David Canevet

Wraparound Hosts for Fullerenes: Tailored Macrocycles and Cages

Custom-made macrocyclic receptors for fullerenes are proving a valuable alternative to achieve the affinity and selectivity required to meet challenges such as the selective extraction of higher fullerenes, their chiral resolution, or the self-assembly of functional molecular materials. In this Minireview, we highlight some of the important breakthroughs that this class of fullerene hosts has already produced.

Macrocyclic Hosts for Fullerenes: Extreme Changes in Binding Abilities with Small Structural Variations

Exploiting the shape and electronic complementarity of C(60) and C(70) with π-extended derivatives of tetrathiafulvalene (exTTF), we have very recently reported a macrocyclic receptor featuring two exTTF recognizing units which forms 1:1 complexes with C(60) with log K(a) = 6.5 ± 0.5 in chlorobenzene at 298 K. This represents one of the highest binding constants toward C(60) reported to date and a world-record for all-organic receptors. Here, we describe our efforts to fine-tune our macrocyclic bis-exTTF hosts to bind C(60) and/or C(70), through structural variations. On the basis of preliminary molecular modeling, we have explored p-xylene, m-xylene, and 2,6-dimethylnaphthalene as aromatic spacers between the two exTTF fragments and three alkene-terminated chains of different length to achieve macrocycles of different size through ring closing metathesis. Owing to the structural simplicity of our design, all nine receptors could be accessed in a synthetically straightforward manner. A thorough investigation of the binding abilities of these nine receptors toward C(60) and C(70) has been carried out by means of UV-vis titrations. We have found that relatively small variations in the structure of the host lead to very significant changes in affinity toward the fullerene, and in some cases even in the stoichiometry of the associates. Our results highlight the peculiarities of fullerenes as guests in molecular recognition. The extreme stability of these associates in solution and the unique combination of electronic and geometrical reciprocity of exTTF and fullerenes are the main features of this new family of macrocyclic hosts for fullerenes.

Varied nanostructures from a single multifunctional molecular material

The control of the morphology of nanostructures formed from a single component molecular material incorporating electron accepting and donating moieties is shown, from both solution and gel states. The compound comprises one tetrathiafulvalene (TTF) and two pyrene units which act as the π-electron rich and deficient units, respectively, and which are united by amide-containing linkers whose additional role is to aide aggregation by hydrogen bonding. This role was demonstrated by IR and NMR spectroscopy. The gels were deposited onto surfaces and the solvent allowed to evaporate, leaving films formed by meshes of fibres with different morphologies in accord with the different solvents used to form the materials. Doping of these xerogels with iodine vapour afforded conducting films whose characteristics were probed with current sensing atomic force microscopy (CS-AFM), providing current maps and I–V curves which show how dramatically the processing solvent can influence the electronic properties of these xerogel-derived materials.

N-Aryl Pyrrolo-tetrathiafulvalene Based Ligands: Synthesis and Metal Coordination

A straightforward general synthetic access to N-aryl-1,3-dithiolo[4,5-c]pyrrole-2-thione derivatives 6 from acetylenedicarbaldehyde monoacetal is depicted. In addition to their potentiality as precursors to dithioalkyl-pyrrole derivatives, thiones 6 are key building blocks to N-aryl monopyrrolo-tetrathiafulvalene (MPTTF) derivatives 10. X-ray structures of four of these thiones intermediates, reminiscent of the corresponding MPTTF derivatives, are provided. When the aryl group is a binding pyridyl unit, the MPTTF derivative 10a can coordinate M(II) salts (M = Pt, Pd). The first examples of metal-directed orthogonal MPTTF-based dimers 11-14, obtained through coordination of 10a to cis-blocked square planar Pt or Pd complexes are described. Studies on the parameters influencing the dimer construction are presented, as well as first recognition properties of the resulting electron-rich clip for C(60).

Boosting electrical conductivity in a gel-derived material by nanostructuring with trace carbon nanotubes

An organogelator with two distinct π-functional units is able to incorporate carbon nanotubes into its mesh of fibres in the gel state. The morphology of the material derived from this nanocomposite after evaporation of the solvent is a complex mesh of fibres which is clearly different from the pure gelator. This feature indicates a role of the nanotubes in assisting the formation of a fibre structure in the gel thanks to their interaction with the pyrene units in the organogelator. The nanocomposite conducts electricity once the p-type gelator is doped with iodine vapour. The change in morphology caused by the carbon material increases the conductivity of the material compared with the purely organic conducting system. It is remarkable that this improvement in the physical property is caused by an extremely small proportion of the carbon material (only present at a ratio of 0.1% w/w). The practically unique properties of TTF unit allow measurements with both doped and undoped materials with conducting atomic force microscopy which have demonstrated that the carbon nanotubes are not directly responsible for the increased conductivity.

Supramolecular Interaction of Single-Walled Carbon Nanotubes with a Functional TTF-Based Mediator Probed by Field-Effect Transistor Devices

The supramolecular interaction between individual single-walled carbon nanotubes and a functional organic material based on tetrathiafulvalene is investigated by means of electric transport measurements in a field-effect transistor configuration as well as by NIR absorption spectroscopy. The results clearly point to a charge-transfer interaction in which the adsorbed molecule serves as an electron acceptor for the nanotubes through its pyrene units. Exposure to iodine vapors enhances this effect. The comparison with pristine carbon nanotube field-effect transistor devices demonstrates the possibility to exploit charge-transfer interactions taking place in supramolecular assemblies in which a mediator unit is used to transduce and enhance an external signal.

Revisiting urea-based gelators: strong solvent- and casting-microstructure dependencies and organogel processing using an alumina template

Urea-based gelators have been thoroughly characterized through various techniques and exhibit a strong solvent-structuration dependency in both the gel and the xerogel states. In a ground-breaking manner, gels were introduced in alumina membranes, which act as templates, in order to shape these materials and force the alignment of the corresponding self-assembled nanofibers by confinement.

Tetrathiafulvalene-Based Architectures: From Guests Recognition to Self-Assembly

Abstract The tetrathiafulvalene (TTF) unit has been successfully used for an incredibly broad range of applications. Beyond the well-established conducting properties of the corresponding cation-radical salts, this unit has appeared as a key redox-active component for various applications supported by its remarkable redox properties: a high π-donating ability and occurrence of three stable redox states. This article reviews the main contribution of the group of Angers to this field, highlighting results obtained in terms of redox-sensing as well as efforts carried out to reach new self-assembled TTF-based architectures.

Internal Probing of the Supramolecular Organization of Pyrene‐Based Organogelators

A thorough study of the unexpected spectroscopic behavior of two new luminescent pyrene-urea-based organogelators is rationalized as a function of their aggregation state and provides a key method to probe the supramolecular organization of the material.

(Super)gelators derived from push–pull chromophores: synthesis, gelling properties and second harmonic generation

The present work takes advantage of the self-assembly process occurring along organogelation, to organize Second Harmonic Generation (SHG) active chromophores. To do so, three push-pull chromophores endowed with a dodecyl urea chain were synthesized and characterized. Their organogelating properties were studied in a wide range of solvents. Despite similar architectures, these derivatives exhibit very different gelling properties, from supergelation to the absence of gelling ability. The utilization of the Hansen solubility parameters allows for observing clear relationships between the gelled solvents and critical gelation concentrations. By evaporating the solvents from the organogels, xerogel materials were prepared and systematically studied by means of optical and electron microscopy as well as SHG microscopy. These studies demonstrate the critical role of the solvent over material structuring and allow generalizing the approach exploiting organogelation as a structuring tool to spontaneously organize push-pull chromophores into SHG-active materials.