Alkoxy Chain Length Research Articles

Experimental standard molar enthalpies of formation of some 4-alkoxybenzoic acids

The present work is part of a research program on the energetics of the linear 4- n-alkoxybenzoic acids, aiming the study of the enthalpic effect of the introduction of an alkoxy chain in the position 4- of the benzoic acid ring. In this work, we present the results of the thermochemical research on 4- n-alkoxybenzoic acids with the alkoxy chain length n = 2, 4, and 8. The standard ( p ∘ = 0.1 MPa ) molar enthalpy of formation of crystalline 4-ethoxybenzoic acid, 4-butoxybenzoic acid, and 4-(octyloxy)benzoic acid was measured, at T = 298.15 K, by static-bomb calorimetry. These values, combined with the values of standard molar enthalpies of sublimation, were used to derive the standard molar enthalpies of formation in the gaseous phase. 4-Alkoxybenzoic acid - Δ c U m ∘ ( cr ) / ( kJ · mol - 1 ) - Δ f H m ∘ (cr ) / ( kJ · mol - 1 ) - Δ f H m ∘ ( g ) / ( kJ · mol - 1 ) 4-Ethoxybenzoic acid 4362.7 ± 1.3 605.5 ± 1.8 482.2 ± 2.0 4-Butoxybenzoic acid 5677.3 ± 2.0 647.1 ± 2.5 518.1 ± 2.6 4-(Octyloxy)benzoic acid 8269.0 ± 3.3 767.9 ± 3.9 604.9 ± 4.1 From those experimental values, the standard molar enthalpies of formation, in the gaseous phase, at T = 298.15 K, are interpreted in terms of structural contributions to the energetics of the substituted benzoic acids and compared with the same parameters estimated from the Benson’s Group Method.

Functional Control on the 2D Self-Organization of Phenyleneethynylenes

Two-dimensional self-organization of a series of phenyleneethynylenes was investigated, at ambient conditions, by varying the length of alkoxy chain and introducing functional groups at the terminal positions using high-resolution scanning tunneling microscopy (STM). The model phenyleneethynylene molecule, which does not possess any functional groups, self-organizes into wire like structures on surface. High-resolution STM imaging revealed that molecules are arranged in a skewed 1D fashion. The spacing between the molecular wires was successfully modulated by replacing hexyloxy (C6) chains with dodecyloxy (C12) chains. The initial step of the formation of all the molecular assemblies involves the alkyl CH···acetylenic π interactions (CH···π) leading to the organization of molecules as two types of strips. These strips further interlock to two types of 2D organizations. The hydroxyl as well as aldehyde groups present at the terminal positions of the phenyleneethynylene molecules play an important role in t...

π‐Conjugated Oligothiophene‐Based Polycatenar Liquid Crystals: Self‐Organization and Photoconductive, Luminescent, and Redox Properties

AbstractA series of liquid‐crystalline (LC) π‐‐conjugated oligothiophenes bearing three or two alkoxy chains at their extremities has been designed and synthesized. These polycatenar oligothiophenes form various LC nanostructures including smectic, columnar, and micellar cubic phases. These properties depend on the number and length of the terminal alkoxy chains. The hole mobilities for the oligothiophenes have been measured. The layered smectic and columnar structures are capable of transporting holes, leading to mobilities of up to 0.01 cm2 V−1 s−1. The columnar LC assemblies have also been explored to produce linearly polarized light‐emission. Fine red polarized fluorescence is observed from a uniaxially aligned film of the oligothiophenes. The redox properties of the oligothiophenes both in solutions and in films have been examined. The oligothiophenes exhibit electrochromism upon applying an oxidative potential. The present design strategy is useful for fabricating a variety of functional electro‐active molecular assemblies.

