Photosensitive Bent-Core Liquid Crystals with Laterally Substituted Azobenzene Unit

Photosensitive liquid crystals represent an important class of functional materials that experience rapid development. Hereby, we present novel bent-core liquid crystals bearing a lateral substitution on the central core and in the vicinity of the photosensitive unit—an azo group. The azo group enables fast (E)-to-(Z)-isomerization upon irradiation with UV-light and visible light, while the substitution facilitates the high stability of the photochemically formed (Z)-isomer. The effectiveness of the irradiation and the composition of photostationary states was determined by UV/Vis and 1H NMR spectroscopy. A nematic phase formed by the materials was characterized by differential scanning calorimetry and optical polarizing microscopy. We show that the materials easily change their relative configuration of the N=N double bond not only in solution, but also in the mesophase, which leads to fast isothermal phase transition from the nematic phase to isotropic liquid.

Interpretation of petrographic anisotropy in ornamental granites based on P wave velocity measurements

The existence of a possible anisotropy, determined by the orientation of any mineral or by micro­crack network in granite rock, isn´t easily detected by the naked eye. Five granitic rocks from Galicia (Spain), namely Albero, Gris Alba, Gris Mondariz, Rosa Porriño and Traspielas, were characterized petrographically by means of textural and mineralogical studies, using optical polarizing microscopy, and fractographic studies were carried out under scanning electron microscopy. Longitudinal wave propagation velocity was measured in three orthogonal directions on cubic samples, oriented according to rift surface (known in quarry works like the preferential partition surface visible in the blocks). Vp was measured on dry and water saturated samples. All the dry samples showed an anisotropic behaviour of Vp. Models of microcrack network distribution and possible mineral grain orientation were developed based on the obtained data.

Synthesis and Mesomorphic Studies of Copper(II) with Carboxylato and N-Donor Ligands

Metal containing liquid crystals also known as metallomesogens is an orientationally ordered liquid that combines properties of both crystalline state and liquid state. Three linear and one branched alkyl chain complexes of general formula [Cu2(RCOO)4(X)2], where R = CH3(CH2)13 (Complex 1, Complex 2), p-CH3(CH2)14OC6H4 (Complex 3) and CH3(CH2)7CH[(CH2)5CH3] (Complex 4), X = pyridine or 2,2-bipyridine were prepared. The single crystal X-ray crystallography of [Cu2(CH3(CH2)13COO)4(py)2] (Complex 1) shows dinuclear complexes with each square pyramidally Cu(II) centre was bridged by four carboxylato molecules and a pyridine molecule. For all complexes, the IR spectra gave the ??coo values in the range of 164 - 240 cm-1 , suggesting two binding modes of the alkylcarboxylate ligands. The UV-vis spectra shows a broad d-d band at ?max ~ 664 – 699 nm (?max ~55 – 341 M-1 cm-1 ), indicating that the distorted square pyramidal geometry at Cu(II). From the results of differential scanning calorimetry (DSC) and optical polarizing microscopy (OPM), complexes 1-4 exhibited liquid crystal mesophases.

Study of the Effects of Lateral Substitution (Bromo) on Mesomorphic Behaviours of Chalconyl Ester Derivatives

Novel homologous series: RO-C6H4-COO-C6H3-Br-CO-CH=CH-C6H4-OC18H3(n) (ortho bromo to –COO-) is synthesized and studied with a view to understand and establish the relation between mesomorphic properties and the molecular structure with reference to lateral substitution of bromine (-Br) at middle phenyl ring. Chalconyl homologous series consists of thirteen between (C1to C18) homologues. Nematogenic mesomorphism commences from C5homologue and continue up to C18homologue in enantiotropic manner. Transition and melting points were determined by an optical polarizing microscopy (POM) equipped with a heating stage. Textures of nematic phase are threaded or schlieren. Transition curve Cr-N/I behaved in normal manner. N-I transition curve exhibited odd-even effect up to C8homologue. It (N-I) rises and fall with negligible deviations from its normal descending tendency which appears in case of homologues C10to C18. Thermal stability for nematic is 142.89 °C and the mesophase lengths vary minimum 8.0 °C to maximum 26.0 °C at the C7and C8homologue respectively. Liquid Crystal properties of present series are evaluated and compared with structurally analogous series and relative group efficiency order derived. Thus ,present series is predominantly nematogenic with absence of Smectic property. Analytical and spectral data supported moleculars of homologues.

Study of the Effects of Decreasing Molecular Rigidity on Mesomorphism

A Chalconyl homologous series: RO-C6H4-CH=CH-CO-C6H4-OC14H29(n) (meta) is synthesized and studied with a view to understand and establish the effect of molecular structure on Liquid crystal behaviour by reducing molecular rigidity through diminishing of a phenyl ring and a central carboxy or vinyl carboxy group from a molecule. Novel series consists of thirteen homologues (C1to C18). First member (C1) homologue is nonliquid crystal and the rest of the homologues (C2to C18) are enantiotropically ( C2to C5) nematogenic or monotropically (C6to C18) nematogenic plus smectogenic of low mesophaselengths and low transition temperatures ( 38°C to 76°C). Transition temperatures were determined by an optical polarizing microscopy (POM) equipped with a heating stage. Cr-N/I, N-I, I-N, N-Sm transition curves behaved in normal manner in a phase diagram. N-I and I-Sm transition curves exhibited odd-even effect. Textures of nematic phase are threaded or schlieren and that of the smectic phase are of the type A or C. Analytical, spectral and thermal data supported molecular structure of homologues. Thermal stability ( N-I/ I-N) of series for nematic is 67.5°C and that of the smectic is very low. Group efficiency order derived on the basis of thermal stability is as under. –Cl with –C6H4.COO- > -OC14H29(n) without –C6H4.COO-with reference to central bridge –CH=CH-CO-.

