Linking Electronic Relaxation Dynamics and Ionic Photofragmentation Patterns for the Deprotonated UV Filter Benzophenone-4

Abstract

Understanding how deprotonation impacts the photophysics of UV filters is critical to better characterize how they behave in key alkaline environments including surface waters and coral reefs. Using anion photodissociation spectroscopy, we have measured the intrinsic absorption electronic spectroscopy (400–214 nm) and numerous accompanying ionic photofragmentation pathways of the benzophenone-4 anion ([BP4–H] − ). Relative ion yield plots reveal the locations of the bright S 1 and S 3 excited states. For the first time for an ionic UV filter, ab initio potential energy surfaces are presented to provide new insight into how the photofragment identity maps the relaxation pathways. These calculations reveal that [BP4–H] − undergoes excited-state decay consistent with a statistical fragmentation process where the anion breaks down on the ground state after nonradiative relaxation. The broader relevance of the results in providing a basis for interpreting the relaxation dynamics of a wide range of gas-phase ionic systems is discussed.

Measurement of the Population of Electrosprayed Deprotomers of Coumaric Acids Using UV–Vis Laser Photodissociation Spectroscopy

“…Similar free radical products have been observed for the deprotonated forms of the sunscreens oxybenzone, 2-phenylbenzimidazole-5-sulfonic acid, and benzophenone-4 in recent work. 36 − 38 …”

“… 34 , 35 Recent photochemical studies on how pH environment could affect the sunscreen performance at the molecular level have demonstrated that the deprotonated forms of oxybenzone, 2-phenylbenzimidazole-5-sulfonic acid, and benzophenone-4 are all able to photogenerate free radicals species via active photodecay channels in the gas phase. 36 − 38 It is therefore important to investigate the deprotonated forms of the antioxidants studied here in the same context.…”

A “one pot” mass spectrometry technique for characterizing solution- and gas-phase photochemical reactions by electrospray mass spectrometry

“…6 displays the photofragmentation data as ion-yield spectra, presenting a clearer picture of the branching into the different photodissociation channels. 37,54 For 1 (Fig. 6a), the loss of CO and PPh 3 (4a) is the strongest channel at all energies above 3.4 eV, but the loss of just CO (4b) can be seen to be enhanced at energies between 3.7-4.2 eV.…”

Photodegradation of Riboflavin under Alkaline Conditions: What can Gas-Phase Photolysis Tell Us About What Happens in Solution?

“…The novelty of our LIMS set-up allows us to monitor the photofragment production intensities at each scanned wavelength to provide further insight into the nature of the excited states. Figure 4b Figure 5 presents the relative photofragment ion yields for [RF−H] − as a function of excitation energy, revealing several maxima that can be attributed to photoexcitation into different electronic states [31,32]. It is evident that between 2.0-3.0 eV, the m/z 241 and 212 photofragment ions are dominant, whereas the m/z 145 ion is not produced across this region.…”

“…This secondary ion subsequently peaks at 48% HCD energy. However, since the m/z 255 fragment clearly dominates in both the gas-phase laser and thermal (i.e., CID and HCD) fragmentation experiments, photofragmentation of [RF−H] − can be categorized as predominantly statistical (ergodic) over the spectral range of this experiment [31,34]. Overall, the CID and HCD fragmentation experiments reveal that [RF−H] − primarily dissociates into the m/z 255 ion, which subsequently dissociates into m/z 212 at higher internal energy, and increasingly into m/z 241 and 145 at the highest internal energies.…”