Design of Ru(II) Complexes Based on Anthraimidazoledione-Functionalized Terpyridine Ligand for Improvement of Room-Temperature Luminescence Characteristics and Recognition of Selective Anions: Experimental and DFT/TD-DFT Study.

In this work we report synthesis and characterization of three rigid and linear rodlike monometallic Ru(II) complexes based on a terpyridine ligand tightly connected to 9,10-anthraquinone electron-acceptor unit through phenyl-imidazole spacer. The motivation of designing these complexes is to enhance their excited-state lifetimes at room temperature. Interestingly it is found that all three complexes exhibit luminescence at room temperature with excited-state lifetimes in the range of 1.6-52.8 ns, depending upon the coligand as well as the solvent. Temperature-dependent luminescence investigations indicate that the energy gap between the emitting3 MLCT state and nonemitting metal-centered state3 MC in the complexes increased enormously compared with parent [Ru(tpy)2 ]2+ . In addition, by taking advantage of the imidazole NH proton(s), which became appreciably acidic upon combined effect of electron accepting anthraquinone moiety as well as metal ion coordination, we also examined anion recognition and sensing behaviors of the complexes in organic, mixed aqueous-organic as well as in solid medium through different optical channels such as absorption, steady-state and time-resolved emission, and1 H NMR spectroscopic techniques. In conjunction with the experiment, computational investigation was also employed to examine the electronic structures of the complexes and accurate assignment of experimentally observed spectral and redox behaviors.