Spectroscopic investigation of inner filter effects by phthalocyanine solutions

In this study we report a systematic investigation of phthalocyanine (Pc) optical properties, showing that the effect of re-absorption of fluorescence plays a critical role in the line-shape of Pc optical spectra. We demonstrate that a strong dependence of the photoluminescence parameters on the concentration of phthalocyanines solution accounts for the apparent experimental evidence of a fluorescent dimer band in the emission at high concentrations. Despite a model based on fluorescent aggregates seems to describe the photophysical behavior of the system, additional experiments, such as electronic absorption spectroscopy, and fluorescence spectroscopy in which the optical pathlength inside the solution is suitably modified, provide a correct explanation of the observed optical behavior. We demonstrate that the shapes of optical spectra are completely independent on phthalocyanine aggregation state and are due only to experimental artifacts, i.e. inner filter effects.