Cécile Roche

[3]- et [4]rotaxanes à base de porphyrines : vers un récepteur moléculaire adaptable: La synthèse et l'étude de rotaxanes et de porphyrines sont deux domaines particulièrement actifs de la recherche en chimie. Cependant, les composés combinant les propriétés intéressantes de ces deux types de structures sont plus rares. De nouveaux multi-rotaxanes à base de porphyrines, dont la préparation représente un défi synthétique, sont décrits dans cette thèse.Des porphyrines liées à deux ou quatre anneaux coordinants ont été synthétisées. Des rails moléculaires à deux chélates ont été enfilés dans les anneaux grâce à l'effet template du cuivre(I); l'introduction de bouchons a mené à la formation de rotaxanes. Dans le cas du bis-macrocycle porphyrinique, un [4]rotaxane a été obtenu. Des études de complexation hôte/invité avec des ligands azotés rigides ont montré que ce rotaxane est un récepteur moléculaire qui peut s'adapter à la taille du substrat invité en se "gonflant" ou en se "dégonflant".Dans le cas du tétra-macrocycle porphyrinique, la formation d'un [3]rotaxane d'architecture originale a étéobservée.La synthèse d'un nouveau bis-macrocycle plus rigide est en cours. Ce composé sera utilisé pour la construction d'un [4]rotaxane, qui pourrait montrer un caractère de presse moléculaire capable de modifier la conformation d'un substrat invité en le comprimant.

The functions of complex crystalline systems derived from supramolecular biological and non-biological assemblies typically emerge from homochiral programmed primary structures via first principles involving secondary, tertiary and quaternary structures. In contrast, heterochiral and racemic compounds yield disordered crystals, amorphous solids or liquids. Here, we report the self-assembly of perylene bisimide derivatives in a supramolecular helix that in turn self-organizes in columnar hexagonal crystalline domains regardless of the enantiomeric purity of the perylene bisimide. We show that both homochiral and racemic perylene bisimide compounds, including a mixture of 21 diastereomers that cannot be deracemized at the molecular level, self-organize to form single-handed helical assemblies with identical single-crystal-like order. We propose that this high crystalline order is generated via a cogwheel mechanism that disregards the chirality of the self-assembling building blocks. We anticipate that this mechanism will facilitate access to previously inaccessible complex crystalline systems from racemic and homochiral building blocks.

We demonstrate a robust graphene-molecule-graphene transistor architecture.

A library of dendronized cyclotriveratrylene (CTV) crowns substituted with chiral, racemic, or achiral peripheral alkyl chains, including enantiopure R and S branched alkyls, “racemic by mixture”, “racemic by synthesis”, n-octyl, and n-dodecyl groups was synthesized. In solvophobic solvents and in bulk they self-assemble in helical columns. Their solution and bulk shape-persistent supramolecular structures were determined by a complementary combination of circular dichroism (CD) and UV in solution and thin film, microspot CD in thin film, differential scanning calorimetry combined with fiber X-ray diffraction, computer simulation, and molecular models. In solution, self-assembly via a cooperative mechanism generates single-handed columns from enantiopure CTVs and mixtures of right- and left-handed columns from racemic by mixture, racemic by synthesis, other combinations of R and S, and even from achiral compounds. In bulk state all supramolecular columns form a 3D hexagonal crystalline phase, Φ_h^k (P6₃ symmetry), that can be obtained only from single-handed columns and a columnar hexagonal 2D liquid crystal, Φ_h. The highest order Φ_h^k consists of enantiopure single-handed columns that are slightly distorted 12-fold triple helices. The “hat-shaped” dendronized CTV assembles in bent-branch pine-tree columns that allow interdigitation of alkyl groups in adjacent columns regardless of their direction. Enantiomerically rich, racemic, and achiral compositions undergo deracemization in the crystal state by transfer of the transient disc-like conformer of dendronized CTV from column to column during crown inversion. Solid state NMR experiments identified motional processes that allow such transfer. This unprecedented supramolecular chiral self-sorting will impact the creation of functions in complex systems.

