Calix[4]arene-functionalized poly-cyclopenta[2,1-b;3,4-b′] bithioplienes with good recognition ability and selectivity for small organic molecules for application in QCM-based sensors

Article abstract of DOI:10.1039/b314345g

Some C_2v symmetric cyclopenta[2,1-b;3,4-b′]bithiophenes differently substituted at the 4 position with a calix[4]arene group were synthesized and electrochemically polymerized by anodic coupling. The polymers were characterized by cyclic voltam

Full text of DOI:10.1039/b314345g

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A R T I C L E
Calix[4]arene-functionalized poly-cyclopenta[2,1-b;3,4-
b’]bithiophenes with good recognition ability and selectivity for
small organic molecules for application in QCM-based sensors{
Simona Rizzo,a Franco Sannicolo`,*a Tiziana Benincori,b Gilberto Schiavon,c
Sandro Zecchinc and Gianni Zotti*c
aUniversita` degli Studi di Milano, Dipartimento di Chimica Organica e Industriale and
Istituto CNR Scienze e Tecnologie Molecolari, CIMAINA Centro Interdisciplinare
Materiali Nanostrutturati, via G. Venezian, 21 – 20133 – Milan, Italy.
E-mail: staclaus@icil64.cilea.it; Fax: 139.02.50314139; Tel: 139.02.50314174 – 73
bDipartimento di Scienze Chimiche ed Ambientali dell’Universita` dell’Insubria,
Via Valleggio, 11 – 22100 – Como, Italy
cIstituto CNR per l’Energetica e le Interfasi, Corso Stati Uniti, 4 – 35127 – Padova, Italy.
E-mail: g.zotti@ieni.cnr.it; Fax: 139.049.8295853; Tel: 139.049.8295868
Received 11th November 2003, Accepted 6th April 2004
First published as an Advance Article on the web 11th May 2004
Some C2v symmetric cyclopenta[2,1-b;3,4-b’]bithiophenes differently substituted at the 4 position with a
calix[4]arene group were synthesized and electrochemically polymerized by anodic coupling. The polymers
were characterized by cyclic voltammetry, UV-vis and FTIR spectroscopy. Quartz crystal microbalance
analysis showed strong affinity and selectivity of the polymers for toluene and acetone from the gas phase. The
absorption process associated with the calix unit was satisfactorily described through a Langmuir isotherm,
while a very small linear contribution was given by the polythiophene backbone. The absorption capacity
of these materials was found to be higher by a magnitude of three orders than those displayed by
cyclopentabithiophene-based polymers devoid of the calix unit, thus supplying strong, though indirect, proof of
the role played by the calix units in the absorption process.
to detect the variations in weight of the film following the
Introduction
absorptive process and suitable electrochemical techniques to
detect the changes in the electrical properties (e.g.: conductivity)
of the poly-conjugated chain. The QCM technique is more
popular than the latter since itissimple, inexpensive and gives fast,
reliable and precise response to the weight increase of the films
following the absorption of vapors. The microbalance apparatus
can be mounted in a closed chamber where solvents were injected,
according to standardized automated procedures.
The aim of the present research was to prepare highly
ordered calix[4]arene-functionalized poly-bithiophenes, which
could exhibit good recognition ability for specific small organic
molecules selectively recognized by the cavity. Monomer 1 was
first selected for this purpose (Scheme 1).
The structural design was based on the following considera-
tions. i) Electron-rich 4H-cyclopenta[2,1-b;3,4-b’]bithiophene
(CPDT),9 designed and successfully employed by us,10 was
chosen as the polymerogenic unit, since its oxidative electro-
polymerization occurs at rather low potentials and overoxidation
defects are not introduced in the polymer. ii) The homotopism
of the positions involved in the polymerization process (1 is C2v
symmetric) assures the regio- and stereo-regularity of the chain.
iii) The 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrahydroxy-
calix[4]arene (3a) and its 25,27-diametrical dimethyl ether (3b)
were chosen to effect the molecular recognition, since they are
accessible through very simple and reliable synthetic pro-
cedures.11 iv) The short linkers between CPDT and the
phenolic oxygen atoms of the 1,3 distal rings of the calix moiety
should guarantee the cone conformation, which is endowed
with higher recognition properties than partial cone or alter-
nate conformations.
