title: Ligand bonding and dynamics on colloidal nanocrystals at room temperature: the case of alkylamines on CdSe nanocrystals.
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 Delta(r)G(o) was calculated as 9.8-11.5 kJ/mol. With a proposed mathematic method, the corresponding chemical kinetic constants for the desorption (kd) and adsorption (ka) processes were measured to be 0.01 s(-1) and 0.5 L mol(-1) s(-1), respectively. K, kd, and ka 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.
authors.affiliation: Department of Chemistry & Biochemistry, University of Arkansas, Fayetteville, AR 72701, USA.
authors.forename: Xiaohui
authors.initials: X
authors.lastname: Ji
authors.forename: Danis
authors.initials: D
authors.lastname: Copenhaver
authors.forename: Christopher
authors.initials: C
authors.lastname: Sichmeller
authors.forename: Xiaogang
authors.initials: X
authors.lastname: Peng
mesh_terms: D000327:Adsorption; D000465:Algorithms; D000588:Amines / Q000737:chemistry*; D019187:Cadmium Compounds / Q000737:chemistry*; D003102:Colloids / Q000737:chemistry*; D007700:Kinetics; D008024:Ligands; D008163:Luminescent Measurements; D009682:Magnetic Resonance Spectroscopy; D053758:Nanoparticles / Q000737:chemistry*; D036103:Nanotechnology / Q000379:methods*; D011725:Pyridines / Q000737:chemistry; D018036:Selenium Compounds / Q000737:chemistry*
chemical_list: D000588:Amines; D019187:Cadmium Compounds; D003102:Colloids; D008024:Ligands; D011725:Pyridines; D018036:Selenium Compounds; C058667:cadmium selenide; C023666:pyridine