Alkoxy Benzoates Research Articles

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.

Mesomorphism of a series of aromatic single tail biphenyl-yl-4-(alkoxy) benzoate and 4-(benzyloxy)phenyl-4-(alkoxy)benzoate liquid crystalline materials

Liquid crystals are widely used in industry. The mesomorphism of two series of single tail ester liquid crystalline materials is reported in this study and compared structurally with a third series of molecules that do not display mesomorphism. The mesomorphic behavior of these two series was elucidated using polarized optical microscopy and differential scanning calorimetry. For longer chain tails in both series, we found that the liquid crystals possess two mesophases namely nematic and smectic A, whereas shorter tail members of both series possess only a nematic phase and in one case no mesophase was observed.

Binary Liquid Crystal Mixtures Based on Schiff Base Derivatives with Oriented Lateral Substituents

Binary mixtures of the laterally substituted Schiff base/ester derivatives, namely 4-((2- or 3-) substituted phenyl imino methyl) phenyl-4”-alkoxy benzoates, Ia–d, were prepared and mesomorphically studied by differential scanning calorimetry (DSC) and their mesophases identified by polarized optical microscopy (POM). The lateral group (1-naphthyl, 2-F, 2-Br, 3-F in Ia–d, respectively) is attached to different positions of the phenyl Schiff moiety. The mixtures investigated were made from two differently shaped compounds that differ from each other in the polarity, size, orientation, and relative positions of the lateral group. The results revealed that the binary mixture Ia/Ib (bearing the naphthyl and 2-flouro substituents) exhibited the SmA phase, which covered the whole composition range. For the mixtures Ib/Id (2-F and 2-Br), the isomeric lateral F-group in compound Ib distributed the SmA arrangement of Id. In the Ic/Id mixture bearing two positionally and structurally different substituents, the addition of Ic to Id resulted in solid binary mixtures where its behavior may be attributed to the negligible steric effect of the small electronegative fluorine atom compared to the Br atom. Density functional theory (DFT) theoretical calculations were carried out to estimate the geometrical parameters of individual components and to show the effect of these parameters in the mesophase behavior of the binary system, where the higher dipole moment of Id (6 Debye) may be the reason for its high π–π molecular stacking, which influences its mesophase range and stability.

Thermal and Photophysical Studies of Binary Mixtures of Liquid Crystal with Different Geometrical Mesogens

Three binary systems were prepared by mixing of two different mesogenic derivatives, homologues, the first is azo/ester, namely 4-alkoxyphenylazo-4′-phenyl-4″-alkoxybenzoates (IIn+m) and the second is Schiff base/ester, namely 4-(arylideneamino)phenyl-4″-alkoxy benzoates (In+m). The two corresponding analogues from both series in the binary mixtures investigated are of the same terminal alkoxy chain length. Mesomorphic properties were investigated by differential scanning calorimetry (DSC) and phases identified by polarized optical microscope (POM). Photophysical studies were investigated by UV spectroscopy connected to a hot stage. Results were discussed based on constructed binary phase diagrams. All mixtures were found to exhibit eutectic compositions, with linear or slightly linear nematic and smectic A stability/composition dependences. Geometrical parameters were predicted applying density functional theory (DFT) calculations. Twist angle (θ), aspect ratio, dipole moment and the polarizability of the individual compounds were discussed and correlated with the experimental results to illustrate the enhanced the mesophase stability and the mesophase range of the mixture at the eutectic composition compared with those of their individual components.

Mesomorphic and geometrical orientation study of the relative position of fluorine atom in some thermotropic liquid crystal systems

ABSTRACTNew series of the Schiff base/esters, 4-((2′-or 3′-fluorophenylimino)methyl)phenyl-4″-alkoxy benzoates were prepared and their mesophase behaviour investigated. The type of the mesophase and its transition temperature were determined by differential scanning calorimetry (DSC) and polarised optical microscopy (POM). The optimised structures of Schiff base/ester and their azo/ester groups have been deduced theoretically by density functional theory (DFT). Each group of homologues differs from the other by the position of the fluorine atom on the terminal benzene ring, in addition to laterally neat homologues. Comparative studies revealed that the position and orientation of the lateral fluorine atom as well as the type of the linking core not only affects the melting temperature but also the mesophase stability. DFT results showed that the type and stability of the mesophase could be illustrated in the terms of calculated dipole moment, polarisability, thermal energy and molecular electrostatic potential.

