Mononuclear complexes [Pt­(ppy)­(S∧S)] (1a, S∧S = O,O′-di­(cyclohexyl)­dithiophos­phate (ctp); 2a, S∧S = O,O′-di­(butyl)­dithiophos­phate (btp)) and [Pt­(bzq)­(S∧S)] (1b, S∧S = ctp; 2b, S∧S = btp) have been prepared by the reaction of precursor complexes [Pt­(C∧N)­Cl­(dmso)], C∧N = deprotonated form of 2-phenylpyrdine (ppy) and 7,8-benzoquinoline (bzq), and potassium salt of S∧S ligands. All complexes were characterized by NMR spectroscopy, and the structure of 2b was further identified by single crystal X-ray determination. Although the complexes are not luminescent in solution at ambient temperature, they become strong emissive materials (bright green) in solid state (at room temperature) with high quantum yields and long lifetimes in the microsecond domain. In frozen glass state or at low temperature (solid state), these complexes become better emissive in relation to room temperature. UV–vis spectra, supported by TD-DFT calculations, indicate that 1ILCT (intraligand charge transfer) predominates over the other transitions (L = C∧N cyclometalated ligand). Accordingly, 1 and 2 exhibit structured emission bands which display a large involvement of 3LCCT (ligand-centered charge transfer) with lower contribution of 3MLCT (metal to ligand charge transfer) transition in the excited states. Also, biological activities of 1 and 2 were evaluated against three human cancer cell lines including A549 (human lung cancer), SKOV3 (human ovarian cancer), and MCF-7 (human breast cancer). 2a presented an effective potent cytotoxic activity regarding to the cell lines. The cellular localization of 1a and 2a in MCF-7 human cells was investigated by fluorescence microscopy.

The known cyclometalated platinum(II) complex [Pt(ppy)(DMSO)(Cl)] (A) in which ppy = 2‐phenylpyridinate, was treated with 2‐(diphenylphosphino)pyridine (PPh2py, PN) (1 equiv.) and readily afforded complex [Pt(ppy)(PPh2py‐κ1P)(Cl)] (1). The transphobia effect (T) and single‐crystal X‐ray diffraction crystallography confirmed that the phosphine ligand in 1 is located trans to the nitrogen atom of the cyclometalating fragment (ppy). Compound 1 was treated with various thiolate reagents (1 equiv.) at room temperature, leading to the displacement of the chloride ligand in 1 by thiolate ligands through a salt metathesis reaction. The reaction led to the formation of a series of monomeric complexes with the general formula [Pt(ppy)(PPh2py‐κ1P)(SR)] (2a–2d), where SR = deprotonated form of pyridine‐2‐thiol (HSpy, 2a), pyrimidine‐2‐thiol (HSpyN, 2b), thiophenol (HSPh, 2c), and 2‐thiazoline‐2‐thiol (HSt, 2d). All complexes have been characterized by NMR spectroscopy. The biological activities of the complexes were evaluated against three human cancer cell lines, including A549 (human lung cancer), SKOV3 (human ovarian cancer), and MCF7 (human breast cancer), by means of the MTT assay [MTT = 3‐(4,5‐dimethylthiazol‐yl)‐2,5‐diphenyltetrazolium bromide]. Compounds 2a and 2b presented effective, potent cytotoxic activity regarding the cell lines. Electrophoretic mobility shift assays on plasmid DNA and molecular modeling investigations were also performed to determine the specific binding mode or the binding orientation of the complexes to DNA.