Study of the Effect of Chalconyl Central Bridge on Mesomorphism

A novel homologous series of chalconyl ester derivatives of thermotropic type of liquid crystals (LC) variety have been synthesized with its general molecular formula RO-C6H4-CH=CH-COO-C6H4-CO-CH=CH-C6H4-N(CH3)2 (Para). Present investigation is planned with a view to understand and establish the relation between molecular structure and the mesomorphic behaviorur of the constituent homologue derivatives as well as to avail novel mesomorphic (LC) substances to the researcher working on multidisciplinary thermotropic LC material with different aims, objects and views at different angles. Novel homologous series consists of twelve homologues C1 to C5 homologues are nonliquid crystals (NLC) and the rest of the C6 to C16 are monotropically nematogenic liquid crystals. Transition temperatures and texture of the LC and NLC were determined by an optical polarizing microscopy equipped with heating stage (POM). Textures of nematic phase are threaded or schlieren. Analytical and spectral data confirms the molecular structures of homologues. Thermal stability for monotropy is very low of the magnitudes of few second and of negligible degree of temperature difference. Thermal properties of present novel series are compared with of structurally similar series, data interpreted in terms of molecular rigidity and flexibility to derive group efficiency order.

Molecular Rigidity/Flexibility Dependence of Mesomorphism

A novel chalconyl homologous series of liquid crystalline derivatives; RO - C6H4- CH : CH - COO - C6H4-CO - CH : CH - C6H4 - OC8H17 (n) (para) have been synthesized and studied with a view to correlate the thermotropic liquid crystal (LC) behavioural properties and the molecular structure of a substance. Present novel series consisted of eleven homologue members (C1 to C16) whose, only nematogenic mesomorphism commences from C3 homologue and continued upto C16 homologue in enantiotropic manner with absence of smectogenic character. Transition temperatures and textures of nematic phase were determined using an optical polarizing microscopy equipped with a heating stage (POM). Transition curve Cr-N/I behaved in normal manner. N-I transition curve exhibited odd-even effect and deviated from its normal descending tendency from and beyond C8 homologue and adopted serpantile shape from C8 to C16 homologue in deviating manner. Textures of the nematic phase are threaded or schlieren. Analytical and spectral data supported molecular structures of homologues. Thermal stability for nematic is 112.66 and the degree of mesomorphism vary from 5.00C to 44.00C at the C12 andC4 homologue respectively. It is a middle ordered melting type series, whose relative group efficiency order for nematic derived.

Effect of Equipolar Endgroup of a Molecule on Mesomorphic-Isotropic Transition Curve

A Homologous series:RO-C6H4-CH=CH-COO-C6H4-CO-CH=CH-C6H4-OC18H37(n) (para) of chalconyl novel ester of dual character as thermotropic and lyotropically bioactive is synthesized and studied with a view to understand and establish the relation between mesomorphism and molecular structure on the basis of molecular rigidity and flexibitity through thermotropic liquid crystalline (LC) state. Novel series consists of thirteen homologues of which four homologues (C1 to C4) are non liquid crystal (NLC) and the rest of the homologues (C5 to C18) are thermotropically enantiotropic nematic without exihibition of smectic property. Thermometric transition temperatures and textures of nematogenic phase are determined by an optical polarizing microscopy equipped with a heating stage (POM).Textures of nematic phase are threaded or schilieren. Transition temperatures of novel homologues are relatively lower than the transition temperature of corresponding dimeric trans n-alkoxy cinnamic acid. Cr-N/I and N-I transition curves behaves in normal manner with negligible abnormality at C18 homologue in phase diagram of a series.Analytical and spectral data conforms the molecular structure of homologues. Thermal stability for nematic is 121.88°C whose degree of mesomorphism vary minimum from 4.0°C to a maximum of 34.0 °C, and hence novel series is of middle ordered melting type, Group efficiency order for-OC18H37 tail groups (series-1&Y) is highest irrespective of type of ester group –COO-and CH=CH-CO derived for nematic.

Study of Mesomorphism Changing on Terminal Side Chain with Different Thioalkyl Group

A novel mesomorphic series is RS-C6H4-COO-C6H4-CO-CH=CH-C6H4-OC18H37(n) (para) of chalconyl ester play double role thermotropic as well as lyotropically bioactive is synthesized and studied with a view to understand and establish the effect on mesomorphism when changing on left thioalkyl chain.the relation between mesomorphism and molecular structure on the basis of molecular rigidity and flex Novel series consists of thirteen homologues of which four homologues (C1 to C3) are non liquid crystal and the rest of the homologues (C5 to C18) are thermotropically enantiotropic nematic absences with smectic property. Thermometric transition temperatures and textures of nematogenic phase are determined by an optical polarizing microscopy equipped with a heating stage (POM).Textures of nematicphas schilieren and threaded type. Cr-N/I and N-I transition curves behaves in as manner with negligible abnormality at C18 homologue in phase diagram of a series.Analytical and spectral data conforms the molecular structure of homologues. Thermal stability for nematic is 123.2 °C whose degree of mesomorphism vary minimum from 4.0°C to a maximum of 24.0 °C, and hence novel series is of middle ordered melting type.