Anthracene-labeled 1,2,3-triazole-linked bispyridinium amide for selective sensing of H2PO4- by fluorescence and gel formation

Article abstract of DOI:10.1002/ejoc.201101240

A new receptor 1 has been designed and synthesized for the selective recognition of anions, which employs hydrogen bonding and electrostatic interactions. Receptor 1 selectively recognizes H₂PO₄ ^- to exhibit a ratiometric

Full text of DOI:10.1002/ejoc.201101240

FULL PAPER
DOI: 10.1002/ejoc.201101240
Anthracene-Labeled 1,2,3-Triazole-Linked Bispyridinium Amide for Selective
–
Sensing of H2PO4 by Fluorescence and Gel Formation
Kumaresh Ghosh,*[a] Avik Ranjan Sarkar,[a] and Asoke P. Chattopadhyay[a]
Keywords: Supramolecular chemistry / Anions / Sensors / Receptors / Gels / Fluorescence
–
A new receptor 1 has been designed and synthesized for the
selective recognition of anions, which employs hydrogen
bonding and electrostatic interactions. Receptor 1 selectively
recognizes H2PO4– to exhibit a ratiometric emission response
and formed a stable gel in CHCl3 that contained 10%
son, receptor 2 did not form a gel with H2PO4 under similar
conditions. Upon interaction with H2PO4–, the intensity of the
monomer and excimer emission peaks of 2 increased mark-
edly. Moreover, F– ions induced quenching of monomer
emission in both 1 and 2 in a nonratiometric manner, which
CH3CN, which is useful to visually sense H2PO4–. In compari- distinguished it from the other anions examined.
–
used for the detection of H2PO4 by the naked eye for the
Introduction
first time. The results were compared with those of receptor
The development of chemosensors for the selective re- 2.
cognition of anionic substrates is an emerging research area
in host–guest chemistry.[1] As analytes, anions are of great
interest in host–guest chemistry due to their biological and
environmental significance.[2] Therefore, their effective re-
cognition by a simple receptor that can show photophysical
change as well as gel formation is of utmost interest. As a
typical soft material, gels have been of particular interest in
colloid chemistry and materials science due to their intri-
guing properties between a solid and liquid.[3] In particular,
low molecular-weight supramolecular gels have received
considerable attention due to their wide range of potential
applications as soft materials in drug delivery, tissue engi-
In recent decades, the design of receptors for anions of
neering, and chemical sensing.[4] Weak noncovalent forces,
different shapes generally consists of urea/thiourea,[8] imid-
such as hydrogen bonding, electrostatic, π-stacking, and
hydrophobic interactions, are responsible for the formation
azolium cations,[9] guanidinium ions,[10] etc, as hydrogen-
bonding synthons attached to fluorophores. In this context,
of supramolecular gels. The gelation of low molecular-
pyridinium amide is a useful anion binder, which provides
weight organic species in the presence of anions is less ex-
a polar C–H bond as a hydrogen-bond donor to the
plored. Anions usually disrupt supramolecular gels, al-
anion,[11] and the complex is stabilized by charge–charge
though there are a few examples where the presence of
interactions. The successful use of this motif in anion bind-
anions stimulates gel formation and allows their detection
ing[7b,7c,12a] inspired us to design a new receptor 1, in which
the pyridinium groups are linked to anthracene-labeled tri-
by the naked eye.[5]
As part of our work on cation[6] and anion[7] recognition,
azole moieties.
we report the design and synthesis of a simple molecular
–
architecture 1, which recognizes H2PO4 fluorometrically
and forms a stable gel in CHCl3 that contains 10% CH3CN
in the presence of H2PO4 . The formation of a gel can be
Results and Discussion
–
Chemosensor 1 was synthesized according to Scheme 1.
The symmetrical bispyridine amide 5, obtained from the
coupling of 3-aminopyridine with 5-(octyloxy)isophthaloyl
[a] Department of Chemistry, University of Kalyani,
dichloride, was treated with 1-[(anthracen-9-yl)methyl]-4-
(chloromethyl)-1H-1,2,3-triazole (4),[12b] which was ob-
tained from 9-(azidomethyl)anthracene by click chemistry,
in dry CH3CN and heated to reflux for 5 d to afford the
Kalyani, Nadia 741235, India
Fax: +91-33-25828282
E-mail: ghosh_k2003@yahoo.co.in
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201101240.
