Toward an Alkahest Canopy for Gold Nanorod Stability in Water and Organic Solvents

Abstract

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.

Gold Nanorods: The Most Versatile Plasmonic Nanoparticles

“…There are two ways to modify the surface of Au NRs. One is ligand exchange through chemical interaction between surface-modifying molecules and Au NRs, such as through the Au–C bond , and the Au–catechol binding. − The thiol group is the most commonly used for ligand exchange. Due to the strong affinity of sulfur with noble metals, thiol-containing molecules can stably bind to the surfaces of Au NRs as an organic protective layer, which significantly improves the colloidal stability .…”

“…There are two ways to modify the surface of Au NRs. One is ligand exchange through chemical interaction between surface-modifying molecules and Au NRs, such as through the Au−C bond 139,140 and the Au− catechol binding. 141−143 The thiol group is the most commonly used for ligand exchange.…”

Plasmon-Mediated Chiroptical Second Harmonic Generation from Seemingly Achiral Gold Nanorods

“…To determine the importance of local structure on plasmon-mediated CD, we studied symmetric nanorods formed by thermal reshaping of the original asymmetric structures (Figures S1 and S4). The AS for the reshaped rods was ∼20% lower than that for the original sample. The SHG yield from reshaped nanorods was too low to reliably quantify polarization metrics, confirming the interpretation that subtle symmetry breaking induces intrinsic CD-SHG, which can be amplified by plasmon-resonant excitation.…”