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

W. Li, S. Courtney, N. Gandra, E.D. Ellis, P.T. Tiyyagura, R. Gao
Jackson State University, US

Keywords: singlet oxygen, nanoparticle-attached sensitizer, titania, silica


The goal of this work was to understand if singlet oxygen (1O2) production from an immobilized dye could be regulated directly on support media such as titania and silica. Two types of pH- responsive, nanoparticle-attached sensitizers were prepared and tested for 1O2 production as a function of pH. The colloidally dispersed Titania-attached 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin (titania-TCPP) behaved as a single-phase colloidal sensitizer at pH 1.0-3.3 with quantum yields of 1O2 production () between 0.20 and 0.25, as a heterogeneous particle sensitizer at pH 3.5-6.0 with  between 0.25 and 0.50, and as homogeneous free TCPP molecules in alkaline solutions with  = 0.53. ΦΔ for colloidal silica nanoparticle-attached meso-tetra(N-methyl-4-pyridyl)porphine (silica-TMPyP) was pH-dependent as well, showing ΦΔ ~ 0.35 in a pH range of 3-6, but decreased to 0.03 at pH 6-10. The changes in  were fully consistent with pH dependent adsorption of porphyrins on nanoparticle surface. Recovery yields of 99.8% for TCPP and 98.8% for titania were obtained in acidic conditions, and 92% for silica-TMPyP in weak basic solutions. 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.
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