Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous, persistent organic pollutants formed by natural and anthropogenic combustion processes. PAHs have been studied for decades because of their adverse health affects in humans and wildlife. Many processes contribute to these adverse health effects, including PAH degradation and PAH-mediated oxygen photosensitization. Oxygen photosensitization mechanisms have been studied extensively and a consensus is emerging regarding singlet oxygen formation by PAH energy transfer. On the other hand, differing mechanisms have been proposed for oxygen sensitization by electron transfer. Reaction progress monitoring has emerged as a powerful tool for investigating the kinetics and mechanism of complex reactions. In this investigation, the progress of oxygen photosensitization by selected anthracene derivatives in a biorelevant solvent was measured using multichannel time-resolved optical spectroscopy. The measurements monitored the PAHs' photodegradation and their singlet oxygen production. Matrix-formatted spectra were collected as anthracene derivatives in octanol were subjected to simulated solar radiation. Singlet oxygen production by photoirradiated anthracenes in octanol was measured by p-nitroso-dimethylaniline (RNO) bleaching. Self-modeling curve resolution was used to isolate the spectra and time dependence of system components from the data matrices collected. The interpretation of these results was complemented by electronic structure calculations. In general, anthracene photodegradation and reactive oxygen species production rates increased for the substituted methyl derivatives relative to the parent compound. Electronic structure calculations indicate that the energy barrier for formation of excited state PAH-oxygen complexes decreases with the degree of parent compound substitution.
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