Terminal Alkoxy Chain Length Research Articles

Unsymmetrical and C3-Symmetrical Partially Fluorinated Hexaarylbenzenes: Effect of Terminal Alkoxy Chain Length on Photophysical and Thermophysical Behavior

Solution-state photoluminescence (PL) is affected by the electronic state; however, solid-state PL varies widely depending on the aggregated state. Although the synthesis and photophysical properties of unsymmetrical and C3-symmetrical hexaarylbenzenes (HABs) have been reported, the influence of their terminal alkoxy chains on their physical properties remains unclear. Therefore, we synthesized a series of unsymmetrical and C3-symmetrical partially fluorinated HABs with different alkoxy chains and investigated the effects of alkoxy chain length on the thermophysical and photophysical properties. While investigating phase transition behavior, the ethoxy-substituted unsymmetrical derivative revealed a columnar liquid-crystalline phase, whereas the other derivatives only exhibited a phase transition between crystalline and isotropic phases. While evaluating PL behavior, both the unsymmetrical and C3-symmetrical analogs exhibited relatively strong blue PL, independent of the alkoxy chain length. Through-space π-conjugation caused the PL spectra of C3-symmetrical derivatives to redshift compared to those of unsymmetrical derivatives. Partially fluorinated HABs exhibited relatively strong fluorescence, even in the crystalline state, depending on the alkoxy chain length, owing to the formation of various aggregated structures. Crystalline fluorinated HABs exhibited photochromism, resulting in the appearance of long-wavelength PL bands when exposed to ultraviolet (UV) irradiation, making them promising candidates for PL sensing materials for UV detection.

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.

Novel maleic anhydride derivatives: liquid crystalline materials with enhanced mesomorphic and optical characteristics.

A new class of liquid crystalline materials, 4-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)phenyl 4-(alkoxy)benzoates (Mn), derived from maleic anhydride, was synthesized and studied for mesomorphic and optical properties. These materials consist of three derivatives with varying terminal flexible chain lengths (6-12 carbons) linked to the phenyl ring near the ester bond. The study employed differential scanning calorimetry and polarized optical microscopy (POM) to characterize the mesomorphic properties. Molecular structures were elucidated using elemental analysis, FT-IR, and NMR spectroscopy. The findings reveal that all the synthesized maleic anhydride derivatives exhibit enantiotropic nematic (N) mesophases. The insertion of the heterocyclic maleic anhydride moiety into the molecular structure influences the stability and range of the N phase. Additionally, entropy changes during N-isotropic transitions are of small magnitude and exhibit non-linear trends independent of the terminal alkoxy chain length (n). This suggests that the ester linkage group does not significantly promote molecular biaxiality, and the clearing temperature values are relatively high. By comparing the investigated materials with their furan derivatives found in existing literature, it was established that the substitution examined in this study induces the formation of nematic phases.

Synthesis, mesomorphic and fluorescent properties of 1,3,4-oxadiazoles/thiadiazoles with a terminal 3-fluoro-4-cyanophenyl group

A series of new liquid crystalline 1,3,4-oxa/thiadiazoles with a terminal 3-fluoro-4-cyanophenyloxy group were synthesized, and their structures were characterized by nuclear magnetic resonance (NMR) and electrospray ionization mass spectrometry (ESI-MS). The liquid crystal properties were studied by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). All of the 1,3,4-oxadizoles exhibited only Nematic mesophase, while the 1,3,4-thiadiazole analogues displayed Smectic A (SmA) and Smectic C (SmC) over a wide temperature range. The fluorescent properties were investigated using ultraviolet–visible spectrophotometer (UV–Vis) and fluorescence spectrometer. The solutions of all final compounds in CH2Cl2 individually displayed one absorption band with λabs-max values at 319–340 nm, and exhibited an intense emission with λem-max values at 432–448 nm, and the photoluminescence quantum yields reached 0.52–0.66. The effects of the heterocyclic structural units, the terminal alkoxy chain length and the lateral fluorine atom on liquid crystalline and fluorescent properties were comparatively discussed.

