Gallic esters of 4,5-dinitrocatechol as potential building blocks for thermotropic liquid crystals

A series of unsubstituted and 1,4-disubstituted gallic catecholates 1, 6 and 7 as possible candidates for wedge-shaped mesogens were prepared starting from the respective benzene derivatives 2a-c and gallic esters 5a-h. The mesomorphic properties were investigated by DSC. However, only the 4,5-dinitro derivatives 1d,f-h with C₈H₁₇ and C₁₀H₂₁ to C₁₂H₂₅ alkyl side chains displayed mesophases, as evaluated by fluidity and optical anisotropy.     

Mesogenic heterocyclic pyrazoles,isoxazoles and 1,3,4-oxadiazoles

Three new series of liquid crystals 1-3 derived from heterocyclic pyrazoles, isoxazoles and 1,3,4-oxadiazoles exhibiting smectic A or C phases were reported. Compound 1a exhibited monotropic smectic A phase, while the other two compounds 2-3a were not mesogenic. In contrast, all other compounds 1-3b bearing longer alkoxy chains exhibited smectic X and C phases, which were confirmed by powder XRD diffractometer. The clearing temperatures decreased in the order of compounds 1b > 2b > 3b, in contrast the temperature range of smectic C phases increased in the order of compounds 1b < 2b < 3b. The smectic phases in 1-3b were formed by a monomeric structure, confirmed and consistent with powder X-ray diffraction data. The formation of mesomorphic behavior might be probably attributed to their exocyclic angles and/or H-bonds. All derivatives showed good stabilities at temperature below T = 346 °C on TGA analysis.     

Amphiphilic and mesogenic carbohydrates. Part III: Synthesis and thermal behavior of di-O-(n-alkyl)-and tri-O-(n-alkyl)-D-glucose derivatives

The homologous series of the 2,3-di-O-(n-alkyl)-3a-e and 4,6-di-O-(n-alkyl)-D-glucopyranoses9a-e, as well as the 5,6-di-O-(n-hexadecyl)-D-glucofuranose15e, the 3,4,6-tri-O- and 1,4,6-tri-O-(n-octyl)-D-glucopyranoses10a and11a were prepared and their mesogenic properties studied. The derivatives3a-e and15e show enantiotropic but9a-e monotropic behavior. In contrast to this the bis single-tailed -D-glucosyl fluorides4e and7a and the tris single-tailed D-glucopyranoses10a and11a do not form any mesophase.     

From mesogens to metallomesogens. Synthesis,characterisation, liquid crystal and luminescent properties

Continuation with our previous investigation which refers to the synthesis of a series of hydrophobic symmetrical azine compounds: 1,2-bis[4-(n-alkoxy)benzylidene]hydrazine (where, n-alkoxy: O(CH₂)_nH, n = 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 16 or 18), a series of hydrophobic asymmetrical azine compounds: [1-(4-propyloxy)-2-(4?-(n-alkoxy))benzylidene]hydrazine (where, n-alkoxy: O(CH₂)_nH, n = 1, 2, 4, 5, 6, 7, 8, 9, 10, 12, 16 or 18) was synthesised following an efficient and practical method. These compounds were synthesised by the condensation reaction of hydrazine hydrate with 4-propyloxybenzaldehyde and appropriately 4-(n-alkoxy)benzaldehydes in acidic medium and ambient conditions (very simple way with no need of any sophisticated techniques). Moreover, two new series of silver(I) complexes based on symmetrical or asymmetrical azines have been synthesised (linear-binuclear type complexes with the general formula [Ag₂(L)(NO₃)₂] were obtained). The organic compounds and their silver(I) complexes were characterised using different techniques: microelemental analysis and spectral data (FTIR, UV–Vis, ¹HNMR, ¹³C{¹H}NMR, 2D ¹H-¹H-COSY, 2D ¹H-¹³C-HSQC and mass spectra) as well as molar conductivity measurements for silver(I) complexes. Liquid crystal behaviour of the prepared compounds were studied using polarised light optical microscopy and confirmed with differential scanning calorimetry and X-ray powder diffraction techniques. The studies revealed that all azine compounds and some of silver(I) complexes are liquid crystal materials. The luminescent properties of all the prepared compounds were also investigated which confirmed that all of these compounds are photo-luminescent in the crystalline solid state and in the mesophase.     

Columnar catenar bisoxazoles and bisthiazoles

Three new series of catenar liquid crystals 1a–c derived from heterocyclic bisoxazoles and bisthiazoles exhibiting columnar phases were reported. All compounds 1a–c exhibited hexagonal columnar phases, which were confirmed by powder XRD diffractometer. Compounds 1a have a slightly wider temperature range of columnar phases than that of compounds 1b, which might be attributed to higher dipole polarized in 1a. A N_cell and R_ar value equal to 2.54–2.76 and 19.99–20.45 Å² within a slice of 9.0 Å thick were obtained for three derivatives 1a–c (all ns=12), indicating that a single molecule was packed within columns in Col_h phases. All derivatives showed good stabilities at temperature below T=408 °C on TGA. The PL spectra of all compounds 1a–c showed one intense peak at λ_max=505–510 nm, and these photoluminescent emissions originated from quinoxaline moiety.     

SYNTHESIS OF SIDE-CHAIN LIQUID CRYSTALLINE POLYSILOXANE CONTAINING SCHIFF′S BASE MESOGENS WITH NO2-END GROUP AND ITS BEHAVIOR IN A DC ELECTRIC FIELD

A side chain liquid crystalline copolysiloxane, which would show electro-optic effects as known from low mass liquid crystal, was synthesized by hydrosilylation reaction, and the two homologous monomers with different length spacers containing Schiff's base mesogen with—NO_2 terminated group were grafted toa polysiloxane main chain. Residual monomer in crude product is effective in reinforcing the response to an electric field over that of pure polymeric liquid crystal.     

Liquid crystals with partially fluorinated side chains: Highly polar materials with very low birefringence

Highly polar liquid crystals with very low birefringence were synthesized by a reaction sequence starting with the radical addition of a secondary alcohol to pentafluoropropene and perfluoropropene, respectively. The mesophases and electrooptical properties of the new materials were interpreted using a detailed computational analysis of the conformational equilibrium.