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The attachment of well-defined charge transfer agents to the surface of nanomaterials is an efficient strategy to control their charge density and also to tune their optical, electrical, and physicochemical properties. Particularly interesting are charge transfer agents that either donate or withdraw electrons depending on the arrangements of their building units and that promise a non-destructive attachment to delicate nanomaterials like sp$^2$ compounds. In this work, we rationally synthesize molecular moieties with versatile functionalities. A reactive anchor group allows to attach them to carbon nanotubes as defined charge transfer agents while preserving the tube $��$-conjugation. The charge transfer agents were synthesized through the stepwise nucleophilic substitution of either one (monosubstituted series) or two chlorine (disubstituted series) atoms of cyanuric chloride by aniline derivatives containing one, two or three methoxy groups in the para and meta positions. Variation in the number and position of methoxy as an electron transferring group help us to manipulate the electronic and optical properties of the molecular probes and their charge transfer to the SWNTs systematically. The correlation between the optical properties of these molecular probes and their functionality was investigated by experiments and quantum chemical calculations. While the optoelectronic properties of the conjugated charge transfer agents were dominated by the aniline segments, the triazine warrants the ability to nondestructively attach to the surface of SWNTs. This study is one step ahead towards the production of SWNTs with desired optical and electrical properties by covalent $��$-preserving functionalization.

To disentangle the process of direct optical excitation of carbon nanotubes coated with photochromic switches from the isomerization of the latters, we functionalized single walled carbon nanotubes with the orthogonal dipole switching moiety dihydroazulene/vinylheptafulvene (DHA/VHF). The orthogonality of the switch decouples the kinetics of the dipole change from the optical excitation of the nanotubes, allowing the independent investigations of the excitation of tubes and switch. DHA to VHF conversion triggered by exposures to UV photons. The back isomerization is thermally activated and cannot be driven optically.

The interaction with surfactants changes from one carbon nanotube species to the other. We used this to replace non-ionic surfactants by ionic ones. By fine-tuning the replacement conditions, we covered some specific nanotubes with non-ionic surfactants and the others with ionic ones. Addition of salt triggers precipitation of the species suspended by the ionic surfactant; this effectively leads to chiral selective enrichment of a carbon nanotube suspension. We hence produce an (8,4)-enriched suspension by replacing a polyglycerol-based custom amphiphile with the commercial SDBS and salting with NaCl.

We recently reported a significant deviation in the photoluminescence intensities of HiPco nanotubes solubilized with a perylene-based surfactant, C16, compared to bile salt surfactants. For C16, the photoluminescence emission of chiralities (9,5), (10,3), and (11,1) is enhanced by up to 430%. Resonant Raman spectroscopy is less sensitive to bundling state and also yields disparate chirality intensity ratios: The (11,0) zigzag tube signal increases by 100% compared to (8,6), (9,4), and (10,2) after suspension with C16. We also report the change in photoluminescence intensity distribution after the swelling of bile salt suspended nanotubes with a series of small organic chromophores in DCM. These changes are attributed to chromophore-induced surfactant reorganization, resulting in better nanotube individualization. The chirality for which the PL intensity is most enhanced is (11,1) for all chromophores, a chirality also increased by 300% in the C16-solubilized sample. Conjointly, these measurements indicate that both preferential solubilization and enhanced debundling contribute to the PL intensity distribution in the C16-solubilized nanotube sample. This has wide ranging implications for the design of chirally selective surfactants and the demonstration of their selectivity, which is typically only shown through luminescence measurements.

Customized polyglycerol-based surfactants incorporating different aromatic cores are used to isolate and suspend carbon nanotubes in water. Different cores yield suspension with distinct chiral species distribution. Increasing the number of the phenyl rings connecting head and tail, the dispersion of the semiconducting species becomes sharper toward the nanotubes with bigger family index.

Molecular switch compounds, consisting of aromatic anchoring groups connected to a spiropyran moiety, are exploited for carbon nanotube functionalization. The effect of the different anchor groups on sample distribution and debundling efficiency is investigated as well as the influence of the anchor–switch distance and hence tube–switch separation. Morphologically similar anchor groups result in similar chiral compositions of the sample. With smaller separation, the tube–switch interaction strength increases as well as the lifetime of the ring opened isomer.

Chemical sensing of gas molecules adsorbed on the tin dioxide nanowires by modulation of their photoluminescence efficiency is investigated. It is shown that adsorption of nitrogen dioxide at the ppm and sub-ppm level leads to quenching of the photoluminescence emission and that larger sensitivities are obtained at room temperature and at low (order of few ppm) nitrogen dioxide concentrations. The luminescence efficiency is found to decrease upon heating of the sample without appreciable variations of the emission spectrum. Experiments performed during heating and cooling of samples in controlled environment stress the role played by oxidation in the luminescence properties.

(Brief Report)

Aiming to enhance the luminescence yield of carbon nanotubes, we introduce a new class of hybrid nanoplasmonic colloidal systems (π-hybrids). Nanotubes dispersed in gold nanorod colloidal suspensions yield hybrid structures exhibiting enhanced luminescence up to a factor of 20. The novelty of the proposed enhancement mechanism relies on including metal proximity effects in addition to its localized surface plasmons. This simple, robust and flexible technique enhances the luminescence of nanotubes with chiralities whose enhancement has never reported before, for example the (8,4) tube.

Stimulus responsive surfactants based on dendritic glycerol azobenzene conjugates were used to solubilize and debundle single-walled carbon nanotubes in aqueous media. Their debundling property as well as their reaggregation behavior upon irradiation with light was examined and light triggered reversible bundling and precipitation are shown.

Il lavoro si inserisce in un programma di ricerca teso a mettere in evidenza alcuni fenomeni termodinamici di non equilibrio proibiti per ragioni di simmetria nei materiali normali, ma permessi nei materiali chirali. Questi fenomeni coinvolgono l’accoppiamento tra una forza termodinamica di tipo polare e un flusso di tipo assiale. La relativa costante di accoppiamento è quindi uno pseudo-scalare. Si tratta, in generale, di effetti molto deboli e difficili da rivelare, poiché il grado di chiralità dei materiali formati da molecole chirali è, in genere, molto piccolo. I cristalli liquidi colesterici, invece, possiedono una chiralità di tipo strutturale, che è molti ordini di grandezza più grande della chiralità di origine molecolare e sono quindi materiali ideali per l’osservazione sperimentale di tali effetti. Il più noto tra gli effetti termodinamici legati alla chiralità dei colesterici è l’effetto Lehman, che è l’oggetto di studio di questo lavoro. L’effetto consiste nella rotazione della struttura colesterica indotta dall’applicazione di un gradiente di temperatura o di un campo elettrostatico. Sebbene il fenomeno sia stato osservato al microscopio da Lehman fin dal 1900, ogni tentativo di misura quantitativa è finora fallito, per via di effetti concomitanti, come l’effetto flesso-elettrico, legati al difficile controllo della geometria sperimentale (usualmente micro-gocce di colesterico in ambiente isotropo). L’idea di base del lavoro è quello di utilizzare un fascio di luce focalizzato per creare la “gocciolina” colesterica in un ambiente nematico che abbia una simmetria cilindrica attorno alla direzione della velocità angolare di rotazione indotta. La luce svolge un ruolo puramente ausiliario, che permette, però, il controllo accurato della geometria del profilo colesterico, in modo da poter escludere gli effetti concorrenti.