Synthesis of Symmetric Liquid Crystal Dimers Based on 1,2-bis{-[-(4-alkoxybenzoyloxy)benzylidene]amino)phenoxy}ethane and Investigation of Phase Behaviour by Varying Alkoxy Terminal Chain Length

With the objective to study the effect of alkoxy terminal chain length on mesomorphic properties of liquid crystals, We have synthesized ester and Schiff base dimers from diamine derivative containing 1,2-dioxyethylene as short spacer with aldehyde derivatives having different lengths of terminal alkoxy chains (n = 6–12). The chemical structure of the final products was investigated by fourier transform infrared (FT-IR) spectroscopy and proton nuclear magnetic resonance (1H NMR) spectroscopy. The mesomorphic properties and optical textures of the resultant dimers were characterized by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). It was found that all the dimers show mesomorphic properties and the increase in terminal alkoxy chain length has pronounced effect on the mesomorphic properties. The temperature range of smectic phase window widens and nematic-isotropic phase window narrows sharply with increasing alkoxy chain length.

Synthesis of Symmetric Liquid Crystal Dimers Based on Azo and Imine Groups and Investigation of Phase Behaviour by Varying Alkoxy Terminal Chain Length

With the objective to study the effect of alkoxy terminal chain length on mesomorphic properties of liquid crystals, we have synthesized two (Azo and Imine) different series of dimesogens by varying terminal alkoxy chain length (n = 6–12) with a short spacer unit in between two mesogens. Transition temperatures and phase characterization were studied by DSC, POM and XRD analysis. It was found that all the dimers show mesomorphic properties and the change in terminal alkoxy chain length has pronounced effect on the smectic phase window. In the DSC cooling scan, the smectic phase window of azo compounds increased from 6.4°C (2A6) to 16.0°C(2A12), whereas in Schiff base compounds, it increased from 9.2°C (2S6) to 31.0°C(2S12). Further, the 2A11 dimer was found to undergo photo induced configurational changes.

Structure–property studies and orientation effects of polythiophenes containing mesogenic side chains

AbstractLiquid crystalline materials display unique properties, which can be exploited in organic light emitting diodes. Polythiophene model compounds containing phenyl groups linked with azomethine, ester, and alkoxy groups [thiophene‐3‐alkyloxy benzoyloxy aniline series (N series) and thiophene‐3‐alkoxy phenoxy amino benzoate series (R Series)] were synthesized. Molecular orbital calculations were performed and the predicted band gaps compared to understand the effects of spacer length and linkage. The experimental photoabsorption characteristics are compared with the theoretically predicted band gap. Photoabsorption and emission studies on N series and R series polymers as the function of polarizer angle suggest that polymers of both series emit polarized light in all base color ranges. The electroemission characteristics of the above‐synthesized polymers were also recorded as the function of polarizer angle. The results show that the compounds also emit polarized electroemission, and the EL polarization ratio decreases with the increase of alkoxy chain length for N and R polymers. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1463–1477, 2008

Synthesis, Structures and Ion‐Association Properties of a Series of Schiff Base Oxidovanadium(V) Complexes with 4‐Substituted Long Alkoxy Chains

