Ultraviolet radiation causes a number of deleterious effects on humans and other living organisms. As such, photoprotection is crucial, and whilst humans produce melanin as a natural defence mechanism, this is not usually sufficient. Therefore, alternative photoprotection is required and one way is through the use of sunscreens. The ultraviolet filters currently used within sunscreens have a number of associated drawbacks. As a result, alternative ultraviolet filters are needed and one approach is taking inspiration from nature. This thesis does exactly that as the molecules of interest are a family of natural ultraviolet filters, mycosporines and mycosporine-like amino acids.

In this thesis, a bottom-up approach has been adopted to glean insight into the simplest system first and then increasing the complexity of the studied system from a photochemical and photophysical standpoint. In Chapter 2, the cyclohexenone building block of mycosporines was investigated as an extension of previous work. Experimental and computational results determined that the majority of population recovers back to the electronic ground state on ultrafast timescales. As a result, the cyclohexenone core is not as poor of an ultraviolet filter as previously thought. In Chapters 3 and 4, a number of mycosporine-like amino acids were explored spectroscopically and computationally. The results linked the ultrafast dynamics to their unrivalled long-term photostability, thus highlighting the efficiency of the photoprotective mechanism in these molecules. Finally, Chapter 5 took the investigations further by examining a crude extract from Palmaria palmata containing mycosporinelike amino acids in more viscous and restricted surface environments. It was found that the photoprotective mechanism was retained in these environments.

Overall, this thesis demonstrates the efficient photon-to-heat conversion capabilities of mycosporine-like amino acids making them ideal candidates as ultraviolet filters. Furthermore, such results can guide the future experiments and chemical design of not only ultraviolet filters in sunscreens but in any field where photon-to-heat conversion is desirable.