“Precipitation on Nanoparticles”: Attractive Intermolecular Interactions Stabilize Specific Ligand Ratios on the Surfaces of Nanoparticles

Abstract

Confining organic molecules to the surfaces of inorganic nanoparticles can induce intermolecular interactions between them, which can affect the composition of the mixed self‐assembled monolayers obtained by co‐adsorption from solution of two different molecules. Two thiolated ligands (a dialkylviologen and a zwitterionic sulfobetaine) that can interact with each other electrostatically were coadsorbed onto gold nanoparticles. The nanoparticles favor a narrow range of ratios of these two molecules that is largely independent of the molar ratio in solution. Changing the solution molar ratio of the two ligands by a factor of 5 000 affects the on‐nanoparticle ratio of these ligands by only threefold. This behavior is reminiscent of the formation of insoluble inorganic salts (such as AgCl), which similarly compensate positive and negative charges upon crystallizing. Our results pave the way towards developing well‐defined hybrid organic–inorganic nanostructures.

A Versatile AuNP Synthetic Platform for Decoupled Control of Size and Surface Composition

“…Recent work by Klajn and co-workers elucidated the effect of electrostatic interactions between different ligand types on the final composition of the ligand shell. 55 For a mixture of a positively charged viologen-based ligand and a zwitterionic sulfobetaine ligand, a variation of the ligand feed ratio by a factor of 5000 changed the effective ligand composition on the nanoparticles by only a factor of 3. In more general terms, we anticipate our approach to be a versatile nanoparticle platform for the study of both size and ligand composition on the resulting ligand shell morphology.…”

“…50,51 The potential of further surface functionalization by ligand exchange was recently validated for alkylthiol, 52 biphenylthiol, 53 azothiol, 54 and charged thiol mixtures. 55 Based on OAm as intermediated capping agent, we herein report on a two-step protocol for independent control over AuNP core and ligand shells. We study the applicability of this approach to produce thiol-capped AuNPs via thiol-for-OAm ligand replacement and establish a successful procedure to tune the core size as well as the capping-layer composition within a broad library of thiol ligands and mixtures thereof.…”