Cyano Biphenyl Research Articles

NOVEL SIDE CHAIN LIQUID CRYSTAL POLYESTERS

Abstract The synthesis and the investigation into the phase behaviour of a set of seven liquid-crystalline side chain polyesters consisting of aromatic diacids and diols bearing cyano biphenyl moieties in the side chain are reported. Five of the materials contain a chiral centre in the main chain. Materials with short spacers exhibit either semi-crystalline or sanidic phases. Materials with long spacers show a cholesteric phase indicative of a helical order with a preferred twis. In addition, they exhibit Tg's below room temperature and smectic bilayer phases. Depending on the substitution pattern of the aromatic core, SC* or SA phases are observed. These polymers were synthesised in a four-step synthesis, starting from commercially available materials.

Relationship between tribological performance of liquid crystals and their molecular structure

The tribological behaviour of nematic and smectic liquid crystals was observed using a two-roller friction tester under the conditions of 735 N load and 220 rpm rotational speed. Each liquid crystal has two typical structures: a flexible structure (alkyl chain) and a rigid structure (cyanophenyl group). Structural features of the liquid crystals were (1) alkyl cyanobiphenyl (CB), (2) alkoxyl cyanobiphenyl (ECB) and (3) alkyl cyanophenyl cyclohexane (CPC). The frictional coefficient of the test samples was lower and the estimated film thickness was larger than those of synthetic oils. The friction coefficient was not affected by the carbon number of the alkyl chain, but was closely dependent on the molecular structure of the rigid part of the liquid crystal module. The frictional coefficient of CB which has a biphenyl group was 0.035, but CPC had a higher friction coefficient of 0.045. The molecular orientation of the rigid group was observed under shearing conditions. It is concluded that the flat structure of the biphenyl group plays an important role on the tribological behaviour.

Fluorescence Studies on Intermolecular Interactions of Cyanobiphenyl Groups Chemisorbed on a Quartz Surface with Liquid Crystals

Fluorescence measurements were made of cyanobiphenyl (CB) residues covalently bound to a quartz plate through silylation to obtain information about molecular interactions between the fluorophore and solvent molecules as well as liquid crystal molecules at an interface. It was found that the fluorescence of surface-attached CB groups is quite different from that of corresponding solutions. A marked red shift was observed at the interface of a quartz plate and a nonpolar solvent like cyclohexane, reflecting a polar microenvironment surrounding the fluorophore residues owing to surface silanols and/or adsorbed water molecules, and a new fluorescent band possibly ascribable to an excimer of CB was also observed on the silica surface in cyclohexane. In contrast to these, the fluorescence from CB units bound on a quartz plate wetted with a nonpolar nematic liquid crystal showed that its red shift was much reduced and the emission band in the longer wavelength region was not observed. On the contrary, no alteration of the fluorescence of a pyrene photoprobe covalently attached to a silica surface was induced by contact with a nematic liquid crystal. These observations are reasonably interpreted as a result of specific molecular interactions between surface CB units and liquid crystal molecules on the interface.

Determination of Rotational Viscosity and Pretilt Angle in Nematic Liquid Crystals from Transient Current: Influence of Ionic Conduction

Abstract A method is described for the measurement of the rotational viscosity y 1 in nematic liquid crystal cell assemblies. Theoretical formulas to determine y 1 from transient current are developed by considering both director rotation and conduction of impurity ions. The pretilt angle and the product of the drift mobility and density of the ions are also obtained with the method. Experimental results for 4-pentyl-4′-cyano biphenyl cells with or without polyimide alignment layers are reported.

Nematic Ordering in nOCB Series from Molecular Polarizabilities

Abstract The molecular polarizabilities (α0, αe,) of the four members of the homologous series of cyano-alkyloxy-biphenyl (CnH2n+1.O.φ.φ.CN for n = 5 to 8) in the nematic range have been calculated using two different internal field models. The additive rule of bond polarizabilities has been adopted to get the mean polarizability (α) and the principal molecular polarizability anisotropy (α1 - α1) values for these compounds. The orientational order parameters have been calculated from these results. The ordering exhibits an odd-even alternation along the series. The results have been compared with different theories. Possible causes for deviation from the theories have been discussed. Besides the relative stabilities of the alkyloxy cyano biphenyls have also been discussed in terms of the molecular parameters.

