Indole-azadiene conjugate as a colorimetric and fluorometric probe for selective fluoride ion sensing

Article abstract of DOI:10.1039/b821466b

An indole-azadiene conjugate (1), synthesized by facile one-step condensation, behaves as a highly selective probe for detection of fluoride ion both in colorimetric and fluorometric analyses. The probe 1 shows F ^--selective color change from colorless to yellow and appearance of green fluorescence. ¹H NMR analysis and ab initio calculation reveal that the F^--induced colorimetric and fluorometric responses of 1 are simply driven by hydrogen bonding interaction between the indolic NH protons and F^-.

Full text of DOI:10.1039/b821466b

View Article Online / Journal Homepage / Table of Contents for this issue
PAPER
www.rsc.org/obc | Organic & Biomolecular Chemistry
Indole-azadiene conjugate as a colorimetric and fluorometric probe for
selective fluoride ion sensing†
Yasuhiro Shiraishi,* Hajime Maehara and Takayuki Hirai
Received 2nd December 2008, Accepted 25th February 2009
First published as an Advance Article on the web 26th March 2009
DOI: 10.1039/b821466b
An indole-azadiene conjugate (1), synthesized by facile one-step condensation, behaves as a highly
selective probe for detection of fluoride ion both in colorimetric and fluorometric analyses. The probe 1
shows F--selective color change from colorless to yellow and appearance of green fluorescence. 1H
NMR analysis and ab initio calculation reveal that the F--induced colorimetric and fluorometric
responses of 1 are simply driven by hydrogen bonding interaction between the indolic NH protons
and F-.
Introduction
Results and discussion
Anions play a fundamental and important role in a wide range of
chemical, biological, medical, and environmental processes. De-
sign and development of efficient anion probes, capable of sensing
the targeted anion highly selectively, has therefore attracted a great
deal of attention.1 Of particular interest is the design of probes for
selective fluoride ion (F-) detection due to pivotal roles of F- in
dental care2 and in the treatment of osteoporosis.3 Various kinds
of colorimetric4 or fluorometric5 probes for selective F- detection
have been synthesized so far. For practical application, probes that
can detect F- by both colorimetric and fluorometric analyses are
favorable due to their ease of use. Several dual mode F- probes have
been proposed;6 however, all of these probes require complicated
synthesis steps (at least two steps). Easily preparable dual mode
F- probes are therefore necessary for practical application.
Herein, we report that a simple-structured molecule (1), 1,4-
bis(3-indolyl)-2,3-diaza-1,3-buthadiene, synthesized by facile one-
step condensation (Scheme 1), behaves as a highly selective F-
probe in both colorimetric and fluorometric analyses. The probe
1 shows F--induced color change from colorless to yellow and
appearance of green fluorescence. We describe that the F--induced
colorimetric and fluorometric responses of 1 are simply driven
by hydrogen bonding interaction between indolic NH protons
and F-.
The symmetrical probe 1 is easily obtained by stirring an ethanol
solution containing indole-3-carbaldehyde and hydrazine mono-
hydrate at room temperature for 36 h,7 as a yellow-white powder,
with 80% yield (Scheme 1). The purity of 1 was fully confirmed by
1H and 13C NMR and EI-MS analyzes (see ESI†, Fig. S2–S4).
Fig. 1 shows changes in absorption and fluorescence spectra
of 1 (25 mM) measured in DMSO upon addition of 50 equiv of
respective anions (F-, Cl-, Br-, I-, AcO-, ClO4 , H2PO4 , HSO4 ,
-
-
-
NO3 , and SCN-) as a n-tetrabutylammonium (n-bu4N+) salt.
-
As shown in Fig. 1a, without anions, 1 exhibits a characteristic
absorption band centered at 352 nm. F- addition leads to a
decrease in this absorption, along with an appearance of red-
shifted absorption centered at 409 nm. As shown in Fig. 2, the
Scheme 1 Synthesis of the probe, 1.
