Laura Maggini

NLO Response of Photoswitchable Azobenzene‐Based Materials

The nonlinear optical (NLO) response of three π-conjugated azobenzene (AB) derivatives was investigated under picosecond laser excitation by means of the Z-scan technique to evaluate the effect of an ethynyl-based conjugated spacer on the NLO properties of ABs. All modules possessed large third-order nonlinearity, but unexpectedly it was the less extended AB derivative that exhibited the largest NLO response. This finding has been confirmed by means of DFT calculations and was attributed to a higher cis/trans ratio of the particular AB derivative in its investigated photoequilibrated state. Furthermore, the influence of the amount of cis isomer on the third-order nonlinear susceptibility [χ((3))] of the less extended AB derivative has been thoroughly investigated. Specifically, modulation of the NLO response has been successfully achieved by tuning the isomeric composition of the investigated photostationary state. These results highlighted the cis-dependent increase of the NLO response to support the general idea that such compounds can be used for multistep switching NLO materials.

A Luminescent Host–Guest Hybrid between a EuIII Complex and MWCNTs

The luminescence performance of a chromophore, in terms of color and intensity, is dramatically dependent on the local chemical environment. Particularly in the solid state, luminescent molecules tend to undergo aggregation phenomena that profoundly alter their emission output, which reduces their usefulness in optoelectronic devices. In solution, quenching with high-energy O H, C H or N H oscillators that belong to the solubilizing medium (either water or organic solvents) may also significantly reduce the performance of some luminescent probes. A novel approach to address the problems outlined above relies on the confinement and insulation of the luminophores within hollow structures. Both inorganic and organic approaches have been attempted. For instance, inorganic materials such as zeolites, high porosity glass films from sol–gel processes, and mesoporous metal oxides have been employed in endohedral functionalization experiments and, likewise, some organic systems, such as calixarenes, cryptands, cyclodextrins, and cucurbiturils. At present, besides the preparation of fullerene C60 peapods, carbon nanotubes (CNTs) are still largely unexplored as hollow hosting structures, and a relatively limited number of organic guest molecules have been incorporated within them. Among these, very few scattered examples of encapsulation of organic luminophores have been reported and their light-emitting properties investigated. In this respect, functionalization of CNTs with strong visible-lightemitting chromophores would enhance their practical applications because carbon nanotubes only exhibit IR emission in some limited cases. Good candidates for this application are complexes based on rare earth (RE) trivalent ions. These compounds are among the most versatile luminophores available and possess intense and chromatically pure emissions thanks to the peculiar nature of the “inner” f electronic levels of lanthanide-ion emitters, which are well shielded by filled 5s and 5p valence orbitals from the interactions with the surrounding environment (ligands, solvent molecules etc). Shi et al. first attempted to combine CNTs with luminescent lanthanide ions by depositing Eu-doped Y2O3 nanophosphors onto the external surface of multiwalled carbon CNTs (MWCNTs), obtaining a red-emitting material upon UV excitation. Subsequently, our groups reported the blending of CNTs with luminescent Eu complexes, which showed a lack of emission quenching by the nearby CNTs in both direct and ionic-liquid-mediated contact. However, despite the increase in stability on going from a hydrophobic to a columbic-based construction, desorption phenomena still represent the technological limitation to the versatile exploitation of these structures. In this respect, Eudoped luminescent SWCNTs recently prepared by direct growth on a Eu-based catalyst by Sitharaman et al. represent an important advancement towards stable emissive carbon nanostructures. With the aim of preparing easily accessible, structurally defined, and tailored luminescent CNT hybrids through host–guest interactions under mild conditions, we report herein on the endohedral functionalization of MWCNTs with a neutral and hydrophobic tris-hexafluoro acetylacetonate Eu complex (1; Scheme 1). In contrast to previous works, which have mainly focused on the response of CNTs to the inclusion of luminescent material that is seen as a dopant to control the CNT properties (e.g., conductance or electronic band gap), we have endeavored to unravel the intimate interaction between the CNTs and the encapsulated Eu complex and the influence on the emitting properties of the resulting hybrid material. Specifically, we have tested MWCNTs, which are still unexplored as wide-diameter carbon containers might present exceptional encapsulating capacity. To the obtain desired luminescent hybrid 2, the nano-extraction methodology described by Iijima et al. was employed. First, pristine MWCNTs (pMWCNTs) were opened by acid treatment by using H2SO4/HNO3 (3:1) as an oxidiz[a] L. Maggini, Dr. H. Traboulsi, Prof. D. Bonifazi Department of Chemistry University of Namur (FUNDP) Rue de Bruxelles 61, 5000 Namur (Belgium) E-mail : davide.bonifazi@fundp.ac.be [b] J. Mohanraj, Dr. G. Accorsi, Dr. N. Armaroli Molecular Photoscience Group Istituto per la Sintesi Organica e la Fotoreattivit del CNR (ISOF-CNR) Via P. Gobetti 101, 40129 Bologna (Italy) E-mail : armaroli@isof.cnr.it [c] Dr. A. Parisini Istituto per la Microelettronica e i Microsistemi del CNR (IMMCNR) Via P. Gobetti 101, 40129 Bologna (Italy) [d] Prof. D. Bonifazi Dipartimento di Scienze Farmaceutiche Universita degli Studi di Trieste Piazzale Europa 1, 34127 Trieste (Italy) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201101216.

