Synthesis and properties of new orange red light-emitting hyperbranched and linear polymers derived from 3,5-dicyano-2,4,6-tristyrylpyridine

Two new orange red light-emitting hyperbranched and linear polymers, poly(pyridine phenylene)s P1 and P2, were prepared by the Heck coupling reaction. In particular, an A(2) + B-3 approach was developed to synthesize conjugated hyperbranched polymer P2 via one-pot polycondensation. The polymers were characterized by NMR, Fourier transform infrared, ultraviolet-visible, and elemental anal-Si. They showed excellent solubility in common solvents such as tetrahydrofuran, CH2Cl2, CHCl3, and N,N-dimethylformamide and had high molecular weights (up to 6.1 x 10(5) and 5.8 x 10(5)). Cyclic voltammetry studies revealed that P2 had a low-lying lowest unoccupied molecular orbital energy level of -3.22 eV and a highest. occupied molecular orbital energy level of -5.43 eV. The thin film of P2 emitted strong orange-red photoluminescence at 595 nm. A double-layer light-emitting diode fabricated with the configuration of indium tin oxide/P2/tris(8-hydroxy-quinoline)aluminum/Al emitted orange-red light at 599 nm, with a brightness of 662 cd/m(2) at 7 V and a turn-on voltage of 4.0 V; its external quantum efficiency was calculated to be 0.19% at 130.61 mA/cm(2), This indicated that this new electroluminescent polymer (P2) based on 3,5-diccano-2,4,6-tristyrylpyridine could possibly be used as an orange-red emitter in polymer light-emitting displays. (C) 2004 Wiley Periodicals, Inc.