Transition-metal-containing rotaxanes can behave as linear motors at the molecular level. The molecules are set into motion either by an electrochemical reaction or using a chemical signal. In a first example, a simple rotaxane is described that consists of a ring threaded by a two-coordination-site axle. The ring contains a bidentate ligand, coordinated to a copper center. The axle incorporates both a bidentate and a terdentate ligand. By oxidizing or reducing the copper center to Cu(II) or Cu(I) respectively, the ring glides from a given position on the axle to another position and vice versa. By generalizing the concept to a rotaxane dimer, whose synthesis involves a quantitative double-threading reaction triggered by copper(I) complexation, a molecular assembly reminiscent of a muscle is constructed. By exchanging the two metal centers of the complex (copper(I)/zinc(II)), a large-amplitude movement is generated, which corresponds to a contraction/stretching process. The copper(I)-containing rotaxane dimer is in a stretched situation (overall length approximately 8 nm), whereas the zinc(II) complexed compound is contracted (length approximately 6.5 nm). The stretching/contraction process is reversible and it is hoped that, in the future, other types of signals can be used (electrochemical or light pulse) to trigger the motion.

A terpyridine ruthenium (II) complex containing a substituted and an unsubstituted terpyridine ligand was synthesized, and its luminescence properties were studied in a solid-state single-layer light-emitting electrochemical cell. The obtained devices emitted light of a very deep red color (CIE, x = 0.717 y = 0.282) at low external applied bias. It is the first example of an electroluminescence device based on a bis-chelated ruthenium complex. Its ambient atmosphere decay is remarkably different from analogous devices using tris-chelated ruthenium complexes.

Three different multicomponent molecular systems have been synthesized by means of the three-dimensional template effect of copper(I). These systems incorporate both a coordinating ring (2,9-diphenyl-1,10-phenanthroline-containing 30-membered ring) and a molecular string which consists of two different coordination sites (2,9-disubstituted-1,10-phenanthroline and 5,5‘ ‘-disubstituted-2,2‘:6‘,2‘ ‘-terpyridine unit). Each end of the string could be functionnalyzed by a small group or by a bulky stopper (tris(p-tert-butylphenyl)(4-hydroxyphenyl)methane), leading to an unstoppered compound, to a semi-rotaxane, or to a real rotaxane. As in the case of a disymmetrical copper [2]-catenane, large reversible molecular motions have been induced both electrochemically and photochemically. The driving force of the rearrangement processes is the high stability of two markedly different coordination environments for the copper(I) and copper(II) ions. In the copper(I) state, two phenanthroline units (one of the ring, one of the string) interact with the metal ion in a tetrahedral geometry (CuI (4)), whereas in the copper(II) state, one phenanthroline belonging to the ring and the terpyridine of the string afford a five-coordinate geometry (CuII (5)). The rates of the molecular motion processes (from CuII (4) to CuII (5) and from CuI (5) to CuI (4)) are respectively faster and slower (minutes time scale) as compared to those for the catenane species. This result could be interpreted on the basis of structural differences between the rotaxane and catenane systems.

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Two ruthenium(II)-based complexes were prepared that show intense deep-red light emission at room temperature. Solid-state electroluminescent devices were prepared using one of the ruthenium complexes as the only active component. These devices emit deep-red light at low voltages and exhibit extraordinary stabilities, demonstrating their potential for low-cost deep-red light sources.

[structure: see text] The selectivity and sensitivity of a benzothiazolium hemicyanine dye toward mercury(II) in aqueous solutions are described. Mercury ions coordinate to the dye forming a 1:1 complex. This interaction induces a color change in the dye at micromolar concentrations of mercury. Furthermore, the color change and quenching of the dye emission are selective for mercury when compared with other ions such as lead(II), cadmium(II), zinc(II), or iron(II).

The present work aims to give insight into the effect that metal coordination has on the room-temperature conductance of molecular wires. For that purpose, we have designed a family of rigid, highly conductive ligands functionalized with different terminations (acetylthiols, pyridines, and ethynyl groups), in which the conformational changes induced by metal coordination are negligible. The single-molecule conductance features of this series of molecular wires and their corresponding Cu(I) complexes have been measured in break-junction setups at room temperature. Experimental and theoretical data show that no matter the anchoring group, in all cases metal coordination leads to a shift toward lower energies of the ligand energy levels and a reduction of the HOMO-LUMO gap. However, electron-transport measurements carried out at room temperature revealed a variable metal coordination effect depending on the anchoring group: upon metal coordination, the molecular conductance of thiol and ethynyl derivatives decreased, whereas that of pyridine derivatives increased. These differences reside on the molecular levels implied in the conduction. According to quantum-mechanical calculations based on density functional theory methods, the ligand frontier orbital lying closer to the Fermi energy of the leads differs depending on the anchoring group. Thereby, the effect of metal coordination on molecular conductance observed for each anchoring could be explained in terms of the different energy alignments of the molecular orbitals within the gold Fermi level.