Iridium complexes containing 2-aryl-benzothiazole ligands: color tuning and application in high-performance organic light-emitting diodes

Abstract

Three 2-aryl-benzothiazole chromophores were designed and synthesized for use as major cyclometalating ligands of iridium complexes, in which the aryl groups were N-phenyl-3-carbazolyl, 2-(9,9-dioctyl)fluorenyl and N-phenyl-2-carbazolyl. The homoleptic tris-cyclometalated and heteroleptic bis-cyclometalated iridium complexes, 1–5, were synthesized using these ligands. By adjusting the chemical structures and then the electronic state of these complexes, we were able to continuously tune the phosphorescence from yellow to saturated red with peak wavelengths in the order of 1 < 2 < 3 < 4 < 5. The quantum chemical calculations and the electrochemical data clearly demonstrate the origin of the phosphorescence color tuning. The organic light-emitting diodes (OLEDs) containing these iridium complexes as doped emitters exhibited yellow to red electrophosphorescence with excellent performance. Particularly, the complex 1 based device produced high efficiencies of 75.9 cd A⁻¹, 48.2 lm W⁻¹, and 23.0% with CIE (0.46, 0.53), which represent the highest efficiencies for yellow OLEDs up to now. Furthermore, 1 was used to fabricate two-element white OLEDs in combination with a blue phosphor and high efficiencies of 57.9 cd A⁻¹ and 21.9% were achieved, which are among the best efficiencies for two-emitting-component white OLEDs reported so far.