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Liscio A.,CNR Institute for Organic Syntheses and Photoreactivity | Palermo V.,CNR Institute for Organic Syntheses and Photoreactivity | Samori P.,University of Strasbourg
Accounts of Chemical Research | Year: 2010

In microelectronics and biology, many fundamental processes involve the exchange of charges between small objects, such as nanocrystals in photovoltaic blends or individual proteins in photosynthetic reactions. Because these nanoscale electronic processes strongly depend on the structure of the electroactive assemblies, a detailed understanding of these phenomena requires unraveling the relationship between the structure of the nano-object and its electronic function. Because of the fragility of the structures involved and the dynamic variance of the electric potential of each nanostructure during the charge generation and transport processes, understanding this structure-function relationship represents a great challenge. This Account discusses how our group and others have exploited scanning probe microscopy based approaches beyond imaging, particularly Kelvin probe force microscopy (KPFM), to map the potential of different nanostructures with a spatial and voltage resolution of a few nanometers and millivolts, respectively. We describe in detail how these techniques can provide researchers several types of chemical information. First, KPFM allows researchers to visualize the photogeneration and splitting of several unitary charges between well-defined nano-objects having complementary electron-acceptor and -donor properties. In addition, this method maps charge injection and transport in thin layers of polycrystalline materials. Finally, KPFM can monitor the activity of immobilized chemical components of natural photosynthetic systems. In particular, researchers can use KPFM to measure the electric potential without physical contact between the tip and the nanostructure studied. These measurements exploit long-range electrostatic interactions between the scanning probe and the sample, which scale with the square of the probe-sample distance, d. While allowing minimal perturbation, these long-range interactions limit the resolution attainable in the measurement of potentials. Although the spatial resolution of KPFM is on the nanometer scale, it is inferior to that of other related techniques such as atomic force or scanning tunneling microscopy, which are based on short-range interactions scaling as d-7 or e-d, respectively. To overcome this problem, we have recently devised deconvolution procedures that allow us to quantify the electric potential of a nano-object removing the artifacts due to its nanometric size. © 2010 American Chemical Society.

Monti S.,CNR Institute for Organic Syntheses and Photoreactivity | Manet I.,CNR Institute for Organic Syntheses and Photoreactivity
Chemical Society Reviews | Year: 2014

In this tutorial review we illustrate how the interaction of photoactive drugs/potential drugs with proteins or DNA in supramolecular complexes can determine the course of the reactions initiated by the drug absorbed photons, evidencing the mechanistic differences with respect to the solution conditions. We focus on photoprocesses, independent of oxygen, that lead to chemical modification of the biomolecules, with formation of new covalent bonds or cleavage of existing bonds. Representative systems are mainly selected from the literature of the last decade. The photoreactivity of some aryl propionic acids, (fluoro)quinolones, furocoumarins, metal coordination complexes, quinine-like compounds, naphthaleneimides and pyrenyl-peptides with proteins or DNA is discussed. The use of light for biomolecule photomodification, historically relevant to biological photosensitization processes and some forms of photochemotherapy, is nowadays becoming more and more important in the development of innovative methods in nanomedicine and biotechnology. This journal is © the Partner Organisations 2014.

Praveen V.K.,CNR Institute for Organic Syntheses and Photoreactivity | Ranjith C.,University of Milan | Bandini E.,CNR Institute for Organic Syntheses and Photoreactivity | Ajayaghosh A.,Indian National Institute for Interdisciplinary Science and Technology | Armaroli N.,CNR Institute for Organic Syntheses and Photoreactivity
Chemical Society Reviews | Year: 2014

Oligo(phenylenevinylene)s (OPVs) are extensively investigated π-conjugated molecules that exhibit absorption and fluorescence in the UV-Vis spectral region, which can be widely tuned by chemical functionalisation and external control (e.g. solvent, temperature, pH). Further modulation of the optoelectronic properties of OPVs is possible by supramolecular aggregation, primarily driven by hydrogen bonding or π-stacking interactions. In recent years, extensive research work has been accomplished in exploiting the unique combination of the structural and electronic properties of OPVs, most of which has been targeted at the preparation of molecules and materials featuring photoinduced energy transfer. This review intends to offer an overview of the multicomponent arrays and self-assembled materials based on OPV which have been designed to undergo energy transfer by means of a thorough choice of excitation donor-acceptor partners. We present a few selected examples of photoactive dyads and triads containing organic moieties (e.g. fullerene, phenanthroline) as well as coordination compounds (Cu(i) complexes). We then focus more extensively on self-assembled materials containing suitably functionalised OPVs that lead to hydrogen bonded aggregates, helical structures, gels, nanoparticles, vesicles, mesostructured organic-inorganic hybrid films, functionalised nanoparticles and quantum dots. In most cases, these materials exhibit luminescence whose colour and intensity is related to the efficiency and direction of the energy transfer processes. This journal is © the Partner Organisations 2014.

