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Efficient blue-green-emitting poly[(5-diphenylamino-1, 3-phenylenevinylene) -alt-(2,5-dihexyloxy-1, 4-phenylenevinylene)] derivatives: Synthesis and optical properties

2006-04-01
Liao, Liang
Çırpan, Ali
DING, Liming
KARASZ, Frank E.
Pang, Yi
New poly(phenylene vinylene) derivatives with a 5-diphenylamino-1,3-phenylene linkage (including polymers 2, 3, and 5) have been synthesized to improve the charge-injection properties. These polymers are highly photoluminescent with fluorescent quantum yields as high as 76% in tetrahydrofuran solutions. With effective pi-conjugation interruption at adjacent m-phenylene units, chromophores of different conjugation lengths can be incorporated into the polymer chain in a controllable manner. In polymer 2, the structural regularity leads to an isolated, well-defined emitting chromophore. Isomeric polymer 3 of a random chain sequence, however, allows the effective emitting chromophores to be joined in sequence by sharing a common m-phenylene linkage (as shown in a molecular fragment). Double-layer light-emitting-diode devices using 2, 3, and 5 as emitting layers have turn-on voltages of about 3.5 V and produce blue-green emissions with peaks at 493, 492, and 482 nm and external quantum efficiencies up to 1.42, 0.98, and 1.53%, respectively. In comparison with a light-emitting diode using 2, a device using 3 shows improved charge injection and displays increased brightness by a factor of similar to 3 to 1400 cd/m(2) at an 8-V bias.