Synthesis and binding properties of calix[4]biscrown-based fluorescent molecular sensors for caesium or potassium ions

Article abstract of DOI:10.1039/b203633a

The synthesis of two new fluorescent molecular sensors based on calix[4]biscrowns is reported. A dioxycoumarin fluorophore was incorporated into one of the crowns or into both crowns, leading to Calix-COU1 and Calix-COU2, respectively. The stability const

Full text of DOI:10.1039/b203633a

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Synthesis and binding properties of calix[4]biscrown-based
fluorescent molecular sensors for caesium or potassium ions
Isabelle Leray,a Zouhair Asfari,b Jacques Vicensb and Bernard Valeur*a,c
2
a Laboratoire de Photophysique et Photochimie Supramoléculaires et Macromoléculaires
(CNRS UMR 8531), Département de Chimie, ENS-Cachan, 61 Av. du Président Wilson,
F-94235 Cachan cedex, France. E-mail: valeur@cnam.fr
b Laboratoire de Chimie des Interactions Moléculaires Spécifiques (CNRS UMR 7512),
ECPM, 25 Rue Becquerel, F-67087 Strasbourg Cedex 2, France
c Laboratoire de Chimie Générale, Conservatoire National des Arts et Métiers,
292 rue Saint-Martin, F-75141 Paris Cedex 3, France
Received (in Cambridge, UK) 15th April 2002, Accepted 27th May 2002
First published as an Advance Article on the web 28th June 2002
The synthesis of two new fluorescent molecular sensors based on calix[4]biscrowns is reported. A dioxycoumarin
fluorophore was incorporated into one of the crowns or into both crowns, leading to Calix-COU1 and Calix-COU2,
respectively. The stability constants of the 1 : 1 and 1 : 2 complexes with potassium and caesium ions in ethanol or
acetonitrile were measured. An anticooperative effect was observed when binding a second cation to the 1 : 1 complex
owing to electrostatic repulsion. The selectivity of Calix-COU1 in ethanol expressed as the ratio of the stability
constants of the 1 : 1 complexes was found to be about 4 × 104 for Csϩ versus Naϩ and greater than 500 for Kϩ versus
Naϩ. The origin of the cation-induced changes in the photophysical properties is discussed.
Introduction
In the design of fluorescent molecular sensors for cation
recognition,1 much attention should be paid to the selectivity
towards a given cation and against possible interfering
cations. In this regard, outstanding selectivities can be obtained
by using calixarene-based ligands,2 and several fluorescent
molecular sensors involving such ligands have been reported.3–9
The photophysical processes perturbed by the presence of a
bound cation can be photoinduced electron transfer, photo-
induced charge transfer, excimer formation or energy transfer.10
Among calixarene-based ligands, calix[4]biscrown ethers
deserve particular attention. In particular, calix[4]biscrown-6
ethers exhibit a high selectivity towards caesium ion against
sodium ion,11–13 so that their use for the removal of caesium
from nuclear waste was suggested. It is therefore of interest to
incorporate a fluorophore into one of the crowns or both
crowns in order to signal the recognition of a cation. After
the first example with naphthalene reported by two of us,11
we decided to incorporate a coumarin derivative. Larger
cation-induced photophysical changes are indeed expected;
the two other reasons are (i) the very good photochemical
stability of coumarin dyes, (ii) the commercial availability of
Fig. 1 Structure of Calix-COU1 and Calix-COU2.
dihydroxymethylcoumarin which can be easily inserted into
ethers towards potassium ion against sodium ion was in
a crown ether by the same method as that used for naphtha-
some cases almost as good as the selectivity for caesium ion.
lene.14 Independently, Brown and coworkers9 reported a
Molecular sensors of potassium are indeed of great interest in
calix[4]biscrown-6 ether in which an anthracene fluorophore is
analytical biochemistry. One of the challenges in this field is
indeed the rapid and reasonably-priced detection of this ion in
blood plasma and urine. Moreover, continuous monitoring is
inserted into both crowns. Such a fluorescent sensor is based on
cation-control of photoinduced electron transfer (PET-type
fluorescent sensor) involving anthracene which has a poor
desirable in the situation of open-heart surgery. The difficulty
photochemical stability. In contrast, our sensor is based on
arises from the presence of sodium ion in those media at a
cation-control of photoinduced charge transfer (PCT-type
concentration much higher than that of potassium ion. High
selectivity is therefore required.
fluorescent sensor) and the dioxycoumarin fluorophore has a
good photochemical stability.
