Conjugated electron mobility

Although MEH-PPV 13 (at the time of discovery) was one of the most efficient soluble polymers for PLEDs application, its performance is not high enough for commercialization as LEP. One of the reasons is unbalanced hole-electron mobility in MEH-PPV (the mobility of holes is 100 times faster than the mobility of electrons) [133]. Copolymerization with other conjugated monomers, to some extent, can improve the electron-transporting properties and increase the EL performance. 

A perfluorinated, para-conjugated oligophenylene with high EA exhibited improved electron transport properties and was investigated as an ETM (100-103) (Scheme 3.32) [155]. The electron mobility of NPF-6 (100), determined by the TOF technique, is much higher than that... 

In all cases there is a need for the rapid transfer of electrons in a controlled direction. It is to be expected that ligands will have mobile, conjugated electronic systems to allow electrons to be transported away rapidly from the metal centre to avoid recombination with the positive hole. In addition to movement of electrons through the binding system, the possibility of electron tunnelling must be considered. 

The purpose of performing calculations of physical properties parallel to experimental studies is twofold. First, since calculations by necessity involve approximations, the results have to be compared with experimental data in order to test the validity of these approximations. If the comparison turns out to be favourable, the second step in the evaluation of the theoretical data is to make predictions of physical properties that are inaccessible to experimental investigations. This second step can result in new understanding of material properties and make it possible to tune these properties for specific purposes. In the context of this book, theoretical calculations are aimed at understanding of the basic interfacial chemistry of metal-conjugated polymer interfaces. This understanding should be related to structural properties such as stability of the interface and adhesion of the metallic overlayer to the polymer surface. Problems related to the electronic properties of the interface are also addressed. Such properties include, for instance, the formation of localized interfacial states, charge transfer between the metal and the polymer, and electron mobility across the interface. 

The conjugated molecules are elongated with a much better electron mobility in the backbone direction than perpendicular to it. The dipole and transition dipole moments are pointing in this direction (x) with Consequently, the second-order hyperpolarizability tensor y is dominated by... 

Polydiacetylenes (PDAs) were the first class of conjugated polymer that could be produced in pure, single crystal form by the polymerization of the corresponding crystals of the monomeric dialkyne derivatives. DC measurements had demonstrated large electron mobilities in such PDA crystals. Because of this they were considered at the time to be of potential application as an organic semiconductor layer in electronic devices. While these hopes were unfulfilled, these... 

Ordered conjugated organic materials exhibit low trap densities and high charge carrier mobilities, for both electrons and holes. As an example, in single crystals of anthracene [87], the hole and electron mobilities are approximately 1 cm V s and the crystal photoluminescence quantum yield at room temperature is almost unity. Both electroluminescence [87] and stimulated emission... 

Interestingly, Vg-controlled electroluminescence and ambipolar characteristics have been recently observed in conjugated polymer OFETs [67,68], which indicates a balanced electron and hole injection. However, low hole and electron mobilities ( 10 cmWs), typical for polymer semiconductors, limit the channel current and therefore may present a serious problem for realizatiou of electrically pumped polymer lasers. For this reasou, ordered smaU-molecule orgauic semicouductors with higher mobilities are very promisiug for research in this direction. 

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