Light emitting polymeric LEDs

By 1988, a number of devices such as a MOSFET transistor had been developed by the use of poly(acetylene) (Burroughes et al. 1988), but further advances in the following decade led to field-effect transistors and, most notably, to the exploitation of electroluminescence in polymer devices, mentioned in Friend s 1994 survey but much more fully described in a later, particularly clear paper (Friend et al. 1999). The polymeric light-emitting diodes (LEDs) described here consist in essence of a polymer film between two electrodes, one of them transparent, with careful control of the interfaces between polymer and electrodes (which are coated with appropriate films). PPV is the polymer of choice. 

The enormous progress in the field of electroluminescent conjugated polymers has led to performances of oiganic light-emitting devices (LEDs) that are comparable and in some aspects superior to their inorganic counterparts 11). Quantum efficiencies in excess of 5% have been demonstrated [2] and show that a high fraction of the injected carriers in a polymeric electroluminescence (EL) device form electronic excitations which recombine radiatively. 

Polymeric gem-peroxides, 18 460 Polymeric light-emitting diodes (LED), 26 803... 

Since the discovery of doped polyacetylene, a range of polymeric semiconductor devices has been studied, including normal transistors, field-effect transistors (FETs) photodiodes, and light-emitting diodes (LEDs). Like conductive polymers, these materials obtain their properties from their electronic nature, specifically the presence of conjugated -bonding systems. 

Electroluminescence (EL) spectra of P-l-P-4 are given in Fig. 6 [29,30]. The EL spectra of the polymers were obtained for the light-emitting diodes (LEDs) fabricated between the indium-tin oxide (ITO) coated glass anode and the aluminum cathode. For P-l-P-3, their organic soluble precursor polymers were coated onto the ITO-coated glass and they were subjected to thermolysis at 270 °C for 12 h to convert them into the final polymers. And then aluminum cathode was vacuum deposited on the polymer films. P-4 obtained by base-catalyzed polymerization of the bis-bromomethyl monomer was organic soluble and, thus,... 

R.W. Mills, A. Uhl, G.B. Blackwell, K.D. Jandt, High power light emitting diode (LED) arrays versus halogen light polymerization of oral biomaterials Barcol hardness, compressive strength and radiometric properties. Biomaterials 23 (2002) 2955-2963. 

Triblock copolymers using NVK, 4-(l-pyrenyl)-butyl vinyl ether, and 2-chloroethyl vinyl ether, have been synthesized in a sequential cationic polymerization technique [43], The block copolymers were further functionalized with 2-(4-hydroxyphenyl)-5-phenyl-l, 3,4-oxadiazole, by reaction of the chlorine in the 2-chloroethyl ether moiety. The modification procedure is illustrated in Figure 1.6. Light-emitting diodes (LED)s that were fabricated from the material show a low electroluminescence. 

Recently, Nobile and coworkers reported a synthesis of polyfluorenylenevinylenes 234, a potential material in active layers in light-emitting diodes (LEDs) [121]. In this Suzuki/Mizorold-Heck protocol, potassium vinyltrifluoroborate reacts first with 233 in the presence of Pd(PPh3)4 as catalyst and K2CO3 as base. Although most of the solvent systems tested did not promote polymerization, up to 77% of the desired polymer were obtained when using dioxane under reflux (Scheme 8.59). 

Typical light sensitive formulations consist in a polymerizable radical or cationic matrix and a more or less complex photoinitiating system (PIS). Mercury lamps, doped Hg lamps, microwave powered lamps, Hg-Xe lamps, Xe lamps and more recently highly packed arrays of light emitting diodes (LEDs) or laser diodes are now used as light sources. Therefore, a photoinitiated polymerization starts upon the exposure of the PIS to a suitable radiation. A PIS can contain (i) a photoinitiator (PI) alone, (ii) a photoinitiator and a photosensitizer (PS), (iii) a photoinitiator and one or more additive, (iv) a photoinitiator, a photosensitizer and additive(s). 

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