A novel class of π-conjugated systems, which combine the indolo[3,2-b]carbazole unit with the formation of four-coordinate boron complexes, is presented. The resulting conjugated compounds have a double-laddered structure that provides interesting optical and electrochemical properties. The wide absorption range, covering most of the visible spectrum, along with the narrowing of the HOMO-LUMO energy gap, due to the presence of diphenylboryl centers, reinforces the potential of these molecules within the area of organic electronics.

The synthesis and electrochemical, optical, and cation-sensing properties of the ferrocene-triazole-pyridine triads 3 and 5 are presented. Azidoferrocene 1 and 1,1'-diazidoferrocene 4 underwent the "click" reaction with 2-ethynylpyridine to give the triads 3 and 5 in 81% and 68% yield, respectively. Electrochemical studies carried out in CH(3)CN in the presence of increasing amounts of Zn(2+), Ni(2+), Cd(2+), Hg(2+), and Pb(2+) metal cations, showed that the wave corresponding to the ferrocene/ferrocenium redox couple is anodically shifted by 70-130 mV for triad 3 and 167-214 mV for triad 5. The maximum shift of the ferrocene oxidation wave was found for 5 in the presence of Zn(2+). In addition, the low-energy band of the absorption spectra of 3 and 5 are red-shifted (Δλ = 5-10 nm) upon complexation with these metal cations. The crystal structures of compounds 3 and 5 and the complex [3(2)·Zn](2+) have been determined by single-crystal X-ray methods. (1)H NMR studies as well as density functional theory calculations have been carried out to get information about the binding sites that are involved in the complexation process.

A number of monosubstituted (3, 4, 6, 8, 9, 11, and 13) and disubstituted (15 and 16) ferrocene-derived triazoles have been prepared, by using the copper-catalyzed click reaction, and fully characterized. The versatility of the click reaction enables the decoration of the ferrocene-triazole core, with additional substituents displaying different optoelectrochemical properties. The most salient features derived from the sensing studies are that receptors 3, 6, 15, and 16 undergo unprecedented cathodic shifts of the oxidation peak of the ferrocene/ferrocenium redox couple in the presence of F–, AcO–, H2PO4 –, and HP2O7 3– anions, whereas receptors 11 and 16 behave as dual redox and optically selective molecular sensors for Hg2+ cations. The isolated [6 3·Ni2+] complex has been characterized by X-ray analysis.

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Natures reliance on multivalency [1] as a means [2] of compensating for weak monovalent protein-ligand interactions is now a widely accepted phenomenon [3] which controls a panoply of biological events and whose delicate manipulations could have far-reaching therapeutic implications. In recent times, the physical basis of multivalency effects, based on a thermodynamic model combined with computational studies, has been explored rigorously [4] and a comprehensive thermodynamic investigation of the calcium-EDTA interactions has been reported.[5] Since thermodynamics seem, by and large, [6] to rule the roost as far as multivalency is concerned, it occurred to us that it should be the perfect phenomenon to probe using the concept of dynamic covalent chemistry.[7] Herein we describe a situation in which the concept works in the exclusive context of the phenomenon; that is, dynamic covalent chemistry can be achieved in a highly efficient manner using multivalent ligands, but fails altogether when no ligand or a monovalent counterpart is employed.As a part of some on-going research to probe multivalency in artificial systems [8] exhibiting molecular recognition, we have recently uncovered a compelling example [9] of multivalency between a tritopic receptor, in which three benzo [24]crown-8 rings are fused onto a triphenylene core, and a trifurcated trication, wherein three dibenzylammonium ions are linked 1,3,5 to a central benzenoid core: the outcome is an extremely stable (K a > 10 7 mol L À1 in CH 2 Cl 2 ) triply threaded, two-component superbundle. This observation led subsequently to the template-directed synthesis [10] of a prototype [11] of an artificial molecular machine, [12] namely, a mechanically interlocked, triply threaded, molecular bundle by kinetically controlled post-assembly covalent modification. The advent of dynamic covalent chemistry [7] has, however, opened up an attractive alternative route [13] to mechanically interlocked molecules which relies upon the thermodynamically controlled strict self-assembly of their covalently linked components proceeding in unison with mechanical bond formation under the guidance of the templation provided by noncovalent interactions. In particular, it has been shown that 1) the reversible ring-closing metathesis (RCM) reaction and 2) the ring-opening, ringclosing metathesis (RORCM) reaction, also operating under equilibrium control, are both mediated by functional-grouptolerant ruthenium-alkylidene catalysts [14] and can be used [15] in the thermodynamically controlled synthesis of catenanes and rotaxanes. [16] In the specific knowledge that [2]rotaxanes [17] and [3]catenanes, [18] where the supramolecular assistance [19] for their formation comes from the interaction [20] of CH 2 NH 2 + CH 2 ion centers, either by developing olefinic crown ether analogues containing 24-membered rings or with dibenzo [24]crown-8, we decided to explore the possibility that the multivalency effect can be exploited during RCM and RORCM. We demonstrate that it can be exploited in a c...