Sorbic Acid as a Triplet Probe: Triplet Energy and Reactivity with Triplet-State Dissolved Organic Matter via <sup>1</sup>O<sub>2</sub> Phosphorescence Kyle J. Moor Markus Schmitt Paul R. Erickson Kristopher McNeill 10.1021/acs.est.9b01787.s001 https://acs.figshare.com/articles/journal_contribution/Sorbic_Acid_as_a_Triplet_Probe_Triplet_Energy_and_Reactivity_with_Triplet-State_Dissolved_Organic_Matter_via_sup_1_sup_O_sub_2_sub_Phosphorescence/8636348 Sorbic acid (2,4-hexadienoic acid; HDA) is commonly used as a probe and quencher for triplet-excited chromophoric dissolved organic matter (<sup>3</sup>CDOM*), an important transient species in natural waters, yet much remains unknown about its reactivity with <sup>3</sup>CDOM* and its triplet energy. To better understand the quenching behavior of HDA, we measured HDA quenching rate constants for various humic substance isolates and whole waters with singlet oxygen (<sup>1</sup>O<sub>2</sub>) phosphorescence and determined the triplet energy of HDA. Low-temperature phosphorescence measurements determined the triplet energy of HDA to be 217 kJ mol<sup>–1</sup>, whereas a complementary method based on triplet quenching kinetics found a triplet energy of 184 ± 7 kJ mol<sup>–1</sup>. Time-resolved <sup>1</sup>O<sub>2</sub> phosphorescence measurements yielded different HDA quenching rate constants depending on the fitting method. Using an approach that considered the reactivity of the entire triplet pool produced values of (∼1–10) × 10<sup>8</sup> M<sup>–1</sup> s<sup>–1</sup>, while an approach that considered only the reactivity of the high-energy triplets output higher rate constants ((∼7–30) × 10<sup>8</sup> M<sup>–1</sup> s<sup>–1</sup>). In addition, the model based on high-energy triplet reactivity found that ∼30–60% of <sup>3</sup>CDOM* is not quenched by HDA. Findings from this study provide a more comprehensive view on the use of HDA as a probe for <sup>3</sup>CDOM*. 2019-06-20 00:00:00 Triplet-State Dissolved Organic Matter Low-temperature phosphorescence measurements triplet quenching kinetics Time-resolved 1 O 2 phosphorescence measurements 3 CDOM triplet energy 1 O 2 HDA quenching rate constants reactivity