Magnetic poly(vinylpyridine)-coated carbon nanotubes: an efficient supramolecular tool for wastewater purification.

Herein, we report the first example of a supramolecular carbon nanotube (CNT)-based magnetic depolluting agent for divalent metal ion (M(2+)) removal from aqueous solutions. In particular, magnetic multi-walled carbon nanotubes (m-MWCNTs) coated with poly(vinylpyridine) (PVPy) self-aggregate in aqueous solutions that contain divalent metal ions (such as Zn(2+), Cu(2+) and Pb(2+)) to form tight insoluble bundles in which the M(2+) ions remain trapped through pyridyl-M(2+)-pyridyl interactions. Magnetic filtration ultimately affords the efficient separation of the depolluted solution from the precipitated M(2+)-CNT agglomerates. Upon acid treatment, the supramolecular threads could be disassembled to afford the free CNT-polymer hybrid, thus allowing recycling of the depolluting agent. All materials and complexation/decomplexation steps were thoroughly characterised by using thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), transmission and scanning electron microscopy (TEM and SEM, respectively). The quantification of the M(2+) residual concentrations in water was evaluated by using inductively coupled plasma optical emission spectroscopy (ICP-OES), which showed that, depending on the metal cation, this material can remove up to 99% of the contaminant.

Luminescent blooming of dendronic carbon nanotubes through ion-pairing interactions with an Eu(III) complex.

A multiwalled carbon nanotube (MWCNT) scaffold was covalently functionalized with a second-generation polyamidoamine (PAMAM) dendron, presenting four terminal amino groups per grafted aryl moiety. These reactive functions were alkylated to obtain a positively charged polycationic dendron/carbon nanotube system (d-MWCNTs⋅Cl), which eventually underwent anion exchange reaction with a negatively charged and highly luminescent Eu(III) complex ([EuL(4)]⋅NEt(4), in which L = (2-naphtoyltrifluoroacetonate)). This process afforded the target material d-MWCNTs⋅[EuL(4)], in which MWCNTs are combined with red-emitting Eu(III) centers through electrostatic interactions with the dendronic branches. Characterization of the novel MWCNT materials was accomplished by means of TGA and TEM, whereas d-MWCNTs⋅Cl and d-MWCNTs⋅ [EuL(4)] further underwent XPS, SEM and Raman analyses. These studies demonstrate the integrity of the luminescent [EuL(4)](-) center in the luminescent hybrid, the massive load of the cationic binding sites, and the virtually complete anion-exchange into the final hybrid material. The occurrence of the ion-pairing interaction with MWCNTs was unambiguously demonstrated through DOSY NMR diffusion studies. Photophysical investigations show that MWCNTs⋅[EuL(4)] is a highly soluble and brightly luminescent red hybrid material in which MWCNTs act as photochemically inert scaffolds with negligible UV/Vis absorption, compared with the grafted Eu complex, and with no quenching activity. The high dispersibility of MWCNTs⋅[EuL(4)] in a polymer matrix makes it a promising luminophore for applications in material science.

Biodegradable Peptide-Silica Nanodonuts.

We report hybrid organosilica toroidal particles containing a short peptide sequence as the organic component of the hybrid systems. Once internalised in cancer cells, the presence of the peptide allows for interaction with peptidase enzymes, which attack the nanocarrier effectively triggering its structural breakdown. Moreover, these biodegradable nanovectors are characterised by high cellular uptake and exocytosis, showing great potential as biodegradable drug carriers. To demonstrate this feature, doxorubicin was employed and its delivery in HeLa cells investigated.