Calixarenes have attracted great attention due to their ability
and selectivity in hosting specifically sized ionic1 and neutral
molecules (benzene and substituted benzenes, acetonitrile,
nitromethane, N,N-dimethylformamide)2 in their cavity and
it is not surprising that they have been chosen as sensing units
associated with electroactive surfaces to prepare materials for
sensors.3 Polymer films either physically incorporating calix-
arenes4 or covalently functionalized with calixarene units5 have
been widely investigated in the past and still are the subject of
intense research efforts aimed at finding new materials for even
more efficient on-line working sensor devices. A continuously
growing number of different architectures capable of giving
selective supramolecular interactions with ionic and neutral
species is now available and recent literature offers clever
examples of second generation calixarene functionalized
polymers successfully applied in sensoristics.6 The different
strategies envisaged to prepare calixarene-based sensors have
been exhaustively reviewed in several publications.7
The oxidative electropolymerization of calixarene-functionalized
five-membered heteroaromatic and bi-heteroaromatic mono-
mers to give electroactive polymers offers some substantial
advantages over the several methodologies available to prepare
polymeric thin films to be used as sensing units.8 In particular,
it is possible to exploit, at least in theory, different techniques
for producing reliable signals from the effects of the supra-
molecular analyte–calixarene interactions: the QCM analysis
{ Electronic supplementary information (ESI) available: 1H-NMR
spectra of compounds 6, 7, 8, 1, 5, 12; experimental procedures of the
reactions of 7 with 3b and of 9 with 1,3-dibromopropane; preparations
and characterization for 4 and 5. See http://www.rsc.org/suppdata/jm/
b3/b314345g/
It is known, however, that the conjugated organic poly-
heterocycles are more or less porous materials, capable of
1 8 0 4
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 1 8 0 4 – 1 8 1 1
T h i s j o u r n a l i s ß T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4

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Scheme 1
adsorbing volatile organic compounds, independently of the
presence of functions specially tailored for this purpose. We
considered it an important point of the research to devise a
system to differentiate the generalized absorption effects
related to the intrinsic porosity of the polymer and those
produced by selective inclusion of organic molecules in the
annulus of the calix units. With this view, we planned to
prepare the monomer 2, similar to 1 in its atomic composition,
connectivity, symmetry and, reasonably, electrochemical oxi-
dative potential, but devoid of the conical receptor (Scheme 1).
The differences in the recognition and absorption data shown
by electrodes coated with poly-1 and poly-2 should be mainly
referable to the inclusion ability shown by the cavities of the
calixarene pendants.
repeated on the latter to give the 4,4’-bis(3-bromopropyl)-
cyclopenta[2,1-b;3,4-b’]bithiophene (7), which was used as a
bifunctional alkylating reagent of the 5,11,17,23-tetra-tert-
butyl-25,26,27,28-tetrahydroxycalix[4]arene (3a). Compound 8
was isolated in satisfactory yields and then methylated at the
diametrical phenolic oxygen atoms to give 1, though in modest
yields (Scheme 3).
The reaction sequence reported above is the sole method
capable of affording 1, even though several other synthetic
schemes have been tried. The reaction of dibromide 7 with
the dianion of the calixarene diametrical dimethyl ether 3b
afforded the monoalkylation product in poor yields, which,
in any case, could not be cyclized to 1 even under drastic
conditions.
This paper reports: i) the syntheses of monomers 1, 2 and two
other C2v symmetric calixarene-functionalized CPDT mono-
mers, 4 and 5 (Scheme 2), we came across, more or less
accidentally, during the development of the work and that we
considered interesting in the general frame of this research; ii)
the electropolymerization of the monomers; iii) the electro-
chemical and spectroscopic characterization of the polymers;
iv) the evaluation of the vapor uptake ability and the selectivity
of the polymers for toluene12 and acetone,13 which are standard
strong (toluene) and weak (acetone) guest molecules.
In a further attempt to produce 1, the mono anion of the
calix[4]arene dimethyl ether 3b reacted with the 4-(3-bromopro-
pyl)cyclopenta[2,1-b;3,4-b’]bithiophene (6), described above, to
give the expected alkylation product 9, together with minor
quantities of the dialkylated compound 4 (Scheme 4). Both
these compounds were separated by chromatography and
recognized on the basis of their analytical and spectral data.
Once again, however, we were not able to convert 9 into 1 by
further alkylation of the phenolic oxygen atom with 1,3-
dibromopropane under basic conditions, followed by base-
promoted cyclization of the resulting alkylation product.
