Homologous Series Of Liquid Crystals Research Articles

Electro-optical Effect of 4-n-alkyl-sulfanyl-4' isothiocyanate-biphenyl Liquid Crystal Homologous Series Under Terahertz Frequency: A Theoretical Approach

Electro-optical Effect of 4-n-alkyl-sulfanyl-4' isothiocyanate-biphenyl Liquid Crystal Homologous Series Under Terahertz Frequency: A Theoretical Approach

Liquid Crystalline Mixtures with Induced Polymorphic Smectic Phases Targeted for Energy Investigations

In this study, 4-Biphenyle-4′-alkyloxybenzenamines were synthesized as a homologous series of liquid crystals based on the biphenyl moiety. Their mesomorphic and optical properties were examined for both pure and mixed components. Elemental analysis, NMR, and FT-IR spectroscopy were used to determine the molecular structures of the developed materials. Using differential scanning calorimetry (DSC), the mesophase transitions were studied, and polarized optical microscopy was used to identify the textures of the mesophases (POM). The obtained results showed that all compounds are dimorphic and only have smectic B (SmB) and smectic A (SmA) phases for all terminal side chains, which are enantiotropic. With variably proportionated terminal side chains and a focus on the mesomorphic temperature range, binary phase diagrams were constructed and an induced smectic C phase was achieved (SmC). It was found that terminal chain length affects both conformation and steric impact in the mixed states. The absorption and fluorescence emission spectra of pure as well as their binary mixtures liquid crystalline films were recorded to investigate the optical and photophysical properties. It was noted that, with the increase in alkyl chain length, the energy bandgap increases from 3.24 eV (for C6H13) to 3.37 eV (for C16H33) and charge carrier lifetime decreases, ascribing to the increase in stearic hindrance causing, consequently, the faster decay of charge carriers.

Investigations on thermotropic hydrogen bond liquid crystals

Novel hydrogen bond liquid crystal homologous series derived from alkyloxy benzoic acids and α-ketoglutaric acid are isolated and experimented. This homologous series referred as KGA + nBAO comprises of eight mesogens in which the alkyloxy benzoic acid varied from pentyloxy to dodecyloxy. Fourier Transform Infrared Spectroscopy analysis confirmed the formation of hydrogen bond. Optical polarizing microscopy reveals that this homologous series exhibits three phases namely nematic, smectic C and smectic G. The transition temperatures obtained by Differential Scanning Calorimetry and optical microscopy and corresponding enthalpy values are tabulated for all the homologues of the series and various thermal parameters are derived.

Novel sulphonic acid liquid crystal derivatives: experimental, computational and optoelectrical characterizations.

A novel liquid crystal homologous series based on the benzene sulphonic acid moiety, namely (E)-4-((4-((4-(alkoxy)benzoyl)oxy)benzylidene)amino)benzenesulfonic acid (Sn), was synthesized and examined via different experimental and theoretical measurements. The four synthesized members have terminally connected alkoxy chain groups, which vary between 6 and 12 carbons. FT-IR and NMR spectroscopy, as well as elemental analyses, were used to confirm their molecular structures. Mesomorphic and optical investigations of the prepared homologues were also conducted using differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The DSC and POM characterization revealed that all of the synthesized sulphonic acid members are monomorphic, exhibiting a pure smectic A (SmA) mesophase with enantiotropic properties. Moreover, all compounds in the group have high thermal transition temperatures. The terminal electron-withdrawing group –SO3H plays a considerable role in the stabilization of the molecule, which in return resulted in high thermal SmA stability. Furthermore, the experimental data relating to the mesophase behavior were substantiated via computational studies using the DFT approach. In addition, the terminal –SO3H moiety has an essential impact on the thermal and physical parameters of possible geometries. All members of the synthesized Sn series exhibit ohmic behavior with electrical resistance in the GΩ range, as revealed by electrical measurements. The S10 electrode had the highest electrical conductivity: 35.16 pS. It also showed two direct optical band gaps of 3.58 and 3.23 eV with Urbach energies of 1261.1 and 502.4 meV. Upon decreasing the number of carbon atoms to n = 6, the main bandgap for S6 reduced to 3.3 eV. The highest conductivity, good absorption, and two large bandgaps recorded for the chain derivative S10 make it suitable for investigations relating to energy-based applications.