In the present paper, we report the synthesis and binding
Results and discussion
properties of fluorescent molecular sensors (Fig. 1) which are
well suited for the recognition of caesium ion. But it is also the
aim of this paper to examine the suitability of these compounds
for recognition of potassium ion. In fact, the data reported on
cation binding showed that the selectivity of calix[4]biscrown-6
Synthesis
The synthesis of Calix-COU2 and Calix-COU1 is presented in
Scheme 1. Compound 1 is obtained by reacting 2-(2-chloro-
DOI: 10.1039/b203633a
J. Chem. Soc., Perkin Trans. 2, 2002, 1429–1434
This journal is © The Royal Society of Chemistry 2002
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Fig. 2 Absorption spectra in ethanol of Calix-COU1 (5.4 × 10Ϫ5 mol
l
Ϫ1) (A) and Calix-COU2 (3.24 × 10Ϫ5 mol lϪ1) (B) in the absence of
cation and in the presence of potassium thiocyanate and caesium
acetate at a concentration of 0.001 M.
Scheme
1
Reagents and conditions: i) ClCH2CH2OCH2CH2OH,
fluorescence intensity decreases moderately but steeply, and the
fluorescence spectrum is blue shifted by 3 nm; in the second
regime (R > 10), the fluorescence intensity decreases more
gradually, but quenching is more efficient. The fluorescence
quantum yield decreases from 0.29 (free ligand) to 0.05 at full
complexation.
K2CO3, CH3CN, ii) TsCl, NEt3, CH2Cl2; iii) calix[4]arene, K2CO3,
CH3CN; iv) calix[4]arene monocrown-6, K2CO3, CH3CN.
ethoxy)ethanol with commercially available 6,7-dihydroxy-4-
methylcoumarin. Ditosylate 2 is synthesized by reaction of 1
with toluene-p-sulfonyl chloride in the presence of triethyl-
amine in CH2Cl2 in 76% yield.
Under the same experimental conditions, the evolution of
the emission spectra of Calix-COU2 on addition of Csϩ is
displayed in Fig. 4A and an example of the titration curve at
410 nm is shown in Fig. 4B. The final level of fluorescence
intensity is higher than in the case of potassium complexation.
The cation-induced changes in fluorescence intensity will be
discussed in the next section.
Calix-COU2 was prepared in 43% yield by condensing
calix[4]arene with 2 equiv. of ditosylate 2 and 10 equiv. of
K2CO3 in refluxing acetonitrile for 2 weeks. The synthesis of
Calix-COU1 was done starting from calix[4]crown-615 with 1
equiv. of ditosylate 2 and 10 equiv. of K2CO3 in refluxing
acetonitrile for 6 days.
Similar trends were observed for complexation of Kϩ and
Csϩ with Calix-COU1 in ethanol, and with Calix-COU1 and
Calix-COU2 in acetonitrile.
Calix-COU1 and Calix-COU2 had 1H NMR spectra charac-
teristic of the 1,3-alternate conformation.
Analysis of the evolution of the whole emission spectra by
means of the SPECFIT programme (using global analysis
with 250 wavelengths) showed that the titration curves were
consistent with the formation of two complexes, 1 : 1 and 2 : 1
(metal : ligand), with Kϩ and Csϩ. The ability of calix[4]-
biscrowns to form such complexes was previously observed by
mass spectroscopy16 and by UV–visible spectroscopy.12 The
constants K11 and K21 of the successive equilibria are defined as
follows:
Cation binding properties of Calix-COU1 and Calix-COU2
Addition of sodium perchlorate, or potassium thiocyanate, or
caesium acetate to solutions of Calix-COU1 and Calix-COU2
induced only slight changes in the absorption spectra in ethanol
(Fig. 2) and acetonitrile which precludes spectrophotometric
titrations.
