Deactivation of Singlet Oxygen by Titanium Dioxide in Aqueous Solution Studied by Phosphorescence Quenching with Porphyrin Photosensitizers

摘要

Deactivation of singlet oxygen (~1O2) by TiO2 nanoparticles was investigated for the first time. ~1O2 was produced by pulse laser-induced photosensitization with either cationic or anionic porphyrin dye. Generation and decay of ~1O2. were measured by its phosphorescence at 1270 nm in the presence of seven commercially available TiO2 powders of various sizes and crystallites. To clarify the quenching mechanisms, the deactivation of the triplet excited state of porphyrin dyes (~3D~*) with TiO2 powders was also measured by the transient T—T absorption. The Stern—Volmer plot suggests that the quenching should take place dynamically by second-order reaction. The obtained rate constants for the deactivation of ~1O2 and ~3D~* with TiO2 were increased with the size of the particles, which is attributable to the increase of the local concentration of ~1O2 and ~3D~* around the TiO2 particles. The intrinsic rate constant for the deactivation of ~1O2 by TiO2 was elucidated to be 1.0 × 10~8 M~(-1) s~(-1).