Exploring the Ultraviolet (UV) Protection Mechanism of Natural Stilbene-Based Sunscreens

A recent study was published in the Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal that combined theoretical calculations and femtosecond transient absorption spectra (FTAS) to investigate the ultrafast non-adiabatic dynamics of hydroxy resveratrol and pterostilbene, two compounds found in plant-based sunscreens (1). Their investigation revealed valuable insights into their photostability and UV absorption properties (1).

Bottles of sunscreen cream on sand against color background | Image Credit: © Pixel-Shot - stock.adobe.com

As a spectroscopic technique, FTAS is regularly used to investigate ultrafast processes in molecules and materials (1). How the technique works is that it uses extremely short laser pulses on the timescale of femtoseconds (10-15 seconds) to probe the dynamics of excited states and photochemical reactions (1). A sample is excited with an initial laser pulse, and then the second pulse is used to probe the changes in the sample's absorption spectrum as a function of time (1). Researchers can capture the transient absorption spectra that arise during the evolution of the excited states this way, because they can control the time delay between the excitation and probing pulses (1). As a result, researchers can study processes such as energy transfer, electron dynamics, and molecular structural changes on incredibly fast timescales (1). The high time resolution and sensitivity of FTAS make it a valuable tool for investigating the intricate details of photoinduced phenomena and understanding the underlying mechanisms governing light-matter interactions (1).

Through UV absorption spectroscopy, the researchers observed that both the hydroxy resveratrol and pterostilbene compounds exhibited strong absorption properties, making them suitable candidates for UV protection (1). Additionally, the compounds demonstrated high photostability, indicating their ability to withstand UV radiation without undergoing significant degradation (1).

The photochemical processes that occurred under UV exposure were also explored in this study (1). The researchers observed that the molecules transitioned to the S1 excited state when exposed to UV light, reaching a critical point called the conical intersection (1). The conical intersection is where a lower energy barrier facilitates the trans–cis isomerization process (1).

FTAS was used to understand the time scale of the trans–cis isomerization process (1). The results indicated that the isomerization occurred within approximately 10 ps, meeting the requirement for fast energy relaxation (1). This finding highlights the efficient and rapid nature of the isomerization process in these natural stilbene-based sunscreen compounds (1).

This study offers guidance on developing novel sunscreen molecules. By unraveling the ultrafast non-adiabatic dynamics and UV protection mechanisms of these plant-derived sunscreens, scientists can harness this knowledge to create more effective and sustainable sun protection formulations (1). With a better understanding of the mechanisms underlying the UV protection offered by natural stilbene-based compounds, researchers can pave the way for the design and synthesis of next-generation sunscreens that combine efficacy, stability, and environmentally friendly characteristics (1).

Reference

(1) Guo, Y.; Wang, M.; Wu, Z.; Shi, Y.; Wang, Y.; Zhang, S.; Jin, B.; Cui, S.; Zhao, G. Ultrafast non-adiabatic dynamics of stilbene-based plant-derived sunscreens with cis–trans isomerization structures. Spectrochimica Acta Part A: Mol. Biomol. Spectrosc. 2023, 298, 122759. DOI: 10.1016/j.saa.2023.122759