Chemistry Reference
In-Depth Information
ering matrices without the
presence of extraneous capping agents is amajor driving force in the search for
designer capping agents. Modi
The incorporation of nanoparticles into di
ed tetramethylpiperidinyloxy/phosphinic
acid-based capping agents have been used to incorporate particles into poly-
styrene, reportedly growing the polymer from the nanoparticle surface.
183
In
similar work, PVP ligands were linked to CdSe nanoparticles
via
phosphonate
groups. Initially, TOPO-capped CdSe QDs were surface-exchanged with
a related phosphine oxide type ligand with one pendant bromobenzyl group
instead of a long alkyl chain. This anchored group was then reacted further
using a palladium-catalysed Heck reaction to give poly(
p
-phenylenevinylene)
(PPV)-functionalised CdSe particles, with a quantum yield of 65%.
184
Capping
with PPV was also carried out with CdSe/ZnS.
185
Interesting optical properties
were observed in such structures, such as 1D emission and absorption
spectra attributed to photoinduced charge transfer from the ligand to the
nanoparticles.
186
Blinking (
d
n
1
y
4
n
g
|
6
uorescence intermittency) was also found to be
suppressed in such structures, again attributed to charge transfer.
187
Again, the suitability of phosphine oxide system as a capping agent has
been exploited and combined with the use of a PEG group to impart water
solubility and compatibility with a cellular environment to Fe
3
O
4
nano-
particles. In a simple reaction, phosphoryl trichloride was reacted with three
equivalents of poly(ethylene glycol)methyl ether to give a range of substituted
PEGylated phosphine oxides. The dissolution of oleic acid-capped Fe
3
O
4
and
the PEGylated phosphine oxide in tetrahydrofuran ensured the ligand
substitution reaction, and allowed the resulting nanoparticles to be
dispersed in water. Ligands could also be prepared that possessed an amine
group such as 1,2-ethylenediamine, using a larger excess of the amine and
only two equivalents of the poly(ethylene glycol)methyl ether during the
ligand synthesis. This functional pendant amine group could then be reacted
further; for example, coupling the particle to a dye molecule. The resulting
nanoparticles were easily transfected into cells and were found to be
non-toxic.
188
To overcome the instability of monodentate ligands, oligophosphines have
been developed that can be tailored to suit speci
.
c environments by altering
the functionality on a pendant side arm,
189
as shown in Figure 6.6. The oli-
gophosphines were described as having three distinct units; a phosphine
layer that coordinated to the particle surface and a second linking layer that
connected to the
nal layer, which consisted of the surface functionality.
Example of functionalities as shown in Figure 6.6 include octyl groups for
allowing particle dispersion in non-polar hydrocarbons, carboxylic acids,
which when deprotonated allowed dispersion in polar solution and further
functionalisation (such as cross-linking, enhancing particle stability) for
bioapplication, and methacrylate for processing into polymeric matrices.
Comparison of the oligophosphine-capped CdSe/ZnS particles and the
monodentate analogues showed increased stability and reduced emission
quenching for the oligomeric species. In similar work, a phosphine oxide-
based polymer has been developed that facilitated the e
ective phase
Search WWH ::
Custom Search