Tetrathiafulvalene (TTF) derivatives: key building-blocks for switchable processes

Anion responsive TTF-appended calix[4]arenes. Synthesis and study of two different conformers

Two new cone- and 1,3-alternate-calix[4]arenes (cone-1 and 1,3-alt-1), bearing four modified TTF (tetrathiafulvalene) substituents on the upper rim, have been synthesized. The binding ability of these two sets of conformers for various anions, including F(-), Cl(-), Br(-), I(-), PF6(-), ClO4(-), HSO4(-), CH3COO(-), H2PO4(-), and HP2O7(3-), was tested in organic media by monitoring the changes in their UV/vis and (1)H NMR spectra as a function of added anion, as well as via cyclovoltammetry (CV) (all anions studied as their respective TBA salts). On the basis of the present findings, we propose that incorporation of four TTF units within an overall calix[4]arene-based recognition framework produces a preorganized receptor system that displays a modest preference for the pyrophosphate (HP2O7(3-)) anion.

Organogelators based on TTF supramolecular assemblies: synthesis, characterization, and conductive property

A closely related family of organogelators 1-2 appended one or two electroactive tetrathiafulvalene (TTF) residues, has been designed and readily synthesized by Sonogashira reactions. These compounds can gelate a variety of organic solvents in view of multiple intermolecular interactions, and compounds 2 with two TTF subunits exhibit higher gelation ability than their corresponding 1. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) investigation of the xerogels from toluene gave a visual image showing that fibrillar aggregates are entangled in three-dimensional network structures. The columnar TTF cores stacking in the fiber, evidenced by the mixed-valence states absorption at around 2000 nm in ultraviolet-visible-near-infrared (UV-vis-NIR) spectra, provide an efficient pathway for the electron conduction. Upon oxidized by iodine, these xerogels exhibit semiconductive behaviors with moderate levels of conductivity. Additionally, the electrical conductivity of doped-xerogels 2 is 1 order of magnitude higher than that of 1 under identical conditions.

Ion Translocation in Artificial Molecule-based Systems Induced by Light, Electrons, or Chemicals

Synthetic molecules and nanodevices, like their more elaborate biological counterparts, have been shown to perform several sophisticated functions, using even fairly simple molecular architectures. One limitation to developing artificial molecular arrays and networks from these miniscule building blocks is the lack of a unifying strategy whereby they can communicate or interact together, which has been successfully developed in natural systems. Understanding and harnessing these efficient biological processes could prove key in the development of future integrated molecule-based nanodevices and networks. Herein, we give a short overview of some manifestations of intra- and intermolecular communication based on chemical messengers in artificial systems, in some ways analogous to natural systems, which are in turn controlled by light, a redox process or a chemical reaction or interaction. Some advantages, limitations, and challenges are highlighted.

Tetrathiafulvalene diindolylquinoxaline: a dual signaling anion receptor with phosphate selectivity

Incorporation of tetrathiafulvalene into the backbone of a known neutral phosphate receptor, diindolylquinoxaline, yields a dual optical-electrochemical chemosensor for dihydrogen phosphate that functions in dichloromethane. This system shows selectivity for dihydrogen phosphate over other small anions and can be used to detect the presence of this analyte via fluorescence quenching or cyclic voltammetry.

Molecular clips and tweezers hosting neutral guests

Intense current interest in supramolecular chemistry is devoted to the construction of molecular assemblies displaying controlled molecular motion associated to recognition. On this ground, molecular clips and tweezers have focused an increasing attention. This tutorial review points out the recent advances in the construction of always more sophisticated molecular clips and tweezers, illustrating their remarkably broad structural variety and focusing on their binding ability towards neutral guests. A particular attention is brought to recent findings in dynamic molecular tweezers whose recognition ability can be regulated by external stimuli. Porphyrin-based systems will not be covered here as this very active field has been recently reviewed.

Highly stable tetrathiafulvalene radical dimers in [3]catenanes

Two [3]catenane 'molecular flasks' have been designed to create stabilized, redox-controlled tetrathiafulvalene (TTF) dimers, enabling their spectrophotometric and structural properties to be probed in detail. The mechanically interlocked framework of the [3]catenanes creates the ideal arrangement and ultrahigh local concentration for the encircled TTF units to form stable dimers associated with their discrete oxidation states. These dimerization events represent an affinity umpolung, wherein the inversion in electronic affinity replaces the traditional TTF-bipyridinium interaction, which is over-ridden by stabilizing mixed-valence (TTF)2•+ and radical-cation (TTF•+)2 states inside the 'molecular flasks.' The experimental data, collected in the solid state as well as in solution under ambient conditions, together with supporting quantum mechanical calculations, are consistent with the formation of stabilized paramagnetic mixed-valence dimers, and then diamagnetic radical-cation dimers following subsequent one-electron oxidations of the [3]catenanes.

A new ex-TTF-based organogelator: formation of organogels and tuning with fullerene

A new ex-TTF-based organogelator with L-glutamide-derived lipid unit (compound 1) was synthesized and characterized. The resulting transparent organogels can be obtained with several organic solvents such as toluene, DMSO, and ethanol. It is interesting that its gelation ability can be further enhanced by addition of C(60). The (1)H NMR and absorption spectral studies indicate that the intermolecular interaction between the ex-TTF unit in 1 and C(60) may be responsible for this phenomenon. Further studies imply that the assembly structures in the gel phases in the absence and presence of C(60) may be different. Additionally, organogels can also be prepared with compound 1 and PCBM, and the corresponding xerogel was used to modify ITO electrode. A stable and rapid photocurrent was generated after exposure of the modified ITO electrode to light. This may provide an alternative way for photocurrent generation with high energy conversion efficiency.