Chemistry

Large-scale debundling of single-walled nanotubes has been demonstrated by dilution of nanotube dispersions in the solvent N-methyl-2-pyrrolidone (NMP). At high concentrations some very large (∼100s of micrometers) nanotube aggregates exist that can be removed by mild centrifugation. By measurement of the absorbance before and after centrifugation as a function of concentration the relative aggregate and dispersed nanotube concentrations can be monitored. No aggregates are observed below C NT ≈ 0.02 mg/mL, suggesting that this can be considered the nanotube dispersion limit in NMP. After centrifugation, the dispersions are stable against sedimentation and further aggregation for a period of weeks at least. Atomic force microscopy (AFM) studies on deposited films reveal that the bundle diameter distribution decreases dramatically as concentration is decreased. Detailed data analysis suggests the presence of an equilibrium bundle number density and that the dispersions self-arrange themselves to always remain close to the dilute/semidilute boundary. A population of individual nanotubes is always observed that increases with decreasing concentration until almost 70% of all dispersed objects are individual nanotubes at a concentration of 0.004 mg/mL. The number density of individual nanotubes peaks at a concentration of ∼10 -2 mg/mL. Both the mass fraction and the partial concentration of individual nanotubes can also be measured and behave in similar fashion. Comparison of the number density and partial concentration also of individual nanotubes reveals that the individual nanotubes have average molar masses of ∼700 000 g/mol. The presence of individual nanotubes in NMP dispersion was confirmed by photoluminescence spectroscopy. Concentration dependence of the photoluminescence intensity confirms that the AFM measurements reflect the diameter distributions in situ. In addition, Raman spectroscopy confirms the presence of large quantities of individual nanotubes in the deposited films. Finally, the nature of the solvent properties required for dispersion are discussed.

In present telecommunication networks, information transfer relies on the interplay of optical and electrical signals. Data are communicated optically but processed electronically. Methods to maintain the propagating signals solely at the optical level must be developed to overcome the transmission capacities and speed limits imposed by the electronic components. We have demonstrated that molecular switches can be used to gate optical signals in response to optical signals. We have realized a simple optical network consisting of three light sources, one cell containing a solution of three fluorescent molecules, one cell containing a solution of a three-state molecular switch and a detector. The light emitted by the three fluorophores is absorbed by the three states of the molecular switch. Using this simple operating principle, we have shown that multichannel digital transmission can be implemented on an ensemble of communicating molecules relying exclusively on the interplay of optical inputs and optical outputs.

Light inputs operate a three-state molecular switch inducing the transfer of a proton to or from a two-state molecular switch. The signal transduction protocol of the two communicating molecular switches is equivalent to that of a sequential logic circuit incorporating three logic gates.

Large-scale debundling of single-walled nanotubes has been demonstrated by dilution of nanotube dispersions in the solvent γ -butyrolactone. This liquid, sometimes referred to as 'liquid ecstasy', is well known for its narcotic properties. At high concentrations the dispersions form an anisotropic, liquid crystalline phase which can be removed by mild centrifugation. At lower concentrations an isotropic phase is observed with a biphasic region at intermediate concentrations. By measuring the absorbance before and after centrifugation, as a function of concentration, the relative anisotropic and isotropic nanotube concentrations can be monitored. The upper limit of the pure isotropic phase was C NT ∼ 0.004 mg ml −1 , suggesting that this can be considered the nanotube dispersion limit in γ -butyrolactone. After centrifugation, the dispersions are stable against sedimentation and further aggregation for a period of 8 weeks at least. Atomic-force-microscopy studies on films deposited from the isotropic phase reveal that the bundle diameter distribution decreases dramatically as concentration is decreased. Detailed data analysis suggests the presence of an equilibrium bundle number density. A population of individual nanotubes is always observed which increases with decreasing concentration until almost 40% of all dispersed objects are individual nanotubes at a concentration of 6 × 10 −4 mg ml −1 . The number density of individual nanotubes peaks at a concentration of ∼6 × 10 −3 mg ml −1 where almost 10% of the nanotubes by mass are individualized.

