Bernd Tieke

Conducting polypyrrole-polyimide composite films

Novel polypyrrole-polyimide composite films are reported which combine high electrical conductivity with high thermal stability. The composite films were prepared either by electrochemical polymerization of pyrrole on a polyimide coated electrode (type I films) or by exposing polyimide films containing ferric chloride as an oxidizing agent to pyrrole vapour (type II films). Type I films consist of a sequence of three layers with the polyimide sandwiched between two layers of polypyrrole. The maximum conductivity is about 10 S cm−1. Type II films consist of polyimide containing finely dispersed polypyrrole particles of 10 to 500 nm in diameter. The maximum conductivity is about 5 × 10−4 S cm−1. The composite films are thermally stable up to 350°C.

Optical second harmonic generation in Langmuir-Blodgett films of novel donor-acceptor substituted pyridine and benzene derivatives

Abstract A series of sixteen novel amphiphiles has been prepared containing substituted nitropyridine and nitroaniline units as polar headgroups. The film forming properties of the amphiphiles at the air-water interface are described. Langmuir-Blodgett-films are characterized by spectroscopic methods and by xray diffraction. A comprehensive study of measurements of optical second harmonic generation in the films is reported. Among the compounds investigated 2-alkylamino-5-nitropyridines with C18 to C26 alkyl chains are best suited for second harmonic generation. Our studies show for the first time that LB-films of a single material not forming an asymmetric head-to-tail (X- or Z-type) structure can produce significant second harmonic signals. Structure models are presented, which explain the observation of nonlinear optical properties in terms of formation of either a non-centrosymmetric herringbonetype structure or an intercalated structure of the molecules with preferential orientation of the polar head...

Optical second-harmonic generation in Langmuir–Blodgett films of 2-docosylamino-5-nitropyridine

The first preparation of non-centrosymmetric Langmuir–Blodgett multilayer films of 2-docosylamino-5-nitropyridine, and the first measurements of optical second-harmonic generation from these films are reported.

Crystal Structure of Undoped and Lithium-Doped Polyparaphenylene

Abstract The crystal structure of prisitine and Li-doped polyparaphenylene (PPP) has been investigated by electron diffraction. The chain setting angle of pristine PPP has been refined to φ = 45°. For Li-doped PPP, a superposition of amorphous and crystalline scattering is observed. A simple intercalation model for the crystalline component is in good agreement with the experimental data.

Electrical properties of new donor amphiphiles in Langmuir-Blodgett films

Abstract The electrical properties of novel Langmuir-Blodgett (LB) films based on tetrathiotetracenes (TTT), dibenzotetraaza[14]annulenes (TA) and carotenoids were studied. Upon doping with iodine vapour the conductivity of the LB films could be increased by several orders of magnitude. The highest conductivity was found for a doped TTT derivative (10 −2 Scm −1 ). LB films of TTT derivatives which had also been electrochemically oxidized and reduced showed a reversible electrochromism with colour changes between blue in the neutral and red in the oxidized state. While LB films of the TTT and TA derivatives were conducting only in the direction parallel to the layer plane, the carotenoid were also conducting in the normal direction. The optical and structural properties of the undoped and doped LB films were also investigated.

Electron and crystal structure of sodium-doped polyparaphenylene

Abstract The electron and the crystal structure of Na-doped polyparaphenylene as a function of dopant concentration has been studied by electron energy-loss spectroscopy and by electron diffraction.

Electroactive carbazole-substituted polysiloxanes

Abstract Polysiloxane homo- and copolymers with various carbazole concentrations in the substituents were prepared and their electroactive properties studied by cyclic voltammetry and optical absorption spectroscopy. Electrochemical oxidation leads to dimerization of the carbazole units, which thereby crosslinks the polymer. The oxidized films exhibit conductivities up to 8 × 10 −4 S cm −1 . Depending on the potential applied, the films are either deep blue, pale green or colourless. The electrochromism is excellently reversible. The chemical processes involved in electrochemical oxidation and cycling of the polymers are discussed in detail.

Thermochromic Langmuir-Blodgett films of a novel amphiphilic azo dye with homogeneous chromophore orientation☆

Abstract Langmuir-Blodgett (LB) multilayers have been prepared from a novel amphiphilic azobenzene derivative. These films were transparent and showed homogeneous polarization of visible light over the whole film area. They exhibit reversible thermochromism with a red shift of 60 nm over a temperature range of less than 10°C. This thermochromism can be explained by a “J-like” aggregation of the azo chromophores that is slightly effected by temperature.

Electrical conduction in novel Langmuir–Blodgett films based on 2-trifluoromethyl-5,6;11,12-bisepidithiotetracene

The first preparation of stable monomolecular layers at the air–water interface and Langmuir–Blodgett (LB) films containing the title compound are described; after exposure to iodine vapour the LB films exhibit an in-plane conductivity of 1.2 × 10–4 S cm–1.

Novel electroactive Langmuir–Blodgett films based on an amphiphilic dibenzotetra-aza[14]annulene derivative

The preparation of stable monomolecular layers and semiconducting Langmuir–Blodgett films based on a copper(II)dibenzotetra-aza[14]annulene derivative is described; their in-plane conductivity was improved upon exposure to iodine vapour or aqueous potassium tri-iodide solution.