Natali M.,University of Ferrara | Campagna S.,Messina University | Campagna S.,CNR Institute for Organic Syntheses and Photoreactivity | Scandola F.,University of Ferrara
Chemical Society Reviews | Year: 2014

Photoinduced electron transfer plays key roles in many areas of chemistry. Superexchange is an effective model to rationalize photoinduced electron transfer, particularly when molecular bridges between donor and acceptor subunits are present. In this tutorial review we discuss, within a superexchange framework, the complex role played by the bridge, with an emphasis on differences between thermal and photoinduced electron transfer, oxidative and reductive photoinduced processes, charge separation and charge recombination. Modular bridges are also considered, with specific attention to the distance dependence of donor-acceptor electronic coupling and electron transfer rate constants. The possibility of transition, depending on the bridge energetics, from coherent donor-acceptor electron transfer to incoherent charge injection and hopping through the bridge is also discussed. Finally, conceptual analogies between bridge effects in photoinduced electron transfer and optical intervalence transfer are outlined. Selected experimental examples, instrumental to illustration of the principles, are discussed. This journal is © the Partner Organisations 2014.

Babu S.S.,Indian National Institute for Interdisciplinary Science and Technology | Praveen V.K.,Indian National Institute for Interdisciplinary Science and Technology | Praveen V.K.,CNR Institute for Organic Syntheses and Photoreactivity | Ajayaghosh A.,Indian National Institute for Interdisciplinary Science and Technology
Chemical Reviews | Year: 2014

The large volume of research related to supramolecular π-gel chemistry indicates the potential of this area in the field of new functional materials useful for a variety of application, particularly to the fabrication of organic electronic devices. For improved electronic properties, it is necessary to avoid/reduce the content of insulating alkyl chains in the gelator molecules, which is the key point in balancing solubility and precipitation. This will improve the 1D ordering of the gelator and thereby the charge transport properties. Postpolymerization approaches and hybrid material assemblies of gels should be further explored to obtain stable structures that can overcome ambient conditions without loosing the electronic properties. π-gelators have great potential to the development of self-assembly based bulk heterojunction solar cells. For improved performance in this field, more appropriate D-A systems with absorption characteristics extendable to the near-IR and IR regions of the electromagnetic spectrum for more solar radiation coverage, improved stability and environmental compatibility are needed.

Palermo V.,CNR Institute for Organic Syntheses and Photoreactivity
Chemical Communications | Year: 2013

What is, exactly, graphene? While we often describe graphene with many superlative adjectives, it is difficult to force this material into a single chemical class. Graphene's typical size is atomistic in one dimension of space, and mesoscopic in the other two. This provides graphene with several, somehow contrasting properties. Graphene can be patterned, etched and coated as a substrate. Though, it can also be processed in solution and chemically functionalized as a molecule. It could be considered as a polymer, obtained by bottom-up assembly of carbon atoms or small molecules, but it can be obtained also from top-down exfoliation of graphite (a mineral). It does not have a well-defined shape, such as that of fullerenes or nanotubes; conversely, it is a large, highly anisotropic, very flexible object, which can have different shapes and be folded, rolled or bent to a high extent. In this feature article, we will discuss the state of the art and possible applications of graphene in its broader sense with a particular focus on how its "chemical" properties, rather than its well-known electrical ones, can be exploited to develop original science, innovative materials and new technological applications. This journal is © The Royal Society of Chemistry 2013.

Armaroli N.,CNR Institute for Organic Syntheses and Photoreactivity | Balzani V.,University of Bologna
Energy and Environmental Science | Year: 2011

The purpose of this review is examination of the present scenario of electricity production and investigation of whether an electricity powered world is possible, indicating which primary energy forms should be preferably utilized. Currently, most of the primary energy used by mankind, including that employed to generate electricity, comes from fossil fuels, which need to be phased out because they bring about severe damage to climate, environment, and human health and, additionally, their stock will be largely depleted during the present century. All the energy technologies poised to replace those based on fossil fuels, namely nuclear and renewables (wind, hydro, concentrated solar power, photovoltaics, biomass, geothermal, tidal, wave) essentially produce electricity, and this suggests that we will progressively shift to an electricity-based economy over the course of the 21st century. The economic, technical, ethical and social issues entangled with nuclear technologies and the unexpectedly fast expansion of renewable energies (particularly wind and solar) point to an increasingly important role of the latter in electricity generation. The present one way utility-to-customer energy system, designed over one century ago, will need substantial reshaping to enable the build up of a smart grid capable of dealing with variable renewable supply and fluctuating end-user demand by exchange of information between customer and utility. To accomplish this result, effort in research and development of storage devices and facilities on the small (e.g., batteries, capacitors) and large (e.g., pumped hydro, compressed air storage, electrolytic hydrogen) scale is needed. In the medium and long term, the expansion of electricity production will also likely lead to progressive replacement of internal combustion engines with electric motors in the automotive sector, accompanied by a shift from individual to mass transportation systems. We have still a long way out of the fossil fuel era, but this challenge can be won only if carbon-free electricity largely replaces the direct combustion of irreplaceable and climate-altering fossil fuel resources. © 2011 The Royal Society of Chemistry.

