Functional aromatic polyethers: Polymers with tunable chromogenic and fluorogenic properties

Article abstract of DOI:10.1021/ma101106a

This paper describes the preparation and chemical modification of pyranone-based aromatic polyethers to yield polymers that contain pyrylium rings, which permit the design of high performance materials with "a la carte" chromogenic and fluorescence behavior. These materials can be used for innovative applications such as luminescent converter (LUCO) materials for hybrid light-emitting diodes (LEDs) or the preparation of selective chromogenic and fluorogenic sensing materials for the preparation of sensing devices. The fluorescence emission maxima of polyether films ranged from 514 to 561 nm, allowing the future development of LUCO-LED devices. Moreover, the interaction of polyether films with different amines leads to color changes and variations in the intensity and emission maxima of fluorescence, which permits the development of amine sensing materials.

Full text of DOI:10.1021/ma101106a

Macromolecules 2010, 43, 7111–7121 7111
DOI: 10.1021/ma101106a
Functional Aromatic Polyethers: Polymers with Tunable Chromogenic
and Fluorogenic Properties
†
,‡,§
‡,§,
ꢀ
ꢀ
ꢀ~
ꢀ
ꢀ
Ana Gomez-Valdemoro, Ramon Martı
ꢀ
´
nez-Manez,* Felix Sancenon,
a*,†
ꢀ
Felix Clemente Garcıa, and Jose Miguel Garcı
´ ´
†
†
´
Departamento de Quımica, Facultad de Ciencias, Universidad de Burgos. Plaza de Misael Banuelos s/n,
‡
ꢀ
E-09001 Burgos, Spain, Instituto de Reconocimiento Molecular y Desarrollo Tecnologico (IDM),
Centro Mixto Universidad Politeꢀcnica de Valencia, Universidad de Valencia, Spain,
§
´
ꢀ
Departamento de Quımica, Universidad Politecnica de Valencia. Camino de Vera s/n, E-46022, Valencia,
´
Spain, and CIBER de Bioingenierıa, Biomateriales y Nanomedicina (CIBER-BBN), Valencia, Spain
Received May 19, 2010; Revised Manuscript Received July 26, 2010
ABSTRACT: This paper describes the preparation and chemical modification of pyranone-based aromatic
polyethers to yield polymers that contain pyrylium rings, which permit the design of high performance
materials with “a la carte” chromogenic and fluorescence behavior. These materials can be used for
innovative applications such as luminescent converter (LUCO) materials for hybrid light-emitting diodes
(LEDs) or the preparation of selective chromogenic and fluorogenic sensing materials for the preparation of
sensing devices. The fluorescence emission maxima of polyether films ranged from 514 to 561 nm, allowing
the future development of LUCO-LED devices. Moreover, the interaction of polyether films with different
amines leads to color changes and variations in the intensity and emission maxima of fluorescence, which
permits the development of amine sensing materials.
Introduction
chromogenic and fluorogenic functional groups that are widely
used in sensing applications.11-14 The chemical reactions used
Aromatic polyethers are high-performance engineering mate-
rials with excellent thermal stability, good mechanical properties,
and superior hydrolysis and oxidation resistance. Moreover,
aromatic polyethers are characterized by a high glass transition
temperature and/or a high melting temperature. The aromatic
backbone contributes to the thermal stability, whereas the ether
linkages facilitate the oxidative and thermal stability of these
compounds during polymer processing.1-6 Thus, poly(phenylene
oxide), poly(ether sulfone)s and poly(ether ketone)s are commer-
cially important polymers that are often used as matrix materials
in composites or as blends with other polymers.
to modify the polyethers were initially evaluated in polyether
models, and the synthesis and characterization of substituted
polyethers are described in this paper. Although the polyether
models have a defined molecular weight and greater solubility,
it was assumed that each model mimicked the behavior of the
corresponding polymer. Thus, polyether models were used to
study the chromogenic and fluorogenic behavior of the polymers
in solution.15,16
Experimental Section
Functionalization of the polymer core can increase the number
of potential applications of a material, especially in new and
cutting edge fields. For instance, fluorescent chemical moieties
can be introduced into aromatic polyethers to form luminescent
converters (LUCO). These materials can be used in combination
with a primary pumping source for the preparation of LEDs,
which have tremendous potential in lighting and backlighting
applications.7-10 Moreover, if the fluorescent moieties are able to
selectively interact with an analyte, the fluorescence behavior of
the materials could be utilized in chemical fluorescent sensors,
which can be used to detect analytes based on the variation
of light emitted by hybrid LUCO/LEDs devices. Furthermore, if
functionalization gives rise to colored host substructures, inter-
actions with guest analytes may lead to color changes, which is
useful in “naked eye” colorimetric sensing materials.11-14
Because of the aforementioned applications of functionalized
aromatic polyethers, novel aromatic poly and copolyethers with
a pyranone core were prepared. The pyranone moiety was che-
mically modified to yield different pyrylium rings, which are
A description of the materials and the synthetic and character-
ization details of the monomer, polyether models, amine sensing
related molecules, polyethers, and copolyethers can be found in
the Supporting Information.
Measurements and Instrumentation. 1H and 13C NMR spectra
were obtained with a Varian Inova 400 spectrometer operating
at 399.92 and 100.57 MHz, respectively, using deuterated chlo-
roform (CDCl3) or deuterated dimethyl sulfoxide (DMSO-d6)
as solvents. Low-resolution electron impact (EI-LR) mass spec-
tra were obtained at 70 eV using an Agilent 6890N mass spec-
trometer. High-resolution mass spectrometry (HRMS) was con-
ducted on a Micromass AutoSpect Waters mass spectrometer.
Infrared spectra (FT-IR) were obtained with a Nicolet Impact
spectrometer, and elemental analyses were performed with a
LECO CHNS-932 microanalyzer. Inherent viscosities were
measured with an Ubbelohde viscometer at 25 ( 0.1 °C, and
0.5 g/dL of NMP was used as the solvent. Differential scanning
calorimetry (DSC) data were obtained using a Perkin-Elmer
Pyris I analyzer with 10 mg of sample under a nitrogen atmo-
sphere at a scan rate of 20 °C/min. Thermogravimetric analysis
(TGA) data were obtained from 5 mg of sample under a flow of
nitrogen or oxygen using a TA Instruments Q50 TGA analyzer
at a scan rate of 10 °C/min.
*Corresponding authors. (J.M.G.) E-mail: jmiguel@ubu.es. (R.M.-M.)
E-mail: rmaez@qim.upv.es.
r 2010 American Chemical Society
Published on Web 08/12/2010
pubs.acs.org/Macromolecules

