Synthesis and Spectroscopy of Anionic Cyclometalated Iridium(III)-Dithiolate and -SulfinatesEffect of Sulfur Dioxygenation on Electronic Structure and Luminescence

A new anionic heteroleptic Ir­(III)-dithiolate
complex Ir­(ppy)2(benzene-1,2-dithiolate) (ppy = 2-phenylpyridine,
[IrSS]−) undergoes very fast air oxidation
to form a monosulfinate complex [IrSSO2]−, which can be further dioxygenated by
O2 or H2O2 to give a disulfinate
complex [IrSO2SO2]−, which has been characterized
by X-ray crystallography. The dioxygenation is accompanied by changes
in the electronic structures of the complexes, leading to blue shift
of emission from [IrSS]− (λmax = 665 nm) to [IrSSO2]− (λmax = 556 nm) and to [IrSO2SO2]− (λmax = 460 nm). The
molecular and electronic structures of the complexes are probed by
DFT calculations. Time-dependent DFT (TD-DFT) calculations show the
lowest energy spin-allowed electronic transitions for [IrSS]− and [IrSSO2]− are mainly ligand (3p orbital of S)-to-ligand
(π* orbitals of ppy)-charge-transfer transition, whereas the
lowest energy electronic transition in [IrSO2SO2]− is predominantly metal-to-ligand-charge transfer in nature.