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 Computational Investigations of New Thioether/Azomethine Liquid Crystal Derivatives

Methylthio moiety was observed to alter the mesomorphic features of rod-like Schiff-base-derived liquid crystalline materials. For this purpose, a new series of (E)-4-(alkoxy)-N-(4-(methylthio)benzylidene)aniline (In) liquid crystals were synthesized and examined using experimental and computational approaches. The compounds in the series differ from each other in the terminal alkoxy chain length that is attached to one end of the aromatic core. Various spectroscopic methods were used to verify the molecular structures of the produced derivatives. All compounds were checked for correct chemical structures using elemental analysis, FT-IR, 1H-NMR, and 13C-NMR. Both a polarized optical microscope (POM) and a differential scanning calorimeter (DSC) were used in order to study the behavior of liquid crystals. Both tested compounds I6 and I8 have monotropic nematogenic properties while the longer chain derivative I16 shows non-mesomorphic behavior. Computational studies were carried out using density functional theory (DFT) calculations to validate the experimental results. All of the analyzed compounds had their reactivity characteristics, dipole moments, and polarizability explained. Finally, in order to determine the chemical shape–mesomorphic property relationship, the present examined series was compared to other structurally comparable homologues.

Amphiphilic benzothiadiazole derivatives: synthesis, self-assembly and applications as light-emitting liquid crystal display and switchable anisotropic scattering device

Series of benzothiadiazole based amphiphilic mesogens consisting of a rigid 4,7-diphenyl-2,1,3-benzothiadiazole core with three lipophilic flexible alkoxy chains at one end and a polar glyceryl group at the other end were synthesized. The influence of the type of the linking groups in the rigid core and the length of terminal alkoxy chain on their self-assembly behavior and photophysical properties was investigated. These compounds can self-assemble into luminescent liquid crystals (LCs) with columnar/p6mm and CubI/Im3m lattices as well as luminescent organo gels with different morphologies. Furthermore, the applications of these compounds as light-emitting liquid crystal display (LE-LCD) as well as electrically switchable anisotropic scattering device were realized.

Experimental and Theoretical Investigations of Three-Ring Ester/Azomethine Materials.

New three-ring ester/azomethine homologues series, (E)-4-((4-hydroxybenzylidene)amino)phenyl 4-(alkoxy)benzoate In, were prepared and their properties were investigated experimentally and theoretically. FT-IR, NMR, and elemental analyses were used to confirm the chemical structures of the synthesized compounds. The mesomorphic activities of the planned homologues were evaluated using differential scanning calorimetry (DSC) and polarized optical microscopy. All of the homologous examined were found to have non-mesomorphic properties. Theoretical calculations using the density functional theory (DFT) were used to validate the experimental data and determine the most stable conformation of the synthesized compounds. All calculated conformers’ thermal properties, dipole moments, and polarizability were discussed. The results show that the terminal alkoxy chain length affects the thermal parameters of the conformers. The correlations between these parameters’ values and the conformer type were demonstrated. The base component was expected to be in two conformers according to the orientation of the N atom of imine-linkage. DFT calculations revealed the more probable of the two possible conformers, and the incorporation of the alkoxy terminal chain in one position affect its geometrical and mesomerphic characteristics.

