Photokinetics in tetraphenylporphyrin - molecular oxygen system at gas/solid interfaces: effect of singlet oxygen quenchers on oxygen-induced delayedfluorescence

The oxygen quenching of excited states and concomitant delayed fluorescence (DF) of meso-tetraphenylporphyrin (TPP) adsorbed on alumina (Al2O3) were s tudied at different TPP and O-2 concentrations and temperatures by the diff use-reflectance laser flash technique. The formation of O-1(2) in the cours e of (TPP)-T-3 quenching by O-3(2) is followed by the energy transfer from O-1(2) to (TPP)-T-3 (O-1(2) feedback) with the generation of TPP fluorescen t state. The global kinetic analysis of DF revealed variations on kinetic p arameters with surface loading which match the aggregation of TPP on the su rface. In concentrated samples the energy exchange between O-1(2) and O-3(2 ) accelerates the O-1(2) feedback more than 10 times. The key role of O-1(2 ) in oxygen-induced DF is confirmed by the DF quenching by coadsorbed O-1(2 ) quenchers (NaN3, 3-methylindole, 1.4-diazabicyclo[2.2.2]octane). This pro cess is in part controlled by the surface which enhances the efficiencies o f amine quenchers but reduces that of NaN3 when compared with the correspon ding efficiencies in solution. (C) 2001 Elsevier Science B.V. All rights re served.