Abstract
The relationship between exposure to ultraviolet (UV) radiation and skin cancer urges the need for extra photoprotection, which is presently provided by widespread commercially available sunscreen lotions. Apart from having a large absorption cross section in the UVA and UVB regions of the electromagnetic spectrum, the chemical absorbers in these photoprotective products should also be able to dissipate the excess energy in a safe way, i.e. without releasing photoproducts or inducing any further, harmful, photochemistry. While sunscreens are tested for both their photoprotective capability and dermatological compatibility, phenomena occurring at the molecular level upon absorption of UV radiation are largely overlooked. To date, there is only a limited amount of information regarding the photochemistry and photophysics of these sunscreen molecules. However, a thorough understanding of the intrinsic mechanisms by which popular sunscreen molecular constituents dissipate excess energy has the potential to aid in the design of more efficient, safer sunscreens. In this review, we explore the potential of using gas-phase frequency- and time-resolved spectroscopies in an effort to better understand the photoinduced excited-state dynamics, or photodynamics, of sunscreen molecules. Complementary computational studies are also briefly discussed. Finally, the future outlook of expanding these gas-phase studies into the solution phase is considered.
Highlights
Despite efforts to raise awareness towards both the correct use of sunscreens and the risks of excessive sun exposure, skin cancer cases have risen in recent years [1,2,3]
We explore the potential of using gasphase frequency- and time-resolved spectroscopies in an effort to better understand the photoinduced excited-state dynamics, or photodynamics, of sunscreen molecules
The three case studies reported in this review have revealed a wide range of research opportunities and are likely to encourage further work on the subject
Summary
Despite efforts to raise awareness towards both the correct use of sunscreens and the risks of excessive sun exposure, skin cancer cases have risen in recent years [1,2,3]. The system will relax back to the ground (lowest energy) electronic and vibrational state via a number of photochemical/photophysical processes [55,56], such as intramolecular vibrational redistribution (IVR) [57], internal conversion (IC) [58], intersystem crossing (ISC) [58], fluorescence [59] or phosphorescence [60], as summarized, where only the photophysical processes are shown for simplicity Some of these processes may induce damage to the skin if, for example, they result in the production of free radicals or other harmful photoproducts [29,61]. An ideal chemical absorber for a sunscreen lotion should strongly absorb UVA/UVB, but should be capable of dissipating the excess energy gained via mechanisms that cause no chemical change to occur, reforming the molecule in its original state without forming any potentially harmful species. These studies provide the initial ground work for an exciting field of research where much is yet to be unravelled, which we briefly expand on in the Summary and outlook
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