another method for designing efficient sensors. This reaction is
only observed in the presence of fluoride, thus BODIPY dye 3
can be used as a selective and sensitive chromogenic and
fluorescent chemodosimeter for fluoride anions. Moreover,
the color change from orange to green, proving the existence
of FÀ, is convenient for dynamic tracking in cellular imaging
owing to the unchanged intense fluorescence.
Scheme 2 Reaction-based chromogenic and fluorescent sensing of
fluoride.
Si–F bond. Therefore, the trihexylsilyl groups present at the
2,6-positions of BODIPY dye 3 can be easily cleaved by
fluoride ions but not by other anions (Scheme 2). The presence
of the CRCH resonance in BODIPY dye 4 is detected at
In conclusion, a clever reaction-based chemodosimeter,
BOIDPY dye 3, was prepared and proved to be an excellent
colorimetric fluoride anion sensor. It is particularly attractive
because of the necessary time to reach equilibrium of 5 min.
Moreover, with a LOD of 67.4 nM (i.e. 1.28 ppb), this
chemodosimeter is totally adequate for detecting fluorides
near and below the concentration allowed in drinking water
according to the US EPA.12 This class of chemodosimeters
should open a new research field for sensor design. The use of
hydrophilic substituents is now desired since preliminary data
with acetone/water (19 : 1, v : v) do not give as good results.
We gratefully acknowledge the National Natural Science
Foundation of China (21077081, 20921062) and the Funda-
mental Research Funds for Central Universities (1101007) for
financial support. PDH thanks the Natural Sciences and
Engineering Research Council of Canada (NSERC), Fonds
1
d = 3.3 ppm by H NMR (Fig. S4, ESIw). The proton comes
from acetone.
When one C–Si bond is broken and one –CRC–H unit is
formed, BODIPY dye 4 exhibits a lesser number of flexible
groups, here Si(C6H13)3. Consequently, FF for BODIPY
dye
3 is lower than that for BODIPY dye 4 since
FF = kF/(kF + kIC + kisc) where kF is the fluorescence rate
constant, kIC and kisc are the non-radiative rate constants for
internal conversion and intersystem crossing, respectively. The
presence of flexible groups increases kIC and decreases FF. So,
the FÀ-treated chromophore shows a stronger fluorescence
(Fig. 2).
The deprotection of the electron-donating trihexylsilyl
group leads to the blue-shift of both the absorption and
fluorescence peaks; changes that can simply be seen by naked
eyes from the color change and luminescence change upon
irradiation with UV lamp. The blue-shift of the absorption
band induced by FÀ has been corroborated by DFT and
TDDFT calculations (see the ESIw). The optimized geometries
for BODIPY dyes 3 and 4 exhibit the expected planar
geometry. The calculated absorption spectra extracted from
the 100 lowest energy electronic transitions exhibit an absorption
peak of BODIPY dye 4 blue-shifted with respect to that for
BODIPY dye 3 from 495 nm to 485 nm (Fig. 6) and the
extinction coefficient (e) is smaller for BODIPY dye 4, which
are in agreement with the experimental results. The two ethylyl
groups being conjugated with the aromatic BODIPY plane
suggest that variations of substituents on the ethylyl groups
should lead to sensitive changes in the photophysical properties
of BODIPY dyes. This is exactly what happens in these
systems. This observation is useful in the design of sensors
when the sensor recognizes a specific substrate.
Que
and Centre d’Etudes des Mate
de l’Universite de Sherbrooke for funding.
´
be
´
cois de la Recherche sur la Nature et la Technologie,
´
riaux Optiques et Photoniques
´
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Fig. 6 The calculated UV-Vis absorption spectra for BODIPY dye 3
(red) and dye 4 (blue).
c
This journal is The Royal Society of Chemistry 2011
Chem. Commun., 2011, 47, 5503–5505 5505