New nematogenic conical-shaped supramolecular H-bonded complexes for solar energy investigations

New conical-shaped geometrical supramolecular H-bonded liquid crystal complexes were formed through 1:2 intermolecular interactions of H-bonding between flexible core (adipic acid, A) and lateral chloro-substituted azopyridines (Bn). The chains of the terminally alkoxy substituted base (n) were changed between 8 and 16 carbons. Mesomorphic and optical examinations of the prepared complexes were measured via differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). Fourier-transform infrared spectroscopy (FT-IR) was used to confirm the Fermi bands of the H- bonding interactions. Induced nematogenic mesophases that cover the whole lengths of alkoxy-chains were detected. The non-linear geometries of the designed supramolecular complexes were also confirmed via Density functional theory (DFT) calculations. It was found that the length of terminal alkoxy chain of the base moiety highly affects the geometrical structure of the investigated complexes. Moreover, it increases the thermodynamic energy and influences the geometrical parameters. The electrical properties of each of the acid component (A), the base (B16) and their 1:2 complex (A/2B16) were evaluated using the Keithley measurement-source unit. The optical properties studies showed that the influences in the optical absorption and the reduction of the energy gap of the complex compared to its individual components made the resulted supramolecular H-bonded complex soft material suitable for solar energy investigations.

Synthesis and study the liquid crystalline behaviors of double Schiff bases bearing ester linkage as a central core

ABSTRACT Two series of 12 homologues, 4-(((4-substituentphenyl)imino)methyl)phenyl 4-((4-(alkoxy) benzylidene)amino)benzoate (Dn, X = –OCH3 and En, X = –-Br), have been synthesised. The two series have different alkoxy terminal chains (OC n H2 n +1, n = 3, 4, 6, 7, 9, 12) on one side of their structures while other side in the series (Dn and En) was substituted by methoxy and Bromo group, respectively. The structures of the synthesised derivatives have been identified using Fourier transform infrared spectrometry (FT-IR) and nuclear magnetic resonance for H and C (1H-NMR, 13C-NMR) and the elemental analysis (CHN). The texture of liquid crystalline phases of the mesogens has been observed by optical polarised microscopy (OPM) while the details of the thermal transition of compounds were investigated by differential scanning calorimetry (DSC). The obtained liquid crystalline results showed that the derivatives of series (Dn) display a broad range of nematic mesophase (N) while the mesogens of (En) series appeared nematic and smectic mesophases. All the studied homologues show a wide range of liquid crystalline mesophases, the stability of mesomorphic behaviour of these compounds was dependent mainly on the length of terminal alkoxy chain (the number of carbon atoms) chain and the effect of substituent groups (OCH3 and Br).

Synthesis, Optical and DFT Characterizations of Laterally Fluorinated Phenyl Cinnamate Liquid Crystal Non-Symmetric System

A new laterally fluorinated unsymmetric liquid crystalline homologous series, based on cinnamate linkage, named 2-fluoro-4-(4-(alkoxy)phenyl)diazenyl)phenyl cinnamate (In), was synthesized and evaluated via different experimental and computational tools. The series had different terminal alkoxy-chain lengths with a lateral F atom in the meta position with respect to the azo moiety. The experimental mesomorphic and optical investigations were carried out using differential scanning calorimetry (DSC) and polarized optical microscopy (POM). Theoretical calculations and geometrical parameter predictions were conducted using the DFT program method at B3LYP/6-311G** level of theory. The results revealed that all the designed compounds exhibited the nematic (N) mesophase enantiotropically. The nematic stability and temperature range were impacted by the terminal alkoxy chain length. Compounds with the shortest chains (I6 and I8) showed a monotropic smectic A (SmA) phase, while the longest chain derivative, I16, possessed enantiotropic Sm A phase. Theoretical density functional theory (DFT) predictions were correlated with the practically observed data from the mesomorphic investigations. Data revealed that the terminal alkoxy and lateral F groups had an essential impact on the total energy of possible geometrical structures and their physical and thermal parameters.

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.

