Oxidized and neutral films of polypyrrole have been prepared electrochemically in the absence of oxygen and water. The neutral rms are insulating and can be readily oxidized by chemical oxidizing agents to give films of greater conductivity than can be achieved by electrochemical oxidation. Optical spectroscopy provides evidence for the similarity of the polymeric carbonium ion produced by both types of oxidation. NMR studies are consistent with the-,a' bonding in these polymers; they also show the expected downfield shifts relative to the neutral polymer on both chemical and electrochemical oxidation. ESR studies of both the electrochemically oxidized and the neutral polymer suggest the presence of highly mobile spins. Oxidized and neutral films of polypyrrole have been prepared electrochemically in the absence of oxygen and water. The neutral films are insulating and can be readily oxidized by chemical oxidizing agents to give films of greater conductivity than can be achieved by electrochemical oxidation. Optical spectroscopy provides evidence for the similarity of the polymeric carbonium ion produced by both types of oxidation. NMR studies are consistent with the a,a' bonding in these polymers; they also show the expected downfield shifts relative to the neutral polymer on both chemical and electrochemical oxidation. ESR studies of both the electrochemically oxidized and the neutral polymer suggest the presence of highly mobile spins.
A series of experiments on the physics and chemistry of polymers derived from pyrroles show that the oxidation of neutral insulating polypyrrole (PP0) to its conducting counterpart (PP+) is a multistep process. In particular, the conductivity of the polymers increases only in the early stages of oxidation, whereas significant changes in the optical and EPR properties occur in later stages of the oxidation when no further changes in the conductivity take place. The early stages of oxidation lead to an ionic (PP+ anion−) polymer and the later stages of oxidation result in chemistry at the nitrogen atoms of the pyrrole rings. Similar behavior is observed for all the oxidized pyrrole polymers independent of the method of oxidation.
The absorption and emission properties of excitons are investigated in a pure "red" phase of luminescent polydiacetylene wires. The values of the binding energy (E b = 0.556 eV) and Bohr radius (r ~ 14 Å) make the "red" exciton similar to the one of the extensively studied "blue" phase, so the conformational modifications which lead to a reordering of excited states and luminescent emission do not strongly affect the exciton structure. The opening of a thermally activated non radiative channel leads to an efficient quenching of the intense luminescence observed at low temperature.
Electroabsorption measurements are performed with solution cast films of poly-(dodecylthiophene) and poly-(phenylphenylenevinylene). The spectra are described within the framework of second-order Stark effect acting on an excitonic transition including field-induced transfer of oscillator strength to higher lying states. The spatial extent of the exciton is two to three repeat units of the polymer backbone consistent with the notion that the absorbers are ordered subunits of the conjugated chain.Es werden Elektroabsorptionsmessungen an Poly-(dodecy1thiophen)-und Poly-(phenylphenylenviny-1en)-Filmen durchgefuhrt, die aus der Losung abgeschieden worden waren. Zur Interpretation wird ein Stark-Effekt xweiter Ordnung, der auf einen exzitonischen obergang wirkt, herangezogen unter Berucksichtigung der Umverteilung von Oszillatorstarke zu hoheren Zustanden. Die Ausdehnung des Exzitons wird zu zwei bis drei Wiederholungseinheiten der Polymerkette abgeschatzt.
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