Unraveling the Mechanism Underlying Surface Ligand Passivation of Colloidal Semiconductor Nanocrystals: A Route for Preparing Advanced Hybrid Nanomaterials

Abstract

Optically bright colloidal semiconductor nanocrystals (CSNCs) are important nanomaterials because of their potential applications such as cellular imaging and solid-state lighting. The optoelectronic properties of CSNCs are strongly controlled by the chemical nature of the surface passivating ligands that are introduced during their synthesis. However, the existing LaMer growth model does not provide a clear understanding of the stage when ligands become attached onto the CSNC surface. Herein, apart from the three stage formation mechanism of CSNCs (supersaturation, nucleation, and growth), an entirely new stage—solely involving surface ligand attachment onto fully grown CSNCs—is now reported that controls their photoluminescence properties. Furthermore, we also demonstrate a fundamentally new surface modification approach using partially passivated CSNCs to introduce a variety of functional groups (azide, alkene, and siloxane), including photoisomerizable molecular machines (e.g., azobenzene), without the use of “state-of-the art” ligand exchange chemistry. Knowledge of the ligand adsorption phenomena and resulting adsorption time dependence expands our fundamental understanding of structure–property relationships while allowing us to engineer novel hybrid functional nanomaterials with both previously unknown optoelectronic properties and supermolecular assembly options for various applications.