Induction of Mesomorphic Properties in Non-Mesogenic Octa(decyloxy) phthalocyanines

Abstract

As it is well known [1, 2], non-peripheral substituted octa (alkoxy)-phthalocyanines (Pc) do not exhibit neither thermotropic nor lyotropic mesomorphism (in binary mixtures with organic solvents). In this work we induced an enantiotropic mesophase due to charge-transfer (CT) interactions in mixtures of PC derivatives I-III (viscous or oil-like liquids) with a strong electron acceptor 2,4,7-trinitro-9-fluorenone (TNF). Decreasing of number and length of substituents and modification of chemical structure of phthalocyanine macrocycle by introduction of four sulfur atoms (compound IV) resulted in crystallinity of this compound. In contact preparation of IV with TNF a wide area of CT-complex showing the monotropic mesomorphic phase is found out. All above mentioned CT-complexes do not form any lyomesophases in binary mixtures with number of organic solvents.     

Synthesis,Characterization and Mesomorphic Properties of New Rod-like Thiophene Based Liquid Crystals

Two new mesogenic homologous series of Schiff base esters, 2-[4-(4′-n-Alkoxy benzoyloxy) benzylidenamino] 3-cyno thiophine (Series-A) and Schiff base cinnamates, 2-[4-(4′-n-alkoxy cinnamoyloxy) benzylidenamino] 3-cyano thiophene (Series-B), comprising a thiophene moiety were synthesized. Structural elucidation was carried out using elemental analysis and spectroscopic techniques such as FT-IR, ¹H-NMR and ¹³C-NMR, and mass spectrometry. The mesomorphic properties and thermal stabilities of the title compounds were studied by using differential scanning calorimetry and optical polarizing microscopy. All the derivatives are mesomorphic in nature showing the nematic phase, and the higher members of Series-A show a smectic C phase whereas Series-B exhibits only the nematic mesophase. The mesomorphic properties of the present series are compared with other structurally related compounds.     

Synthesis and mesomorphic properties of 2,4-bis(4′-n-pentyloxybenzoyloxy)- benzylidine-4″- n-alkoxyaniline

The synthesis and mesomorphic properties of a new series of 2,4-bis(4′-npentyloxybenzoyloxy)- benzylidine-4″ -n-alkoxyaniline (DC5An) are reported. The molecular structure of compounds was confirmed by FTIR, ¹H-NMR, ¹³C-NMR, mass spectroscopy and elemental analysis. The mesomorphic properties were studied by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM) measurements. All compounds of the series exhibit nematic (N) and smectic C (SmC) phases. The first four homologues (DC5A1-DC5A4) display a N mesophase, whereas the highest homologues (DC5A5-DC5A10) exhibit an enantiotropic dimorphism N and SmC phases. The mesomorphic properties of the present series are compared and discussed with other structurally related series.     

New Mesogenic Compounds Containing a Terminal-Substituted Benzoxazole Unit

A series of novel mesogenic 2-(4-alkoxyphenyl-1-yl)-benzoxazole derivatives bearing different substituents (H, NO₂, CH₃, Cl, coded as nPB-H, nPB-N, nPB-M, and nPB-C, respectively) at the 5-position were prepared and characterized. nPB-N, nPB-M, and nPB-C exhibited enantiotropic smectic mesophases with the mesophase ranges 3 °C–32 °C and 3 °C–82 °C on heating and cooling processes, whereas nPB-H showed no mesophases. The substituents with the stronger electron withdrawing effect let to the wider mesomorphic temperature domain. The nPB-M, nPB-C, and nPB-H displayed intense emission in CH₂Cl₂ solutions with λ_max peaks of the photoluminescence spectra at 350–355 nm when excited at their absorption maxima.     

