Can we predict indirect photochemical reactions?
Rachele Ossola recently published her master thesis work on the competing reactivity of singlet oxygen (1O2) and triplet chromophoric dissolved organic matter (3CDOM*) in Environmental Science and Technology. In this work, we investigated the indirect photochemistry of furan carboxamides, a class of compounds derived from the fungicide fenfuram, with a combination of steady-state and laser flash photolysis experiments. Our results showed that 1O2 reactivity observed in the steady-state could be successfully predicted using the bimolecular rate constants obtained via laser measurements. On the other hand, the use of bimolecular triplet quenching rate constants overestimated the triplet reactivity observed in the steady-state due to radical repair pathways (antioxidant repair, superoxide repair, etc.).
Our work suggests that structure-reactivity relationships can be used to predict the extent of 1O2-induced reactions, but more investigations are needed to be able to do the same for triplets. Some knowledge gaps include the identification, prediction and quantification of radical repair mechanism(s), the correct estimation of “effective” 3CDOM* steady-state concentrations, and the importance of using DOM, and not model sensitizers, to measure bimolecular triplet rate constants.
Furan carboxamides as model compounds to study the competition between two modes of indirect photochemistry
Rachele Ossola, Markus Schmitt, Paul R. Erickson*, Kristopher McNeill*
Env. Sci. Technol. 2019 https://pubs.acs.org/doi/full/10.1021/acs.est.9b02895