The polymerization of PPV via the sulfinyl precursor route has been investigated with respect to its mechanism. When polymerized in sec-butanol, a purely radical polymerization mechanism is observed as in most precursor polymerization routes. Accordingly, an increase in the reaction temperature induced an increase in the overall yield alongside with a reduction of the average molecular weight of the polymer. Upon changing the monomer concentration in solution before addition of the base NatBuO, an increase in molecular weight is observed, signifying that the polymerization is faster than the mixing of the two reaction components. When changing the solvent to NMP, a competition of anionic and radical polymerization has been established while in THF an anionic polymerization mechanism occurs exclusively. To prevent termination reactions, LDA and LHMDS were introduced as base whereby LHMDS shows less propensity to initiate anionic chain growth due to higher steric hindrance. With polymerizations in presence of the radical quencher TEMPO, the anionic polymerization mechanism could unambiguously be proven.
The synthesis of, two new poly(thienylene vinylene) derivatives is described, i.e. poly(3-octyl-2,5-thienylene vinylene) (O-PTV) and poly(bis[octylphenyl-2,5-thienylene vinylene]) (BOP-PTV). Both polymers have been prepared via the dithiocarbamate (DTC) precursor route. The polymerization protocol of the monomer toward the precursor polymer has been optimized by the use of different bases, leading to improved reproducibility of the polymerization step. Processability has been guaranteed by the introduction of alkyl side chains. Finally the precursor polymers were converted toward conjugated polymers and they were fully characterized by UV/vis, IR, GPC, and cyclic voltammetry. Bulk heterojunction solar cells with PCBM as acceptor showed promising power conversion efficiencies of 0.80% for BOP-PTV and 0.92% for O-PTV.
Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. The interpretation of electron currents in conjugated polymers is strongly hindered by the occurrence of hysteresis. We investigate the transport of electrons in electron-only devices based on derivatives of poly͑p-phenylene vinylene͒ ͑PPV͒ for various hole-blocking bottom electrodes as well as purification of the polymer. The use of a variety of hole blocking bottom contacts, as metallic electrodes and n-type doped polymers, did not give any improvement in the observed hysteresis. By purification of the PPV, hysteresis free electron-only currents can be obtained. The deep traps responsible for hysteresis, with a concentration in the 10 16 cm −3 range, are not responsible for the trap-limited electron transport as observed in purified PPV.
Conjugated polymers continue to attract increasing attention as a result of their promising properties for optoelectronic applications such as light-emitting diodes, 1 solar cells, 2 sensors, 3 and field effect transistors. 4 Whereas for selected applications suitable conjugated polymers are available, the quest for materials with improved properties continues. One method to achieve this objective is the introduction of functional groups. A more radical approach focuses on the design of hitherto unknown polymer backbone architectures. We have combined both tactics and prepared the novel poly(p-fluoranthene vinylene) (PFV) (Scheme 1), with a new backbone architecture containing nonalternant polycyclic aromatic hydrocarbon repeating units, in which the base structure of poly(p-phenylene vinylene) PPV remains readily recognizable.Our search for novel materials was inspired by the field of organic solar cells. In such solar cells, which currently can already reach efficiencies as high as 5%, 5 a p-type conjugated polymer such as poly(3-hexylthiophene) (P3HT) or OC 1 C 10 -PPV is combined with a soluble derivative of C 60 , PCBM, as the electron acceptor. 2,5 However, an n-type polymeric alternative for PCBM is of interest to facilitate the formation of an optimal morphology. 6 Whereas it is possible to incorporate C 60 as the substituent in a polymer, 7 this approach is rather laborious and hence not necessarily cost-effective for future applications. Fortunately, remarkable progress has been made in the synthesis of functionalized substructures of C 60 by researchers in the field of nonalternant hydrocarbons. 8 This prompted us to incorporate one of these substructures, i.e. fluoranthene, in the backbone of a conjugated polymer. The incorporation of such substructures can have a considerable impact on the electronic properties. 9 Furthermore, the use of cyclopenta-fused nonalternant hydrocarbons is expected to result in a significantly increased electron affinity of the resulting materials, which would render them possibly indeed n-type. 10 The novel conjugated polymer PFV described in this Communication is of particular interest since it is the first PPV-type polymer with nonalternant repeating units.The synthesis of PFV starts with the straightforward onestep synthesis of dimethylfluoranthene-7,10-dicarboxylic ester (1) from acenaphtenequinone, acetone dicarboxylic ester, and norbornadiene followed by the conversion of the ester groups into the diol 2 by reduction with LiAlH 4 according to a literature procedure (Scheme 1). 8 Subsequently, 7,10-bis(chloromethyl)-fluoranthene (3) was obtained by reaction with thionyl chloride in THF solution. The rather limited solubility of 2 and 3 required the use of dilute solutions. After recrystallization from chloroform, pure 3 was obtained in 62% yield as light yellow crystals (melting point 232-234°C).For the polymerization, the dithiocarbamate (DTC) precursor route 11,12 was chosen. The DTC precursor route was previously developed in our laboratory and offers not only a st...
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