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
