Ligand Chemistry - Semiconductor Quantum Dots: Organometallic and Inorganic Synthesis - page 197

d n 1 y 4 n g | 6

Figure 6.9 Coupling reactions of amine box dendron-passivated particles. Reprinted
with permission fromW. Guo, J. J. Li, A. Wang and X. Peng, Chem. Mater. ,
2003, 15 , 3125. Copyright 2003 American Chemical Society.

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have also been used on CdSe/CdS particles. 243 In a related study, second-
generation polyamidoamine (PAMAM) dendrimers were used as capping
agents, although the terminal amine groups caused irreversible precipitation
by cross-linking on the CdSe surface. Capping the dendrimer

s terminal
groups with 1,2-epoxyethane resulted in a long-chain alkyl that did not
interact with the nanoparticle surface. The dendrimers coordinated to the
particle surface through the internal amines in the branched structure, with
dendrimers consisting of secondary and tertiary amines providing the better
surface protection. 244 Similarly, PAMAM dendrimers of various generations
were used to phase-transfer QDs of CdSe/ZnS using a simple solution
method, where the ester terminated dendrimers were dissolved in water
with a surfactant (poloxamer 188) and the chloroform solution of the QDs
was added and stirred until the chloroform evaporated. In this case, the
resulting material was not dendrimer-capped nanoparticles, but in fact
a composite of QDs, dendrimers and surfactant, with a

'

nal particle size
much larger than that of the parent QDs. The use of amine-terminated
dendrimers resulted in a precipitate that could not be dissolved in most
solvents, and the generation of dendrimers used also dictated emissive
properties, with the use of a 4.5G dendrimer resulting in a material with
a quantum yield of ca. 40%, which is notably high for QD materials in water.
Lower-generation dendrimers had notably lower quantum yields, which
limited their use in labelling. 245

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