Synthesis of novel coumarin-terminated poly (p-phenylene vinylene)s for application in LEDs

Novel coumarin-terminated poly (p-phenylene vinylene)s were synthesized successfully via Gilch methodology. The resulting coumarin end-capped poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene vinylene (CT-MEH-PPV) film gives yellow photoluminesence with a maximum intensity at 560 nm, which is noticeably blue-shifted about 40 nm from that of MEH-PPV (598 nm). Light-emitting diode based on a double-layer structure (ITO/PEDOT/CT-MEH-PPV/Ba/Al) showed yellow emission with a maximum brightness of 956 cd m−2 at 8.8 V and an external quantum efficiency of 0.28% at 49.5 mA cm−2. The coumarin-terminted poly(2,3-diphenyl-5-hexyl-1,4-phenylene vinylene (CT-DPH-PPV), however, has similar emission spectrum with that of DPH-PPV, but its photoluminescence efficiency (0.78) is much more improved than that of DPH-PPV (0.55). The electroluminescent device (ITO/PEDOT/CT-DPH-PPV/Ba/Al) gave green emission peaked at 510 nm with a maximum brightness of 350 cd m−2 at 18 V and an external quantum efficiency of 0.04% at 61 mA cm−2. These results suggest that it is a convenient way to modify the structure of conjugated polymers by terminating to tune the emission color and improve photoluminescent and electroluminescent efficiencies as well. C 2005 Springer Science + Business Media, Inc.