Ultrafast dynamics of UV-excited trans- and cis-ferulic acid in aqueous solutions

Abstract

The ultrafast UV-induced processes of the neutral, anionic and dianionic forms of trans- and cis-ferulic acid (FA) in aqueous solution were studied by static and femtosecond time-resolved emission and absorption spectroscopy combined with quantum chemical calculations. In all cases, initial excitation populates the first ππ* state. For the dianionic cis-isomer cFA, electronic deactivation takes place with a time constant of only 1.4 ps, whereas in all other cases, excited-state deactivation happens more than ten times slower, on a time scale of ≈20 ps. The data suggest sequential de-excitation pathways, where initial sub-picosecond solvent rearrangement and structural changes are followed by internal conversion to an intermediate excited electronic state from which deactivation to the ground state proceeds. Considering the time scales, barrierless excited-state pathways are suggested only in the case of cFA, where the observed formation of the isomerisation photoproduct tFA provides clear evidence for a cis ⇄ trans isomerisation coordinate. In the other cases, pathways with an excited-state energy barrier, presumably along the same coordinate, are likely, given the longer excited-state lifetimes.

Direct Observation of Photochemical Free Radical Production from the Sunscreen 2‐Phenylbenzimidazole‐5‐Sulfonic Acid via Laser‐Interfaced Mass Spectrometry

“…This allows us to monitor how the absorbance of the anion varies with wavelength, while simultaneously measuring the production of any photoproducts . Our laser‐based approach is in the spirit of a number of recent studies where advanced spectroscopic techniques have been applied to sunscreen molecules under highly‐controlled conditions …”

The role of symmetric functionalisation on photoisomerisation of a UV commercial chemical filter

“…6 Chemical filters based on cinnamates 7,8 are currently being used as a class of UVR absorbing molecules in commercial formulations due to their strong absorption of UVR and potent antioxidant properties. [9][10][11][12] Investigations into their photochemistry has shown a photoisomerisation pathway as a main route of deactivation, irrespective of solvent environment, [13][14][15][16][17] and starting geometric isomer (either E or Z); 14,18 although a change in lifetimes is noted. One such cinnamate-derivative contained in sunscreen formulations is the FDA and EU approved 2-ethylhexyl-E-4-methoxycinnamate (E-EHMC).…”

Investigating isomer specific photoprotection in a model plant sunscreen

“…17 The resulting time-constants (t n ), which describe the timescale for each step in the relaxation pathway, are shown in Table 1, (see ESI † for evolution associated difference spectra). The dynamics responsible for the time-constants produced in our sequential global fits have been extensively discussed in previous literature for the E-isomer; 5,6,18 we shall provide a quick overview here. After the initial photoexcitation, E-ES undergoes a rapid geometry relaxation, in the form of intramolecular vibrational redistribution (IVR), which we assign the time-constant t ivr .…”