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

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 O2 concentrations and temperatures by the diffuse-reflectance laser flash technique. The formation of 1O2 in the course of 3TPP quenching by 3O2 is followed by the energy transfer from 1O2 to 3TPP (1O2 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 1O2 and 3O2 accelerates the 1O2 feedback more than 10 times. The key role of 1O2 in oxygen-induced DF is confirmed by the DF quenching by coadsorbed 1O2 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.