Chemistry Reference
In-Depth Information
aggregation of dye molecules. In the former case, when surfactant molecules such as
alkyltrimethylammonium ions are co-intercalated together with dye molecules, it locates
between the adjacent dyes and avoids the aggregation of them by acting as a ''spacer''. In
the latter case, when the separation distances between the adjacent anionic sites in the host
material and between the adjacent cationic charges in the porphyrin molecules were
approximately equal, a surprisingly large value of 0.8 porphyrin molecules/nm
2
for the
loaded amount of porphyrin without aggregation is achieved. A similar 'spacer effect' of
perfluoroalky groups is also expected, if hybrid intercalation compounds containing
perfluoroalky groups are used as hosts [76-78]. As shown in Figure 15.9, when the
monomer
excimer
360
400
440
480
520
560
600
wavelength
/
nm
Figure 15.9 Fluorescence spectra of pyrene attached to silylated graphite oxide containing
perfluoroalkyl groups reacted with N-(3-triethoxysilylpropane)-1-pyrenemethaneimine of (A):
10 and (B): 100mmol/L at 85
C for 1 h. (unpublished data)
concentration of N-(3-triethoxysilylpropane)- 1-pyrenemethaneimine was enough low,
the fluorescence due to pyrene excimer around 490 nm was not observed, indicating the
suppression of aggregation of pyrene attached to the film of silylated graphite oxide
containing perfluoroalkyl groups.
Rose Bengal shown in Figure 15.10 was also used to estimate the micropolarity in the
((((perfluoroalkanoyl)amino)ethyl)hexadecyl)dimethylammoniumion-intercalated sapo-
nite dispersed in benzene, based on its absorption and fluorescence maxima in the
unaggregated state [79]. In this case, the absorption and fluorescence peaks of Rose
Bengal are observed at lower wavelengths and the micropolariy was surprisingly higher
than that in surfactant/clay hybrids without perfluoroalkyl groups. This was attributed to
the larger amounts of adsorbed water molecules in the vicinity of ammonium part in hybrid
with perfluoroalkyl groups. Quartz crystal microbalance measurements indicated ca. 4
water molecules per ammonium groups were reversibly adsorbed and desorbed. While the
surfactant with perfluoroalkyl groups can take linear conformation of hydrocarbon and
fluorocarbon chains, alkyl groups have a bent structure as shown in Figure 15.11. The
linear conformation facilitates the access of water molecules, which results in the increase
of the number of adsorbed water molecules and hydrophilic microenvironment. As a
consequence, concentration of molecular oxygen became a high value of 4.5
10
4
M,
when estimated from the triplet lifetime of RB in intercalation compound. Interestingly,
