Determination of excited triplet states of dissolved organic matter using chemical probes: A comparative and mechanistic study.

Dissolved organic matter (DOM) plays an important role in the biogeochemical cycle in natural waters. The determination and characterization of the excited triplet state of DOM (DOM*) have attracted much attention recently. However, the underlying differences of determined DOM* through different pathways are not yet fully understood. In this study, the differences and underlying mechanisms of the determined DOM* using 2,4-hexadien-1-ol (HDO) through an energy transfer pathway and 2,4,6-trimethylphenol (TMP) through an electron transfer pathway, were investigated. The results showed that the determined quantum yields of DOM* (Φ) for four commercial and four isolated local DOMs are different using HDO ((0.04 ± 0.00) × 10 to (2.9 ± 0.17) × 10)) and TMP ((0.08 ± 0.01) × 10 to (1.2 ± 0.17) × 10), respectively. For 17 DOM-analogs, significant differences were also observed with the quantum yields of their DOM* determined using HDO (Φ) and the triplet-state quantum yield coefficients determined using TMP (f). It indicates the different reactivity of TMP and HDO with the excited triplet of the chromophores with different structures within the isolated DOM. Based on the experimental and predicted values of f and Φ for different DOM-analogs, the impact of substituents on differences in DOM* values were further revealed. These results demonstrated that the levels of DOM* depended on the chemical functionalities present in the DOM-analogs.