Fluorimetric titrations of Calix-COU1 and Calix-COU2
with Csϩ, Kϩ and Naϩ were carried out in ethanol and
acetonitrile. Let us consider first the complexation of Calix-
COU2 with Kϩ in ethanol. The ratio R = [Mϩ]/[ligand] was
varied from 0 to 2100. Evolution of the emission spectra of
Calix-COU2 on addition of Kϩ is displayed in Fig. 3A and an
example of the titration curve at 410 nm is shown in Fig. 3B.
Addition of Kϩ causes fluorescence quenching. Two regimes
can be distinguished: in the first regime (up to R ≈ 10), the
(1)
(2)
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Table 1 Stability constants of the complexes of Calix-COU1 and Calix-COU2 with alkali metal ions in ethanol and acetonitrile
Ligand
Solvent
EtOH
Cation
log K11
log K21
log β21
Calix-COU1
Csϩ
Kϩ
6.9 0.15
5.03 0.09
2.3 0.05
5.77 0.03
5.03 0.03
2.57 0.12
6.68 0.09
4.81 0.07
2.48 0.06
6.0 0.1
3.91 0.15
2.47 0.09
10.8 0.15
7.5 0.04
Naϩ
Csϩ
Kϩ
CH3CN
EtOH
3.36 0.07
2.3 0.03
9.1 0.1
7.33 0.04
Naϩ
Csϩ
Kϩ
Calix-COU2
3.81 0.1
2.46 0.06
10.0 0.1
7.29 0.06
Naϩ
Csϩ
Kϩ
CH3CN
4.3 0.2
2.19 0.03
10.3 0.2
6.44 0.03
4.25 0.02
2.38 0.06
Naϩ
Fig. 3 A: Evolution of the emission spectrum of Calix-COU2 (1.9 ×
Fig. 4 A: Evolution of the emission spectrum of Calix-COU2 (1.9 ×
10Ϫ5 mol lϪ1) upon addition of caesium acetate in ethanol. λexc = 310
nm. B: Titration curve at 410 nm.
10Ϫ5 mol lϪ1) upon addition of potassium thiocyanate in ethanol. λexc
=
310 nm. B: Titration curve at 410 nm.
The global equilibrium for the formation of the complex M2L is
(3)
Regarding the complexation with Naϩ, satisfactory fits of the
titration curves were found with a single 1 : 1 complex in the
investigated range of concentration because a much larger
excess of sodium salt would be required to observe a significant
effect due to the formation of the 2 : 1 complex. The stability
constants of the 1 : 1 complexes of Calix-COU1 and Calix-
COU2 with Naϩ are much lower than those of the complexes
with Csϩ or Kϩ. This is consistent with a poorer fit of Naϩ to
the size of the crown cavity as compared to Csϩ, and to a lesser
extent, Kϩ.
The values of K11, K21 and β21 obtained from the titration
data analyzed by SPECFIT are given in Table 1. K21 turned
out to be much smaller than K11, which means that the
complexation of a second cation is made more difficult by the
presence of a bound cation. The system can be considered as
anticooperative because the ratio K21/K11 is in all cases much
smaller than the statistical value of 1/4 that would be observed
if the two binding sites were identical and independent.17 Such
an anticooperative effect is most likely due to electrostatic
repulsion between the two cations; an unfavorable conform-
ational change induced in the free crown by the bound cation
in the other crown can also be invoked.