Research Center for Solar Energy Chemistry, and Division of Chemical
Engineering, Graduate School of Engineering Science, Osaka Univer-
sity, Toyonaka 560-8531, Japan. E-mail: shiraish@cheng.es.osaka-u.ac.jp;
Fax: +81 6 6850 6273; Tel: +81 6 6850 6271
† Electronic supplementary information (ESI) available: Evidence for no
FHF- dimer formation, supplementary data (Fig. S1–S9 and Table S1),
and Cartesian coordinates for 1 and 1–F- and 1–2F- complexes. See DOI:
10.1039/b821466b
Fig. 1 Changes in (a) absorption and (b) fluorescence (lex = 420 nm)
spectra of 1 (25 mM) measured in DMSO upon addition of 50 equiv of
respective anions (as a n-bu4N+ salt).
2072 | Org. Biomol. Chem., 2009, 7, 2072–2076
This journal is
The Royal Society of Chemistry 2009
©

View Article Online
Fig. 2 Change in (a) color and (b) fluorescence color of 1 upon addition
of F- (as a n-bu4N+ salt) in DMSO.
solution color changes from colorless to yellow upon addition
of F-. In contrast, addition of other anions does not show any
spectral change. As shown in Fig. 1b, without anions, 1 does
not show any fluorescence (lex = 420 nm). F- addition, however,
leads to an appearance of fluorescence at 420–600 nm. As shown
in Fig. 2, bright green fluorescence is observed upon addition
of F-. In contrast, addition of other anions does not show any
fluorescence. These data clearly suggest that the probe 1 behaves
as a colorimetric and fluorometric probe for selective F- sensing.
It must be noted that the F--induced changes in absorption and
fluorescence spectra are unaffected by other anions (see ESI†,
Fig. S5), indicating that the simple probe 1 can detect F- selectively
even in the presence of other anions. It must also be noted that
indole itself shows F--selective fluorescence enhancement, but
the absorption spectrum scarcely changes. In contrast, indole-3-
carbardehyde, the starting material, shows F--selective red-shift of
the absorption band, but does not show fluorescence enhancement
(see ESI†, Fig. S6 and S7).
Fig. 3 shows the results of absorption titration of 1 with F-.
The F- addition leads to a decrease in 352 nm absorption, along
with an increase in the 409 nm band. The spectral change almost
stops upon addition of 30 equiv of F-. The clear isosbestic points
at 304 and 376 nm indicate that a single component is produced
in response to the interaction between 1 and F-. Fig. 4 shows
the results of fluorescence titration (lex = 420 nm) of 1 with F-.
Addition of F- leads to continuous increase in the 420–600 nm
fluorescence. The intensity increase is saturated upon addition of
30 equiv of F-, which is similar to the results of absorption titration
(Fig. 3). Although the fluorescence quantum yield of 1 is low (fF =
0.0017 with 30 equiv of F-),8 the fluorescence enhancement upon
Fig. 4 Fluorescence (lex = 420 nm) titration of 1 (25 mM) with F- (as a
n-bu4N+ salt) in DMSO. Inset: change in fluorescence intensity monitored
at 455 nm.
F- addition is much higher than that of early-reported fluorescent
F- probes.6,9
The probe 1 associates with F- in a 1:2 stoichiometry. This is
confirmed by the Benesi-Hildebrand analysis.10 When assuming a
1:2 association between 1 and F-, the Benesi-Hildebrand equation
is given as follows:
È
Í
˘
1
1
1
=
+ 1
(1)
˙
˚
FI - FI0 FI• - FI0 ÎK[F- ]02
FI0 is the fluorescence intensity of 1, FI• is the intensity
measured with excess amount of F-, FI is the intensity measured
with F-, K is the association constant (M-2), and [F-]0 is the
concentration of F- added (M). As shown in Fig. 5, plot of 1/(FI–
FI0) against 1/[F-]0 shows a liner relationship, indicating that 1
2
actually associates with F- in a 1:2 stoichiometry. The association
constant, K, between 1 and two F-, is determined from the ratio
of intercept/slope to be 1.1 ¥ 106 M-2.
Fig. 5 Benesi-Hildebrand plots (lem = 455 nm) of 1 using eqn 1, assuming
1:2 stoichiometry for association between 1 and F-. The plots assuming
1:1 association is shown in Fig. S8 (ESI†).
