School of Chemistry - Theses
Permanent URI for this collection
Search Results
1 - 2 of 2
-
ItemZwitterionic Donor-Bridge-Acceptor Solvatochromic Dyes( 2023-03)Push-pull molecules are widely used luminophores for applications in optoelectronics and photonics. They are discrete, functionally desymmetrised molecules, bearing donor and acceptor substituents as end-groups, with their delocalized pi-electron system responsible for nonlinear optical effects. Oligomeric systems with a donor phenol group and an acceptor pyridyl moiety separated by a conjugated para-phenylene chain or fluorene spacer were obtained by iterative Suzuki–Miyaura or Horner–Wadsworth–Emmons couplings. For synthesis of desymmetrised molecules, aryl or heteroaryl halides and aryl triflates are typically used as substrates in the former case. Due to moderate reactivity of aryl triflates and their high cost, aryl nonaflates have been proposed as a good alternative. So far, only few reports related to the application of aryl nonaflates in Suzuki–Miyaura coupling have been published, where aryl nonaflates have shown slightly higher reactivity and better yields compared to corresponding triflates. Zwitterionic forms of these donor-bridge-acceptor molecules were generated by consequent N-methylation and deprotonation reactions leading to large redshifts in absorbance maxima. UV-vis absorbance studies also revealed negative solvatochromic behaviour: a smooth bathochromic shift was observed with the decrease of the solvent polarity. Most of the examples have shown strong solvatochromic characteristics, where the magnitudes of these shifts in the studied polarity range were close or even greater to the one for Reichardt’s dye — one among the most solvatochromic organic dyes known. Additionally, systems with increased disparity between the donor and acceptor ends were synthesised and studied. It was achieved by introducing a stronger acceptor, which lead to molecules with more unusual electronic and structural properties. Among them there were species with a bulky donor phenolate moiety and an acceptor pyridinium group separated by a bridging unit of a different nature. One of the molecules incorporating a vinyl bridge and 2,4-dinitrobenzene acceptor group demonstrated the broadest and the most redshifted absorption profile in the N-arylated series. It also showed extraordinary behaviour in its 1H NMR spectrum as well as in its crystal structure compared to its analogues. Thus, it was found to be near the cyanine limit, which makes it to be a potential candidate for photorefractive materials.
-
ItemThe Carbonylation of Organic Compounds by Visible Light Photoredox Catalysis( 2020)Palladium-catalysed alkoxy- and aminocarbonylation of aryl (pseudo)halides provides efficient access to aromatic esters and amides. The broad application of this approach has been restricted by functional group tolerance, high reaction temperatures and moderate catalyst efficiency. Free-radical carbonylation is a complementary approach not confined by the same inherent limitations of palladium-catalysed carbonylative cross-coupling methodology. The development of free-radical carbonylation has been hindered by the ability to selectively generate the carbon-centred radical species and the high pressures of carbon monoxide required to drive the carbonylation step. This thesis describes the development of visible light photoredox-catalysed alkoxy- and aminocarbonylation of aryl (pseudo)halides. Visible light photoredox-catalysis is a potent method to generate carbon-centred radicals selectively under mild reaction conditions. Aryl radicals can be trapped by carbon monoxide to afford carbonyl compounds. Continuous flow chemistry is utilised throughout, employing tube-in-tube semipermeable membrane reactor technology, to enable precise control over reactions conditions and safe use of carbon monoxide. Chapter 1 introduces carbonylation and elaborates on carbonylative cross-coupling of aryl (pseudo)halides. It further introduces continuous flow processing in synthetic chemistry (flow chemistry) and details the application of flow chemistry to carbonylative cross-coupling and photochemical reactions. Chapter 2 established a continuous flow platform for high pressure gas-liquid photochemistry. The flow system consisted of a pumping module, a reagent delivery module, a Teflon AF-2400 tube-in-tube reactor for saturation of the reaction stream with carbon monoxide, a photoreactor and pressure regulation devices. The photoredox-catalysed alkoxycarbonylation of aryl diazonium salts was selected to evaluate the performance of the flow system. It was determined that excellent yields of the benzoate ester could be achieved at significantly lower partial pressures of carbon monoxide and processing time than in batch. Chapter 3 details the development of a free-radical annulative addition/alkoxycarbonylation cascade reaction. The developed methodology was applied to the synthesis of a diverse library of novel 3-acetate functionalized 2,3-dihydrobenzofurans from widely accessible allyl aryl diazonium ethers. Application of the previously established continuous flow system enabled dilute reaction conditions to effectively control the propagation of competitive intermolecular radical addition side reactions without compromising on reaction throughput or space-time yield. Chapter 4 describes the development of photoredox-catalysed aminocarbonylation of aryl halides. The developed methodology was applied to the synthesis of both electron rich and electron deficient benzamides at room temperature. Spectroscopic and theoretical computational studies were conducted to elucidate the reaction mechanism. A novel tandem photoredox catalytic manifold was proposed that features the transformation of Ir(dtbbpy)(ppy)2]PF6 in the presence of DIPEA to generate a distinct highly reducing Ir-complex capable of engaging energy demanding aryl halides. Chapter 5 provides a summary of the work described in this thesis. Supplementary data is included in the appendix.