It should be noted that the stability constants of the com-
plexes with Calix-COU1 and Calix-COU2 (Table 1) are in good
agreement with those previously reported for calix[4]arene-
biscrown ethers.12
An important point concerns the selectivity for Csϩ or Kϩ
J. Chem. Soc., Perkin Trans. 2, 2002, 1429–1434
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Table 2 Fluorescence characteristics of Calix-COU1 and Calix-COU2 and their complexes with alkali and alkaline-earth metal ions in ethanol:
wavelengths of the emission maxima (λem) and fluorescence quantum yields (ΦF)
Charge density/Q ÅϪ1
Stoichiometry
λem/nm
ΦF
a
Ligand
Cation
Calix-COU2
408
408
405
397
406
399
408
408
406
395
406
400
0.29
0.26
0.26
0.05
0.24
0.12
0.28
0.26
0.25
0.06
0.24
0.12
Naϩ
Kϩ
1.03
0.75
0.75
0.60
0.60
1 : 1
1 : 1
2 : 1
1 : 1
2 : 1
Kϩ
Csϩ
Csϩ
Calix-COU1
Naϩ
Kϩ
1.03
0.75
0.75
0.60
0.60
1 : 1
1 : 1
2 : 1
1 : 1
2 : 1
Kϩ
Csϩ
Csϩ
a Error: 5–10%.
versus Naϩ, expressed as the ratio of the stability constants.
Taking the stability constants of the 1 : 1 complexes in ethanol,
the selectivity for Csϩ versus Naϩ was found to be 4.0 × 104 with
Calix-COU1 and 1.6 × 104 with Calix-COU2. The selectivity
for Kϩ versus Naϩ was found to be 540 with Calix-COU1 and
220 with Calix-COU2.
The fluorescence spectra of the 1 : 1 and 2 : 1 complexes of
Calix-COU2 with Kϩ or Csϩ are provided by data analysis
using the SPECFIT programme. These spectra are shown in
Fig. 5 together with the spectrum of the free ligand. According
Spectral characteristics and fluorescence quantum yields of
Calix-COU1, Calix-COU2 and their complexes with alkali
metal ions
The photophysical data are collected in Table 2. The molar
absorption coefficient of Calix-COU2 is twice as large as that
of Calix-COU1, and the fluorescence quantum yields are
identical. Therefore, it can be concluded that there is no
interaction in the ground and excited state between the two
coumarin moieties in Calix-COU2, as expected.
The data of Table 2 show that complexation with alkali ions
induces a more or less efficient quenching of fluorescence. For
understanding this effect, it should be recalled that coumarin
itself (i.e. without any substituent on the phenyl ring) is non-
fluorescent and that introduction of an electron-donating
group at the 7-position (e.g. amino or methoxy groups) leads
to intense fluorescence accompanied by a red shift of the
fluorescence spectrum. This can be interpreted in terms of
intramolecular charge transfer from the donor group at the
7-position to the lactone carbonyl group (acceptor). The case of
methoxy substituents at the 7- and 6-positions has been the
object of particular attention.18
In our compounds a bound cation that is in interaction with
the oxygen atoms at the 7- and 6-positions decreases the
electron-donating character of these atoms, which reduces the
intramolecular charge transfer; therefore, in addition to a blue
shift of the fluorescence spectrum, the fluorescence quantum
yield is decreased and ultimately tends to be that of coumarin
without substituents. It can be thus expected that the quenching
efficiency is larger when the distance between the cation and
those oxygen atoms is shorter, and/or when the charge density
of the cation is larger.
Table 2 shows that for a given cation, the fluorescence
quantum yields of the 1 : 1 complexes of Calix-COU1 and
Calix-COU2 are identical within experimental error (5–10%).
This is consistent with the fact that the affinity of the crowns for
a cation does not significantly depend on whether it contains a
coumarin moiety or not. For these 1 : 1 complexes, the quench-
ing efficiency increases in the order Naϩ < Kϩ < Csϩ, i.e. in the
order of the size of the cations. In fact, the size of Csϩ fits well
the cavity size of the crown whereas the size of Kϩ—and a
fortiori Naϩ—is smaller, which results in looser complexes,
i.e. with a larger average distance between the cation and the
oxygen atoms.19 Similar trends were previously reported for
complexes of Naϩ and Kϩ with another fluoroionophore con-
taining the same dioxycoumarin20 included in a crown-ether.
