB) and smectic A (SmA) mesophases. The results obtained were further correlated with the density functional theory (DFT) theoretical calculations. The results are compared to a series of compounds bearing biphenyl moiety in their mesogens. The thermal stabilities of the different mesophase reduced upon the increment of the alkoxy chain length. The temperature ranges of both the smectic mesophases of new compounds bearing the 4-phenyl pyridine moiety are generally expanded higher than the other series. In addition, the total mesophase range is greater in the new compounds when compared to their biphenyl analogues. The DFT results were investigated in terms of the molecular geometries and the frontier molecular orbitals as well as the charge distribution mapping to show and illustrate the difference in the mesomorphic properties.

Mesomorphic Behaviour and DFT Insight of Arylidene Schiff Base Liquid Crystals and Their Pyridine Impact Investigation

A new series of Schiff base liquid crystal have been prepared and studied. Schiff bases of p-alkyl aniline derivatives and 4-phenyl pyridine-4′-carbaldehyde were prepared. The terminal alkyl groups substituting aniline are of varied chain length, namely C8, C12 and C14. The structures of the compounds were elucidated by 1H NMR and 13C NMR. The mesomorphic thermal and optical characteristics of the samples were determined via differential thermal analysis (DSC) and polarization optical microscopy (POM). All compounds exhibit enantiotropic dimorphic mesophase behaviour, referred to as smectic X1 (SmX1) and smectic X2 (Sm A). Experimental results obtained for the mesophases were correlated with density functional theory (DFT) theoretical calculations. The results of the new series are further compared to two series of compounds bearing pyridine (two ring Schiff bases) and biphenyl, respectively, in their mesogens. The series of compounds of one pyridine ring are generally not mesomorphic. The results indicate that the alkyl chain length has a strong impact on the mesomorphic characteristics and thermal stabilities of the different mesophases. As a trend, the temperature ranges of both of smectic mesophases of all compounds are higher in new compounds bearing the 4-phenyl pyridine moiety. In addition, the total mesophase range is generally higher in the new compounds when compared to their biphenyl analogues. Finally, theoretical DFT calculations were performed to illustrate the experimental finding of the mesomorphic behaviour in terms of the molecular geometry and aromaticity, π–π stacking and LOL-π.

Optical investigations and photoactive solar energy applications of new synthesized Schiff base liquid crystal derivatives

New homologues series of liquid crystalline materials namely, (E)-3-methoxy-4-[(p-tolylimino)methyl]phenyl 4-alkloxybenzoates (I-n), were designed and evaluated for their mesomorphic and optical behavior. The prepared series constitutes three members that differ from each other by the terminally attached alkoxy chain group, these vary between 6 and 12 carbons. A laterally OCH3 group is incorporated into the central benzene ring in meta position with respect to the ester moiety. Mesomorphic characterizations of the prepared derivatives are conducted using differential scanning-calorimetry (DSC), polarized optical-microscopy (POM). Molecular structures were elucidated by elemental analyses and NMR spectroscopy. DSC and POM investigations revealed that all the synthesized derivatives are purely nematogenic exhibiting only nematic (N) mesophase, except for the longest chain derivative (I-12) that is dimorphic possesses smectic A and N phases. Moreover, all members of the group have a wide mesomorphic range with high thermal nematic stability. A comparative study was established between the present derivative (I-6) and their previously prepared isomer. The results indicated that the location exchange of the polar compact group (CH3) influences the N mesophase stability and range. The electrical measurements revealed that all synthesized series I-n show Ohmic behaviors with effective electric resistances in the GΩ range. Under white light illumination, the effective electric conductivity for the compound I-8 is five times that obtained in dark conditions. This derivative also showed two direct optical band gaps in the UV and visible light range. In addition, I-6 has band energy gaps of values 1.07 and 2.79 eV, which are suitable for solar energy applications.