The association of 1 and F- occurs through a hydrogen bonding
interaction between the NH protons of 1 and F-. Several F-
probes driven by F--induced removal of NH protons have been
1
proposed.11 In these cases, H NMR titration with F- detects a
formation of FHF- dimer at ca. 15–17 ppm.11a–c However, in the
present case, 1H NMR titration of 1 with F- (DMSO-d6, 303 K)
reveals that FHF- dimer does not form by the reaction of 1 with
Fig. 3 Absorption titration of 1 (25 mM) with F- (as a n-bu4N+ salt) in
DMSO. Inset: change in absorbance monitored at 409 nm.
This journal is
The Royal Society of Chemistry 2009
Org. Biomol. Chem., 2009, 7, 2072–2076 | 2073
©

View Article Online
F- (see ESI†, evidence for no FHF- dimer formation), indicating
that removal of NH protons does not occur. The interaction
1
between the NH protons of 1 and F- is confirmed by H NMR
analysis. As shown in Fig. 6, the indolic NH protons of 1 (d =
11.7 ppm) disappear completely upon F- addition, indicating that
F- indeed interacts with indolic NH protons.4e,f In this case, other
protons of 1 shift upfield, suggesting that this interaction affects
p-electrons of 1 and, hence, may lead to the change in absorption
and fluorescence spectra.
Fig. 6 Change in partial 1H NMR spectra of 1 in DMSO-d6 upon
addition of (a) 0, (b) 5, (c) 30, and (d) 50 equiv of F- (as a n-bu4N+
salt).
To clarify the mechanism for the changes in absorption and fluo-
rescence spectra of 1, electronic properties of ground state and ex-
cited state of 1 and 1–2F- complex were studied by ab initio molecu-
lar orbital calculation. The calculation was performed on the time-
dependent density functional theory (TDDFT) using a B3LYP/
6-31G* basis set within the Gaussian 03 programs. As shown in
Table S1 (see ESI†), the lowest singlet electronic transition for both
1 and 1–2F- complex is HOMO-LUMO transition. The lowest
singlet transition energy of 1 is determined to be 374 nm, which is
similar to that of the observed absorption maximum of 1 (352 nm,
Fig. 3). In contrast, the transition energy of the 1–2F- complex
(414 nm) is much lower than that of 1 (374 nm) and is similar to
the absorption maximum of 1 obtained with F- (409 nm).
Fig. 7 shows the HOMO and LUMO orbitals of 1 and 1–2F-
complex, respectively. Electronic transition of both compounds
has a p,p* character; however, the LUMO orbital of each
compound is different. The p-electrons of LUMO orbital of 1
are localized on the azadiene moiety and the electron density on
the indole moieties is poor. This is probably due to the inherent
electron donating property of the indole moieties.12 The less
populated p-electron density on the indole moieties of 1, therefore,
results in no fluorescence of 1 (Fig. 4). In contrast, as shown in
Fig. 7, p-electrons of LUMO orbital of the 1–2F- complex are
extended to the indole moieties (see red circle). This is because the
hydrogen bonding interaction between the indolic NH protons
and F- promotes a negative charge transfer from the azadiene
moiety to the indole moieties.13 The population of p-electrons on
the indole moieties, therefore, probably allows an appearance of
420–600 nm fluorescence (Fig. 4).
Fig. 7 HOMO and LUMO orbitals of 1 and 1–2F- complex calculated
on the DFT level using a B3LYP/6-31G* basis set.
positive charge on the indolic NH proton interacting with F-
(Fig. 7). Therefore, solvents with higher dielectric constants would
stabilize the dipole and, hence, cause a red-shift of the charge-
transfer transition. As shown in Fig. S9 (ESI†), a roughly linear
relationship exists between the lmax of the absorption band of the
1–2F- complex and the dielectric constant of the medium. The data
clearly indicates that the 1–2F- complex has a charge-transferred
electronic configuration, as shown in Fig. 7.
