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∧N)]+PF6- (1−6) (piq =1-phenyl-isoquinoline) containing
N∧N ligands with different conjugated lengths were synthesized, where the six N∧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∧N ligands.