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New liquid crystals categorised as cholesteryl dimers have been successfully synthesised through the reaction between cholesteryl 4-(prop-2-ynyloxy)benzoate moieties with n-azido(cholesteryloxy-carbonyl)alkane. All the dimers display enantiotropic mesophases. Whilst the odd-numbered dimers exhibit chiral nematic (N*), twisted grain boundary (TGB) and chiral smectic C (SmC*) phases, the even-numbered members from the same series show chiral smectic A and C. A detailed inspection on mesophase reveals that the chiral centres and the bent conformation of the odd-numbered members are essential for the induction of TGB phase. However, upon decreasing the temperature, the ratio of the transition temperatures (TSmC*-SmA*/TSmA*-I) is found to be 0.95, which indicate the second order transition according to the McMillan’s molecular theory. In addition, the X-ray diffraction study supports the presence of the smectic A phase on the even members rather than the N* by the appearance of the Bragg diffraction peaks at 190°C. A comparison study with the other analogues in which the cholesterol entity is substituted by azobenzene or biphenyl tails has been carried out to assess the relationship between the molecular structure and mesomorphic behaviour.

Some new Cu(II) complexes containing [1,2,3]-triazole-based bidentate salicylaldimine and its analogues with terminal substituent (F, Cl, Br and I) have been synthesieed. All the target complexes and their uncoordinated ligands were elucidated by elemental analysis and spectroscopic techniques (UV-visible, FT-IR, 1D, 2D 1H and 13C-NMR). The polarising optical microscope and differential scanning calorimetry (DSC) have disclosed all complexes and ligands are mesomorphic except the complex without any terminal substituent. The fluoro-substituted complexes with even parity C14H29 and C16H33 exhibit new enantiotropic nematic phase which was absent in their corresponding ligands, whereas the suppression of SmC phase occurred for all complexes with longer C16H33 and C18H37. X-ray diffraction confirmed the existence of SmA, SmC and N phases for complexes and ligands. The other notable feature is that the self-ordering of terminal alkyl chain occurred in SmA and SmC phases of complexes with even terminal alkyl ch...

Series of symmetrical liquid crystal dimers wherein the spacer connected to two mesogenic units of salicylideneimines consists of the aliphatic chain ‒(CH2)n‒ where n adopts even parity numbers from 2 to 10 have been synthesized and characterized. These dimers function as tetradentate ligands which possess strong affinity toward the Cu(II) ion leading to the formation of four-coordinated complexes with Cu‒N and Cu‒O modes. The uncoordinated dimers exhibit enantiotropic nematic as well as smectic C phases. However, the Cu(II) complexes behave predominantly as nematogens. Correlation study between the effect of variable spacer length and the mesomophic behaviors of these dimers along with their related Cu(II) complexes are reported. The Cu(II) complexes in which the ligands possess shorter spacers were seemed to exhibit higher thermal stability.

A new series of non-symmetric liquid crystal dimers N-(4-(n-(4-(benzothiazol-2-yl)phenoxy)alkyloxy)benzylidene)-4-chloroaniline containing benzothiazole and benzylideneimine units connected by a flexible alkyl spacer, –(CH2) n –, with n ranging from 4 to 12 in even parity have been prepared. All five members of this homologous series exhibit an enantiotropic nematic phase. The compounds with greater n of 8–12 exhibit both nematic and smectic phases upon cooling. A notable feature among this series is that for the member with n = 10, the smectic–nematic transition is also present. The nematic–isotropic transition temperatures and associated entropy changes with respect to all compounds in this series exhibit a dramatic dependence on the length of the flexible spacer. A comparison of the transitional properties of this series with those of α-(4-benzylidenechloroaniline-4′-oxy)-ω-[4-(thiophene-2-carboxyl)benzylideneaniline-4′-oxy]alkanes reveals that replacing benzothiazole moiety at one side of the flexible...

A new series of benzothiazole-phenyl esters intersected by azo N˭N has been isolated and their structures were characterized. These compounds exhibit enantiotropic nematic phase. The transition temperatures and the enthalpy values associated with these derivatives were found to be dictated by the variation of the lengths of the flexible alkoxyl chains (OOCC n H2n+1 where n adopts even numbers from 5 to 17). A noteworthy characteristic of this series is the clearing temperatures, which decrease upon lengthening of the alkoxyl chains from n = 5 to n = 17. A descending stability associated with the nematic phase range was also observed when the carbon number in the alkyl group increased. A comparative study between the title compounds and 6-ethoxy-2-(4-alkanoxybenzylidenamino)benzothiazole shows that the present compounds favor the formation of N phase while the previously reported analogs, which contain C˭N instead of N˭N, exhibited enantiotropic N and SmC phases.