The interaction between the indolic NH protons and F- also
affects the electronic configuration of HOMO orbitals. As shown
in Fig. 7, upon F- interaction, p-electrons of the HOMO orbitals
of 1 are extended to the indole moieties (see pink circle) due to
the negative charge transfer.13 As summarized in Fig. 8, upon
F- interaction, the HOMO energy level increases significantly
The 1–2F- complex formation generates a dipolar situation,
with a partial negative charge on the indole nitrogen and a partial
2074 | Org. Biomol. Chem., 2009, 7, 2072–2076
This journal is
The Royal Society of Chemistry 2009
©

View Article Online
DMSO-d6, TMS): d (ppm) = 7.14–7.24 (m, 4H, ArH), 7.45–7.48
(d, 2H, ArH), 7.89–7.90 (d, 2H, ArH), 8.32–8.35 (d, 2H, ArH),
8.89 (s, 2H, -CH=N-), 11.64 (s, 2H, -NH-). 13C NMR (68 MHz,
DMSO-d6, TMS): d (ppm) = 111.6, 111.9, 120.2, 121.8, 122.3,
124.5, 131.4, 136.9, 154.6. EI-MS: Calcd for C18H14N4: 286.1,
found: m/z 286.2 (M). Elemental Anal.: Calcd: C, 75.50; H, 4.93;
N, 19.57. Found: C, 75.28; H, 4.58; N, 19.46.
Computational details
Preliminary geometry optimizations were performed using the
WinMOPAC version 3.0 software (Fujitsu Inc.) at the semiem-
pirical PM3 level,17 where the optimization of 1–F- and 1–2F-
complexes was done using a bound structure, in which F atoms are
directly bound to the NH protons. The obtained structures were
fully refined in the gas-phase with tight convergence criteria at the
DFT level with the Gaussian 03 package,18 using the B3LYP/6-
31G* basis set for all atoms. The excitation energies and the
oscillator strengths of the compounds were calculated with the
TD-DFT calculation.
Fig. 8 Energy diagrams of HOMO and LUMO orbitals of 1 and 1–2F-
complex calculated on the DFT level using a B3LYP/6-31G* basis set.
(D1.08 eV), although the increase in LUMO energy level is not
so large (D0.76 eV). As a result of this, the HOMO-LUMO
gap decreases (3.67 → 3.35 eV). This may therefore lead to
red shift of the absorption spectrum (Fig. 3). The above DFT
calculation results fully support the change in absorption spectra
upon association of the indolic NH protons of 1 with two F-.14
Several colorimetric and fluorometric cation probes with aza-
diene moiety have been proposed,15 where the azadiene moiety
behaves as a cation binding site. In the present case, p-electrons
on HOMO and LUMO orbitals of 1 are localized on the azadiene
moiety and the electron density on the indole moieties is poor.
However, upon interaction with F-, p-electrons are extended to
the indole moieties, leading to dynamic changes in absorption and
fluorescence spectra. This suggests that the azadiene moiety of
1 acts as a “controller” that tunes p-electron population on the
indole moieties upon interaction with F-.
Acknowledgements
This work was partly supported by the Grant-in-Aid for Scientific
Research (No. 19760536) from the Ministry of Education, Culture,
Sports, Science and Technology, Japan (MEXT).
Notes and references
1 (a) For reviews: R. Mart´ınez-Maneˆz and F. Sanceno´n, Coord. Chem.
Rev., 2006, 250, 3081; (b) R. Mart´ınez-Maneˆz and F. Sanceno´n,
J. Fluoresc., 2005, 15, 267; (c) C. Suksai and T. Tuntulani, Chem. Soc.
Rev., 2003, 32, 192; (d) R. Mart´ınez-Maneˆz and F. Sanceno´n, Chem.
Rev., 2003, 103, 4419; (e) C. R. Bondy and S. J. Loeb, Coord. Chem. Rev.,
2003, 240, 77; (f) P. A. Gale, Ed. Special issue: 35 Years of Synthetic
Anion Receptor Chemistry. Coord. Chem. Rev., 2003, 240, 191; (g) P. D.
Beer and P. A. Gale, P. A., Angew. Chem. Int. Ed., 2001, 40, 486; (h) F. P.
