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An integrated computational and experimental approach to designing novel nanodevices

Simbanegavi, Nyevero Abigail (2014) An integrated computational and experimental approach to designing novel nanodevices. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

Small molecules that can organise themselves through reversible bonds to form new molecular structures have great potential to form self-assembling systems. In this study, C60 has been functionalized with components capable of self-assembling via hydrogen bonds in order to form supramolecular structures. Functionalizing the cage not only enhances the solubility of C60 but also alters its electronic properties. In order to analyse the changes in electronic properties of C60 and those of the new derivatives and self-assembled structures, an integrated computational and experimental approach has been used. DNA bases were among the components chosen for functionalizing C60 since these structures are the best example for self-assembly in nature. Experimental routes for novel C60 derivatives functionalised with thymine, adenine, cytosine and guanine have been explored using the Prato reaction. A number of challenges in synthesizing the aldehyde analogues of the DNA bases have been identified, and a number of different solutions have been tested. Samples of N-methyl-2-thymin-N-ylfulleropyrrolidine have been isolated and N-methyl-2-adenin-N-ylfulleropyrrolidine has also been characterised. Zeolites, because of their ordered cages and channels, were selected as a template for the self-assembly of the fullerene derivatives to enable the formation of ordered arrays. The adsorption of the thymine-fullerene derivative (N-methyl-2-thymin-N-ylfulleropyrrolidine) into the openings of zeolite channels has been confirmed by powder X-ray diffraction and thermogravimetric analysis. Two additional hydrogen-bonding fullerene derivatives have been modelled: N-propylthymine and diaminopyridine. Furthermore, methanofullerene derivatives functionalised with DNA bases have also been modelled. Monomer and dimer structures have been optimised using semi-empirical methods and density functional theory (DFT) using B3LYP/6-31G**. The HOMO, LUMO and HOMO-LUMO gap energies as well as the frontier HOMO and LUMO electron density distribution of the structures have been calculated to get an insight into the reactivity of the C60 derivatives. Results for the HOMO, LUMO and band gap energies in the gas phase are comparable with previous studies. Solvent effects on the electronic properties of the monomers have been calculated. It is shown that the electronic properties are altered in the solvent environments, which may be important when choosing solvents to prepare devices. The dimers have been modelled in seesaw and dumb-bell conformations and the formation energies have been calculated to predict the preferred growth pattern of the molecular architectures. In summary, it can be seen that the computational calculations can help experimentalists identify molecules with interesting properties and the challenges encountered developing effective synthesis pathways emphasise the need for even more integration of approaches to designing novel fullerene derivatives with tailored properties.

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