Visible colorimetric fluoride ion sensors

Article abstract of DOI:10.1021/ol0507470

(Chemical Equation Presented) Five new urea derivative naphthalene compounds were synthesized by a reaction of 1,8-diaminonaphthalene and the corresponding isocyanates and showed a distinct color change only when treated with fluoride ions.

Full text of DOI:10.1021/ol0507470

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ORGANIC
LETTERS
2005
Vol. 7, No. 13
2607-2609
Visible Colorimetric Fluoride Ion
Sensors
Eun Jin Cho, Byung Ju Ryu, Young Ju Lee, and Kye Chun Nam*
Department of Chemistry and Institute of Basic Science, Chonnam National UniVersity,
300 Yongbong-Dong, Bukgu, Gwangju 500-757, Korea
kcnam@chonnam.ac.kr
Received April 7, 2005
ABSTRACT
Five new urea derivative naphthalene compounds were synthesized by a reaction of 1,8-diaminonaphthalene and the corresponding isocyanates
and showed a distinct color change only when treated with fluoride ions.
Anions play an important role in a wide range of chemical
and biological processes, and considerable attention has been
focused on the design of host molecules that can recognize
and sense anion species selectively through visible, electro-
chemical, and optical responses.1,2 Color changes, as signal-
ing an event detected by the naked eye, are widely used
owing to the low cost or lack of equipment required. Those
chemosensors are constructed according to the receptor-
chromophore general binomial, which involves the binding
of a specific anion substrate with receptor sites and a
chromophore responsible for translating the receptor-anion
association into an optical signal. This color variation can
be related to either structural or conformational changes in
the receptor structure when a complex is formed or to the
formation of a charge-transfer complex.3-6
However, excess fluoride can lead to fluorosis,9 which is a
type of fluoride toxicity that generally manifests itself
clinically in terms of increases in bone density. This diversity
of its function, both beneficial and otherwise, makes the
detection of fluoride ion important. Even though some
receptor compounds for fluoride ions have been reported,10
there is a paucity of reports on a selective visible chemo-
sensor for fluoride ions.11 Naphthalene urea receptors for
carboxylate and dihydrogen phosphate have been reported
as fluorogenic and chromogenic chemosensors,12 but the
(7) Kirk, K. L. Biochemistry of the Halogens and Inorganic Halides;
Plenum Press: New York, 1991; p 58.
(8) Kleerekoper, M. Endocrinol. Metab. Clin. North Am. 1998, 27, 441.
(9) (a) Wiseman, A. Handbook of Experimental Pharmacology XX/2;
Springer-Verlag: Berlin, 1970; Part 2, pp 48-97. (b) Weatherall, J. A.
Pharmacology of Fluorides. In Handbook of Experimental Pharmacology
XX/1; Springer-Verlag: Berlin, 1969; Part 1, pp 141-172. (c) Dreisbuch,
R. H. Handbook of Poisoning; Lange Medical Publishers: Los Altos, CA,
1980.
(10) (a) Dusemund, C.; Sandanayake, K. R. A. S.; Shinkai, S. J. Chem.
Soc., Chem Commun. 1995, 333. (b) Yamamoto, H.; Ori, A.; Ueda, K.;
Dusemund, C.; Shinkai, S. Chem. Commun. 1996, 407. (c) Scherer, M.;
Sessler, J. L.; Gebauer, A.; Lynch, V. Chem. Commun. 1998, 85.
(d) Anzenbacher, Jr. P.; Jurs´ıkova´, K.; Lynch, V. M.; Gale, P. A.; Sessler,
J. L. J. Am. Chem. Soc. 1999, 121, 11020. (e) Nicolas, M.; Fabre, B.
Simonet, J. Chem. Commun. 1999, 1881. (f) Camiolo, S.; Gale, P. A. Chem
Commun. 2000, 1129. (g) Lee, D. H.; Im, J. H.; Lee, J. H.; Hong, H. I.
Tetrahedron Lett. 2002, 43, 9637. (h) Yun, S.; Ihm, H.; Kim, H. G.; Lee,
C. W.; Indrajit, B.; Oh, K. S.; Gong, Y. J.; Lee, J. W.; Yoon, J.; Lee, H.
C.; Kim, K. S. J. Org. Chem. 2003, 68, 2467.
Among the range of biologically important anions, fluoride
is of particular interest owing to its established role in
preventing dental caries.7 The fluoride ion has also been
examined extensively as a treatment for osteoporosis.8
(1) Bianchi, E.; Bowman-James, K.; Garcia-Espana, E. Eds. Supra-
molecular Chemistry of Anions; Wiley-VCH: New York, 1997.
(2) Martinez-Manez R.; Sancenon, F. Chem. ReV. 2003, 103, 4419.
(3) Dietrich, B. Pure Appl. Chem. 1993, 65, 1457.
(4) Atwood, J. L.; Holman, K. T.; Steed, J. W. Chem. Commun. 1996,
1401.
(5) Gale, P. A. Coord. Chem. ReV. 2001, 213, 79.
(6) Beer, P. D.; Gale, P. A. Angew. Chem., Int. Ed. 2001, 40, 486.
10.1021/ol0507470 CCC: $30.25
© 2005 American Chemical Society
Published on Web 05/25/2005

