Fine tuning of the photophysical and electroluminescent properties of DCM-type dyes by changing the structure of the electron-donating group

Using 2H-indene-1,3-dione as an electron-withdrawing group and aromatic amines of different structures as electron-donating groups, four new DCM-type dyes, IN-1, IN-2, IN-3, and IN-4, were designed and synthesized for application in organic light-emitting diodes (OLEDs) as red light-emitting materials. IN-2 exhibits a red shift in fluorescence but a blue shift in absorption with respect to IN-1. Similarly, IN-4 exhibits a red shift in fluorescence but a blue shift in absorption with respect to IN-3. These unique photophysical properties were utilized to optimize the electroluminescence color purity and efficiency of these red emitters in OLEDs. In EL devices with the configuration of ITO/NPB (60 nm)/ Alq(3) (or Gaq(3) with the configuration of ITO/NPB ( 60 nm)/ Alq(3) ( or Gaq(3)) : red dopant (2.0 wt%) ( 7 nm)/BCP) : red dopant ( 2.0 wt%) ( 7 nm)/ BCP ( 12 nm)/ Alq(3) ( 45 nm)/ LiF (0.3 nm)/Al ( 300 nm), IN-3 in Alq(3) and IN-1 in Gaq(3) show CIE coordinates of (0.64, 0.36) and (0.65, 0.34), and current efficiencies of 3.24 cd A(-1) and 3.02 cd A(-1), respectively, much better than the other guest/host combinations. This can be ascribed to the good spectrum overlap either between IN-3 and Alq(3) or between IN-1 and Gaq(3), indicating that the absorption spectrum has the same importance as the fluorescence spectrum in the improvement of color purity of red emitters.