Spectral and flash kinetic studies of water-soluble zinc porphyrins in poly-N-vinyl-2-pyrrolidone matrix

Abstract

Abstract A series of water-soluble zinc porphyrins, ZnTPPS, ZnTPPC and ZnTPPOH, have been synthesized. Their absorption, emission, singlet and triplet state quenching by electron acceptors like MV2+ and 1,5-AQDS2− have been studied in homogeneous aqueous solutions and bound to a PVP matrix. Binding constants for the systems under study do not vary much and give a low value for ΔG0 = −13.37 kJ M−1. However, the number of monomer units required for binding any individual porphyrin species varies with the size of the molecule. It appears that these water-soluble porphyrins are embedded in hydrophobic pockets in the polymer matrix and are only partially available to outside quenchers like MV2+ and 1,5-AQDS2−. From flash photolysis studies, formation of porphyrin radical cations and quencher anions is observed. Porphyrin cations are long-lived and are also formed on self-quenching and by disproportionation reactions in the absence of quencher. ZnTPPOH behaves differently.