Eur. J. Org. Chem. 2012, 1311–1317
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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K. Ghosh, A. R. Sarkar, A. P. Chattopadhyay
FULL PAPER
dichloride salt 6. The anion exchange of 6 with NH4PF6 sion is attributed to the activation of thermodynamically
gave 1 in 89% yield as a light yellow solid. Receptor 2 was favorable PET processes, which occur between the binding
synthesized by the reaction of 5 with 9-(chloromethyl)an- site and the excited state of anthracene.[1b] Figure 4 shows
thracene followed by anion exchange with NH4PF6. Com- the Stern–Volmer plot, which demonstrates that F– is the
pounds 1 and 2 were fully characterized by 1H and 13C best quencher of the anions studied. The slight deviation
–
NMR spectroscopy and mass spectrometry.
from linearity of the curves for F– and H2PO4 illustrates
that the quenching is a mixture of both static and dynamic
quenching. To gain further insight, time-resolved lumines-
–
cence decays of 1 alone and in the presence of H2PO4 and
F– were recorded. Receptor 1 (c = 4.02ϫ10–5 m) showed a
biexponential decay with lifetimes of 0.12 (28.3%) and
–
5.30 ns (71.7%). Upon titration with both H2PO4 and F–,
the short decay time and long lifetime underwent minor
changes. The Stern–Volmer plots of the lifetimes from the
time-resolved measurement are nonlinear (Supporting In-
–
formation). This indicates that H2PO4 binding-induced
quenching is not purely static in nature but is complex with
both static and dynamic components.[13] A similar finding
was observed with F– (see Supporting Information).
Scheme 1. Syntheses of 1 and 2.
The anion binding ability of 1 was evaluated by 1H
NMR, fluorescence, and UV/Vis spectroscopy. Figure 1 (a)
shows the fluorescence change of 1 (c = 4.02ϫ10–5 m, λex
=
365 nm) in CH3CN upon addition of 10 equiv. of different
anions as their Bu4N salts. Figure 1 (a) shows a new peak
at 507 nm, assigned to excimer emission, which is observed
–
only in the presence of H2PO4 followed by the quenching
of monomer emission. Figure 1 (b) shows the change in
–
emission upon titration with H2PO4 ions. The ratiometric
change in the emission spectra produced an isosbestic point
at 452 nm, which corresponds to the formation of new spe-
cies that may remain in equilibrium with the free receptor
in solution. It is presumed that both the pyridinium and
triazole motifs of 1 participate in the complexation of
–
H2PO4 , which pulls the appended anthracene units close
together to form the excimer. This peak intensified as the
titration progressed. Among the other anions, only F–,
which is more basic and electron rich, perturbed the emis-
sion significantly. However, no emission peak at higher
wavelengths due to excimer formation was observed. Fig-
Figure 1. (a) Emission changes of 1 (c = 4.02ϫ10–5 m) upon ad-
dition of various anions (10 equiv.) in CH3CN (λex = 370 nm); (b)
fluorescence titration spectra of 1 (c = 4.02ϫ10–5 m) with H2PO4
–
in CH3CN (λex = 370 nm); inset: change in emission intensity at
ure 2, displays the emission spectra with F–. The emission 412 and 507 nm with the guest concentration in CH3CN.
of 1 with time was stable (Supporting Information), and the
effect of molecular oxygen on the emission of 1 was negligi-
Job plot[14] analysis of the fluorescence titration spectra
–
ble (Supporting Information). Like the emission, the exci- exhibited a maximum at a 0.66 mol fraction of H2PO4 ,
–
tation titration spectra for 1 with H2PO4 and F– show sig- which indicates the formation of a 2:1 guest/host complex
–
nificant change in intensity; they are similar to the nature between H2PO4 and 1 (Supporting Information).[11c] This
of absorption spectrum of 1 (Figure 3), which suggests non- was also true for F–. On the basis of 2:1 stoichiometry in
covalent interactions instead of chemical changes or reac- the excited state, the association constants[15] of 1 for
tions in the excited state. The quenching of monomer emis- H2PO4– and F– were calculated using fluorescence data and
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Eur. J. Org. Chem. 2012, 1311–1317

Anthracene-Labeled 1,2,3-Triazole-Linked Bispyridinium Amide
Figure 2. Fluorescent titration of 1 (c = 4.02ϫ10–5 m) with F– in
CH3CN (λex = 370 nm).
