Chemistry Reference
In-Depth Information
This approach demonstrated the ease of desymmetrization opening new access to
multifunctional and amphiphilic structures. Ru-bipy complexes are important chro-
mophores and sensitizers in solar cells, which underlines the coupling with other
chemical entities such as organic dyes and the anchoring on surfaces.
5.8 SENSING OF VOLATILE ORGANIC COMPOUNDS
Voids of interior are perfectly suited for the uptake of volatile solvents/gases.
The suitability of polyphenylene dendrimers as sensor layers for monitoring volatile
organic compounds (VOCs) in the gas phase was demonstrated. The coating of the
quartz micro balance (QMB) with second-generation dendrimers possessing different
cores (
) was performed by using a procedure
from mass spectrometry known as electrospray. The dendrimers were dissolved in
THF and accelerated by a high DC voltage through a thin capillary and sprayed onto
the top electrode of the QMB. All investigated dendrimers showed similar behavior;
all compounds responded very selectively to polar aromatic VOCs, such as acet-
ophenone, aniline, benzaldehyde, benzonitrile, fluorobenzene, nitrobenzene, and
2-methyl-benzonitrile. Remarkably neither chlorinated nor unsubstituted aliphatic
hydrocarbons, alcohols, amines, aldehydes, and carbonyl compounds became
included into these hosts. The number of included guest molecules depends on both
the structure and the size of the dendrimers. A structure-property relationship may be
feasible. Incorporating functional groups enables fine tuning of the sensor properties,
which makes it possible to detect even aliphatic solvents. The sensitivity of
dendrimer-coated QMB sensors was remarkably high, for example, for aniline and
acetophenone around 5 ppm and it has now been further optimized in the group of
Waldvogel [68].
Upon such optimizations, it was found that with a combination of three different
matrices triacetonetriperoxide can be distinguished from water, hydrogen peroxide,
acetone, and other omnipresent molecules. Specific shape-persistent phenylene
dendrimers with pyridine in the scaffold (
B-G2, Biph-G2, TPM-G2, HPB-G2
) were found to have an extremely high
affinity toward TATP, while rejecting polar compounds. The additional internal
pyridyl moieties turned out to be very beneficial for the selectivity, while other
internal functionalities are under investigation. The crucial role of the voids was
revealed by testing different dendrimer generations G1-G3 and, in particular, G4 are
unique affinity materials since they provide cavities, which are complementary to the
shape of the TATP molecule. The limit of detection for TATP could be optimized far
below 0.1 ppm. Thereby these dendritic sensors can be applied for many volatile
compounds. It is considered that the design of new functionalized scaffolds is the key
element for further promising sensors with high affinity for such analytes.
In another attempt to use the hydrophobic polyphenylene dendrimers for sensing of
volatile organic compounds they were functionalized with disulfide and attached to
gold nanoparticles. The disulfide functionalization was achieved via coupling of
thioacetic acid (5-[1,2]dithiolan-3-ylpentanoicacid) to polyphenylene branches via
esterification resulting in
56
87
(Scheme 5.28) [88].
