A KINETIC-STUDY ON SINGLET MOLECULAR-OXYGEN (O-2((1)DELTA(G))) GENERATION AND QUENCHING BY DIHYDROXYNAPHTHALENES

A kinetic study on the aerobic (O-2((1) Delta(g))-mediated) photooxida tion of a series of dihydroxynaphthalenes was carried out. Members of this family of compounds include important environmental contaminants. The interaction with O-2((1) Delta(g)), determined by both time-resol ved phosphorescence and static methods, yields a quenching rate consta nt in the range of 10(5)-10(9) M(-1) s(-1), depending on the solvent p olarity, pH, and substitution pattern of the dihydroxynaphthalene. Acc ording to experimental evidence, the mechanism of the interaction seem s to be mediated by an encounter complex with a considerable charge tr ansfer component. From a mechanistic point of view this characteristic of DHN indicates a behaviour very similar to that of simple substitut ed phenols and dihydroxybenzenes. Quantum yields for DHN photooxidatio n (Phi(r)) indicate that these substrates are excellent candidates for O-2((1) Delta(g))-mediated degradation under environment conditions. Furthermore, these compounds proved to be good self-sensitizers upon i rradiation at 337 nm. Quantum yields (Phi(Delta)) for the production o f O-2((1) Delta(g)) were determined to be on the order of 0.25 in benz ene.