Electron Injection Process of Porphyrin Dye into a Heterogeneous TiO2/Re(I) Photocatalyst

Abstract

We now report full details of the collisional ET process at the interface between the solvated porphyrin dye (a representative molecular dye) and heterogeneous TiO2 particles (a well-defined n-type semiconductor), which can be another major electron injection route in dye-sensitized photocatalytic (DSPC) systems based on TiO2 semiconductor besides the typical injection route by oxidative quenching of the TiO2-anchored dye. From temperature-dependent transient profiles of the reductively quenched porphyrin dye (porphyrin(center dot-)) with and without TiO2 particles, it was found that there exists a high activation energy (E-a = 57-58 kJ/mol, solvated dye -> TiO2 particles) for the collisional electron transfer from the dissolved porphyrin(center dot-) to heterogeneous TiO2 semiconductor, which could originate from the low collisional probability between the solution-phase anionic dye and heterogeneous TiO2 particle. This quenching kinetic study provides the first quantitative results showing how the solution-phase dye radical anions transport their photoinduced electrons to the heterogeneous semiconductor side. In addition, the complex photosensitizing behaviors of photo-labile porphyrin dye were investigated with the preparation of the photomodified porphyrin species (ZnPAcet and ZnPEt), which are identified from in situ UV-vis spectroscopy and ESI-mass analysis of the dye solution after photolysis.