LED there be white light
Cyclometalated iridium(III) complexes are arguably the most studied family of phosphorescent emitters for OLEDs. This is due to their suitable photophysical properties – high photoluminescence efficiency, short lifetime of triplet excited state and tunability of emitted colour over the entire visible spectrum. Such complexes have found wide use in monochromatic OLED devices. However, white OLEDs suffer from stability issues and high processing costs, both greatly hindering their market entry. Within MULTHIC (Multiphosphorescent emitters based on tris-heteroleptic iridium complexes), researchers skirted these limitations by developing a new family of dual phosphorescent iridium(III) complexes that can directly emit white light, without the need to combine multiple emitting centres. The strategy revolved around tris-heteroleptic iridium complexes in which the ligands can undergo controlled geometric deformation in the excited state, leading to two emitting triplet states. Researchers developed improved synthetic methodology for preparing cyclometalated iridium complexes bearing N-heterocyclic carbenes, phenylimidazoles and pyrazoles with significantly good yields. As a result, they successfully prepared tris-heteroleptic iridium complexes with a first phosphorescent band below 500 nm and a second one around 600 nm. Project results open up new avenues for designing white emitters with a single centre, overcoming issues regarding the colour drift. When combining two emitting centres, one emitter typically degrades faster than the other, and the lighting device experiences a colour drift. Development of white OLED devices is highly useful for solid-state lighting applications.
Keywords
White light, OLEDs, cyclometalated iridium, phosphorescent, solid-state lighting
