15. Design of Novel Iridium Complexes to Obtain Stable and Efficient Light-Emitting Electrochemical Cells

摘要

In its simplest form electroluminescence (EL) involves the generation of species at electrode surfaces that undergo electron-transfer reactions to form excited states that emit light. Thus, EL is a direct conversion of electrical into radiative energy in solution and in solid state as well. In 1964, Hercules [1] showed EL for the first time in a series of hydrocarbons such as anthracene, diphenyl-anthracene, and rubrene in acetonitrile or dimethylformamide solutions using an electric pulse. No detailed electrochemical or spectroscopic results were reported, just the detection of the emitted light by the eye. Approaches to a theoretical understanding of the EL response, both in terms of the reason for excited-state formation and of the nature of the electrochemical EL transients, followed soon after the first experiment. For example, one of the most studied systems was the [Ru(bpy)_3]~(2+), bpy = 2,2'-bipyridine, whose EL process in acetonitrile was reported in 1972 [2]. This process was ascribed to the generation of oxidized and reduced species at the electrode surfaces (Figure 15.1a), which then undergo electron-transfer reactions to recombine and form the exciton species, that is, the [Ru(bpy)_3]~(2+*) in its triplet excited state. The excitons emit light following the same principle as in photoluminescence in solution (Figure 15.1b).