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 boolean AND N)](+) PF6- ( 1 - 6) ( piq = 1-phenyl-isoquinoline) containing N boolean AND N ligands with different conjugated lengths were synthesized, where the six N boolean AND 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 ( (MLCT)-M-3), triplet ligand-to-ligand charge transfer ( (LLCT)-L-3), and ligand-centered ( cyclometalated) ( (LC)-L-3) transitions simultaneously. Importantly, the emission wavelength can be tuned significantly from 586 to 732 nm by changing the conjugated length of N boolean AND N ligands.