[Show abstract][Hide abstract] ABSTRACT: The generation, under self-assembly conditions, of coordination polymers on surface based combinations of a terpyridine-antracene-pyridine based tecton and Co(ii) or Pd(ii) cations is primarily governed by the coordination geometry of the metal center (octahedral and square planar respectively). While the octahedral Co(ii) based polymer self-assembles in insulating films exhibiting randomly oriented crystalline domains, the planarity of Pd(ii) based polymers leads to the formation of conductive π-π stacked fibrillar structures exhibiting anisotropically oriented domains. In the latter case, the favorable Pd-Pd and anthracene-anthracene wavefunction overlaps along the fiber direction are responsible for the large electronic couplings between adjacent chains, whereas small electronic couplings are instead found along individual polymer chains. These results provide important guidelines for the design of conductive metal coordination polymers, highlighting the fundamental role of both intra- as well as inter-chain interactions, thus opening up new perspectives towards their application in functional devices.
[Show abstract][Hide abstract] ABSTRACT: The self-assembly of multiple molecular components into complex supramolecular architectures is ubiquitous in nature and constitutes one of the most powerful strategies to fabricate multifunctional nanomaterials making use of the bottom-up approach. When spatial confinement in two-dimensions on a solid substrate is employed, this approach can be exploited to generate periodically ordered structures from suitably designed molecular tectons. In this manuscript we demonstrate that physisorbed directional periodic arrays of monometallic or hetero bimetallic coordination polymers can be generated on HOPG surface by combinations of suitably designed directional organic tecton or metallatecton based on a porphyrin or Ni(II) metallaporphyrin backbone bearing both a pyridyl and a terpyridyl units acting as coordinating sites for CoCl2. The periodic architectures were visualized at the solid/liquid interface with a sub-molecular resolution by scanning tunneling microscopy (STM) and corroborated by combined density functional and time-dependent density functional theory (DFT and TD-DFT) calculations. The capacity to nanopattern the surface for the first time with two distinct metallic centers exhibiting different electronic and optical properties is a key step towards the bottom-up construction of robust multicomponent, thus, multifunctional molecular nanostructures and nanodevices.
Full-text · Article · Jun 2015 · Journal of the American Chemical Society
[Show abstract][Hide abstract] ABSTRACT: The controlled assembly of the prototypical n-type organic semiconductor N,N′-1H,1H-perfluorobutyl dicyanoperylenecarboxydiimide (PDIF-CN2) into ordered nanoarchitectures and the multiscale analysis of the correlation between their structural and their electrical properties is reported. By making use of the Langmuir–Blodgett (LB) technique, monolayers of PDIF-CN2 arranged in upright standing molecular packing on different substrates are formed. Postdeposition thermal treatment makes it possible to trigger a reorganization into layered ultrathin crystalline nanostructures, exhibiting structural and photophysical properties similar to those of microscopic crystals obtained by solvent-induced precipitation. The controlled engineering of these molecular architectures on surfaces enables us to identify both a dependence of the monolayer resistance on the molecular tilt angle in vertical junctions and a pronounced charge-transport anisotropy with enhanced transport along the π–π stacking direction of the PDI core. While a charge carrier mobility for electrons as high as 10–2 cm2 V–1 s–1 is determined in monolayer field-effect transistors for the in-plane direction, being the highest yet reported value for a n-type LB monolayer, the out-of-plane mobility measured by conductive atomic force microscopy in multilayered structures is found to be one order of magnitude lower.
No preview · Article · Mar 2015 · Advanced Functional Materials
[Show abstract][Hide abstract] ABSTRACT: We report here the design of two sets of multifluorophoric silica nanoparticles, observing unprecedented efficiencies in the energy-transfer processes among the doping dyes. These nanomaterials show a very high overall sensitization, allowing under a single wavelength excitation to obtain many different colors (one per nanoparticle) in emission with negligible crosstalk. Moreover, each particle can present very large and tunable pseudo-Stokes shifts (up to 435 nm), a very high brightness even exciting the bluest donor, and a negligible residual emission intensity from all donor dyes. All these features, combined with colloidal stability and synthetic method reliability, make these multicomponent nanoparticles very promising for multiplex analysis and for all the diagnostic techniques requiring high sensitivity associated with a large Stokes shift.