Schiff base/ester liquid crystals with different lateral substituents: mesophase behaviour and DFT calculations

ABSTRACTFour new groups of 4-((2ʹ-substitutedphenylimino)methyl)phenyl-4”-alkoxy benzoates, Ina-d, of Schiff base ester liquid crystals, were prepared and investigated for their mesophase formation and stability. Each group constitutes four homologous series that differ from each other by the lateral attached polar group X in the ortho position for the imine mesogen at terminal benzene ring that alternatively changed from F, Br, NO2 and lateral benzene ring. Within each homologous series, the number (n) of carbons in the alkoxy chain varies between 6, 8, 10 and 12. Molecular structures of the prepared compounds were confirmed via elemental analysis, FT-IR, and 1H NMR spectroscopy. Mesomorphic properties were investigated by differential scanning calorimetry (DSC) and the phase identified by polarised light microscopy (PLM). A comparative study was made between the investigated compounds and their previously prepared laterally neat, 4-((4ʹ-phenylimino)methyl)phenyl-4”-alkoxy benzoates (IIn); the result revealed that all lateral substituents not only decrease the melting temperature but also the mesophase stability and shown only nematic phase. Density functional theory (DFT) calculations for new lateral derivatives were discussed.

Synthesis and mesophase behaviour of Schiff base/ester 4-(arylideneamino)phenyl-4″-alkoxy benzoates and their binary mixtures

Four new groups of Schiff base ester liquid crystal compounds, 4-(arylideneamino)phenyl-4″-alkoxy benzoates, Ina–d, were prepared and investigated for their mesophase formation and stability. An alkoxy group of variable chain length (n = 6, and 16 carbons) is attached to the terminal phenylazo benzoate moiety. Each group constitutes two homologous series that differ from each other by the polar substituent X (CH3O, H, NO2, and F). The molecular structure of the prepared compounds was confirmed via FT-IR, 1H NMR, mass spectroscopy and elemental analysis. The mesomorphic properties were investigated by differential scanning calorimetry (DSC) and polarized light microscopy (PLM). For n = 6, all compounds exhibit nematic phase. Amongst them methoxy and nitro derivatives have widest mesophase range. For n = 16, nitro and flouro derivatives exhibit SmA phase, while methoxy and unsubstituted derivative are nematogenic. The change of the mesophase stability is well correlated with van der Waals volume and polarizability of the substituent X and not satisfactory with the dipole moment of the whole molecule. The mesophase behavior of binary mixtures made from each individual derivatives bearing the same substituent X but varies with alkoxy chains length is presented. Results provide insights into the role of substituent X and alkoxy chain length on the mesophase behavior within the whole composition range of the mixtures.

Polarity and steric effect of di-lateral substitution on the mesophase behaviour of some azo/ester compounds

ABSTRACTEight homologous series of 2-(or 3-)substituted phenyl 4ʹ-(4″-alkoxy (2ʹ-, or 3″-substituted phenylazo) benzoates (InXY) were prepared in which the suffix ‘X’ refers to the lateral substituent X attached to the terminal benzene ring that carries the alkoxy group, and the suffix ‘Y’ refers to the substituent attached to the other terminal phenyl group. Within each homologous series, the length of the terminal alkoxy group varies from 8 to 16 carbons, while the lateral polar substituents, X and Y, alternatively varies between CH3 and F. The mesophase behaviour was investigated by differential scanning calorimetry and identified by polarised optical microscopy. The results were discussed in terms of the polarity and steric effects of the two lateral substituents. Comparative correlations were made to investigate the effect of the second lateral substituent on the mesophase behaviour of the previously investigated mono-laterally substituted analogues. UV–vis spectroscopic study revealed that the compounds I8XY exhibited two absorption bands: low intense bands at 254–263 and a broad band at 364–376 nm. These bands are attributed to the π–π∗ transition of the phenyl rings and the whole mesogenic portion.

