Dithiolane ligands for semiconductor quantum dots

We have investigated the potential of the dithiolane ring to anchor organic compounds on the surface of CdSe-ZnS core-shell quantum dots. In particular, we have synthesized three monomeric ligands, incorporating an azobenzene chromophore and a single dithiolane anchor in their molecular skeleton, as well as a polymeric ligand with multiple chromophoric labels and anchoring groups. All compounds co-adsorb on the surface of preformed quantum dots, together with their native tri-n-octylphosphine oxide surfactants, when chloroform dispersions of the organic ligands and the inorganic nanoparticles are heated under reflux for 24-72 h. The reaction time dictates the average number of azobenzene chromophores incorporated in the final assemblies, which can range from 6 up to 92. However, the modified quantum dots retain a substantial hydrophobic character and are not soluble in water, despite the presence of hydrophilic poly(ethylene glycol) chains in three of the four dithiolane ligands. The adsorbed azobenzene chromophores can be switched from trans to cis configurations with ultraviolet stimulations. The photochemical process is thermally reversible and, in the case of the polymeric ligand, results in the photomodulation of the luminescence intensity of the nanostructured construct.