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Paolo Samorì

Publications and source records attributed to Paolo Samorì.

At least 19 recordsLinked to original sources
PubMed2007

Self-assembly of an alkylated guanosine derivative into ordered supramolecular nanoribbons in solution and on solid surfaces.

We report on the synthesis and self-assembly of a guanosine derivative bearing an alkyloxy side group under different environmental conditions. This derivative was found to spontaneously form ordered supramolecular nanoribbons in which the individual nucleobases are interacting through H-bonds. In toluene and chloroform solutions the formation of gel-like liquid-crystalline phases was observed. Sub-molecularly resolved scanning tunneling microscopic imaging of monolayers physisorbed at the graphite-solution interface revealed highly ordered two-dimensional networks. The recorded intramolecular contrast can be ascribed to the electronic properties of the different moieties composing the molecule, as proven by quantum-chemical calculations. This self-assembly behavior is in excellent agreement with that of 5'-O-acylated guanosines, which are also characterized by a self-assembled motif of guanosines that resembles parallel ribbons. Therefore, for guanosine derivatives (without sterically demanding groups on the guanine base) the formation of supramolecular nanoribbons in solution, in the solid state, and on flat surfaces is universal. This result is truly important in view of the electronic properties of these supramolecular anisotropic architectures and thus for potential applications in the fields of nano- and opto-electronics.

Chloroform↗
PubMed2006

Functional polymers: scanning force microscopy insights.

Scanning force microscopy (SFM) and related techniques make it possible to visualize polymer systems with a molecular resolution. Beyond imaging, they also enable the unveiling of a variety of (dynamic) physico-chemical properties of both isolated polymer chains and their supramolecular architectures, including structural, mechanical and electronic properties. This article reviews recent progress in the use of SFM on polymers, with a particular emphasis on the mechanical properties of copolymers and single polymer chains, as well as on the bottom-up fabrication of supramolecular polymeric (helical) nanostructures in particular based upon pi-conjugated macromolecules as building blocks for nanoelectronics. Through a detailed understanding of the polymer behavior, we propose solutions for the generation of organic functional (nano)systems.

Journal Article↗
PubMed2006

Reversible interconversion between a supramolecular polymer and a discrete octameric species from a guanosine derivative by dynamic cation binding and release.

[reaction: see text] The tunable interconversion between two highly ordered supramolecular motifs (G-quartet K(+)-templated column and G-ribbon) of a lipophilic guanosine derivative fueled by cation complexation and release in a cryptand [2.2.2] containing guanosine solution is reported. The process is controlled by the sequential addition of acid and base.

Cations↗
PubMed2006

Nanoscale structural and electronic properties of ultrathin blends of two polyaromatic molecules: a Kelvin probe force microscopy investigation.

We describe a Kelvin Probe Force Microscopy (KPFM) study on the morphological and electronic properties of complex mono and bi-molecular ultrathin films self-assembled on mica. These architectures are made up from an electron-donor (D), a synthetic all-benzenoid polycyclic aromatic hydrocarbon, and an electron-acceptor (A), perylene-bis-dicarboximide. The former molecule self-assembles into fibers in single component films, while the latter molecule forms discontinuous layers. Taking advantage of the different solubility and self-organizing properties of the A and D molecules, multicomponent ultrathin films characterized by nanoscale phase segregated fibers of D embedded in a discontinuous layer of A are formed. The direct estimation of the surface potential, and consequently the local workfunction from KPFM images allow a comparison of the local electronic properties of the blend with those of the monocomponent films. A change in the average workfunction values of the A and D nanostructures in the blend occurs which is primarily caused by the intimate contact between the two components and the molecular order within the nanostructure self-assembled at the surface. Additional roles can be ascribed to the molecular packing density, to the presence of defects in the film, to the different conformation of the aliphatic peripheral chains that might cover the conjugated core and to the long-range nature of the electrostatic interactions employed to map the surface by KPFM limiting the spatial and potential resolution. The local workfunction studies of heterojunctions can be of help to tune the electronic properties of active multicomponent films, which is crucial for the fabrication of efficient organic electronic devices as solar cells.

Journal Article↗
PubMed2006

Processing of giant graphene molecules by soft-landing mass spectrometry.

The processability of giant (macro)molecules into ultrapure and highly ordered structures at surfaces is of fundamental importance for studying chemical, physical and biological phenomena, as well as their exploitation as active units in the fabrication of hybrid devices. The possibility of handling larger and larger molecules provides access to increasingly complex functions. Unfortunately, larger molecules commonly imply lower processability due to either their low solubility in liquid media or the occurrence of thermal cracking during vacuum sublimation. The search for novel strategies to process and characterize giant building blocks is therefore a crucial goal in materials science. Here we describe a new general route to process, at surfaces, extraordinarily large molecules, that is, synthetic nanographenes, into ultrapure crystalline architectures. Our method relies on the soft-landing of ions generated by solvent-free matrix-assisted laser desorption/ionization (MALDI). The nanographenes are transferred to the gas phase, purified and adsorbed at surfaces. Scanning tunnelling microscopy reveals the formation of ordered nanoscale semiconducting supramolecular architectures. The unique flexibility of this approach allows the growth of ultrapure crystalline films of various systems, including organic, inorganic and biological molecules, and therefore it can be of interest for technological applications in the fields of electronics, (bio)catalysis and nanomedicine.

