Polymer bound pyrrole compounds, IX. Photophysical and singlet molecular oxygen photosensitizing properties of mesoporphyrin IX covalently bound to a low molecular weight polyethylene glycol

The photophysical and singlet molecular oxygen photosensitizing properties of two amphiphilic systems consisting of mesoporphyrin bound to one polyoxyethylene chain through ester or amide bonds (MPEGE and MPEGA, respectively) have been determined in aqueous and organic solvents. Steady-state and time-resolved UV-Vis-NIR absorption and emission, as well as chemical trapping studies indicate that both systems are essentially monomeric in CH₂Cl₂, their properties resembling those of mesoporphyrin dimethyl ester. In aqueous solutions the photoproperties show a remarkable dependence on the concentration which is attributed to aggregation phenomena. Below 10 μM the process can be described as a monomer-dimer equilibrium with constant K = (1.6 ± 0.5) X 10⁶ in water. The absorption, fluorescence, and singlet oxygen production characteristics of both monomer and dimer have been determined.