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Gomez-Valdemoro et al.
7112 Macromolecules, Vol. 43, No. 17, 2010
Scheme 1. Monomer Synthesis
Table 1. Synthesis of Aromatic Polyethers
UV/vis and fluorescence spectra were recorded on a Varian
Cary3-Bio UV-vis spectrophotometer and a Varian Cary
Eclipse fluorometer, respectively.
with their surroundings and presented no further changes in
weight.
Dense membranes or films of homopolyethers were prepared
by casting the polymers from a solution of NMP (7% w/v).
Copolyether films were prepared by casting a mixture of the
corresponding copolymer and the homopolymer derived from
the homopolymerizaton of 2,6-difluorobenzonitrile and 4,40-
(1-phenylethylidene)bisphenol in NMP. Each film contained
0.04 equiv of pyrylium residue per bisphenol subunit.
Polymer solubility was determined by mixing 10 mg of sample
with 1 mL of solvent, and the resultant solution was stirred for
24 h at room temperature. To prepare polymer films, a solution
of the polymer was cast from DMA, and the solvent was
evaporated. In most cases, a polymer concentration of 10% by
weight was employed, and the solvent was removed by heating
the sample at 100 °C for 4 h in an air-circulating oven and at
120 °C for 4 h under vacuum (1 mmHg).
Results and Discussion
Water sorption experiments were conducted gravimetri-
cally at room temperature. Two hundred milligrams of the
powdered sample was dried at 120 °C for 24 h over phosphorus
pentoxide, and the sample was placed in a closed box containing
a saturated aqueous solution of NaNO2 at 20 °C, which pro-
vided a relative humidity of 65%. The samples were weighed
periodically over a period of 8 days until they equilibrated
This paper describes the synthesis, characterization, and prop-
erties of aromatic poly and copolyethers that contain a pyranone
moiety in the polymer chain, which was incorporated as a
subgroup in one of the monomers used in the preparation of
the polymers. Copolymers containing the pyranone ring were
chemically modified to obtain polymers with tuned chromogenic

