Abstract
Sinapoyl malate is a natural plant sunscreen molecule which protects leaves from harmful ultraviolet radiation. Here, the ultrafast dynamics of three sinapoyl malate derivatives, sinapoyl L‐dimethyl malate, sinapoyl L‐diethyl malate and sinapoyl L‐di‐t‐butyl malate, have been studied using transient electronic absorption spectroscopy, in a dioxane and methanol solvent environment to investigate how well preserved these dynamics remain with increasing molecular complexity. In all cases it was found that, upon photoexcitation, deactivation occurs via a trans‐cis isomerisation pathway within ∼20–30 ps. This cis‐photoproduct, formed during photodeactivation, is stable and longed‐lived for all molecules in both solvents. The incredible levels of conservation of the isomerisation pathway with increased molecular complexity demonstrate the efficacy of these molecules as ultraviolet photoprotectors, even in strongly perturbing solvents. As such, we suggest these molecules might be well‐suited for augmentations to further improve their photoprotective efficacy or chemical compatibility with other components of sunscreen mixtures, whilst conserving their underlying photodynamic properties.
Highlights
The two positive features are readily attributed to excited state absorption (ESA), through comparison with previously studied molecules,[13,14] originating from the molecule’s 11ππ* electronic state
In the above work we studied the ultrafast photodynamics of three sinapoyl malate (SM) derivatives: sinapoyl L-dimethyl malate (SdiMM), sinapoyl L-diethyl malate (SdiEM) and sinapoyl
We have demonstrated that the isomerisation of Sinapoyl malate (SM) is preserved throughout major physical changes to the molecule,[14] with the transient absorption spectra of all three derivatives in methanol and dioxane remaining remarkably similar to one another
Summary
Introduction response to varying levels ofUV exposure.[6,8,9,10,11,12] Recently, a number of studies have been carried out focussing on the photophysical properties of SM, how solution-phaseSM photodeactivates after UV-B photoexcitation.[13,14,15,16] These point to SM (and similar derivatives[17,18,19,20]) exhibiting a relaxation mechanism upon UV excitation involving ultrafast internal conversion from a photoexcited ππ* state to reform predominantly the original ground state trans-isomer, occurring along a trans-cis isomerisation reaction coordinate.This relaxation mechanism, being mediated by the trans-cis isomerisation coordinate, is interesting since it is readily observed in the solution phase and involves ππ*dynamics, whereas analogous gas-phase experiments involve significant nπ* dynamics and the different isomers are not readily distinguished.[15,17,18,19,21,22] It is on this solution phase mechanism where this work focusses. The assignment of the final EADS to the cis-isomer is supported by the difference spectra recorded in the steady state irradiation experiments (see Figure 4(A), (C), and (E)).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
