Iridium cyclometalated complexes with axial symmetry. Synthesis and photophysical properties of a trans-biscyclometalated complex containing the terdentate ligand 2,6-diphenylpyridine.

The first example of an iridium biscyclometalated complex with a C wedge N wedge C 2,6-diphenylpyridine (dppy)-type ligand, [(4'-(4-bromophenyl)-2:2',6':2' '-terpyridine)Ir(2,6-diphenyl-4-(4-tolyl)pyridine)](NO(3)) (1), has been synthesized and characterized by various techniques such as X-ray crystallography, mass spectrometry, (1)H and (13)C NMR, cyclic voltammetry, and both steady-state and time-resolved emission and absorption studies. Preliminary density functional theory calculations have also been conducted. 1 crystallizes in the monoclinic space group P2(1)/n. The crystallographic data are as follows: C(45)H(31)BrN(4)IrO(3).2H(2)O, a = 17.4308(4) A, b = 9.0312(2) A, c = 26.7601(7) A, beta = 104.496(1) degrees, V = 4078.5(2) A(3), Z = 4. The relatively long Ir-C distances (2.122 and 2.094 A) reflect the strong mutual trans effect of the cyclometalating carbons. The complex exhibits strong visible absorption and long-lived (1.7 micros) emission (lambda(max), 690 nm) in room temperature solution. The inherent asymmetry of the coordination environment offers a unique directional character to the emitting excited state, which is predominantly ligand-to-ligand charge transfer (dppy --> 2,2':6',2' '-terpyridine) in nature.