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previous studies introduced one urea group at the 1-position
of naphthalene and combined two or three naphthalene urea
units togenther with spanners. However, we introduced two
urea groups into the 1,8-positions of naphthalene, which can
provide selective fluoride binding sites. In pursuit of
fluorescent fluoride ion chemosensors, a naphthalene urea
derivative 1 was synthezied, and its spectral characteristics
with fluoride ions were investigated.13 Five new naphthalene
urea derivatives that were selective, visible fluoride ion
sensors were synthesized by introducing a nitro group and
an azo unit into an aromatic moiety, and their anion binding
properties were investigated by UV-vis spectroscopy and
color changes. All of the naphthalene urea derivatives showed
significant bathochromic shifts in the presence of fluoride.
However, ligands 2, 4, 5, and 6 could be utilized as visible
chemosensors owing to the noticeable color changes in the
presence of fluoride ion.
disappears and a new peak appears at 384 nm, red-shifted
by a ∆λmax of 66 nm. However, a bathochromic shift of other
ions was also observed with a small change.
Figure 1 shows the absorption spectra of compound 2 in
the presence of the anions. The absorption peak at 350 nm
Figure 1. Absorption spectra of compound 2 (3 × 10-5 M) upon
addition of tetrabutylammonium fluoride, chloride, bromide, iodide,
dihydrogen phosphate, hydrogen sulfate, benzoate, and acetate
(3 × 10-3 M) in DMSO.
was shifted to 498 nm (∆λmax 148 nm) when fluoride was
added to compound 2 in the DMSO solution. On the other
hand, the absorption peaks at 319 and 415 nm of m- and
o-nitrophenyl derivatives 3 and 4 were shifted to 379 and
502 nm (∆λmax ) 60 and 87 nm), respectively, with a similar
concentration of added fluoride as summarized in Table 1.
Table 1. Absorption Peak (λmax) Change in Ligands 1-6 in
the Presence of Fluoride Ion
Ligands 1-4 were prepared using the one-step reaction13
of 1,8-diaminonaphthalene and appropriate isocyanates in a
tetrahydrofuran solution in high yield. Two azo naphthalene
urea derivatives 5 and 6 were prepared from 1,8-diaminon-
aphthalene and the corresponding azo isocyanates. The azo
isocyanates were obtained easily by treating 4-phenylazoa-
niline and disperse orange with triphosgene.
ligands
λmax (ligand)a
λmax (ligand + F-)b
∆λmax
1
2
3
4
5
6
318 nm
350 nm
319 nm
415 nm
361 nm
404 nm
384 nm
498 nm
379 nm
502 nm
542 nm
662 nm
66
148
60
87
181
258
The UV-vis experiments were carried out in a DMSO
solution. A receptor solution (3 × 10-5 M) was treated with
the representative anions such as tetrabutylammonium (TBA)
fluoride, chloride, bromide, iodide, dihydrogen phosphate,
hydrogen sulfate, benzoate, and acetate. When compound 1
forms a complex with F-, the absorption peak at 318 nm
a Absorption spectra were taken at a concentration of 3 × 10-5 M in
DMSO. b Tetrabutylammonium fluoride (3 × 10-3 M) was added.
As predicted from the ab initio calculation,14 it is obvious
that the ligand (L) exists as L- when treated with fluoride,
which can be visualized by the large red shift. The largest
red shift (258 nm) was observed when ligand 6 was
complexed with fluoride ion. This was attributed to the
elongated conjugation by the nitro group at the para position
of the azo phenyl derivative.
(11) (a) Boiocchi, M.; Boca, L. D.; Gomez, D. E.; Fabbrizzi, L.; Licchelli,
M.; Monzani, E. J. Am. Chem. Soc. 2004, 126, 16507. (b) Miaji, H. Sessler,
J. L. Angew. Chem., Int. Ed. 2001, 40, 154. (c) Jose, D. A.; Kumar, D. K.;
Ganguly, B.; Das, A. Org. Lett. 2004, 6, 3445.
(12) (a) Xia, H.; Wu, S.; Yang, X.; Wu, S. New. J. Chem. 1999, 23,
1105. (b) Mei, M.; Wu, S. New. J. Chem. 2001, 25, 471. (c) Hennrich, G.;
Sonnenschein, H.; Resch-Genger, U. Tetrahedron Lett. 2001, 42, 2805.
(d) Wu, J.; He, Y.; Wei, L.; Meng, L.; Yang, T.; Liu, X. Aust. J. Chem.
2005, 58, 53. (e) Wei, L.; He, Y.; Wu, J.; Wu, X.; Meng, L.; Yang, X.;
Liu, X. Supramol. Chem. 2004, 16, 561.
A color change could be observed easily by mixing the
ligand and anion as shown in Figure 2. A receptor solution
(13) Cho, E. J.; Moon, J. W. Ko, S. W.; Lee, J. Y.; Kim, S. K.; Yoon,
J.; Nam, K. C. J. Am. Chem. Soc. 2003, 125, 12376.
(14) Lee, J. Y.; Cho, E. J.; Mukamel, S.; Nam, K. C. J. Org. Chem.
2004, 69, 943.
2608
Org. Lett., Vol. 7, No. 13, 2005