10 pages; International audience; Seven members of the homologous series of the liquid crystal dimers, the bis(ω-(cholesteryloxycarbonyl)alkyl) disulfides, which contain a sulfur−sulfur link in the flexible spacer have been synthesised and their liquid crystal properties characterised. The dimers are referred to using the acronym Chol-n-SS-n-Chol in which n denotes the number of carbon atoms linking the cholesteryl-based groups and the sulfur atoms, and was varied between 3, 5, 6, 8, 10, 11 and 12. All seven homologues exhibit a chiral nematic phase and for the longest three members a smectic A phase was also observed. An odd−even effect is apparent in both the transition temperatures and the values of the entropy change associated with the chiral nematic−isotropic transition, SN∗I/R, in which dimers with even values of n show the higher values. This is interpreted in terms of the average molecular shapes in which the C−S−S−C dihedral angle is around 90◦. The values of SN∗I/R shown by these dimers are very small for liquid crystal dimers and this is attributed to the increased molecular biaxiality arising from the C−S−S−C dihedral angle. The smectic A phase exhibited by the homologues with n = 10, 11 and 12 is proposed to consist of an intercalated arrangement of the dimers which is driven by the mismatch in cross-sectional areas of the cholesteryl-based groups and alkyl chains.

A series of six non-symmetric liquid crystal dimers α-(4-benzylidene-substituted-aniline-4′-oxy)-ω-[pentyl-4-(4′-phenyl)benzoateoxy]hexane have been synthesized and characterized. These dimers vary from one another in terms of the terminal substituent (H, CH3, C2H5, F, Cl and Br) with different polarizabilities and molecular sizes. Investigation on the thermal behaviour shows that the dimer with a more polarizable terminal substituent of Br atom exhibits a smectic A phase as well as an enantiotropic nematic phase. Influence of the molecular size of the terminal substituent in stabilizing the liquid crystalline properties is also studied.

Ten new non-symmetric liquid crystal dimers belonging to the family of compounds α-(4-benzylidene-substituted-aniline-4′-oxy)-ω-(2-methylbutyl-4′-(4″-phenyl)benzoateoxy)-alkanes have been synthesised and their transitional properties characterised. The dimers contain either a hexamethylene or octamethylene spacer, while the terminal substituents on the 4-benzylideneaniline fragment are H, CH3, F, Cl and Br. The unsubstituted dimers are not liquid crystalline, while the remaining compounds exhibit enantiotropic nematic behaviour. The trends in the clearing temperatures, according to the chemical nature of the terminal substituent, are largely consistent with those established for conventional low molar mass liquid crystals. Three of the dimers also exhibit an intercalated smectic A phase, specifically the two bromo-substituted dimers and the chloro-substituted dimer containing a hexamethylene spacer. The driving force for the formation of this phase is considered to be, at least in part, the specific aniso...

The series of eight symmetric trimers, 4,4′-bis[ω-[2-methylbutyl-4′-(4″-phenyl)benzoateoxy]-3-bromo-4-alkyloxybenzylidene]-1,4-phenylenediamines has been synthesized and characterized. Except pentyl and undecyl homologues, the seven-ring chiral trimers exhibit the enantiotropic N* phase. In addition to the N* phase, the odd trimers with heptyl and nonyl spacers also exhibit the blue phase with platelet texture. The nematogenic properties of the trimers are attributed to the presence of two lateral bulky bromine atoms in the central mesogenic core. The suppression of mesophase thermal stability is largely due to the increase in molecular breadth at positions the bromine atoms are attached, which results in weaker overall lateral intermolecular attraction. The thermal properties of the trimers are also compared to those of the earlier reported analogous trimers that do not possess any lateral substituents in the mesogenic cores.