Even though 9 is a calixarene-functionalized CPDT-based
system, we did not consider it a suitable monomer for the
present investigation, since Cs symmetric monomers unavoid-
ably produce stereochemically disordered polymers. We
employed, instead, as a monomer C2v symmetric compound
6, bearing two distal CPDT-terminated substituents, even
though, in this case, the partial-cone seemed favored over the
Results and discussion
(1) Synthesis of the monomers
The synthesis of monomer 1 was achieved starting from CPDT:
its anion in position 4 was alkylated with 1,3-dibromopropane
at 270 uC to give the 4-(3-bromopropyl)cyclopenta[2,1-b;3,4-
b’]bithiophene (6) in good yields. The same sequence was
Scheme 2
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 1 8 0 4 – 1 8 1 1
1 8 0 5

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Scheme 3
Scheme 4
cone conformation and extensive cross-linking during the
polymerization was expected.
general situations were observed: when very sharp signals were
found, we could infer that the system was present in solution as
a single conformational isomer, even though a clear discrimi-
nation between cone and partial cone conformers was impos-
sible, since both display C2v symmetry. This was the case for all
the twin bridged CPDT systems 1, 5, 8, and 12. Broad signals
indicated that the compound was present in solution as a
mixture of conformational diastereoisomers in a dynamic
equilibrium. Mono-functionalized CPDT monomers 4 and 9
were found to be constituted by mixtures of slowly inter-
converting stereoisomers.
We also prepared substrate 5, reasonably displaying the cone
as the preferred conformation thanks to its rather rigid
architecture and probably able to produce a better-organized
polymer than 4. Its synthesis was achieved by alkylation of
calixarene 3a with the dibromo derivative 11, to give the distal
diphenol 12, which was further methylated (NaH/MeI) to
afford 5. Dibromo compound 11 was prepared by dialkylation
with 1,4-dibromobutane of the 1,3-bis[4-(4H-cyclopenta[2,1-
b;3,4-b’]bithiophen)yl]propane (10), which was synthesized in
turn by stoichiometry-controlled alkylation of CPDT with 1,3-
dibromopropane (Scheme 5).
(2) Electrochemical synthesis of the polymers
The synthesis of compound 2, bearing a CPDT unit func-
tionalized with a non-conical, quasi-isomeric, substituent of the
calix, was successfully achieved through the monomethylation
of known bis(5-tert-butyl-2-hydroxyphenyl)methane to give 13,
followed by reaction of the anion of the latter with 4,4’-bis(3-
bromopropyl)cyclopenta[2,1-b;3,4-b’]bithiophene (7) described
above (Scheme 6).
Monomers 1 and 5 were found to be slightly soluble in aceto-
nitrile (ca. 1024 M), whereas higher solubility was shown by 4
and 2 (ca. 1023 and w1022 M respectively). The voltammo-
grams, performed in 0.1 M Bu4NClO4 acetonitrile solution,
displayed an oxidation peak at ca. 0.7 V (scan rate: 0.1 V s21),
quite similar for all the monomers (Table 1).
The 1H NMR spectra of the calixarene-functionalized CPDTs
were examined in CDCl3 solution at room temperature.14 Two
With continuous potential cycling, the redox cycle, due to the
growing polymer, developed, as shown for monomer 1 in Fig. 1.
1 8 0 6
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 1 8 0 4 – 1 8 1 1

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Scheme 5
Scheme 6
The charge yield (ratio of the reversible charge over that for
deposition, measured at the neutral state) was about 15% for 1,
30% for 4 and 5 and only 3% for the open-calix functionalized
system 2. The latter observation might be attributed to a rather
high solubility of the oligomers.
perchlorate anion is involved in the mass exchange. The
simple uptake of perchlorate to counterbalance the injected
positive charge is
polythiophenes.16
a feature commonly encountered in
All the polymers displayed the CV characteristics expected
for a polythiophene film with a twin redox process. A typical
cyclic voltammogram is shown for poly-1 in Fig. 2.
The redox potentials Eu, taken as the average of oxidation
and reduction peak potentials, are reported in Table 1 for all
the polymers. The average Eu values are about 0.1 V, i.e. close
to those shown by analogous CPDT-based polymers.15
QCM analysis indicates that the reversible oxidation pro-
cess involves one electron per monomeric unit and that one
Table 1 Oxidation peak potentials (Ep) for monomers and redox
potentials (Eu) and maximum UV absorption (l) for polymers
1
4
5
2
CPDT
Ep/Va
Eu/V
l/nm
0.70
0.10; 0.25
560
0.68
0.15; 0.30
520
0.68
0.10; 0.25
550
0.70
0.15; 0.30
520
0.65
0.10
545
Fig. 1 Repetitive cyclic voltammetry of
Bu4NClO4 acetonitrile solution. Scan rate: 0.1 V s21
1 M
(1024 M) in 0.1
a Scan rate: 0.1 V s21
.
.
