Andrea Minoia

Modular Engineering of H-Bonded Supramolecular Polymers for Reversible Functionalization of Carbon Nanotubes

A H-bond-driven, noncovalent, reversible solubilization/functionalization of multiwalled carbon nanotubes (MWCNTs) in apolar organic solvents (CHCl(3), CH(2)Cl(2), and toluene) has been accomplished through a dynamic combination of self-assembly and self-organization processes leading to the formation of supramolecular polymers, which enfold around the outer wall of the MWCNTs. To this end, a library of phenylacetylene molecular scaffolds with complementary recognition sites at their extremities has been synthesized. They exhibit triple parallel H-bonds between the NH-N-NH (DAD) functions of 2,6-di(acetylamino)pyridine and the CO-NH-CO (ADA) imidic groups of uracil derivatives. These residues are placed at 180° relative to each other (linear systems) or at 60°/120° (angular modules), in order to tune their ability of wrapping around MWCNTs. Molecular Dynamics (MD) simulations showed that the formation of the hybrid assembly MWCNT•[X•Y](n) (where X = 1a or 1b -DAD- and Y = 2, 3, or 4 -ADA-) is attributed to π-π and CH-π interactions between the graphitic walls of the carbon materials and the oligophenyleneethynylene polymer backbones along with its alkyl groups, respectively. Addition of polar or protic solvents, such as DMSO or MeOH, causes the disruption of the H-bonds with partial detachment of the polymer from the CNTs, followed by precipitation. Taking advantage of the chromophoric and luminescence properties of the molecular subunits, the solubilization/precipitation processes have been monitored by UV-vis absorption and luminescence spectroscopies. All hybrid MWCNTs-polymer materials have been also structurally characterized via thermogravimetric analysis (TGA), transmission electron microscopy (TEM), atomic force microscopy (AFM), scanning tunneling microscopy (STM), and X-ray photoelectron spectroscopy (XPS).

Expression of chirality in molecular layers at surfaces: insights from modelling

This tutorial review illustrates how modelling can be used to understand the structure and properties of chiral surfaces formed by adsorption of molecular layers. The two major theoretical approaches for such modelling (Density Functional Theory and classical force-field methods) are briefly described and compared. A few examples of their use are given, focussing on: (i) the expression of chirality at the local and global scale in layers of chiral molecules, (ii) the appearance of chirality in layers of achiral molecules on achiral surfaces, and (iii) the molecular organisation in layers formed from racemic mixtures.

Synthesis and Characterization of Nanocomposites Based on Functional Regioregular Poly(3-hexylthiophene) and Multiwall Carbon Nanotubes.

New functionalized poly(3-hexylthiophene)s (P3HT) have been designed and synthesized with the aim of increasing the dispersion of carbon nanotubes (CNT) in solutions and in thin films of semiconducting polymers. Dispersion in solution has been assessed by sedimentation tests while the thin film morphology has been analyzed by TEM and AFM. Both the physisorption of P3HT chains (via pyrene end-groups) or their chemical grafting (onto amine functions generated on the CNT surface) lead to a much better dispersion in solution and in the solid. In thin films, P3HT fibrils are observed to arrange perpendicular to the CNT surface, which can be understood on the basis of molecular modeling simulations. Finally, the effect of dispersing those P3HT/CNT nanocomposites in bulk-heterojunction P3HT-based photovoltaic devices has been evaluated.

Light-Enhanced Liquid-Phase Exfoliation and Current Photoswitching in Graphene-Azobenzene Composites

Multifunctional materials can be engineered by combining multiple chemical components, each conferring a well-defined function to the ensemble. Graphene is at the centre of an ever-growing research effort due to its combination of unique properties. Here we show that the large conformational change associated with the trans–cis photochemical isomerization of alkyl-substituted azobenzenes can be used to improve the efficiency of liquid-phase exfoliation of graphite, with the photochromic molecules acting as dispersion-stabilizing agents. We also demonstrate reversible photo-modulated current in two-terminal devices based on graphene–azobenzene composites. We assign this tuneable electrical characteristics to the intercalation of the azobenzene between adjacent graphene layers and the resulting increase in the interlayer distance on (photo)switching from the linear trans-form to the bulky cis-form of the photochromes. These findings pave the way to the development of new optically controlled memories for light-assisted programming and high-sensitive photosensors.