The identification of strategies to establish communication between independent molecules is an essential requirement for the development of operating principles to manipulate information at the molecular level. In this context, we have devised a strategy to exchange signals between pairs of complementary molecular switches. It is based on the photoinduced ring closing of a merocyanine to produce a spiropyran with the concomitant release of a proton. The liberated proton is captured by either one of two pyridine derivatives with the formation of their conjugate acids. This transformation induces a significant increase in chemical shift for the resonances of the pyridyl protons and, in one instance, also a pronounced color change. The overall process is fully reversible and the pair of communicating molecules reverts to the original state in the dark. Relying on this mechanism, an optical input is transduced into a detectable spectroscopic output after the controlled intermolecular exchange of protons. A simple analysis of the signal transduction operated by the communicating molecular switches reveals that a binary digit is passed unaltered from the input to the output even although the nature of the signal carrying the information changes at each step. Furthermore, the different nature of input and output implies that the state of the ensemble of molecules can be probed non-destructively at any point in time. The timescales of the switching steps, however, are seriously limited by the slow reaction kinetics. The photoinduced transformation occurs within minutes, but the thermal reaction reverts the switch state only after several hours. q

A B S T R A C T We report the synthesis and characterization of several hybrid [60]fullerene-SWCNT materials that combine [60]fullerenes with appended photoactive ferrocenyl or porphyrinyl functionalities and SWCNTs into a single multifunctional structure, where the dyads are covalently attached to the exo-surface of SWCNTs. The structural properties of all hybrids have been characterized using a large variety of spectroscopic and HR-TEM techniques. Raman spectra showed how all SWCNTs were functionalized and the presence of functional groups in the nanotube derivatives. Furthermore, these spectra reveal a new electronic activity of the compounds due to the interaction of the functional groups with the SWCNT frameworks. XPS investigations have documented the presence of [60]fullerene derivatives around the exo-surface of the oxidized SWCNT walls, exhibiting a characteristic photoelectron N 1s emission peak at 400.3 eV. Very importantly, by means of HR-TEM investigations we have also observed the presence of the [60]fullerene functions on the SWCNT outer surface by imaging spherical structures. The presence of the porphyrinyl and ferrocenyl fragments, which can act as effective chromophores and electroactive species, makes this class of materials very interesting for applications in optoelectronics and photovoltaics, and bio-applications, for example in the field of diagnosis and treatment.

The emerging applications of functionalized carbon nanotubes (CNTs) in various research domains necessitate the use of many different analytical techniques to confirm their structural modifications in a fast and reliable manner. Thus far, NMR spectroscopy has not been among the main tools for characterization of organically modified carbon nanostructures. 1 H analysis is limited because the signals in these derivatives are typically weak and broad, resulting in uncertainties of a few parts per million, and because of the strong interference of residual solvent signals. To overcome these limitations, we investigated the applicability of proton NMR spectroscopy based on gradient-edited diffusion pulse sequences (1D diffusion-ordered spectroscopy, DOSY) in the characterization of CNT derivatives. In general, diffusion NMR experiments allow the separation of NMR signals of different species present in a mixture, according to their own diffusion coefficients, merging spectroscopy information with size analysis. In the present study, a selected set of CNT derivatives was synthesized and analyzed using 1D DOSY experiments by applying strong magnetic field gradients (up to 42.6 G cm -1 ). Colorimetric tests (i.e., Kaiser test) and TGA analysis support the NMR findings, which are related to isolated and/or bundled short SWNTs, on the basis of TEM and AFM characterization. The overall results show that the diffusion-based NMR spectroscopy is a fast and promising approach for the characterization of covalently modified CNT derivatives.

