Ultrafast Photoprotecting Sunscreens in Natural Plants

Abstract

We explore the ultrafast photoprotective properties of a series of sinapic acid derivatives in a range of solvents, utilizing femtosecond transient electronic absorption spectroscopy. We find that a primary relaxation mechanism displayed by the plant sunscreen sinapoyl malate and other related molecular species may be understood as a multistep process involving internal conversion of the initially photoexcited 1(1)ππ* state along a trans-cis photoisomerization coordinate, leading to the repopulation of the original trans ground-state isomer or the formation of a stable cis isomer.

Photoprotection: extending lessons learned from studying natural sunscreens to the design of artificial sunscreen constituents

“…Further insights into the decay mechanism have been provided by ultrafast UV pump -UV/vis absorption probe studies of sinapoyl malate in a range of solvents (dioxane, acetonitrile and methanol), 17 which confirm that photoexcitation of the majority E-isomer at B330 nm results in ultrafast deactivation. Global fitting the measured transient absorption spectra revealed three decay processes with respective time constants t 1 (sub-ps), t 2 (B1-5 ps) and t 3 (B20-30 ps), the precise values of which are solvent dependent.…”

“…115,116 In the We also emphasise that steady state measurements have long been used to explore photophysical properties of many sunscreen components, individually and in mixtures. Differences in the UV/vis absorption spectra of samples illuminated using, for example, an arc lamp and non-illuminated samples can provide information on photochemical stability, unwanted photoinduced production of singlet oxygen, and/or signatures of photodegradation products, 17,122 with NMR spectroscopy offering another route to product identification. 123 Such 'classical' photochemical studies have been crucial in the development of the many commercial sunscreens used today but are not discussed further since they do not report directly on the excited state photophysics that is the primary focus of this Review.…”

“…16 The high degrees of polymerisation of the chromophores give both pigments a broad absorption profile. Sinapoyl malate (blue) in dioxane, 17 on the other hand exhibits a relatively narrow absorption band, mostly in the UV-B region.…”

Observing and Understanding the Ultrafast Photochemistry in Small Molecules: Applications to Sunscreens

“…Aside from commercial sunscreens, TEAS has been utilised to investigate how biological sunscreens provide the photoprotection nature has selected them for 50 . An example of this is sinapoyl malate, a molecule highly suspected to fulfil the role of a sunscreen 16;51;52 which is deposited in the upper epidermis of the leaves of many plants.…”

Efficient and accurate evaluation of potential energy matrix elements for quantum dynamics using Gaussian process regression

“…1,2 for example, quantum simulations of organic molecules, [3][4][5][6][7][8][9][10][11][12][13][14] inorganic complexes, 15 and biological systems 7,9,10,16,17 have all provided insight into relaxation dynamics following photochemical excitation, while other studies have highlighted the role of quantum-mechanical tunnelling or zero-point energy (ZPE) in multidimensional dynamics. [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] The power of these simulation approaches is that they provide a direct view of real-time quantum dynamics with access to all properties of interest, such as position expectation values, electronic state populations, and branching ratios; as a result, direct solution of the TDSE is an important route to reconciling experimental observations and atomistic dynamics.…”