Spectral properties of cationic water-soluble metallo-porphyrins immobilized in a perfluorosulfonated ion-exchange membrane

Abstract

The behavior of palladium(II), platinum(II) and rhodium(III) complexes with two cationic water-soluble porphyrins: meso-tetrakis(4-N-methylpyridyl)porphyrin and meso-tetrakis(4-N,N,N-trimethylaminophenyl)porphyrin in Nafion® membrane and in Nafion® solution have been studied by UV-visible absorption and emission spectroscopy. All metalloporphyrins are localized in the interfacial region of Nafion®. The six-coordinate Rh(III) complexes are monomeric inside Nafion®, but immobilized four-coordinate Pd(II) and Pt(II) complexes form face-to-face dimers with a characteristic blue shifted Soret band. All immobilized complexes exhibit a strong red phosphorescence at room temperature in the absence of oxygen. Phosphorescence decays for all metalloporphyrins were found to be a single exponential but phosphorescence lifetimes noticeably increased in the Nafion® membrane as compared to lifetimes in aqueous solution.