Understanding light-matter interaction and optical phenomena is still a highly challenging task due to the complexity of the phenomena involved. However, it is imperative that we gain a better understanding of the chemical reaction dynamics and mechanisms that occur following light absorption for the purposes of designing functional molecules for light-driven applications. This project will make use of novel laboratory based ultrafast optical spectroscopies (transient electronic absorption spectroscopy and multidimensional optical spectroscopy) and advanced light source-based X-ray techniques (X-ray absorption, emission and their time-resolved variants) to explore the electronic and nuclear dynamics in complex molecular systems. As well as exploring the fundamental physical phenomena following photoexcitation and associated modelling methods, this project will focus largely on porphyrin compounds with applications in photodynamic therapy, medical imaging, energy storage and photocatalysis. By identification of key design criteria for molecules well-suited for these applications that can be monitored through ultrafast spectroscopy, this project will explore the effects of chemical substitution on those criteria and lead to the creation of new design rules for such applications.