Tomasz Martyński

Derivatives of 4-amino-N-ethylnaphthalimide for use in nematic liquid crystals

Abstract The order parameters of some dichroic fluorescent dyes {derivatives of 4-amino-N-ethylnaphthalimide} in three nematic liquid crystal mixtures (W52, E7 and ZLI 2359) have been determined by means of optical spectroscopy methods and the influence of the dye addition on the nematicisotropic phase transition temperature has also been investigated. The voltages characterizing the impact of the electric field on the dye-liquid crystal mixtures have been estimated. It was found that the dyes can be utilized in guest-host liquid crystal display devices.

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.

Spectral properties of fluorescent dyes in nematic liquid crystals

Abstract The basic spectral properties and the orientation of some dichroic fluorescent dyes (derivatives of 4-amino-(N-ethylnaphthalimide)) in several nematic liquid crystal matrices have been studied. Moreover, the temperature of the nematic—isotropic phase transition for the dye—liquid crystal mixtures has been determined. It has been found that the dyes investigated are characterized by parameters which make them applicable to both passive and active “guest—host” liquid crystal display devices.

Influence of the alkyl chain length of some mesogenic molecules on their Langmuir film formation ability

Langmuir films of members of two homologous series, the 4‐n‐alkyl‐4′‐cyanobiphenyls (nCB) for n = 2–14 and trans‐4‐n‐alkyl(4′‐cyanophenyl)cyclohexanes (PCHn) for n = 2–12, have been studied by recording surface pressure/area isotherms and by Brewster angle microscopy. It has been found that the compounds with very short chains (n⩽3) and very long chains (n>12 for nCB, n>10 for PCHn) are unable to form compressible monolayers at the air–water interface. Other members of both series can form stable Langmuir films, but both their rigidity and stability as well as the molecular packing vary with the alkyl chain length. The isotherms and BAM images imply that the organization of the liquid crystal molecules in the films is to some extent correlated with their ability to form corresponding mesophase in the bulk: nematogenic compounds tend to form rounded droplet‐like domains, whereas smectogenic compounds tend to form flat domains.

Optical spectroscopy study of some 3,4,9,10-tetra-(n-alkoxy-carbonyl)-perylenes in Langmuir–Blodgett films

Abstract Langmuir (L) and Langmuir–Blodgett (LB) films of some 3,4,9,10-tetra-( n -alkoxy-carbonyl)-perylenes have been studied. On the basis of the surface pressure–mean molecular area isotherms, the molecular alignment on the air–water interface has been estimated. The optical spectroscopic study of the LB films has allowed conclusions to be drawn about the arrangement of the molecules on the quartz slides. The fluorescence spectra of the LB films of the perylene-derivatives investigated have revealed the formation of excited dimers.

Influence of the molecular structure of thermotropic liquid crystals on their ability to form monolayers at interface

Langmuir and Langmuir–Blodgett (LB) films of some thermotropic liquid crystals of rod-like shape have been studied. It has been found that the compounds with the terminal isothiocyanato (–NCS) group are not able to form a compressible monolayer at the air–water interface. Very short and very long alkyl or alkoxy chains attached to the rigid molecular core also hinder the creation of the stable films. The Langmuir films have been characterised by the surface pressure-area and surface potential-area isotherms and by Brewster angle microscopy (BAM). The analysis of the isotherms and the BAM images suggests that the organisation of the mesogenic molecules on the water surface is dependent on their structure and to some extent reflects their ability to form an appropriate mesophase in the bulk. For the LB films of the liquid crystals the electronic absorption spectra have been recorded. On the basis of these spectra the conclusions about the creation of the self-aggregates by mesogenic molecules at the air-solid substrate interface have been drawn. The polarised absorption spectra have allowed one to determine the alignment of molecules on the quartz surface.

Molecular organization in binary mixtures of derivatives of naphthalenebicarboxylic acid and naphthoylenebenzimidazole with a liquid crystal in two-dimensional layers II. Langmuir-blodgett films

Langmuir–Blodgett (LB) films of some dichroic dyes, namely derivatives of naphthalenebicarboxylic acid and derivatives of naphthoylenebenzimidazole, and of their mixtures with mesogens: 4‐octyl‐4′‐cyanobiphenyl or 4‐pentyl‐4″‐cyano‐p‐terphenyl were prepared. Absorption and fluorescence studies using unpolarized and linearly polarized light were carried out. Both absorption and fluorescence spectra indicated the formation of aggregates of dye molecules in monomolecular layers. Moreover, it was found that dye molecules are more tilted to the quartz surface in LB films than to the plane of the air–water interface in Langmuir films.

Intermolecular interactions in Langmuir-Blodget films of liquid crystalline perylene derivatives

Langmuir-Blodgett (LB) films formed of some discotic liquid crystals, namely 3,4,9,10-tetra-(n-alkoxy-carbonyl)-perylenes, mixed with arachid acid have been studied. The absorption and fluorescence spectra were recorded. The results obtained have led to conclusions about formation of self-aggregates of dye molecules both in ground and excited states at the air-solid substrate interface. It was found that some fraction of J-aggregates can be created in the ground state. In the excited state, mostly excimers appear and the number of this kind of aggregates depends on the length of the alkyl chains substituted to the perylene core, as well as on the dye concentration and the number of layers in LB films.

Langmuir films of dichroic dyes with fluorescent properties

Abstract Langmuir films of various dyes, namely derivatives of 3,4,9,10-perylenetetracarboxylic acid and 3,4,9-perylenetricarboxylic acid, derivatives of naphthalenebicarboxylic acid and derivatives of naphthoylenebenzimidazole were investigated. Surface pressure–mean molecular area isotherms were recorded from which the alignment of the molecules in a monomolecular layer at the air–water interface was determined. It was found that both the stability and the rigidity of the monolayer are strongly affected by the molecular structure of the side groups substituted on the skeleton of the molecule.

Alignment of liquid crystal and dichroic dye molecules in mixed Langmuir and Langmuir-Blodgett films

A study of dichroic dye-liquid crystal mixtures (guest-host systems) in monolayers formed at a gas-liquid interface (Langmuir films) and at a solid surface (Langmuir-Blodgett films) has been made. As a host 4- n -octyl-4′-cyanobiphenyl (8CB) or 4- n -pentyl-4″-cyano- p -terphenyl (5CT) were chosen, while three dichroic azo dyes with various molecular structures were used as guest species. The dyes were added to the liquid crystal matrices at a concentration corresponding to the whole range of molar fractions and the surface pressure-mean molecular area isotherms for Langmuir films were recorded. On the basis of the isotherms, conclusions about the molecular organization and the miscibility of the components in the ultrathin films were drawn. The Langmuir films were transferred onto the quartz plates at surface pressures below the collapse point. The polarized absorption spectra of the Langmuir-Blodgett films were recorded and information about the alignment and intermolecular interactions in the mixtures of the non-amphiphilic dichroic dyes and the liquid crystals with strongly polar terminal groups were obtained.