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Fig. 4 Partial 1H NMR spectra of 1 only and 1 in the presence of
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From the above experimental evidence of both the binding
stoichiometry and the 1H NMR analysis of the Ag+ titrations,
we can conclude that, in aqueous solutions, the binding of Ag+
with the adenine moiety in probe 1 results in the formation of
the 1–Ag+–1 complex, bringing the inner two heptamethine
cyanine chromophores of this complex into proximity, and this
conformation is similar to that of ‘‘H’’-aggregates, leading to a
change in the solution color from blue to pink and to changes in
the ratiometric fluorescence behavior.10
In summary, compound 1 was designed for use in a new
fluorescent sensor by making use of the binding of adenine
with Ag+ to induce cyanine aggregation in aqueous solution.
The fluorescent spectral results clearly indicate that compound
1 can be used as a ratiometric fluorescent sensor for Ag+ with
good selectivity and extraordinarily high sensitivity, and it is
likely that the experimental results of this study will provide
the basis for a new strategy for the design of various hepta-
methine cyanine based fluorescent chemosensors.
This work was financially supported by the MOST of China
(No. 2011CB910403), the National Natural Science Foundation
of China (No. 20675067 and No. 20835005), the Natural Science
Foundation of Fujian Province of China 2010J01051, and the
NFFTBS (No. J1030415), which are gratefully acknowledged.
8 The MCL (maximum contamination level) limit for silver is 0.1 ppm
(100 mg LÀ1) according to USEPA 2001.
9 W. C. Vosburgh and G. R. Copper, J. Am. Chem. Soc., 1941, 63, 437.
10 The reversibility of 1 to Ag+ was preliminary investigated by
adding IÀ to the 1 + Ag+ solutions. It was found that even
addition of 100 equiv. of IÀ relative to Ag+ could not obviously
change the fluorescent behavior of 1ÀAg+ solution. Since the
interaction of the adenine group with Ag+ is by coordination,
therefore, these IÀ experiments implied the far more stronger
binding of 1 to Ag+, and this stronger binding is also responsible
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.
c
This journal is The Royal Society of Chemistry 2012
Chem. Commun., 2012, 48, 2243–2245 2245