Experimental investigation of the surface energy of a nematic liquid crystal

Abstract The temperature dependences of surface tension, γ=f ≠ (t), are experimentally studied and discussed for homologous series of liquid crystalline 4-alkyl-4′-cyano biphenyls, 4-alkyl-4′-cyanophenylbenzoates, 4-alkyloxy-4′-cyanophenylbenzoates and also for several nematic liquid crystals of other chemical classes. The surface energy anisotropy of 5CB is measured at fixed temperature.

Molecular flexibility in nematics: from alkanes to dimer mesogens

The ‘chord model’ of flexible alkane solute ordering in the nematic phase (D. J. Photinos, E. T. Samulski and H. Toriumi, J. Phys. Chem., 1990, 94, 4688; 4694) is extended to dimer molecules. Using the same parametrization of the modular potential of mean torque that successfully describes alkane solutes in the nematic field and monomer mesogens in neat phases, we are able to generate correctly the segmental orientational ordering profiles of a variety of mesogenic and non-mesogenic dimer solutes in a nematic solvent. The effects of the linkage between the mesogenic core and flexible spacer on the ordering properties of the dimers are explored by studying the homologous series of cyanobiphenyl (CB) ethers, CBO—(CH2)N—OCB, (N= 2–10) with different primary structural topologies, i.e. with para, meta and ortho linkages. The observed 2H-NMR spectra of para-linked dimers with N= 9, 10 and of ortho-linked dimer with N= 10 are readily reconstructed using the simplest parametrization of the chord model potential. This parametrization is then used to predict the 2H-NMR spectra of the respective meta-linked dimers and also to make inferences about how the propensities of the topologically different series of dimers for conforming to the nematic field depend on spacer length and spacer parity. Finally, the effect of the core size on the overall ordering of dimers is studied by considering para-cyanophenyl (CP) ether linked dimers, CPO—(CH2)N—OCP. It is found that, although the NMR spectra of the spacer chain in the CPO dimer series are not profoundly different from those of the respective CBO dimers, the average value of their orientational energy is indicative of substantially reduced (self) orientability of these dimers. Generally, these findings corroborate the predictive power of the chord model and its utility for describing orientational ordering of flexible solutes, even when molecular topology is complex.

Submillimetre wave spectroscopy of 4-n-alkyl-4′-cyano biphenyl liquid crystals

Abstract The absorption coefficient of the 4-n-alkyl-4′-cyano biphenyls has been studied in the submillimetre wave range 50–220 cm−1. Molecular processes which give rise to superimposed but distinct absorption bands are reported. These processes have been analysed using a multi-oscillator model for the observed absorption and are assigned to the Poley absorption as well as to intermolecular and intramolecular mechanisms. Spectra at temperatures in the range 20–70°C and of solutions in cyclohexane support the proposed assignments.

Guest-Host Systems: a Comparison of low Molecular and Polymeric Systems

Abstract Some properties of low molecular and polymeric guest-host systems are compared. Central points are the dependence of the order parameter S(Dye), measured by absorption spectroscopy, as a function of the dye concentration and its influence on the phase behaviour. The systems used were anthraquinone dyes dissolved in phases containing cyano biphenyl derivatives as mesogenic groups. Some few statements concerning copolymeric guest-host systems were given.

Molecular structural changes at the phase transitions in thermotropic liquid crystals: A spectroscopic study of 4-dodecyloxy-4′-cyano biphenyl

The analysis of the vibrational infrared and Raman spectra of 4-dodecyloxy-4′-cyano biphenyl (12-OCB) reveals characteristic structural markers which describe the evolution of the molecular structure through K–SA and SA–I phase transition. The conformational collapse of the dodecyloxy residue into a ‘‘liquid-like’’ structure unquestionably occurs at K–SA transition. A rearrangement of the conformation of the biphenyl residue is also observed.

The Anisotropy of the Surface Tension of Polar Liquids: The Case of Liquid Crystals

Abstract The contact angle of the liquid crystal (LC) 4-phentyl, 4′-cyano biphenyl (5CB) on glass or polyethylene does not correspond to the value expected from its surface tension measured by the “du Nouy” method (29 × 10−3 JM−2). The value deduced from the Young-Dupre law is 40 × 10−3 JM−2. Both these values have already been reported in the literature. Their apparent discrepancy is explained by the LC surface tension anisotropy. We show that 5CB as many other LCs orient perpendicular to the free surface but parallel to glass or polyethylene Thus both values of the surface tension correspond to two different molecular orientations. The LC oriented perpendicularly has a surface tension of 29 × 10−3 JM−2 and 40 × 10−3 JM when it lies parallel to the surface. We suggest that the anisotropy between the perpendicular and parallel state of LCs also exists between two perpendicular orientations. Furthermore, such anisotropy associated with any polar molecules explains the difference of the interfacial energy o...

