Adam Tracz

Macroscopically aligned films of discotic phthalocyanine by zone casting

This work describes a room temperature liquid crystalline phthalocyanine processed by using zone casting. Highly oriented films that were uniform over several square centimeters were obtained on glass support from a mixed solvent (1:1 mixture of toluene and ethylene chloride) solution. A columnar planar alignment of Colr in the film layers has been determined by optical polarized microscopy, ultraviolet–visible absorption, atomic force microscopy and x-ray diffraction studies. The films consist of uniaxially oriented ribbon-like structures with molecular columns perpendicular to the solidification direction. The pronounced alignment makes these thin films promising for application in optoelectronic devices.

Highly Polarized Emission from Oriented Films Incorporating Water‐Soluble Conjugated Polymers in a Polyvinyl Alcohol Matrix

Highly oriented luminescent films are produced by stretching a 30-mu m-thick polyvinyl alcohol matrix doped with water-soluble polyrotaxanes and their unthreaded analogues. Photoluminescence experiments reveal that over 95% of the emitted light is polarized along the orientation direction. A hybrid organic-inorganic light-emitting diode is built to investigate the possibility of using these films as polarizing filters for solid-state lighting and display technology.

Properties and microstructure of crystalline BEDT-TTF polyiodide network in polycarbonate matrix

A conducting network of crystalline [bis(ethylenodithio)tetrathiafulvalene]2I3 (ET2I3) can be formed within the surface layer of polycarbonate by exposure of films containing 2 wt.% of molecularly dispersed ET to vapours of iodine solution in CH2Cl2, THF or TCE. The relationship between the microstructure and properties of conducting networks formed under different conditions is reported. Depending on the iodine concentration in the solution, the kind of solvent and the treatment time, networks of a-ET2I3 or β-ET2I3 crystallites are formed. Their preferential orientation (c-axis perpendicular to the film plane) can be deduced from X-ray diffraction. Morphological studies performed using a scanning electron microscope revealed a nanoscopic size of crystallites and different habits: plate-like or river-stone-like. The presence of a less organised layer covering the crystallites, possibly formed of salts of another composition, is also discussed. The conductivity of the films is higher than that reported for polycrystalline layers obtained by the evaporation method and for pressed pellets of ET2I3. Films with a-ET2I3 show semiconducting behaviour with some deviation of the temperature dependence of conductivity at 160–200 K. Films with β-ET2I3 show metallic conductivity down to 60 K. Studies of the optical absorption have shown that the conducting network does not contribute much to the UV-VIS spectra of conducting films.

Thermal switching of the optical anisotropy of a macroscopically aligned film of a discotic liquid crystal

We have studied the temperature dependence of anisotropy in the optical absorption and charge transport properties of an aligned film of hexakis-dodecyl-hexa-peri-hexabenzocoronene (HBC-C12) formed by zone-casting on a quartz substrate. At room temperature the film displays a large anisotropy in (photo)conductivity, as determined using the flash photolysis time-resolved microwave conductivity technique, with charge transport in the casting direction favoured by a factor of at least 10. The anisotropy in the optical absorption is however negligible. At the temperature corresponding to the transition from the crystalline solid to the liquid crystalline mesophase (c. 110°C), the optical anisotropy increases abruptly, with absorption of light polarized in the direction perpendicular to the alignment direction favoured by a factor of c. 3. On cooling, the dichroism reverts to its initial very low value with a hysteresis of c. 30°C. The results are explained in terms of a reversible change in the orientation of the molecules with respect to the axis of the aligned columnar stacks from tilted (at c. 45°) in the crystalline phase to close to orthogonal in the liquid crystalline phase.

Structure and optical properties of polycarbonate films with microcrystallites of BEDT-TTF polyiodides

Abstract The morphology, structure and optical properties of thin layers of crystalline bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF or ET) polyiodides formed within the surface layer of polycarbonate film were investigated. The samples were obtained by exposing the polymer films containing 2 wt.% of molecularly dispersed ET to vapors of I 2 /CH 2 Cl 2 solutions of different I 2 concentration. X-ray diffraction, scanning electron microscopy (SEM) and atomic force microscopy (AFM) show that, depending on the preparation conditions, ET polyiodides form plate-like crystals, flakes and some less organized layer covering microcrystallites. In all cases only (001) reflexes attributed to the α-ET 2 I 3 phase were registered in the X-ray diffraction (XRD) experiments. Reaction of iodine with already formed crystals leads to new morphological structures. Using saturated iodine solutions the nonconducting polyiodides are formed which, under ambient conditions, undergo transformation into a stable conducting salt.

