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

摘要

The oxygen quenching of excited states and concomitant delayed fluorescence (DF) of meso-tetraphenylporphyrin (TPP) adsorbed on alumina (Al_2O_3) were studied at different TPP and O_2 concentrations and temperatures by the diffuse-reflectance laser flash technique. The formation of ~1O_2 in the course of ~3TPP quenching by ~3O_2 is followed by the energy transfer from ~1O_2 to ~3TPP (~1O_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 ~1O_2 and ~3O_2 accelerates the ~1O_2 feedback more than 10 times. The key role of ~1O_2 in oxygen-induced DF is confirmed by the DF quenching by coadsorbed ~1O_2 quenchers (NaN_3, 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 NaN_3 when compared with the corresponding efficiencies in solution.