Synthesis and Characterization of Phosphorescent Cyclometalated Iridium Complexes

The preparation, photophysics, and solid state structures of octahedral organometallic Ir complexes with several
different cyclometalated ligands are reported. IrCl3·nH2O cleanly cyclometalates a number of different compounds
(i.e., 2-phenylpyridine, 2-(p-tolyl)pyridine, benzoquinoline, 2-phenylbenzothiazole, 2-(1-naphthyl)benzothiazole,
and 2-phenylquinoline), forming the corresponding chloride-bridged dimers, C∧N2Ir(μ-Cl)2IrC∧N2 (C∧Nis a
cyclometalated ligand) in good yield. These chloride-bridged dimers react with acetyl acetone (acacH) and other
bidentate, monoanionic ligands such as picolinic acid (picH) and N-methylsalicylimine (salH), to give monomeric
C∧N2Ir(LX) complexes (LX = acac, pic, sal). The emission spectra of these complexes are largely governed by
the nature of the cyclometalating ligand, leading to λmax values from 510 to 606 nm for the complexes reported
here. The strong spin−orbit coupling of iridium mixes the formally forbidden 3MLCT and 3π−π* transitions
with the allowed 1MLCT, leading to a strong phosphorescence with good quantum efficiencies (0.1−0.4) and
room temperature lifetimes in the microsecond regime. The emission spectra of the C∧N2Ir(LX) complexes are
surprisingly similar to the fac-IrC∧N3 complex of the same ligand, even though the structures of the two complexes
are markedly different. The crystal structures of two of the C∧N2Ir(acac) complexes (i.e., C∧N = ppy and tpy)
have been determined. Both complexes show cis-C,C‘, trans-N,N‘ disposition of the two cyclometalated ligands,
similar to the structures reported for other complexes with a “C∧N2Ir” fragment. NMR data (1H and 13C) support
a similar structure for all of the C∧N2Ir(LX) complexes. Close intermolecular contacts in both (ppy)2Ir(acac) and
(tpy)2Ir(acac) lead to significantly red shifted emission spectra for crystalline samples of the ppy and tpy complexes
relative to their solution spectra.