Figure 4. Stern–Volmer plot at 412 nm for 1 (c = 4.02ϫ10–5 m)
with different anions in CH3CN.
–
also had 2:1 guest/host stoichiometries with both H2PO4
and F– in the excited state. The association constants[15]
were appreciable: K1
=
2.09Ϯ0.16ϫ104 m–1, K2
=
=
–
1.40Ϯ0.12ϫ104 m–1 for
H2PO4
and
K1
1.84Ϯ0.40ϫ104 m–1, K2 = 5.19Ϯ0.16ϫ103 m–1 for F–, but
smaller in magnitude than those of 1 (Supporting Infor-
–
3–
mation). Like H2PO4 , HP2O7 perturbed the emission of
2 moderately, and showed an excimer with significant inten-
sity (Figure 5).
Figure 3. Change in excitation spectra of 1 (c = 4.02ϫ10–5 m) with
gradual addition of (a) Bu4NH2PO4 (c = 8.04ϫ10–4 m) and (b)
Bu4NF (c = 8.04ϫ10–4 m) up to 10 equiv. [λeem = 412 nm, slit =
10:5].
the values are K1
=
2.45Ϯ0.1ϫ104 m–1, K2
=
=
2.21Ϯ0.1ϫ104 m–1 and K1 = 1.06Ϯ0.08ϫ104 m–1, K2
8.21Ϯ0.8ϫ103 m–1 for H2PO4– and F–, respectively. Due to
the small change in emission for the other anions, we were
unable to determine their association constants.
–
Thus, H2PO4 binding induced a ratiometric change in
emission of 1, and F– induced a greater quenching of mono-
mer emission in a nonratiometric manner, which distin-
guished these two anions from the others examined. On the
contrary, such a ratiometric change in emission was not ob-
Figure 5. Change in emission spectra of 2 (c = 4.02ϫ10–5 m) with
–
3–
Bu4N salts of (a) H2PO4 and (b) HP2O7 in CH3CN (λex
=
370 nm).
served with 2, which is similar to 1 but without triazole
The stoichiometry of the complex of 2 with HP2O73– was
–
rings at the lower rim. Upon interaction with H2PO4 , al- determined to be 1:1 guest/host (Figure S4, c and d, Sup-
though the intensity of the monomer and excimer emission porting Information). However, we were unable to deter-
peaks of 2 increased markedly, they were quenched upon mine the association constant for this species due to poor
addition of F– (see Supporting Information). Receptor 2 fitting of the emission data in both linear and nonlinear
Eur. J. Org. Chem. 2012, 1311–1317
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K. Ghosh, A. R. Sarkar, A. P. Chattopadhyay
FULL PAPER
equations. The emission of 2 was observed to be stable with bond lengths are shorter than the distances in the AM1
time like that of 1 (Supporting Information). Compound geometries (Supporting Information). Importantly, the
–
2 behaved exactly as our previously reported receptor.[16] binding of two H2PO4 ions as a dimer in a single receptor
Triazole-based 1 is a new example of a ratiometric chemo- structure is known in the literature.[19] However, the com-
–
–
sensor for H2PO4 . A literature survey indicated that ra- plexation of one H2PO4 ion could not orient the anthra-
tiometric chemosensors for H2PO4– are rare.[17] Ratiometric cene units in an organized manner to make an effective exci-
chemosensors offer advantages over the conventional moni- mer (Supporting Information). The experimental findings
toring of fluorescence intensity at a single wavelength. A in Figure 1 (b) support this. The addition of 1 equiv. of
–
dual emission system can minimize measurement errors be- H2PO4 to the solution of 1 formed a weak excimer, which
–
cause of factors such as phototransformation, receptor con- became intense and prominent when 2 equiv. of H2PO4
centrations, and environmental effects.[18]
were added. We also calculated various global param-
To check the sensing ability of 1 towards anions in aque- eters,[20] such as electronegativity (χ), hardness (η), and elec-
ous CH3CN (CH3CN/H2O = 4:1 v/v), emission titrations trophilicity (ω), for the receptor and its complexes with one
–
were carried out with all the anions studied along with salts and two H2PO4 ions (Supporting Information). Among
such as NaH2PO4 and NH4H2PO4. Interestingly, no mea- these parameters, the change in global electrophilicity is
surable selectivity was observed, which indicated its inef- more marked; it is 0.6848 for 1 alone, 0.2796 for a 1:1 com-
–
ficiency in an aqueous system (Supporting Information).
