Manuela Melucci

High-Contrast Visualization of Graphene Oxide on Dye-Sensitized Glass, Quartz, and Silicon by Fluorescence Quenching

We present a novel approach for detecting and visualizing graphene oxide (GO) with high contrast on different substrates, including glass, quartz, and silicon. Visualization of GO sheets is accomplished through quenching the fluorescence of a thiophene dye, giving high optical contrast without the need to use interference methods. A comparison of fluorescence, AFM, and XRD measurements confirmed that even a single GO sheet can completely quench the fluorescence and thus be quickly visualized.

Local Current Mapping and Patterning of Reduced Graphene Oxide

Conductive atomic force microscopy (C-AFM) has been used to correlate the detailed structural and electrical characteristics of graphene derived from graphene oxide. Uniform large currents were measured over areas exceeding tens of micrometers in few-layer films, supporting the use of graphene as a transparent electrode material. Moreover, defects such as electrical discontinuities were easily detected. Multilayer films were found to have a higher conductivity per layer than single layers. It is also shown that a local AFM-tip-induced electrochemical reduction process can be used to pattern conductive pathways on otherwise-insulating graphene oxide. Transistors with micrometer-scale tip-reduced graphene channels that featured ambipolar transport and an 8 order of magnitude increase in current density upon reduction were successfully fabricated.

Asymmetrical flow field-flow fractionation with multi-angle light scattering detection for the analysis of structured nanoparticles

Synthesis and applications of new functional nanoparticles are topics of increasing interest in many fields of nanotechnology. Chemical modifications of inorganic nanoparticles are often necessary to improve their features as spectroscopic tracers or chemical sensors, and to increase water solubility and biocompatibility for applications in nano-biotechnology. Analysis and characterization of structured nanoparticles are then key steps for their synthesis optimization and final quality control. Many properties of structured nanoparticles are size-dependent. Particle size distribution analysis then provides fundamental analytical information. Asymmetrical flow field-flow fractionation (AF4) with multi-angle light scattering (MALS) detection is able to size-separate and to characterize nanosized analytes in dispersion. In this work we focus on the central role of AF4-MALS to analyze and characterize different types of structured nanoparticles that are finding increasing applications in nano-biotechnology and nanomedicine: polymer-coated gold nanoparticles, fluorescent silica nanoparticles, and quantum dots. AF4 not only size-fractionated these nanoparticles and measured their hydrodynamic radius (r(h)) distribution but it also separated them from the unbound, relatively low-M(r) components of the nanoparticle structures which were still present in the sample solution. On-line MALS detection on real-time gave the gyration radius (r(g)) distribution of the fractionated nanoparticles. Additional information on nanoparticle morphology was then obtained from the r(h)/r(g) index. Stability of the nanoparticle dispersions was finally investigated. Aggregation of the fluorescent silica nanoparticles was found to depend on the concentration at which they were dispersed. Partial release of the polymeric coating from water-soluble QDs was found when shear stress was induced by increasing flowrates during fractionation.

Microwave-assisted synthesis of oligothiophene semiconductors in aqueous media using silica and chitosan supported Pd catalysts

We report an innovative heterogeneous procedure for the preparation of highly pure thiophene oligomers via microwave-assisted Pd catalysis by using silica- and chitosan-supported Pd complexes. This approach is very efficient and greener than the existing homogeneous methodology as it combines a very efficient reaction with improved catalyst separation. Our new, efficient and cleaner microwave approach smoothly afforded the preparation of coupled products in high yields (up to 87% isolated yield, 30–100 min). Thienyl iodides or activated bromides were employed as starting materials and KF as base. The microwave reaction was carried out in aqueous ethanol. The heterogeneous catalyst can be easily removed from the reaction mixture by filtration and reused in consecutive reactions (up to 4 times).

Thienopyrrolyl dione end-capped oligothiophene ambipolar semiconductors for thin film- and light emitting transistors

The design, synthesis and structure-property investigation of a new thienopyrrolyl dione substituted oligothiophene material showing reduced band gap energy, low lying LUMO energy level and ambipolar semiconducting behaviour is described.

Poly(lactic acid) as a transparent matrix for luminescent solar concentrators: a renewable material for a renewable energy technology

The suitability of L-poly(lactic acid) (L-PLA) as a transparent matrix, alternative to poly(methylmetacrilate) (PMMA), for use in luminescent solar concentrators is herein demonstrated. Low molecular weight L-PLA-based films, both chemically modified or blended with an oligothiophene luminescent dye (T5OH), showed excellent processability, photostability, and exhibited fluorescence quantum yields (of about 35%) even higher than T5OH-doped PMMA.

