Theoretical study of new blue iridium complexes comprising a bipyridine derivative and various ancillary ligands.

Abstract

New blue emitting ligand Iridium(III) complexes with two phosphines trans to each other and two ancillary ligands, such as Ir(dfpypy)(PPh3)2(H)(CI) and Ir(dfpypy)(PPh3)2(H)(CN), [dfpypy = 2,6-difluoro-3-(pyridin-2-yl)pyridine] were designed and studied to tune the phosphorescence wavelength to the deep blue region and to enhance the luminescence efficiencies. To gain insight into the factors responsible for the emission color change and the different luminescence efficiency, we performed the DFT and TD-DFT calculations on the ground and excited states of these phosphors. (1) The fluorine-substituted dfpypy ligand lower the HOMO energy levels because a N of the pyridyl ligand is more electronegative than a C of the nonsubstituted phenyl ligand and also (2) mono-cyclometalated Iridium(III) complexes using two phosphines trans to each other increased HOMO-LUMO gap by strong field effects of ancillary ligands. From these results, we discuss how the dfpypy ligand and the ancillary ligand influences the emission peak as well as the metal to ligand charge transfer (MLCT) transition efficiency. As the maximum emission spectra of FIrpic known as blue phosphorescence material is about 475 nm. The resulting Iridium(III) complexes, Ir(dfpypy)(PPh3)2(H)(CN), would appear pure blue region about 415 nm with more intensified efficiency.