Design and Synthesis of Perylene-Based Supramolecular Hybrids for Novel Technological Applications

2013/2014Negli ultimi 50 anni, l’uomo ha attribuito un valore crescente alla ricerca scientifica in quanto strumento di innovazione e di evoluzione tecnologica. La Scienza è diventata uno strumento in grado di migliorare la qualità di vita dell’uomo portando svariate migliorie, ma anche di cambiare radicalmente il suo stile di vita a seguito di scoperte e di strumenti sconosciuti prima di allora. Il progresso tecnologico, la crescita della popolazione mondiale e delle sue esigenze ha causato degli squilibri nel nostro pianeta, dovuti soprattutto and una non omogenea distribuzione delle risorse, in primis quelle energetiche. Dunque, il ruolo della ricerca scientifica contemporanea ha assunto un’ulteriore valenza, quello di appianare gli squilibri sociali ed economici del pianeta. La ricerca di nuove risorse energetiche, o di vettori nei quali conservare l’energia, è uno dei campi scientifici più fertili; in accordo con le ultime tendenze, massima importanza è riposta nelle tecnologie in grado di convertire l’energia solare e renderla disponibile sotto altre forme più pratiche (procedure di storage più semplici) o più facilmente manipolabili. La scelta di sfruttare l’energia solare si basa su alcuni presupposti logici: (i) abbondanza, (ii) distribuzione pressoché uniforme dell’energia solare sulla superficie del pianeta, (iii) esempi disponibili nel mondo naturale che possono essere studiati, compresi, migliorati. La fotosintesi clorofilliana è sicuramente il processo naturale maggiormente conosciuto; perpetrato da una fetta consistente di forme di vita (in particolare del mondo vegetale), permette a queste di sfruttare l’energia contenuta nella radiazione solare e trasformare acqua ed anidride carbonica in carboidrati (la loro riserva di energia) ed ossigeno. Ispirandosi a questo modello, la scienza dei materiali è alla continua ricerca di substrati in grado di trasformare la luce solare in altri vettori energetici a partire da sostanze semplici ed ampliamente disponibili. La scissione dell’acqua in idrogeno ed ossigeno molecolari è uno di questi possibili traguardi; l’acqua è estremamente abbondante sul nostro pianeta (ricoprendone ben il 69% della sua superficie), l’idrogeno è un combustibile che promette di sostituire i derivati del petrolio nel prossimo futuro, e l’ossigeno è di estremo interesse in quanto fonte stessa della vita sul nostro pianeta, almeno nella forma da noi conosciuta. Il progetto di ricerca descritto in questa tesi pone le basi su queste premesse. L’obiettivo prefissato è stato quello di progettare, realizzare, caratterizzare e testare materiali in grado di attuare processi fotosintetici. Durante la fase di progettazione, si è stati costretti a ragionare su quale potesse essere la classe di materiali appropriata a tale scopo, e ci si è orientati verso nano-ibridi organici/inorganici per una serie di motivi: (i) le (nano)-dimensioni avrebbero permesso di lavorare con precursori molecolari e pilotare con maggiore facilità la fase sintetica; (ii) questa classe di materiali possiede generalmente elevate aree superficiali; (iii) l’uso di materiali organici ed inorganici avrebbe permesso di scegliere building blocks che potessero offrire ciascuno le caratteristiche migliori della loro classe di appartenenza. Il lavoro di tesi si è dunque articolato in due sezioni fondamentali: • determinazione di una classe appropriata di cromofori capaci di catturare efficientemente la luce solare ed attivare una specie catalitica ad essi accoppiati. Relativamente a questo punto, scopo non secondario è stato quello di sviluppare nuovi cromofori rispetto a quelli attualmente riportati nella letteratura scientifica e/o sviluppare nuovi protocolli di sintesi capaci di migliorare rese ed efficienza dei processi attualmente noti • scelta di una appropriata specie catalitica e sviluppo dei materiali ibridi contenenti il/i fotosensibilizzanti e il/i catalizzatori; una volta isolata la potenziale diade, si sarebbe proceduto con la fase di monitoraggio dell’attività fotocatalitica del nuovo materiale. Nello sviluppo di questo progetto, i derivati peilenici sono stati scelti quali potenziali fotosensibilizzanti in virtù di una interessante combinazione di caratteristiche elettroniche e chimico-fisiche (approfonditi nel Capitolo 2), ed in particolare ci si è concentrati su composti solubili in acqua. Quest’ultimo dettaglio non è da sottovalutare in quanto, nell’ottica di effettuare i test finali di scissione ossidativa dell’acqua, l’uso di composti idrofilici avrebbe permesso di utilizzare al contempo l’acqua quale reagente e mezzo di reazione. Prima giungere a questa fase, la chimica dei perileni è stata scandagliata a fondo, e vari derivati sono stati isolati e caratterizzati utilizzando protocolli di sintesi sia classici che innovativi (Capitolo 4). La parte centrale del lavoro di tesi ha riguardato lo studio delle diadi costituite da uno dei perileni isolati (PBI2+) e due diversi catalizzatori: (i) Ru4POM, catalizzatore molecolare a base di rutenio, testato per esperimenti sia in fase omogenea che per la realizzazione di un ibrido