We report in this work a new family of bis-tridentate ruthenium(II) and osmium(II) complexes bearing a terpyridyl ligand rigidly link to pyrenyl-benzimidazole moiety (tpy-HImzPy = 10-(4-[2,2':6',2''-terpyridine]terpyridin-4'-yl-phenyl)-9H-9,11-diaza-cyclopenta[e]pyrene) along with other tridentate ligands such as 4'-(2-naphthyl)-2,2':6',2″-terpyridine (tpy-NaPh) and 2,6-bis(benzimidazole-2-yl)pyridine (H2pbbzim). All the complexes are thoroughly characterized by their elemental analysis, ESI mass spectrometry, and (1)H NMR spectroscopy. The molecular structures of two complexes [Ru(tpy-HImzPy)2](ClO4)2 (3) and [(pbbzim)Ru(tpy-HImzPy)] (2a) in the solid state were determined by X-ray crystallography. The absorption, steady-state, and time-resolved luminescence and electrochemical properties of all the four compounds have been studied. On excitation at their MLCT bands, all four compounds exhibit moderately strong room-temperature luminescence with lifetimes ranging between 3.8 and 161.1 ns in aerated condition, whereas in the deaerated (N2 purged) condition, the lifetimes vary between 8.2 and 199.1 ns, depending upon the nature of the solvents. The presence of imidazole N-H protons in all the complexes motivates us to study anion sensing properties of the complexes in solution through different channels. Spectrophotometeric, fluorometric, (1)H NMR spectroscopic, and cyclic voltammetric studies of the complexes in presence of anions reveal that the complexes sense principally F(-), CN(-), and to a lesser extent for AcO(-). Multichannel anion sensing studies also indicate that anion-induced deprotonation of the imidazole N-H protons occur in all four compounds. The equilibrium constant of this deprotonation steps have been estimated from UV-vis absorption and emission titration data. Anion-induced modulation of lifetimes makes all the four complexes suitable for lifetime-based sensors for selective anions.

We report in this work a new family of homo- and heterobimetallic complexes of the type [(bpy)2M(Py-Biimz)M'(II)(bpy)2](2+) (M = M' = Ru(II) or Os(II); M = Ru(II) and M' = Os(II)) derived from a pyrenyl-biimidazole-based bridge, 2-imidazolylpyreno[4,5-d]imidazole (Py-BiimzH2). The homobimetallic Ru(II) and Os(II) complexes were found to crystallize in monoclinic form with space group P21/n. All the complexes exhibit strong absorptions throughout the entire UV-vis region and also exhibit luminescence at room temperature. For osmium-containing complexes (2 and 3) both the absorption and emission band stretched up to the NIR region and thus afford more biofriendly conditions for probable applications in infrared imaging and phototherapeutic studies. Detailed luminescence studies indicate that the emission originates from the respective (3)MLCT excited state mainly centered in the [M(bpy)2](2+) moiety of the complexes and is only slightly affected by the pyrene moiety. The bimetallic complexes show two successive one-electron reversible metal-centered oxidations in the positive potential window and several reduction processes in the negative potential window. An efficient intramolecular electronic energy transfer is found to occur from the Ru center to the Os-based component in the heterometallic dyad. The binding studies of the complexes with DNA were thoroughly studied through different spectroscopic techniques such as UV-vis absorption, steady-state and time-resolved emission, circular dichroism, and relative DNA binding study using ethidium bromide. The intercalative mode of binding was suggested to be operative in all cases. Finally, computational studies employing DFT and TD-DFT were also carried out to interpret the experimentally observed absorption and emission bands of the complexes.

Two heterobimetallic Ru(II)-Os(II) complexes of compositions [(bpy)2M(II)(phen-Hbzim-tpy)M'(II)(tpy-PhCH3)](4+), where M(II) = Ru and M'(II) = Os (4) and M(II) = Os and M'(II) = Ru (5), phen-Hbzim-tpy = 2-(4-(2,6-di(pyridin-2-yl)pyridine-4-yl)phenyl)-1H-imidazole[4,5][1,10]phenanthroline, bpy = 2,2'-bipyridine, and tpy-PhCH3 = 4'-(4-methylphenyl)-2,2':6',2''-terpyridine have been synthesized and characterized by elemental analyses, ESI mass spectrometry, and (1)H NMR and UV-vis absorption spectroscopy. The absorption spectra, redox behavior, and luminescence properties of the complexes have been thoroughly investigated and compared with that of monometallic model compounds [(bpy)2M(II)(phen-Hbzim-tpy)](2+) [M(II) = Ru (1) and M(II) = Os (2)] and [(phen-Hbzim-tpy)Ru(II)(tpy-PhCH3)](2+) (3). The complexes display very intense, ligand-centered absorption bands in the UV and moderately intense MLCT bands in the visible regions. The bimetallic complexes show two successive one-electron reversible metal-centered oxidations, whereas the monometallic complexes display one-electron oxidation in the positive potential window. Steady state and time-resolved luminescence data at room temperature show that an efficient intramolecular electronic energy transfer takes place from the Ru-center to the Os-based component in both the heterometallic dyads in all the solvents. The complexes under investigation contain an imidazole NH proton which became appreciably acidic due to metal coordination and can be utilized for recognition of selective anions in solution either via hydrogen bonding interaction or by proton transfer. Accordingly, the anion binding properties of the two heterobimetallic complexes as well as parent bridging ligand, phen-Hbzim-tpy, have been studied in solutions using absorption, steady state and time-resolved luminescence spectral measurements. The metalloreceptors act as sensors for F(-), CN(-) and AcO(-) ions. It is evident from sensing studies that in the presence of excess of selective anions, deprotonation of the imidazole N-H proton occurs in all cases.

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 emitting MLCT state and nonemitting metal-centered stateMC in the complexes increased enormously compared with parent [Ru(tpy)]. 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, and 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.

We designed in this work a new family of anthraquinone and imidazole functionalized bifunctional terpyridine receptor, 2-(4-(2,6-di­(pyridine-4-yl)­phenyl)-1H-anthra­[1,2-d]­imidazole-6,11-dione (tpy-HPhImz-Anq) for recognition and sensing of selective anions and cations as well as for the construction of multifunctional logic devices. The terpyridine motif in the receptor was utilized for the cation coordination site and the imidazole moiety as the anion binding site. Both anion and cation recognition aspects of the receptor were thoroughly investigated in acetonitrile, mixed DMSO–water, as well as in solid media via different optical channels such as absorption, steady state, and time-resolved emission spectroscopic techniques. On the basis of the absorption and emission spectral responses toward a specific set of ionic inputs, this unique bifunctional receptor can mimic several advanced logic functions such as those of half-subtractor, key-pad lock, and memory device. We also report the implementation of the fuzzy logic approach to develop an infinite-valued logic system based on the luminescence dependence of the receptor upon concentration of different ionic inputs. In conjunction with the experimental investigation, density functional theory (DFT), and time-dependent density functional theory (TD-DFT), studies were carried out to investigate the structural and electronic properties of the receptor.