Fig. 5 Fluorescence spectra of the 1 : 1 and 2 : 1 complexes of Calix-
COU2 in ethanol calculated from titration data analysis using the
SPECFIT programme. (A) potassium; (B) caesium.
to Scheme 2 showing the various complexes, and taking into
account the fact that the two binding sites of Calix-COU2 have
the same affinity for a cation, the fluorescence spectrum of the
1 : 1 complex was expected to be the half sum of the spectrum
of the free ligand and that of the 2 : 1 complex. In contrast to
this expectation, the fluorescence spectrum of the 1 : 1 complex
appears to be closer to that of the free ligand than it should be.
Moreover, the cation-induced blue shift of the fluorescence
spectrum is much less marked for the 1 : 1 complex than for the
2 : 1 complex.
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Conclusion
The calix[4]biscrown-based fluorescent molecular sensors
described in this paper exhibit an excellent selectivity towards
caesium ion versus sodium ion. The selectivity towards
potassium ion versus sodium ion is less good but still quite
promising for practical applications. The poor solubility of
these new sensors in water is not a drawback because our aim is
to design an optical device in which the molecular sensor will be
immobilized in a polymer or a sol-gel film. Insolubility in water
is then preferable to minimize leaching.
Regarding the cation-induced photophysical changes, further
experiments are necessary to further characterize the photo-
disruption of the cation–coumarin interaction, and to see
whether the cation moves towards the tube-shaped cavity
composed of four phenyl rings where it can be stabilized by
cation–π interaction.25 Time-resolved fluorescence and
pump-probe experiments are in progress with this aim.
Scheme 2
These observations led us to conclude that the interaction
between a bound cation and an excited coumarin fluorophore is
weaker in the 1 : 1 complex than in the 2 : 1 complex. The first
explanation that comes to mind is the closer distance between
cation and coumarin in the 2 : 1 complex because the electro-
static repulsion between the two bound cations forces them to
be closer to the coumarin moiety as compared to the 1 : 1
complex. However, another cause arises from the photoinduced
charge transfer that occurs from the two oxygen atoms linked to
the phenyl moiety of the coumarin to the electron-withdrawing
carbonyl group of the coumarin. In fact, such a charge
transfer upon excitation reduces the electron density on those
oxygen atoms which may even become positively polarized,
and results in a decrease of the coordination strength between
the bound cation and those oxygen atoms, as already observed
in benzenocoronands.21,22 Similar effects have been reported
in complexes of a “crowned” laser dye, DCM-crown,23 in
which the bound cation is in interaction with the azacrown
nitrogen atom conjugated with an electron-withdrawing
group. Photoinduced disruption of this interaction was
demonstrated.24
Experimental
Starting materials for synthesis
All commercial solvents and all starting materials and basic
reagents were used without further purification.
Analytical procedures
Melting points were measured in sealed capillaries under nitro-
gen with a Büchi 500 apparatus. Chromatography columns were
prepared from Merck Kieselgel No. 11567. H NMR spectra
1
were recorded at room temperature on a Bruker SY 200 spectro-
meter. FAB-MS spectra were obtained on a VG-Analytical
ZAB-HF apparatus. Elemental analyses were performed at the
Service de Microanalyse de l’Institut de Chimie de Strasbourg.
