Site-Specific Ligand Exchange on Colloidal Semiconductor Nanocrystals: On-Edge Exchange versus On-Facet Position...

Area of Science:

• Materials Science
• Nanotechnology
• Physical Chemistry

Background:

• Ligand exchange reactions are crucial for tuning the properties of colloidal nanocrystals (NCs).
• Understanding the kinetics and mechanisms of these reactions at a molecular level is essential for precise NC functionalization.

Purpose of the Study:

• To quantitatively investigate the ligand exchange reaction of alkanoates with alkylthiolates on CdSe NCs using in situ FTIR.
• To elucidate the distinct reaction channels and their associated kinetics and thermodynamic parameters.

Main Methods:

• In situ liquid-phase Fourier transform infrared (FTIR) spectroscopy.
• Solid-state Nuclear Magnetic Resonance (NMR) spectroscopy.
• Monte Carlo simulations.

Main Results:

• The forward ligand exchange on CdSe (100) facets occurs via two channels with time constants of ~5 s and ~10^6 s.
• FTIR and NMR indicate a transition of alkanoate ligands from chelating to bridging motifs.
• Monte Carlo simulations identified two on-facet ligand position swapping pathways with time constants of ~240 s and ~450 s.
• The reverse ligand exchange has a high equilibrium constant but is limited to specific binding sites.

Conclusions:

• Ligand exchange on CdSe NCs can be quantitatively studied with molecular resolution.
• The findings provide a detailed mechanistic understanding of ligand exchange, crucial for advanced NC applications.
• This work establishes a quantitative framework for colloidal NC ligand chemistry.