Eryk Wolarz

Spectroscopic studies of Langmuir–Blodgett films of 3,4,9,10-tetra(heptyloxycarbonyl)perylene and its mixtures with a liquid crystal

Langmuir (L) and Langmuir–Blodgett (LB) films of 3,4,9,10-tetra(heptyloxycarbonyl)perylene and its binary mixtures with 4-octyl-4′-cyanobiphenyl (8CB) and 4-pentyl-4″-cyano-p-terphenyl (5CT) have been studied. On the basis of the surface pressure–mean molecular area isotherms of L films, the alignment of the molecules on the air–water interface has been estimated. The L films were transferred onto quartz plates at surface pressures below the collapse point. The absorption and fluorescence spectra of LB films, obtained using unpolarized and linearly polarized light, were recorded. The results obtained have led to conclusions on the arrangement of the dye and liquid crystal molecules on the air–solid substrate interface. The fluorescence spectra revealed the formation of excited dimers in LB films.

Fluorescent 3-oxy benzanthrone dyes in liquid crystalline media

Abstract The behaviour of novel 3-oxy benzanthrone derivatives of intense fluorescence emission in liquid crystalline media has been studied with regard to their potential for display application. The optical properties of the dyes were examined both in organic solvents, nematic liquid crystal (LC) and polymer film. The influence of the dyes upon the phase transition temperatures and the electro-optical properties of LC in dye/LC systems was investigated in surface-stabilised display cells. The dichroism D(λ) and the orientational order parameters SA and SF of the dyes in LC were determined from absorption and fluorescence anisotropy. The effect of a polymer component added to the dye/LC systems upon the transition temperatures of LC was established.

Polarized Fluorescence Studies of Orientational Order in Some Nematic Liquid Crystals Doped with Stilbene Dye

Abstract The measurements of the polarized fluorescence intensity for a stilbene guest molecule dissolved in nematic liquid crystals (5CB, 7CB and PCH7) have been used to study the molecular orientational order in thin aligned samples. The temperature dependence of the order parameters ⟨P2⟩ and ⟨P4⟩ have been investigated. The attempt for the explanation of the different behaviour of ⟨P4⟩ parameter in the various liquid crystals has been undertaken. On the basis of the experimental ⟨P2⟩ and ⟨P4⟩ values some information about the orientational distribution of molecules in guest-host mixture have been obtained.

Molecular Orientation in Liquid Crystalline Side Chain Polymers Doped with Dichroic Dye as Studied by Optical Spectroscopy Methods

Abstract The polarized absorption and emission spectra of fluorescent stilbene dye dissolved in two side chain liquid crystalline polysiloxanes have been recorded as a function of temperature in the mesomorphic and glassy phases. From these spectra the order parameters and as well as the orientational distribution function of the side mesogenic groups have been estimated. The results have been compared with the data obtained for low molecular weight liquid crystal by using the same optical methods.

Molecular Orientation of Perylene-Like Dyes in Liquid Crystal 80CB

Abstract The polarized absorption and fluorescence spectra of some dichroic fluorescent dyes (derivatives of 3,4,9-perylenetricarboxylic acid and 3,4,9,10-perylenetetracarboxylic acid) oriented in liquid crystal 80CB have been recorded as a function of temperature. On the basis of these spectra the order parameters and and orientational distribution function have been determined. The conclusions about the influence of the molecular structure of the dyes on their orienting properties in uniaxial liquid crystalline phases have been drawn.

Polarization-insensitive metamaterial absorber of selective response in terahertz frequency range

We present an experimental and numerical analysis of a planar metamaterial that selectively absorbs terahertz radiation. The metamaterial is produced as a planar two-dimensional network of electromagnetic resonators and is characterized by electric and magnetic responses in a narrow frequency range. The unit cell of the metamaterial has fourfold symmetry about the axis perpendicular to the planes containing the metallic resonators. Such a planar metamaterial is polarization-insensitive to the electromagnetic waves. A good agreement of the absorption characteristics obtained from the numerical simulations and from the spectroscopic experiments is shown. The analysis of wave impedance, refractive index, permittivity and permeability of the metamaterial allows the identification of the characteristic electromagnetic resonance and antiresonance in the system. It is shown that the absorption is mostly the result of the electric field energy accumulation in the metamaterial absorber.