AbstractSchiff base VO2V and VOV complexes with long 4‐substituted alkoxy chains have been synthesised from the corresponding VOIV complexes, [VO{(4‐CnH2n+1O)xsalen}] [x = 1, 2, n = 3–16 and salen = N,N′‐ethylenebis(salicylideneiminato)], in solutions in the absence or presence of HClO4 under aerobic conditions. The green single‐crystals of the VOIV complexes (x = 2, n = 3, 4, 6) coexisting with solutions without HClO4 turned slowly to the yellow single‐crystals of the species with n = 3 (1) and 4 (2), a process which took several months. An X‐ray crystallographic analysis revealed that the VOIV complexes are transformed into the dimeric VO2V complexes with the tridentate sal‐en (sal‐en = N‐salicylideneethylenediamine) ligand from the tetradentate salen moieties. However, the single crystals of the VOIV complexes with longer alkoxy chains of n ≥ 8 did not yield the corresponding yellow crystals of the VO2V complexes. This crystal‐to‐crystal transformation is discussed in relation to the crystal packing structures of the VOIV complexes. In contrast, addition of HClO4 solution to two series with one and two alkoxy chains in the 4‐positions immediately afforded the corresponding blue VOV perchlorate complexes, [VO{(4‐CnH2n+1O)xsalen}]ClO4 (x = 1, 2) without transformation of the salen moieties. The structure of 8·MeOH·0.5H2O determined from an X‐ray crystallographic analysis was a unique dimeric structure supported by electrostatic stacking and CH–π interactions in an octahedral environment. The DFT calculations were studied to obtain the stabilisation energy for the dimerisation. Furthermore, in methanol solution, the effects of the alkoxy chain lengths on the ion association were investigated by conductivity measurements. The ion‐association state in methanol solution is discussed with the solid‐state structure.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Supramolecular Hydrogen-Bonded Liquid Crystals Formed from 4-(4′-Pyridylazophenyl)-4″–Substituted Benzoates and 4-Alkoxybenzoic Acids

Phase diagrams of the binary mixtures of the title compounds were constructed to investigate the effect of different polar substituents, on the pyridine-based derivatives, as well as the alkoxy-chain length, on the acids, on the extent and stability of the supramolecular liquid crystal phases induced by intermolecular hydrogen bonding. None of the newly prepared pyridine-based derivatives is mesomorphic, but the hydrogen-bonded complexes are. The mixtures prepared were characterized for their mesophase behavior by differential scanning calorimetry (DSC) and polarized light microscopy (PLM). Five pyridine-based derivatives (I a-e), with molecular formula X-C6H4COOC6H4-N=N-C5H4N, were prepared that differ from each other by the substituent X. The latter varies between CH3O, CH3, H, Br, and NO2. Four 4-alkoxybenzoic acids (CnH2n+1OC6H4COOH, II 10–II 18) were used; the number of carbons (n) of their alkoxy groups varies between 10, 12, 14, and 18. Smectic C mesophase is induced in most of the binary mixtures investigated.

Variation of Helical Twisting Power in Self-Assembled Sugar-Appended Schiff Base Chiral Rod−Coil Amphiphiles

A series of sugar-appended Schiff base chiral rod−coil amphiphiles with various alkoxy chain lengths have been synthesized in order to elucidate the variation of the helical twisting power (HTP), that is, the inverse of the pitch length, of the helical texture in the self-assembly of the amphiphiles. The HTP induced by chiral sugar in the self-assembled helical morphology was dependent upon the alkoxy chain length. Increasing the alkoxy chain length caused the self-assembled morphology to change from platelet-like texture to helical-twist morphology with varying pitch length and then revert to the platelet-like texture. This result demonstrates that the HTP reaches a maximum as the alkoxy chain length changes. The transformation from platelet-like to helical-twist morphology is induced by significant steric hindrance, when the effective size of adjacent alkoxy chains reaches the threshold of helical twisting and bending, resulting in the formation of a chiral smectic C phase. However, as the alkoxy chain ...

Rigid tetracatenar liquid crystals derived from 1,10-phenanthroline

Tetracatenar liquid crystals were obtained by substituting the 1,10-phenanthroline central core unit at the 3- and 8-positions by extended, rigid acetylene moieties, equipped at the termini with two alkoxy chains of various lengths (n = 6, 8, 10, 12, 14). The liquid crystals exhibit a rich mesomorphism including smectic C, cubic, hexagonal and rectangular columnar phases, depending on the alkoxy chain length. The corresponding rhenium(I) complexes containing the bulky [ReBr(CO)3] fragment are not liquid-crystalline. The ligands and rhenium(I) complexes were investigated by scanning tunneling microscopy (STM). Both the ligands and the rhenium(I) complexes can be self-assembled into monolayers at the TCB–graphite and octanoic acid–graphite interfaces. The ligands and rhenium(I) complexes are luminescent.

