Juin 2019. Nouvelle publication de Narcis Avarvari dans le journal ACS Omega

 

 

Large Synthetic Molecule that either Folds or Aggregates through Weak Supramolecular Interactions Determined by Solvent

Cristina Oliveras-González, Mathieu Linares, David B. Amabilino and Narcis Avarvari


ABSTRACT: Weak noncovalent interactions between large disclike molecules in poorly solvating media generally lead to the formation of fibers where the molecules stack atop one another. Here, we show that a particular chiral spacing group between large aromatic moieties, which usually lead to columnar stacks, in this case gives rise to an intramolecularly folded structure in relatively polar solvents, but in very apolar solvents forms finite aggregates. The molecule that displays this behavior has a C3 symmetric benzene-1,3,5-tris(3,3′- diamido-2,2′-bipyridine) (BTAB) core with three metalloporphyrin units appended to it through short chiral spacers.
Quite well-defined chromophore arrangements are evident by circular dichroism (CD) spectroscopy of this compound in solution, where clear exciton coupled bands of porphyrins are observed. In more polar solvents where the molecules are dispersed, a relatively weak CD signal is observed as a result of intramolecular folding, a feature confirmed by molecular modeling. The intramolecular folding was confirmed by measuring the CD of a C2 symmetric analogue. The C3 symmetric BTAB cores that would normally be expected to stack in a chiral arrangement in apolar solvents show no indication of CD, suggesting that there is no transfer of chirality through it (although the expected planar conformation of the 2,2′-bipyridine unit is confirmed by NMR spectroscopy). The incorporation of the porphyrins on the 3,3′-diamino-2,2′-bipyridine moiety spaced by a chiral unit leaves the latter incapable of assembling through supramolecular π−π stacking. Rather, modeling indicates that the three metalloporphyrin units interact, thanks to van der Waals interactions, favoring their close interactions over that of the BTAB units. Atomic force microscopy shows that, in contrast to other examples of molecules with the same core, disclike aggregates (rather than fibrillar one dimensional aggregates) are favored by the C3 symmetric molecule. The closed structures are formed through nondirectional interlocking of porphyrin rings.
The chiral spacer between the rigid core and the porphyrin moieties is undoubtedly important in determining the outcome in polar or less polar solvents, as modeling shows that this joint in the molecule has two favored conformations that render the molecule relatively flat or convex.

 

Accès à la publication

 

Juin 2019. PHYSICAL REVIEW. Nouvelle publication de Narcis Avarvari.

 

Strong electrical magnetochiral anisotropy in tellurium

 G. L. J. A. Rikken
Laboratoire National des Champs Magnétiques Intenses, UPR 3228 CNRS/EMFL/INSA/UGA/UPS, Toulouse and Grenoble, France

N. Avarvari
MOLTECH-Anjou, UMR 6200, CNRS, Université Angers.

 

We report the experimental observation of strong electrical magnetochiral anisotropy in trigonal tellurium (t-Te) crystals.

We introduce the tensorial character of the effect and determine several tensor elements. We present a simple model based on the band structure of t-Te and the Boltzmann relaxation time approximation which gives a reasonable description of the principal results.

Accès à la publication

 

Septembre 2019. Nouvelle publication des groupes ERDySS et SOMaF

 

 

Supramolecular chemistry of helical foldamers at the solid–liquid interface: self-assembled monolayers and anion recognition

C. Adam, L. Faour, V. Bonnin, T. Breton, E. Levillain, M. Sallé, C. Gautier, D. Canevet.

 

The synthesis of a redox-active helical foldamer and its immobilization onto a gold electrode are described. These large molecular architectures are grafted in a reproducible manner and provide foldamer-based self-assembled monolayers displaying recognition properties.

Chem. Commun., 2019, 55, 8426-8429.

 

Aout 2019. CHEMICAL REVIEWS. Nouvelle publication de Narcis Avarvari.

 

 

Main-Group-Based Electro- and Photoactive Chiral Materials

 (Flavia Pop, Nicolas Zigon, Narcis Avarvari)

MOLTECH-Anjou, UMR 6200, CNRS, Université Angers.

 

 

 

 

This Review discusses the structure–property relationships in chiral molecules, macromolecules (polymers), and supramolecules (crystals, liquid crystals, or thin films) containing main-group elements. Chirality is a major property in our world, having a prominent influence on processes in biology, chemistry, and physics. Its impact in optics due to its interaction with electromagnetic waves gave rise to a multitude of effects, such as the Cotton effect and circularly polarized luminescence, making possible applications such as 3D displays and polarized sunglasses. Herein, a particular emphasis will be given to the influence of chirality on the conducting and optical properties of molecules or materials containing frontier heteroelements, particularly boron, silicon, phosphorus, and sulfur. These synergic materials are expected to become game-changers in the field of materials science by bringing new properties into the realm of reality, such as chirality-induced spin-selectivity, circularly polarized luminescence, and electrical magnetochiral anisotropy. This Review should be of interest for chemists and also physicists working in the fields of molecular and supramolecular chemistry, and molecular materials in the broadest sense.


Accès à la publication : DOI: 10.1021/acs.chemrev.8b00770

 

Septembre 2019. Nouvelle publication du groupe SOMaF et de l'IMMM.

 

 

Robust supramolecular nanocylinders of naphthalene diimide in water

T. Choisnet, D. Canevet, M. Sallé, E. Nicol, F. Niepceron, J. Jestin, O. Colombani.

 

Abstract

Naphthalene-diimide (NDI)-containing nanocylinders were formed by supramolecular self-assembly in water through cooperative hydrogen bonds between bis(urea) units, reinforced by hydrophobic and aromatic-stacking interactions. The nanocylinders, decorated with poly(ethylene oxide) arms ensuring their solubility in water, exhibit a huge aspect ratio (diameter 13 nm, length 300 nm) and are extremely stable.

Chem. Commun., 2019, 55, 9519-9522.