Here, we highlight the potential of aromatic charged polymer/dye complexes as candidates to integer new functional formulations and materials with specific characteristics given by complexation through aromatic-aromatic interactions. Highly porous sponges made of alginate as main structural component and containing poly(sodium 4-styrenesulfonate)/methylene blue complexes have been synthesized by freeze-drying aqueous mixtures of the three components. The aromatic polyelectrolyte allowed controlling the state of aggregation of the dye both in solution and in the solids since aromatic-aromatic interactions between the complementary charged molecules are favorable over the cooperative character of dye self-aggregation. The ratio monomer/dimer of the dye could be tuned by changing the aromatic polymer concentration. The effect of the state of aggregation of the dye in the production of reactive oxygen species, both in solution and in the solid materials, has been evaluated by chemical detection using potassium iodide and Singlet Oxygen Sensor Green. In addition, the phototoxicity against Staphylococcus aureus of complexes in solution and in the sponges has been tested. As a matter of control, similar experiments have been done with sponges containing the aliphatic polyelectrolyte poly(sodium vinylsulfonate), or in the absence of any added polyelectrolyte.