On the Dynamic Stoichiometry of Metal Chalcogenide Nanocrystals: Spectroscopic Studies of Metal Carboxylate Binding and Displacement

Details

• Alternative Title:
  J Am Chem Soc
• Personal Author:
  Anderson, Nicholas C. ; Hendricks, Mark P. ; Choi, Joshua J. ; Owen, Jonathan S.
• Description:
  We demonstrate that metal carboxylate complexes (L-M(O2CR)2, R = oleyl, tetradecyl, M = Cd, Pb) are readily displaced from carboxylate-terminated ME nanocrystals (ME = CdSe, CdS, PbSe, PbS) by various Lewis bases (L = tri-n-butylamine, tetrahydrofuran, tetradecanol, N,N-dimethyl-n-butylamine, tri-n-butylphosphine, N,N,N',N'-tetramethylbutylene-1,4-diamine, pyridine, N,N,N',N'-tetramethylethylene-1,2-diamine, n-octylamine). The relative displacement potency is measured by (1)H NMR spectroscopy and depends most strongly on geometric factors such as sterics and chelation, although also on the hard/soft match with the cadmium ion. The results suggest that ligands displace L-M(O2CR)2 by cooperatively complexing the displaced metal ion as well as the nanocrystal. Removal of up to 90% of surface-bound Cd(O2CR)2 from CdSe and CdS nanocrystals decreases the Cd/Se ratio from 1.1 ± 0.06 to 1.0 ± 0.05, broadens the 1S(e)-2S(3/2h) absorption, and decreases the photoluminescence quantum yield (PLQY) from 10% to <1% (CdSe) and from 20% to <1% (CdS). These changes are partially reversed upon rebinding of M(O2CR)2 at room temperature (∼60%) and fully reversed at elevated temperature. A model is proposed in which electron-accepting M(O2CR)2 complexes (Z-type ligands) reversibly bind to nanocrystals, leading to a range of stoichiometries for a given core size. The results demonstrate that nanocrystals lack a single chemical formula, but are instead dynamic structures with concentration-dependent compositions. The importance of these findings to the synthesis and purification of nanocrystals as well as ligand exchange reactions is discussed.
• Subjects:
  Binding Sites Carboxylic Acids Chalcogens Ligands Metals Nanoparticles Quantum Theory Temperature
• Keywords:
  CdS CdSe Ligand Exchange Nanocrystals PbS PbSe Quantum Dots Quantum Yield Stoichiometry
• Source:
  J Am Chem Soc. 135(49):18536-18548
• Pubmed ID:
  24199846
• Pubmed Central ID:
  PMC4102385
• Document Type:
  Journal Article
• Funding:
  C06 RR017528/RR/NCRR NIH HHSUnited States/ ; C06 RR017528-01-CEM/CE/NCIPC CDC HHSUnited States/
• Volume:
  135
• Issue:
  49
• Collection(s):
  CDC Public Access
• Main Document Checksum:
  urn:sha256:cefbde6034ec154162822f255cd5d7562e8b43974bcc19a1a61773b3d8552d4d
• Download URL:
  https://stacks.cdc.gov/view/cdc/30039/cdc_30039_DS1.pdf
• File Type:
  [PDF - 1.39 MB ]