plex, and 0.1171 for a 1:2 host/guest complex with H2PO4
To obtain an insight into the ground state interaction, ions in the gas phase. Clearly, the greater electrophilic char-
we recorded the UV/Vis spectra of 1 in CH3CN in the pres- acter of 1 enables it to undergo successive complexation
–
–
ence of the same anions. Among the anions, only H2PO4
with H2PO4 ions, which involves a complex hydrogen-
and F– brought about meaningful change in the UV/Vis bonded network. This network possibly induced the gela-
spectrum of 1 (Supporting Information). However, the tion in CHCl3 that contained 10% CH3CN that was ob-
greater change in the absorbance of 1 at 330 nm in the pres- served while studying the interaction of
1
(c =
ence of a high concentration of F– was attributed to F–- 4.62ϫ10–3 m) with Bu4NH2PO4 in ca. 10–3 m concentration
induced deprotonation. This was confirmed by the observa- range (Table 1). No gel formation was observed for 1 alone
tion of a similar change in absorbance when Bu4NOH was (Figure 9).
added to a solution of 1 in CH3CN (Figure 6).
Figure 7. UV job plots of 1 with H2PO4 and F–, where [G] = [H]
–
= 3.54ϫ10–5 m at 365 nm in CH3CN.
Figure 6. Effect of addition of Bu4NOH and Bu4NF on the UV/
At 86 °C, the gel underwent a gel-to-sol phase transition.
On cooling the sol below 86 °C, gel formation occurred
Vis spectrum of 1.
A Job plot indicated their 1:1 stoichiometric interactions again. However, under similar conditions no such anion
(Figure 7), which is different from the stoichiometry in the binding-induced gel formation took place in the presence
excited state. We presume that it is due to the more polar of the other anions. On the contrary, 2, which has no tri-
character of 1 in the excited sate, in which both the pyrid- azole rings, did not produce a gel in presence of anions
inium and triazole rings collaborate to bind two anions at under similar conditions, which underlined the key role of
a time. Accordingly, we presume a binding structure that the triazole rings in 1 to selectively sense H2PO4– fluoromet-
was optimized by the AM1 method in the gas phase and in rically and visually. Receptor 1, in the concentration range
–
CH3CN solvent (Figure 8). It appears from Figure 8 that of ca. 10–5 m, is highly selective to H2PO4 , which was estab-
–
the complexation of two H2PO4 ions by the cavity brings lished by its characteristic ratiometric change in emission
the two pendant anthracene units close together. In conse- upon complexation and gel formation in the concentration
–
quence, the possibility of the formation of an excimer be- range ca. 10–3 m. H2PO4 -selective gel formation by 1 could
tween the anthracenes is anticipated. This binding structure be employed as an alternative means to visually sense
–
was further optimized by the PM6 method in the gas phase H2PO4 . The gel was characterized by scanning electron mi-
and CH3CN solvent. However, the PM6 structures look croscopy (Figure S9) and displayed a network of spherical
very similar to the AM1 structures except the hydrogen- aggregates. Some fibrous portions are adhered with spheres
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Anthracene-Labeled 1,2,3-Triazole-Linked Bispyridinium Amide
(Ho), and olefinic hydrogen atoms (Hf) of the triazole ring
in 1 shifted downfield and became broad upon addition of
–
2 equiv. of H2PO4 (Figure 10). This indicated the involve-
ment of both the pyridinium amide and triazole rings of 1
–
in the hydrogen bonding with H2PO4 . However, when the
guest/host ratio was changed from 1 to 2, there was no obvi-
ous change in chemical shift of the interacting protons ex-
cept the amide –NH. In comparison, the addition of an
equivalent amount of F– to 1 caused deprotonation of Ho
(Supporting Information). The signal for the amide protons
became too broad to detect accurately, and Ho of the tri-
azole ring moved downfield.
–
Figure 8. AM1-optimized geometry of 1·2H2PO4 and the hydro-
gen bond lengths.
Table 1. Gelatination study of 1 with Bu4NH2PO4 in various sol-
vents at 25 °C.[a]
Solvent
mgc
[mg/mL]
Gel status
CH3CN
6.1
6.1
6.1
6.1
not formed (ppt)
gel formed (transparent)
not formed (s)
1
Figure 10. H NMR titration of (a) 1 (c = 4.73ϫ10–3 m) itself, (b)
10% CH3CN in CHCl3
10% DMSO in CH3CN
Dimethyl sulfoxide (DMSO)
with 1 equiv. Bu4NH2PO4 (c = 2.32ϫ10–2 m) and (c) with 2 equiv.
