Series of New Cationic Iridium(III) Complexes with Tunable Emission Wavelength and Excited State Properties:  Structures, Theoretical Calculations, and Photophysical and Electrochemical Properties

A series of new cationic iridium (III) complexes Ir (piq) 2 (N/) +PF6- (1-6) (piq =1-phenyl-isoquinoline) containing N/ ligands with different conjugated lengths were synthesized, where the six N/ ligands were bipyridine, phenanthroline, 2-pyridyl-quinoline, 2, 2'-biquinoline, 1, 1'-biisoquinoline, and 2- (2-quniolinyl) quinoxaline. Single-crystal X-ray diffraction spectra of three complexes were studied, and the iridium (III) centers were found to adopt a distorted octahedral coordination geometry with cis metalated carbons and trans nitrogen atoms. UV-vis, photoluminescence, cyclic voltammetry, and theoretical calculations were employed for studying the photophysical and electrochemical properties. And the excited-state properties were investigated in detail. The excited state of complexes is complicated and contains triplet metal-to-ligand charge transfer (3MLCT), triplet ligand-to-ligand charge transfer (3LLCT), and ligand-centered (cyclometalated) (3LC) transitions simultaneously. Importantly, the emission wavelength can be tuned significantly from 586 to 732 nm by changing the conjugated length of N/ ligands.