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The ferulic acid (FA) is a kind of phenolic acid widely exists in nature plants. Apart from its medicinal values, the FA is also widely applied in cosmetic industry. Recently, it was found to have potential applications in commercial sunscreens for its strong photostability and photoprotection property from harmful UV rays. Such excellent property lies in the ultrafast decay process of the FA system when exposure to the UV light, but the underlying detailed relaxation pathway is still less clear-cut. In the current work, high-level ab initio electronic structure calculations and on-the-fly surface hopping dynamics simulations were employed to explore the photoinduced decay mechanism of the FA system both on the S 1 and S 3 states in the gas phase. The results provide a reasonable explanation for the wavelength dependent decay patterns of FA system. The S 1 state decay pathway is driven by a re-emission process to dissipate excess energy. While for the S 3 state deactivation process, the pathway is dominated by a non-adiabatic process driven by the internal conversion process through the conical intersection regions. A S 3 -S 1 -S 0 two step decay pattern is proposed, and the pathways are mainly driven by a puckering distortion motion of the aromatic ring and a twisting motion around the bridging double bond. The calculation results contribute to a better understanding of detailed dynamics behavior of the FA deactivation process, and provide theoretical guidance for further design of efficient and environmentally friendly sunscreens. Unlabelled Image • Provide fundamental and intrinsic photochemical properties of FA in gas phase • Provide the photoprotection mechanism of FA after exposure to the UV light • Explain the wavelength dependent deactivation mechanism of FA [ABSTRACT FROM AUTHOR]

In spite of the pivotal role of excited state electronic structures as regulation of photoinduced electron transfer (PET) process, the effect of excited state conformation on PET remains elusive. Here we exploit distinguishable emission characters of trans and cis singlet excited states of donor-acceptor-donor ensemble MTPAAZO to reveal that its PET efficiency and rate are closely depended on its singlet excited state conformation. The PET process occurs solely in cis conformation of MTPAAZO singlet excited states. Novel molecule (MTPA) 2 Ab as-designed with similar structure of MTPAAZO cis singlet excited states shows high PET efficacy and rate, leading to long-lived CS states. Our findings enable the rational design of the novel molecules with highly efficient PET process suitable for charge separation applications. Unlabelled Image • Different fluorescence emission features from the trans and cis singlet excited states were identified. • Cis → trans conversion in ground states and trans → cis isomerization in singlet excited states were discovered. • The PET process was observed only in cis conformation of MTPAAZO singlet excited states. [ABSTRACT FROM AUTHOR]