Synthesis and mesomorphism of novel chalconyl esters with a lateral nitro group

ABSTRACTA new chalconyl homologous novel series with lateral nitro group: 4-(3-4-(heptyloxy)phenyl) acryloyl-2/-nitro phenyl 4′-alk oxy benzoate have been synthesized and all the members are differed by the terminal chain length CnH2n+1, where n = 1,2,3,4,5,6,7,8,10,12,14,16,18. Their transition temperatures and mesophase characteristics are studied with the help of polarizing optical microscope (POM). All 13 homolog of series except the C1–C4 are enantiotropically mesogenic. The molecular structures have been confirmed by the analytical techniques of NMR, IR, and elemental analysis.

The effect of inversion of the ester group on the mesophase behaviour of some azo/ester compounds

Five homologous series of 4-substituted phenyl 4′-(4″-alkoxy phenylazo) benzoates (Ina–−e) were prepared in which, within each homologous series, the length of the terminal alkoxy group varies between 8, 10, 12, 14 and 16 carbons, while the other terminal substituent, X, is a polar group that alternatively changed from CH3O, CH3, H, Br, and CN groups. Compounds prepared were characterised by infrared, mass, and H1-NMR spectroscopy and their mesophase behaviour investigated by differential scanning calorimetry (DSC) and polarised light microscopy (PLM). The results were discussed in terms of mesomeric and polarisability effects. Only for the lower group of compounds, I8a-e, that showed a nematic phase, the nematic-to-isotropic transition temperatures (TN–I) were successfully correlated to the polarisability anisotropy of bonds to the substituent X. A comparative study was made between the investigated compounds and two previously prepared isomeric groups. In the first group of isomers, 4-(4′alkoxy phenylazo) phenyl 4″-substituted benzoates (IIna–e), the ester groups are inverted. While in the second, 4-(4′-substituted phenylazo) phenyl 4″-alkoxy benzoates (IIIna–e), two modifications were made, inversion of the COO group, and exchange of the two wing substituents

Mesophase stability in binary mixtures of monotropic nematogens

Binary phase diagrams were constructed from laterally substituted methyl azo/ester derivatives, namely 4-(4″-substituted phenylazo)-3-methyl phenyl-4″-alkoxy benzoates (Ina–d). In this group of compound the unsubstituted and chloro-substituted derivatives possess the nematic phase monotropically, while the nitro and methyl analogues are enantiotropically nematogenic. The binary phase diagrams constructed were made once from the monotropic nematogens with each other, and another with the enantiotropic nematogens. In both the cases enantiotropic nematic phase was observed that covers a wide range of composition. The mesophase behaviour of all binary mixtures was investigated by differential scanning calorimetry (DSC) and polarised light microscopy (PLM). The nematic phase was exhibited in all binary mixtures. Independent of the alkoxy chain length, the entropy change, ΔSN–I of the N–I transition of pure components was found to vary irregularly with the anisotropy of polarisability (∆αX) of the polar substituent, X.

Effect of lateral substituent and chain length on mesomorphic properties of novel alkoxy benzyloxy benzoates of cyanophenyl rod-shaped compounds

Three novel homologous series of rod-shaped cyanophenyl alkoxy benzoate liquid crystalline compounds with lateral polar fluorine and chlorine substituent were prepared, and chemical structures of novel materials have been characterized by standard spectral technique and elemental analysis. The mesophase characterization was carried out using the combination of polarized optical microscopy and differential scanning calorimetry. All the compounds exhibit wide thermal range of enantiotropic SmA phase.

Effect of lateral substitution of different polarity on the mesophase behaviour in pure and mixed states of 4-(4′-substituted phenylazo)-2-substituted phenyl-4″-alkoxy benzoates

Two groups of 4-(4′-substituted phenylazo)-2-phenyl-4″-alkoxy benzoates were prepared and their mesophase formation and stability investigated. Each group (I n a-e and II n a-e) constituted five homologous series differing in their terminal substituent, CH3O, CH3, H, Cl or NO2. Within each series the number of carbons in the terminal alkoxy chain was 8, 10, 12, 14 or 16. The two main groups of compounds (I and II) differed in the polarity of the lateral substitutent attached to the central benzene ring. Group I had a chlorine atom adjacent to the ester group, replaced in Group II by the weakly electron-donating methyl group. Binary phase diagrams were constructed in which the two components were terminally-substituted analogues from within each group. The study was designed to investigate the effect of a lateral chloro or methyl group on the mesomorphic properties of the resulting derivatives, in pure or mixed states. The mesophase behaviour of the compounds themselves and their binary mixtures was investigated by differential scanning calorimetry and polarised light microscopy. The nematic phase was exhibited in most of the compounds, including their binary mixtures.

