Orange and red organic light-emitting devices using aluminum tris(5-hydroxyquinoxaline)

Energy transfer in dye-doped organic light-emitting diodes (OLEDs) often occurs by Förster energy transfer processes. In many cases this energy transfer process can be very efficient, leading to fairly large Förster radii. We have recently shown that saturated red emission can be achieved by doping tetraphenylporphine (TPP) into aluminum tris(8-hydroxyquinolate) (Alq3) in an ITO/TPD/Alq3/Mg-Ag device (TPD = N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′biphenyl-4,4′ diamine; ITO = indium-tin oxide). Predominant red emission is observed even at very low doping levels, as expected for the large Förster radius for TPP in Alq3 (33 Å). In order to increase the degree of overlap between the dopant absorption for red fluorescent dyes and the host emission we prepared a strongly red-shifted analog of Alq3, i.e. aluminum tris(8-hydroxyquinoxalate) (Alx3). The photoluminescent efficiency for Alx3 is significantly lower than that of Alq3, leading to a significant decrease in the electroluminescent quantum yield for Alx3-based OLEDs relative to Alq3-based devices. We have examined the doping of several dyes into Alx3, giving red and orange OLEDs.