Phase separation and affinity between a fluorinated perylene diimide dye and an alkyl-substituted hexa-peri-hexabenzocoronene

Fluorination of alkyl groups is a known strategy for hindering miscibility, thus promoting phase separation, when blends are prepared with a hydrocarbon compound. A new perylene bis(dicarboximide) derivative functionalized with branched N-perfluoroalkyl moieties (BPF-PDI) has been synthesized as electron acceptor to be potentially used in conjunction with the electron donor hexakis(dodecyl)hexabenzocoronene (HBC-C12) in bulk heterojunction solar cells. Aiming at controlling self-assembly between the two components at the supramolecular level, stoichiometric blends in CHCl3 have been prepared either by spin- or drop-casting onto silicon surfaces, and further subjected to solvent vapour annealing (SVA) treatment in a CHCl3-saturated atmosphere. Spectroscopic investigation in solution shows the formation of supramolecular BPF-PDI–HBC-C12 dimers, with an association constant Kass = (2.1 ± 0.3) × 104 M−1, pointing to a strong and unexpected affinity between the two species within the mixture. Characterization through optical and atomic force microscopies of the deposited samples revealed that the self-assembly behaviour of the blends on SiOx is remarkably different from mono-component films, thus confirming the absence of a macroscopic phase-separation between the two components featuring isolated domains of the neat acceptor or donor compound. In addition, X-ray studies provided evidence for the existence of a local-scale phase separation. These findings are of importance for organic photovoltaics, since they offer a new strategy to control the phase separation at different scales in electron acceptor–donor blends.

“Click” on Tubes: a Versatile Approach towards Multimodal Functionalization of SWCNTs

Organic functionalization of carbon nanotube sidewalls is a tool of primary importance in material science and nanotechnology, equally from a fundamental and an applicative point of view. Here, an efficient and versatile approach for the organic/organometallic functionalization of single-walled carbon nanotubes (SWCNTs) capable of imparting multimodality to these fundamental nanostructures, is described. Our strategy takes advantage of well-established Cu-mediated acetylene-azide coupling (CuAAC) reactions applied to phenylazido-functionalized SWCNTs for their convenient homo-/heterodecoration with a number of organic/organometallic frameworks, or mixtures thereof, bearing terminal acetylene pendant arms. Phenylazido-decorated SWCNTs were prepared by chemoselective arylation of the CNT sidewalls with diazonium salts under mild conditions, and subsequently used for the copper-mediated cycloaddition protocol in the presence of terminal acetylenes. The latter reaction was performed in one step by using either single acetylene derivatives or equimolar mixtures of terminal alkynes bearing either similar functional groups (masked with orthogonally cleavable protecting groups) or easily distinguishable functionalities (on the basis of complementary analytical/spectroscopic techniques). All materials and intermediates were characterized with respect to their most relevant aspects/properties by TEM microscopy, thermogravimetric analysis coupled with MS analysis of volatiles (TG-MS), elemental analysis, cyclic voltammetry (CV), Raman and UV/Vis spectroscopy. The functional loading and related chemical grafting of both primary amino- and ferrocene-decorated SWCNTs were spectroscopically (UV/Vis, Kaiser test) and electrochemically (CV) determined, respectively.

Graphene–organic hybrids as processable, tunable platforms for pH-dependent photoemission, obtained by a new modular approach

We describe a new approach to attach organic dyes to graphene oxide (GO) sheets with high loading and minimal perturbation of the electronic and optical properties of the dye. The dye unit used (a pH-sensitive terthiophene) is grafted to GO using a new modular synthetic approach, passing through a C6-aminic linker which makes GO more soluble in different organic solvents and allows straightforward attachment at high yield not only of terthiophene but of many commercially available amino-reactive dyes. The covalent engraftment to GO does not perturb the absorption and emission properties of the dye, and in particular the pH sensing capability through amidic group reversible protonation. This approach can allow (i) high solubility of the GO intermediate in organic solvents, (ii) convenient coupling with commercial, stable amino-reactive dyes under mild conditions, (iii) easy control of the spacer length between the GO and oligothiophene dye and finally (iv) high (up to 5 wt%) dye functionalization loadings.

Facile tuning from blue to white emission in silica nanoparticles doped with oligothiophene fluorophores

Oligothiophenes (TFs) with blue, green and orange emission have been used for the first time as doping fluorophores of silica nanoparticles (SiO2NPs). High purification of the new nanoparticles (TFsSiO2NPs) from free molecular fluorophores was achieved by means of asymmetrical flow field-flow fractionation on-line combined with multi-angle light scattering and fluorescent detection (AF4-MALS-FD). The synthesis, structural, compositional and optical characterizations of the new TFsSiO2NPs are reported. We show that the tailored co-assembly of TFs in bi- and tricomponent TFsSiO2NPs allows for the fine-tuning of the emission of the nanoparticles from blue to white by means of FRET processes between adjacent TFs. These unique optical signatures make TFsSiO2NPs potentially effective tools for fluorescent sensing and labeling.