Symmetrical and asymmetrical liquid crystal dimers: synthesis, characterisation and mesomorphic behaviour

ABSTRACTA series of new asymmetrical liquid crystal dimers, RnO–S2O–ORn (n = 2–10), linked by an ethylene spacer having carbothiol – COS – and carboxyl – COO – linkages to the core centre of the molecule and bearing different lengths of terminal alkoxy chains were synthesised in order to study the effects of the length of the terminal alkoxy chains on mesomorphic properties. As well as, five symmetrical and asymmetrical dimers linked by butylene spacers bearing different linkages to the core and various terminal chains were also synthesized in order to study the effect of the nature of the spacer and terminal groups. The structures of the synthesised dimers were confirmed by physico-chemical techniques, i.e. FTIR, NMR and mass spectra. Differential scanning calorimetry and polarising optical microscopy verified the liquid crystal behaviour transition temperatures. The isotropic transition temperatures of the dimers RnO–S2O–ORn (n = 2–10) decreased with increasing length of alkoxy chain. Structural effects on the mesomorphic and physical properties were investigated in terms of alteration of carboxylate and thioester groups linking the spacer. The mesomorphic investigation reveals that all the dimers formed an enantiotropic Nematic phase except for dimer HO2SH which is not a liquid crystal.

Experimental and theoretical approaches of molecular geometry and mesophase behaviour relationship of laterally substituted azopyridines

ABSTRACTNew 10 laterally chloro azopyridine-based derivatives, with terminal alkoxy chain length varies between 6 and 16 carbons, were prepared. The mesophase behaviour was investigated for prepared homologues by differential scanning calorimetry and polarised light microscopy. Each homologous series differ from each other by the lateral attached Cl group in the ortho- or meta-position with respect to the ester carbonyl core in the central benzene ring. Elemental analyses, FT-IR, 1H NMR and C13 NMR spectroscopy were used for molecular structure confirmation of the prepared compounds. All prepared homologues were found to be nematogenic. Density functional theory theoretical calculations used to confirm the experimental data and the results are consistent with the experimental investigations. It was found that the nematic range and stability is influenced by the length of the alkoxy chain and the orientation of the lateral chloro group. Moreover, an experimental and theoretical comparative study between the Cl-lateral isomers with respect to the previously reported methyl lateral derivatives as well as the laterally neat one in determination of the type, the stability of the mesophase and the molecular geometry.

Synthesis and Mesogenic Properties of Liquid Crystals Based on Cholesterol and Cinnamic Acid Derivatives

A group of new mesomorphic compounds with cholesterol-based, which have derivative of the cinnamic acid, with different lengths of terminal alkoxy chains, are synthesized and characterized. The mesomorphic properties were investigated by DSC and POM. All target compounds showed a cholesteric phase. For 12-TC and 14-TC besides a cholesteric phase, also revealed a SmA* phase. The experimental results demonstrated that with the increase in the terminal chain lengths, the thermal stability of the smectic mesophases of these liquid crystals was increased, and these compounds shows brilliant color changes in the temperature ranges of cholesteric phase.

The Gelation Ability and Morphology Study of Organogel System Based on Calamitic Hydrazide Derivatives

The gelation property of a series of LMOG bearing hydrazide and azobenzene groups, namely, N‐4‐(alkoxyphenyl)‐N′‐4‐[(4‐methoxyphenyl)azophenyl] benzohydrazide (BNBC‐n, n = 8,12,14), has been systematically studied in this work. The obtained results demonstrate that the gelling ability in organic solvents is significantly influenced by the length of terminal alkoxy chain. In different organic solvents, it is hard to observe the organogel formation for BNBC‐8 molecule. On the contrary, the organogelators BNBC‐12 and BNBC‐14 bearing longer terminal chains have shown great ability to gel organic solvents to form stable organogels. The critical gelation concentration for BNBC‐12 reaches as low as 5.3 × 10−3 M, which can be considered as a supergelator. It has been manifested that the aggregation morphology of organogel strongly depends on the nature of the gelling solvents and the length of the terminal alkoxy chain. The gelation of BNBC‐n provides an easy method for the preparation of multidimensional structure and manipulation of morphology from ribbons, hollow tube fiber to 3D net‐like structure in different solvents. The cooperation of hydrogen bonding, π‐π interaction, and Van der Waals force is suggested to be the main contribution to this self‐assembled structure.