Synthesis and Properties of Some 2- n-Alkyl-6-(4′-cyanophenyl)-naphthalenes -3,4-dihydronaphthalenes, and -1, 2, 3, 4-tetra-hydronaphthalenes

Abstract Five (ethyl to n-hexyl) of each of the series of 2-n-alkyl-6-(4′-cyanophenyl)-naphthalenes and -3,4-dihydronaphthalenes, and three (ethyl, n-butyl, and n-hexyl) of the corresponding series of -1,2,3,4-tetrahydronaphthalenes were prepared. All these compounds exhibit nematic phases (no smectic phases were found) and the nematic-isotropic transition temperatures of these compounds are compared with those of the corresponding 4- n-alkyl-4′-cyano biphenyls and 4- n-alkyl-4”-cyano- p-terphenyls. Some explanation is given for the observed nematic thermal stabilities of the titled compounds. Assessments of the viscosities of the titled compounds have been carried out, and the effects on viscosity of substituting 2- n-pentyl-6-(4′-cyanophenyl) naphthalene for 4- n-pentyl-4”-cyano- p-terphenyl in commercially available mixtures have also been investigated.

Induced Smectic Phase in Binary Systems Containing Alkyl Cyano Phenylcyclohexane

Abstract The experimental investigation of the induced smectic phase (ISP) phenomenon in the binary system of the homologous series of alkyl cyano phenylcyclohexane (PCH) and 4-n-hexyloxyphenyl 4'-pentyl benzoate ester (5.0.6) is reported. The phase transition temperatures were determined by differential scanning calorimetry and the optical textures were observed through a polarizing microscope in conjunction with a hot-stage. We found that the ISP-effect on equimole mixture of PCH and 5.0.6 increased sharply with the increasing of the length of terminal alkyl chain. By comparing PCH with Cyanobiphenyl (CBP) we also found that the ISP-effect was influenced by molecular framework.

Studies on induced smectic phases (III). Fourier transform infrared and laser‐raman spectral differences between isotropic and induced smectic phase of binary mixtures of nematogens with contrasting dielectric anisotropies

AbstractThe SE, SB, SA induced phase sequence was detected in binary mixtures of two nematogens, 4,4′‐di‐n‐heptyl azobenzene (7AB) with 4‐n‐pentyl‐4′‐cyano biphenyl (5CB). The mixtures as well as the single components were studied by Fourier transform IR and laser‐Raman spectroscopy at different temperatures. Charge redistribution of 5CB is demonstrated by the spectral differences found by the ratio‐recorded IR spectra and also by integrating the intensities of some Raman lines. The spectra of the different phases of the 7AB—5CB mixture, built up from components of different length, indicate a population increase of the gauche conformers of 7AB in the smectic A phase.

Studies on Induced Smectic Phases (II) Transition Enthalpies, X‐ray Patterns and Layer Spacings of Orthogonal Phases of Binary Mixtures of Nematogens with Contrasting Dielectric Anisotropies

AbstractBinary mixtures of two nematogens, 4,4′‐di‐n‐heptyl‐azobenzene with 4‐n‐pentyl‐4′ ‐cyano biphenyl were studied by optical, calorimetric and X‐ray measurements. At a given concentration induced phases with a sequence SA, SB, SE were detected, the properties of which were discussed.

