Determination of the Aggregation Degree of Zinc-Phthalocyanines Derivatives into Polymeric Films via the Characterization of the Linear-Optical Absorption

We investigated the aggregation effects in films composed by zinc-phtalocyanine and its derivative, dispersed into a poly( methyl methacrylate) matrix, by analyzing the absorption coefficient at an increasing concentration. The ratio by weight of the compound to the host polymer was varied within two different ranges in order to extrapolate the solubility limit for both molecules. Measurements performed by spectroscopic analysis, allowed the calculation of the linear-optical absorption coefficient. Experimental data were interpolated by adopting a set of three Lorentzian oscillators characterized by three different sets of parameters, i.e., the intensity factor, resonance frequency, and line width, respectively. With the obtained data, the degree of monomer and dimer concentration in the films was evaluated. Within the investigated concentration range, the maximum solubility was found to be very different for the two investigated molecules, where the substituted phthalocyanine was very efficient in reducing the aggregation tendency.