Schmidtchen and M. Berger, Chem. Rev., 1997, 97, 1609.
2 (a) K. L. Kirk, Biochemistry of the Halogens and Inorganic Halides,
Plenum Pless, New York, 1991, p 58; (b) P. E. Rakita, J. Chem. Educ.,
2004, 81, 677.
3 (a) M. Kleerekoper, Endocdinol. Metab. Clin. North Am., 1998, 27, 441;
(b) D. Briancon, Rev. Rhum., 1997, 64, 78; (c) E. Kissa, Clin. Chem.,
1987, 33, 253.
4 (a) For example: X. He, S. Hu, K. Liu, Y. Guo, J. Xu and S. Shao, Org.
Lett., 2006, 8, 333; (b) E. J. Cho, B. J. Ryu, Y. J. Lee and K. C. Nam,
Org. Lett., 2005, 7, 2607; (c) D. Esteban-Go´mez, L. Fabbrizzi and M.
Licchelli, J. Org. Chem., 2005, 70, 5717; (d) M. Va´zquez, L. Fabbrizzi,
A. Taglietti, R. M. Pedrido, A. M. Gonza´lez-Noya and M. R. Bermejo,
Angew. Chem. Int. Ed., 2004, 43, 1962; (e) D. A. Jose, D. K. Kumar, B.
Ganguly and A. Das, Org. Lett., 2004, 6, 3445; (f) J. Y. Lee, E. J. Cho,
S. Mukamel and K. C. Nam, J. Org. Chem., 2004, 69, 943; (g) M. H.
Lee and F. P. Gabba¨ı, Inorg. Chem., 2007, 46, 8132.
5 (a) For example: K. M. K. Swamy, Y. J. Lee, H. N. Lee, J. Chun, Y.
Kim, S.-J. Kim and J. Yoon, J. Org. Chem., 2006, 71, 8626; (b) X. Y. Liu,
D. R. Bai and S. Wang, Angew. Chem. Int. Ed., 2006, 45, 5475; (c) J.-S.
Wu, J.-H. Zhou, P.-F. Wang, X.-H. Zhang and S.-K. Wu, Org. Lett.,
2005, 7, 2133; (d) G. Xu and M. A. Tarr, Chem. Commun., 2004, 1050;
(e) E. J. Cho, J. W. Moon, S. W. Ko, J. Y. Lee, S. K. Kim, J. Yoon and
K. C. Nam, J. Am. Chem. Soc., 2003, 125, 12376; (f) X. Jiang, M. C.
Vieweger, J. C. Bollinger, B. Dragnea and D. Lee, Org. Lett., 2007, 9,
3579.
Conclusions
We found that an indole-azadiene conjugate, 1, synthesized by
one-step facile condensation, behaves as a highly sensitive F-
probe in both colorimetric and fluorometric analyses. The changes
in absorption and fluorescence spectra are simply driven by
interaction between indolic NH protons and F-. The simple probe
design presented here may contribute to the development of more
efficient and more useful dual mode anion probes.
Experimental
All of the reagents used were of the highest commercial quality
and used without further purification. Fluorescence spectra were
measured on a JASCO FP-6500 fluorescence spectrophotometer
(lex = 420 nm).16 Absorption spectra were measured on an UV-
vis photodiode-array spectrophotometer (Shimadzu; Multispec-
1500). All of the spectroscopic measurements were carried out at
298 0.1 K under dry N2. 1H and 13C NMR spectra were recorded
by a JEOL JNM-GSX270 Excalibur. EI-MS chart was obtained
by a JEOL JMS 700 mass spectrometer.
Synthesis of probe 1
Indole-3-carbaldehyde (0.20 g, 1.35 mmol) and hydrazine mono-
hydrate (0.03 g, 0.67 mmol) were dissolved in ethanol (15 mL)
and stirred at room temperature for 36 h under dry N2. The
precipitate formed was recovered by filtration, washed thoroughly
with ethanol, and dried in vacuo, affording 1 as a yellow-white
6 (a) R. M. F. Batista, E. Oliveira, S. P. G. Costa, C. Loderio and M. M. M.
