A bistren cryptand with a remote thioether function: Cu(II) complexation in solution and on the surface of gold nanostars

A new macrobicyclic ligand capable of binding two Cu2+ cations has been synthesized and its protonation and coordinative properties fully determined in aqueous solution. A thioether moiety was appended on the ligand backbone. This does not influence the ligand coordination ability but allows us to graft its bis-copper complex on the surface of a self-assembled monolayer of gold nanostars (GNS), in turn grafted on glass slides pre-functionalized with a layer of a silane-bearing polyethyleneimine polymer. The release of copper ions from the GNS monolayers was also investigated, finding a general agreement with the coordination properties of the complex in solution, although the bis-copper complex displays an increased kinetic inertness when grafted on the glass slides. The photothermal properties of the GNS monolayer were studied with and without the overlayer of the Cu2+ complex, finding no influence of the latter but disclosing that the bis-copper complex detachment is promoted by local T increase due to laser irradiation.