| Abstract
| - The synthesis and characterization of octasubstituted cyclooctatetraenes (COTs) as well as their useas electron transporting materials in organic LEDs are reported. Tetraaryl-tetraarylethynyl-cyclooctatetraenes[C8Ar4(C⋮CAr)4] were prepared from diaryldiynes with a RuH2(CO)(PPh3)3 catalyst in good yield (40−80%). Octaaryl-cyclooctatraenes were prepared from diarylacetylenes by treatment with lithium and iodine in50% yield. Cyclic voltametry indicates that these COTs are reduced in sequential one-electron steps. C8Ar4(C⋮CAr)4 and C8Ar8 are thermally stable to sublimation and have wide optical energy gaps [λmax(emission)= 392−412 nm] making them good candidates for use in organic LEDs. These octasubstituted COTs havebeen used as electron transport layers in single heterostructure organic LEDs, i.e. ITO/NPD 400 Å/octasubstitutedCOT 400 Å/Mg−Ag (ITO = indium−tin oxide, NPD = N,N‘-diphenyl-N,N‘-dinaphthylbenzidine). Externalquantum efficiencies of 0.1−0.2% (photons/electrons) were observed, with turn-on voltages of ca. 6 V. Theemission from this device comes exclusively from the NPD hole transporting layer, with a λmax of 435 nm.Doping the NPD layer with 1% perylene leads to an increased quantum efficiency of 0.6% and anelectroluminescence spectrum indicative of emission solely from the perylene dopant, confirming exclusiveemission from the NPD hole transporting layer.
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