Pyridine-Based Three-Ring Bent-Shape Supramolecular Hydrogen Bond-Induced Liquid Crystalline Complexes: Preparation and Density Functional Theory Investigation

A series of new supramolecular three-ring bent-shape Schiff base liquid crystal (LC) complexes were prepared and studied. On one side, two alkoxy chain lengths of the carboxylic acids were used, namely eight and sixteen carbons. Moreover, on the other side, terminal small compact groups, which substituted aniline, with different polarities were utilized. Furthermore, the hydrogen-bonding interactions in the formed complexes were elucidated by Fourier-transform infrared (FT–IR) spectroscopy. The mesomorphic thermal and optical characteristics of the samples were determined by differential thermal analysis (DSC) and polarized optical microscopy (POM). The complexes exhibited enantiotropic and dimorphic mesophase behaviors. The results indicate that the polarity of the compact groups and the lengths of the alkoxy chains greatly impacted the mesomorphic characteristics and thermal stabilities of the mesophases. The observed values of the enthalpy changes (ΔH) associated with the crystalline smectic-A (TCr-SmA) transitions were extremely small compared with the conventional values that characterize supramolecular hydrogen-bonded liquid crystalline complexes. ΔH, which corresponded to the nematic isotropic transitions (TN-I), varied from 0.13 to 9.54 kJ/mol depending mainly on the polarity of the groups that were para-attached to the aniline moiety. Finally, the theoretical results obtained by density functional theory (DFT) calculations were discussed. The DFT geometrical structures showed non-coplanar structures. The mesomorphic range was correlated with the calculated dipole moment, polarizability and the aspect ratios of the investigated compounds.

Mesomorphic study and DFT simulation of calamitic Schiff base liquid crystals with electronically different terminal groups and their binary mixtures

ABSTRACT Two series of Schiff bases liquid crystals with electronically different terminal substituents, 4-(alkoxy)phenylimino)methyl)benzonitrile (In-a) and N-(4-(hexyloxy)benzylidene)-4-(alkoxy)benzenamine (In-6), were synthesise. Their molecular geometries were elucidated via FT-IR, 1 H-NMR and elemental analysis. Mesomorphic and optical properties were investigated by differential scanning calorimetry (DSC) and polarised optical microscopy (POM). The effect of electronic nature of in the attached terminals, extra-conjugation E- withdrawing (CN) and E-donating (hexyloxy), is investigated. All members of the investigated compounds were enantiotropically mesomorphic comprising mono or dimorphic phases depending on the electronic and complexity nature of attached terminals. Computational parameters of both series were related with the experimental findings of the mesophase stability and the length of alkoxy chains to investigate the effect of the terminals on the stability of possible architectures. Density functional theory (DFT) calculations revealed that all investigated members are non-co-planar with twist angles between the rings around the CH = N linkage. The relations of the experimentally mesophase range and stability of the enhanced phases with simulated parameters were studied to conclude that these factors contributed in different extent to affect the mesomorphic behaviour. The binary phase diagrams were constructed between In-6 components and achieved very low melting temperatures at their eutectic mixtures.

Synthesis, Optical, and Geometrical Approaches of New Natural Fatty Acids' Esters/Schiff Base Liquid Crystals.

Schiff base liquid crystals, known as [4-(hexyloxy)phenylimino)methyl]phenyl palmitate (IA), [4-(hexyloxy)phenylimino)methyl]phenyl oleate (IIA) and [4-(hexyloxy)phenylimino)methyl]phenyl linoleate (IIIA), were synthesized from palmitic, oleic, and linoleic natural fatty acids. The prepared compounds have been investigated for their thermal and optical behavior as well as phase formation using differential scanning calorimetry (DSC) and polarized optical microscopy (POM). Molecular structures of all studied compounds were confirmed via elemental analysis, FT-IR, 1H NMR, and 13C NMR. Smectic phase is the observed mesophase for all compounds; however, their type and range depend upon the terminal alkanoate chains attached to the phenyl ring. Computational calculations, Density functional theory (DFT), energy difference of the frontier molecular orbital (FMOs), as well as the thermodynamic parameters of different molecular configurations isomers were discussed. It was found that the mesophase behavior and the geometrical characteristics were affected by the degree of unsaturation of fatty terminal chains. Furthermore, the geometrical structure of the CH=N linkage plays an important role in the thermal stability and optical transition temperature.

