title: Characterizing mixed phosphonic acid ligand capping on CdSe/ZnS quantum dots using ligand exchange and NMR spectroscopy.
abstract: The ligand capping of phosphonic acid functionalized CdSe/ZnS core-shell quantum dots (QDs) was investigated with a combination of solution and solid-state (31) P nuclear magnetic resonance (NMR) spectroscopy. Two phosphonic acid ligands were used in the synthesis of the QDs, tetradecylphosphonic acid and ethylphosphonic acid. Both alkyl phosphonic acids showed broad liquid and solid-state (31) P NMR resonances for the bound ligands, indicative of heterogeneous binding to the QD surface. In order to quantify the two ligand populations on the surface, ligand exchange facilitated by phenylphosphonic acid resulted in the displacement of the ethylphosphonic acid and tetradecylphosphonic acid and allowed for quantification of the free ligands using (31) P liquid-state NMR. After washing away the free ligand, two broad resonances were observed in the liquids' (31) P NMR corresponding to the alkyl and aromatic phosphonic acids. The washed samples were analyzed via solid-state (31) P NMR, which confirmed the ligand populations on the surface following the ligand exchange process. Copyright © 2015 John Wiley & Sons, Ltd.
authors.affiliation: School of Molecular Sciences, Arizona State University, Tempe, AZ, 85287, USA.
authors.forename: Stephen K
authors.initials: SK
authors.lastname: Davidowski
authors.affiliation: Thermo Fisher Scientific, Eugene, OR, 97402, USA.
authors.forename: Carmen E
authors.initials: CE
authors.lastname: Lisowski
authors.affiliation: School of Molecular Sciences, Arizona State University, Tempe, AZ, 85287, USA.
authors.forename: Jeffery L
authors.initials: JL
authors.lastname: Yarger
keywords: CdSe/ZnS; NMR; phosphonic acid; quantum dots