A novel fluorescence enhancing F- probe based on intermolecular energy transfer

Article abstract of DOI:10.1007/s11458-010-0105-9

A supramolecular fluorescent sensor of F^- based on intermolecular energy transfer is described. The maximum absorption wavelength of a pyrrolic compound 1 is 472 nm, which is coincident with the emission wavelength of a dipyridylamine-anthracene compound 2. In the CH₂Cl₂ solution of 1 and 2, the fluorescence of 2 was quenched because of the presence of intermolecular energy transfer from 2 to 1. When F^- was added to this solution, the absorption maximum wavelength of 1 shifted from 472 to 594 nm due to a deprotonation process. Simultaneously, the fluorescence of 2 was recovered because of the interruption of the intermolecular energy transfer. Based on these observations, the combination of 1 and 2 can be regarded as a novel supramolecular fluorescence enhancing F^- probe.

Full text of DOI:10.1007/s11458-010-0105-9

Front. Chem. China 2010, 5(2): 162–165
DOI 10.1007/s11458-010-0105-9
COMMUNICATION
binding part to form H-bonding or to induce deprotonation,
the fluorophore converts the changes into optical outputs,
including the quenching or enhancing of the fluorescence [17–
20]. Based on the intramolecular energy transfer, various
fluorescent fluoride sensors have been synthesized. However,
the linkage of the binding unit with a fluorophore through
properly designed covalent bonds usually requires rather
complicated multistep organic synthesis [21–24]. On the other
hand, if a supramolecular sensor system is constructed
through intermolecular energy transfer, the complicated
organic synthesis could be avoided, and a wide range of
well known fluorophores could be readily selected and
utilized. Based on these considerations, we designed a novel
and simple supramolecular fluorescence enhancing fluoride
recognition system based on the intermolecular energy
transfer mechanism, i.e., we selected a fluoride binding
agent whose absorption maximum wavelength is coincident
with that of the emission of a fluorescent compound. In the
absence of F–, the fluorescence was quenched by an
intermolecular energy transfer process. The binding of F–
resulted in the shift of the absorption wavelength of the host
molecule, and the intermolecular energy transfer was inter-
rupted. Thus, the fluorescence was recovered.
A novel fluorescence
enhancing F– probe based
on intermolecular energy
transfer
Quanguo WANG, Yubin DING, Weihong ZHU
and Yongshu XIE (✉)
A supramolecular fluorescent sensor of F– based on
intermolecular energy transfer is described. The max-
imum absorption wavelength of a pyrrolic compound 1
is 472 nm, which is coincident with the emission
wavelength of a dipyridylamine-anthracene compound
2. In the CH2Cl2 solution of 1 and 2, the fluorescence of
2 was quenched because of the presence of intermole-
cular energy transfer from 2 to 1. When F– was added to
this solution, the absorption maximum wavelength of 1
shifted from 472 to 594 nm due to a deprotonation
process. Simultaneously, the fluorescence of 2 was
recovered because of the interruption of the intermo-
lecular energy transfer. Based on these observations,
the combination of 1 and 2 can be regarded as a novel
supramolecular fluorescence enhancing F– probe.
2 Experimental
2.1 Instruments and materials
Absorption spectra were measured on a Varian Cary 500 UV/
Vis spectrophotometer (1 cm quartz cell was used). Fluores-
cence spectra were recorded on a Varian Cary Eclipse
fluorescence spectrophotometer. All reagents used in this
work were commercially available and used without further
purification.
Keywords fluoride sensor, intermolecular energy trans-
fer, fluorescence enhancement
1 Introduction
Over the past decade, great efforts have been devoted to
fluoride sensing due to its importance in a wide range of
chemical and biological processes [1–8]. Among the
methodologies that have been reported, fluorimetric sensing
plays critical roles in the recognition and sensing due to its
simplicity and low detection limit [9–12]. As the most
electronegative atom, F– can form the strongest H-bond
interaction with hydrogen-bond donors; such property has
been adopted in F– detection by neutral receptors [13–16].
Accordingly, the strategy for the design and construction of
classical fluorescent fluoride sensors is to covalently link a
fluorophore with a binding unit. When F– interacts with the
2.2 Preparation
The target sensor 1 (Figure 1) was synthesized in two steps
with good yields. First, the condensation of 3,5-di-tert-butyl-
4-hydroxybenzaldehyde with pyrrole under acidic conditions
Received January 13, 2010; accepted February 1, 2010
Key Laboratory for Advanced Materials and Institute of Fine Chemicals,
East China University of Science and Technology, Shanghai 200237,
China
E-mail: yshxie@ecust.edu.cn
Figure 1 The chemical structures of sensor 1 and compound 2.
© Higher Education Press and Springer-Verlag Berlin Heidelberg 2010

