Research Projects

In the context of organic-based UV filters/sunscreen agents, diarylketones such as benzophenones, oxybenzones, chalcones and their derivatives exhibit promising features through an effective absorption of UV radiation and relaxation predominantly via non-radiative pathways. The analysis of the underlying excited-state dynamics is not well reported in the literature, primarily due to the ultrafast time scales of the transient species as a consequence of involvement of non-adiabatic curve crossings, ultrafast isomerization etc. Such molecules also exhibit very low fluorescence quantum yields due to non-radiative relaxation and an effective intersystem crossing to triplet states upon photoexcitation. Chalcones are flavonoid chemicals found in nature and are extensively utilized as additives in sunscreen formulations due to their efficacy in blocking ultraviolet radiation. 4-Hydroxychalcones and derivatives have shown molar absorptivity in the range of 104 in the UV region with the sun-protection factors in the range of 18–21. However, the underlying intricate details of the excited-state reaction dynamics of these compounds are not been explored well. In this project, we propose to investigate the excited-state photoreactive mechanism of chalcone derivatives, under various conditions using femtosecond–, nanosecond– transient absorption, femtosecond fluorescence up-conversion and femtosecond Raman scattering studies. In particular, fs-Raman measurements help in unraveling the excited-state structural dynamics of various transient species that would play crucial roles in the fate of reaction dynamics. These studies would eventually be beneficial in strategic design of these compounds for the effective applications.

Chalcones, oxybenzones, sunscreen agents, transient absorption, femtosecond Raman