Deposizione elettrochimica di film polimerici foto-attivi per la realizzazione di celle solari

Plastic solar cells bear the potential for large-scale power generation based on flexible, lightweight, inexpensive materials. Since the discovery of the photo-induced electron transfer from a conjugated polymer (electron-donor) to fullerene or its derivatives molecules (electron-acceptors), followed by the introduction of the bulk heterojunction concept which means donors and acceptors blended together to realize the fotoactive layer, materials and deposition techniques have been extensively studied. In this work, electrochemical-deposition methods of polymeric conductive films were studied in order to realize bulk heterojunction solar cells. Indium Tin Oxide (ITO) glass electrodes modified with a thin layer of poly(3,4-ethylenedioxythiophene) (PEDOT) were electrochemically prepared under potentiodynamic and potentiostatic conditions; then those techniques were applied for the electrochemical co-deposition of donor and acceptor on modified ITO electrode to produce the active layer (blend). For the deposition of the electron-donor polymer the electropolymerization of many functionalized thiophene monomers was investigated while, as regards acceptors, fullerene was used first, then the study was focused on its derivative PCBM ([6,6]-phenyl-C61-butyric acid methyl ester). The polymeric films obtained (PEDOT and blend) were electrochemically and spectrophotometrically characterized and the film thicknesses were evaluated by atomic force microscopy (AFM). Finally, to check the performances and the efficiency of the realized solar cells, tests were carried out under standard conditions. Nowadays bulk heterojunction solar cells are still poorly efficient to be competitively commercialized. A challenge will be to find new materials and better deposition techniques in order to obtain better performances. The research has led to several breakthroughs in efficiency, with a power conversion efficiency approaching 5 %. The efficiency of the solar cells produced in this work is even lower (lower than 1 %). Despite all, solar cells of this type are interesting and may represent a cheaper and easier alternative to traditional silicon-based solar panels.

Tetrafenilciclopentadienon-derivati ed analoghi: sintesi, "self-assembly" e caratterizzazione reologica

Gels are materials that are easier to recognize than to define. For all practical purpose, a material is termed a gel if the whole volume of liquid is completely immobilized as usually tested by the ‘tube inversion’ method. Recently, supramolecular gels obtained from low molecular weight gelators (LMWGs) have attracted considerable attention in materials science since they represent a new class of smart materials sensitive to external stimuli, such as temperature, ultrasounds, light, chemical species and so on. Accordingly, during the past years a large variety of potentialities and applications of these soft materials in optoelectronics, as electronic devices, light harvesting systems and sensors, in bio-materials and in drug delivery have been reported. Spontaneous self-assembly of low molecular weight molecules is a powerful tool that allows complex supramolecular nanoscale structures to be built. The weak and non-covalent interactions such as hydrogen bonding, π–π stacking, coordination, electrostatic and van der Waals interactions are usually considered as the most important features for promoting sol-gel equilibria. However, the occurrence of gelation processes is ruled by further “external” factors, among which the temperature and the nature of the solvents that are employed are of crucial importance. For example, some gelators prefer aromatic or halogenated solvents and in some cases both the gelation temperature and the type of the solvent affect the morphologies of the final aggregation. Functionalized cyclopentadienones are fascinating systems largely employed as building blocks for the synthesis of polyphenylene derivatives. In addition, it is worth noting that structures containing π-extended conjugated chromophores with enhanced absorption properties are of current interest in the field of materials science since they can be used as “organic metals”, as semiconductors, and as emissive or absorbing layers for OLEDs or photovoltaics. The possibility to decorate the framework of such structures prompted us to study the synthesis of new hydroxy propargyl arylcyclopentadienone derivatives. Considering the ability of such systems to give π–π stacking interactions, the introduction on a polyaromatic structure of polar substituents able to generate hydrogen bonding could open the possibility to form gels, although any gelation properties has been never observed for these extensively studied systems. we have synthesized a new class of 3,4-bis (4-(3-hydroxy- propynyl) phenyl) -2, 5-diphenylcyclopentadienone derivatives, one of which (1a) proved to be, for the first time, a powerful organogelator. The experimental results indicated that the hydroxydimethylalkynyl substituents are fundamental to guarantee the gelation properties of the tetraarylcyclopentadienone unit. Combining the results of FT-IR, 1H NMR, UV-vis and fluorescence emission spectra, we believe that H-bonding and π–π interactions are the driving forces played for the gel formation. The importance of soft materials lies on their ability to respond to external stimuli, that can be also of chemical nature. In particular, high attention has been recently devoted to anion responsive properties of gels. Therefore the behaviour of organogels of 1a in toluene, ACN and MeNO2 towards the addition of 1 equivalent of various tetrabutylammonium salts were investigated. The rheological properties of gels in toluene, ACN and MeNO2 with and without the addition of Bu4N+X- salts were measured. In addition a qualitative analysis on cation recognition was performed. Finally the nature of the cyclic core of the gelator was changed in order to verify how the carbonyl group was essential to gel solvents. Until now, 4,5-diarylimidazoles have been synthesized.