We report the spectroscopic changes of tetraphenylporphyrin carbon nanotube composites in a variety of chlorinated solvents such as chloroform, dichloroethane and dichlorobenzene as a result of sonication. Detailed data analysis suggests that protonation of the porphyrin core nitrogen atoms occurs as a result of sonodegradation of the solvent molecules. Extreme care must be taken when working with carbon nanotube composite solutions in chlorinated solvents, as sonication is always employed to disperse the nanotubes. When working with molecules that are capable of acting as a base some

The design, synthesis and complete characterization of a smart material composed of single-walled nanotubes functionalized with spiropyran-based photo switchable molecules are reported. The chemical complexity of the system requires the use of a range of complementary techniques in order to provide a complete picture of the composition and performance of the nanomaterial. Thermal gravimetric analysis ensured both the high degree of chemical functionalization and the presence of molecular switches in the nanotube sample; micro-Raman indirectly confirmed the successful oxidation of the tubes, FT-IR proved the nature of the functional groups introduced based on their characteristic stretching vibrations and atomic force microscopy demonstrated nanotube lengths of approximately 600 nm. UV-Vis-NIR absorption spectroscopy was used to evaluate the photoresponsive behaviour of the nanomaterial, and the intensity of the absorption band at 556 nm could be modulated by light-induced reversible conversion of the spiropyran molecules attached to the SWCNT from the spiro close conformation to

A novel versatile approach for the functionalization of multilayer fullerenes (carbon nano-onions) has been developed, which involves the facile introduction of a variety of simple functionalities onto their surface by treatment with in situ generated diazonium compounds. This approach is complemented by use of "click" chemistry which was used for the covalent introduction of more complex porphyrin molecules.

Single-wall carbon nanotubes (SWCNT) are severely restricted in their applications, as they exist in rope-like bundles. Recently, J. Coleman et al. demonstrated a spectroscopic method to monitor bundle dissociation in low concentration NT-polymer composites. 1 The method relies on the measurement of the ratio of free-polymer to the nanotube-bound polymer in the SWCNT-polymer solutions via luminescent spectroscopy. A theory has been developed to transform this data into the bundle surface area, which is of course related to the bundle size. This method clearly shows that individual, isolated SWCNT are stable in low concentration dispersions. The main aim of this work is to better understanding of the physics behind polymer -SWCNT interactions, the binding scheme, and the magnitude of the polymer -SWCNT binding energy. In an effort to broaden the understanding of the physical processes governing the NT de-bundling a wide range of suitable polymers and short-chain molecules have been examined. We found a strong dependence of the concentration at which individual NTs become stable with the nature of the dispersant molecule.

The ability of a carboxylic acid functionalized spiropyran, SP, to act as a reversible and selective receptor for metal ions has been systematically examined. A series of spectroscopic measurements, combined with single-crystal X-ray diffraction have been employed in order to determine metal-ion sensitivity and selectivity, binding constants, solution compositions, binding kinetics as well as solid-state structure of a metal-complex of this ligand. This molecule acts as a chelating ligand and binds to metal ions using a triad of functionalities and will release the metal ion by application of visible light. Altering the complex from ZnCl 2 and Zn(ClO 4 ) 2 , leads to only a small change in the complex absorption maxima from 494 to 492 nm, but produced a drastic increase in the sensitivity for the zinc(II) ion. Fluorescence spectroscopy was employed to establish that the detection limit for Zn(II) is approximately 3 ¥ 10 -7 M for Zn(ClO 4 ) 2 . The counterion also influences binding constants and the equilibrium constants for Cu(ClO 4 ) 2 and CuCl 2 are K = 3.37 ¥ 10 4 M -1 to K = 2.04 ¥ 10 3 M -1 , respectively. Additionally, in the presence of perchlorate, the spiropyran-Cu complex formation is fast enough to allow for real-time naked eye detection of this metal ion in less than three minutes; the formation of other metal complexes takes between 50 minutes to 2 hours. Finally, the single-crystal structure determination of the SP-zinc chloride complex shows that the Zn(II) ion displays a distorted square-pyramidal arrangement, and neighbouring metal ions are bound together into a 1-D coordination polymer with a hydrophilic core, surrounded by hydrophobic 'cladding'.

