In this paper we have utilized a heteroditopic polypyridyl− imidazole system 4′-[4-(4,5-dipyridin-2-yl-1H-imidazol-2-yl)-phenyl]-[2,2′;6′,2″]terpyridine (tpy-Hbzim-dipy), wherein the terpyridine moiety has been utilized as the cation binding site and the imidazole motif as the anion binding site. This system is an efficient deep-blue emitter in chloroform with Commission Internationale de L'Eclairage (CIE) coordinates of 0.14 and 0.06. On the basis of the response profiles in terms of absorption or emission intensity and wavelength toward selected anions and cations, we developed a molecular system which can mimic sequential Boolean logic functions capable of integrating into a "Writing−Reading−Erasing−Reading" combinational circuit. In this work, we also examined the effect of selective anions and cations on the optical properties of the receptor by means of computational (DFT and TD-DFT) studies.

A mixed-ligand monometallic ruthenium(ii) complex of composition [(bipy)2Ru(tpy-Hbzim-dipy)](ClO4)2 (), where tpy-Hbzim-dipy = 4'-[4-(4,5-di-pyridin-2-yl-1H-imidazol-2-yl)-phenyl]-[2,2';6',2'']terpyridine and bipy = 2,2'-bipyridine has been synthesized and characterized using standard analytical and spectroscopic techniques including X-ray crystallography. The complex displays very intense, ligand centered absorption bands in the UV and moderately intense MLCT bands in the visible region. On excitation at the MLCT bands, the complex exhibits strong luminescence at room temperature with lifetimes in the range of 116-257 ns, depending upon the nature of the solvents. The complex is found to undergo one reversible oxidation in the positive potential window (0 to +1.8 V) and two successive quasi-reversible reductions in the negative potential window (0 to -2.0 V). Both anion and cation binding properties of the receptor were thoroughly investigated in acetonitrile solution using (1)H NMR, absorption, steady state and time-resolved emission spectral studies and by cyclic voltammetry. The anion sensing studies revealed that the receptor acts as a "turn on" luminescence sensor for H2PO4(-) and HSO4(-) ions, and as a "turn off" sensor for F(-) and AcO(-) ions. It is evident that in the presence of excess F(-) and AcO(-) ions, deprotonation of the imidazole N-H fragment of the receptor occurs, an event which is signaled by the change of color from orange yellow to red visible to the naked eye. On the other hand, the probable mode of interaction of the receptors with H2PO4(-) and HSO4(-) ions is through hydrogen bonding interaction. The cation-sensing properties showed that the receptor was found to exhibit a colorimetric sensing ability that was highly selective for Fe(2+), as evidenced by the distinct color change from yellow orange to deep red-violet to the naked eye over the other cations studied (Mn(2+), Fe(3+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), and Hg(2+)).

Combined experimental and density functional theory (DFT) and time-dependent density functional theory (TD-DFT) studies were carried out to investigate the structural and electronic properties of a terpyridyl-phenylimidazole system covalently linked to pyrene, 10-(4-[2,2':6',2"-terpyridine]terpyridin-4'-yl-phenyl)-9H-9,11-diazacyclopenta[e]pyrene (tpy-HImzPy). X-ray crystal structure determination shows that the compound crystallized in monoclinic form with the space group P21/c. The anion and cation sensing properties of tpy-HImzPy were thoroughly studied in dimethyl sulfoxide and in mixed dimethyl sulfoxide-water medium through different channels such as absorption, steady-state and time-resolved emission, and (1)H NMR spectroscopic methods. In this work, by grafting the pyrene moiety into the terpyridyl chelating unit, an intraligand-charge-transfer sensitive chromophore has been developed whose absorption and emission behaviors are highly sensitive to selective anions and cations, and the response profiles in terms of absorption or emission intensity and wavelength toward the tested ions varied quite a lot. On the basis of these observations, we developed a unique molecular system capable of performing multiple logic functions such as INHIBIT, OR, XOR, NOR, and XNOR by simply varying the combination and level of various ionic inputs in a systematic manner. In this work, we will also be particularly interested to see the effect of selective anion and cation on the optical properties of receptor by means of computational studies and correlate them with the experimentally observed data.

A new family of trimetallic complexes of the form [(bpy)2 M(phen-Hbzim-tpy)M'(tpy-Hbzim-phen)M(bpy)2](6+) (M=Ru(II), Os; M'=Fe(II), Ru(II), Os; bpy=2,2'-bipyridine) derived from heteroditopic phenanthroline-terpyridine bridge 2-{4-[2,6-di(pyridin-2-yl) pyridine-4-yl]phenyl}-1H-imidazole[4,5-f][1,10]phenanthroline (phen-Hbzim-tpy) were prepared and fully characterized. Zn(2+) was used to prepare mixed-metal trimetallic complexes in situ by coordinating with the free tpy site of the monometallic precursors. The complexes show intense absorptions throughout the UV/Vis region and also exhibit luminescence at room temperature. The redox behavior of the compounds is characterized by several metal-centered reversible oxidation and ligand-centered reduction processes. Steady-state and time-resolved luminescence data show that the potentially luminescent Ru(II)- and Os(II)-based triplet metal-to-ligand charge-transfer ((3)MLCT) excited states in the triads are quantitatively quenched, most likely by intercomponent energy transfer to the lower lying (3)MLCT (for Ru and Os) or triplet metal-centered ((3)MC) excited states of the Fe(II) subunit (nonluminescent). Interestingly, iron did not adversely affect the photophysics of the respective systems. This suggests that the multicomponent molecular-wire-like complexes investigated here can behave as efficient light-harvesting antennas, because all the light absorbed by the various subunits is efficiently channeled to the subunit(s) in which the lowest-energy excited states are located.

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