Capillaries↗
PubMed2006

Influence of the side functionalization of quinquethiophene-S,S-dioxides on the morphology of blends with poly(3-hexylthiophene): scanning force microscopy reveals.

Blends of an electron donor, i.e. a regioregular poly(3-hexylthiophene) (P3HT), with electron acceptors, a series of soluble quinquethiophene-S,S-dioxides (T5Os) bearing different alkyl side groups were self-assembled at surfaces. Scanning Force Microscopy (SFM) studies revealed that while the T5O symmetrically functionalized with two hexyl groups in the central thiophene (1) self-organizes into micrometer sized crystals embedded in a grainy matrix of P3HT, by substituting the central thiophene of 1 with one hexyl and one methyl unit (2) smaller and less anisotropic crystals of the acceptor having a sub-micrometer scale size were formed. The generation of these crystals is due to the joint effect of different non-covalent intermolecular interactions between the T5Os that self-segregate from the P3HT. By derivatizing the compound 1 with cyclo-hexyl moieties in the four external thiophenes molecule 3 was obtained. Such system was found to assemble into grainy disordered structures when co-deposited with P3HT, providing evidence for the absence of a phase segregation between the two components. Generally, the self-assembly at surfaces is governed by the interplay of intramolecular as well as intermolecular and interfacial interactions. In the present case, the cyclo-hexyl side groups in 3 both induce an intramolecular loss of planarity of the thiophene rings and hinders intermolecular interactions, reducing the tendency of the molecules to self-associate forming large crystals, whereas the symmetrical functionalization of the two central thiophenes with hexyl chains favours the crystallization of the T5O. The reported results demonstrate that subtle differences in the chemical functionalization can lead to different types of molecular architectures at surfaces. This is of importance since controlling the self-organization of pi-conjugated molecules at surfaces towards pre-programmed assemblies is a viable approach to enhance their electronic and luminescent properties, which should help to improve the performance of organic devices.

Crystallization↗
PubMed2005

Influence of molecular order on the local work function of nanographene architectures: a Kelvin-probe force microscopy study.

We report a Kelvin-probe force microscopy (KPFM) investigation on the structural and electronic properties of different submicron-scale supramolecular architectures of a synthetic nanographene, including extended layers, percolated networks and broken patterns grown from solutions at surfaces. This study made it possible to determine the local work function (WF) of the different pi-conjugated nanostructures adsorbed on mica with a resolution below 10 nm and 0.05 eV. It revealed that the WF strongly depends on the local molecular order at the surface, in particular on the delocalization of electrons in the pi-states, on the molecular orientation at surfaces, on the molecular packing density, on the presence of defects in the film and on the different conformations of the aliphatic peripheral chains that might cover the conjugated core. These results were confirmed by comparing the KPFM-estimated local WF of layers supported on mica, where the molecules are preferentially packed edge-on on the substrate, with the ultraviolet photoelectron spectroscopy microscopically measured WF of layers adsorbed on graphite, where the molecules should tend to assemble face-on at the surface. It appears that local WF studies are of paramount importance for understanding the electronic properties of active organic nanostructures, being therefore fundamental for the building of high-performance organic electronic devices, including field-effect transistors, light-emitting diodes and solar cells.

Journal Article↗
PubMed2005

Pyrazolino[60]fullerene-oligophenylenevinylene dumbbell-shaped arrays: synthesis, electrochemistry, photophysics, and self-assembly on surfaces.

Symmetrically substituted oligophenylenevinylene (OPV) derivatives bearing terminal p-nitrophenylhydrazone groups have been prepared and used for the synthesis of dumbbell-shaped bis(pyrazolino[60]fullerene)-OPV systems. In these triad arrays, the OPV-type fluorescence is dramatically quenched as a consequence of ultrafast OPV-->C60 singlet energy transfer. In its turn the fullerene singlet state is quenched by pyrazoline-->C60 electron transfer, in line with the behavior of the corresponding reference fullerene molecule. The occurrence of electron transfer in the multicomponent arrays is evidenced by recovery of fullerene fluorescence at 77 K in CH2Cl2 and in toluene at 298 K. Under these conditions the OPV-->C60 energy transfer is unaffected. The rate of this process turns out to be higher for the OPV trimer than for the corresponding pentameric OPV arrays, in agreement with energy-transfer theory expectations. Scanning tunneling microscopy (STM) and scanning force microscopy (SFM) revealed that the bis(pyrazolino[60]fullerene)-OPV can self-assemble into ordered layered crystalline architectures on the basal plane of highly oriented pyrolitic graphite.

Journal Article↗
PubMed2005

Exploring supramolecular interactions and architectures by scanning force microscopies.

