triplet states; photochemistry; reactive oxygen species; natural organic matter; singlet oxygen; indirect photolysis; humic substances
Pflug Nicholas C, Schmitt Markus, McNeill Kristopher (2019), Development of N-cyclopropylanilines to probe the oxidative properties of triplet-state photosensitizers, in Environmental Science and Technology
Davis Caroline A., McNeill Kristopher, Janssen Elisabeth M.-L. (2018), Non-Singlet Oxygen Kinetic Solvent Isotope Effects in Aquatic Photochemistry, in Environmental Science & Technology
, 52(17), 9908-9916.
Erickson Paul R., Moor Kyle J., Werner Jeffrey J., Latch Douglas E., Arnold William A., McNeill Kristopher (2018), Singlet Oxygen Phosphorescence as a Probe for Triplet-State Dissolved Organic Matter Reactivity, in Environmental Science & Technology
, 52(16), 9170-9178.
Davis Caroline, Erickson Paul, McNeill Kristopher, Janssen Elisabeth (2017), Environmental photochemistry of fenamate NSAIDs and their radical intermediates, in Environmental Science: Processes and Impacts
, 19 (5 ), 656-665.
Schmitt Markus, Erickson Paul, McNeill Kristopher (2017), Triplet-State Dissolved Organic Matter Quantum Yields and Lifetimes from Direct Observation of Aromatic Amine Oxidation, in Environmental Science and Technology
, 51(22), 13151-13160.
McNeill Kristopher, Canonica Silvio (2016), Triplet state dissolved organic matter in aquatic photochemistry: reaction mechanisms, substrate scope, and photophysical properties, in Environmental Science: Processes & Impacts
, 18, 1381-1399.
Triplet state chromophoric dissolved organic matter (3CDOM) is formed in all natural waters that are exposed to sunlight. This reactive species plays a central role in environmental photochemistry, where it acts as a powerful oxidant and a source of other reactive species, such as singlet oxygen. Despite its centrality, there are many open questions about the nature of 3CDOM. This proposal aims to fill gaps in our knowledge regarding this important species by quantifying its key excited state parameters.The specific objectives of this proposal are to (1) Determine the quantum yields of 3CDOM formation; (2) Assess the extent to which the pool of 3CDOM species responsible for energy transfer sensitization overlap with the 3CDOM species responsible for oxidation; (3) Estimate the excited state redox potential values (E0*) for DOM samples of terrestrial and aquatic origins; and, (4) Assess the extent to which pre-association of a donor compound to DOM enhances its oxidation rate. The work plan is organized into two Subprojects that will be carried out by two PhD students. The expected scientific outcomes include achieving the immediate goal of improving the understanding of the fundamental excited state properties (e.g., excited state energy and redox potential). This understanding promises to impact a larger scientific community, including biogeochemists studying element cycling in aquatic systems, environmental chemists interested in the fate of organic pollutants, and environmental engineers studying photochemical water treatment. The fundamental aspects of this work will also reach over to pure physical chemistry. Facets of our work related to the oxidation of organic molecules by triplet excited states may also impact research on photobiology. We expect to make significant methodological advances beneficial to the environmental chemistry community working on the photochemistry of natural waters. The proposed project will also achieve education outcomes that include the education of two PhD students. In addition, four related master thesis projects are anticipated. Numerous synergisms are expected to arise from the parallel projects on distinct yet closely related topics.