The influence of alkoxy chain length on the ferroelectric properties of chiral fluorenol liquid crystals

A series of isomeric chiral fluorenol mesogens with different alkoxy chain length combinations have been prepared in order to test a model for the origin of polar order in the chiral SmC* phase formed by these compounds. The results show that the transposition of alkoxy side chains has no effect on the sign of spontaneous polarization, PS, which is inconsistent with a model suggesting that polar order arises from a rotational bias of antiparallel hydrogen-bonded dimers that minimizes free volume in the tilted SmC* phase.

Thermally stable oxadiazole-containing polyacetylenes: Relationship between molecular structure and nonlinear optical properties

Two novel high molecular weight functional polyacetylenes bearing oxadiazole groups as pendants, poly(2-(4-decyloxyphenyl)-5-(4-ethynylphenyl)-1, 3, 4-oxadiazole) (P1) and poly(2-(4-butyloxyphenyl)-5-(4-ethynylphenyl)-1, 3, 4-oxadiazole) (P2) were designed and synthesized by a multistep reaction route. The structures and properties were characterized and evaluated with FTIR, NMR, UV, TGA, GPC, optical-limiting (OL) and nonlinear optical (NLO) analyses. The incorporation of oxadiazole into polyacetylene significantly endows polyacetylenes with higher thermal stability and optical limiting property. The solubility, stereoregularity and optical properties of resultant polyacetylenes are obviously affected by flexible terminal alkoxy chain length. The cis olefinic structure content in polyacetylene backbone increases with increasing terminal alkoxy group length. The functional polyacetylene with the higher cis olefinic structure content shows higher thermal stability, better optical limiting property and larger third-order nonlinear optical performance. The optical limiting mechanism of resulting polymers was investigated, which is mainly originated from larger excitation state absorption cross-section of molecules to result in reverse saturable absorption.

Syntheses, Structures, and Mesomorphism of a Series of Cu(II) Salen Complexes with 4-Substituted Long Alkoxy Chains

A series of copper(II) salen complexes containing 4-substituted alkoxy chains of aromatic rings [Cu((4-C n H2n+1O)2salen)] (n = 3 ( 1 ), 4 ( 2 ), 6 ( 3 ), 8 ( 4 ), 10 ( 5 ), 12 ( 6 ), 14 ( 7 ), 16 ( 8 ), 18 ( 9 ), and 20 ( 10 ) and salen (N,N'-ethylenebis(salicylideneiminato)) has been prepared, and single-crystal structures of 2 · H2O, 4 , and 6 by an X-ray crystallographic analysis have been revealed. Complexes 4 and 6 form tetrahedrally distorted square planer structure with one-dimensional polymeric stacking by van der Waals interaction between the dramatically distorted salen moieties. Complexes 1 – 3 did not exhibit any mesophases, but complexes 4 – 10 with longer alkoxy chains of n = 8–20 showed the metallomesogen of a lamello-columnar (ColL) mesophase in the smectic layers with the nearly constant stacking distances, irrespective of the variation of the alkoxy chain lengths by the X-ray diffraction measurements, which show similar behaviors to the corresponding Ni(II) complexes of n = 14–20. The molecular assemblies and mesomorphic properties in relation to the single-crystal structures of 4 and 6 with the liquid crystals at higher temperature are discussed.

Twist viscoelastic coefficient of novel thiol terminated alkoxy-cyanobiphenyl nematic liquid crystals

We report our studies on the refractive indices and twist viscoelastic coefficient of novel thiol terminated alkoxy-cyanobiphenyl nematic liquid crystals. Dynamic light scattering (DLS) was employed to measure the twist viscoelastic coefficient as a function of temperature and the length of alkoxy chain. Our studies show that the twist viscoelastic coefficient is about three times smaller than that of the ordinary alkoxy-cyanobiphenyl nematic liquid crystals. DLS experiments carried out on this system with applied electric field show that the director relaxation frequency increases. These measurements yield the ratio of dielectric anisotropy to twist viscosity. We have also estimated the activation energy corresponding to twist viscosity.

