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Design and synthesis of multi-porphyrin arrays: supramolecular networks, covalent pentamers and polymeric capsules
thesisposted on 2017-02-22, 01:51 authored by Wang, Shuang
The work conducted in this thesis investigates the non-covalent and covalent construction of a number of multiporphyrin structures. These materials can be divided into three categories according to their chemical bonding interactions and the different synthetic protocols employed. Chapter 1 provides a general introduction for the work conducted in this thesis. It describes the importance of multiporphyrin systems to life itself then investigates bioinspired processes that lead to wholly-synthetic arrays from a supramolecular and crystal engineering viewpoint. Rational synthetic approaches are highlighted that take advantage of a template directed approach, specifically to forming cyclic systems. Finally, the use of porphyrins in gas storage is briefly reviewed through MOFs and solvent exchange processes. Chapter 2 describes the formation and properties of a series of discrete molecular networks – the socalled supramolecular porous materials, or SPMs - constructed from Sn(IV) porphyrin diphenolates through non-classical supramolecular interactions. Self-assembly optimisation investigations were carried out in different solvent systems with different phenols to improve and control the stereostacking within the arrays which ultimately instruct the level of functionalisation within the SPM inner surface. Consequently, ways to systematically tune the pore lining by substituting different groups on phenolic ring, which also allows pore size modulation with diameters ranging from 9-11 Å, were found. TGA analysis was carried out to investigate the robustness of these networks, indicating a surprising stability for the SPMs. To better understand their configuration, X-ray crystallography was extensively applied to confirm all structures. PXRD characterisation was also investigated before and after evacuation on selected porphyrin diphenolates to examine the porosity of their crystalline forms for gas adsorption studies. To evaluate the gas uptake selectivity on different functionalised pore surfaces, N2, CO2, and CH4 adsorption on Sn(IV)TTP(4)2, Sn(IV)TTP(7)2 and Sn(IV)TTP(10)2 were studied at different temperatures. Although no obvious difference in CO2 uptake was observed at 273K, the adsorption amount of CO2 on Sn(IV)TTP(4)2 at 195K was much higher CH4 and H2 uptake under the same condition, thereby exhibiting a potential for better gas selectivity compared with Sn(IV)TTP(7)2 or Sn(IV)TTP(10)2. Furthermore, different solvent vapour adsorption including cyclohexane, benzene, toluene, para-xylene, and n-hexane were examined on evacuated Sn(IV)TTP(10) 2. Interestingly, this SPM undergoes single-crystal-to-single-crystal transformations during cyclohexane inclusion. Iodine adsorption studies on Sn(IV)TTP(10)2 also demonstrated the SPM has an affinity for iodine, being able to adsorb approx. one iodine for every Sn(IV)porphyrin diphenolate. Chapter 3 investigates the design-to-synthesis of a guest responsive cavitand by linking several alkene-bearing porphyrin monomers together via cross metathesis. Reduction of the ensuing semi- VII rigid alkene linkers within the pentameric structure preceded successfully for the first time to achieve flexible porphyrin pentamer, which was confirmed and characterised by 1H NMR spectroscopy and MALDI-TOF analysis. The preparation of the other components to prepare a light-harvesting device were also prepared in good yield and characterized fully. Chapter 4 describes the concentration controlled synthesis of a variety of porphyrin polymers based on 5,10,15,20-tetrakis(4-(3-butenyl)phenyl)-21H,23H-porphyrin via cross metathesis. TEM images of corresponding polymenrs achieved under different conditions (initial concentration, catalyst, reaction time) were collected to investigate the polymer shape and morphology. Although several interesting novel motifs such as porphyrin ‘eggplant’, ‘balloon’, ‘sheets’ and multi-layered ‘nanorings’ were observed under TEM for the first time, separation of the desired nanomaterials proved to be difficult. DLS analysis was used to characterise the average size distribution of the polymeric nanoparticles.