Luminescent Iridium-Terpyridine Complexes with Various Bis-Cyclometalated Ligands.

A series of luminescent bis-cyclometalated iridium complexes with 2,2':6',2″-terpyridine (tpy), [Ir()(tpy)]PF ( = 2-phenylpyridinate (ppy) for ; benzo[h]quinolinate (bzq) for ; 1-phenylisoquinolinate (piq) for ; and 2-phenylbenzothiazolate (pbt) for ), have been synthesized and structurally characterized. Single-crystal X-ray diffraction analyses reveal that the tpy ligands of - are coordinated to the iridium center in a bidentate fashion, and the uncoordinated pendant pyridine rings in the tpy ligands of - form intramolecular π-π stacking interactions with a phenyl moiety of ligands. In addition, the pendant pyridine ring in the tpy ligand of forms an intramolecular hydrogen bonding interaction, unlike in -. Of interest, the photophysical properties of - are strongly influenced by the ligands; shows a luminescence band at 572 nm, with a short lifetime (τ) value of 80 nsec and a lower absolute luminescence quantum yield (Φ) of 3.72%, whereas exhibits an intense luminescence band at 588 nm with a long τ value of 1965 nsec and a moderate Φ value of 9.57%. The density functional theory calculations revealed that the luminescence originates from the triplet metal-ligand to ligand charge transfer (MLL'CT) excited state.