Synthesis and Mesomorphic Characteristics of Fluoroaniline Derivatives with Different Lateral Groups

Two new homologous series of liquid crystals viz. 4-(4'-n-alkoxybenzoyloxy)-2-chlorophenylazo-4”-fluorobenzenes(I) and 4-(4'-n-alkoxybenzoyloxy)-2-methylphenyl azo-4”-fluorobenzenes(II) with terminal fluoro, lateral chloro(I) and methyl(II) group and central ester and azo linkages are synthesized and their mesomorphic properties are studied. Both the series are similar in molecular structure with the difference in their lateral substitutions; series I has chloro group and series II has methyl group as laterally substituted groups. All the twelve homologues of each of the series are mesogenic in nature. Series I shows nematic mesophase from the first C₁ to the last C₁₆ derivative synthesized; smectic mesophase is exhibited by last two viz. C₁₄ and C₁₆ derivative, where as all the members from C₁ to C₁₆ of series II only show nematic mesophase. The nematic mesophase shows marble texture and the smectic mesophase shows Schlirene texture of the Smectic C variety. Both the series are compared with structurally related series.     

Synthesis and Study of New Mesogens II: p-(p′-n-Alkoxycinnamoyloxy)-benzylidene p″ -anisidines (1) and p-(p′-n-Alkoxycinnamoyloxy)- benzylidene anilines (2)

Two new homologous series of liquid crystals viz. p-(p'-n-alkoxycinnamoyloxy) benzylidene p”-anisidines (1) and p-(p'-n-alkoxycinnamoyloxy) benzylidene anilines (2) comprising twenty four mesogens have been synthesized. Both are high melting series of mesomorphs. In the homologous series (1) the nematic mesophase is exhibited from the very first member; however, the first five compounds decompose at high temperatures before passing into isotropic liquid condition. Polymesomorphism is exhibited with the appearance of the smectic mesophase at the octyl derivative and remains up to the last viz. octadecyl homologue. Within polymesomorphic region the nematic mesophase is homeotropic; however, it shows a clear threaded texture where it is the only mesophase shown i. e. in the first seven members of the homologous series (1). The smectic mesophase shows focal conic fan shape texture belonging to smectic-A variety. The nematic-isotropic curve shows descending tendency as the series is ascended-a characteristic of high melting series. The smectic-nematic transition curve rises steeply and shows a levelling off tendency at the octadecyl derivative. In the homologous series (2), no decomposition occurs. The smectic mesophase commences a little early i. e. from hexyl derivative; while polymesomorphism is clearly exhibited up to the dodecyl derivative, the last two homologues are purely smectogens. The usual odd-even effect is observed in case of the nematic-isotropic curve for series (2). The smetic-nematic curve rises gradually and seems to be merging with the falling nematic-isotropic curve at the fifteenth homologue. The mesomorphic ranges in both series are quite wide; however, that of series (1) is wider than one obtained in series (2). Thermal stabilities are good and are in keeping with the molecular characteristics. The textures of the smectic and nematic mesophases are similar to that of the series (1). Both series are comparable with each other and other related series.     

Liquid-Crystalline State of Cholesterol-Containing Monomers

A series of cholesterol-containing monomers was synthesized: cholesteryl esters of N-acryloyl-ω-aminocarboxylic acids, N-methacryloyl-ω-aminocarboxylic acids, ω-acryloyloxycarboxylic acids and ω-methacryloyloxycarboxylic acids. The mesomorphic properties, temperatures and heats of transitions of monomers were investigated in comparison with the cholesteryl alkanoates. The temperature range of cholesteric mesophase of monomers—derivatives of oxycarboxylic acids was shown to be wide. Such monomers can be used in thermographic composites and for synthesis of the liquid-crystalline polymers.     

Columnar Mesomorphism of the Mixed Substituted Apolar Triphenylenes: Prognosis and Experimental Data

Abstract

The calculations of molecular parameters (MP) of triphenylene derivatives with the mixed substituents were carried out here. The prognosis of columnar mesomorphism (CM) for this series of compounds was made on the basis of the value of MP. The compounds Ia-If are synthesized, their thermotropic and lyotropic mesomorphism have been studied. The good agreement of calculation and experimental data has been found for a new series of triphenylenes.     

