Iridium cyclometalated complexes with axial symmetry:: Time-dependent density functional theory investigation of trans-bis-cyclometalated complexes containing the tridentate ligand 2,6-diphenylpyridine

new series of iridium cyclometalated complexes with a Cboolean ANDNboolean ANDC dppy-type ligand and a Nboolean ANDNboolean ANDN tpy-type ligand have been synthesized and characterized by various techniques such as mass spectrometry, H-1 and C-13 NMR, cyclic voltammetry, both steady-state and time-resolved emission and absorption studies, and time-dependent DFT (TDDFT) calculations. The complexes exhibit strong visible absorptions and long-lived (1.6-2.0 mus) emissions (lambda(max), ca. 680 nm) in room-temperature solution. DFT calculations on the ground-state geometry match that of an X-ray crystal structure. TDDFT calculations give accurate predictions of the electronic absorption energies and intensities, while geometry optimizations on the lowest energy triplet state give accurate energies for the emission. Examination of the relevant molecular orbitals shows that the inherent asymmetry of the coordination environment offers a unique directional character to the emitting excited state, which is predominately LLCT (dppy --> tpy) in nature.