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 Cboolean ANDNboolean ANDC 2,6-diphenylpyridine (dppy)-type ligand, [(4'-(4-bromophenyl)-2:2',6':2-terpyridine)lr(2,6-diphenyl-4-(4-tolyl)pyridine)](NO3) (1), has been synthesized and characterized by various techniques such as X-ray crystallography, mass spectrometry, H-1 and C-13 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)lrO(3).2H(2)O, a = 17.4308(4) Angstrom, b = 9.0312(2) Angstrom, c = 26.7601(7) Angstrom, beta = 104.496(1)degrees, V = 4078.5(2) Angstrom,, Z = 4. The relatively long Ir-C distances (2.122 and 2.094 Angstrom) reflect the strong mutual trans effect of the cyclometalating carbons. The complex exhibits strong visible absorption and long-lived (1.7,mus) 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 predominately ligand-to-ligand charge transfer (dppy --> 2,2':6',2-terpyridine) in nature.