A kinetic study on singlet molecular oxygen (O2(1Δg)) generation and quenching by dihydroxynaphthalenes

A kinetic study on the aerobic (O 2 ( 1 Δ g )-mediated) photooxidation of a series of dihydroxynaphthalenes was carried out. Members of this family of compounds include important environmental contaminants. The interaction with O 2 ( 1 Δ g ), determined by both time-resolved phosphorescence and static methods, yields a quenching rate constant in the range of 10 5 –10 9  M −1 s −1 , depending on the solvent polarity, pH, and substitution pattern of the dihydroxynaphthalene. According to experimental evidence, the mechanism of the interaction seems to be mediated by an encounter complex with a considerable charge transfer component. From a mechanistic point of view this characteristic of DHN indicates a behaviour very similar to that of simple substituted phenols and dihydroxybenzenes. Quantum yields for DHN photooxidation (Φ r ) indicate that these substrates are excellent candidates for O 2 ( 1 Δ g )-mediated degradation under environment conditions. Furthermore, these compounds proved to be good self-sensitizers upon irradiation at 337 nm. Quantum yields (Φ Δ ) for the production of O 2 ( 1 Δ g ) were determined to be on the order of 0.25 in benzene. Key words: dihydroxynaphthalenes, photooxidation, quenching, sensitization.not available