The work outlined in this thesis aims to shed light on the electronic structure and dynamics of several sulphur-containing organic chromophores. A general introduction to molecular photochemistry and photoelectron spectroscopy of neutral molecules and anions is provided in Chapter 1.

For the work reported here, two experimental apparatus are used: a pulsed molecular beam for the preparation of cold, gas-phase neutral molecules and an electrospray ionisation mass spectrometer for the production of anions. Both of these apparatus employ photoelectron spectroscopy with velocity map imaging in order to measure the energy and angular distribution of photoelectrons, and are detailed in Chapter 2. For the molecular beam apparatus, UV femtosecond lasers are used for either one-colour, static or two-colour, time-resolved photoelectron spectroscopic measurements. The electrospray apparatus utilises nanosecond lasers for one-photon detachment.

Chapter 3 of this thesis describes the static and time-resolved photoelectron spectroscopy performed on a molecular beam of neutral thiophene. These measurements have allowed us to gain insight into the molecular energy levels involved in photoexcitation, as well as the ultrafast dynamics.

Chapter 4 describes use of the molecular beam to produce gas-phase thiophenol molecules for static photoelectron measurements, enabling the determination of the electronically excited states following direct photoexcitation. This work is supplemented by excited state theory calculations, providing a more complete picture of the electronic structure and dynamics of thiophenol.

Finally, Chapter 5 reports on the use of electrospray ionisation to produce anions of 6-mercaptopurine, which were interrogated using a nanosecond optical parametric oscillator for photoelectron spectroscopic studies. The experimental measurements are also supported by excited state calculations. The combination of experiment and theory has allowed for a dominant deprotomer to be assigned to the features in the photoelectron spectra. Additionally, methylated analogues of the 6-mercaptopurine anion were investigated to aid in identifying the dominant anionic species.

Overall, this thesis provides valuable insight into the electronic structure and dynamics of sulphur-containing organic chromophores. The combination of angle-resolved photoelectron spectroscopy with computational chemistry has helped to provide a comprehensive understanding the interaction of light with these complex molecules. The results of this work can find application in a variety of scientific fields, from biophysics to materials science.