Substituent position effects on sunscreen photodynamics: a closer look at methyl anthranilate

<p>Towards the development of a <em>bottom-up</em> rationale for sunscreen design, the effects of substituent position on the ultrafast photodynamics of the sunscreen precursor methyl anthranilate (MA, an <em>ortho</em> compound) were evaluated by studying <em>para-</em> and <em>meta-</em>MA in vacuum. Time-resolved ion yield (TR-IY) measurements reveal a long-lived S₁ excited state (≫ 1.2 ns) for <em>para-</em>MA, proposed to be the result of a weakly fluorescent, bound excited state. In the case of <em>meta-</em>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 <em>meta-</em>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.</p> <p>This archive contains example computational input and output files for both species, including:</p> <ol> <li>TD-DFT files for use with NWChem</li> <li>SA-CASSCF conical intersection search files for use with Gaussian 03</li> <li>CASPT2 files for use with Gaussian 03</li> <li>DFT relaxed geometries for&nbsp;<em>para</em>-MA and&nbsp;<em>meta-</em>MA&nbsp; (<em>e.g</em>. para_0_opt.xyz)</li> <li>SA-CASSCF conical intersection geometries from both molecules as (<em>e.g</em>. p1.xyz)</li> </ol>