Arylfluorenyl-substituted metoxytriphenylamines as deep blue exciplex forming bipolar semiconductors for white and blue organic light emitting diodes

Abstract Arylfluorenyl-substituted triphenylamines were prepared by acid promoted Friedel-Crafts-type substitution reaction. The synthesized compounds were found to be capable of glass formation with glass transition temperatures above 152 °C. The ionization potentials of the layers of the derivatives were found to be in the range of 5.25–5.41 eV. Time-of-flight hole and electron drift mobility values of the layer of tris[3-methoxy-4-(9-phenyl-9-fluorenyl)phenyl]amine well exceeded 10 −3  cm 2 /V at high electric fields at room temperature. The results obtained by means of density functional theory calculations were used to discuss on the charge-transporting and optical properties of the compounds. Deep blue exciplexes formed by the newly synthesized arylfluorenyl-substituted triphenylamines and the known electron-transporting materials 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) or 4,7-diphenyl-1,10-phenanthroline (Bphen) were discovered and studied. Based on these exciplexes, we propose an original structure of cold white OLED with CIE chromaticity coordinates ranging from (0.286, 0.378) to (0.24, 0.29) depending on applied voltages. Electroluminescence spectra of cold white OLED consist of deep blue and green emissions which originate from bulk and interface. The origin of green emission is thermally activated delayed fluorescence (TADF) from exciplex formed between 4,4′,4″-tris[3-methylphenyl(phenyl)amino]triphenylamine (m-MTDATA) and Bphen. Based on the newly discovered exciplex emitters, deep blue OLED with the electroluminescence maximum at 428 nm and with CIE chromaticity coordinates of (0.179; 0.104) was fabricated. The cold white and deep blue devices showed external quantum efficiencies of 2.55% and 1.2%, respectively.