Synthesis and Characterisation of Macrocyclic Liquid Crystalline Ligands and their Metal Complexes

Abstract

Four macrocyclic liquid crystalline ligands derived from 1,8 dihydroxy ethyl 1,3,6,8,10,13 hexa aza cyclotetradecane(DHAT) and trans-4-n-alkoxy cinnamoyl chloride have been synthesised and their metal complexes using Cu(II),Ni(II),Pb(II), V(V) and U(VI) metal ions have been isolated. The ligands and their metal complexes were characterised by elemental analysis, FTIR,NMR,X-Ray and DSC studies. Polarising microscope was used to identify mesomorphic textures of the ligands and the complexes.

The transition temperature and mesophase textures of the ligands and complexes have been compared. The effect of presence of different metal ions on mesomorphic properties has been discussed.     

Control of the Discotic to Isotropic Transition in Alkoxy-Substituted Silicondihydroxo-Phthalocyanines by Axial Substituents

The synthesis of a homologous series of octaalkoxy-substituted silicondihydroxo-phthalocyanines is described. The mesomorphic properties of these new materials were studied by DSC, optical microscopy and X-ray investigations. Compounds with n ≤ 4 (n is the number of carbon atoms in a single alkoxy side chain) show a discotic mesophase transition. A transition to the isotropic state is only observed when n ≤ 8. X-ray diffraction patterns of the mesophases confirm that all compounds form a hexagonal columnar mesophase of the type D_hd.     

Variation in Mesomorphic Characteristics with Certain Alterations in Molecular Structure: Homologous Series iso-Propyl p-(p'-n-Alkoxy CinnamoyIoxy) Benzoates and iso-Propyl p-(p'-n-AIkoxy Benzoyloxy) Benzoates

Mesomorphic characteristics of homologous series n-propyl p-(p'-n-alkoxy cinnamoyloxy)benzoates (I)¹ are quite in keeping with the general molecular structure and molecular forces accruing therefrom. Continuing the work further, the right hand terminal group of the series (I) has been replaced by a branched group with iso disposition of the alkylchain but having the same number of carbon atoms. Thus the new homologous series iso-propyl p-(p'-n-alkoxy cinnamoyloxy)benzoates (II) with all other molecular geometry the same, gets mesomorphic characteristics changed considerably. The first few members become non-mesogenic, nematic orientation is altogether eliminates and the smectic mesophase range is reduced to about one third of that of the series (I). Another new homologous series (III) with all the molecular geometry of the series (II). but with a shorter central bridge —COO— than —CH=CH—COO—receives a further jolt in its exhibition of mesomorphic characteristics. The first seven members and the last member of the series (III) become non-mesomorphic; however, some middle members exhibit monotropic smectic mesophase. The effect of the branching of the terminal substituent and shortening of the central bridge are thus quite evident and arouse good interest. The smectic texture as determined by optical microscopy and by the study of mixtures² is of fan shaped focal conic smectic A variety.     

Studies of Specific Adsorption Sites for Sodium Ion and Water on the Interface of Mixed Micelles of Novel Type II Lyomesophases

Novel aqueous type II lyotropic mesophases that align in magnetic fields have been synthesized for binary and ternary mixtures of amphiphiles. A system in which major components of the micelle bilayer are decyltrimethylammonium and dodecanoate ions is an aligning mesophase from 100% to 35% dodecanoate, but replacement of the cationic amphiphile with hexadecyltrimethylammonium facilitates the extension to aligning mesophases up to 100% replacement of the dodecanoate ions. A study of sodium and deuterium quadrupole splittings observed in their nuclear magnetic resonance spectra, confirms and extends a three site adsorption theory for sodium ion in the mixed head group interface. The first site is associated with more strongly hydrated ions and head groups and involves adjacent dodecanoate head groups, the second is not so strongly hydrated and involves one dodecanoate group while the third is a weakly bound water at - N(CH₃)⁺ groups and a sodium remote from the interface layer in close to average isotropic motion.