New Liquid Crystalline Stilbene Derivatives Containing 1,2-Dienylalkoxy Chains

New liquid crystalline stilbene derivatives containing 1,2-dienylalkoxy chains 1 (n = 7, 9, 11) have been synthesized and their mesomorphic properties have been measured by polarizing optical microscopy, differential scanning calorimetry, and absorption spectroscopy. The effect of terminal alkoxy chain length and polimerisable function on the mesomorphic behaviour is discussed.

Crystal Nucleation, Growth, and Morphology of the Synthetic Malaria Pigment β-Hematin and the Effect Thereon by Quinoline Additives: The Malaria Pigment as a Target of Various Antimalarial Drugs

The morphology of micrometer-sized beta-hematin crystals (synthetic malaria pigment) was determined by TEM images and diffraction, and by grazing incidence synchrotron X-ray diffraction at the air-water interface. The needle-like crystals are bounded by sharp {100} and {010} side faces, and capped by {011} and, to a lesser extent, by {001} end faces, in agreement with hemozoin (malaria pigment) crystals. The beta-hematin crystals grown in the presence of 10% chloroquine or quinine took appreciably longer to precipitate and tended to be symmetrically tapered toward both ends of the needle, due to stereoselective additive binding to {001} or {011} ledges. Evidence, but marginal, is presented that additives reduce crystal mosaic domain size along the needle axis, based on X-ray powder diffraction data. Coherent grazing exit X-ray diffraction suggests that the mosaic domains are smaller and less structurally stable than in pure crystals. IR-ATR and Raman spectra indicate molecular based differences due to a modification of surface and bulk propionic acid groups, following additive binding and a molecular rearrangement in the environment of the bulk sites poisoned by occluded quinoline. These results provided incentive to examine computationally whether hemozoin may be a target of antimalarial drugs diethylamino-alkoxyxanthones and artemisinin. A variation in activity of the former as a function of the alkoxy chain length is correlated with computed binding energy to {001} and {011} faces of beta-hematin. A model is proposed for artemisinin activity involving hemozoin nucleation inhibition via artemisinin-beta-hematin adducts bound to the principal crystal faces. Regarding nucleation of hemozoin inside the digestive vacuole of the malaria parasite, nucleation via the vacuole's membranous surface is proposed, based on a reported hemozoin alignment. As a test, a dibehenoyl-phosphatidylcholine monolayer transferred onto OTS-Si wafer nucleated far more beta-hematin crystals, albeit randomly oriented, than a reference OTS-Si.

Intercalated liquid-crystalline phases formed by symmetric dimers with an α,ω-diiminoalkylene spacer

Four series of symmetric, dimeric molecules with flexible α,ω-diiminoalkylene spacers have been synthesised and characterised by polarising optical microscopy, differential scanning calorimetry, and X-ray diffraction. The effects on the mesomorphism of the various alkylene spacer (number of methylene units m = 5 to 8) as well as the terminal alkoxy chain length (n = 4 to 14) on the mesomorphic properties have been studied. The compounds with an even-numbered spacer display, in addition to a nematic phase, various smectic phases whose nature depends on the ratio between the length of the terminal chain and the length of the spacer (n/m). A modulated Smà phase was found for the ratio n/m = 1 to 1.6 and a SmC/crystal G polymorphism emerges at n/m > 1.7. In contrast, all liquid-crystalline dimers with odd-numbered spacers display an intercalated B6 phase regardless of the chain length. The preference for intercalated structures is discussed based on dipolar considerations following electronic structure calculations using a model molecule.

