Untersuchungen zur Photoleitf�higkeit von alkoxysubstituierten Oligo- und Poly(1,4-phenylenethenylen)en

Abstract

Investigations on the Photoconductivity of Alkoxy Substituted Oligo‐ and Poly(1,4‐phenyleneethenylene)s The photoreactivity and the photoconductivity of the mono‐ and dialkoxy substituted oligo‐ and poly(1,4‐phenyleneethenylene)s 1/1′a‐n were investigated in order to optimize the photoconducting properties of these materials. Increasing the length of the side chains enhances the average length of the main chain during the polycondensation and decreases the band gap till the limit of convergence is reached. The highest photoconductivity was observed for the 2,5‐dipropyloxy system 1/1′j. Longer side chains render the charge transfer from chain to chain more difficult. The measurements were performed in dispersion layers and related to the industrial standard 3. Compound 1m was also measured in a pure state as transparent film and compared to a poly(N‐vinylcarbazole) film which shows a dye‐sensitized photoconductivity. In both cases the optimized systems 1/1′ were markedly superior to the standards. The highest sensitivity could be observed for wavelengths λ lying close to the absorption maxima λmax. The compounds 1/1′ have a high photostability on irradiation with visible light; however, they are rapidly destroyed by UV light (254 nm).

Supramolecular self-assembly and opto-electronic properties of semiconducting block copolymers

“…Although the oligomer route has the advantage of exact control of end-groups and molecular weight, it is extremely time-consuming for higher molecular weight polymers. Hence, we use the Siegrist [75,76] polycondensation technique, originally described by Kretzschmann and Meier [77,78], to obtain PPV blocks with exactly one aldehyde end-group. The subsequent attachment of the initiator to the rigid PPV block occurs via the nucleophilic attack of a Grignard reagent to the aldehyde group.…”

Pentadecamer 2,5-Dipropoxy-1,4-phenylenevinylene

“…have been reported. [1] We showed in early studies [2,3] that the 2,5-substitution of the benzene rings with propoxy groups guarantees an optimum photoconductivity. Shorter or much longer alkoxy side chains are less favorable concerning the solubility and processability and/or the charge transfer from chain to chain.…”

Synthesis, Structure and Solvatochromism of the Emission of Cyano-Substituted Oligo(phenylenevinylene)s

“…This response of the chromophore 6 towards polarity can be tuned by additional auxochromic or electron-withdrawing groups. Electron-donating alkoxy groups maintain the quantum yield remarkably (8,9,12), while electron-accepting trifluoromethyl groups further reduce the fluorescence by a factor of 2Ϫ3 (7,11). The latter groups promote charge transfer from the centre of the molecules to the terminal moieties.…”

“…When the reaction was complete (15 min to 3 h), the mixture was poured into water (100 mL) and either the precipitate was collected (7, 10Ϫ12) or the compounds (6, 8, and 9) were isolated by extraction with chloroform (3 ϫ 50 mL) and the pooled organic solutions were washed with water and brine and dried with Na 2 SO 4 . Purification was done by recrystallisation from chloroform/isopropyl alcohol (6, 7, 10؊12) or chromatography on silica gel, using toluene as eluent (8,9). …”

“…These materials are promising candidates as emissive layers in light-emitting diodes (LEDs), [2Ϫ6] as well as for non-linear optics or photoconducting devices. [7,8] The light emission of LEDs is generated by the recombination of electrons and holes injected from the electrodes into the luminescent layer. Balanced charge injection and charge carrier mobilities are decisive for high device efficiencies.…”