Water-soluble aminoacid functionalized perylene diimides: the effect of aggregation on the optical properties in organic and aqueous media

We report on the straightforward preparation and photophysical characterization of four symmetrically substituted water soluble perylene diimides, obtained by functionalizing the imide positions with l-threonine, l-aspartic acid, l-cysteine and l-methionine. The presence of carboxylic groups on the two sides of the aromatic structure conveys a pH-dependent water solubility to all the molecules. The combined effect of the hydrophobic perylene core with the specific aminoacidic functionalities leads to different aggregation behaviors in both aqueous and organic media affecting the optical absorption and emission of the aromatic chromophore. By a comparative study of the optical properties we shed light on the main characteristics of these perylene derivatives in organic and aqueous diluted solution. These aminoacid perylene diimide molecules have the potential to be exploited in new sensing applications based on assembly/disassembly-driven fluorescence switching off-on in aqueous media.