Luminescence properties of aminobenzanthrones and their application as host emitters in organic light-emitting devices

Abstract

A series of aminobenzanthrone derivatives, possessing a keto and an amino group on the aromatic ring, are synthesized and their photoluminescence (PL) and electroluminescence (EL) properties are studied in detail. These compounds emit strongly in solution and in the solid state, with the emission maxima in the range of 528-668 nm resulting from charge-transfer transitions from the amino group to the keto moiety. The emission wavelength depends greatly on the polarity of the solvent. A red shift of nearly 100 nm is observed from n-hexane to dichloromethane for each of these compounds. The PL quantum yields of these molecules also depend tremendously on the solvent. The values are between 88 and 70 % in n-hexane and decrease as the polarity of the solvent increases. The single-crystal X-ray diffraction data reveal that the aminobenzanthrone planes of these molecules stack in the crystals in an antiparallel head-to-tail fashion. This strong dipole-dipole interaction accounts for the observed red-shifted emissions of the aminobenzanthrone molecules in powders and in films relative to those in nonpolar solvents. Electroluminescent devices using aminobenzanthrone derivatives as the host emitters or dopants emit orange to red light in the range 590-645 nm. High brightness, current efficiency, and power efficiency are observed for some of these devices. For example, the device using N-(4-t-butylphenyl)-N-biphenyl-3-benzanthronylamine as the emitter gives saturated red light with a current efficiency of 1.82 cd A-1, brightness of 11253 cd m-2, and Commission Internationale de l'Éclairage (CIE) coordinates of (0.64,0.36); the device using N-(2-naphthyl)-N-phenyl-3-benzanthronylamine as the emitter gives orange-red light with a current efficiency of 3.52 cd A-1, brightness of 25 000 cd m-2, and CIE coordinates of (0.61,0.38). © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.