Stereochemistry of the C-S Bond Cleavage in cis-2-Methylcyclopentyl Phenyl Sulfoxide Radical Cation

The TiO(2) photocatalyzed oxidation of cis-2-methylcyclopentyl phenyl sulfoxide in the presence of Ag(2)SO(4) in MeCN/H(2)O leads to the formation of 1-methylcyclopentanol, 1-methylcyclopentyl acetamide, and phenyl benzenethiosulfonate as the main reaction products. It is suggested that the C-S heterolysis in the radical cation is an unimolecular process leading to an ion radical pair. Fast 1,2-hydride shift in the secondary carbocation leads to 1-methylcyclopentyl carbocation that forms the observed products by reaction with H(2)O and MeCN. Attack of H(2)O on the ion radical pair may also occur, but as a minor route (<3%), with formation of trans-2-methylcyclopentanol.

Diagnostic Implementation of Fast and Selective Integrin-Mediated Adhesion of Cancer Cells on Functionalized Zeolite L Monolayers.

The rapid and exact identification and quantification of specific biomarkers is a key technology for always achieving more efficient diagnostic methodologies. We present the first application of a nanostructured device constituted of patterned self-assembled monolayers of disk-shaped zeolite L coated with the cyclic integrin ligand c[RGDfK] via isocyanate linker, to the rapid detection of cancer cells. With its high specificity toward HeLa and Glioma cells and fast adhesion ability, this biocompatible monolayer is a promising platform for implementation in diagnostics and personalized therapy formulation devices.

Carbon nanotube-based metal-ion catchers as supramolecular depolluting materials.

Herein, we report the first example of supramolecular carbon nanotube (CNT)-based ion catchers as simple and effective tools for removing divalent metal ions from organic solvents. In particular, covalently functionalized multi-walled carbon nanotubes (MWCNTs) appended with pyridyl groups self-aggregate in solution into bundles in the presence of divalent metal ions (e.g., Cd²⁺, Cu²⁺, Ni²⁺, Pb²⁺, Zn²⁺). Such self-aggregation behavior leads to insoluble materials that, upon treatment with weak acids, can be regenerated and reused for further complexation. All materials and complexation/decomplexation steps were thoroughly characterized by using X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and different microscopy-based techniques, namely, transmission electron, scanning electron, and atomic force microscopy (TEM, SEM, and AFM). The supramolecular system engineered in this work is the first example of an easy and fully sustainable material with great potential applications for depolluting liquid waste from metal contamination.

Monodisperse CNT Microspheres for High Permeability and Efficiency Flow‐Through Filtration Applications

Carbon nanotube (CNT)-based filters have the potential to revolutionize water treatment because of their high capacity and fast kinetics in sorption of organic, inorganic, and biological pollutants. To date, CNT filters either rely on CNTs dispersed in liquids, which are difficult to recover and cause safety concerns, or on CNT buckypaper, which offers high efficiency, but suffers from an intrinsic trade-off between filter permeability and capacity. Here, a new approach is presented that bypasses this trade-off and achieves buckypaper-like efficiency combined with filter-column-like permeability and capacity. For this, CNTs are first assembled into porous microspheres and then are packed into microfluidic column filters. These microcolumns exhibit large flow-through filtration efficiencies, while maintaining membrane permeabilities an order of magnitude larger then CNT buckypaper and specific permeabilities double that of activated carbon for similar flowrates (232 000 L m-2 h-1 bar-1 , 1.23 × 10-12 m2 ). Moreover, in a test to remove sodium dodecyl sulfate (SDS) from water, these microstructured CNT columns outperform activated carbon columns. This improved filtration efficiency and permeability is an important step toward a broader implementation of CNT-based filtration devices.

Direction-dependent secondary bonds and their stepwise melting in a uracil-based molecular crystal studied by infrared spectroscopy and theoretical modeling

Abstract Three types of supramolecular interactions are identified in the three crystallographic directions in crystals of 1,4-bis[(1-hexylurac-6-yl) ethynyl]benzene, a uracil-based molecule with a linear backbone. These three interactions, characterized by their strongest component, are: intermolecular double H-bonds along the molecular axis, London dispersion interaction of hexyl chains connecting these linear assemblies, and π – π stacking of the aromatic rings perpendicular to the molecular planes. On heating, two transitions happen, disordering of hexyl chains at 473 K, followed by H-bond melting at 534 K. The nature of the bonds and transitions was established by matrix-isolation and temperature-dependent infrared spectroscopy and supported by theoretical computations.