Adam Krówczyński

Fluorinated metallomesogens – lamellar versus columnar phase formation

Two series of tetradental cis-enaminoketone Ni(II) and Cu(II) complexes with their mesogenic core substituted by different combination of hydrocarbon or fluorocarbon chains have been synthesized. Depending on the type and position of the substituted groups, compounds reveal either calamitic or columnar mesophases. Replacing the alkyl chains by perfluorinated chains stabilizes the columnar phase. A unique phase sequence of isotropic–columnar hexagonal–re-entrant isotropic–smectic (I–Colh–Ire–SmA) has been observed on cooling for some of the obtained compounds.

CALAMITIC OR COLUMNAR MESOMORPHISM DETERMINED BY NUMBER AND POSITION OF SUBSTITUENTS IN ENAMINOKETONE CU(II), NI(II) AND CO(II) COMPLEXES

New enaminoketone metalomesogens with an almost equilateral triangular shape of the mesogenic core have been synthesized. They form either calamitic or columnar mesophases depending on the number and position of the substituted chains. The stability of the columnar as well as of the calamitic phases depends substantially on the central metallic ion.

Smectic polymorphism in a series of three-ring enaminoketone compounds

Abstract Liquid crystalline properties of 1 - (4′ - alkoxyphenylamino) - 3 - (4′ - hexyloxyphenyl)-prop-1-en-3-ones, from methoxy to heptadecyloxy, have been examined by optical, DSC, and X-ray methods. The phase diagram for the series exhibits a rich polymorphism of tilted smectic phases, for example, five mesophases were found for the hexyloxy derivative. A characteristic feature of the phase diagram is a gap in the crystal G phase area. For the heptyloxy homologue, a direct crystal H-smectic F phase transition was found; in the case of shorter as well as longer terminal substituents, the phase sequence crystal H–crystal G–smectic F is observed. Calorimetric and X-ray studies revealed the existence of a tricritical point on the crystal G–smectic F transition line.

Formation of mesophases by fluorinated enaminoketone Ni(II), Cu(II) and VO(II) complexes

Mesogenic tetradentate cis‐enaminoketone Ni(II), Cu(II) and VO(II) complexes with rod‐like and disc‐like molecular shapes were synthesized. In these compounds some of the alkyl chains were perfluorinated. Replacing the alkyl chains by fluorinated chains stabilizes the columnar hexagonal Colh phase whereas lamellar phases are destroyed.

Paramagnetic liquid-crystalline complexes based on novel enaminoketone ligands

Abstract Calamitic ligands having aminopropenone-3 ring substituted with alkyl-trans-cyclohexyl-phenyl and alkyl groups are low melting nematogens. Copper(II) complexed to the ligands gives thermally stable rod-like liquid crystals which exhibit an enantiotropic paramagnetic nematic phase. It is shown that modifications of the terminal groups as well as synthesis of asymmetric complexes enables us to extend the nematic range and depress the melting points.

Phenyl-cyclohexyl enaminoketone ligands and their Cu(II) complexes

Abstract The liquid crystalline properties of 1-(alkylamino)-3-[(4″-hexyl-trans-cyclohexyl-4′-phenyl]-prop-1-en-3-one-s, from methyl to octadecyl, and their copper (II) complexes have been examined by optical, DSC, X-ray and EPR methods. The compounds are enantiotropic nematogens except those having the shortest and the longest terminal chains. Short chains promote the SA phase in both ligands and complexes, whereas long chains promote SC and crystal H phases for the ligands or SA and SC phases for the complexes. A partly bilayer smectic Ad phase is observed from ligands terminated with short non-polar substituents. Direct isotropisation from the crystal H phase for some of the compounds, as well as other phase transitions have been studied. The molecular shape of the complexes and the organization of their mesomorphic phases are discussed, based on the refractive indices and X-ray data.

Binuclear liquid crystals incorporating dia- or para-magnetic transition metals

Abstract Discotic binuclear Ni(II) and Cu(II) complexes of 1,2,4,5-tetrakis-(2′-alkyl-2′-homoalkylcarbonylvinylamino)benzene ligands were synthesized. These compounds exhibit columnar liquid crystal phases.

Orthogonal hexatic smectic phase-rare or common?

Abstract The hexatic smectic B (Hex B) phase is commonly encountered among hydrogen-bonded liquid crystal materials. Among enaminoketone and Schiffs base compounds, twenty homologous series (c. 102 compounds) exhibiting orthogonal mono-or bi-layer hexatic phases were identified by combined microscopy and DSC. Phase transitions from crystal B (CrB) of Sf to Hex B as well as from Hex B to Sf, Sa or Sc phases were observed within the range 50 to 190°C. Temperature ranges of the Hex B phase detectable by DSC varied from 0.2 to 20°C. Within two groups of three-ring enaminoketones, the formation of the Hex B phase was found to be controlled by both inductive and mesomeric components of the Hammett constants of the terminal substituents of the molecules.

Enaminoketones as new hydrogen bonded liquid crystals

Abstract The relation between molecular structure of enaminoketone derivatives and their mesomorphic properties is discussed. It has been observed that the electron accepting terminal groups (F,Cl,Br,CN) promote formation of orthogonal phases while strongly electron donating groups (OCnH2n+1) favour tilted phases. Among the synthesised compounds, materials useful for structural studies of two dimensional (2D) melting in orthogonal, as well as the tilted systems, were found. It has been determined that the heat effects in the melting process from crystalline smectic into liquid-like smectic, through the hexatic state, are correlated to the density changes.

Structural studies on aryl-substituted enaminoketones and their thio analogues. Part I. Analysis of high-resolution (1)H, (13)C NMR and (13)C CP MAS spectra combined with GIAO-DFT calculations.

A series of aryl‐substituted enaminoketones and their thio analogues in CDCl3 solution and in the solid state were studied by the use of high‐resolution 1H and 13C as well as 13C cross polarization magic angle spinning (CP MAS) NMR spectra in combination with gauge including atomic orbitals‐density functional theory (GIAO‐DFT) calculations performed at the B3PW91/6–311 + + G(d,p) level of theory using the B3PW91/6‐311 + + G(d,p)‐optimized geometries. The analysis of the 13C NMR spectra in solution was done by using the Incredible Natural Abundance DoublE QUAntum Transfer Experiment (INADEQUATE) technique, whereas trends observed in the 13C shielding constants, calculated for the compounds studied, were a great help in assigning most of the signals in the 13C CP MAS NMR spectra. It was established on the basis of the experimental and theoretical NMR data that both groups of compounds exist in the form of Z‐s‐Z‐s‐E isomers in CDCl3 solution as well as in the solid state, with the NH hydrogen atom involved in intramolecular hydrogen bonding. This conclusion is in agreement with the fact that some of the compounds studied reveal liquid‐crystalline properties. Three‐bond H, H and C, H coupling constants measured in solution played a crucial role in the structure elucidation. Copyright