Isoxazoline- and isoxazole-liquid crystalline schiff bases: A puzzling game dictated by entropy and enthalpy effects

Two series of Schiff base (SB) liquid crystals (LC) containing the 5-membered rings isoxazoline or isoxazole were synthesized and characterized; 27 isoxazoline and 20 isoxazole compounds were obtained. Nematic, smectic A, and smectic C mesophases were found and characterized by Polarized optical microscopy (POM), Differential scanning calorimetry (DSC), and X-ray diffraction. The scientific problem addressed was how the isoxazoline and isoxazole rings affect the mesophase structure and stability. Molecular packing and anisotropic interactions based on enthalpy and entropy properties were used to explain the thermal and structural behaviour observed for both series. The proposed mechanism was assisted by Density functional theory (DFT) calculations, providing new insights into the molecular organization of this kind of system.

Synthesis and Mesophase Behavior of Schiff Base Liquid Crystals with Long-chain Aliphatic-acid

Utilizing p-chloroaniline, p-hydroxybenzaldehyde and aliphatic diacids with different chain length as raw materials, the Schiff base liquid crystals Cl-SBPA4, Cl-SBPA6, Cl-SBPA8 and Cl-SBPA10 were synthesized by condensation and esterification. Their chemical structures were confirmed by FTIR and 1H NMR spectra. The mesophase behaviors were studied by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). The influence of molecular structure on mesophase behavior and optical property were discussed. The results demonstrated that Cl-SBPA4 exhibited smectic mosaic texture, Cl-SBPA6 and Cl-SBPA8 showed nematic droplet and schlieren texture, while Cl-SBPA10 had no mesomorphic phases. With the increase of the length of flexible chain, their melting transition (Tm) and crystallization temperature (Tc) exhibited a trend of decreasing first and then going up.

Adsorption Study of Malachite Green Dye of New Schiff Base Liquid Crystal Surface (Thermodynamic and Kinetic)

This work incorporates blends of new heterocyclic mixes of (2-amino-6-methoxy benzothiazole), from response with (p-hydroxybenzaldehyde) to yield Schiff bases, the compound have been distinguished (FT-IR ,HNMR) the misomorphic stages were recognized by energized light magnifying lens (POM) and estimated change temperatures for compound by differrntion checking calorimeter (DSC) at that point investigation of fluid precious stone properties and we will contemplate the adsorption of malachite green color on this fluid gem as a surface. Likewise The examination incorporated the trial of applying the isotherm models of Langmuir, Freundlich, harkinsjura and Temkin to the handy adsorption information of the color under investigation utilizing the UV spectroscopy. The active information were demonstrated by utilizing pseudo-first-arrange, pseudo-second-request, Elovich and intra-molecule dispersion energy conditions, Adsorption adsorbents were additionally used to get the estimations of the thermodynamic capacities (Free vitality ∆G, enthalpy ∆H, and ∆S entropy and actuation vitality).

Photochemical behaviour of Schiff base liquid crystals based on isoxazole and isoxazoline ring. A kinetic approach

ABSTRACTThe kinetic study on the hydrolysis of Schiff bases (SBs) 1a-c and 2a-c induced by UV-vis was undertaken as a complementary study of the stability in solution and in bulk of the SBs. Solutions in chloroform were exposed to UV-vis and acquisition data occurred for 1a-c and for 2a-c in 21°C, 30 °C, 35°C and 40°C. Kinetic profile for 1a-c and 2a-c displayed the similar photochemical behaviour in that four temperature values. At 21°C, two kinetic regimes were observed where the decomposition of SBs is faster at the initial stage, with no linear plot of absorbance vs time, and after the kinetic profile obeyed a linear behaviour. A mathematical treatment of the experimental data was applied, which allowed associating the initial stage data with a second-order reaction, and the final stage of the hydrolysis with a first-order reaction. The mechanism of photochemical hydrolysis of SBs 1a and 2a was addressed. It was composed of three parts, the excitation, then the isomerisation and activation processes of tetrahedral intermediate and, the last process, a collapse of the intermediate to the yielded products of the hydrolysis aldehydes and amines which were detected by their UV-vis spectrum.

