Toward An Alkahest Canopy For Gold Nanorod Stability In Water And Organic Solvents

Controlling the surface chemistry of nanoparticles is crucial and affects everything from performance to synthesis, processability, and toxicity. Many times, however, stability requirements during synthesis, processing, and integration are contradictory and necessitate phase transfer methods and surface modifications that lead to waste and limit functionalization options. Herein, we demonstrate that the solvation of colloidal gold nanorods (AuNRs) can be tuned from water to aprotic organic solvents by thermodynamically tuning the morphology of its ligand bilayer assembly (cetyltrimethylammonium bromide, CTAB), performing as an alchemical alkahest canopy. As CTAB concentration decreases below the critical micelle concentration (CMC), the bilayer is depleted due to an equilibrium between surfactant molecules in solution and on the AuNR surface. These aqueous stable AuNRs with a depleted ligand stabilization layer directly transfer to aprotic polar organic solvents. This behavior is consistent with a structural inversion of the weakly coordinating, defective CTAB bilayer in response to the polarity of the solvent medium. This process also affords the creation of anhydrous dispersions and enables the formulation of dispersions in nonpolar organic solvents. The utility of these organically stable AuNR dispersions is demonstrated by substantially increasing the effectiveness of grafting-to reactions of thiolated apolar polymers and the formation of Au-C bonds via anhydrous Grignard surface reactions.