Computational photochemistry of heteroaromatic biomolecules : photodynamic therapy and ultrafast relaxation
Bergendahl, L. Therese
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This thesis focuses on the photochemistry of heteroaromatic biomolecules. These molecular systems have a rich photochemistry and take part in photochemical reactions that have many very topical applications. Small heteroaromatics constitute important biological building blocks and are therefore a fundamental components of living organisms. Even though these compounds absorb light very efficiently, they also have ultrafast relaxation processes available to them. This means that they can remove the absorbed energy very fast and avoid harmfull photoproducts forming, which can lead to cell damage. Larger heteroaromatics have a similarly efficient absorption of electromagnetic light, and are present in compounds that are responsible for the harvesting of energy in nature, for example the chlorophyll molecule in green plants and bacteria. If large heteroaromatics are artificially presented to living cells however, the excess energy absorbed by these systems may also cause cell damage. This destructive force can however be utilised in therapy forms where there is a need to get rid of unwanted cells, such as in anti-cancer therapy. A form of therapy based on this principle is photodynamic therapy. The use of computational chemistry in the investigations of photochemical phenomena has increased following the improvements in the efficiency of computers and algorithms. Modern techniques have now reached a stage where ultrafast relaxation processes can be calculated for small heteroaromatics. As the experimental community has also reached a stage where these compounds can be probed using ultrafast laser experiments, there is a need for computational input to aid in the interpretation of the data of these phenomena. This thesis will present computational results concerning the relaxation dynamics of important small heteroaromatic biomolecules, and discuss them in terms of experimental data collected by collaborative groups. For the development of molecules to be used in photodynamic therapy, a lot of work is needed to ensure safety for use in human beings. With the computational chemistry community now being able to carry out absorption studies for large heteroaromatics, computational structure-absorption relationships can aid the development of this form of therapy. At the limits of modern photochemistry, methods are also appearing that can be used for studies of ultrafast relaxation in larger systems. These computations could contribute hugely to the understanding of the behaviour of these types of systems and aid their development. In a large component of this thesis, new structure-absorption relationships are presented for interesting heteroaromatics with potential for use in photodynamic therapy. One section is also devoted to exploratory work using methods that have not before been used in systems that are larger in size, and presents some promising results as well as current challenges in the field.