Mixed detergent mesophases of type II, which spontaneously align in the field, have also been synthesized from variable mixtures of hexadecyltrimethylammonium bromide and decylammonium chloride and from mixtures of potassium dodecanoate and sodium decylsulphate. In the mixed cationic system the sodium quadrupole splittings are always low but water is tightly bound to the -NH₃ ⁺ head group. In the anionic detergent mixture sodium appears about as strongly bound to dodecanoate and decylsulphate head groups. In most of the mixed mesophases some decanol is required (maximum 25% of the bilayer) in order to render the desired type II mesophase stable over a range of mixtures of the charged detergents. Specific site adsorption for sodium and water, peculiar to different head groups renders the effect of the added decanol as primarily a convenient diluent in the bilayer to preserve mesophase integrity.     

Mesomorphic Properties of an Homologous Series of Alkoxy-Terminated Enamine-Ketone Containing Liquid Crystals

An homologous series of enamine-ketone compounds has been synthesized and their thermal properties investigated. The bis [3- p-n-alkoxyanilino)-2-butenoyl] benzenes exhibited nematic mesophases when the terminal alkoxy substituents were short and both nematic and smectic mesophases when the terminal alkoxy substituents contained twelve or more carbons. The thermal data indicate that although crystalline order is largely determined by the packing of the hydrocarbon tails, there is a low degree of interaction by the tails in the nematic mesophase.     

Influence of Changes in the Central Core on the Mesomorphic Properties of 4,4’ -Dialkoxybenzalazines and Derivatives (II)

Two homologous series of benzalazines were synthesized, namely, the 4,4′-di-n-alkoxy-2-hydroxybenzalazines and 4,4′-di-n-alkoxybenzalazines, and their mesomorphic properties were studied.

All the prepared compounds of these series exhibit mesomorphism and some of them possess crystalline polymorphism also.

A comparative study of the mesomorphic properties of these series with those of 4,4′-di-n-alkoxy-2,2′-dihydroxybenzalazines and the analogous α,α'-dimethylbenzalazines was carried out in order to determine the influence of the central core on the mesomorphic properties.     

Metachromasy Bands of Disk-Like Guests in the Host Lyotropic Liquid Crystal Disodium Chromoglycate-Water

Electronic absorption spectra of Crystal Violet (CV), Malachite Green (MG) and Methylene Blue (MB) have been investigated in the 500–700 nm region using lecithin-water and disodium chromoglycate (DSCG)-water lyotropic liquid crystals as hosts. Metachromasy bands of CV and MG, indicative of associations of guest molecules, are observed even in the mesophase of the DSCG-water system, in spite of the suppression effect of the host which tends to reduce the degree of association of guest molecules with increasing host concentration. This contrasts with the case of a rod-like guest such as MB, where no indication of association of guest molecules is observed in the DSCG lyotropic mesophase. These spectral observations on the guests in the host DSCG lyotropic liquid crystal are explained in terms of some crucial structural parameter of the guests and a lyotropic columnar structure of the host such as that proposed by Attwood et al.     

Conoscopic image of a biaxial nematic phase in a sodium decyl sulfate – decanol – D2O mixture

ABSTRACT

The nematic phases of a lyotropic system NadS/ decanol/ heavy water are investigated using optical conoscopy and image processing. The phase diagram obtained from these lyotropic materials predicts the occurrence of a direct phase transition, which does not present the biaxial nematic phase, between the discotic (N_D) and calamitic (N_C) nematic phases. A biaxial nematic (N_B) phase is optically characterized and confirmed through conoscopic image, inside the biaxial range, between the two uniaxial nematic phases. Also, their respective transition points are determined by means of image processing. The N_B phase observed here is discussed as part of the nature of the micellar configuration of lyotropic materials which exhibit uniaxial nematic phases.     