Lateral protrusion and mesophase behaviour in pure and mixed states of model compounds of the type 4-(4′-substituted phenylazo)-2-(or 3-)methyl phenyl-4'-alkoxy benzoates

Two groups of the title compounds were prepared and investigated for their mesophase formation and stability. Each group constitutes five homologous series that differ from each other by the polar substituent X (CH3O, CH3, H, Cl, and NO2). Within each homologous series, the number (n) of carbons in the alkoxy chain varies between 8, 10, 12, 14 and 16. The difference between the two groups of compounds lies in the orientation protrusion of the lateral methyl group attached to the central benzene ring. In the first group (Group I) the methyl substituent, introduced into the o-position with respect to the ester group, makes an angle of 60° with the long axis of the molecule. In the other series of compounds (Group II), the orientation angle is 120° as it is introduced into the position-3. All possible binary phase diagrams could be constructed in which the two components are corresponding positional isomers from either group. The study aimed to investigate the effect of inclusion of the lateral methyl group, as well as its spatial orientation, on the mesomorphic properties of the produced derivatives in their pure and mixed states. The compounds prepared in both groups were characterised for their mesophase behaviour by differential scanning calorimetry and polarised light microscopy. The nematic phase is the mesophase observed in most of the compounds prepared and their binary mixtures.

DFT Study of Lewis Base Interactions with the MgCl2 Surface in the Ziegler−Natta Catalytic System: Expanding the Role of the Donors

We present a computational study, using density functional theory, of the role of internal and external donors in supported heterogeneous Ziegler−Natta polymerization catalyst systems. The focus of the investigation is the ability of the donors to stabilize the MgCl2 support through the zip mode of coordination. Phthalates and alkoxy benzoates have been considered as representative internal and external donors, respectively. Models for the α (ccp) and the β (hcp) phases of the (110) MgCl2 lateral cut have been considered. Studies were first done with a “Fully Fixed Model”, where the atoms in the MgCl2 lateral cuts were kept fixed. The studies indicated that the phthalate donors would preferentially stabilize the α phase of MgCl2, while the alkoxy benzoate donors would stabilize the β phase more, corroborating experimental results. A comparison of the zip coordination mode with other modes of coordination (mono, chelate, and bridge) indicates that it would be preferred over the mono and chelate coordinatio...

Effect of lateral substitution on supramolecular liquid crystal associates induced by hydrogen-bonding interactions between 4-(4′-pyridylazo-3-methylphenyl)-4′′-alkoxy benzoates and 4-substituted benzoic acids

Five laterally methyl-substituted pyridine-based derivatives of the title compounds (I 8–I 16), with molecular formula 4-CnH2n+1O-C6H4COOC6H3(3-CH3)-N=N-C5H4N were prepared and their molecular formulae elucidated via elemental analyses, infrared, nuclear magnetic resonance and mass spectra. The number of carbon atoms in the alkoxy chain (n) varies between 8, 10, 12, 14, and 16 carbons. The newly prepared pyridine-based derivatives were investigated for their mesophase behaviour by differential scanning calorimetry and polarised optical microscopy; most of them were found to possess monotropic smectic C (SmC) mesophase. Two groups (A and B) of the 1:1 hydrogen-bonded associates, formed between each of the derivatives I 8– I 16 and two types of 4-substituted benzoic acids (II), were prepared and similarly characterised to investigate the effect of lateral methyl substitution on the central phenylene ring, as well as terminal polar substituents and alkoxy-chain length on the stability of the mesophases induced by intermolecular hydrogen bonding. In Group A complexes, mesomorphic 4-alkoxy benzoic acids, that carry the terminal n-alkoxy group of varying chain length, were used. The other series of complexes (Group B) is composed from the same pyridine-based derivatives and each of the non-mesomorphic 4-substituted benzoic acids that carries small compact polar groups, varying between CH3O, CH3, H, Cl, Br, and CN. All complexes prepared were investigated for their mesophase behaviour by differential scanning calorimetry and polarised optical microscopy and found to be purely smectogenic, possessing SmC as the only mesophase observed. The formation of the hydrogen-bonded complexes was confirmed by constructing their binary phase diagrams, which cover the whole range of concentration of the two complements.

