Synthesis, characterization, and investigation of photophysical and redox behaviors of a new class of homoand heterotrimetallic complexes of composition [(bpy/ phen) 2 Ru(dipy-Hbzim-tpy)M(tpy-Hbzim-dipy)Ru(bpy/ phen) 2 ] 6+ (M = Fe II , Ru II , and Os II ) derived from a conjugated heteroditopic bipyridine−terpyridine bridge were carried out in this work. Trimetallic RuZnRu complexes of composition [(bpy/phen) 2 Ru(dipy-Hbzim-tpy)Zn(tpy-Hbzim-dipy)Ru(bpy/phen) 2 ] 6+ were also synthesized in situ as their photophysical properties are of particular interest in demonstrating the absorption and emission spectra of the complexes in the presence of a metal (Zn 2+ ) that has neither metal-toligand charge transfer (MLCT) nor metal-centered ( 3 MC) states. Complexes display intense absorption bands spanning almost the entire UV and visible region. The complexes also exhibit rich electrochemical behaviors with a number of metal-centered reversible oxidation and ligand-centered reduction waves. All complexes are luminescent at room temperature, and timeresolved emission spectral studies indicate that peripheral Ru II -centered emissive 3 MLCT states are quantitatively quenched, by intramolecular energy transfer to the low lying 3 MLCT (for central Ru and Os) or 3 MC states of the Fe II center (nonluminescent). Interestingly, Fe(II) does not adversely deteriorate the photophysics of the RuFeRu assembly. Thus, multicomponent complexes in the present work can serve as well-organized light-harvesting antennas as the light absorbed by multiple chromophoric subunits is efficiently channeled to the distinct component having the lowest-energy excited state.

Two pyrenyl-biimidazole based mononuclear Ru(II) and Os(II) complexes of the type [(bpy)2M(Py-BiimzH2)](2+) (M = Ru(II) and Os(II)), where Py-BiimzH2 = 10-(1-H-imidazole-2-yl)-9H-pyreno[4,5-d]imidazole and bpy = 2,2'-bipyridine, have been synthesized and thoroughly characterized in this work using various analytical tools and spectroscopic techniques. These complexes were designed to recognize and sense cyanide ions in pure aqueous media. The single crystal X-ray structure of the Ru(II) complex shows that the compound is crystallized in a monoclinic system with the P2(1)/c space group. Both complexes show intense absorptions throughout the entire UV-vis region and also exhibit luminescence at room temperature. In case of Os(II), both the absorption and emission bands stretched up to the NIR region and thus a more bio-friendly condition for the detection of the anions is provided. Both steady state and time-resolved studies suggest that the emission originates predominantly from the (3)MLCT excited state mainly centered in the [M(bpy)2](2+) moiety of the complexes which is only slightly affected by the pyrene moiety. The electrochemical properties of the complexes are characterized using one reversible metal-centered oxidation and several ligand-centered reduction processes. The anion sensing properties of the complexes in both acetonitrile and pure aqueous media were thoroughly examined through different channels such as absorption, steady state and time-resolved emission spectroscopic methods and cyclic and square wave voltammetric measurements. Both complexes possess a very high selectivity towards cyanide ions in aqueous media in the presence of an excess of other anions. Moreover, the complexes display a visual detection of cyanide ions with a very low detection limit of the order of 10(-8) M. Finally, theoretical calculations employing density functional theory (DFT) and time-dependent density functional theory (TD-DFT) were carried out to elucidate the details of the electronic structure and transitions involved in the complexes and their cyanide adducts.

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.

We report here the synthesis, characterization, and photophysics of two bis-tridentate Ru­(II) complexes based on a heteroditopic ligand and thoroughly studied their stimuli-responsive behaviors toward the design of functional materials. Both complexes display emission at room temperature having lifetimes in the range of 0.5–70.0 ns, depending on coligand and solvent. Substantial modulations of absorption and emission spectral behaviors of the complexes were done upon interaction with anions, and anion-induced changes in the properties lead to recognition of selected anions in both organic and aqueous media. Photophysical properties of the complexes were also tuned by changing the pH of the medium, and pK a values in both ground and excited states were determined. The presence of free pyridine-imidazole motifs in the complexes leads to substantial modulation of the optical properties and switching of the emission properties upon interaction with selected cations as well as with protons. Fe2+, Co2+, Ni2+, and Cu2+ trigger emission quenching, while Zn2+ induces finite enhancement of the emission intensity in the complexes. In essence, modulation of the optical properties and switching of luminescence properties of the complexes were accomplished by a variety of the external stimuli such as anions, cations, protons, and pH, as well as solvent polarity. Importantly, the optical outputs in response to an appropriate set of stimuli were utilized to mimic the functions of two-input IMPLICATION, NOR, and XNOR logic gates.

A series of heterobimetallic complexes of compositions [(bpy/phen)Ru(dipy-Hbzim-tpy)Os (tpy-PhCH/Hpbbzim)] (bpy = 2,2'-bipyridine, phen = 1,10-phenanthroline, tpy-PhCH = 4'-(4-methylphenyl)-2,2':6',2''-terpyridine and Hpbbzim = 2,6-bis(benzimidazole-2-yl)pyridine)), derived from a heteroditopic bpy-tpy bridging ligand, were synthesized and thoroughly characterized in this work. The heterometallic complexes exhibit two successive one-electron reversible metal-centered oxidations corresponding to Os/Os at lower potential and Ru/Ru at higher potential. All the four dyads exhibit very intense, ligand centered absorption bands in the UV region and moderately intense MLCT bands in the visible region. The dyads also show intense infrared emission with the emission maximum spanning between 734 nm and 775 nm with reasonably long room temperature lifetimes varying between 30 ns and 104 ns. Both steady state and time resolved luminescence spectroscopic investigations indicate that efficient and fast intramolecular energy transfer from the MLCT state of the Ru(ii) center to the Os-center takes place in all the four dyads. In addition, the rate of energy transfer was found to depend on the terminal ligand on the Os-site. Due to the presence of a number of imidazole NH protons in the dyads, significant modulation of both the ground and excited state properties of the complexes was made possible by varying the pH of the solution. By varying the terminal ligand, pH-induced "on-off", "off-off-on" and "on-off-on" emission switching of the complexes was nicely demonstrated in the infrared region.

No abstract

A new family of bimetallic Ru(ii) complexes derived from an asymmetric bridging ligand (tpy-Hbzim-dipy) consisting of both bipyridine and terpyridine chelating sites covalently connected via phenyl-imidazole spacer were designed in this work to demonstrate intramolecular energy transfer from one component to the other in asymmetric dyads. To fine tune the photo-redox properties, both bidentate and tridentate terminal ligands in the complexes were varied systematically. Both steady state and time-resolved luminescence spectral results indicated photo-induced intramolecular energy transfer from the excited MLCT state of the [(bpy/phen)Ru(dipy-Hbzim-tpy)] component to the MLCT state of the tpy-containing unit [(dipy-Hbzim-tpy)Ru(tpy-PhCH/Hpbbzim)] in dyads with rate constant values on the order of 10-10 s. Temperature-dependent luminescence studies indicated an enhancement in the luminescence intensity and excited state lifetimes upon decreasing the temperature.