Synthesis and mesomorphic behavior of symmetrical chiral liquid crystal dimers incorporating ester linked biphenyl- naphthyl cores and terminal vinyl group

A series of symmetrical chiral, liquid crystal dimeric molecules possessing ester- linked, biphenyl-naphthyl cores with varied spacer lengths and terminal vinyl groups have been synthesized using Naproxen as the synthetic precursor. The synthesized symmetrical chiral dimers were characterized by 1H NMR spectroscopy, and their liquid crystalline behavior was confirmed by DSC and HOPM studies. Structural effects on the mesomorphic and physicochemical properties were investigated in terms of variation of chiral chain length. The synthesized dimeric compounds exhibited SmX^*, SmC^*, SmA^*, N^*, BPI^*, and BPII^* mesophase sequences. An odd-even effect was observed in the dimers and the duration of the mesophase decreased with increasing spacer length. The synthesized vinyl substituted liquid crystalline dimers are particularly useful in understanding liquid crystal polymorphism and act as model compounds for liquid crystal polymers.     

Multirings Aromatic Aldehyde Liquid Crystal with Azo Linkage and Their Photosensitivity in Mesophase

Ten new rod-like aromatic aldehyde liquid crystalline molecules with azo linkage were synthesized, in which bi(trans-cyclohexyl), cyclohexyl phenyl, and biphenyl carboxylic acid mesogenic cores with terminal ethyl, n-propyl, n-butyl, and n-pentyl substituents were esterified with azo benzoic aldehyde. These molecules were designed in an attempt to construct a series of new azo liquid crystalline molecules to investigate the influence of ultraviolet (UV) light on their mesophase. All compounds have been characterized on the basis of their spectral data, differential scanning calorimeter (DSC), and hot stage polarizing optical microscope (HS-POM). All these compounds exhibited liquid crystalline phase that belonged to nematic and photosensitive properties. Their temperature ranges of mesophase are from 101 °C to 150 °C. Under irradiated 365 nm UV light, they showed photosensitivity in the solvent of methanol. Observed under HS-POM, the UV light also did change the textures of these compounds. The result showed that terminal ethyl is enough for these molecules to exhibit wider temperature range of mesophase, and these new molecules have photosensitivities observed under illumination of UV light not only in solution but also in mesophase due to the change of their structures from trans isomer to cis one.     

Mesophase design: I. Molecular structure and crystal packing motifs of 4-alkylcyanobiphenyls

A comparative study of the crystal and molecular structures of 4-alkylcyanobiphenyls (ACB-n) C _n H_{2n + 1}-C₆H₄-C₆H₄-CN (n = 2, 4–12) belonging to liquid-crystal compounds revealed no direct relationship between the molecular geometry of these compounds and their liquid-crystalline properties. Mesogenic properties are determined by the alternation of the loosely packed aliphatic and closely packed aromatic regions in the crystals. Graphs describing the crystals and mesophases were designed for ACB-n. The graph for nematic mesogens of ACB-n (n = 5−7) has one structure-forming element. The graph for smectic-nematic (n = 8 and 9) and smectic (n = 10−12) mesogens have more than one structure-forming element. If different types of secondary bonds in the smectic mesophase have equal energies, the disruption of these interactions caused by the temperature rise occurs simultaneously and the system undergoes a transition from the smectic phase to the isotropic liquid. If the energies of different types of secondary bonds are different, the destruction of the mesophase occurs in steps and the phase transitions are more complicated (smectic-nematic-isotropic transitions).     

Conformation of two 1-benzenesulphonyl-2-oxo-5-alkylthiopyrrolidine cognition activators

The molecular structures of the cognition activators (±)1-benzenesulphonyl-2-oxo-5-ethylthiopyrrolidine (1) and (±)1-benzenesulphonyl-2-oxo-5-isopropylthiopyrrolidine (2) were determined by means of X-ray diffraction and semi-empirical quantum mechanical methods. The conformational properties of the compounds, in the solid state andin vacuo (free molecule), were compared with those of the corresponding oxygenated derivatives bearing, in position 5, ethoxy and isopropyloxy substituents, respectively. The molecular arrangements of (1) and (2) in the solid state are similar, with the exception of the side chain on C(5), and they are retained alsoin vacuo. Both present an envelope conformation of the five-membered ring, and the relative positions of the five- and six-membered rings look similar and parallel those of their oxygenated parents. Fromin vacuo calculations another low-energy arrangement seems to be possible, and a detailed examination of the side-chain freedom in (1) and (2) gives more insight in the conformational properties of the compounds.