Photophysical properties of protoporphyrin IX and thionine covalently attached to macromolecules

Abstract

Protoporphyrin IX and thionine were covalently linked to the macromolecules poly(acrylic acid) and poly(methylolacrylamide). The absorption and emission properties of the dye molecules bound to the macromolecules were studied. In addition, the fluorescence lifetimes of the bound dyes were measured by time-resolved methods; the decay curves were fitted well to biexponential kinetics, indicating that the chromophore is located in two different environments of the macromolecules. It was inferred from the fluorescence lifetime measurements and emission intensities that the excited state of the porphyrin is quenched by thionine bound to the same macromolecular chain. It is suggested that the quenching process is mediated by the macromolecular random coil which appears to be more efficient when the polymer chain is poly(methylolacrylamide). Stern-Volmer plot analysis of the quenching process suggests that it follows a static mechanism when the polymer chain contains acrylamide groups.