Raposo, Org. Lett., 2007, 9, 3201; (b) C.-I. Lin, S. Selvi, J.-M. Fang,
P.-T. Chou, C.-H. Lai and Y.-M. Cheng, J. Org. Chem., 2007, 72, 3537;
(c) V. Luxami and S. Kumar, Tetrahedron Lett., 2007, 48, 3083; (d) Z.
Lin, S. Ou, C. Duan, B. Zhang and Z. Bai, Chem. Commun., 2006, 624;
(e) Y. Zhao, Z. Lin, S. Ou, C. Duan, H. Liao and Z. Bai, Inorg. Chem.
1
powder (0.153 g, 0.53 mol, yield 79.6%). H NMR (270 MHz,
This journal is
The Royal Society of Chemistry 2009
Org. Biomol. Chem., 2009, 7, 2072–2076 | 2075
©

View Article Online
Commun., 2006, 9, 802; (f) S. K. Kim, J. H. Bok, R. A. Bartsch, J. Y. Lee
and J. S. Kim, Org. Lett., 2005, 7, 4839; (g) Z.-Q. Liu, M. Shi, F.-Y. Li,
Q. Fang, Z.-H. Chen, T. Yi and C.-H. Huang, Org. Lett., 2005, 7, 5481;
(h) Y. Kubo, M. Yamamoto, M. Ikeda, M. Takeuchi, S. Shinkai, S.
Yamaguchi and K. Tamao, Angew. Chem. Int. Ed., 2003, 42, 2036; (i) S.
Yamaguchi, S. Akiyama and K. Tamao, J. Am. Chem. Soc., 2000, 122,
6793; (j) T. W. Hudnall and F. P. Gabba¨ı, J. Am. Chem. Soc., 2007, 129,
11978; (k) M. H. Lee, T. Agou, J. Kobayashi, T. Kawashima and F. P.
Gabba¨ı, Chem. Commun., 2007, 1133; (l) T. H. Kim, M. S. Choi, B.-H.
Sohn, S.-Y. Park, W. S. Lyoo and T. S. Lee, Chem. Commun., 2008,
2364; (m) W. Tan, D. Zhang, Z. Wang, C. Liu and D. Zhu, J. Mater.
Chem., 2007, 17, 1964; (n) M. Zhang, M. Li, F. Li, Y. Cheng, J. Zhang,
T. Yi and C. Huang, Dyes Pig., 2008, 77, 408.
14 The probe 1 has two NH protons; therefore, 1–F- 1:1 complex may
form. As shown in Table S1 (ESI†), ELUMO and EHOMO values for the
1:1 complex are determined by DFT calculation to be -0.98 eV and
-4.38 eV (D E = 3.40 eV), respectively. The D E values are similar to
that of the 1:2 complex (Fig. 8). However, the isosbestic points in the
absorption spectrum (Fig. 3) and the linear relationship in the Benesi-
Hildebrand plot (Fig. 5) indicate the formation of only 1:2 complex. As
shown in Table S1 (ESI†), heat of formation (DHf◦; 1 atm, 298.15 K)
for free 1 and 1:1 and 1:2 complexes is determined by DFT calculation
to be -4083, -5066, and -5634 kJ mol-1, respectively. This suggests that
the 1:2 complex is more stable than the 1:1 complex. This is probably
the reason for almost no formation of 1:1 complex.
15 P. Molina, A. Ta´rraga and A. Cabollero, Eur. J. Inorg. Chem., 2008,
7 N. R. El-Rayyes and A. H. Katrib, J. Chem. Eng. Data, 1983, 28, 132.
8 Fluorescent quantum yield of 1 was determined using fluorescein as a
standard (in 0.1 M aqueous NaOH solution, fF = 0.85 0.01): C. A.
Parker and W. T. Rees, Analyst, 1960, 85, 587.
3401.
16 (a) G. Nishimura, H. Maehara, Y. Shiraishi and T. Hirai, Chem. Eur. J.,
2008, 14, 259; (b) X. Zhang, Y. Shiraishi and T. Hirai, Org. Lett., 2007, 9,
5039; (c) Y. Shiraishi, R. Miyamoto, X. Zhang and T. Hirai, Org. Lett.,
2007, 9, 3921; (d) Y. Shiraishi, R. Miyamoto and T. Hirai, Langmuir,
2008, 24, 4273.