Enhanced conductivity in nanoparticle doped hydrogen bonded binary mixture

A homologous series of liquid crystals were newly prepared containing low molar mass moieties through intermolecular hydrogen bond (HB) interactions. A non mesogenic chloro substituted Schiff base is synthesized which acts as the proton acceptor. Mesomorphic 4-n-alkyloxy benzoic acids (where n = 3, 4, 5, 7, 8 and 12) are used as the proton donors. The influence of chlorine as a substituent on mesomorphic nature of the compounds, their thermal stabilities, melting and clearing temperatures are studied. A nanocomposite of the potent liquid crystal of the series with ZnO nanoparticle is prepared and the conductivity measurements are carried out.

Structural and thermo-optic studies on linear double hydrogen bonded ferroelectric liquid crystal homologous series

ABSTRACTA novel series of supramolecular hydrogen bonded ferroelectric liquid crystal (HBFLC) is formed through hydrogen bonding interaction between nonmesogenic dextro-levo tartaric acid (DLTA) and mesogenic p-n-alkyloxy benzoic acids (nBAO, where n = 7 to 12). The formation of hydrogen bond in the complex is confirmed through Fourier transform infrared spectroscopy (FTIR) studies. Optical and thermal behaviors for mesomorphic phases of individual complex in the series are meticulously studied by means of differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). Computation of the enthalpy values in the homologous series of complex during both heating and cooling cycles is proved that thermal equilibrium exhibited by the complex system. Extended thermal span width and rich liquid crystallinity is observed in the present complex due to the presence of aromatic ring with chiral center. Thermal stability factor and thermal equilibrium are also discussed. Presence of alkyloxy chain on either side of chiral molecules hinder the abundant reduction in phase transition temperature and lowered melting point compared to the individual mesogens. Optical tilt angle for smectic C* phase is determined and the same is fitted to a power law.

Dependence of thermotropic mesomorphism on molecular flexibility of changing tail group

ABSTRACTA novel chalconyl ester homologous series of liquid crystals has been synthesized and studied with a view to understanding and establishing the effect of molecular structure on liquid crystalline properties. Novel series consisted of 13 members (C1–C18) of a series. C1–C4 member of a series is nonliquid crystals and, the rest of the homolog members (C5–C18) are enantiotropically nematogenic with absence of smectogenic property. None of the homolog is monotropically mesomorphic. Transition and melting temperatures were determined by an optical microscope equipped with a heating stage. Textures of nematic phase are threaded or schlieren. Spectral and analytical data of selected members of a series confirms the molecular structures of homologues. Cr-N and N-I transition curves of a phase diagram behaved in normal manner with exhibition of odd-even effect of very short range as observed for N-I transition curve. Thermal stability for nematic is 122.0°C and the nematogenic mesophase ranges from 7.0°C to 38.0°C. Liquid crystal properties of a present series are compared with the structurally similar known homologous series.

Comparison of mesomorphic properties exhibited by linear hydrogen bonded thermotropic liquid crystals

ABSTRACTTwo linear hydrogen-bonded liquid crystal homologous series have been isolated in the present investigation and compared. Palmitic acid is chemically bonded with alkyloxy benzoic acids, and alkyl benzoic acids to yield 15 mesogenic complexes. The formation of inter molecular hydrogen bonding is confirmed by Fourier transform infrared spectroscopy (FTIR). Phase polymorphism exhibited by the two linear homologous series is evinced by various textural observations made through polarizing optical microscopic (POM) studies. Differential scanning calorimetry (DSC) studies revealed the transition temperatures and the corresponding enthalpy values exhibited by the individual phases. Phase diagrams has been constructed through POM and DSC data. Thermal equilibrium, thermal stability factor, and order of phase transition data are obtained from DSC study. Influence of oxygen atom attached/detached to the rigid chemical moiety toward the properties of the homologous series is discussed. Light filtering action of the nematogens at different temperatures is also conferred.

