A Novel Linking Strategy of Using 9,10-Dihydroacridine to Construct Efficient Host Materials for Red Phosphorescent Organic Light-Emitting Diodes.

Three novel 9,10-dihydroacridine derivatives, 4'-(10-methyl-9,9-diphenyl-9,10-dihydroacridin-4-yl)[1,1'-biphenyl]-4-carbonitrile (MeAcPhCN), 4'-(9,9,10-triphenyl-9,10-dihydroacridin-4-yl)[1,1'-biphenyl]-4-carbonitrile (PhAcPhCN), and 5-[4-(9,9,10-triphenyl-9,10-dihydroacridin-4-yl)phenyl]picolinonitrile (MeAcPyCN), were prepared by the attachment of [1,1'-biphenyl]-4-carbonitrile or 5-phenylpicolinonitrile to the 4-position of 9,10-dihydroacridine. This special linking strategy limited the conjugation length, maintained the triplet energy, and inhibited the intermolecular charge-transfer (ICT) characteristics of these compounds. Notably, the enhanced accepting strength of the picolinonitrile segment relative to that of benzonitrile led to relatively strong ICT characteristics, a low energy gap, and a low triplet energy for MeAcPyCN. The thermal, photophysical, electrochemical, and electroluminescent properties of these host materials were studied systematically. Consequently, (acetylacetonato)bis(2-methyldibenzo[f,h]quinoxaline)iridium(III) [Ir(MDQ)2 (acac)]-based red phosphorescent organic light-emitting diodes (PHOLEDs) were fabricated with these three host materials. As a result, the device hosted by MeAcPhCN showed good device performance with a maximum external quantum efficiency of 20.5 %.