Fabrication and Characterization of pH-Responsive, Nanoparticle-Attached Porphyrins for Singlet Oxygen Production

摘要

The goal of this work was to understand if singlet oxygen ('O_2) production from an immobilized dye could be regulated directly on support media such as titania and silica nanoparticles. Two types of pH-responsive, nanoparticle-attached sensitizers were prepared and tested for ~1O_2 production as a function of pH. The colloidally dispersed itania-attached 5,10,15,20-tetrakis(4-rncarboxyphenyl)porphyrin (titania-TCPP) behaved as a single-phase colloidal sensitizer at pH 1.0-3.3 with quantum yields of ~1O_2 production (Φ_Δ) between 0.20 and 0.25, as a heterogeneous particle sensitizer at pH 3.5-6.0 with Φ_Δ between 0.25 and 0.50, and as homogeneous free TCPP molecules in alkaline solutions with Φ_Δ = 0.53. Φ_Δ for colloidal silica nanoparticle-attached meso-tetra(N-methyl-4-pyridyl)porphine (silica-TMPyP) was pH-dependent as well, showing the higher Φ_Δ in weak acidic solution. The changes in Φ_Δ were fully consistent with pH dependent adsorption of porphyrins on nanoparticle surface. Those studies provide insights into the effect of support media on the photosensitization ability of porphyrin molecules, and the possibility of manipulation between photosensitization and recovery based on different type of support media.