Association behavior and fluorescence quenching between cationic zinc porphyrin pendant groups on water-soluble polymers and anionic iron porphyrin guests

An amphiphilic cationic tripyridiniumylporphyrin monomer, i.e., ZnTrMPyP, was synthesized and copolymerized with acrylamide in water and dimethyl sulfoxide, respectively, to prepare the water-soluble random copolymer P-D and microblock copolymer P-W. The association behavior and fluorescence quenching between the copolymers and tetra(p-sulfonato phenyl)porphyrin (Fe(III)TSPP(Cl)) were studied via absorption and emission spectra. The results showed that relatively discrete pendant groups of ZnTrMPyP within P-D could form a ground state complex with FeTSPP by electrostatic interactions, and both static and dynamic mechanisms were active in this quenching process. In contrast, the microblock porphyrin pendant groups within P-W interacted with FeTSPP as an entity, and static quenching was dominant in this process. Salt effects on the formation of the copolymers and FeTSPP complex were also investigated through the addition of KNO3, and the results showed that this association can be weakened by the electrostatic shielding effect, and the fluorescence quenching constant could be reduced.