Nuovi complessi carbenici-N-eterociclici di argento e rutenio: il ruolo del sale di imidazolio.

Il presente lavoro di tesi si inserisce in un progetto di ricerca volto alla sintesi di nuovi complessi di metalli di transizione per lo sviluppo di catalizzatori bifunzionali metallo-legante da impiegare in reazioni di catalisi omogenea come, ad esempio, l’idrogenazione di doppi legami polari. In particolare, il mio progetto ha riguardato la sintesi e la caratterizzazione di nuovi complessi carbonilici di rutenio che combinano diversi leganti quali tetrafenilciclopentadienoni e carbeni N-eterociclici. Inizialmente è stato preparato il complesso dimerico ciclopentadienonico di rutenio carbonilico dicarbonil(η4-3,4-bis(4-metossifenil)-2,5-difenilciclopenta-2,4-dienone)dimero, utilizzato come precursore in tutte le sintesi dei nuovi complessi di rutenio. Successivamente, sono stati preparati numerosi sali di imidazolio da impiegare come precursori dei leganti carbenici N-eterociclici e i corrispondenti complessi di argento. La reattività dei complessi di argento nei confronti del precursore dimerico di rutenio dicarbonil(η4-3,4-bis(4-metossifenil)-2,5-difenilciclopenta-2,4-dienone)dimero ha portato alla formazione di complessi differenti a seconda dell’ingombro sterico del legante carbenico N-eterociclico. È stato inoltre approfondito lo studio della reattività dei sali di imidazolio, variandone ingombro sterico e sostituenti, per combinazione diretta con il precursore dimerico di rutenio dicarbonil(η4-3,4-bis(4-metossifenil)-2,5-difenilciclopenta-2,4-dienone)dimero.

Synthesis of novel cobalt and iron complexes for sustainable catalytic hydrogenations

Aim of the present work of thesis is to synthesize new non-noble metal based complexes to be employ in redox reactions by a metal-ligand cooperative mechanism. The need of replacing toxic and expensive precious metal complexes with more available and benign metals, has led to the development of new compounds based on cobalt and iron, which are the metals investigated in this study. A carbonyl-tetrahydroborato-bis[(2-diisopropylphosphino)ethyl]amine-cobalt complex bearing a PNP-type ligand is synthesized by a three-step route. Optimization attempt of reaction route were assessed in order to lowering reaction times and solvent waste. New cobalt complex has been tested in esters hydrogenation as well as in acceptorless dehydrogenative coupling of ethanol. Other varieties of substrates were also tested in order to evaluate any possible applications. Concerning iron complex, dicarbonyl-(η4-3,4-bis(4-methoxyphenyl)-2,5-diphenylcyclopenta-2,4-dienone)(1,3-dimethyl-ilidene)iron is synthesized by a three steps route, involving transmetallation of a silver complex, derived from an imidazolium salt, to iron complex. In order to avoid solvent waste, optimization is assessed. Studies were performed to assess activity of triscarbonyl iron precursor toward imidazolium salt and silver complexes.