Bu4NH2PO4 (c = 2.32ϫ10–2 m) in CDCl3 that contained 10%
CD3CN at 25 °C.
not formed (s)
[a] mgc = minimum gelation concentration, s = soluble, ppt = pre-
cipitate.
Conclusions
We have synthesized a simple chemosensor 1 based on
a pyridinium–triazole conjugate that selectively recognized
–
H2PO4 by exhibiting a ratiometric response in emission
and formed a stable gel in CHCl3 that contained 10%
–
CH3CN, which is useful in to visually sense H2PO4 . Scru-
–
tiny of the literature revealed that H2PO4 -selective gel for-
mation by an abiotic receptor is as yet unknown. Chemo-
sensor 1 is a new addition to the existing sensors[21] of
H2PO4 .
–
Figure 9. Photographs showing the phase changes for the gel of 1
–
with H2PO4 in CHCl3 that contained 10% CH3CN: (a) 1
–
(4.62ϫ10–3 m), (b) 1 with H2PO4 .
Experimental Section
in some regions. The AFM image of the gel additionally
demonstrated the surface morphology (Figure S8).
General: Materials were obtained from commercial suppliers and
were used without further purification. TLC was carried out using
Merck 60 F254 plates with a thickness of 0.25 mm. Melting points
were determined with a hot-plate melting point apparatus in an
To learn more about the binding of H2PO4– in the cavity
of 1, we recorded the 1H NMR spectrum of 1 in dry CDCl3
that contained 10% CD3CN. On gradual addition of
Bu4NH2PO4, the solution of 1 became viscous and finally
a thick gel formed when the guest/host ratio reached 2. Sig-
1
open-mouthed capillary. H and 13C NMR spectra were recorded
with a Bruker 400 MHz instrument. For NMR spectra, CDCl3,
CD3CN, and [D6]DMSO were used as solvents with TMS as an
nals for amide –NH, pyridinium ortho hydrogen atoms internal standard. IR spectra were recorded with a Perkin–Elmer
Eur. J. Org. Chem. 2012, 1311–1317
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K. Ghosh, A. R. Sarkar, A. P. Chattopadhyay
FULL PAPER
Spectrum One using KBr discs. Fluorescence spectra were recorded
with a Perkin–Elmer Model LS 55 spectrophotometer, and UV/Vis
spectra were recorded with a Perkin–Elmer Model Lambda 25.
was dissolved in hot CH3OH (5 mL) and the volume was reduced
to 2 mL. An aqueous solution of NH4PF6 (0.055 g, 0.333 mmol)
was added to exchange the Cl– ions. After stirring the reaction mix-
ture for 35 min, a precipitate appeared. The precipitate was col-
lected by filtration and washed with diethyl ether to afford 2
5-(Octyloxy)-N1,N3-di(pyridin-3-yl)isophthalamide (5): Compound
5 was obtained by coupling 3-aminopyridine (0.59 g, 6.34 mmol)
with 5-(octyloxy)isophthaloyl dichloride (0.7 g, 2.11 mmol) in dry
CH2Cl2 (60 mL) followed by the addition of triethylamine (1 mL)
under a nitrogen atmosphere. The reaction mixture was stirred
overnight. After completion of the reaction, the solvent was re-
moved under vacuum. The residue was extracted into CHCl3/
CH3OH (3ϫ30 mL). The organic layer was washed with NaHCO3
solution (3ϫ15 mL), dried with anhydrous Na2SO4, and filtered.