Twenty years ago, researchers considered the synthesis of simple rotaxanes a challenging task, but with the rapid development of this field, chemists now view these interlocking molecules as accessible synthetic targets. In a major advance for the field, researchers have developed transition metals or organic molecules as templating structures, making it easier to construct these molecular systems. In addition, chemists have found ways to introduce new functional groups, which have given these compounds new properties. Today researchers can also construct multirotaxanes consisting of several individual components, but the synthesis of the most complex structures remains challenging. This Account primarily discusses the cyclic [4]rotaxanes incorporating porphyrins that the Strasbourg group has synthesized and studied during the past few years. These cyclic [4]rotaxanes consist of two rigid rods threaded through the four rings of two molecules of a bis-macrocycle, and the synthetic strategy used for making them relies on the copper(I)-driven “gathering-and-threading” reaction. The formation of the threaded precursors was mostly quantitative, and the quadruple stoppering reaction leading to the target compound produces high yields because of the efficient copper-catalyzed azide–alkyne cycloaddition (CuAAC) or click chemistry reaction. These rotaxanes behave as receptors for various ditopic guests. We prepared and studied two types of molecules: (i) a rigid compound whose copper(I) complex has a well-defined shape, with high selectivity for the guest geometry and (ii) a much more flexible [4]rotaxane host that could act as a distensible receptor. The rigid [4]rotaxane was crystallized, affording a spectacular X-ray structure that matched the expected chemical structure. In addition, metalation or demetalation of the rigid [4]rotaxane induces a drastic geometric rearrangement. The metal-free compound is flat without a binding pocket, while the copper-complexed species forms a rectangle-like structure. The removal of copper(I) also expels any complexed guest molecule, and this process is reversible, making the rigid porphyrinic [4]rotaxane a switchable receptor. The rigid [4]rotaxane was highly selective for short, ditopic guests in its copper(I)-complexed form, but the flexible copper(I)-complexed [4]rotaxane proved to be a versatile receptor. Its conformation can adjust to the size of the guest molecule similar to the induced fit mechanism that some enzymes employ with substrates.

Self‐assembling dendrons are biologically inspired complex systems that can form self‐organized periodic arrays in the bulk state. Here we adopt the point of view of Constitutional Dynamic Chemistry (CDC) to discuss the design and properties of self‐assembling dendrimers and dendronized structures. Among other objectives, CDC seeks to generate chemical diversity through constitutional dynamics, and to improve the design of dynamic materials using adaptive systems. Can we address these issues with dendrimer chemistry? We will show that generational and co‐assembly approaches in the synthesis of self‐assembling dendritic systems lead to a remarkable collection of periodic lattices and quasi‐periodic arrays. Moreover, in some cases the morphological properties of the resulting supramolecular structures can be tuned by external signals. These dendron‐based adaptive systems find applications in various fields such as nano‐machines and switches or porous protein mimics.

A new cyclic [4]rotaxane composed of two flexible bis-macrocycles and two rigid axles is described. Each bis-macrocycle consists of two rings attached to antipodal meso positions of a central Zn porphyrin through single CC bonds. Each ring incorporates a 2,9-diphenyl-1,10-phenanthroline chelation site. The axles contain two coplanar bidentate sites derived from the 2,2′-bipyridine motif. The building blocks were assembled by using a one-pot threading-and-stoppering reaction, which afforded the [4]rotaxane in 50 % yield. The “gathering-and-threading” effect of copper(I) was utilised in the formation of a [4]pseudorotaxane, which was immediately converted to the corresponding [4]rotaxane by a quadruple CuAAC stoppering reaction. The rotaxane contains two face-to-face zinc porphyrins, which allowed the coordination of ditopic guest substrates. The rotaxane host showed remarkable flexibility and was able to adjust its conformation to the guest size. It can be distended and accommodate rod-like guests of 2.6 to 15.8 Å in length.

Biological macromolecules are homochiral, composed of sequences of stereocenters possessing the same repeated absolute configuration. This chapter addresses the mechanism of homochiral selection in polypeptides. In particular, the relationship between the stereochemistry (l or d) of structurally distinct α-amino acids is explored. Through functionalization of Tyr–Xaa dipeptides with self-assembling dendrons, the effect of stereochemical sequence of the dipeptide on the thermodynamics of self-assembly and the resulting structural features can be quantified. The dendritic dipeptide approach effectively isolates the stereochemical information of the shortest sequence of stereochemical information possible in polypeptide, while simultaneously allowing for dendron driven tertiary and quaternary structure formation and subsequent transfer of chiral information from the dipeptide to the dendritic sheath. This approach elucidates a mechanism of selecting a homochiral relationship between dissimilar but neighboring α-amino acids through thermodynamic preference for homochirality in solution-phase and bulk supramolecular helical polymerization.

The syntheses of a porphyrin bearing four peripheral rings and of the corresponding [3]rotaxane are reported. The porphyrinic tetra-macrocycle consists of four 1,10-phenanthroline-containing rings attached to the meso positions of a central zinc porphyrinvia single C–C bonds. The [3]rotaxane is composed of one central porphyrin and of two short rigid axles that contain two bidentate coordination sites and end with bulky stoppers. The rotaxane displays a novel architecture where each axle is threaded through two adjacent rings of the porphyrin. The free-base porphyrin was synthesised in 25% yield under optimised conditions. A microwave-enhanced procedure derived from the Adler–Rothemund method was developed for this condensation. The “gathering-and-threading” effect of copper(I) and subsequent stoppering by click chemistry were used to synthesise the [3]rotaxane in a two-step, one-pot reaction.