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 1 8 0 4 – 1 8 1 1
1 8 0 7

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Fig. 3 QCM mass increase for poly-1 following subsequent additions
of toluene (0.1; 0.2; 0.3; 0.5; 0.75; 1.0; 1.5; 2.0; 2.5; 3.0 mL). Initial mass:
9 mg cm22. Polymer density assumed as 1.0 g cm23
.
Fig. 2 Cyclic voltammogram of poly-1 in 0.1 M Bu4NClO4 acetoni-
trile solution. Scan rate: 0.1 V s21. Reversible charge: 0.7 mC cm22
.
(3) Characterization of the polymers
Undoped poly-1 and poly-2 are soluble in CHCl3, while poly-4
and poly-5 were found to be insoluble. Expected crosslinking
could be responsible for these different solubility properties.
The IR spectrum of the undoped polymers, dominated by
the calixarene bands, displayed a strong band at ca. 820 cm21
due to the inner C–H bond stretching and a weak one at
640 cm21 due to the terminal C–H bond stretching of CPDT
units, in agreement with the medium DP value of the polymers
(about 10).
The electronic spectral data indicated that the absorption
maxima of the polymer films were located at about 580 ¡ 20 nm,
in agreement with the data shown by previously investigated
CPDT-based materials.15
An analogous trend was found to be followed by the redox
potentials. Poly-4 and poly-2 exhibited absorption maxima at
520 nm, while poly-1 and poly-5 showed maxima at 550–
560 nm, probably as a consequence of slightly different DPs
(Table 1).
Fig. 4 QCM mass increase for poly-1: plot of toluene concentration in
the polymer (Cp) vs. toluene concentration in nitrogen (Cv). Initial
mass: 9 mg cm22. Line: fitting to model (x2 ~ 2 6 1027).
The conductivity of poly-4 was found to be about 1 S cm21
,
The absorption process was found to be fully reversible, again
with short response times, by flushing the cell with dry nitrogen.
The concentration of the guest toluene in the polymer vs.
its concentration in the gas phase showed approximately
Langmuir-type absorptive behavior (Fig. 4).
In fact, a significant positive slope was observed in the high-
concentration side of the plots. This result may be accounted
for by a twin-process Langmuir law: C ~ b1C/(1 1 b1C) 1
b2C/(1 1 b2C), where C is the fraction of adsorbed molecules
[Dm/DmL, i.e. the ratio of mass uptake (Dm) over the maximum
allowed mass uptake (DmL)], C is the analyte concentration in
the gas phase and b are the adsorption constants. The equation
may be simplified to: C ~ b1C/(1 1 b1C) 1 b2C, given the low
value of the second coordination constant b2 (1–4% of b1).
A very good fitting was observed and the resulting partition
equilibrium constant b1 values are reported in Table 2 for the
various polymers.
while the conductivity of the other polymers could not be
measured through the in situ technique17 due to the low
deposition yields.
The failure to determine reliable conductivity data for the
polymers ruled out the possibility of searching for possible
relationships between the vapor uptake levels in the materials
and their conductivities. Thus, we resorted to the QCM
technique.
(4) Vapor uptake monitoring by QCM
The ability of the poly-(calixarene-functionalized-CPDT)s to
uptake organic vapors has been checked for thin films
deposited on the QCM electrode. In order to test the
adsorption ability of the plain CPDT backbone, we planned
to carry out absorption measurements also on poly-CPDT
itself.15 As anticipated, tests were performed with a strong
(toluene) and a weak (acetone) guest molecule.18
The films were produced by potential cycling, followed by a
conditioning step constituted by three further CV cycles in a
monomer-free electrolyte solution and final flushing of the
coated electrodes with nitrogen till steady weight (about
10 minutes). The conditioning procedure was necessary to
obtain reproducible results, since inaccurate storage of the films
in the dry state was found to lead to a progressive decrease of
their vapor uptake ability, which could decay to 50% in 24 hours.
In the cases of poly-1, poly-4 and poly-5, the mass increases
regularly with the vapor additions with a very fast response time,
roughly corresponding to the mixing time (ca. 100 s) (Fig. 3).
DmL values, referred to the mass of the polymers, corres-
ponded to a maximum absorption level of about the 10% for
both solvents. Taking into account the molecular weights of
Table 2 Partition equilibrium constants b1 for toluene b1(Tol) and
acetone b1(Ac)
1
4
5
2
CPDT
b1(Tol)a
b1(Ac)a
a g21 cm3. b Not measured.