A novel fluorescence enhancing F- probe based on intermolecular energy transfer
afforded corresponding dipyrromethane, which was then
163
oxidized with DDQ to afford 1 [25]. Compound 2 was
synthesized according to a reported method [26].
3 Results and discussion
In our previous work [25], sensor 1 has been demonstrated to
be an efficient colorimetric fluoride sensor as a result of a
deprotonation process. From the UV-Vis titration of 1 with F–
(TBA salt) (Figure 2), we noticed that upon the addition of F–,
the intensity of the band at 472 nm decreased, and a new band
at 594 nm developed, which can be ascribed to internal charge
transfer (ICT). The addition of other anions, such as Cl–, Br–,
and I–, did not induce noticeable spectral responses (Figure 3).
Figure 3 UV-Vis absorption change of 1 (1.0 Â 10–5 mol$L–1 in
CH2Cl2) upon addition of 10.0 equivalents of the anions (F–, Cl–,
Br–, or I–).
Figure 2 UV-Vis spectral changes of 1 (1.0 Â 10–5 mol$L–1 in
CH2Cl2) observed upon the addition of F– (TBA salt) in CH2Cl2.
Figure 4 The fluorescence quenching of compound 2
(0.049 μmol$L–1 in CH2Cl2) upon the addition of 1. Excitation
wavelength was fixed at 397 nm (one of the isosbestic points).
Based on the fact that the emission peak of 2 is 472 nm,
which is almost equal to the lmax at 472 nm for sensor 1, we
designed a novel supramolecular system for the fluorescent
detection of F– based on intermolecular energy transfer. When
1 was added to a CH2Cl2 solution of 2, the energy of the
excited state of 2 was transferred to 1, and the fluorescence of
2 was quenched (Figure 4) due to the presence of the
intermolecular energy transfer process. Thus, when 300
equivalents of 1 was added to the solution of compound 2,
the fluorescence of 2 was quenched by 48 percent (Figure 4),
and 600 equivalents of 1 quenched the fluorescence by 71
percent.
When F– was added to a mixture of compound 2 and 600
equivalents of 1, a deprotonation process of 1 was caused by
F–, and the absorption maximum of 1 shifted from 472 to
594 nm, resulting in a cut-off of the intermolecular energy
transfer accompanied with the recovering of the fluorescence
of 2. When 100 equivalents of F- was added, the fluorescence
increased by a factor of 2.2 (Figure 5(a)).
This anion sensing system based on the fluorescence
enhancement has good selectivity for F– over other halides. As
mentioned above, Cl–, Br–, and I– could not induce obvious
changes in the UV-Vis spectra of 1 (Figure 3). Thus, no
obvious fluorescence change could be observed even when
1000 equivalents of Cl–, Br–, or I– was added to the solution of
compound 2 and sensor 1 (Figure 5(b)). Based on these
results, the combination of 1 and 2 may be developed as a
novel promising supramolecular system for the detection of
F–.
4 Conclusions
In summary, we have developed a novel supramolecular
approach for detecting F- via fluorescence enhancement based
Frontiers of Chemistry in China Vol. 5, No. 2, 2010

164
Quanguo WANG, Yubin DING, Weihong ZHU and Yongshu XIE
New Century Excellent Talents in University (NCET), the National
Natural Science Foundation of China, the Project Sponsored by the
Scientific Research Foundation for the Returned Overseas Chinese
Scholars, State Education Ministry.
Yongshu XIE received his Ph.D. degree in
1998 from Zhejiang University. He worked as
a postdoctoral fellow and an associate profes-
sor in University of Science and Technology
of China (1998–2006). He also worked as a
visiting researcher in Prof. Shieming Peng’s
group at National Taiwan University (2003),
in Prof. Hiroyuki Furuta’s group at Kyushu
University (2004–2006) and in Dr. Katsuhiko
Ariga’s group at National Institute for Materials Science, Japan
(2006–2007). In 2007, he joined East China University of Science
and Technology as a professor. He currently works on the synthesis
of novel porphyrinoids and metal-organic compounds for supramo-
lecular assemblies, optoelectronic and magnetic materials.
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Acknowledgements This work was financially supported by the
Shanghai Pujiang Program (Grant No. 08PJ14037), the Program for
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