Engineering photon-to-heat conversion in cinnamate-based UV filters using photoelectron velocity map imaging

Efficient ultraviolet (UV) filters must not only absorb harmful radiation, but also dissipate the absorbed energy rapidly and safely while avoiding long-lived reactive states and photochemical degradation. This thesis investigates how molecular substitution controls energy conversion in a series of nature-inspired cinnamate chromophores.
A central part of the work was the construction, characterisation, and calibration of a velocity map imaging (VMI) apparatus for kinetic-energy-resolved photoelectron detection. The instrument combines resonance-enhanced multiphoton ionisation spectroscopy with electron VMI, enabling conformer- and state-selective excitation while directly probing the electronic state from which ionisation occurs and the cationic states that are formed. Calibration using xenon and low-energy photoelectrons established the operating range required for the subsequent molecular studies.
The apparatus was applied to a number of cinnamate-based derivatives. Photoelectron spectra revealed how the ordering and character of low-lying excited states determine dissipation of absorbed energy. The results show that, within the cinnamate systems investigated, electron-donating substituents can tune electronic-state ordering, whereas steric substitution can reshape the excited-state potential energy surface and promote access to conical intersections.
Overall, this work establishes photoelectron VMI as a state-sensitive tool for studying molecular energy conversion and provides design principles for more efficient nature-inspired UV filters and photon-to-heat converters.