Pt(II) Complexes with a Novel Pincer N∧C∧N 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.

Automated summary

A series of new platinum square planar complexes with various ligands have been synthesized and characterized. These complexes exhibit strong blue emission with high quantum yields and long excited state lifetimes in solid, solution, and polymeric matrix. The molecular architecture can transform to give a heteronuclear complex with the Pt-Ag-Pt coordination core.