Accorsi G.,CNR Institute for Organic Syntheses and Photoreactivity | Armaroli N.,CNR Institute for Organic Syntheses and Photoreactivity
Journal of Physical Chemistry C | Year: 2010

The optical, electrochemical and excited state properties of C60 fullerene and its derivatives, combined with their peculiar structural features, have made them ideal modules for the construction of complex architectures which feature light induced processes. Here are described three selected classes of such systems investigated in our group by taking advantage of some intrinsic excited state properties of C60 fullerenes such as fluorescence, triplet lifetimes, or sensitized singlet oxygen luminescence. Fullerene hybrid assemblies with Cu(I), Ru(II), and Re(I) complexes undergo ultrafast photoinduced electron transfer (PET) upon excitation of the metalto-ligand-charge-transfer (MLCT) excited states of the metal-complexed moiety. In the case of the Cu(I) system, occurrence of PET by fullerene excitation depends on the specific functionalization of the carbon sphere. Fullerodendrimers equipped with oligophenylenevinylene moieties and showing enhanced or reduced PET as a function of dendrimer structure and size are presented along with simpler monochromophoric fullerodendrimers which illustrate the capability of fullerene triplets to probe dendritic shielding effects. The peculiar ground and excited-state properties of rigid and conformationally flexible fullerene-porphyrin systems arranged in a face-to-face fashion are described, both with meso,meso-linked or triply fused porphyrin oligomers. Control of the direction and nature of photoinduced processes is achieved in such systems, which additionally show charge transfer or porphyrin-centered near-infrared luminescence. The whole work is discussed in a historic perspective and further development for photoactive fullerodendrimers and face-to-face arrays, particularly in solar energy Conversion Devices, is envisaged. Copyright © 2010 American Chemical Society.

Armaroli N.,CNR Institute for Organic Syntheses and Photoreactivity | Balzani V.,University of Bologna
ChemSusChem | Year: 2011

Hydrogen is often proposed as the fuel of the future, but the transformation from the present fossil fuel economy to a hydrogen economy will need the solution of numerous complex scientific and technological issues, which will require several decades to be accomplished. Hydrogen is not an alternative fuel, but an energy carrier that has to be produced by using energy, starting from hydrogen-rich compounds. Production from gasoline or natural gas does not offer any advantage over the direct use of such fuels. Production from coal by gasification techniques with capture and sequestration of CO2 could be an interim solution. Water splitting by artificial photosynthesis, photobiological methods based on algae, and high temperatures obtained by nuclear or concentrated solar power plants are promising approaches, but still far from practical applications. In the next decades, the development of the hydrogen economy will most likely rely on water electrolysis by using enormous amounts of electric power, which in its turn has to be generated. Producing electricity by burning fossil fuels, of course, cannot be a rational solution. Hydroelectric power can give but a very modest contribution. Therefore, it will be necessary to generate large amounts of electric power by nuclear energy of by renewable energies. A hydrogen economy based on nuclear electricity would imply the construction of thousands of fission reactors, thereby magnifying all the problems related to the use of nuclear energy (e.g., safe disposal of radioactive waste, nuclear proliferation, plant decommissioning, uranium shortage). In principle, wind, photovoltaic, and concentrated solar power have the potential to produce enormous amounts of electric power, but, except for wind, such technologies are too underdeveloped and expensive to tackle such a big task in a short period of time. A full development of a hydrogen economy needs also improvement in hydrogen storage, transportation and distribution. Hydrogen and electricity can be easily interconverted by electrolysis and fuel cells, and which of these two energy carriers will prevail, particularly in the crucial field of road vehicle powering, will depend on the solutions found for their peculiar drawbacks, namely storage for electricity and transportation and distribution for hydrogen. There is little doubt that power production by renewable energies, energy storage by hydrogen, and electric power transportation and distribution by smart electric grids will play an essential role in phasing out fossil fuels. Energy: The hydrogen economy is often proposed by media and also by some scientists as the way out from fossil fuels. Is it an achievable goal? How far are we from it? This Review makes a critical analysis of the use of hydrogen in several different technologies. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Praveen V.K.,CNR Institute for Organic Syntheses and Photoreactivity | Ranjith C.,University of Milan | Armaroli N.,CNR Institute for Organic Syntheses and Photoreactivity
Angewandte Chemie - International Edition | Year: 2014

Let there be light, let it be white: Recent developments in the use of chromophore-based gels as scaffolds for the assembly of white-light-emitting soft materials have been significant. The main advantage of this approach lies in the facile accommodation of selected luminescent components within the gel. Excitation-energy-transfer processes between these components ultimately generate the desired light output. © 2014 WILEY-VCH Verlag GmbH.

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