Studies of temperature and frequency dependence of dielectric permittivities of two Schiff's base liquid crystal compounds

Abstract Effect of temperature and frequency on the dielectric permittivities of two Schiff's base liquid crystal compounds p-ethoxybenzylidine p-heptylaniline(EBHA) and p-butoxybenzylidine p-heptylaniline(BBHA) have been studied by using a digital LCR bridge (HIOKI 3532-50 LCR HiTESTER). Due to the changes of CH 2 groups at the oxygen containing flexible side chain between these two compounds, some changes occur in the behavior of their temperature dependent physical properties such as dielectric anisotropy, splay elastic constant, relaxation time, which has been studied extensively. The frequency dependent electrical conductivity of these two compounds has also been carried out. At the nematic mesophase the values of activation energy have been estimated from the temperature dependent DC and AC conductivity curves. The optical band gap of EBHA and BBHA has been calculated from UV spectra.

Electric behaviour of a Schiff's base liquid crystal compound doped with a low concentration of BaTiO3 nanoparticles

We report here a low frequency (1Hz–10MHz) dielectric study of a Schiff base liquid crystal compound, N-(4-n-Pentyloxybenzalidene) 4′-n-Pentylaniline (in short 5O.5) dispersed with Barium titanate (BaTiO3) nanoparticles (0.4%). The compound 5O.5 exhibit N, SmA, SmC, SmF and SmG phases. The isotropic-nematic phase transition temperature and the dielectric anisotropy (∆ε) have been determined. The compound in pure state exhibits negative dielectric anisotropy. The effect of the ferroelectric nanoparticles (FNPs) on dielectric permittivity and dielectric anisotropy as a function of temperature as well as frequency has been discussed. It has been found that due to permanent dipole moment of FNPs, the majority of ions in isotropic and nematic phases gets trapped, consequently Maxwell-Wagner-Sillars (MWS) effect has diminished. The conductivity of the dispersed samples was found to decrease. Comparative dielectric relaxation behavior of the liquid crystal molecules of pure and BaTiO3 dispersed samples are discussed in nematic, SmA and SmC phases of the compound.

Effect of azo and ester linkages on rod shaped Schiff base liquid crystals and their photophysical investigations

Two new series of rod shaped Schiff base containing liquid crystal compounds with azo and ester linkages have been synthesized and characterized respectively. The rod like molecules containing cinnamate linkages with four different alkyl spacers (n = 6, 8, 10 and 12) and influence of linking group have been elucidated. Considerable changes in mesomorphic properties were noticed starting from Nematic to Smectic-C on changing of azo and ester linkages along with different terminal alkyl chain lengths. The mesomorphic properties of both series are compared. Photosensitive azobenzene group undergoes photoisomerization under UV light and monitored by UV–Visible spectroscopy.

Synthesis and Mesomorphic Properties of New Fluorinated Schiff Base Liquid Crystals

Two new compounds, 4-alkanoyloxybenzylidene-4′-fluoroaniline and 4-fluorobenzylidene-4′-n-alkanoyloxyaniline comprising a terminal fluorosubstituent were studied. The fluoro substituent contributes to the molecular polarizability, thus affecting intermolecular interactions and hence resulting in smectic mesomorphism. The mesomorphic properties were studied using differential scanning calorimetry and polarizing optical microscopy techniques. The mesomorphic properties of compounds studied are strongly dependent on the orientation of the imine (CH=N) linkage. The former Schiff base exhibited smectic A phase whereas the latter compound did not display any mesophase. Reversed imine linkage has caused depression of mesomorphic property in the compound studied (4-fluorobenzylidene-4′-n-alkanoyloxyaniline). The mesomorphic properties of the present compounds were compared with other structurally related series to establish the chemical structure-mesomorphic property relationship.