Orientational properties of perylene tetracarboxylic diimide molecules in liquid–crystalline matrices

Molecular orientational order of perylene tetracarboxylic diimide, N,N’-di(n-hexyl)-1,6,7,12-tetrachloroperylene-3,4,9,10-carboxylic acid imide (Cl4-PTCDI-6C), dissolved in homologous series of liquid crystals, i.e. 4-(trans-4′-n-alkylcyclohexyl)-isothiocyanato-benzene (nCHBT) and 4-n-alkyl-4′-cyanobiphenyl (nCB), is investigated by using UV–V is absorption and fluorescence spectroscopies. The orientational order parameter , determined experimentally for Cl4-PTCDI-6C molecules in nCHBT and nCB, is much lower than that for some other derivatives of perylene dissolved in the same liquid crystal hosts. The order parameter , obtained for Cl4-PTCDI-6C in nCHBT and nCB, is also smaller than obtained previously from Raman scattering in the liquid crystal hosts. The orientational order parameter for the Cl4-PTCDI-6C probe takes extremely low negative values, which indicates the importance of higher rank order parameters in the description of the dye distribution in the liquid–crystalline matrices. The bulky chlorine atoms, substituted in the perylene tetracarboxylic diimide molecular core, seem to be primarily responsible for the small orientational order parameters of the dye molecules. Finally, the odd–even effect, manifesting itself in an alternating increase and decrease of and for Cl4-PTCDI-6C along with increasing number of carbon atoms in the alkyl chains in nCHBT homologous series, is discussed.

Morphology and molecular organisation of liquid-crystalline perylene-3,4,9,10-tetra-(n-hexylester) deposited on a solid substrate

Liquid-crystalline perylene-3,4,9,10-tetra-(n-hexylester) forms characteristic dendritic or flower-like structures at room temperature when it is deposited on a hydrophilic glass substrate using the zone-casting technique. It was found that such unique structures were not possible to be created simply by recrystallisation of this dye from a liquid-crystalline columnar phase. On the basis of the observations using a confocal microscope and the study of wide angle X-ray scattering (WAXS) as well as the analysis of the absorption and fluorescence spectra, some conclusions, concerning the molecular organisation in the dendritic structure, are drawn. Based on the research, one can assume that the dendrites are formed by columnar molecular aggregates with the column axes parallel to the substrate. Such an organisation of the molecules can be interesting from the point of view of organic electronics.

Orientational order of tetra n-hexylesters of perylene and tetrachloroperylene tetracarboxylic acids in low-molar-mass liquid crystal investigated using absorption and fluorescence methods

The orientational order parameters and of perylene-3,4,9,10-tetra-(n-hexylester) (PTHE) and 1,6,7,12-tetrachloroperylene-3,4,9,10-tetra-(n-hexylester) (4Cl-PTHE) dye molecules dissolved in low-molar-mass liquid crystal, 4-(trans-4-n-hexylylcyclohexyl)-isothiocyanobenzene, are calculated from the experimental values of polarised absorption and fluorescence anisotropies. The experimental data show that the substitution of chlorine atoms instead of hydrogen in the perylene core reduces the value of parameter. Moreover, the and values for molecules of the perylene derivatives, playing the role of the guest in the liquid crystal matrix, are much less than these values for molecules of the liquid crystal host. The extremely low negative values of for the perylene dyes are explained as the result of the preferable oblique orientation of the main molecular symmetry axis of the probe with respect to the direction of the macroscopic orientation of the liquid crystal host molecules.

Spectral and orientational properties of new group of naphthalene derivatives of bicarboxylic acid in liquid crystal 7CB

The spectral and orientational properties of some dichroic fluorescent dyes (naphthalene derivatives of bicarboxylic acid) in some isotropic solvents and in an anisotropic matrix have been studied. The order parameter of the dyes in the nematogenic liquid crystal 7CB has been determined from measurements of polarized electronic absorption and fluorescence. The influence of the dye addition on the nematic-isotropic phase transition temperature of 7CB has been investigated. It was found that some of the dyes studied could be successfully utilized in guest-host liquid crystal display devices.