Ladder Polysiloxanes for Optoelectronic Applications

Abstract

Electroluminescence (EL) of conjugated polymers was first reported in 1990 with poly(pphenylenevinylene) by Burroughes et al. (Burroughes et al., 1990) Since then polymer lightemitting diodes (PLED) have attracted the attention of many researchers and many efforts have been made to develop PLED in recent years (Kido et al.,1995; Service, 2005; Holder et al., 2005; D’Andrade & Forrest, 2004) because of the significant advantages that PLED present for displays, especially for flat panel displays. Those advantages include highly luminous efficiency, wide viewing angle, low operating voltage, high brightness, vivid color, low cost, light weight, and particular flexibility. Many approaches have been used in attempts to improve the performance of PLED device, for instance, improving deposition technologies (de Gans & Schubert, 2003; Singhet al., 2010) and controlling the interfacial microstructure of multilayerstructured devices (Segalman et al., 2009) in the process of preparing the devices; improving the electrical and optical properties of the light-emitting material layer (Grimsdale et al., 2009) and so on. Especially, the light-emitting material layer is crucial to get a high performance PLED device. Considerable efforts have been devoted to developing conjugated materials as the active layers in PLED. (Gather et al., 2010; Wang et al., 2009; Xiao et al., 2010) The ongoing preparation of new light-emitting materials has produced in higher efficiencies, enhanced brightness, and longer lifetimes of optoelectronic devices. (Martin & Diederich, 1999; van Hutten & Hadziioannou, 2000; Műllen & Wegner, 1999) However, the stability of these materials under operating conditions needs further improvement if they are to be widely used in real products, some common causes resulting in degradation of PLED still remain to be unsolved. For instance, molecular aggregation induced by the π-π stacking of polymer chain results in quenching of fluorescence; (Wu, et al., 2002; Amrutha & Jayakannan, 2007) poor film-forming property and poor morphological stability; low thermal stability (Weinfurtner et al., 2000) and so on. For the first case, controlling the π-π stacking induced molecular aggregation of the polymer chains is one of important tasks in the development of ideal PLED devices. To solve this problem, one method is that units of structural asymmetry are introduced in order to limit the ability of chains to pack effectively in the solid state. For example, Son et al. (Son, et al., 1995) controlled the distribution of cis-linkages in poly(phenylenevinylene) chains, the cis-linkages interrupt conjugation and interfere with the packing order of the polymer chains. Liao et al