tri-componente per futuri studi di elettrocatalisi (Capitoli 5-6); (ii) nanoparticelle di ossido di iridio per la preparazione di fotoanodi da applicare in celle fotoelettrochimiche (Capitolo 7). La confidenza acquisita coi derivati perilenici ha permesso di sviluppare anche progetti paralleli che non riguardassero applicazioni in ambito energetico; un dettagliato studio di perileni bisimmidi quali SERS markers è trattato nella parte finale di questa tesi (Capitolo 8).In the last half-century, scientific evolution allowed humanity to reach important goals; probably the highest impact factor is related to bio-medical conquests, but the acquired knowledge in physics, chemistry and in material science for sure produced several devices which radically changed humanity life-style. Among all, electronics and electronic devices are deeply present in humanity ordinary life and in its new habits. However, an increased interest in scientific research recently rose due to some global problems and challenges that humanity has to face. The high energy demand characterizes Modern Age, and the rapid economic evolution of some areas of the World have caused (and continue to cause) social instability and tension at global level. For this reason, scientific research is focusing more and more on the development of solar devices able to store or eventually manipulate solar energy in other energetic vectors. Interest around solar energy is related to three considerations: basically, it is (i) abundant all over Earth’s surface, (ii) it is uniformly distributed, and (iii) Nature already offers some examples from which it is possible to take inspirations. Natural Photosynthesis is a process (or better a sequence of processes) which has been deeply understood after decades of basic research; this is also the most well-known example of solar light conversion operated from living beings (mainly vegetables) into a new energetic vector (carbohydrates) starting from simple and abundant raw materials (water and carbon dioxide). Material Science is particularly involved in the design of novel materials able to emulate natural photosynthesis and/or perform similar processes; water splitting has a prominent role because its decomposition in molecular hydrogen and oxygen offers the possibility to produce two precious chemical species. Hydrogen is currently the most credited candidate for the substitution of petrol and its derivatives as energetic vectors, while oxygen has basilar importance for life in our planet; moreover, water is extremely abundant on the Earth’s surface (almost 69% of the surface is covered from water), thus it is an easy-accessible raw material. The present thesis work roots in the points discussed in this preface; the primary target is the design, realization, characterization and test of novel materials able to act as artificial photosynthetic units. During the design of the materials, it was chosen to privilege the realization of organic/inorganic nanohybrids in order to have materials possessing huge surface area; moreover, the design of hybrid materials would imply the use of molecular building blocks, which could be easily realized with well-established chemical procedures. Preliminary work was necessary for: • the determination of an appropriate class of chromophores able to trap solar light and induce the activation of another unit able to perform the catalytic process. Starting from chromophore molecules already known in the literature, new molecules would be designed and synthesized in order to possess the necessary characteristics emerging from the hybrids design process • the choice of an appropriate catalytic unit, so to be combined with the chromophore units and realize the final dyad to be used in the catalytic tests. During the development of the thesis, perylene derivatives were chosen as potential photosensitizers, on the base of an interesting combination of physical and photochemical features (deeply discussed in Chapter 2). Particular attention was given to water-soluble molecules because, if the final target would be water splitting process, it would be worthy to have the possibility to use water both as reagent and reaction medium. Perylene chemistry was deeply scanned, and several derivatives were isolated in order to gain experience on this family of photosensitizers; classical reported procedures were employed, but also novel strategies were tested (Chapter 4). The main part of the laboratory work concerned the characterization of novel dyads based on the combination of PBI2+, one of the isolated chromophores, and two different catalytic species: (i) Ru4POM, tetra-ruthenate molecular polyoxometalate for performing water splitting in homogeneous conditions and later for the formation of a three-component hybrid system for electrocatalytic studies (Chapters 5-6); (ii) iridium oxide nanoparticles for the preparation of photoelectrochemical cells (Chapter 7). The expertise gained with perylene derivatives allowed to develop other parallel projects not directly related to energetic applications; a detailed study over perylene diimides as SERS reporters is described in the final part of this thesis (Chapter 8).XXVII Ciclo198