Two series of novel trimers with benzylidene-1,4-phenylenediamine core units attached by two (S)-2-methylbutyl 4-(4′-phenyl)benzoate moieties via methylene groups at terminal ends have been synthesized and characterized. In each series, the title compounds differ from each other in term of spacers -OCnH2nO- wherein n ranges from 5 to 12. The difference of the second series from their analogues in the first series is due to the presence of two OCH3 groups residing at the meta position in the benzylidene-1,4-phenylenediamine mesogenic core. The trimers without lateral OCH3 groups exhibit the SmC* and SmA phases in addition to the N* phase suggesting the possession of high molecular shape anisotropy. The higher-order tilted smectic phases and the blue phase are also observed for the members with odd n numbers in the first series. In the second series, however, the smectogenic characteristics are absent. Whilst the even-parity trimers are nematogenic, the trimers with odd spacers are not mesogenic. The trimer...

Series of non-symmetric liquid crystal dimers, α-(4-benzylidenechloroaniline-4′-oxy)-ω-[4-(thiophene-2-carboxyl)benzylideneaniline-4′-oxy]alkanes incorporating a thiophene-based moiety in one of the two mesogenic units have been synthesized and characterized. The nematogenic properties of the dimers were studied wherein the flexible spacers made up by n methylene units (–CH2-) ranging from n=5 to n=12. These dimers exhibit enantiotropic N phase with high thermal stability (>187.0°C). The N phase temperature range for the present homologues is found to be strongly dependent on the length and parity of the methylene spacer which connects the 4-benzylidenechloroaniline and 4-(thiophene-2-carboxyl)- benzylideneaniline mesogenic cores.

Series of nonsymmetric 4-ethyl- and 4-fluoroanilinebenzylidene-2′,4′-oxy-bis(4″-halogenoanilinebenzylidene-4″′oxy)alkanes trimers have been synthesized and characterized. Every member in this series possesses either Cl or Br terminal atoms. The molecular structure of these novel trimers is composed of six aromatic rings interconnected via two methylene spacers and three azomethine linking groups. In each molecule, the two identical methylene spacers vary from either C4H8 or C6H12. The trimers exhibit relatively low Tm and Tc (

An overview on new isoflavones comprising 7- and 3-disubsituted-4H-1-benzopyran-4-ones has been carried out. The derivatives thus obtained exhibit different molecular orientation and phase sequences as evident by texture observation under polarized light as well as differential scanning calorimetry. Typical examples from these newly derived isoflavones include those compounds possessing butanoyloxy and hexanoyloxy groups at both 7- and 3-position in benzopyran-4-ones which favour the nematic phases. The compounds attached by heptanoyloxy and longer side chains at both 7- and 3-positions show SmC phase. The monotropic SmC phase has been observed for the compound with octadecanoyloxy moiety only. The analogues 7-decanoyloxy-3-(4′-substitutedphenyl)- 4H-1-benzopyran-4-one possessing different substituents at 4′-position exhibiting various polymorphism. The results on the structural changes, the electronic polarizability, the presence of lateral dipole associated with the intermolecular interaction within the...

A series of new isoflavonic esters 7‐decanoyloxy‐3‐(4′‐substitutedphenyl)‐4H‐1‐benzopyran‐4‐ones containing a heterocycle in their central core with one flexible alkyl chain and various substituents, R (where R = F, Cl, Br, CH3, OCH3, or H) at 4′‐position at one end, have successfully been synthesised, isolated, and characterised. The physical properties of title compounds were studied using spectroscopic techniques (Fourier transform infrared, 1H and 13C nuclear magnetic resonance). The liquid crystalline properties and the textures of these compounds along with their thermal stabilities were investigated via polarising optical microscopy and differential scanning calorimetry. All the compounds except the member without the substituent were enantiotropic mesogens exhibiting smectic A and/or nematic phases. The layer periodicities in relation to different phases were substantiated by X‐ray diffraction wherein the molecules within the SmA phase were found to be intercalated. The structural changes that res...

A series of eight liquid crystalline compounds, N,N′‐bis[(2‐hydroxy‐4‐alkoxyphenyl)methylene]benzene‐1,4‐diamines, has been synthesized and characterized. These homologous compounds differ in the length of terminal alkyl group C n H2n+1 wherein n is an even number ranging from 4 to 18. The spectroscopic techniques, FTIR, 1H NMR and 13C NMR, were employed to characterize the molecular structure. The transition temperatures of all the title compounds and their mesophases were studied by differential scanning calorimetry and polarizing microscopy. All the compounds were smectogenic, exhibiting both tilted and non‐tilted molecular orientation in their smectic phases. Further investigation to ascertain the anisotropic nature of subphases within the smectogenic region was carried out using X‐ray diffraction.