A mössbauer study of anisotropic molecular diffusion in the supercooled nematic liquid crystalline phase

The effect of the anisotropic diffusion of the Mössbauer probe 1,1'-diacetyl ferrocene (DAF) dissolved in the cold liquid crystals p-methoxybenzylidence- p-butylaniline and an eutectic mixture of cyano biphenyls and terphenyls, commercially known as E8, on the Mössbauer line broadening has been studied using 57Fe Mössbauer spectroscopy in the temperature range 80–300 K. The Mössbauer spectral lines begin to broaden as one approaches the glass transition temperature (∼199 K for MBBA and ∼ 175 K for E8). The anisotropy in the line broadening is due to the easier transport of the DAF molecules in the direction parallel to the liquid crystal molecular direction than in the perpendicular direction. The diffusion coefficients in the directions parallel ( D ⌈) and perpendicular ( D ⊥) to the liquid crystal molecular direction have been calculated assuming a continuous diffusion model. It has been found that D ⌈> D ⊥. The disappearance and subsequent reappearance of the Mössbauer effect above the glass transition temperature is shown to be due to the nematic liquid crystal glass converting itself into supercooled liquid and then the recrystallization of the supercooled liquid crystal. The anisotropic diffusive line broadening in the supercooled liquid crystalline phase is associated with the anisotropy of the Lamb-Mössbauer factor.

Static and Dynamic Depolarized Rayleigh Scattering of Cyano Biphenyl Series in Dilute Solutions and Intrinsic Molecular Even-Odd Effect in Liquid Crystals

Abstract We report here a detailed description of our experimental work about both static and dynamic investigations of depolarized Rayleigh scattering and Kerr effect in diluted solutions of the cyanobiphenyl series, and show how a carefully performed conformational analysis can lead to a possible interpretation of the intrinsic molecular even-odd effect experimentally evidenced.

ChemInform Abstract: INVESTIGATION OF THE DIELECTRIC CONSTANTS AND THE DIAMAGNETIC ANISOTROPIES OF CYANOBIPHENYLS (CB), CYANOPHENYLCYCLOHEXANES (PCH), AND CYANOCYCLOHEXYLCYCLOHEXANES (CCH) IN THE NEMATIC PHASE

Chemischer InformationsdienstVolume 11, Issue 7 Physical Organic Chemistry ChemInform Abstract: INVESTIGATION OF THE DIELECTRIC CONSTANTS AND THE DIAMAGNETIC ANISOTROPIES OF CYANOBIPHENYLS (CB), CYANOPHENYLCYCLOHEXANES (PCH), AND CYANOCYCLOHEXYLCYCLOHEXANES (CCH) IN THE NEMATIC PHASE HP. SCHAD, HP. SCHADSearch for more papers by this authorG. BAUR, G. BAURSearch for more papers by this authorG. MEIER, G. MEIERSearch for more papers by this author HP. SCHAD, HP. SCHADSearch for more papers by this authorG. BAUR, G. BAURSearch for more papers by this authorG. MEIER, G. MEIERSearch for more papers by this author First published: February 19, 1980 https://doi.org/10.1002/chin.198007064AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume11, Issue7February 19, 1980 RelatedInformation

Investigation of the dielectric constants and the diamagnetic anisotropies of cyanobiphenyls (CB), cyanophenylcyclohexanes (PCH), and cyanocyclohexylcyclohexanes (CCH) in the nematic phase

We have measured the dielectric constants of cyanobiphenyls (CB), cyanophenylcyclohexanes (PCH), and cyanocyclohexylcyclohexanes (CCH) using a capacitance bridge with a dielectric cell having a guard ring. The ratio Δχ/Δε was also measured for these materials using a new technique which is applicable when Δχ is small or even negative. As a surprising result we have found that this ratio is almost independent of temperature. The temperature dependence of the diamagnetic anisotropies and the dielectric constants of these compounds are given and the results are discussed in terms of the molecular properties.

A Convenient Method for the Preparation of 4 - n - Alkyl - 4″ -cyano - p - Terphenyl

Abstract A new and general procedure for the preparation of 4-n-alkyl-4″ -cyano-p-terphenyl is described starting from p-terphenyl. This procedure consists of the Friedel-Crafts reaction on p-terphenyl with an acyl halide and reducing the resulting ketone by the Wolff-Kishner method to the 4-n-alkyl-p-terphenyl. This is acylated with acetyl chloride to the corresponding 4-n-alkyl-4″- acetyl-p-terphenyl, which in turn is oxidised to the carboxylic acid. This acid is converted to the amide through its acid chloride. Dehydration of this amide affords the desired 4-n-alkyl-4″- cyano-p-terphenyl. This convenient method offers better yields than the procedure of Gray et al.1 and could also be utilised for the preparation of 4-n-alkoxy-, and 4-n-alkyl-4′ -cyano biphenyls. In addition to the cyano derivatives, some intermediate compounds also exhibit mesomorphic properties.