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

The oxygen quenching of excited states and concomitant delayed fluorescence (DF) of meso-tetraphenylporphyrin (TPP) adsorbed on alumina (Al2O3) were studied at different TPP and O-2 concentrations and temperatures by the diffuse-reflectance laser flash technique. The formation of O-1(2) in the course 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 fluorescent state. The global kinetic analysis of DF revealed variations on kinetic parameters with surface loading which match the aggregation of TPP on the surface. 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 process is in part controlled by the surface which enhances the efficiencies of amine quenchers but reduces that of NaN3 when compared with the corresponding efficiencies in solution. (C) 2001 Elsevier Science B.V. All rights reserved.