Pt(II) Complexes with a Novel Pincer NCN Ligand: Synthesis, Characterization, and Photophysics

A series of new platinum square planar complexes [Pt(NCN)L](+/0) with the pincer (NCN)-C-boolean AND-N-boolean AND cyclometallated ligand (NC(H)N = 1,3-bis(1-phenyl-1H-phenanthro[9,10-d]imidazol-2-yl)benzene) containing the following L: Cl-, acetonitrile, pyridine, dimethylaminopyridine, 2,6-dimethylphenylisocyanide, has been synthesized. Application of bridging acetate ion as L ligand allowed obtaining a binuclear [Pt(NCN)](2)OOCCH3 complex. The bulky and rigid structure of (NCN)-C-boolean AND-N-boolean AND-ligand provokes instability of its pincer coordination that makes possible transformation of the molecular architecture to give a heteronuclear complex with the Pt-Ag-Pt coordination core. The composition and structure of the obtained compounds were characterized in solution and in the solid state using ESI mass-spectrometry, NMR spectroscopy, elemental analysis, and single-crystal XRD crystallography. The complexes luminesce in solid state, solution, and in polymericmatrix demonstratingmoderate to bright emission at ca. 550 nmwith quantumyields up to 22% and lifetime of excited state up to 22 mu s. TD DFT computational approach togetherwith analysis of the photophysical properties in differentmedia reveals the predominant ligand-centered (IL)-I-3 nature of the radiative excited state localized at the (NCN)-C-boolean AND-N-boolean AND-ligand. The ancillary ligand L demonstrates aminor influence on the energy of emission but affects dramatically emission efficiency and lifetime. The chloride complex displays dual (fluorescence and phosphorescent) luminescence due to labile coordination of an N-coordinated functionality that produces a dangling aromatic fragment, which gives emission froma singlet excited state.