Shedding Light on Graphene Quantum Dots: Key Synthetic Strategies, Characterization Tools, and Cutting-Edge Applications

During the last 20 years, the scientific community has shown growing interest towards carbonaceous nanomaterials due to their appealing mechanical, thermal, and optical features, depending on the specific nanoforms. Among these, graphene quantum dots (GQDs) recently emerged as one of the most promising nanomaterials due to their outstanding electrical properties, chemical stability, and intense and tunable photoluminescence, as it is witnessed by a booming number of reported applications, ranging from the biological field to the photovoltaic market. To date, a plethora of synthetic protocols have been investigated to modulate the portfolio of features that GQDs possess and to facilitate the use of these materials for target applications. Considering the number of publications and the rapid evolution of this flourishing field of research, this review aims at providing a broad overview of the most widely established synthetic protocols and offering a detailed review of some specific applications that are attracting researchers’ interest

Semitransparent Perovskite Solar Cells for Building Integration and Tandem Photovoltaics: Design Strategies and Challenges

Over the past decade, halide perovskite systems have captured widespread attention among researchers since their exceptional photovoltaic (PV) performance was disclosed. The unique combination of optoelectronic properties and solution processability shown by these materials has enabled perovskite solar cells (PSCs) to reach efficiencies higher than 25% at low fabrication costs. Moreover, PSCs display enormous potential for modern unconventional PV applications, since they can be made lightweight, semitransparent (ST), and/or flexible by means of appropriate design strategies. In particular, by enabling transparency and high efficiency simultaneously, ST-PSCs hold great promise for future versatile utilization in the context of building-integrated PVs (BIPVs) or as top cells to be coupled with conventional lower-bandgap bottom cells in tandem PV devices. The present Review wants to provide a detailed overview of latest research about ST-PSCs for BIPVs and tandems, by critically reporting on the most updated and effective design strategies in view of these two possible future applications. The differences and similarities between the available approaches are punctually highlighted, emphasizing the importance of a rigorous application-orientated ST-PSC design. Last but not least, the main challenges and issues about device design, operation, and stability that need to be addressed before commercialization are thoroughly scanned

Artificial Biosystems by Printing Biology

The continuous progress of printing technologies over the past 20 years has fueled the development of a plethora of applications in materials sciences, flexible electronics, and biotechnologies. More recently, printing methodologies have started up to explore the world of Artificial Biology, offering new paradigms in the direct assembly of Artificial Biosystems (small condensates, compartments, networks, tissues, and organs) by mimicking the result of the evolution of living systems and also by redesigning natural biological systems, taking inspiration from them. This recent progress is reported in terms of a new field here defined as Printing Biology, resulting from the intersection between the field of printing and the bottom up Synthetic Biology. Printing Biology explores new approaches for the reconfigurable assembly of designed life-like or life-inspired structures. This work presents this emerging field, highlighting its main features, i.e., printing methodologies (from 2D to 3D), molecular ink properties, deposition mechanisms, and finally the applications and future challenges. Printing Biology is expected to show a growing impact on the development of biotechnology and life-inspired fabrication

Application of graphene quantum dots in heavy metals and pesticides detection

Graphene Quantum Dots (GQDs) were produced using electrochemical oxidation of graphite rods. Obtained GQDs were gamma-irradiated in the presence of the N atoms source, ethylenediamine. Both structural and morphological changes were investigated using UV-Vis, X-ray photoelectron and photoluminescence (PL) spectroscopy as well as atomic force microscopy. The ability of both types of dots to change PL intensity in the presence of pesticides such as malathion and glyphosate, as well as copper (II) ions was detected. These preliminary results indicated a high potential of produced GQDs to be applied as non-enzymatic PL sensors for the detection of selected pesticides and metal ions

Gamma irradiation as a tool for modification of graphene oxide-silver nanowires composites

Graphene oxide (GO) was produced using the Hummers' method while silver nanowires (AgNWs) were obtained by polyol synthesis. Composite was produced by simple mixing of GO and AgNWs dispersions. The composite was produced in a form of free/standing films by vacuum filtration and exposed to gamma irradiation in an oxygen-free atmosphere. After irradiation, without any additional cleaning, the structure, morphology and electrical properties were investigated. Gamma irradiation was shown to be an efficient tool to induce a chemical reduction of GO, and it was able to improve the electrical conductivity of produced composites. Due to avoiding the usage of reagents and solvents, this method belongs to green chemical approaches

