Harnessing energy from the sun is a challenge arising from dependence on fossil fuels and necessity to find sustainable solutions. Photovoltaic (PV) solar cells (SC) can convert light into electricity by photovoltaic effect. Silicon-based SC show the highest efficiencies but they present high production and disposal costs. Organic solar cells (OSCs) attract increasing attention due to their potential advantages over inorganic-based SC: low manufacturing costs, lightweight, flexibility and portable characteristics. Furthermore, OSCs are more environmentally friendly and industrially convenient. Among all types of emerging OSC, Bulk Heterojunction (BHJ) devices probably offer the best growth prospects. In BHJ SC the photoactive layer is made of organic π-conjugated donor materials (oligomers or polymers) blended with acceptor compounds. Among all types of donor materials, the ones with high level of fusion of aromatic units on the conjugated backbone are fascinating: high fusion facilitates π-electron delocalization, reduces the band-gap and enhances charge mobility (higher efficiency). The aim of this thesis is the design and synthesis of new π -conjugated monomers, with high level of fusion, for OSC, paying attention to synthetic simplicity and scalability. The crucial step in the synthesis of the monomers is the formation of the carbon framework. DHA (direct hetero-arylation) reactions are fascinating: they follow a Pd-catalyzed cross-coupling methodology whithout pre-activation of the starting monomers with organometallic reagents; they are regioselective, efficient and chromatographic purifications can be avoided. To obtain monomers with a sustainable and scalable method, Prof. Pasini and coworkers designed and developed a one-pot DHA-cross-aldol condensation cascade reaction, combining atom and steps economy of DHA reactions with the advantages of cascade multicomponent reactions. Following this synthetic protocol, starting from 2,5-dibromoterephthalaldehyde and 3-tiophenacetic acid, anthradithiophenic monomer 7 was obtained and it showed promising properties and efficiency in experimental cells. In this thesis work the synthesis of 7 was optimized, reducing the steps for the preparation of the aldehyde. We also tried to prepare a derivative of compound 7 which presents methoxylic substituents on the central benzene (compound 15). The presence of electron-donating groups should affect the electronic properties. The 2,5-dibromo-3,6-dimethoxyterephthalaldehyde was obtained but the DHA-cross aldol condensation didnt work probably because of the steric hindrance on the central exa-substituted benzene. The second target of this thesis is the synthesis of a new penta-cyclic conjugated monomer (18) with two thiophene-lactones fused with a central benzene (substituted with two esters). The precursor 17 was obtained but the following cyclization by DHA didnt work; this is probably due to the steric hindrance on the central exa-substituted benzene. Inspired by the promising properties of 7, we also tried to obtain a similar compound (26) in which the central benzene is substituted by thieno[3,2-b]thiophene. The new precursor diethyl 2,2'-(thieno[3,2-b]thiophene-3,6-diyl)diacetate (23) proposed was obtained by Negishi coupling. The cyclization with thiophenic derivatives was attempted with DHA and with oxidative couplings but the product wasnt obtained. Screening of catalyst and reaction conditions will be object of future studies: the synthetic path design and the target molecule are very promising. Precursor 23 was finally used to attempt the synthesis of compound 34, inspired by TPT monomer widely used in OSC. The key step of is the cyclization of the precursor promoted by acids. We made one attempt but the product wasnt obtained. Screening of acidic conditions and temperature will be object of future studies: the synthetic path design and the target molecule are very promising.
Lo sfruttamento dellenergia solare è una sfida derivante dalla dipendenza dai combustibili fossili e dalla necessità di trovare soluzioni sostenibili. Le celle solari (SC) sono dispositivi in grado di convertire luce in elettricità. Le SC a base di silicio hanno migliori efficienze ma costi elevati. Le SC organiche (OSC) attraggono crescente attenzione per i vantaggi rispetto alle SC inorganiche: bassi costi, leggerezza, flessibilità, sostenibilità. Tra le tipologie di OSC, le Bulk Heterojunction SC sembrano più promettenti; in esse lo strato fotoattivo vede materiali organici donatori π-coniugati (oligomeri o polimeri) miscelati con composti accettori. Tra i materiali donatori, quelli con elevato grado di fusione di anelli aromatici sulla catena principale sono particolarmente promettenti: lelevata fusione aumenta la delocalizzazione elettronica, riduce il band-gap, aumenta la mobilità dei trasportatori di cariche; ne deriva una più elevata efficienza. Scopo del presente lavoro di tesi è la progettazione e sintesi di nuovi monomeri con estesa fusione/grado di coniugazione, per OSC, con particolare attenzione a semplicità e scalabilità sintetiche. Cruciale nella sintesi dei monomeri è la formazione dello scheletro carbonioso. Per tale scopo larilazione diretta (DHA) è una reazione promettente: segue i classici coupling Pd-mediati, ma non richiede pre-attivazione di uno dei reagenti sottoforma di derivato organometallico; è regioselettiva, efficiente e spesso non richiede purificazioni cromatografiche. Per ottenere monomeri in maniera sostenibile e scalabile, il Prof. Pasini e il suo gruppo di ricerca hanno sviluppato un protocollo one-pot di DHA-condensazione aldolica, combinando atom e step economy della DHA con i vantaggi offerti dalle reazioni multicomponente. Seguendo questo protocollo sintetico, partendo da 2,5-dibromotereftalaldeide e acido 3-tiofenacetico, si è ottenuto il monomero antraditiofenico 7, che ha mostrato proprietà ed efficienze promettenti in SC sperimentali. In questo lavoro di tesi la sintesi di 7 è stata ottimizzata, riducendo gli step della sintesi