Robert Hertmanowski

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.

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.

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.

Miscibility of dl-α-tocopherol β-glucoside in DPPC monolayer at air/water and air/solid interfaces

The role of newly synthesized tocopherol glycosidic derivative in modifying molecular organization and phase transitions of phospholipid monolayer at the air/water interface has been investigated. Two-component Langmuir films of dl-α-tocopheryl β-D-glucopyranoside (BG) mixed with dipalmitoyl phosphatidylcholine (DPPC) in the whole range of mole fractions were formed at the water surface. An analysis of surface pressure versus mean molecular area (π-A) isotherms and Brewster angle microscope images showed that the presence of BG molecules changes the structure and packing of the DPPC monolayer in a BG concentration dependent manner. BG molecules incorporated into DPPC monolayer inhibit its liquid expanded to liquid condensed phase transition proportionally to the BG concentration. The monolayers were also transferred onto solid substrates and visualized using an atomic force microscope. The results obtained indicate almost complete miscibility of BG and DPPC in the monolayers at surface pressures present in the biological cell membrane (30-35·10(-3) N·m(-1)) for a BG mole fraction as high as 0.3. This makes the monolayer less packed and more disordered, leading to an increased permeability. The results support our previous molecular dynamics simulation data.

Study of binary mixtures of liquid crystals with terminal -CN and -NCS group at the air-water interface

Abstract Langmuir films of two liquid crystal materials, 4-octyl-4′-cyanobiphenyl (8CB) and 4-octyl-4′-isothiocyanatobiphenyl (8BT), and of their mixtures have been studied by recording surface pressure–area isotherms and by Brewster angle microscopy (BAM) images. It has been found that 8BT is not able to create compressible monolayers at the air–water interface. However, if this liquid crystal is mixed with 8CB, the formation of a Langmuir film is possible, although, as revealed by the BAM images, it is not homogeneous. The surface pressure–area isotherms of films formed from 8BT/8CB mixtures reveal that both components are at least partially miscible when the molar fraction of 8BT is not higher than 0.5. The analysis of the isotherms and BAM images suggests that the organization of the liquid crystal molecules at the water surface can be connected to certain degree with their ability to form the appropriate mesophase in the bulk.

Thermodynamic properties of Langmuir layers created of monoimide perylenetetracarboxylic acid derivatives

Langmuir films formed of some fluorescent dyes, 3,4-bis-pentyl ester of 9,10-N-(n-pentylimide)-perylenetetracarboxylic acid, as well as their mixtures with arachidic acid, were studied. Surface pressure versus mean molecular area isotherms for Langmuir films were reordered and the alignment of molecules at the air–water interface was estimated. The isotherms show that the dye molecules do not lie flat onto the water surface but are tilted with respect to the normal to the interface. The surface pressure–area isotherms of Langmuir films formed from the dye/arachidic acid mixture provide evidence for phase separation of the components within almost the entire range of mole fractions. A repulsive interaction between molecules was observed in all two components of Langmuir films.

Fluorescent discotic liquid crystals in Langmuir-Blodgett films for application in organic light emitting diodes

Langmuir-Blodgett (LB) films formed of some discotic liquid crystals, namely 3,4,9,10-tetra-(n-alkoxy-carbonyl)- perylenes, have been studied. The absorption and fluorescence spectra were recorded. The results obtained have led to conclusions about formation of dimers both in ground and excited states at the air-solid substrate interface. Moreover, information about the molecular arrangement in LB films has been obtained.

Fluorescent dyes mixed with liquid crystals in Langmuir and Langmuir-Blodgett films

Langmuir and Langmuir-Blodgett films of various dyes, namely derivatives of: 3,4,9,10-perylenetetracarboxylic acid, 3,4,9-perylenetricarboxylic acid, naphthalenebicarboxylic acid and naphthoylenebenzimidazole as well as of their mixtures with a liquid crystal were investigated. The dependence of the surface pressure -- on the mean molecular area for Langmuir films was measured, from which the molecular organization and the miscibility of components in the monomolecular layer at the air-water interface were determined. For Langmuir-Blodgett films the absorption and emission spectra were recorded and information about the spectral properties and molecular alignment of dyes and liquid crystals in ultrathin layers at solid substrates was obtained.

Langmuir film formation ability of liquid crystals with -CN an -NCS terminal group

Surface pressure-mean molecular area isotherms of Langmuir films of some liquid crystals with CN or --NCS terminal group as well as of their binary mixtures have been recorded. It was found that only the liquid crystals which molecules have CN group are able to form a stable monolayer at the air-water interface. Information about the molecular organization and intermolecular interaction in two dimensional layer has been obtained. Moreover, the miscibility or phase separation of two components in the mixtures of various compositions has been determined by using excess area criterion and surface phase rule.