Fluorescent signal transduction in a self-assembled Hg²⁺ chemosensor tuned by various interactions in micellar aqueous environment

A new OFF-ON fluorescent chemosensor for ions Hg in water has been designed by associating fluorophore 10-methylacridinium perchlorate (MAClO) with a selective lipophilic sulfur-containing ligand, such as N,N-bis (2-hydroxyethylthio-1-ethyl)dodecyl amine (DBSO). The communication between the two subunits is only due to their spatial closeness, ensured by sodium dodecyl sulfate (SDS) micellar aggregates. The quenching of MA fluorescence is ascribed to a photoinduced electron-transfer from the ligand to the excited fluorophore, still the emission is quickly restored by addition of Hg (as chloride salt) due to the complex formation between ligand and metal. The sensitivity of the system improves by decreasing the ligand concentration, as well as by changing the stoichiometry of the ligand-Hg complex from 1:1 to 2:1. DFT calculations give interesting insights into the structures of the complexes and provide useful information on the sensorial activity experimentally observed. The replacement of MAClO with 9-cyanoanthracene, a fluorophore differently localized on the micellar aggregate, highlights the effect of Cl coordination to the complexed Hg on the operating mechanism of the sensor. These results demonstrate as the micellar aggregates provide for a straightforward means to regulate the response of the sensorial system without altering the recognition or reporter unit.