Series of elongated Schiff base esters containing three aromatic rings with palmitoyl moiety as one of the terminal carbon chain and various substituents R(R=H, F, Cl, Br, OCH3, CH3, and C2H5) at the other end of molecule have been isolated, and their structures were proposed via physical measurement. The mesomorphic properties of these compounds were investigated via differential scanning calometry and polarizing optical microscopy. The thermal data indicate that all of these compounds exhibit mesomorphic properties. Although compounds with R=H, OCH3, CH3, and C2H5 show nematic phases, the remaining compounds containing halogen F, Cl, and Br are smectogenic in nature. The structural changes that result in the variation of transition temperature and the electronic polarizability of the respective molecules are discussed.

A series of homologous symmetrical dimers N,N′-bis[(3-methoxy-4-alkoxybenzylidene)-1,4-phenylenediamine with different lengths of terminal alkyl groups of even parity ranging from butyl to octadecyl were prepared and characterized. Spectroscopic methods FT-IR, 1H NMR, and 13C NMR and mass spectrometry were carried out to determine the physical properties of the target compounds. The texture with respect to each compound within this series has been investigated along with their thermal stabilities. A diversity of phase-transition behavior was observed for the members of this series and explanation was given based on the possible molecular conformation. Almost all title compounds were nematogenic except the dimers containing butyl and hexyl chains as well as the longest octadecyl dimer in which the mesogenic properties were absent.

A series of new chalcone derivatives with a general formula of CH3CnH2nCOOC6H4CH:CHCOC6H4 where n = 10, 12, 14, and 16 were well synthesized and crystallized from organic solution. The physical properties as well as the chemical formulations of these compounds were determined by the microanalysis and spectroscopic methods (FTIR, and 1H and 13C NMR). Crystal structure of CH3C10H20COOC6H4CH:CHCOC6H4 was determined by single-crystal X-ray diffraction analysis. The space group of this crystal is triclinic with a = 5.8570(3) A, b = 8.5640(5) A, c = 24.1592(12) A, V = 1175.82(11) A3, and Z = 2, and its structure was refined to R(F) = 0.055 and ωR(F 2 ) = 0.161. The elongated terminal alkyl chain is fully stretched in solid phase. Phase-transition temperatures and the thermal parameters were obtained from differential scanning calorimetry (DSC). The texture observation was carried out with a polarizing optical microscope (POM) over heating and cooling cycles. All of the title compounds except undecylcar...

An investigation of cholesteryl 4‐n‐alkoxybenzoates via Fourier transform IR at ambient temperature revealed that the cholesteryl fragment in the solid crystals is rigid, and the terminal alkyl chains of different lengths attached to the benzoyloxy group are fully extended. Conformational analysis in chloroform (CDCl3) at the same temperature was done for the first time via high resolution 1H and 13C NMR spectra using DEPT, 2D COSY, NOESY, ROESY, gradient heteronuclear multiple quantum‐coherence spectroscopy (gradient HMQC spectroscopy), and gradient heteronuclear multiple bond correlation spectroscopy (gradient HMBC spectroscopy). Normal 1D NMR, on the other hand, has disclosed that in CDCl3 solution, there exists conformations wherein the O˭C–O bridging the benzoyloxy group and the cholesteryl fragment is kinked, which entailed the cholesteryl fragment to fold up.

A series of new compounds o-n-hydroxy-p-n-hexadecanoyloxybenzylideneaniline and its substituted derivatives was synthesized from the esterification of palmitic acid with intermediary Schiff bases, which posssess various terminal substituents X (X = H, F, Cl, Br, OCH3, CH3, and C2H5). All compounds possess mesomorphic properties wherein compounds with X = H, F, Cl, Br, and OCH3 exhibit smectic A (SmA) phases and those with terminal substituents CH3 and C2H5 are monotropic liquid crystals showing smectic C phases (SmC). Correlation studies of the clearing temperature (Tc) of the title compounds and polarizability related to mesophase stability and molecular anisotropy are reported.