Salen-Aluminum Complexes as Host Materials for Red Phosphorescent Organic Light-Emitting Diodes

Abstract

The properties of monomeric and dimeric salen-aluminum complexes, [salen(3,5-Bu-t)(2)Al(OR)], R = OC6H4-p-C6H6 (H1) and R = [salen(3,5-Bu-t)AlOPh]C(CH3)(2) (H2) (salen = NN'-bis-(salicylidene)-ethylenediamine) as host layer materials in red phosphorescent organic light-emitting diodes (PhOLEDs) were investigated. H1 and H2 exhibit high thermal stability with decomposition temperature of 330 and 370 degrees C. DSC analyses showed that the complexes form amorphous glasses upon cooling of melt samples with glass transition temperatures of 112 and 172 degrees C. The HOMO (ca. -5.2 similar to -5.3 eV) and LUMO (ca. -2.3 similar to -2.4 eV) levels with a triplet energy of ca. 1.92 eV suggest that H1 and 112 are suitable for a host material for red emitters. The PhOLED devices based on H1 and H2 doped with a red emitter, Ir(btp)(2)(acac) (btp = bis(2-(2'-benzothienyl)pyridinato-N,C-3; acac = acetylacetonate) were fabricated by vacuum-deposition and solution process, respectively. The device based on vacuum-deposited H1 host displays high device performances in terms of brightness, luminous and quantum efficiencies comparable to those of the device based on a CBP (4,4'-bis(N-carbazolyl)biphenyl) host while the solution-processed device with H2 host shows poor performance.