Towards the development of a bottom-up rationale for sunscreen design, the effects of substituent position on the ultrafast photodynamics of the sunscreen precursor methyl anthranilate (MA, an ortho compound) were evaluated by studying para- and meta-MA in vacuum. Time-resolved ion yield (TR-IY) measurements reveal a long-lived S₁ excited state (≫1.2 ns) for para-MA, proposed to be the result of a weakly fluorescent, bound excited state. In the case of meta-MA, TR-IY transients reveal a much faster (∼2 ns) excited state relaxation, possibly due to multiple low-lying S₁/S₀ conical intersections of prefulvenic character. While meta-MA may not be an ideal sunscreen ingredient due to a low ultraviolet absorbance, its comparatively efficient relaxation mechanism may constitute an alternative to common sunscreen relaxation pathways. Thus, our results should prompt further studies of prefulvenic relaxation pathways in potential sunscreen agents.

为了开发自下而上的防晒设计原理，通过在真空中研究对-和间-MA来评估取代基位置对防晒前体邻氨基苯甲酸甲酯（MA，一种邻位化合物）的超快光动力学的影响。时间分辨的离子产率（TR-IY）测量显示，对-MA的S ₁激发态具有长寿命（≫1.2 ns），这被认为是弱荧光束缚激发态的结果。在meta -MA的情况下，TR-IY瞬变显示出更快（约2 ns）的激发态弛豫，这可能是由于多个低洼的S ₁ / S ₀先兆性状的圆锥形交叉点。虽然metaMA由于紫外线吸收率低而可能不是理想的防晒成分，但其​​相对有效的舒张机制可能构成了普通防晒舒张途径的替代方法。因此，我们的结果应促使人们进一步研究潜在防晒剂中的前静脉放松途径。