Mesomorphism dependence on molecular flexibility

ABSTRACTA novel ester homologous series of liquid crystals with a highly polar laterally substituted –OCH3 group is synthesized and studied with a view to understanding and establishing the effects of molecular structure involving lateral substitution on liquid crystal behavior. The novel series RO·C6H4·COO·C6H3·OCH3(ortho)CH=CH·COO·C2H5 consists of 12 homologs of which C7, C8, C10 are nematogenic and C12, C14, C16 homologs are smectogenic. The rest of the homologs are nonliquid crystals. The textures of nematic phase are threaded and the smectic phase is of the type A or C. Transition temperatures and the textures of mesophases were determined by an optical polarizing microscope equipped with a heating stage. Analytical and spectral data support the molecular structures. The N-I and Sm-I transition curves behave in normal manner without exhibition of an odd-even effect. Average thermal stability for smectic and nematic are 127.3°C and 129°C, respectively. The total mesophase length ranges from 17°C to 57°C and series is of a middle ordered melting type with transition temperatures varying between 82°C and 148°C. The liquid crystal properties of present novel series are compared with, structurally similar known homologous series.

Dependence of LC state on molecular flexibility

ABSTRACTA novel azoester homologous series of liquid crystals (LCs) viz. RO‒C6H4COOC10H6-N˭N(ortho)-C6H4‒OC4H9(para) has been synthesized and studied with a view to understanding and establishing the effect of molecular structure on LC properties. Homologous Series consists of thirteen members (C1 to C18). C1 to C3 members are nonliquid Crystals and the rest of the homologues are LC in an enantiotropic manner. C7 to C18 are smectogenic in addition to nematogenic whereas C4, C5, and C6 are only nematogenic. The Sm-N and N‒I transition curves behave in a normal manner with the usual exhibition of an odd–even effect. The Cr-M/I curve also behaves in a normal manner. Analytical and spectral data confirm the molecular structures of homologues. The average smectic and nematic thermal stabilities are 60.31°C and 79.6°C, respectively, with total mesophase length varying minimum to maximum is 21°C to 57°C at the C6 and C14 homologue, respectively. Thus, present novel azoester homologous series is partly smectogenic and predominantly nematogenic with low ordered melting type and useful to construct LC devices workable at low temperatures or room temperature.

Study of a new homologous series of liquid crystals: Isopropyl-p-(p/-n-alkoxy cinnamoyloxy) cinnamates

A new homologous series: isopropyl-p-[p/-n-alkoxy cinnamoyloxy] cinnamates was synthesized and studied with a view to understanding and establishing the relation between liquid crystal property and molecular structure. Twelve homologues were synthesized. Methyl to butyl homologues are not liquid crystals, while pentyl, hexyl, heptyl, octyl, decyl, dodecyl, tetradecyl, and hexadecyl derivatives are enantiotropic liquid crystal in nature with nematogenic character. Smectogenic character is totally absent. A phase diagram is obtained by plotting a graph of transition temperatures versus number of carbon atoms is n-alkyl chain of left n-alkoxy terminal end group. Solid-isotropic or solid-nematic transition curve rises steeply from methyl to propyl derivatives and falls to pentyl homologue through butyl homologue, and follows a zigzag path of rising and falling values as the series is ascended. Nematic–isotropic transition curve shows descending tendency as series is ascended in a normal manner with exhibition of odd-even effect. Smectic mesophase does not appear even in the monotropic condition. Phase transition temperatures are determined by hot stage polarizing microscope. Analytical data support the structure of molecules. Texture of nematic mesophase is of threaded type. Mesomorphic properties are compared with structurally similar homologous series.

