Optical properties of bicyclometalated Ir(III) and Rh(III) complexes of benzo[h]quinoline with (N∧S)− and (N∧O)− chelating ligands

[M(bzq) 2 (N∧X)] complexes (M = Rh(III), Ir(III); (bzq) − is the deprotonated form of benzo[h]quinoline, and (N∧X) − are 2-thiolpyridine, 2-hydroxypyridine, and 2-thiolbenzothiazole ions) are studied by absorption and emission spectroscopy and voltammetry. The long-wavelength absorption bands of [Rh(bzq) 2 (N∧X)] in the range of 420–424 nm are attributed to the optical metal-to-ligand charge transfer (MLCT) transitions, while the low-temperature (77 K) phosphorescence in the range of 490–610 nm is assigned to the intraligand (IL) transition of the {Rh(bzq) 2 } metal-complex fragment. The phosphorescence of the [Ir(bzq) 2 (N∧X)] complexes in liquid solutions in the range of 585–675 nm is assigned to the radiative MLCT transition, while the low-temperature (77 K) phosphorescence occurs from the thermally nonequilibrium MLCT and IL excited states of the {Ir(bzq) 2 } metal-complex fragment.