Synthesis
6,7-Bis[2-(2-hydroxyethoxy)ethoxy]-4-methylchromen-2-one
(1). 6,7-Dihydroxy-4-methylcoumarin (14.41 g, 75.0 mmol) and
K2CO3 (31.10 g, 225.0 mmol) were stirred at room temperature
in acetonitrile (500 ml) for 2 h. Then, the mixture was heated to
reflux and 2-(2-chloroethoxy)ethanol (22.42 g, 180.0 mmol) was
added. After 3 days of reflux, additional K2CO3 (15.55 g, 112.5
mmol) and 2-(2-chloroethoxy)ethanol (11.21 g, 90.0 mmol)
were added. After refluxing for 3 days, the solvents were
evaporated. The residue was neutralized with 1 M HCl and the
aqueous phase was extracted with dichloromethane. The
organic phase was dried over Na2SO4, filtered and evaporated
to dryness. Chromatography on a silica column with an 80 : 20
dichloromethane : acetone mixture as eluent gave pure diol 1
(13.60 g; 37%) as a white solid, mp = 72–73 ЊC. 1H NMR (200
MHz; CDCl3) δ in ppm from TMS: 2.28 (s, 3H; CH3), 2.77
(s, 2H; OH), 3.67–3.80 (m, 8H; OCH2), 3.92–3.98 (m, 4H;
OCH2), 4.19–4.22 (m, 4H; OCH2), 6.17 (s, 1H; ArH), 6.85
(s, 1H; ArH), 7.03 (s, 1H; ArH). Elemental analysis calcd for
C18H24O8: C, 58.69; H 6.57; found: C, 58.73; H, 6.53%.
Ditosylate of 6,7-bis[2-(2-hydroxyethoxy)ethoxy]-4-methyl-
chromen-2-one (2). A mixture of 1 (5.90 g, 16.0 mmol) and
toluene-p-sulfonyl chloride (12.41 g, 64.0 mmol) in dichloro-
methane (150 ml) was cooled at 0 ЊC. Then, triethylamine (12.91
g, 128.0 mmol) was added dropwise. After 24 h, the reaction
mixture was neutralized to pH ∼ 1 by addition of 1 M HCl. The
organic layer was dried over Na2SO4, filtered and evaporated
under reduced pressure. The crude product was chromato-
graphed on a silica column with a 95 : 5 mixture of dichloro-
methane : acetone as eluent to give pure ditosylate 2 (8.35 g;
76%) as a colorless oil. 1H NMR (200 MHz, CDCl3): δ in ppm
from TMS: 2.37 (s, 3H, CH3), 2.41 (s, 6H, CH3), 3.72–3.81 (m,
8H, OCH2), 4.12–4.18 (m, 8H, OCH2), 6.16 (s, 1H, ArH), 6.80
(s, 1H, ArH), 7.09 (s, 1H, ArH), 7.30 (d, J = 8.2 Hz, 4H, ArH of
tosyl), 7.78 (d, J = 8.2 Hz, 4H of tosyl). Elemental analysis
Regarding the 2 : 2 complexes, the fluorescence quantum
yield of the caesium complex was found to be larger than that
of the potassium complex. The smaller charge density of Csϩ
can account for this difference.
J. Chem. Soc., Perkin Trans. 2, 2002, 1429–1434
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calcd for C32H36O12S2: C, 56.79; H, 5.36; found: C, 56.88; H,
5.41%.
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25,27:26,28-Bis{4-methyl-2-oxochromene-6,7-diylbis[2-
(2-oxyethoxy)ethoxy]}calix[4]arene (3). Calix[4]arene (2.12 g;
5.0 mmol) and K2CO3 (13.38 g; 100.0 mmol) were stirred
in acetonitrile (300 ml) at room temperature for 1 h. Then,
ditosylate 2 (6.76 g; 10.0 mmol dissolved in 10 ml of
acetonitrile) was added and the reaction mixture was refluxed
for 10 days. After cooling to room temperature, the solvents
were removed under reduced pressure. The residue was
dissolved in dichloromethane and water and neutralised to pH
∼ 1 with 1 M HCl. The organic layer was dried over Na2SO4,
filtered and evaporated. Chromatography on a silica column
with an 80 : 20 mixture of dichloromethane : acetone as eluent
followed by precipitation with methanol gave product 3 (2.39 g;
1
43%) as a white solid, mp = 164–165 ЊC. H NMR (200 MHz,
CDCl3): δ in ppm from TMS: 2.41 (s, 6H; CH3), 3.59–3.62
(m, 20H; OCH2), 3.78 (s, 8H; ArCH2Ar), 3.89–3.91 (m, 4H;
OCH2), 4.13–4.16 (m, 8H; OCH2), 6.19 (s, 2H; ArH), 6.70 (t, J
= 7.4 Hz, 4H; ArHcalix-para), 6.90 (s, 2H; ArH), 7.08 (d, J = 7.4
Hz, 8H; ArHcalix-meta), 7.16 (s, 2H; ArH). FAB positive, m/z =
1089.2. Elemental analysis calcd for C64H64O16: C, 70.57; H
5.92; found: C, 70.64; H, 5.88%.