No preview · Article · Apr 2014 · The Journal of Physical Chemistry C
[Show abstract][Hide abstract] ABSTRACT: Fast and efficient energy transfer among dyes confined in nanocontainers provides the basis of outstanding functionalities in new-generation luminescent probes. This feature article provides an overview of recent research achievements on luminescent Pluronic-Silica NanoParticles (PluS NPs), a class of extremely monodisperse core-shell nanoparticles whose design can be easily tuned to match specific needs for diverse applications based on luminescence, and that have already been successfully tested in in vivo imaging. An outline of their outstanding properties, such as tuneability, bright and photoswitchable fluorescence and electrochemiluminescence, will be supported by a critical discussion of our recent works in this field. Furthermore, novel data and simulations will be presented to (i) thoroughly examine common issues arising from the inclusion of multiple dyes in a small silica core, and (ii) show the emergence of a cooperative behaviour among embedded dyes. Such cooperative behaviour provides a handle for fine control of brightness, emission colour and self-quenching phenomena in PluS NPs, leading to significantly enhanced signal to noise ratios.
[Show abstract][Hide abstract] ABSTRACT: Integrating carbon nanoparticles (CNPs) with proteins to form hybrid functional assemblies is an innovative research area with great promise for medical, nanotechnology, and materials science. The comprehension of CNP-protein interactions requires the still-missing identification and characterization of the 'binding pocket' for the CNPs. Here, using Lysozyme and C 60 as model systems and NMR chemical shift perturbation analysis, a protein-CNP binding pocket is identified unambiguously in solution and the effect of the binding, at the level of the single amino acid, is characterized by a variety of experimental and computational approaches. Lysozyme forms a stoichiometric 1:1 adduct with C 60 that it is dispersed monomolecularly in water. Lysozyme maintains its tridimensional structure upon interaction with C 60 and only a few identified residues are perturbed. The C 60 recognition is highly specific and localized in a well-defined pocket.
[Show abstract][Hide abstract] ABSTRACT: Near-infrared (NIR) imaging of the lymphatic system offers a sensitive, versatile, and accurate lymph node mapping to locate the first, potentially metastatic, draining nodes in the operating room. Many luminescent nanoprobes have received great attention in this field, and the design of nontoxic and bright nanosystems is of crucial importance. Fluorescent NIR-emitting dye doped silica nanoparticles represent valuable platforms to fulfill these scopes, providing sufficient brightness, resistance to photobleaching, and hydrophilic nontoxic materials. Here, we synthesized these highly stable core-shell nanoparticles with a programmable surface charge positioning and determined the effect of these physicochemical properties on their in vivo behavior. In addition, we characterized their fluorescence kinetic profile in the right axillary lymph node (RALN) mapping. We found that nanoparticles with negative charges hidden by a PEG shell are more appropriate than those with external negative charges in the mapping of lymph nodes. We also demonstrated the efficient excretion of these nanostructures by the hepatobiliary route and their nontoxicity in mice up to 3 months postinjection. These results indicate the potential future development of these fluorescent nanosystems for LN mapping.
[Show abstract][Hide abstract] ABSTRACT: The photophysical properties of two 7-aminocoumarin molecules with flexible and rigid alkyl moieties at the 7-nitrogen atom have been investigated in ethanol and in Pluronic-silica nanoparticles (PluS NPs) by means of time-resolved emission spectroscopy (TRES) and time-dependent density functional theory (TDDFT). Although the two coumarin derivatives have very different photophysical properties in solution, they show quite similar photophysical behaviour when embedded into the NPs, where an increase in the fluorescence quantum yield of about 10 times was observed for the more flexible molecule. TDDFT calculations employing long-range corrected functionals and with proper account of environmental effects reveal that the formation of an accessible twisted-intramolecular charge transfer state (TICT) is possible for 7-aminocoumarin molecules with flexible alkyl groups in fluid solution, where a conical intersection between the S1 and S0 states is observed at a dihedral angle of about 80°. The excited state dynamics of the population density of this reaction coordinate in ethanol and in silica NPs investigated through the resolution of a generalized Smoulochowsky equation shows that this deactivation mechanism is drastically hampered in a silica matrix, in good agreement with experimental evidence. Steady state and time resolved measurements also suggest that at high concentration for both the dyes intermolecular interactions into the silica matrix lead to fluorescence quenching. TDDFT/PCM calculations clearly indicate that the strong quenching and red shift observed is imputable to the formation of excimers with CT character after absorption of the monomeric species.
