The starting complexes [PtCl(C^N)(dmso)], in which C^N is either ppy = 2-phenylpyridinate, , or bhq = 7,8-benzo[h]quinolinate, , were prepared by a known method using the reaction of [PtCl2(dmso)2] with ppyH or bhqH, respectively, in toluene under reflux conditions. The reaction of [PtCl(C^N)(dmso)], or , with 1 equiv. of a number of biphosphine ligands, P^P, gave the cationic monomeric complexes [Pt(ppy)(P^P)]Cl, for which P^P is either 1,2-bis(diphenylphosphino)ethane (dppe), , 1,3-bis(diphenylphosphino)propane (dppp), , or bis(diphenylphosphino)methane (dppm), ; the bhq analogous complex [Pt(bhq)(dppe)]Cl, , was prepared similarly. However, the complex [Pt(ppy)(dfppe)]Cl, , in which dfppe is 1,2-bis(dipentafluorophenylphosphino)ethane, was prepared by the reaction of with excess amount of dfppe. When each of the starting complexes [PtCl(C^N)(dmso)], or , were reacted with 0.5 equiv. of any of the P^P ligands, the dimeric complexes [Pt2Cl2(ppy)2(μ-P^P)], , or [Pt2Cl2(bhq)2(μ-P^P)], , were formed. The complexes were fully characterized using multinuclear ((1)H and (31)P) NMR spectroscopy and elemental analysis. The structures of typical complexes , , , and were also confirmed by X-ray crystallography. The effect of ligands on the luminescent properties of the complexes was investigated and DFT calculations were performed to confirm the assignments.

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Cycloplatinated(ii) complexes 1–4 were synthesized and characterized. All complexes exhibit strong luminescence except 3.

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.