3 6 106
5 6 104
7 6 106
—
5 6 106
1 6 105
1 6 103
4 6 104
5 6 103
—
b
b
1 8 0 8
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 1 8 0 4 – 1 8 1 1

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toluene (92), acetone (58) and the repeating unit of poly-1
(932), these data corresponded to a 1.1 : 1 analyte : calix unit
molar ratio for toluene and 1.6 : 1 for acetone. This con-
sideration suggested that, at the saturation level, one molecule
of solvent is hosted in one calix annulus, in agreement with the
literature data regarding toluene and acetone clathrates.12,13,18
Extra adsorption (b2), related to inclusion in the polymer
matrix, is considerably more difficult and probably involves
cavities located amongst the calixarene units. This suggestion is
supported by results recently reported on LB films of
calixarenes, for which an accumulation of liquid adsorbate
within the nanopores of the matrix was found.19
We have also verified that the vapor uptake does not depend
on the oxidation level of the polythiophene backbone.
The absorption constants b1(Tol) shown by the calix-
functionalized polymers poly-1, poly-4 and poly-5, can be
considered as extremely high. These materials display an
adsorption capacity even more efficient than that shown by the
highly sorbent Ni(SCN)2(4-picoline)4 complex.20
Instead, poly-2 and poly-CPDT can be considered to have
absorption properties comparable to those known for other
polymeric materials (e.g. polybutadiene), which are currently
used for QCM analysis of organic vapors, including toluene.21
It is interesting to note that the absorption properties for
toluene of poly-1, poly-4 and poly-5 are higher by a magnitude
of three orders than those exhibited by poly-2, which is devoid
of the calixarene function, and by poly-CPDT (Table 2), for
which much longer response times (ca. 20 minutes) were also
observed.
and stereochemical order, thanks to the homotopism of the
positions involved in the polymerization process.
—The polymers have been spectroscopically and electro-
chemically characterized.
—Electrodes coated with the polymers have been tested as
sensors for the selective recognition of toluene and acetone
present in the gas phase, since they are the standard analytes for
evaluating the hosting ability of the calix moieties present in
functional materials.
—The polymers could not be obtained as films thick enough
to allow reliable conductivity measurements. Thus, the search for
a conductivity–vapor absorption relationship was precluded.
—QCM measurements demonstrated that the absorption
properties for toluene of the calixarene-functionalized poly-
mers are extremely high, more than three orders of magnitude
higher than those exhibited by poly-CPDT and poly-2,
which are devoid of the calixarene function, and at least one
order of magnitude higher than other calix[n]arene thin films,
generally suffering for comparable analyte–surface and –bulk
interactions.
—Much shorter response times (100 s) are required for the
calixarene-functionalized materials than for the polymers
devoid of the calixarene functions (ca. 20 minutes).
—In the cases of polymers bearing the calix units, the
absorption process stops when one molecule of analyte per
calix unit is absorbed.
—The absorption process follows the ideal behavior con-
trolled by the Langmuir equation, with a very modest linear
contribution due to the polymer matrix.
—Poly-1, poly-4 and poly-5 display very different affinities
for toluene and acetone.
These data demonstrate that the calix functions play a
crucial role in determining the absorption capacity of the
polymers.
—The films were found not to suffer from swelling as a
consequence of the absorption process into the polymer matrix.
These data demonstrate that the calix unit is the main unit
responsible for the great absorption capacity and for the selec-
tivity shown by the calix[4]arene functionalized poly-CPDTs.
It is also worth noting that poly-1, poly-4 and poly-5 are
expected to have different morphology, roughness, porosity
and solubility, since, as anticipated, crosslinking is certainly
active in the polymerization of 4 and 5, while it is precluded in
the case of 1. The absorption properties of all three polymers
for toluene and acetone are, however, very similar. This
observation is further proof that the calix cavity is nearly
exclusively responsible for the absorption properties of these
materials, since the generic vapor diffusion into a polymer
matrix, related to its inherent porosity, should be strongly
influenced by its morphological features.
Experimental
Synthesis of the monomers
CPDT was prepared according to the procedure previously
described by us.9
The uptake of acetone appears, instead, quite undifferen-
tiated amongst all the polymers, with constants falling in the
range 104–105. The ratio of the adsorption constants for
toluene over those for acetone is about 50–60, in agreement
with the known different affinity of calix[4]arenes for these
solvents.12,13
4-(3-Bromopropyl)cyclopenta[2,1-b;3,4-b’]bithiophene (6). A
1.6 M BuLi solution in n-hexane (3.0 mL, 4.8 mmol) was
dropped into a solution of CPDT (840 mg, 4.7 mmol) in dry
THF (25 mL) at 270 uC under nitrogen. The temperature was
allowed to rise to 220 uC, maintained for 20 minutes, then
cooled again to 270 uC. 1,3-Dibromopropane (2 mL, 20 mmol)
was added dropwise, then the cooling bath was removed and
the mixture left to stand for 12 hours. MeOH (5 mL) was added
and the solvent removed under reduced pressure. The residue
was treated with H2O, extracted with Et2O, then, after the
usual work-up, column chromatographed (silica gel/n-hexane).
