A photochemical and photophysical investigation was carried out on (tbubpy)Pt-II(dpdt) and (tbubpy)Pt-II(edt) (1 and 2, respectively, where tbubpy = 4,4’-di-tert-butyl-2,2’-bipyridine, dpdt = meso-1,2-diphenyl-1,2-ethanedithiolate and edt = 1,2-ethanedithiolate). Luminescence and transient absorption studies reveal that these complexes feature a lowest excited state with Pt(S)(2) --> tbubpy charge transfer to diimine character. Both complexes are photostable in deoxygenated solution; however, photolysis into the visible charge transfer band in air-saturated solution induces moderately efficient photooxidation. Photooxidation of 1 produces the dehydrogenation product (tbubpy)Pt-II-(1,2-diphenyl-1,2-ethenedithiolate) (4). By contrast, photooxidation of 2 produces S-oxygenated complexes in which one or both thiolate ligands are converted to sulfinate (-SO(2)R) ligands. Mechanistic photochemical studies and transient absorption spectroscopy reveal that photooxidation occurs by (1) energy transfer from the charge transfer to diimine excited state of 1 to O-3(2) to produce O-1(2) and (2) reaction between O-1(2) and the ground state 1. Kinetic data indicates that excited state 1 produces O-1(2) efficiently and that reaction between ground state 1 and O-1(2) occurs with k approximate to 3 x 10(8) M(-1) s(-1).