No preview · Article · Jun 2013 · Physical Chemistry Chemical Physics
[Show abstract][Hide abstract] ABSTRACT: Stars that shine bright: A high local dye concentration in doped silica-based core-shell nanoparticles causes self-quenching and spectral broadening (top images). This phenomenon jeopardizes the potential advantages of heavily doped systems. Förster resonance energy transfer (FRET) to an acceptor co-included in the silica led to ultrabright nanoparticles (bottom images) with a preselected narrow-band emission and a pseudo-Stokes shift of 129 nm.
No preview · Article · Jun 2013 · Angewandte Chemie International Edition
[Show abstract][Hide abstract] ABSTRACT: In this work, monoolein-based cubosomes were doped with two fluorescent probes, namely fluorescein and dansyl, properly modified with a hydrocarbon chain to increase their encapsulation efficiency within the monoolein palisade. The same nanocarriers were also loaded with quercetin, a hydrophobic molecule with potential anticancer activity. Particularly, the cubosomes doped with the modified fluorescein probe were successfully exploited for single living cell imaging. The physicochemical and photophysical characterizations here reported, along with the well-known ability of cubosomes in hosting molecules with pharmaceutical interest, strongly encourage the use of these innovative fluorescent nanocarriers for theranostic purposes.
[Show abstract][Hide abstract] ABSTRACT: Mineralized tissues grow through biologically controlled processes in which specific macromolecules are involved. Some of these molecules, which are present in very low concentrations and are difficult to localize and characterize, become entrapped inside the mineralized tissue. Herein, a protein fragment, GP, which was obtained by the alkaline digestion of the green sheet of the abalone shell, is used as a probe to study the changes in molecular structure that occur during the precipitation of calcium carbonate. This important goal was achieved by exploiting a fluorescent tag in GP. The experimental results that were obtained by using spectroscopic-, chromatographic-, and microscopic techniques indicate that GP controls the precipitation kinetics and morphology of calcium carbonate crystals, and that it only undergoes structural reorganization when entrapped inside calcium carbonate crystals. To the best of our knowledge, this report represents one of the first studies on the conformational changes of a protein fragment that is involved in biomineralization processes on moving from the solution phase into the mineral phase.
No preview · Article · Sep 2012 · Chemistry - A European Journal
[Show abstract][Hide abstract] ABSTRACT: Warm oder kalt? Ein Cu5‐Metallcluster hat markante photophysikalische Eigenschaften, die in Lösung und Festkörper zwischen −45 und +80 °C in einer temperaturabhängigen Fluoreszenzquantenausbeute und Lebensdauer angeregter Zustände resultieren. Der Komplex ermöglicht eine beispiellose Genauigkeit der Temperaturbestimmung durch Fluoreszenzmessungen und eignet sich damit für Anwendungen z. B. in der Biologie und den (Nano)materialwissenschaften.
No preview · Article · Sep 2012 · Angewandte Chemie
[Show abstract][Hide abstract] ABSTRACT: Despite the recent introduction of targeted bio-drugs, the scarcity of successful therapeutic options for advanced colorectal cancer remains a limiting factor in patient management. The efficacy of curative surgical interventions can only be extended through earlier detection of metastatic foci, which is dependent on both the sensitivity and specificity of the diagnostic tools.
We propose a high-performance imaging platform based on silica-poly(ethylene glycol) nanoparticles doped with rhodamine B and cyanine 5. Simultaneous detection of these dyes is the basis for background subtraction and signal amplification, thus providing high-sensitivity imaging. The functionalization of poly(ethylene glycol) tails on the external face of the nanoparticles with metastasis-specific peptides guarantees their homing to and accumulation at target tissues, resulting in specific visualization, even of submillimetric metastases.
The results reported here demonstrate that our rationally designed modular nanosystems have the ability to produce a breakthrough in the detection of micrometastases for subsequent translation to clinics in the immediate future.
Full-text · Article · Sep 2012 · International Journal of Nanomedicine
[Show abstract][Hide abstract] ABSTRACT: The heat is on: A Cu(5) metal cluster presents distinctive photophysical properties that result in a temperature-dependent fluorescent quantum yield and excited-state lifetime between -45 and +80 °C, both in solution and as a solid. Unprecedented accuracy in temperature determination by fluorescence measurements was achieved with this complex, thus making it suitable for applications in, for example, biology and (nano)materials research.