The title product 6 was recovered from the first fractions eluted
Conclusions
The experiences developed in this research have demonstrated
the good opportunities offered by calix[4]arene-functionalized
CPDTs to design sensors for efficient and selective recognition
of small organic molecules present in the gas phase. The results
can be summarized as follows:
—Some calix[4]arene-functionalized cyclopentabithiophene
monomers (1, 4 and 5), displaying C2v symmetry, have been
synthesized.
1
as a pale-orange oil (720 mg, yield 51%). H NMR (80 MHz,
CDCl3) d 7.19 (d, J ~ 2.13 Hz, 2H, a thiophene), 7.05 (d, J ~
2.13 Hz, 2H, b thiophene), 3.7 (t, J ~ 2.67 Hz, 1H, 4’H), 3.4 (t,
J ~ 2.35 Hz, 2H, CH2Br), 2.0 (m, 2H, CH2CH2CH2Br), 1.9
(m, 2H, CH2CH2CH2Br).
—Monomer 2, similar to 1 in its atomic composition,
connectivity, symmetry and electrochemical oxidative poten-
tial, but devoid of the conical receptor, has been synthesized in
order to discriminate the absorption effects related to the pre-
sence of the calix function from the generalized absorption of
the vapors into the micropores of the polymer matrix.
—All the monomers have been electrochemically poly-
merized to give materials endowed with high constitutional
4,4’-Bis(3-bromopropyl)cyclopenta[2,1-b;3,4-b’]bithiophene (7).
A 1.6 M BuLi solution in n-hexane (1.5 mL, 2.4 mmol) was
dropped into a solution of 6 (700 mg, 2.34 mmol) in dry THF
(20 mL) at 270 uC under nitrogen. 1,3-Dibromopropane
(2.1 ml, 20 mmol) was added dropwise, then the cooling
bath was removed and the mixture left to stand for 12 hours
(hexane : CH2Cl2 97 : 3). MeOH (5 mL) was added and the
solvent removed under reduced pressure. The residue was
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 1 8 0 4 – 1 8 1 1
1 8 0 9

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treated with water, extracted with ether, then flash chromato-
graphed (hexane : CH2Cl2 97 : 3). The title product 7 was
recovered as a pale-orange solid (710 mg, yield 73%). 1H NMR
(80 MHz, CDCl3) d 7.21 (d, J ~ 4.90 Hz, 2H, a thiophene),
6.96 (d, J ~ 4.90 Hz, 2H, b thiophene), 3.20 (t, J ~ 6.56 Hz,
4H, CH2Br), 2.10 (m, 4H, CH2CH2CH2Br), 1.40 (m, 4H,
CH2CH2CH2Br).
adjusted to 5 with conc. HCl solution. After the usual work-up,
the residue of the organic layer was column chromatographed
(silica gel/hexane : AcOEt 9 : 1). The central fractions gave 13
as a colorless solid (860 mg, yield ~ 60%). 1H NMR (300 MHz,
CDCl3) d 7.33 (d, J ~ 2.53 Hz, 1H, H–Ar), 7.29 (d, J ~
2.51 Hz, 1H, H–Ar), 7.19 (dd, J1 ~ 8.70 Hz, J2 ~ 2.53 Hz, 1H,
H–Ar), 7.11 (dd, J1 ~ 8.42 Hz, J2 ~ 2.52 Hz, 1H, H–Ar), 7.00
(s, 1H, OH), 6.81 (d, J ~ 8.70 Hz, 1H, H–Ar), 6.78 (d, J ~
8.44 Hz, 1H, H–Ar), 3.96 (s, 3H, OCH3), 3.92 (s, 2H, CH2),
1.30 (s, 9H, 3 t-Bu), 1.28 (s, 9H, 3 t-Bu).
Synthesis of 8. Dry K2CO3 (0.29 g, 2.1 mmol) and 7 (0.72 g,
1.71 mmol) were added to a stirred suspension of calix[4]arene
(3a) (1.12 g, 1.73 mmol) in dry CH3CN (50 mL). The mixture
was refluxed for 20 hours, then filtered and evaporated to
dryness. Column chromatography (silica gel/petroleum ether :
Et2O 95 : 5) gave 8 (0.94 g, yield 60%) in a pure state as a
Synthesis of monomer 2. A solution of 13 (761 mg,
2.33 mmol) in dry DMF (30 ml) was dropped into a stirred
mixture of a 60% NaH slurry in mineral oil (97 mg, 2.42 mmol)
and dry DMF (30 ml) under nitrogen at room temperature.