dellaldeide. Si è inoltre indagata la sintesi di un derivato di 7, metossilato sul benzene centrale (composto 15); i gruppi metossilici elettron-donatori potrebbero infatti incrementare le proprietà elettroniche della molecola. La 2,5-dibromo-3,6-dimetossitereftalaldeide è stata ottenuta, ma la DHA-condensazione aldolica non ha portato al prodotto, probabilmente per leccessivo ingombro sterico sul benzene centrale. Secondo obbiettivo della tesi è la sintesi di un nuovo monomero pentaciclico coniugato, con due tiofen-lattoni fusi con un benzene centrale (18). Il precursore 17 è stato ottenuto ma la sua ciclizzazione con DHA non ha portato ad alcun risultato, anche in questo caso probabilmente per lelevata congestione sterica. Alla luce delle promettenti proprietà di 7, si è quindi indagata la sintesi di un composto simile (26) in cui il benzene centrale fosse sostituito dal tieno[3,2-b]tiofene. Il nuovo precursore 23 proposto è stato ottenuto mediante coupling di Negishi. La ciclizzazione con opportuni derivati tiofenici è stata tentata con DHA e con coupling ossidativi, ma senza risultati. Uno screening dei catalizzatori e delle condizioni di reazione saranno oggetto di studi futuri: la molecola e la sintesi proposta sono estremamente promettenti. Il precursore 23 è stato infine usato per un tentativo di sintesi del monomero 34, ispirato al TPT ampiamente usato nel fotovoltaico organico. Step chiave della sintesi è la ciclizzazione del precursore mediante trattamento con acidi. Il primo tentativo effettuato non ha portato a risultati, tuttavia lo screening delle condizioni acide e della temperature di reazione saranno oggetto di studi futuri: la molecola e la sintesi proposta sono estremamente promettenti.
Sistemi Policiclici π-coniugati tramite Arilazione Diretta per il Fotovoltaico Organico
CATENAZZI, MATTEO
2018/2019
Abstract
Harnessing energy from the sun is a challenge arising from dependence on fossil fuels and necessity to find sustainable solutions. Photovoltaic (PV) solar cells (SC) can convert light into electricity by photovoltaic effect. Silicon-based SC show the highest efficiencies but they present high production and disposal costs. Organic solar cells (OSCs) attract increasing attention due to their potential advantages over inorganic-based SC: low manufacturing costs, lightweight, flexibility and portable characteristics. Furthermore, OSCs are more environmentally friendly and industrially convenient. Among all types of emerging OSC, Bulk Heterojunction (BHJ) devices probably offer the best growth prospects. In BHJ SC the photoactive layer is made of organic π-conjugated donor materials (oligomers or polymers) blended with acceptor compounds. Among all types of donor materials, the ones with high level of fusion of aromatic units on the conjugated backbone are fascinating: high fusion facilitates π-electron delocalization, reduces the band-gap and enhances charge mobility (higher efficiency). The aim of this thesis is the design and synthesis of new π -conjugated monomers, with high level of fusion, for OSC, paying attention to synthetic simplicity and scalability. The crucial step in the synthesis of the monomers is the formation of the carbon framework. DHA (direct hetero-arylation) reactions are fascinating: they follow a Pd-catalyzed cross-coupling methodology whithout pre-activation of the starting monomers with organometallic reagents; they are regioselective, efficient and chromatographic purifications can be avoided. To obtain monomers with a sustainable and scalable method, Prof. Pasini and coworkers designed and developed a one-pot DHA-cross-aldol condensation cascade reaction, combining atom and steps economy of DHA reactions with the advantages of cascade multicomponent reactions. Following this synthetic protocol, starting from 2,5-dibromoterephthalaldehyde and 3-tiophenacetic acid, anthradithiophenic monomer 7 was obtained and it showed promising properties and efficiency in experimental cells. In this thesis work the synthesis of 7 was optimized, reducing the steps for the preparation of the aldehyde. We also tried to prepare a derivative of compound 7 which presents methoxylic substituents on the central benzene (compound 15). The presence of electron-donating groups should affect the electronic properties. The 2,5-dibromo-3,6-dimethoxyterephthalaldehyde was obtained but the DHA-cross aldol condensation didnt work probably because of the steric hindrance on the central exa-substituted benzene. The second target of this thesis is the synthesis of a new penta-cyclic conjugated monomer (18) with two thiophene-lactones fused with a central benzene (substituted with two esters). The precursor 17 was obtained but the following cyclization by DHA didnt work; this is probably due to the steric hindrance on the central exa-substituted benzene. Inspired by the promising properties of 7, we also tried to obtain a similar compound (26) in which the central benzene is substituted by thieno[3,2-b]thiophene. The new precursor diethyl 2,2'-(thieno[3,2-b]thiophene-3,6-diyl)diacetate (23) proposed was obtained by Negishi coupling. The cyclization with thiophenic derivatives was attempted with DHA and with oxidative couplings but the product wasnt obtained. Screening of catalyst and reaction conditions will be object of future studies: the synthetic path design and the target molecule are very promising. Precursor 23 was finally used to attempt the synthesis of compound 34, inspired by TPT monomer widely used in OSC. The key step of is the cyclization of the precursor promoted by acids. We made one attempt but the product wasnt obtained. Screening of acidic conditions and temperature will be object of future studies: the synthetic path design and the target molecule are very promising.È consentito all'utente scaricare e condividere i documenti disponibili a testo pieno in UNITESI UNIPV nel rispetto della licenza Creative Commons del tipo CC BY NC ND.
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https://hdl.handle.net/20.500.14239/20703