Molecular engineering of an electron-transport triarylphosphine oxide-triazine conjugate toward high-performance phosphorescent organic light-emitting diodes with remarkable stability

Abstract

Organic electron-transport materials are an essential component to boost performances and stability of organic light-emitting diodes. We present a robust organic electron-transport compound 3-(6-(3-(4,6-bis(4-biphenylyl)-l,3,5-triazin-2-yl)phenyl)pyridin-2-yl)phenyldiphenylphosphine oxide by facilely coupling the triphenylphosphine oxide moiety to the 2-phenyl-4,6-bis(4-biphenylyl)-1,3,5-triazine unit via a 2,6-pyridinylene linker. It is well soluble in weakly polar solvents and possesses a high T_g of 123 °C with an exceptional T_d≈470 °C at 1% weight loss and deep HOMO/LUMO levels of ca. −6.45/-3.06 eV. The phos-phorescent spectrum measured in solid state at 77 K reveals a notable triplet energy of 2.88 eV. n-Doping with 8-hydroxyquinolatolithium (Liq) produces the electron mobility value of 4.66×10⁻⁵-3.21×10⁻⁴ cm V⁻¹s⁻¹ @(2–5)×10⁻⁵ V cm⁻¹. Moreover, the contrasting solubility of the bromo reaction intermediate and the new compound in alcoholic solvents facilitates separation. The characterizations of bottom- and top-emission green phosphorescent OLEDs involving this single Liq-doped electron-transport layer reveal long stability. In particular, the latter provides outstanding performances with 77.4 cd A⁻¹ (corresponding to an EQE of 18.7%) and 86.8 lm W⁻¹@ca. 1000 cd m⁻², based on the green emitter bis(2-phenylpyridine)(2-(4-methyl-3-phenylphenyl)pyridine)iridium(III). Moreover, driven by a constant current for ca. 640 h, the initial luminance of 1000 cd m⁻² appears almost no decay.