TY - JOUR
T1 - Ab initio study of potential ultrafast internal conversion routes in oxybenzone, caffeic acid, and ferulic acid
T2 - Implications for sunscreens
AU - Karsili, Tolga N.V.
AU - Marchetti, Barbara
AU - Ashfold, Michael N.R.
AU - Domcke, Wolfgang
N1 - Publisher Copyright:
© 2014 American Chemical Society.
PY - 2014/12/26
Y1 - 2014/12/26
N2 - Oxybenzone (OB) and ferulic acid (FA) both find use in commercial sunscreens; caffeic acid (CA) differs from FA by virtue of an -OH group in place of a -OCH3 group on the aromatic ring. We report the results of ab initio calculations designed to explore the excited state nonradiative relaxation pathways that provide photostability to these molecules and the photoprotection they offer toward UV-A and UV-B radiation. In the case of OB, internal conversion (IC) is deduced to occur on ultrafast time scales, via a barrierless electron-driven H atom transfer pathway from the S1(11nπ∗) state to a conical intersection (CI) with the ground (S0) state potential energy surface (PES). The situation with respect to CA and FA is somewhat less clear-cut, with low energy CIs identified by linking excited states to the S0 state following photoexcitation and subsequent evolution along (i) a ring centered out-of-plane deformation coordinate, (ii) the E/Z isomerism coordinate and, in the case of CA, (iii) an O-H stretch coordinate. Analogy with catechol suggests that the last of these processes (if active) would lead to radical formation (and thus potential phototoxicity), encouraging a suggestion that FA might be superior to CA as a sunscreen ingredient. (Figure Presented).
AB - Oxybenzone (OB) and ferulic acid (FA) both find use in commercial sunscreens; caffeic acid (CA) differs from FA by virtue of an -OH group in place of a -OCH3 group on the aromatic ring. We report the results of ab initio calculations designed to explore the excited state nonradiative relaxation pathways that provide photostability to these molecules and the photoprotection they offer toward UV-A and UV-B radiation. In the case of OB, internal conversion (IC) is deduced to occur on ultrafast time scales, via a barrierless electron-driven H atom transfer pathway from the S1(11nπ∗) state to a conical intersection (CI) with the ground (S0) state potential energy surface (PES). The situation with respect to CA and FA is somewhat less clear-cut, with low energy CIs identified by linking excited states to the S0 state following photoexcitation and subsequent evolution along (i) a ring centered out-of-plane deformation coordinate, (ii) the E/Z isomerism coordinate and, in the case of CA, (iii) an O-H stretch coordinate. Analogy with catechol suggests that the last of these processes (if active) would lead to radical formation (and thus potential phototoxicity), encouraging a suggestion that FA might be superior to CA as a sunscreen ingredient. (Figure Presented).
UR - http://www.scopus.com/inward/record.url?scp=84919916766&partnerID=8YFLogxK
U2 - 10.1021/jp507282d
DO - 10.1021/jp507282d
M3 - Article
AN - SCOPUS:84919916766
SN - 1089-5639
VL - 118
SP - 11999
EP - 12010
JO - Journal of Physical Chemistry A
JF - Journal of Physical Chemistry A
IS - 51
ER -