HETIRIDIUM · Tris-heteroleptic cyclometalated iridium(III) complexes for white electroluminescence

Tris-heteroleptic cyclometalated iridium(III) complexes for white electroluminescence

The aim of the project was to develop new phosphorescent iridium complexes as single emitters for white electroluminescence. The underlying challenge was to design such complexes so that they allow for simple device architecture as a strategy to decrease the economic and energetic costs of device fabrications. The European Union targets 20% reduction in energy consumption by 2020. About 20% of the European electrical energy is used for lighting and considerable savings could be achieved by developing more efficient lighting solutions. Electroluminescent (EL) devices based on organic thin-films are considered as one of the most promising response to the demand for efficient lighting technology. Organic Light-Emitting Diodes (OLEDs, a family of EL devices) based on phosphorescent emitters mark a breakthrough allowing for 100% of the excitons to be harvested; hence unitary internal quantum efficiencies can be obtained, which is 400% improvement over devices based on fluorescent materials. Cyclometalated iridium(III) complexes are arguably the most studied family of phosphorescent emitters for OLEDs. The work resulted in a multitude of new tris-homoleptic (Ir(L)3) and bis-heteroleptic (Ir(L)2(La)) complexes and monochromatic OLEDs with efficiencies approaching theoretical limits. However, the panchromatic (white) OLEDs suffer from stability and high processing costs issues that impedes the development of lighting applications. To achieve the overarching aim, a new family of cyclometallated iridium complexes with three different bidentates ligands, Ir(L1)(L2(L3) was developed. Only six examples of such complexes based on limited types of ligands were reported in the literature before the start of the project. During the period of the project we have established synthetic procedures and have significantly broadened the scope of such materials attainable to a wide range of cyclometallating ligands including, for example, pyridine, carbene, imidazole, pyrazole with various substituents. We have also developed systems based on non-symmetric ancillary ligand. The study of the optoelectronic properties of these new materials have given us valuable insights into the unique photophysical processes at play. The design tools developed during the project allowed us in particular to obtain a handful of complexes that emit from 450 nm (or below) up to 600 nm (and above) as single emitters. As such we have developed complexes that are genuinely single white emitters.

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