Ligand Surface Density Decreases with Quantum Rod Aspect Ratio

Yuetian Chen, Emily Grace Ripka, John M. Franck, Mathew M. Maye

Research output: Contribution to journalArticle

Abstract

The relationship between phosphonic acid (PA) binding strength, surface coverage, and quantum rod or dot aspect ratio was studied. Seven nanocrystals with an aspect ratio (l/w) between 1.0 and 11.7, including five CdSe with l/w between 1.0 and 5.2 and two CdSe/CdS with dot-in-rod and rod-in-rod microstructures with l/w between 7.5 and 11.7, were synthesized. The nature of phosphonic acid binding was studied in situ using one-dimensional 1H nuclear magnetic resonance (NMR) spectroscopy as well as two-dimensional diffusion ordered spectroscopy (DOSY) and relaxation ordered spectroscopy (ROSY). The DOSY results were used to separate strongly binding phosphonic acid signatures from weakly binding ones, thus allowing for estimates of ligand densities (LDs) to be calculated, which showed a significant drop from LD = 2.21 nm-2 for spherical CdSe with l/w = 1.0 to LD = 0.23 nm-2 for CdSe/CdS with l/w = 11.7. Interestingly, intermediate l/w = 1.7 showed a higher LD of 4.81 nm-2. The results suggest a wrapping or relatively flat binding by phosphonic acids on the sides of the rods, leading to decent surface coverage for low aspect ratios but lower LD for more elongated rods. This model was further confirmed using ROSY, which revealed similar relaxation times (T1) for each proton of the phosphonic acids on the rods, indicating similar ligand-quantum rod (QR) interface.

Original languageEnglish (US)
JournalJournal of Physical Chemistry C
Volume123
Issue number38
DOIs
StatePublished - Sep 26 2019

Fingerprint

aspect ratio
Aspect ratio
rods
Ligands
ligands
Phosphorous Acids
Acids
Spectroscopy
acids
spectroscopy
low aspect ratio
Relaxation time
Nanocrystals
Nuclear magnetic resonance spectroscopy
Protons
magnetic resonance spectroscopy
nanocrystals
Microstructure
relaxation time
signatures

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Energy(all)
  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films

Cite this

Ligand Surface Density Decreases with Quantum Rod Aspect Ratio. / Chen, Yuetian; Ripka, Emily Grace; Franck, John M.; Maye, Mathew M.

In: Journal of Physical Chemistry C, Vol. 123, No. 38, 26.09.2019.

Research output: Contribution to journalArticle

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