Asymmetric oxadiazole mesogens as candidates for low-temperature biaxial nematics

We report the synthesis and properties of a homologous series of asymmetric, mesogenic derivatives of 2,5-bis-(p-hydroxyphenyl)-1,3,4-oxadiazole (ODBP). Benzyloxy (BnO-), alkoxy benzoate ester derivatives BnO-ODBP-Ph-O-C n , where n = 4, 5, 6, 7, 8, 9, 12, were studied by 2H-NMR, X-ray diffraction and polarising microscopy in order to ascertain if the lower temperature nematic phases exhibited biaxiality. Deuterium nuclear magnetic resonance (NMR) of labelled probes in these asymmetric mesogens does not show evidence of biaxiality. The absence of biaxiality is discussed in terms of the statistical non-linearity of these asymmetric ODBP mesogens.

Studies of Mesomorphic Properties of a Series of Bimetallic Os (III,III) Benzoates and Their Polymeric Axial Pyrazine Adducts

Synthesis, characterization and mesomorphic properties of tetra(alkoxy benzoate)diosminum(III) of the formula Os2(k,l,m-BgOCn)4 (where B is the benzoate group; g is the number of alkoxy chains on the aromatic ring; k, l and m are their positions of attachments; and n is the number of carbon atoms in each alkoxy chain) and their corresponding pyrazine adducts have been carried out. The complexes synthesized are Os2 (3,4,5-B3OCn)4 for n = 2, 10, 16 and 20; Os2(3,4-B2OCn)4 for n = 2, 9, and 14; Os2(3,5-B2OCn)4 for n = 2, 10, 16 and 20; as well as the corresponding adducts[Os2(3,4,5-B3OCn)4px]x for n = 2, 10, 16 and 20; Os2(3,4-B2OCn)4 for n = 2, 9 and 14; Os2(3,5-B2OCn)4 for n = 14, 16 and 19. Full characterization of the compounds were carried out using elemental analyses, 1H NMR and IR. A single crystal X-ray diffraction studies confirmed that the pyrazine adducts prepared via connected metallic centers have a polymeric structure. Diffrential scanning calorimetry (DSC), optical microscopy and XRD studies revealed the liquid-crystalline (LC) properties of most of them as cubic mesophases with melting transition temperatures close or below room temperatures. The mesomorphic character of the pyrazine compounds, compared to the non-mesomorphic aliphatic carboxylate analogues, can be interpreted in terms of the ability of the equatorial ligands to fill the interdimeric space efficiently.

Phase behaviour of binary mixtures of LC compounds of different molecular structure and comparable molecular length: I. 4-(4′-Substituted phenylazo)phenyl-4″-alkoxybenzoates and 4-(4′-substituted phenyl carbonyloxy)phenyl-4″-alkoxybenzoates

Phase diagrams were constructed for the various binary systems made from compounds of structurally different mesogens; one component is from the five homologous series 4-(4′-substituted phenylazo)phenyl-4″-alkoxybenzoates ( I a–e) and the other from the similarly substituted homologous series 4-(4′-substituted phenyl carbonyloxy)phenyl-4″-alkoxy benzoates ( II a–e). Transition temperatures of all mixtures prepared were measured by differential scanning calorimetry and identified by polarized light microscopy. Polarity and polarizability of the investigated compounds could be varied by changing the substituent X (CH 3O, CH 3, Cl, CN and NO 2), which covers a wide range of polarity, and the alkoxy-chain length, which varied between 6, 8, 14, or 16 carbons.

Correlation between dielectric and optical measurements in the smectic-C(*)(alpha) phase.

We present optical and dielectric measurements in the smectic-C(*)(alpha) (SmC(*)(alpha)) phase of three homologues of an alkoxy benzoate series. Two different behaviors are observed depending on the values and the temperature evolution of the azimuthal angle difference alpha between two adjacent layers. For moderate values of alpha, the Goldstone mode is predominant over the whole SmC(*)(alpha) phase. For large values of alpha, we can distinguish the soft mode near the SmA*-SmC(*)(alpha) phase transition and the Goldstone mode at lower temperatures. In this case, discontinuities are also observed at the SmC(*)(alpha)-SmA* phase transition. These dielectric features are correlated with optical properties using simulations based on the discrete phenomenological "clock model."