Spectroscopic characterization of thionine species in different media

The influence of pH on aggregate formation and changes in the structure of thionine monomers in solution has been determined. Spectroscopic data (UV–vis and 1H NMR) revealed that a free base form of the dye is formed at basic pH values, which displays highly hydrophobic behavior. The cationic monomeric form can be photoreduced in both organic and aqueous solution, while the free base form did not show any photoactivity in such media.