Dependence of liquid crystallinity on molecular rigidity

A novel homologous series of liquid crystals (LC) of chalconyl derivatives is synthesized and studied with a view to understanding and establishing the effects of molecular structure on liquid crystal properties. The novel series consists of 12 homologues. Nematogenic LC property commences from C3 and continues up to C14 and the smectogenic mesophase is exhibited from C4 to C16. The C3 homologue is a monotropic nematic and the rest of the homologues are enantiotropically smectic and nematic or only smectic (C16). Transition curves Cr-Sm, Sm-N, Cr-I, and N-I behave in normal manner with exhibition of odd-even effect, showing phase behaviors of the series.

Mesomorphism dependence on terminal end groups

ABSTRACTA novel homologous series of liquid crystals (LC) 4-(4′-n-alkoxy cinnamoyloxy)-4′′-bromobenzylbenzoate was synthesized and studied with a view to understanding and establishing the relation between LC properties and the molecular structure. The novel series comprises 11 members, and all the members exhibit mesomorphism as enantiotropic smectic. None of the homologues are nematogenic, even in the monotropic condition. Transition temperatures were determined by an optical polarizing microscope equipped with a heating stage. The textures of smectic phase are of the type A or C. The transition curves Sm-I and Cr-Sm behave in a normal manner in the phase diagram. An odd-even effect is exhibited by the Sm-I transition curve. Thermal stability for smectic is 102.6°C. Mesomorphism commences from the very first member of the series. The series is entirely smectogenic and of middle-order melting type whose mesomorphic phase length ranges from 7.4°C to 60.9°. Analytical and spectral data confirmed the molecular structures of homologues. The mesomorphic properties of the present series are compared with structurally similar homologous series.

Synthesis and Study of Novel Mesogenic Homologous Series: 4-(4′-n-alkoxy benzoyloxy)-n-propyl Cinnamates

A novel homologous series of liquid crystals viz. 4-(4′-n-alkoxy benzoyloxy) n-propyl cinnamates comprising of 11 homologues has been synthesized. It is a middle ordered melting type of series with exhibition of smectic and nematic mesophases. The first to fifth members of the series are non-mesomorphic. Mesomorphic behavior commences from the sixth homologue. The octyloxy (C8) and decyloxy (C10) homologues are polymesomorphic. The smectic–nematic and nematic–isotropic transition curves behave in a normal manner except for the hexadecyl derivative, which slightly deviates from normal behavior (N–I). An odd–even effect was not observed for the N–I or Sm–N transition curves. The texture of nematic phase is threaded or Schlieren and that of the smectic phase is focal conic fan shaped of the smectic-A type. Transition temperatures and textures of mesophases were observed through an optical polarizing microscope equipped with a heating stage. Thermal stability and mesomorphic characteristics are compared with a structurally related series. Analytical and spectral data support the structure of the molecules.

Dependence of Mesomorphism on Terminal End Group of a Molecule

A novel azoester homologous series of liquid crystals consisting of 12 members is majorly nematogenic without the exhibition of smectic mesomorphism, except for the hexadecyloxy derivative. The methoxy and ethoxy members are monotropically nematic and the rest of the homologs are enantiotropically nematogenic. Transition temperatures and mesophase morphology were determined on an optical polarizing microscope equipped with a heating stage. The textures of the nematic mesophase are threaded or Schlieren in type. Infra red, 1H NMR, mass spectral data, and elemental analysis data confirm the molecular structures of the novel homologs. The mesophase length varies from 00 to 72°C and the average thermal stability for the nematic phase is 133.5°C. Liquid crystal properties vary from homolog to homolog in present novel series. The liquid crystal behavior of the presently investigated novel series is compared with structurally similar known series. The transition curves (Cr-N/Cr-I and N-I/I-N) behave in a normal manner. The N-I/I-N transition curve exhibit an odd-even effect. The series is majorly nematogenic without exhibition of smectogenic character. Only the C16 homolog is nonmesogenic.

