Triaryl boron derivatives of pyridine as electron transporting materials for blue phosphorescent organic light-emitting diodes

Abstract

Two duryl borane derivatives, tris(2,3,5,6-tetramethyl-4-(pyridin-3-yl)phenyl)borane (TDPB) and tris(2,3,5,6-tetramethyl-4'-(pyridin-3-ye)biphenyl-4-yl)borane (TDPPB), which contain heteroaromatic pyridine rings at peripheral positions were synthesized to investigate the effects of bridging phenyl group on their thermal, photophysical, and electrochemical properties. Upon adding a phenyl unit between duryl and pyridine units, TDPPB showed slightly higher thermal stability (T-d = 446 degrees C and T-g = 166 degrees C) than TDPB (T-d = 439 degrees C and T-g = 142 degrees C). Both TDPB and TDPPB have deep highest occupied molecular orbital levels to block the holes/ excitons and appropriate lowest unoccupied molecular orbital levels for smooth electron injection. Notably, TDPB and TDPPB exhibited relatively high triplet energies of 2.84 eV and 2.69 eV, respectively. Thus, the triplet energy level of TDPB is sufficient for use in bis[2-(4,6-difluorophenyepyridinato-C-2,N](picolinato)iridium(III) (FIrpic) based blue phosphorescent organic light-emitting diodes (PHOLEDs) as an electron transport material. Accordingly, TDPB was used as an electron transport material in FIrpic-based blue PHOLEDs and the optimized device showed high external quantum efficiency of up to 18.8%.