Photodynamics of oxybenzone sunscreen: Nonadiabatic dynamics simulations

• Published in: The Journal of chemical physics Vol. 145; no. 7; p. 074308
• Main Authors: Li, Chun-Xiang, Guo, Wei-Wei, Xie, Bin-Bin, Cui, Ganglong
• Format: Journal Article
• Language: English
• Published: United States American Institute of Physics 21.08.2016
• Subjects: Benzophenones - chemistry; Deactivation; Dynamics; ELECTRONIC STRUCTURE; EXCITED STATES; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; INTERNAL CONVERSION; Intersections; Light; Physics; POTENTIAL ENERGY; Quantum Theory; SIMULATION; Sun screens; Sunscreening Agents - chemistry
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/1.4961261

Herein we have used combined static electronic structure calculations and “on-the-fly” global-switching trajectory surface-hopping dynamics simulations to explore the photochemical mechanism of oxybenzone sunscreen. We have first employed the multi-configurational CASSCF method to optimize minima, conical intersections, and minimum-energy reaction paths related to excited-state intramolecular proton transfer (ESIPT) and excited-state decays in the 1 ππ ∗, 1 nπ ∗, and S0 states (energies are refined at the higher MS-CASPT2 level). According to the mapped potential energy profiles, we have identified two ultrafast excited-state deactivation pathways for the initially populated 1 ππ ∗ system. The first is the diabatic ESIPT process along the 1 ππ ∗ potential energy profile. The generated 1 ππ ∗ keto species then decays to the S0 state via the keto 1 ππ ∗/gs conical intersection. The second is internal conversion to the dark 1 nπ ∗ state near the 1 ππ ∗ /1 nπ ∗ crossing point in the course of the diabatic 1 ππ ∗ ESIPT process. Our following dynamics simulations have shown that the ESIPT and 1 ππ ∗ → S0 internal conversion times are 104 and 286 fs, respectively. Finally, our present work demonstrates that in addition to the ESIPT process and the 1 ππ ∗ → S0 internal conversion in the keto region, the 1 ππ ∗ → 1 nπ ∗ internal conversion in the enol region plays as well an important role for the excited-state relaxation dynamics of oxybenzone.