Abstract
A series of new 1,3,5-oxadiazines (NON) is prepared by the condensation of substituted arylhydrazines and cyclohexylcarbaldehyde in a 2:3 ratio with moderate to high yields. This straightforward “one-pot” procedure proceeds via the interrupted Fischer indolization mechanism and enables the formation of indoline-containing derivatives with three fused heterocyclic rings and two stereogenic centres. The NON materials emit UV-fluorescence in the range of 315–338 nm, with fast radiative rates up to 1.7·108 s–1, while possessing highly desirable characteristics for application in deep-blue Organic Light-Emitting Diodes (OLED) devices: good thermal stability, a wide energy gap (3.9 eV), a well-stabilised HOMO (–6.1 eV), a destabilised LUMO (–2.2 eV), a high triplet energy level of (3.3 eV), and excellent volatility during sublimation. The most promising NON material was tested as a host for a Carbene-Metal-Amide complex in an OLED device. The NON-host blue-shifts the electroluminescence while significantly improving OLED colour purity by narrowing the electroluminescence profile of the charge transfer TADF emitter in comparison to devices containing conventional hosts. This work informs the molecular design of new NON-host materials, enabling deep-blue OLED devices with a peak external quantum efficiency of 21%.