Ligand Chemistry - Semiconductor Quantum Dots: Organometallic and Inorganic Synthesis - page 189

d n 1 y 4 n g | 6

Figure 6.6 The structure of oligomeric phosphine capping agents with di erent

functionalities. Reprinted with permission from S. Kim and M. G.
Bawendi, J. Am. Chem. Soc. , 2003, 125 , 14652. Copyright 2003
American Chemical Society.

transfer of a variety of materials, from QDs, to metals, and metal oxides. 190
The resulting products retained the majority of their original optical prop-
erties and were proven in magnetic resonance imaging (MRI), labelling and
catalytic applications.

.

6.6.3 Amine-Based Surfactant Exchange
As amines make excellent capping agents for QDs, it makes sense that they
are used as versatile phase-transfer reagents too. Indeed, pyridine was
considered one of the rst phase-transfer reagents, which initially was

thought to be essential for the deposition of a shell layer, as mentioned
earlier. 121 The use of dodecylamine (DDA) as a phase-transfer reagent for
metal ions and its subsequent use in metal and semiconductor nano-
particle synthesis highlights the versatility of amines. 191 Following the
above reports, 4-polyethyleneglycol pyridine has been used to transfer
TOPO-capped CdSe QDs to water, either by



rst removing the initial ligand
with pyridine, or by direct addition of the aqueous solution of the
substituted pyridine ligand. The resulting particles were soluble in water
for months, unlike monothiol analogues, which were found to be unstable
due to disul



de formation. The optical spectra showed that the position of
the features was maintained a



er phase transfer, although the quantum
yield was not reported. 192 Pyridine-type ligands have also been prepared
that, when attached to the surface of CdSe QDs, can be used as an iodide

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