5 C. Perez-Jimenez, S. Harris and D. Diamond, J. Chem. Soc., Chem.
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25,27-{4-Methyl-2-oxochromene-6,7-diylbis[2-(2-oxyethoxy)
ethoxy]}-26,28-{ethylenebis[2-(2-oxyethoxy)ethoxy]}calix-
[4]arene (4). Calix[4]arene monocrown-6 (1.25 g; 2.0 mmol)
and K2CO3 (2.76 g; 20.0 mmol) were stirred at room
temperature for 2 h in acetonitrile (120 ml). Then ditosyl-
ate 2 (1.35 g; 2.0 mmol dissolved in 10 ml of acetonitrile) was
added. After 7 days of reflux, the mixture was cooled to
room temperature and the solvents were removed under
reduced pressure. The residue was dissolved in dichloromethane
and water and acidified to pH ∼ 1 with 1 M HCl. The organic
layer was dried over Na2SO4, filtered and evaporated. Chroma-
tography on a silica column with a mixture of 90 : 10 dichloro-
methane : acetone followed by precipitation with methanol gave
product 4 (1.36 g; 71%) as a white solid, mp = 132–133 ЊC.
1H NMR (200 MHz, CDCl3): δ in ppm from TMS: 2.42 (s,
3H; CH3), 3. 38 (t, J = 6.2 Hz, 4H; OCH2), 3.47–3.67 (m, 20H;
OCH2), 3.71 (s, 8H; ArCH2Ar), 3.80 (s, 4H; OCH2), 3.86 (t, J =
6.2 Hz, 4H; OCH2), 4.10 (t, J = 6.2 Hz, 2H; OCH2), 4.19 (t, J =
6.1 Hz, 2H; OCH2), 6.19 (d, J = 1.2 Hz, 1H; ArH), 6.70 (t, J =
7.4 Hz, 2H; ArHcalix-para), 6.87 (t, J = 7.4 Hz, 2H; ArHcalix-
para), 6.89 (s, 1H; ArH), 7.06 (s, 1H; ArH), 7.08 (d, J = 7.4 Hz,
4H; ArHcalix-meta), 7.15 (d, J = 7.4 Hz, 4H; ArHcalix-meta).
FAB positive, m/z = 959.40. Elemental analysis calcd for
C56H62O14: C, 70.13; H 6.52; found: C, 70.14; H, 6.58%.
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Solvent and salts
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for absorption and fluorescence measurements. Sodium
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they were of the highest quality available and vacuum dried
over P2O5 prior to use.
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Spectroscopic measurements and calculations
UV–visible absorption spectra were recorded on a Varian Cary
5E spectrophotometer. Corrected emission spectra were
obtained on an SLM-Aminco 8000C spectrofluorometer. The
fluorescence quantum yields were determined using quinine
sulfate dihydrate in H2SO4 (0.05 M) as a reference (ΦF = 0.546).
All solvents used were of spectroscopic grade.
Global analysis of the evolution of the whole fluorescence
spectra was performed with Specfit Global Analysis System
V3.0 for 32-bit Window System. This programme uses singular
value decomposition and non linear regression modelling by
the Levenberg–Marquardt method.26
1434
J. Chem. Soc., Perkin Trans. 2, 2002, 1429–1434