The mixture was heated at 40 uC for 20 minutes, then a solution
of 7 (482 mg, 1.15 mmol) in dry DMF (50 mL) was added.
After 12 hours standing at room temperature, solvent was
removed under reduced pressure and the residue treated with
Et2O and H2O. The residue obtained from the organic layer
after the usual work-up was column chromatographed (silica
gel/hexane : AcOEt 95 : 5) to give 2 as a colorless solid (789 mg,
1
colorless solid (dec. 320 uC). H NMR (300 MHz, CDCl3) d
9.35 (s, 2H, 2 OH), 7.19 (d, J ~ 4.90 Hz, 2H, a thiophene), 7.15
(d, J ~ 4.90 Hz, 2H, b thiophene), 7.10 (s, 4H, H–Ar), 7.04 (s,
4H, H–Ar), 4.36 (d, J ~ 12.72 Hz, 4H, CH2–Ar), 3.41 (d, J ~
12.72 Hz, 4H, CH2–Ar), 4.08 (broad t, 4H, 2 CH2O), 2.45
(broad m, 8H, 2 CH2CH2CH2O), 1.21 (s, 18H, 2 t-Bu), 1.18 (s,
18H, 2 t-Bu). EI-MS m/z (relative intensity) 906.
1
yield 75%) (mp 54–61 uC from i-PrOH). H NMR (300 MHz,
Synthesis of monomer 1. A 60% NaH slurry in mineral oil
(150 mg, 3.75 mmol) was added portionwise to a stirred
solution of 8 (605 mg, 0.67 mmol) in THF–DMF 10 : 1(30 mL).
When gas evolution stopped, (CH3)2SO4 (0.80 mL, 8.4 mmol)
was added, then the mixture was refluxed for 2 hours. Solvent
was removed under reduced pressure and the residue treated
with a 5% NaOH solution and Et2O under stirring. The residue
obtained from the organic layer, after the usual work-up, was
column chromatographed (silica gel/petroleum ether : Et2O 95 :
5) to give 1 in a pure state (219 mg, yield 35%) as a colorless
solid with mp w 210 uC. 1H NMR (300 MHz, CDCl3) d 7.28 (d,
J ~ 5.00 Hz, 2H, a thiophene), 7.20 (d, J ~ 5.00 Hz, 2H, b
thiophene), 7.15 (s, 4H, H–Ar), 6.60 (s, 4H, H–Ar), 4.40 (d, J ~
15.00 Hz, 4H, CH2–Ar), 3.19 (d, J ~ 15.00 Hz, 4H, 2 CH2–Ar),
3.85 (s, 6H, 2 OCH3), 3.76 (t, J ~ 4.00 Hz, 4H, 2 CH2O), 2.60
(m, 4H, 2 CH2CH2CH2O), 2.21 (m, 4H, 2 CH2CH2CH2O),
1.30 (s, 18H, 2 t-Bu), 1.20 (s, 18H, 2 t-Bu). EI-MS m/z (relative
intensity) 934. Elemental analysis: calc for C61H74S2O4: C
78.17, H 8.06%; found C 78.08 H 7.95%.
CDCl3) d 7.15–7.07 (m, 6H, H–Ar and a thiophene), 7.01 (d,
J ~ 2.48 Hz, 2H, H–Ar), 6.83 (d, J ~ 4.88 Hz, 2H, b
thiophene), 6.75 (d, J ~ 8.50 Hz, 2H, H–Ar), 6.59 (d, J ~
8.38 Hz, 2H, H–Ar), 3.90 (s, 4H, 2 CH2–Ar), 3.78 (s, 6H, 2
OCH3), 3.65 (t, J ~ 6.26 Hz, 4H, 2 CH2O), 1.94 (m, 4H, 2
CH2CH2CH2O), 1.29 (m, 4H, 2 CH2CH2CH2O), 1.21 (s, 18H,
2 t-Bu), 1.18 (s, 18H, 2 t-Bu); EI-MS m/z (relative intensity)
910. Elemental analysis: calc for C59 H74S2O4: C 77.76, H
8.18%; found C 77.44 H 8.07%.
Electrochemical experiments
Chemicals and reagents. Acetonitrile was distilled twice over
P2O5 and once over CaH2. Tetrabutylammonium perchlorate
(Bu4NClO4) was dried under vacuum at 70 uC. All other
chemicals were reagent grade and used as received.