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As the receptor bound the fluoride ions, hydrogen bonds
were constructed to form stable complexes, and the electron
density in the supramolecular system was increased, which
enhanced the charge-transfer interactions between the electron-
rich and electron-deficient moieties, resulting in a visible
color change (Figure 3).
Figure 3. Charge-transfer transition occurring in the deprotation
form of compound 2
Figure 2. Color changes of ligands 2 (a) and 6 (b) (2 × 10-5 M)
in DMSO with the addition of tetrabutylammonium anions (2 ×
10-3 M). A ) free receptor, B ) fluoride, C ) chloride, D )
bromide, E ) iodide, F ) dihydrogen phosphate, G ) hydrogen
sulfate, H ) acetate, I ) benzoate.
In conclusion, five new urea derivatives were synthesized
by a reaction of 1,8-diaminonaphthalene and the correspond-
ing isocyanates. A distinct color change was observed when
ligands 2, 4, 5, and 6 were treated with fluoride ions by
extending the conjugated system of the ligand anion, which
is formed only when complexed with a fluoride ion. Due to
the poor solubility of receptors, we are unable to study the
ion binding properties in the aqueous solution as well as other
organic solvents except in DMSO.
was simply treated with various anions such as F-, Cl-, Br-,
-
-
I-, H2PO4 , HSO4 , CH3COO-, and C6H5COO-. Noticeable
color changes were observed when ligands 2, 4, 5, and 6
were treated with the anions. In particular, it was remarkable
that a pale yellow ligand solution became red when fluoride
ions were added to compound 2 in DMSO, but no color
changes were observed when the other anions were added.
A similar red color was observed when the azo phenyl ligand
5 was treated with fluoride ions. However, a blue color was
observed in the case of ligand 6 with fluoride ion, and the
yellow color was deepened when chloride, dihydrogen
phosphate, benzoate, and acetate were added.
Acknowledgment. This study was financially supported
by Chonnam National University in the program, 2003.
Supporting Information Available: Spectroscopic data
for ligands 2-6, UV-vis spectra and color change of ligands
1, 3, 4, and 5 upon addition of tetrabutylammonium anions,
The origin of the color change in the host solution could
be ascribed to the charge-transfer interactions between
the electron-rich donor units and the electron-deficient
p-nitrophenyl and azo phenyl moieties.
1
and H NMR titration spectra of ligand 3. This material is
available free of charge via the Internet at http://pubs.acs.org.
OL0507470
Org. Lett., Vol. 7, No. 13, 2005
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