Specific emission and quenching of photoexcited tetraphenylporphyrin derivatives incorporated in a Nafion film

Abstract

According to the absorbance and fluorescence emission spectral changes, zinc ion in the ZnTPP (5,10,15,20-tetraphenylporphyrinatozinc (II)) was demonstrated to be replaced by two protons to form the free base tetraphenylporphyrin (H 2TPP) and further protonated to [H 4TPP] 2+ when the complex was incorporated into the hydrophobic fluorocarbon cluster in the Nafion alcoholic solution. This ion replacement and protonation took place very rapidly by incorporating the ZnTPP into a solid Nafion matrix. The photoexcited [H 4TPP] 2+ underwent a concentration quenching in the solid Nafion matrix. Although a dynamic quenching was involved (the second-order rate constant was 9.5 × 10 7 M −1 s −1), the static quenching was the major mechanism. Assuming that the probe molecules were distributed randomly in the Nafion matrix, the quenching distance between the center to center of the porphyrin molecules was calculated to be 1.6 nm. This diffusion coefficient was estimated to be 4.0 × 10 −8 cm 2 s −1.