SYNTHESIS OF A GREEN-EMITTING ALTERNATING BLOCK-COPOLYMER

An alternating block copolymer, poly(1,8-octanedioxy-2, 6-dimethoxy-1, 4-phenylene-1,2 -ethenylene-1, 4-phenylene-1,2-ethenylene-1,4-phenyle ne-1,2- ethenylene-3,5-dimethoxy-1,4-phenylene), 1, was synthesized an d characterized using Fourier transform infrared spectroscopy, nuclear magnetic resonance, gel permeation chromatography differential scanni ng calorimetry ultraviolet and elemental analysis. Light-emitting sing le-layer test diodes using this soluble processible copolymer as the a ctive layer (i.e. indium tin oxide/1/Ca,AI) emit green light with a lu minescent spectral maximum at 513 nm. The single-layer device had a br ightness of about 80 cd/m(2) at a current density of 100 mA/cm(2) with an internal quantum efficiency of 0.3% photon/electron. Optimization of the light-emitting properties of I was achieved through variation o f a key Wittig polymerization step in the synthesis, using trialkyl ra ther than triaryl phosphonium salts in an appropriate solvent mixture to achieve nearly regiospecific trans-olefination. This provided an im provement over earlier procedures, which require a post-Wittig isomeri zation to minimize the presence of electroluminescence-inhibiting cis- bonds. (C) 1998 John Wiley & Sons, Ltd.