The filtrate was concentrated under reduced pressure. The crude
product was purified by column chromatography over silica gel
using ethyl acetate/hexane (3:2 v/v) as eluent to afford 5 (0.820 mg,
1
(0.95 g, 77%); m.p. 182–185 °C. H NMR (400 MHz, CDCl3 with
a few drops of [D6]DMSO): δ = 11.26 (s, 2 H, amide NH), 9.78 (s,
2 H), 9.06 (d, J = 8 Hz, 2 H), 8.71 (s, 2 H), 8.33 (s, 1 H), 8.26 (d,
J = 8 Hz, 2 H), 8.18 (d, J = 8 Hz, 4 H), 8.12 (d, J = 8 Hz, 2 H),
7.81–7.77 (m, 2 H), 7.68 (t, J = 8 Hz, 4 H), 7.58–7.54 (m, 6 H),
6.80 (s, 4 H), 3.99 (t, J = 8 Hz, 2 H), 1.78–1.75 (m, 2 H), 1.44–1.29
(m, 10 H), 0.91 (t, J = 6.40 Hz, 3 H) ppm. 13C NMR (100 MHz,
CDCl3 with a few drops of [D6]DMSO): δ = 165.5, 159.3, 140.6,
137.8, 135.1, 134.5, 134.1, 131.7, 131.4, 131.1, 129.7, 128.7, 128.0,
125.7, 122.1, 119.8, 119.0, 118.2, 68.51, 57.3, 31.6, 29.1, 29.0, 28.8,
25.7, 22.4, 14.0 ppm. FTIR (KBr): ν = 3392, 3091, 2926, 2855,
˜
1
86%); m.p. 90–92 °C. H NMR (400 MHz, [D6]DMSO): δ = 9.85
1684, 1626, 1591, 1553, 1501 cm–1. MS: m/z = 637.4 [M –
2PF6 –1]+. C56H52F12N4O3P2 (1118.98): calcd. C 60.11, H 4.68, N
5.01; found C 60.18, H 4.76, N 5.08.
(s, 2 H, amide NH), 8.90 (d, J = 4 Hz, 2 H), 8.37–8.34 (m, 4 H),
8.18 (s, 1 H), 7.73 (s, 2 H), 7.32 (t, J = 8 Hz, 2 H), 4.09 (t, J =
8 Hz, 2 H), 1.86–1.79 (m, 2 H), 1.49–1.44 (m, 2 H), 1.35–1.25 (m,
8 H), 0.91 (t, J = 8 Hz, 2 H) ppm. 13C NMR (100 MHz, [D6]-
DMSO): δ = 165.0, 158.7, 144.8, 142.1, 135.9, 135.6, 127.4, 123.5,
119.4, 116.8, 68.2, 31.2, 28.7, 28.7, 28.6, 25.5, 22.1, 13.9 ppm. FTIR
General Procedure for Fluorescence and UV/Vis Titrations: A stock
solution of the receptor was prepared in CH3CN in the concentra-
tion range ca. 10–5 m. A 2.5 mL portion of the receptor solution
was taken in a cuvette. Stock solutions of guests in the concentra-
tion range ca. 10–4 m, were prepared in the same solvent and were
added in different amounts to the receptor solution. For fluores-
cence, the solution was irradiated at 370 nm maintaining the exci-
tation and emission slits 12 and 10, respectively. Upon addition of
guests, the change in emission of the receptor was noted. The same
stock solutions for receptor and guests were used to perform the
UV/Vis titration experiment. Guest solution was successively added
in different amounts to the receptor solution (2.5 mL) in a cuvette,
and the absorption spectra were recorded. Both fluorescence and
UV/Vis titration experiments were carried out at 25 °C. All the ex-
periments were repeated three times to check the reproducibility.
(KBr): ν = 3349, 2914, 2850, 1668, 1596 cm–1. MS: m/z = 447.2 [M
˜
+ 1]+, 240.2, 224.2.
Receptor 1: To a solution of 5 (0.100 g, 0.224 mmol) in CH3CN
(15 mL) and dry N,N-dimethylformamide (DMF, 2 mL) was added
1-[(anthracen-9-yl)methyl]-4-(chloromethyl)-1H-1,2,3-triazole[12b] (4,
0.208 g, 0.674 mmol) in CH3CN (20 mL). The reaction mixture was
heated to reflux with stirring for 5 d under a nitrogen atmosphere.
