The activation of a C_Ph-H bond in the phenyl ring of 3,8-dinitro-6-phenylphenanthridine (HC^{^}N) can be achieved by refluxing the intermediate [PtCl(η³-2-Me-C₃H₄)(HC^{^}N-κN)] (1) (η³-2-Me-C₃H₄ = η³-2-methylallyl) in 2-methoxyethanol to render the new cyclometalated complex [{Pt(?-Cl)(C^{^}N)}₂] (2). The cleavage of the bridging system in 2 by the neutral ligands L rendered the mononuclear complexes [PtCl(C^{^}N)L] (L = tht 3, PPh₃ 4, CN^tBu 5) with the geometry (trans C, Cl).
The air- and temperature-stable cationic compound [Pt(C^{^}N)(CNXyl)₂]ClO₄ (6) could be prepared from 2 by addition of CNXyl (1:4 molar ratio) after the Cl abstraction with AgClO₄. Compound [Pt(C^{^}N-κC)(tht)₃]ClO₄ (7) was prepared similarly to 6 but using a significant excess of tht, which produces the N-dissociation of the C^{^}N ligand. The photophysical properties of compounds 3-6 have been studied with the help of time-dependent density functional theory (TD-DFT) calculations. In 2-Me-THF at low temperature (77 K) the green emission of the HC^{^}N ligand turns to red phosphorescence in compounds 3-6, which was assigned to a mixed metal-to-ligand charge transfer/intraligand/ligand-to-ligand charge transfer [³MLCT/³IL/³L'LCT] excited state. In the solid state at low temperature (77 K) the emissive behaviors are quite similar to that observed in glassy solutions with some contribution of excimeric π-π* emissions in the neutral chloro derivatives. Compounds 4-6 are also emissive in the solid state at room temperature with photoluminescence quantum yields (Φ) between 0.032 and 0.05.