Effect of conjugation in photophysics of methoxycinnamate

Methoxycinnamates, especially octyl methoxycinnamate, are common active ingredients in sunscreens. Its photoprocesses have experimentally shown ultrafast quenching of UV-B light and photoproduct formation and eventual degradation. It is known to absorb intensely around 310 nm. However, the molecular origin and mechanism of these photoprocesses and excited state channels remain elusive. Due to these reasons, it is imperative to study the molecular mechanism of the excited state photoactivated reactions of octyl methoxycinnamate and compare it to several molecules with similar structural motifs. The excited state quenching mechanism and molecular pathways need to be elucidated along with the effect of different structural motifs on its excited states. Therefore, in this work, we have studied the photoprocesses of methoxycinnamates using state-of-the-art multireference methods. We find a crucial role played by the extended conjugation and the ester group on the excitation energies, and this is, therefore, expected to have a significant effect on the quenching pathways.

Graphical Abstract

Para methoxymethylcinnamate, an active ingredient in sunscreens, gets photoexcited at around 310 nm. In this work, we have investigated its photoprocesses. Energetically accessible conical intersections favour its non-radiative decay to the ground state. Comparing molecules sharing a similar structural motif, we find that extended conjugation plays a vital role.