Interaction of UV photostabilizers with singlet molecular oxygen ([O2(1Δg)]).: The case of 1′-hydroxy-2′-acetonaphthone

The interaction between photochemically generated singlet molecular oxygen [O-2((1)Delta(g))] and the relatively recently reported photostable compound, 1'-hydroxy-2'-acetonaphthone (1OH2AN) has been studied. The behavior of the isomer 2'-hydroxy-1-acetonaphthone (2OH1AN) was also investigated for comparative purposes. The former belongs to the family of extremely photostable intramolecular hydrogen bonded systems, much used in polymer photoprotection. Our study analyses the properties of these compounds as generators, by direct photoirradiation, and quenchers of the known oxidative species O-2 ((1)Delta(g)) upon indirect, dye-sensitized photoirradiation. Time resolved phosphorescence detection of O-2 ((1)Delta(g)) and polarographic and spectrophotometric measurements demonstrate that both 1OH2AN and 2OH1AN are excellent O-2 ((1)Delta(g)) quenchers in alkaline media (ionized-phenolic form). Nevertheless the process of quenching has a mainly chemical component, producing photodegradation of both isomers with photooxidation quantum efficiencies of 0.33 and 0.16 for 1OH and 2OH derivatives, respectively. These compounds are poor O-2 ((1)Delta(g)) quenchers when the molecular (non-ionized) phenolic form predominates through an exclusive O-2 ((1)Delta(g))-physical quenching process. The failure of O-2 ((1)Delta(g)) generation upon direct photoirradiation of 1OH2AN constitutes a desirable condition for a polymer photoprotector against photooxidative damage. (C) 1999 Elsevier Science Ltd. All rights reserved.