High triplet energy host material with a 1,3,5-oxadiazine core from a one-step interrupted Fischer indolization

Abstract

Energy-efficient and deep-blue organic light-emitting diode (OLED) with long operating stability remains a key challenge to enable a disruptive change in OLED display and lighting technology. Part of the challenge is associated with a very narrow choice of the robust host materials having over 3 eV triplet energy level to facilitate efficient deep-blue emission and deliver excellent performance in the OLED device. Here we show the molecular design of new 1,3,5-oxadiazines (NON)-host materials with high triplet energy over 3.2 eV, enabling deep-blue OLED devices with a peak external quantum efficiency of 21%. A series of NON-host materials are prepared by the condensation of substituted arylhydrazines and cyclohexylcarbaldehyde in a 2:3 ratio. This straightforward “one-pot” procedure enables the formation of indoline-containing derivatives with three fused heterocyclic rings and two stereogenic centres. All materials emit UV-fluorescence in the range of 315–338 nm while possessing highly desirable characteristics for application in deep-blue OLED devices: good thermal stability, a wide energy gap (3.9 eV), a high triplet energy level of (3.3 eV), and excellent volatility during sublimation. Diluting phosphorescent and thermally activated delayed fluorescence emitter molecules in solid-state host matrices has proven to be a useful strategy to hinder self-quenching mechanisms, but host materials must meet several criteria to enable energy efficient and stable OLEDs. Here, the authors report the synthesis of a series of 1,3,5-oxadiazines from a one-pot interrupted Fischer indolization, and demonstrate that they possess highly desirable characteristics as host materials in deep-blue OLED devices.