Synthesis and photophysical studies of iridium complexes having different ligands

Abstract

The synthesis and photophysical study of efficient phosphorescent iridium(III) complexes having two different (C<^>N) ligands are reported. In order to improve the luminescence efficiency by avoiding triplet-triplet (T-T) annihilation, the iridium complexes, Ir(ppy)(2)(piq) and Ir(ppy)(2)(piq-F), are designed and prepared where ppy, piq and piq-F represent 2-phenylpyridine, 1-(phenyl)isoquinoline and 2-(4'-fluorophenyl)isoquinoline, respectively. Two ppy ligands and a piq derivative act as a source of energy supply and a piq derivative acts as a chromophore. Since Ir(ppy)(3), Ir(piq)(3) and Ir(piq-F)(3) can be placed in the metal-to-ligand charge transfer (MLCT) excited state, they absorb light effectively. When Ir(ppy)(2)(piq-F) is placed in excited state, the excitation energy is neither quenched nor deactivated but quickly intramolecular transferred from two ppy ligands to one luminescent piq-F ligand. This can occure because the triplet energy level of ppy is higher than that of piq-F and light is emitted from piq-F ligand in the end. Thus, Ir(ppy)(2)(piq-F) shows strong photoluminescence, originated from piq-F ligand because piq-F ligand is known to have a shorter lifetime than that of ppy ligand. To analyze luminescent mechanism, we calculated these complexes having two different ligand sets theoretically by using computational method.