Excited-state dynamics of cinnamate-based UV filters: bringing decay pathways to light by photoelectron velocity map imaging

Cinnamic acids and cinnamates are attracting considerable interest as starting point for the rational development of novel UV filters. Key to their optimization is a fundamental understanding of the nonradiative processes that occur after photon absorption. Here we employ kinetic-energy-resolved photoelectron spectroscopy to uncover the deactivation mechanisms occurring after photoexcitation of a series of substituted cinnamates. We find that the recorded photoelectron spectra (i) confirm and extend conclusions on pathways involving the triplet manifold previously obtained indirectly, (ii) provide insight into the electronic structure of the excited singlet manifold, and (iii) elucidate the influence of substituents on their photodynamics. In addition, they have allowed for the determination of accurate ionization energies that so far had not been determined.