Strategies for the Molecular Design of Donor-Acceptor-type Fluorescent Emitters for Efficient Deep Blue Organic Light Emitting Diodes

We describe several strategies for the molecular design of high-efficiency blue fluorescent emitters. Asymmetric donor-acceptor (D-A) and symmetric A-D-A-type fluorescent emitters were designed with spiroacridine donors and diphenyltriazine acceptors. Substituting a toluene or xylene moiety for the phenyl group connecting the donor and acceptor and replacing the diphenylsilane group with a fluorene moiety resulted in a deeper blue emission without any losses in luminescence efficiency. On the basis of these substitutions, deep blue organic light emitting diodes (OLEDs) with Commission Internationale de LEclairage (CIE) coordinates of (0.149, 0.082) and an external quantum efficiency (EQE) of 7.7% were fabricated using a D-A-type emitter. Symmetrizing the D-A structure to an A-D-A structure increased the proportion of horizontally oriented emission dipoles in the organic film from 70 to 90%. OLEDs incorporating symmetric A-D-A-type emitters had EQEs as high as 8.5% due to increased outcoupling efficiencies and also showed deep blue emission with CIE coordinates of (0.142, 0.116). The molecular design strategies described herein can be applied to donor-acceptor-type fluorescent emitters for the fabrication of efficient deep blue OLEDs.