Single-wall carbon nanotubes (SWCNT) are severely restricted in their applications, as they exist in rope-like bundles. Recently, J. Coleman et al. demonstrated a spectroscopic method to monitor bundle dissociation in low concentration NT-polymer composites. 1 The method relies on the measurement of the ratio of free-polymer to the nanotube-bound polymer in the SWCNT-polymer solutions via luminescent spectroscopy. A theory has been developed to transform this data into the bundle surface area, which is of course related to the bundle size. This method clearly shows that individual, isolated SWCNT are stable in low concentration dispersions. The main aim of this work is to better understanding of the physics behind polymer -SWCNT interactions, the binding scheme, and the magnitude of the polymer -SWCNT binding energy. In an effort to broaden the understanding of the physical processes governing the NT de-bundling a wide range of suitable polymers and short-chain molecules have been examined. We found a strong dependence of the concentration at which individual NTs become stable with the nature of the dispersant molecule.

The in Vitro toxic response of spiropyrans in cellular models has not been previously addressed, despite the fact that such photoswitchable molecules have shown great potential as versatile and tunable components for bionanodevices and imaging agents. In this study, we examine the cytotoxic effects of a spiropyran, namely, 8-methoxy-6-nitro-BIPS (1′,3′-dihydro-1′-ethanol-3′,3′-dimethyl-8-methoxy-6-nitrospiro(2H-1-benzopyran-2,2′-(2H)-indole) [1], in three cultured cellular models (THP-1, AGS, and A549 cell lines) by High Content Screening and Analysis (HCSA) and by enzyme-linked immunosorbent (ELISA) assays (Interleukin-6 and Tumor Necrosis Factor-alpha). The HCSA results show that low concentrations of 8-methoxy-6-nitro-BIPS (10 -6 , 10 -8 , and 10 -9 M) do not induce any cytotoxic response after 24 and 72 h exposure time, while at the highest concentrations (10 -3 and 10 -4 M) the exposure time becomes a critical parameter of the toxic response. The cell viability is reduced by 60% for THP-1 cells, 50% for AGS cells, and 40% for A549 cells at a spiropyran concentration of 10 -3 M after 24 h incubation, whereas at 72 h, the cell loss increases above 90%. Interestingly, at 10 -4 M no significant cytotoxic response is registered after 24 h exposure, where contrarily cytotoxicity is verified after 72 h. Our ELISA results show that consistently with the HCSA analysis a robust inflammatory response is present at 10 -3 M after 24 h exposure and at 10 -3 M and 10 -4 M after 72 h, in all three cell lines investigated.

Nanoparticles have enormous potential in diagnostic and therapeutic studies. We have demonstrated that the amyloid beta mixed with and conjugated to dihydrolipoic acid-(DHLA) capped CdSe/ZnS quantum dots (QDs) of size approximately 2.5 nm can be used to reduce the fibrillation process. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) were used as tools for analysis of fibrillation. There is a significant change in morphology of fibrils when amyloid β (1-42) (Aβ(1-42)) is mixed or conjugated to the QDs. The length and the width of the fibrils vary under modified conditions. Thioflavin T (ThT) fluorescence supports the decrease in fibril formation in presence of DHLA-capped QDs.

The presence of carboxylated carbonaceous material in nitric acid-treated single-walled carbon nanotube (SWNT) samples has recently brought renewed focus on the processes by which covalent functionalization of such materials are carried out. Using a widely reported 2-step purification/ oxidation procedure, we have investigated the effect of basic treatment and solvent washing on the functionalization and final properties and behavior of SWNTs. We have demonstrated, using a number of spectroscopic techniques, that in the absence of NaOH treatment, COOH functionality is introduced directly onto SWNTs, and not only onto carbonaceous material present in the sample. Covalent functionalization of the oxidized materials was also investigated by attachment of a fluorescent probe, and ultimately, whether treated with base or solvent washed, the resulting materials are close to identical with respect to both their appearance and properties. In addition, we have demonstrated that using either of these purification/oxidation strategies, functionalized materials can be produced that still exhibit distinctive optical/electronic properties, as demonstrated by sustained structured spectroscopic absorption and emission features.