Highly Luminescent Mono- and Dinuclear Cationic Iridium(III) Complexes Containing Phenanthroline-Based Ancillary Ligand

A new family of mononuclear (1-2) and dinuclear (3-5) cationic iridium(III) complexes have been synthesized and fully characterized. These complexes contain 2-(4-(trifluoromethyl)phenyl)pyridine (cf(3)ppy, L1) and 1-(4-(trifluoromethyl)phenyl)isoquinoline (cf(3)piq, L2) as cyclometalating ligands, 1,10-phenanthroline (LX-1) as the ancillary ligand and 1,4-bis(1-phenyl-1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)benzene (biphen, LX-2) as the bridging ligand. The crystal structure of LX-2 has been determined by X-ray analysis. All of the complexes are green-red emissive with quantum yields of 16.6-93.5 % and lifetimes of 1.66-2.89 mu s in solution at room temperature. Density functional theory (DFT) calculations have been carried out to gain insight into the nature of the low-lying transitions and also to rationalize the electrochemical and photophysical properties. These research results reveal that the pi-conjugation system of (CN)-N-<^> ligands and the diiridium system with conjugated bridging ligand are both benefical for the red-shift of the absorption and emission spectra.