Synthesis and characterization of diphenylamine derivative containing malononitrile for thermally activated delayed fluorescent emitter

Abstract

To increase the efficiency of blue organic light-emitting diodes (OLEDs), new blue dopants, 2-(bis(4-(diphenylamino)phenyl)methylene)malononitrile (4-DPM) and 2-(bis(3-(diphenylamino)phenyl) methylene)malononitrile (3-DPM), with thermally activated delayed fluorescence were synthesized. 4-DPM with a p-phenyl linker between the electron-donating diphenylamine unit and the electron withdrawing malonitrile unit showed a large overlap in the phenyl linker as well as the malonitrile unit, while 3-DPM with an m-phenyl linker showed a weak overlap in the phenyl linker. The OLED with the 3-DPM dopant showed higher efficiencies of 12.62 cd/A and 8.81 lm/W compared to that with the 4-DPM dopant (1.38 cd/A and 0.70 Im/W). This result was attributed to the small overlap between the electron-donating and electron-withdrawing units, the small charge-transfer singlet-triplet state splitting below 0.1 eV, and the well-aligned structure in the horizontal direction, as determined by grazing incidence X-ray diffraction. (C) 2017 Elsevier Ltd. All rights reserved.