Thermotropic Liquid Crystalline Dimers with Varying Alkoxy Terminal Chain Length

We have design and synthesized of homologous Series I dimers and to study the effect of molecular structure variation and change in alkoxy terminal chain length (n = 6, 7, 8) on mesomorphic properties of liquid crystals. Explore further understanding of the structure-property relationship of liquid crystal homologous Seriesl dimers having varying alkoxy terminal chain length. It was found that the decrease in crystalline phase, smectic C and nematic phase transition temperatures with increasing terminal alkoxy chain length. The molecular structures of the Seriesl dimer were characterized by Fourier transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance (1H NMR) spectroscopy. Their mesomorphic properties were investigated by differential scannning calorimetry (DSC) and on the hot-stage of a polarizing microscope (POM).

Effect of alkoxy terminal chain length on mesomorphism of 1,6-disubstituted pyrene-based hexacatenar liquid crystals: columnar phase control

Synthesis and mesophase-transition behaviors of six 1,6-disubstituted pyrene-based hexacatenar liquid crystals 1n (n=8–18) are reported here. They were synthesized by the Sonogashira coupling between 1,6-diethynylpyrene and 2-bromothiophene bearing a trialkoxybenzoyl group. The phase-transition behavior was studied by differential scanning calorimetry and polarized optical microscopy; a few mesophase progressions, I–Col/I–X–Col and Col–Sm, were observed, where X was an optically isotropic but unidentified phase. The structures of Colr, Colh, and Sm phases were analyzed by the X-ray crystallography, and the effect of the terminal alkoxy chain length on the mesomorphism was evaluated.

Effects of symmetrically 2,5-disubstituted 1,3,4-oxadiazoles on the temperature range of liquid crystalline blue phases: a systematic study

Four series of symmetrically 2,5-disubstituted 1,3,4-oxadiazoles with different lateral substituents and terminal alkoxy chain length were synthesised and characterised. Then, all these bent-shaped compounds were separately doped into the blue phase (BP) liquid crystal host and their effects on the BP range of the host were investigated, which shows that the BP ranges varied greatly with the difference in the structure of 2,5-disubstituted 1,3,4-oxadiazoles and their doped concentration. Moreover, in order to explore the influence of the inherent molecular geometry and properties of the bent-shaped molecules on the stability of BPs, the molecular structures of all the compounds were studied by using the theory of density functional theory, and the optimised structural parameters of the molecules were calculated at the B3LYP/6–31G* level.

Liquid Crystalline Properties of Dimers Having o-, m- and p- Positional Molecular Structures

With the objective to design and synthesis of Schiff's base symmetrical liquid crystal dimmers and to study the effect of molecular structure variation (o-ortho, m-meta, p-para) and change in alkoxy terminal chain length on mesomorphic properties of liquid crystals, We have synthesized Schiff base dimers from dialdehyde derivative containing 2-hydroxy-1,3-dioxypropylene as short spacer with aniline derivatives having different lengths of terminal alkoxy chains (n = 5, 7, 9). The chemical structure of the final products was characterized by proton nuclear magnetic resonance ( 1 H NMR) spectroscopy and fourier transform infrared (FT-IR) spectroscopy. The mesomorphic properties and optical textures of the resultant dimers were characterized by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The existence of smectic A phase transition was confirmed by the observation of bâtonnets and fan shaped textures in optical microscopy when compound were heated from crystalline phase. All of the dimers of this series, with the exception of 2S5 -ortho, -meta, -para, were thermotropic liquid crystal. The compound 2S9 -meta was monotropic, while the rest were enantiotropic. It was found that the change in terminal alkoxy chain length has pronounced effect on the mesomorphic properties. The temperature range of smectic A phase window widens with increasing alkoxy chain length.