17 (a) Y. Shiraishi, N. Saito and T. Hirai, J. Am. Chem. Soc., 2005, 127,
8304; (b) Y. Shiraishi, H. Maehara, K. Ishizumi and T. Hirai, Org. Lett.,
2007, 9, 3125.
18 Gaussian 03, Revision B.03, M. J. Frisch, G. W. Trucks, H. B. Schlegel,
G. E. Scuseria, M. A. Robb, J. R. Cheeseman, J. A. Montgomery, Jr.,
T. Vreven, K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar,
J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega,
G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R.
Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao,
H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratchian, J. B. Cross,
V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann,
O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, P. Y.
Ayala, K. Morokuma, G. A. Voth, P. Salvador, J. J. Dannenberg, V. G.
Zakrzewski, S. Dapprich, A. D. Daniels, M. C. Strain, O. Farkas,
D. K. Malick, A. D. Rabuck, K. Raghavachari, J. B. Foresman,
J. V. Ortiz, Q. Cui, A. G. Baboul, S. Clifford, J. Cioslowski, B. B.
Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. L. Martin,
D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara,
M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen, M. W.
Wong, C. Gonzalez and J. A. Pople, Gaussian, Inc., Wallingford CT,
2004.
9 The detection limit of 1 for F- is determined to be 222 mM: M.
Shortreed, R. Kopelman and B. Hoyland, Anal. Chem., 1996, 68, 1414.
10 (a) H. A. Benesi and J. H. Hildebrand, J. Am. Chem. Soc., 1949, 71,
2703; (b) J. J. B. Nevado, J. A. M. Pulgarin and M. A. G. Laguna,
Talanta, 2001, 53, 951; (c) M. Maffi, J.-J. Aaron and C. Lion, J. Incl.
Phenom., 1998, 30, 227.
11 (a) F. Han, Y. Bao, Z. Yang, T. M. Fyles, J. Zhao, X. Peng, J. Fan, Y. Wu
and S. Sun, Chem. Eur. J., 2007, 13, 2880; (b) X. Peng, Y. Wu, J. Fan, M.
Tian and K. Han, J. Org. Chem., 2005, 70, 10524; (c) A. B. Descalzo, K.
Rurack, H. Weisshoff, R. Mart´ınez-Ma´nez, M. D. Marcos, P. Amoro´s,
K. Hoffmann and J. Soto, J. Am. Chem. Soc., 2005, 127, 184; (d) Y. Wu,
X. Peng, J. Fan, S. Gao, M. Tian, J. Zhao and S. Sun, J. Org. Chem.,
2007, 72, 62; (e) M. Boiocchi, L. Del Boca, D. E. Go´mez, L. Fabbrizzi,
M. Licchelli and E. Monzani, J. Am. Chem. Soc., 2004, 126, 16507.
12 (a) B. K. Kaletas¸, H. C. Joshi, G. von der Zwan, M. Fanti, F. Zerbetto,
K. Goubitz, L. De Cola, B. Ko¨nig and R. M. Williams, J. Phys. Chem.
A., 2005, 109, 9443; (b) B. K. Kaletas¸, C. Mandle, G. von der Zwan, M.
Fanti, F. Zerbetto, L. De Cola, B. Ko¨nig and R. M. Williams, J. Phys.
Chem. A., 2005, 109, 6440; (c) S. Kim, H. Moon, J. Hwang, J. Sohn, J.
Seo, S. Y. Park, T. I. Kang and B. R. Cho, Chem. Phys., 2000, 256, 289.
13 (a) H. Miyaji and J. L. Sessler, Angew. Chem. Int. Ed., 2001, 40, 154;
(b) P. Anzenbacher, Jr., M. A. Palacios, K. Jurs´ıkova´ and M. Marquez,
Org. Lett., 2005, 7, 5027.
2076 | Org. Biomol. Chem., 2009, 7, 2072–2076
This journal is
The Royal Society of Chemistry 2009
©