New heteroleptic tris-cyclometalated iridium(III) complexes containing difluorophenylpyridine and phenylpyridine

The synthesis and the photophysical properties of iridium (III) complexes having two different (G-N) ligands, F-2-ppy and ppy, were studied, and their photonic properties were investigated to study the effect of the phenylpyridine (ppy) / difluorophenylpyridine (F-2-ppy) ratio in the complex on the emission properties. Ir(ppy)(3) is known to have a high phosphorescence efficiency in EL emissions owing to its strong metal-to-ligand charge transfer (MLCT) excited state. However, the emissive quantum efficiency of Ir(F-2-ppy)(3) was found to be low due to weak MLCT. Thus, for tuning of blue phosphors, heteroleptic tris-cyclometalated iridium complexes, Ir(ppy)(2)(F-2-ppy) and Ir(ppy)(F-2-ppy)(2), were prepared with systematic changes in their ligand systems and were investigated. Replacement of ppy by F-2-ppy in the iridium complex system stepwise leads to an increase in the HOMO-LUMO gap, resulting in a hypsochromic shift in emission wavelength. The emission wavelengths of Ir(ppy)(3), Ir(ppy)(2)(F-2-ppy)), Ir(ppy)(F-2-ppy)(2), and Ir(F-2-ppy)(3) were thus, observed at 514, 502, 495, and 474 nm, respectively. To investigate the suggested luminescent mechanism, we calculated these complexes theoretically by using a computational method.