Synthesis of poly(L-lactide) and gradient copolymers from a L-lactide/trimethylene carbonate eutectic melt

A 50 : 50 wt% mixture of L-lactide and trimethylene carbonate yields a eutectic at 21.3 °C. This mixture was exploited to prepare poly(L-lactide) homopolymers at r.t. without addition of extra solvent. The intrinsic kinetic behavior of the DBU organocatalyst also allowed for the sequential polymerization of both comonomers, leading to well defined gradient copolymers.

Bottom-up assembly of high density molecular nanowire cross junctions at a solid/liquid interface

A monoalkylated tetrathiafulvalene derivative forms multilayer structures at the solid-liquid interface, with high density of cross junctions, which are interesting for molecular electronic circuit self-assembly.

A multivalent hexapod: Conformational dynamics of six-legged molecules in self-assembled monolayers at a solid-liquid interface

A molecular hexapod having a benzene core and six oligo(p-phenylene vinylene) (OPV) legs is an ideal system to probe various types of (intramolecular) dynamics of individual molecules in physisorbed self-assembled monolayers at a solid-liquid interface. Scanning tunneling microscopy reveals that molecules adsorb in 2D crystalline as well as disordered domains. Strikingly, not all molecules have the six OPV units in contact with the graphite substrate: 4% of the molecules in the 2D crystalline domains and up to 80% of the molecules in the disordered domains have one or two OPV units desorbed. In addition, the presence of such a defect promotes the coexistence of another defect adjacent to it. Time-dependent STM experiments and molecular dynamics simulations reveal in detail the different dynamics involved and the multivalent nature of the interactions between hexapod and surface.

Poly(amino-methacrylate) as versatile agent for carbon nanotube dispersion: an experimental, theoretical and application study

Carbon nanotubes (CNTs) dispersion in aqueous and organic media was studied in presence of poly(N-(2-(dimethylamino) ethyl)-methacrylate) (PDMAEMA). Theoretical and experimental studies were performed in order to emphasize the CNT⋯PDMAEMA character of the interactions. The rationalization of a CH⋯π interaction was fully supported by molecular dynamics simulations and confirmed the potential role of PDMAEMA to behave as anchoring agent toward the CNTs. This efficient strategy was applied to the formation of polylactide-based CNTs nanocomposite materials, targeting biomedical applications.

Two-Leg Molecular Ladders Formed by Hierarchical Self-Assembly of an Organic Radical

The supramolecular organization of a new polychlorotriphenyl (PTM) radical bearing three long alkyl chains has been studied by scanning tunneling microscopy (STM) at the liquid-solid interface. This radical hierarchically self-assembles on graphite forming head-to-head dimers that organize in rows following an interesting spin-containing two-leg molecular ladder topology, in which the alkyl chains determine the space between the radical rows and act as diamagnetic barriers. In addition, these double-rows also self-assemble three-dimensionally, leading to a multilayer organization which is still influenced by the HOPG substrate symmetry. The observed nanostructures are sustained by different intermolecular interactions such as Cl...Cl, Cl...Ph, pi-pi, van der Waals, and CH...pi interactions. Theoretical calculations were used to model the observed assemblies, and the results were in complete agreement with the experimental data. Remarkably, atomic force microscopy (AFM) studies confirmed that this tendency to form double rows composed by the PTM magnetic heads surrounded by the alkyl chains is maintained after the complete evaporation of the solvent. The electrochemical and magnetic properties of these PTM nanostructures were also demonstrated.

Monolayer self-assembly at liquid-solid interfaces : chirality and electronic properties of molecules at surfaces

The spontaneous formation of supramolecular assemblies at the boundary between solids and liquids is a process which encompasses a variety of systems with diverse characteristics: chemisorbed systems in which very strong and weakly reversible bonds govern the assembly and physisorbed aggregates which are dynamic thanks to the weaker interactions between adsorbate and surface. Here we review the interest and advances in the study of chiral systems at the liquid–solid interface, and also the application of this configuration for the study of systems of interest in molecular electronics, self-assembled from the bottom up.