The development of new methodologies based on scanning force microscopy (SFM) has made it possible to map topographies, chemical functionalities, and numerous other physicochemical properties of complex assemblies, to unravel dynamic processes, to measure forces generated along a reaction coordinate, to nanopattern surfaces and to nanomanipulate objects. This tutorial review highlights the most recent applications of these SFM-based capabilities, on and beyond imaging, to the exploration of supramolecular interactions and architectures, to the fabrication of smart materials and to the optimization of (nano)devices.

Hydrogen Bonding↗
PubMed2004

Tuning intermolecular interactions in a rodlike polymer assembled at surfaces and in solution.

The isolation of single polyelectrolyte chains of water-soluble poly(isocyanodipeptide)s (PICs) bearing carboxylic acid terminated side chains occurring both at surfaces and in solution was accomplished by reducing the intermolecular interactions through complexation with cations or positively charged surfactants. Scanning force microscopy and viscosity analyses revealed that this method allows to tune the conformation of the macromolecule, which is of importance for tailoring the physicochemical properties of the material. This is particularly significant for the use of these polymer chains as seed for biomineralization processes.

Carboxylic Acids↗
PubMed2004

Self-assembly of electron donor-acceptor dyads into ordered architectures in two and three dimensions: surface patterning and columnar "double cables".

We report the synthesis and characterization of covalent dyads and multiads of electron acceptors (A) and donors (D), with the purpose of exploiting their nanophase separation behavior toward (a) two-dimensional (2D) surface patterning with well-defined integrated arrays of dissimilar molecular electronic features and (b) bulk self-assembly to noncovalent columnar versions of the so-called "double cable" systems, the likes of which could eventually provide side-by-side percolation pathways for electrons and holes in solar cells. Soluble, alkylated hexa-peri-hexabenzocoronenes (HBCs) bearing tethered anthraquinones (AQs) are shown by scanning tunneling microscopy (STM) to self-assemble at the solution-graphite interface into either defect-rich polycrystalline monolayers or extended 2D crystalline domains, depending on the number of tethered AQs. In the bulk, the thermal stability of the room-temperature HBC columnar phase is increased, which is attributed to the desired nanotriphase separation of HBC columns, insulating alkyl sheaths, and AQ units. Homeotropic alignment (columns normal to surfaces), predicted to be ideal for potential exploitation of such "double cables" in photovoltaic devices, is demonstrated.

Journal Article↗
PubMed2003

Supramolecular helices via self-assembly of 8-oxoguanosines.

The cooperative effect of solvophobic interactions and hydrogen bonding has been exploited to self-assemble supramolecular helical architectures of 8-oxoguanosines in different environments. This self-assembly into helical structures is completely different from that of the parent guanosines which, in the same experimental conditions, form flat, ribbonlike structures. While optical microscopy and X-ray diffraction suggest a chiral columnar aggregate in the LC phase, NMR and Circular Dichroism reveal the presence of a helical structures in solution. Scanning Tunneling Microscopy made it possible to visualize hexagonally arranged G-quartets on graphite, which are sections of the helices packed with their long axis perpendicular to the basal plane of the substrate. Due to their rectifying electrical properties, such helices are interesting for fabricating (opto)electronic biodevices.

Circular Dichroism↗
PubMed2003

Ordered architectures of a soluble hexa-peri-hexabenzocoronene-pyrene dyad: thermotropic bulk properties and nanoscale phase segregation at surfaces.

An alkylated hexa-peri-hexabenzocoronene with a covalently tethered pyrene unit serves as a model to study self-assembling discotic pi-system dyads both in the bulk and at a surface. Wide-angle X-ray scattering, polarized light microscopy, and differential scanning calorimetry revealed bulk self-assembly into columnar structures. Relative to a control without a tethered pyrene, the new dyad exhibits a more ordered columnar phase at room temperature but with dramatically lowered isotropization temperature, facilitating homeotropic alignment. These two features are important for processing such materials into molecular electronic devices, e.g., photovoltaic diodes. Scanning tunneling microscopy at a solution-solid interface revealed uniform nanoscale segregation of the large from the small pi-systems, leading to a well-defined two-dimensional crystalline monolayer, the likes of which may be employed in the future to study intramolecular electron transfer processes at surfaces, on the molecular scale.

Journal Article↗
PubMed2003

Shape-persistant macrocycles with terpyridine units: synthesis, characterization, and structure in the crystal.

The synthesis of a variety of shape-persistent macrocycles with either one (1a-d, 2) or two (opposing) terpyridine units (3, 4, 5a-c) and inner diameters of up to 2 nm is described. The sequences are mainly based on transition metal cross-coupling reactions and, whenever appropriate, compared with one another regarding their respective efficiency. Typical overall yields and amounts prepared range from 8% (4) to 27% (3) and 25 mg (1a) to 290 mg (1b), respectively. For solubility and processing of the targeted cycles, all precursors have already been decorated with flexible side chains (hexyloxy or hexyloxymethyl). The cycles' characterization is based on MALDI-TOF mass spectrometry, 2D NMR spectroscopy, and/or low-temperature single-crystal X-ray diffraction. Their packing in the crystal is discussed in terms of both number and length of side chains. Cycle 1d was physisorbed into an ordered structure at the solution-HOPG interface and investigated by scanning tunneling microscopy (STM).

Journal Article↗