Boosting the Performance of One-Step Solution-Processed Perovskite Solar Cells Using a Natural Monoterpene Alcohol as a Green Solvent Additive

The perovskite film is the core of a perovskite solar cell (PSC), and its quality is crucial for the performance of such devices. The morphology, crystallinity, and surface coverage of the perovskite layer greatly affect the power conversion efficiency (PCE), hysteresis, and long-term stability of PSCs. The incorporation of appropriate solvent additives in the perovskite precursor solution is an effective strategy to control the film morphology and reduce the defects and grain boundaries. However, the commonly used solvent additives are environmentally harmful and highly toxic. In this work, α-terpineol (a nontoxic, eco-friendly, and low-cost monoterpene alcohol) is employed for the first time as an alternative green solvent additive to improve the quality of one-step solution-processed CH3NH3PbI3–xClx films and to restrain nonradiative recombination in the corresponding devices. An in-depth investigation of the physicochemical effects induced by such a high-boiling-point, polar protic solvent when incorporated into a conventional perovskite solvent system is provided. The collected data demonstrate that the addition of a precise amount of α-terpineol can generate uniform and highly crystalline perovskite films with improved photovoltaic performances. Through this approach, the PCE of planar n–i–p PSCs is boosted up to 17.5% (against 16.1% of the top control device) with reduced hysteresis and enhanced ambient stability

Diarylethenes in Optically Switchable Organic Light‐Emitting Diodes: Direct Investigation of the Reversible Charge Carrier Trapping Process

The design, fabrication, and characterization of optically switchable organic light-emitting diodes (OSOLEDs) based on the combination of the commercially available light-emitting polymer poly(9,9′-dioctylfluorene-alt-benzothiadiazole), F8BT, doped with a diarylethene derivative is reported. The photochromic activity of the dopant in the solid state has been investigated both via UV/vis absorption and photoluminescence spectroscopy, whereas the morphology of different blends is investigated via atomic force microscopy. OSOLEDs embedding dopant loadings of 1, 5, and 10 wt% exhibit optical responsivity with a maximum reversible optical threshold voltage shift of 4 V. The best performing devices containing 5 wt% dopant show a maximum current density and luminance ON/OFF ratio of ≈20 and ≈90, respectively. For the first time, the impact of the diarylethene isomerization on hole and electron transport has been decoupled and directly investigated, via the design, fabrication, and characterization of single-carrier switchable devices based on the same blends. Not only do these results confirm the photo-responsive trapping activity of the diarylethenes on both charge carriers, but they also demonstrate its asymmetry, with a predominant effect on electron transport that is over 3.4 times larger as compared to hole transport

Application of graphene quantum dots in heavy metals and pesticides detection

Graphene Quantum Dots (GQDs) were produced using electrochemical oxidation of graphite rods. Obtained GQDs were gamma-irradiated in the presence of the N atoms source, ethylenediamine. Both structural and morphological changes were investigated using UV-Vis, X-ray photoelectron and photoluminescence (PL) spectroscopy as well as atomic force microscopy. The ability of both types of dots to change PL intensity in the presence of pesticides such as malathion and glyphosate, as well as copper (II) ions was detected. These preliminary results indicated a high potential of produced GQDs to be applied as non-enzymatic PL sensors for the detection of selected pesticides and metal ions.26th International Symposium on Analytical and Environmental Problems, Szeged, Hungary, November 23-24, 202

Label-free approaches for extracellular vesicle detection

Extracellular vesicles (EVs) represent pivotal mediators in cell-to-cell communication. They are lipid-membranous carriers of several biomolecules, which can be produced by almost all cells. In the current Era of precision medicine, EVs gained growing attention thanks to their potential in both biomarker discovery and nanotherapeutics applications. However, current technical limitations in isolating and/or detecting EVs restrain their standard use in clinics. This review explores all the state-of-the-art analytical technologies which are currently overcoming these issues. On one end, several innovative optical-, electrical- and spectroscopy-based detection methods represent advantageous label-free methodologies for faster EV detection. On the other end, microfluidics-based lab-on-a-chip tools support EV purification from low-concentrated samples. Altogether, these technologies will strengthen the routine application of EVs in clinics