Synthesis and Physicochemical Properties of Perfluorinated Organic Gelators

This paper describes synthesis and physicochemical properties of low molecular-mass organic gelators; 4-(2-perfluorooctyl)ethoxy- and 4-(2-perfluorooctyl)ethylthio-1 -alkoxybenzenes (compounds 1-n and 2-n). These compounds show remarkable gelation ability in various organic solvents, such as methanol, cyclohexane, acetonitrile, DMF, and so on. The critical gel concentration of 1-n is superior to that of 2-n; while the elongation of alkoxy chain length increase gelation ability in both compounds.

Fluorescence Spectroscopic Properties and Crystal Structure of a Series of Donor−Acceptor Diphenylpolyenes

A series of p-nitro-p'-alkoxy(OR)-substituted (E,E,E)-1,6-diphenyl-1,3,5-hexatrienes (1a, R = Me; 1b, R = Et; 1c, R = n-Pr; 1d, R = n-Bu) were prepared. The absorption and fluorescence spectra in solution were almost independent of the alkoxy chain length. The absorption maximum showed only a small dependence on the solvent polarity, whereas the fluorescence maximum red-shifted largely as the polarity increased. The solid-state absorption and fluorescence spectra were red-shifted relative to those in low polar solvents and were clearly dependent on the alkoxy chain length. The fluorescence maxima for the crystals of 1b and 1d were observed at 635-650 nm, which were red-shifted by 40-50 nm relative to those for 1a and 1c. The Stokes shifts were all relatively small (3000-3500 cm-1). For all four compounds, the fluorescence decay curves in the solid state were able to be analyzed by single-exponential fitting to give the lifetimes of 1.1-1.3 ns. This indicates that the emission of 1a-d is not originated from an excimer or molecular aggregates, but from only one emitting monomeric species. The fluorescence quantum yields of 1a-d were considerably high compared with the values for organic solids, which is consistent with their monomeric origin of emission. Single-crystal X-ray structure analyses of 1a, 1c, and 1d showed that the crystal packing was dependent on the alkoxy chain length. The crystals of 1a and 1c had herringbone structure, whereas that of 1d had pi-stacked structure. Strong pi-pi interaction in the crystal of 1d would be the cause of the spectral red shifts relative to those for 1a and 1c. No observation of excimer fluorescence from crystal 1d can be attributed to the limited overlap between the pi-planes of the molecules due to its "slipped-parallel" structure.

Palladium(II) metallomesogens of crown ether derivatized imines, and their sodium adducts

A series of imines HL n ( 1) ( n stands for the alkoxy chain length: 4, 6, 8, 10, and 12) has been synthesized by condensation of 4-aminobenzo-15-crown-5 and p-alkoxybenzaldehyde. Orthopalladation afforded the dinuclear derivatives [Pd(μ-OAc)L n ] 2 ( 2) which, by substitution reactions, led to dinuclear and mononuclear derivatives [Pd(μ-Cl)L n ] 2 ( 3) and [Pd(β-diket)L n ] ( 4) (β-diket = H 25C 12OH 4C 6–C(O)–CH–C(O)–C 6H 4OC 12H 25). The imine ligands and the acetato bridged complexes are non-mesogenic whilst the chloro-bridged and the diketonato complexes are enantiotropic liquid crystals. They display smectic A mesophases. Complexation with sodium perchlorate afforded the corresponding derivatives [(O 2ClO 2)Na Crown] ( Crown = crown derivatives 1– 4 for n = 4). None of the sodium adducts is mesogenic. The acetato bridged complexes consist of a mixture of syn and anti isomers and a dramatic increase in the syn: anti ratio is produced upon complexation of NaClO 4 ( syn: anti = 4:96 for complexes 2 versus 54:46 for the corresponding [(O 2ClO 2)Na Crown2]). The crown ether derivatives extract sodium picrate from aqueous solutions and the presence of the palladium centers improves clearly the extraction, [Pd(μ-Cl)L n ] 2 being the best and the fastest extractor. A model for the extraction and transport process in these complexes is proposed.