Full-text · Article · Aug 2012 · Angewandte Chemie International Edition
[Show abstract][Hide abstract] ABSTRACT: This review aims to give an overview on the state of the art in the precise context of metal complexes-based ECL dyes directly adsorbed on, included in or interacting with nanoparticles of various nature. Electrogenerated chemiluminescence, or electrochemiluminescence (ECL), is the process through which species generated at electrodes undergo homogeneous high-energy electron transfer reactions to give excited states that emit light. When stable ECL probes such as ruthenium coordination complexes are used, this process can be performed several times, free of the interferences typical of photoluminescence such as the excitation light, providing a clear and stable signal suitable for highly sensitive assays. The ECL emission is initiated and controlled by the electrode potential and immobilization of the ECL probes on the electrode surface allows one to reduce the consumption of expensive reagents, simplifies the experimental design, and creates regenerable sensing devices. The organization of the electrode surface is thus the key point to optimize the device performance. Nanoparticles have proved their potential as tools to organize the ECL probes, to increase the active area and to improve the electrochemical properties of the interface. There is an extended research devoted on one hand to optimize the materials, and on the other hand to explore the wide horizon of possibilities that arise from the combination of nanoparticles and ECL probes, co-reagents, (bio)markers and other functional moieties. The results discussed in this review clearly show that the use of nanoparticles aimed to obtain signal enhancement represents one of the most interesting research lines for the development of the ECL technique. The activity in this field is so dynamic that outstanding results could reasonably be expected in the near future.
No preview · Article · Aug 2012 · Coordination Chemistry Reviews
[Show abstract][Hide abstract] ABSTRACT: Colour emission of core-shell silica-PEG nanoparticles in water is tuned with an electrochemically induced energy transfer approach. The lack of solubility problems, side electrochemical reactions involving donors and acceptors within the nanoparticle, and the possibility of using many classes of dyes in ECL applications confirm the validity of this strategy.
No preview · Article · Mar 2012 · Chemical Communications
[Show abstract][Hide abstract] ABSTRACT: Devices are systems able to perform specific functions, which result from the coordinated action of different components. The design of these systems is, hence, based on the identification or the development of the necessary parts, and in their integration in a suitable supramolecular architecture. The main challenge in such a process is undoubtedly synthetic: the control of the mutual interactions between the active moieties, in fact, requires a fine-tuning of the distance and orientation of the components and, in the case of physically connected donor-acceptor moieties, of the electronic properties of the interconnecting linkers. Organization through covalent bonding has, in this context, several advantages, and many examples of covalent supramolecular devices have been reported in the last two decades. Besides, the covalent approach led to the design of fascinating and efficient prototypes, that often require the preparation of beautiful but complicated chemical systems, through time-demanding multistep synthetic paths and that are not suitable for large-scale production. Many examples of devices derived from a more traditional supramolecular approach based on self-assembly and host-guest interactions have also been reported. In this chapter, some relevant examples of both covalent and self-organizing supramolecular devices based on energy-transfer (ET) processes are reviewed. The basic principles of ET are also discussed. Recently, the advent of nanomaterials offered to supramolecular chemists new active components and structural platforms suitable for the design of nanometric molecular devices. At the present stage, nanomaterials represent, in fact, an ideal platform to achieve a reasonable degree of spatial organization especially when the integration of a large number of components is required or desired. This approach allows the achievement of complex, extensive devices otherwise not accessible. Moreover, some nanomaterials have unique photophysical properties and can become themselves active nanosized component of the final device. In this chapter, we discuss selected examples of ET-based supramolecular devices with increasing complexity and size; going from dyads to multicomponent nanostructures.Keywords:energy transfer;nanoparticles;fluorescence;luminescence;electron transfer
[Show abstract][Hide abstract] ABSTRACT: Biocompatible highly bright silica nanoparticles were designed, prepared and tested in small living organisms for both in vivo and ex vivo imaging. The results that we report here demonstrate that they are suitable for optical imaging applications as a possible alternative to commercially available fluorescent materials including quantum dots. Moreover, the tunability of their photophysical properties, which was enhanced by the use of different dyes as doping agents, constitutes a very important added value in the field of medical diagnostics.