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.

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Wavepacket深入了解了紫外线过滤器邻氨基苯甲酸甲酯的光保护机理。

Meradimate是一种广谱紫外线吸收剂，用作商业防晒霜中的化学过滤器。在本文中，我们探讨了在用紫外线进行光激发后立即在邻氨基苯甲酸甲酯（前驱体为Meradimate）中发生的超快光动力学，以了解支撑Meradimate光保护的机理。使用时间分辨光电子能谱，邻氨基苯甲酸甲酯的第一个单重态激发态的信号显示出振荡行为，即量子拍。我们的研究揭示了所观察到的跳动频率对光激发波长和光电子动能的依赖性，揭示了邻氨基苯甲酸甲酯的电子基态，初电子激发态和阳离子基态的振动能级之间存在不同的弗兰克-康登重叠。通过评估这些节拍随光子能量增加的行为，我们发现了在第一电子激发态下分子内振动能重新分布的证据。这种能量的重新分配阻碍了电子激发态的有效弛豫，使得邻氨基苯甲酸甲酯成为高效，有效的防晒化学过滤器的较差的选择。