Intrinsic Nature of the Ultrafast Deexcitation Pathway of Mycosporine-like Amino Acid Porphyra-334

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2022-10, Vol.126 (41), p.7460-7467
• Main Authors: Hatakeyama, Makoto, Nakamura, Shinichiro
• Format: Article
• Language: English
• Subjects: A: Structure, Spectroscopy, and Reactivity of Molecules and Clusters
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/acs.jpca.2c05034

Porphyra-334 is a member of natural UV-screening compounds named mycosporine-like amino acids found in several marine organisms. The UV excited porphyra-334 has been identified to deexcite quickly by puckering the intramolecular cyclohexenimine ring; however, the reason for such a ring-puckering occurrence is yet unclear. In this study, we show the ring-puckering to be the relaxation pathway of the UV excited π electron which shifts from the in-ring bond to the out-of-ring bond. The ring-puckering is characterized by the torsion among the in-ring and out-of-ring bonds. Since the π electron shift is possible in two different directions at the Franck–Condon UV excited state, it enables two ring-puckering pathways: the previously reported pathway and another one newly identified at present. We also examine the ring-unpuckering pathways which are an analogy of cis/trans photoisomerization, and we find them to be not suited for the π electron shift character of the UV excited state and thus not related to the deexcitation pathway. The present study provides insight into how porphyra-334 exerts the UV-screening ability based on its cyclohexenimine ring structure.