Wavepacket insights into the photoprotection mechanism of the UV filter methyl anthranilate.

Abstract

Meradimate is a broad-spectrum ultraviolet absorber used as a chemical filter in commercial sunscreens. Herein, we explore the ultrafast photodynamics occurring in methyl anthranilate (precursor to Meradimate) immediately after photoexcitation with ultraviolet radiation to understand the mechanisms underpinning Meradimate photoprotection. Using time-resolved photoelectron spectroscopy, signal from the first singlet excited state of methyl anthranilate shows an oscillatory behavior, i.e., quantum beats. Our studies reveal a dependence of the observed beating frequencies on photoexcitation wavelength and photoelectron kinetic energy, unveiling the different Franck-Condon overlaps between the vibrational levels of the ground electronic, first electronic excited, and ground cationic states of methyl anthranilate. By evaluating the behavior of these beats with increasing photon energy, we find evidence for intramolecular vibrational energy redistribution on the first electronic excited state. Such energy redistribution hinders efficient relaxation of the electronic excited state, making methyl anthranilate a poor choice for an efficient, efficacious sunscreen chemical filter.