Aggregation studies of benzoporphyrin derivative

The photophysical properties of a ring B benzoporphyrin derivative 1,3-dien e dimethylester were investigated in solution (water-DMSO mixtures). At low proportions of water in DMSO, the diester obeys Beer's law at all pH value s and ionic strengths investigated. For solvent systems containing more tha n 30% water, the extent of deviation from Beer's law as a function of porph yrin concentration is attributed to formation of porphyrin dimers. Dimeriza tion equilibrium constants (Kd) have been determined in different percentag e of solvent mixtures, using absorption and fluorescence spectroscopies, an d were found to exhibit a linear correlation between log (Kd) and the inver se of the dielectric constant (log (Kd) = 24.6 - 1060.4 x 1/epsilon (mix)). This equation permits the calculation of Kd in mixtures of water-DMSO.