General procedures and apparatus. Experiments were per-
formed at 25 uC under nitrogen in three electrode cells in 0.1 M
Bu4NClO4 acetonitrile solution. The counterelectrode was
platinum; reference electrode was a silver/0.1 M silver per-
chlorate acetonitrile solution (0.34 V vs. SCE). The voltam-
metric apparatus (AMEL, Italy) included a 551 potentiostat
modulated by a 568 programmable function generator and
coupled to a 731 digital integrator.
The working electrode for cyclic voltammetry was a plati-
num minidisc electrode (0.003 cm2). For electronic spectro-
scopy a 0.8 6 2.5 cm2 indium tin oxide (ITO) sheet (ca. 80%
transmittance, ca. 20 ohm/square resistance, from Balzers,
Liechtenstein) was used.
Bis(5-tert-butyl-2-hydroxyphenyl)methane. A solution of
4-tert-butylphenol (11.91 g, 79.3 mmol) in dry Et2O (25 mL)
was added dropwise to a stirred solution of EtMgBr (26 mL,
78 mmol) in dry Et2O (70 mL) under nitrogen. Most of the
solvent was removed by careful heating and replaced with dry
toluene (70 mL), then the mixture was progressively heated
to the reflux temperature removing the residual Et2O by
distillation. After a further addition of dry toluene (150 mL),
paraformaldehyde (1.18 g, 39.3 mmol) was added and the
mixture refluxed for 3 hours, then treated with water. After the
usual work-up, the crude reaction product (12.8 g), constituted
by a mixture of oligomers, was flash chromatographed (silica
gel/CHCl3). The final fractions eluted gave bis(5-tert-butyl-2-
hydroxyphenyl)methane, as a colorless solid (4.84 g, yield 40%)
(mp 151–154 uC). 1H NMR (300 MHz, CDCl3) d 7.32 (d, J ~
2.44 Hz, 2H, H–Ar), 7.12 (broad s, 2H, 2 OH), 7.10 (dd, J1 ~
8.42 Hz, J2 ~ 2.43 Hz, 2H, H–Ar), 6.75 (d, J ~ 8.40 Hz, 2H,
H–Ar), 3.95 (s, 2H, CH2), 1.30 (s, 18H, 2 t-Bu); EI-MS m/z
(relative intensity) 312.
Electronic spectra were taken with a Perkin-Elmer Lambda
15 spectrometer; FTIR spectra on a Perkin Elmer FTIR 2000
spectrometer. The apparatus and procedures used in the in-situ
conductivity experiments were previously described in detail.17
QCM measurements were performed with a platinum-coated
AT-cut quartz electrode (0.2 cm2), resonating at 6 MHz, onto
which the polymers were deposited as thin (ca. 10 mg cm22
)
films. Calibration of the quartz crystal microbalance was
performed with silver deposition from a 1022 M solution of
AgNO3 in acetonitrile 1 0.1 M Bu4NClO4. The oscillator
circuit was home-made and the frequency counter was a
Hewlett-Packard mod.5316B. Monitoring of vapor uptake was
performed with the QCM inserted in a cell taking part of a
closed loop of 5 L, flushed with nitrogen by a gas pump
operating at a rate of 2.5 L min21 flow. Vapor additions were
performed by injecting the solvent as a liquid by means of a
microsiringe.
(5-tert-Butyl-2-hydroxyphenyl)-(5-tert-butyl-2-methoxyphenyl)-
methane (13). Sodium metal (112 mg, 4.87 mmol) was dissolved
into a solution of bis(5-tert-butyl-2-hydroxyphenyl)methane
(1.37 g, 4.38 mmol) in dry EtOH (35 mL) under nitrogen at
room temperature. Iodomethane (692 mg, 4.87 mmol) was
added and the solution refluxed for 2 hours at 80 uC. After
removal of the solvent, H2O and Et2O were added and the pH
1 8 1 0
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 1 8 0 4 – 1 8 1 1

View Article Online
ed. Z. Asfari, V. Bo¨hmer, J. McB. Hanonfield and J. Vicens,
Kluwer Academic Publishers, Dordrecht, 2001, p. 612.
L. Mandolini and R. Ungaro, Calixarenes in Action, Imperial
College Press, London, 2000.
Acknowledgements
7
8
T. Benincori is grateful to the Dipartimento di Chimica
Organica e Industriale of the Universita` degli Studi di Milano
for hospitality. S. Rizzo thanks FIRB (Manipolazione mole-
colare per macchine nanometriche) for financial support. Mrs
A. Randi and Mr S. Sitran of CNR are acknowledged for
support in the experimental work.
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