Electronics, polymer-based

Organic light emitting diodes are currently being developed by numerous companies and research institutions worldwide. From the perspective of printed electronics, polymer-based hght emitting diodes are very attractive. Polymer LEDs are essentially diodes... 

The simplest polymer-based EL device consists of a single layer of semiconducting fluorescent polymer, c.g., PPV, sandwiched between two electrodes, one of which has to be transparent (Fig. 1-1). When a voltage or bias is applied to the material, charged carriers (electrons and holes) are injected into the emissive layer and these earners arc mobile under the influence of the high (> 105 V enr1) elec-... 

In recent years further concepts have been developed for the construction of polymer-based diodes, requiring either two conjugated polymers (PA and poly(A-methyl-pyrrole) 2 > or poly(A-methylpyrrole in a p-type silicon wafer solid-state field-effect transistor By modifying the transistor switching, these electronic devices can also be employed as pH-sensitive chemical sensors or as hydrogen or oxygen sensors 221) in aqueous solutions. Recently a PPy alcohol sensor has also been reported 222). 

The field of modified electrodes spans a wide area of novel and promising research. The work dted in this article covers fundamental experimental aspects of electrochemistry such as the rate of electron transfer reactions and charge propagation within threedimensional arrays of redox centers and the distances over which electrons can be transferred in outer sphere redox reactions. Questions of polymer chemistry such as the study of permeability of membranes and the diffusion of ions and neutrals in solvent swollen polymers are accessible by new experimental techniques. There is hope of new solutions of macroscopic as well as microscopic electrochemical phenomena the selective and kinetically facile production of substances at square meters of modified electrodes and the detection of trace levels of substances in wastes or in biological material. Technical applications of electronic devices based on molecular chemistry, even those that mimic biological systems of impulse transmission appear feasible and the construction of organic polymer batteries and color displays is close to industrial use. 

New natural polymers based on synthesis from renewable resources, improved recyclability based on retrosynthesis to reusable precursors, and molecular suicide switches to initiate biodegradation on demand are the exciting areas in polymer science. In the area of biomolecular materials, new materials for implants with improved durability and biocompatibility, light-harvesting materials based on biomimicry of photosynthetic systems, and biosensors for analysis and artificial enzymes for bioremediation will present the breakthrough opportunities. Finally, in the field of electronics and photonics, the new challenges are molecular switches, transistors, and other electronic components molecular photoad-dressable memory devices and ferroelectrics and ferromagnets based on nonmetals. 

We can see that ferrocene is ideally suited to this application from model compounds. Using Cr(CNBun)5 as our model for the polymer-based Cr complex (21), we can estimate that the eq for reaction between ferricenium and Cr(CN [P])6, leading to removal of one electron, is approximately 10. It is also thermodynamically favorable [Ken = 1012] for a second electron to be removed to give the bound Cr(II) species. 

The history and development of polysilane chemistry is described. The polysilanes (polysilylenes) are linear polymers based on chains of silicon atoms, which show unique properties resulting from easy delocalization of sigma electrons in the silicon-silicon bonds. Polysilanes may be useful as precursors to silicon carbide ceramics, as photoresists in microelectronics, as photoinitiators for radical reactions, and as photoconductors. 

Deen, M. Kazemeini, M. Haddara, Y. Yu, J. Vamvounis, G Holdcroft, S. Woods, W. 2004. Electrical characterization of polymer-based FETs fabricated by spin-coating poly(3-alkylthiophene)s. IEEE Trans. Electronic Dev. 51 1892-1901. 

S. Beaupre and M. Leclerc, Optical and electrical properties of TT-conjugated polymers based on electron-rich 3,6-dimethoxyfluorene unit, Macromolecules, 36 8986-8991, 2003. 

M. Granstrom, M. Berggren, D. Pede, O. Inganas, M.R. Andersson, T. Hjertberg, and O. Wennerstrom, Self-organizing polymer films — a route to novel electronic devices based on conjugated polymers, Supramol. Sci., 4 27-34, 1997. 

Incorporation of the (.S )-2-mcthyloctoxy group afforded optically active polymers with preferential helical screw sense (see Section 3.11.6.1). The observed helicity was corroborated by force field calculations, which indicated similar helical conformations for both dialkoxy- and dialkyl-substituted polymers. Based on their similar conformational properties, it was suggested that the origin of the spectral red shift was electronic, due to a a-n mixing interaction, as for polymers 76 above, rather than conformational. 

Since this reaction involves ions, electrons, and gas molecules in three separate phases, the edge of the o/y interface that makes contact with the gas phase /3 is often described as the three-phase (or triplephase) boundary (TPB). The concept of the TPB actually dates to the 1920s, when workers studying the oxidation of H2 on platinum introduced this concept to explain why Pt must be exposed simultaneously to both solution and gas to get significant reaction. This type of electrode, which Schmid called die diffusiongaselektrode or gas-diffusion electrode (GDE), is still called this today by workers studying solution- or polymer-based fuel cells. As... 

An example of the difficulties encountered when trying to fabricate an ohmic electrode, able to sustain a space-charge-limited current, is the recent work of the Neher group [179]. The authors deposited barium as an electron injection cathode on top of an electron transporting polymer based on a naphthalene diimide core whose LUMO is as low as 4 eV below vacuum level. Although the Fermi level of barium should be above the LUMO of the polymer, the electron current is. 

M. S. Freund and N. S. Lewis. 1995. A Chemically Diverse Conducting Polymer-Based Electronic Nose. Proceedings of the National Academy of Sciences U.S.A. 92 2652-2656. 

Electroluminescence. In Section 6.3.2.5, we saw that some materials—in particular, semiconductors—can reemit radiation after the absorption of light in a process called photoluminescence. A related type of emission process, which is common in polymer-based semiconductors, called electroluminescence, results when the electronic excitation necessary for emission is brought about by the application of an electric field rather than by incident photons. The electric field injects electrons into the conduction band, and holes into the valence band, which upon recombination emit light. 

---