Relation between optical properties and formation of reactive intermediates from different size fractions of organic matter

The photophysics and photochemistry of aquatic organic matter (OM) are of interest due to their role in defining the reactivity of this material in the environment. Studies have demonstrated that molecular size and composition are important determinants of the photochemical behavior of OM, including the formation of reactive intermediates (RIs). The present study expands on previous works by evaluating both photophysical and photochemical processes of OM of distinct origins and molecular sizes through the analysis of absorbance and fluorescence along with the formation of various RIs of interest ( ³OM, HO•, ¹O₂). In general, larger size fractions displayed higher absorptivity that extends further into the visible region. On the other hand, smaller components displayed higher quantum yields for fluorescence and all RIs measured. In accordance with hypotheses previously formulated, possible explanations for the observed results are proposed based on the increased prevalence of non-radiative energy decay processes in larger OM molecules.