Abstract:

With CdSe nanocrystals stabilized with very weak ligands (pyridine) as the starting materials, NMR techniques were applied to distinguish the bonded and free alkylamine ligands in an equilibrated adsorption/desorption system for the CdSe−amine nanocrystal−ligand pair. NMR and photoluminescence (PL) measurements were further correlated to identify the linear relationship between PL intensity and the surface ligand coverage of the amine-coated CdSe nanocrystals. For 3.5 nm CdSe nanocrystals and octylamine ligands, the chemical equilibrium constant (K) of the CdSe−amine nanocrystal−ligand adsorption/desorption process was found to be around 50−100, and the corresponding Δ_rG^o was calculated as 9.8−11.5 kJ/mol. With a proposed mathematic method, the corresponding chemical kinetic constants for the desorption (k_d) and adsorption (k_a) processes were measured to be 0.01 s^-1 and 0.5 L mol^-1 s^-1, respectively. K, k_d, and k_a obtained here are generally 2−4 magnitudes different from those estimated in literature. Analysis indicates that these constants are well consistent with the existing experimental observations.