The Dependence of Mesomorphism on the Terminal Group

A novel azoester homologous series of liquid crystals (LCs) was synthesized and studied with a view to understanding and establishing the effect of molecular structure on LC behavior. The series consists of twelve members. All the members of the series exhibit a nematogenic mesophase. The methoxy and propyloxy derivatives are monotropic and the rest of the homologs are enantiotropic nematogenic. Smectic mesophase formation is completely absent. Transition temperatures and the textures of the nematic phase were observed and determined through an optical polarizing microscope equipped with a heating stage. Transition curves (Cr‒N and N‒I) of a phase diagram behave in a normal manner except for the hexadecyloxy homolog which deviates from normal behavior in the N‒I transition curve. The N‒I transition curve exhibits an odd-even effect. The textures of the nematic phase are threaded or Schlieren in type. The average thermal stability for the nematic phase is 158°C. The nematogenic mesophase length ranges from 27°C to 226°C. The analytical and spectral data confirms the molecular structures of the homologs. The LC properties of the presently investigated novel series are compared with a structurally similar known series. The novel azoester series is entirely nematogenic without exhibition of smectogenic character.

Dependence of Liquid-Crystal Behavior of a Substance on Molecular Structure

A novel azoester homologous series of liquid crystals (LCs) consisting of 12 members has been synthesized and evaluated. All members of the series exhibit the nematic mesophase enantiotropically without the exhibition of a smectic mesophase. The textures of the nematic phase are threaded or Schlieren in type. The transition curves in the phase diagram behave in a normal manner. The N-I transition curves exhibit an odd-even effect. The analytical and spectral data support the molecular structures of the homologs. The transition temperatures and mesophase morphology were determined by an optical polarizing microscope equipped with a heating stage. The azoester compounds consist of three phenyl rings with a meta substituted ‒Cl group at the middle phenyl ring and –OR and ‒OCH3 as terminal end groups. The average nematic thermal stability is 195°C and the nematogenic mesophase length ranges from 9°C to 186°C. The LC behaviors of the series are compared with a structurally similar series. The novel series is entirely nematogenic and of a high melting point type.

Mesomorphism Dependence on Terminal/Lateral Substitution of Nonlinear Azoester Molecules

A novel azo ester homologous series of liquid crystals (LCs) 2(4′-n-alkoxy benzoyloxy) napthyl 1 azo-3″ nitrobenzenes consists of eleven members of a series with enantiotropic nematogenic mesophase formation and without exhibition of smectogenic property by all the eleven homologs. The nematogenic mesophase textures are threaded or Schlieren. Solid-nematic and nematic-isotropic transition curves of the phase diagram behave in normal manner except for the decyloxy, dodecyloxy, and tetradecyloxy homologs. Analytical and spectral data confirm the molecular structures of homologues. Thermal stability for the nematic phase is 132.6°C, and the degree of mesomorphism varies between 34°C and 79°C and the series if of a middle-ordered melting type. An odd-even effect is observed for the N-I transition curve with alternation of transition temperatures. The LC behavior of the series is compared with other structurally similar known homologous series to establish the relation between mesomorphism and molecular structure.

New features of a smectic-A-crystal-B phase transition in a homologous series of liquid crystals

The components Lj of the Lorentz tensor and the polarizability density of molecules G in the smectic-A and crystalline-B phases have been determined for homologues of the series of alkyl-p-(4-alkoxybenzylideneamino-)cinnamates. The quantity Lj (G) in both phases is a linear (quadratic) function of the orientational order parameter of molecules S, which is invariant (noninvariant) with respect to the A-B transition, which is manifested in the form of jumps δLj and δG and enhancement of the G(S) dependence. An increase in the length of terminal molecular chains and weakening of interlayer correlation of molecules are accompanied by strengthening of the A-B transition of the first order and G(S) dependences in both phases together with an increase in δLj and δG. Change δG and dependence G(S) in the B phase are related to change in the conformation (flattening) of aromatic molecular cores.

Ferroelectric and antiferroelectric odd–even behavior in a tricarbosilane-terminated liquid crystal homologous series

An odd–even behavior for the alternative appearance of ferroelectricity and antiferroelectricity in a tricarbosilane-terminated liquid crystal homologous series is reported.