On cooling the reaction mixture, a precipitate appeared. The pre-
cipitate was collected by filtration and washed with CH3CN several
times and then with diethyl ether to give pure dichloride salt 6
(0.137 g, 62%). Dichloride 6 (0.130 g, 0.131 mmol) was dissolved
in hot CH3OH (5 mL) and dry DMF (1 mL) and the volume was
reduced to 2 mL. An aqueous solution of NH4PF6 (0.064 g,
0.393 mmol) was added for the anion exchange reaction. After stir-
ring the reaction mixture for 35 min, a precipitate appeared. The
precipitate was collected by filtration and washed with diethyl ether
to afford 1 (0.149 g, 89%); m.p. 82–84 °C. 1H NMR (400 MHz,
CDCl3 and a few drops of [D6]DMSO): δ = 11.17 (s, 2 H, amide
NH), 9.72 (s, 2 H), 8.90 (d, J = 8 Hz, 2 H), 8.62 (d, J = 8 Hz, 2
H), 8.57 (s, 2 H), 8.38 (d, J = 8 Hz, 4 H), 8.19 (s, 1 H), 8.08 (d, J
= 8 Hz, 4 H), 7.89 (s, 2 H), 7.85 (t, J = 8 Hz, 2 H), 7.69 (s, 2 H),
7.63 (t, J = 8 Hz, 4 H), 7.53 (t, J = 8 Hz, 4 H) 6.57 (s, 4 H), 5.74
(s, 4 H), 4.09 (t, J = 8 Hz, 2 H), 1.86–1.82 (m, 2 H), 1.50–1.24 (m,
2 H), 1.36–1.31 (m, 8 H), 0.90 (t, J = 6.4 Hz, 3 H) ppm. 13C NMR
(100 MHz, CDCl3 with a few drops of [D6]DMSO): δ = 165.4,
162.5, 159.6, 140.2, 139.1, 138.5, 135.2, 134.1, 131.2, 130.5, 129.8,
129.3, 127.9, 127.6, 125.3, 125.1, 123.6, 122.9, 119.0, 118.0, 55.9,
46.5, 36.4, 31.7, 29.2, 29.1, 29.0, 25.9, 22.5, 14.0 ppm. FTIR (KBr):
Method for Job Plots: The stoichiometry was determined by the
continuous variation method (Job Plot). Solutions of host and
guest of equal concentration were prepared in the solvents used in
the experiment. Then host and guest solutions were mixed in dif-
ferent proportions to maintain a total volume of 3 mL of the mix-
ture. All the prepared solutions were kept for 1 h with occasional
shaking at room temperature. Then emission and absorbance of
the solutions of different compositions were recorded. The concen-
tration of the complex, i.e. [HG] (H = host, G = guest), was calcu-
lated using the equation [HG] = ΔI/I0 ϫ[H] or [HG] = ΔA/A0 ϫ[H],
where ΔI/I0 and ΔA/A0 indicate the relative emission and ab-
sorbance intensities, respectively. The mol fraction of the host (XH)
was plotted against concentration of the complex [HG]. In the plot,
the mol fraction of the host at which [HG] is maximum gives the
stoichiometry of the complex.
Determination of Binding Constants: Binding constants were deter-
mined by fluorescence and UV/Vis spectroscopy. The change of
ν = 3392, 3093, 2927, 2855, 1685, 1661, 1593, 1549, 1506 cm–1. MS
˜
– +
– +
(EI): m/z = 1136.4 [M + H – PF6 ] , 990.4 [M – 2PF6 ] , 719.2. fluorescence intensity as a function of guest concentration gave
C62H58F12N10O3P2 (1281.13): calcd. C 58.13, H 4.56, N 10.93;
found C 58.01, H 4.49, N 10.84.
binding constants for 1 and 2 with the guests according to Equa-
tion (1).[15]
2
Receptor 2: To a solution of 5 (0.09 g, 0.202 mmol) in CH3CN
(15 mL) and dry DMF (2 mL) was added 9-chloromethylanthra-
cene (0.137 g, 0.605 mmol) in CH3CN (20 mL). The resulting solu-
tion was heated to reflux with stirring for 2 d under a nitrogen
atmosphere. On cooling the reaction mixture, a precipitate ap-
peared. The precipitate was collected by filtration and washed with
CH3CN several times and then with diethyl ether to give pure di-
chloride salt 7 (0.125 g, 69%). Dichloride 7 (0.100 g, 0.111 mmol)
I = (I0 + K1·CG·I[1:1] + K1·K2·Ilim·CG2)/(1 + K1·CG + K1·K2·CG
)
(1)
I represents the fluorescence intensity, I0 represents the intensity of
pure host, and I[1:1] represents intensity at [G]/[H] = 1:1. CG is the
corresponding concentration of the guest and K is the association
constant. The association constant and correlation coefficients (R)
were obtained by a nonlinear least-square analysis of I vs. CG.
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Eur. J. Org. Chem. 2012, 1311–1317

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Received: August 24, 2011
Published Online: January 16, 2012
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Eur. J. Org. Chem. 2012, 1311–1317
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www.eurjoc.org
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