Kinetics of surface roughening via pit growth during the oxidation of the basal plane of graphite. II. Theory and simulation

Analytical expressions for the description of the oxidation kinetics of the basal planes of the graphite surface are proposed. They are developed from an ansatz that extends former theories of phase transformations by nucleation and growth to multilayer systems in which the kinetics of transformation in subsequent layers is recurrently related. The results from analytical theory are compared with computer simulations obtained for an adequate model. Correspondence of these results to the structural changes observed in the oxidation of the graphite surface, as revealed by scanning tunneling microscopy, is discussed.

Colourless, transparent conductive polymer films with ultrathin networks of organic crystals

The possibilities of increasing the transparency of conductive organic polymeric composites obtained by growing crystalline conductive networks in situ are discussed and new methods of preparation of practically colourless conductive polymer films are presented. We show that in most cases the colour which appears during the preparation of a conducting composite by reticulate doping is not directly related to the conducting network, which usually consist of relatively well-formed microcrystals, but results instead from the additive molecules present in the polymer matrix as less organised aggregates or a molecularly dispersed phase. By an appropriate choice of preparation conditions or electrochemically one can get rid of the strongly absorbing part of the complex so that the absorption in the visible range can be substantially reduced without losing conductivity and without deterioration of the conductive network. n n n nThese phenomena are demonstrated on polycarbonate with fine networks of BEDO-TTF iodine and bromine salts obtained by casting or spin coating in order to obtain thin homogeneous films, e.g. to prepare electrodes for electro-optical investigations. Transparent, colourless conductive films 20-2 μm thick (surface resistivity of the order of 103–104 Ω/□) have been obtained and the structure of the conductive networks in these materials, their optical properties in the visible and near-infrared range as well as their electrical properties are discussed.

Phase transformations of ET polyiodides leading to superconducting polymer in situ composites

Abstract Conducting in situ composites made by two-step reticulate doping of polymers with ET polyiodides show several exceptional characteristics like high conductivity at low dopant amount, transparency and easiness of production in a form of large-area, flexible films. The most interesting finding is that the ET polyiodides forming the crystalline network can be transformed into the superconducting β-phase of ET 2 I 3 , yielding polymer composites showing the transitions to superconducting state at low temperatures. Systematic studies on the phase structure of the as-obtained films and on conditions controlling the transformation into the superconducting form were performed allowing optimization of the key parameters like composition, temperature, time and atmosphere of annealing.

Increased luminescence efficiency by synergistic exploitation of lipo/hydrophilic co-solvency and supramolecular design

We use steady-state and time-resolved photoluminescence (PL) spectroscopy to investigate the luminescent properties of a sulfonated poly(diphenylenevinylene) lithium salt (PDV.Li) in water/propanol solutions at different concentrations, with a view to assessing its aggregation behavior. In particular, we compare results from uninsulated PDV.Li and cyclodextrin-threaded PDV.Li polyrotaxane (PDV.Li⊂β-CD). We find that addition of 1-propanol (≥20 weight%) leads to a significant blue-shift (of ∼0.20 eV) of the PL spectra, that we assign to suppressed interchain aggregation in PDV.Li solutions, with a concomitant fourfold increase in the fluorescence quantum efficiency (i.e. from 14 to 60%). Surprisingly, a moderate concentration of propanol increases further the luminescence efficiency even for PDV.Li⊂β-CD, whose supramolecular encapsulation already provides a shield against aggregation. Indeed, addition of propanol reduces the solvent polarity, and therefore helps solubilizing these materials that are still largely aromatic in nature. Interestingly, however, both uninsulated PDV.Li and polyrotaxane solutions exhibit signs of aggregation at high propanol fraction (>70%) with a distinctively weaker coupling than that of interchain states in PDV.Li at high water concentration and in pure water in particular. While we ascribe such behavior to a poor solvation of the polar moieties, we also report a different strength of aggregation for PDV.Li and PDV.Li⊂β-CD that can be attributed to the presence of the cyclodextrin rings. In PDV.Li⊂β-CD hydrogen bonding between the cyclodextrin rings may lead to closer packing between the polymer chains. We therefore suggest that a content of propanol between 30 and 70% provides a good balance of hydrophobic and hydrophilic interactions both for PDV.Li and PDV.Li⊂β-CD.

Does β-ET2I3 really have a definite interlayer spacing?

Abstract X-ray diffractograms of conducting polycrystalline layers of β-ET 2 I 3 obtained within a surface layer of polycarbonate films show only ( 001 ) reflexes thus the comparison with single crystal data is reduced to one parameter — the spacing between the conducting layers. It is shown that β-ET 2 I 3 , formed at room temperature, with larger interlayer spacing can be transformed by annealing into the form of smaller interlayer spacing. The difference in interlayer spacing between the two states of β phase is ca 0.07A.