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](-) (λ(max) = 665 nm) to [IrSSO2](-) (λ(max) = 556 nm) and to [IrSO2SO2](-) (λ(max) = 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.