Article
Macromolecules, Vol. 43, No. 17, 2010 7113
and photoluminescent properties. Moreover, the selective reac-
tion of modified pyrylium copolymers with amines produced
chemosensing materials: due to their chromogenic and photo-
luminescence behavior, these polymers respond upon interacting
with certain amines.
Model compounds were used to determine the optimal reac-
tion conditions for transformation of the pyranone subgroup into
synthpyrylium substituted rings. Moreover, upon modification,
the models were used as representatives of pyrylium-based
copolymers, and characterization data of the models were helpful
in order to characterize the copolymers. The models also per-
mitted the chemical characterization of the species obtained upon
selective reaction of a variety of amines with the pyrylium
substructure of the copolyethers.
Monomer and Polymer Synthesis. The monomer (4) was
prepared in a straightforward manner from simple, commer-
cially available materials, as shown in Scheme 1. The difluoro
monomer (4) was easily purified by recrystallization from
ethanol, yielding a high purity condensation monomer.
The difluoro monomer (4) was condensed with four
commercially available diphenols following a standard pro-
cedure for the preparation of aromatic polyethers, yielding
four new aromatic pyranone-based polyethers. The structure
of the polymer and the polymerization conditions are shown
in Table 1, and the elemental analyses and viscosities of the
polymers are provided in Table 2. As an example, Figure 1
shows the characterization data of polyether II. The spectra
of monomer 4 and model 5 were used to assign the peaks in
the 1H and 13C NMR of polyether II.
Synthesis and Characterization of the Models. The synth-
esis of polyether model 5 was conducted according to a
synthetic procedure similar to the one used in the prepara-
tion of the polymers (Scheme 2). Difluoro monomer 4 was
reacted with two equivalents of 4-hydroxytoluene, providing
model 5 in good yield and high purity. A phenol with a
methyl group in the para position was used to simplify the
analysis of the NMR spectra.
The pyranone moiety of model 5 was transformed into
four different pyrylium rings (Scheme 3, model 6 to 9). The
pyrylium ring was chosen due to its fluorescent and chro-
momeric properties, and its ability to selectively interact with
different nucleophiles, which is a defining characteristic of
chemosensors. The reaction conditions were optimized to
Scheme 2. Synthesis of the Pyranone Model
Table 2. Inherent Viscosities and Elemental Analyses of the Poly-
ethers
elemental analysis
theoretical
found
polymer
η
inh (dL g-1
)
C (%)
H (%)
C (%)
H (%)
I
II
III
IV
0.23
0.44
0.40
0.24
81.16
82.97
66.10
81.85
5.32
5.08
3.29
5.69
81.37
83.03
66.66
82.68
5.28
5.00
3.62
5.56
Figure 1. Characterization of polyether II: (a) IR-FT, (b) 1H NMR, and (c) 13C NMR (NMR solvent: CDCl3).

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Gomez-Valdemoro et al.
7114 Macromolecules, Vol. 43, No. 17, 2010
Figure 2. 1H NMR and 13C NMR: (a) model 5; (b) model 8 (NMR solvent: CDCl3).
Scheme 3. Synthesis of the Pyrylium Model
obtain the maximum yield and purity. The optimization of the
reaction conditions was very important because these condi-
tions were applied to the copolymers, as described below. As an
example, Figure 2 depicts the NMR spectra of the parent
compound (5) and the modified model (8) and Figure 3 shows
the NMR spectra of corresponding copolymers V and Vc.
Copolymer Synthesis, Modification, and Characterization.
A copolymer containing homopolymer II was prepared from

Article
Macromolecules, Vol. 43, No. 17, 2010 7115
Figure 3. 1H NMR and 13C NMR: (a) copolymer V; (b) copolymer Vc (NMR solvent: CDCl3).
the commercially available diphenol, 4,40-(1-Phenylethylide-
ne)bisphenol, and from the difluoro comonomers 2,6-di-
fluorobenzonitrile and 2,6-bis(4-fluorophenyl)-4H-pyran-
4-one (4) (Scheme 4). Because the copolyether was insoluble
in CHCl3 and other polar aprotic solvents under stoichio-
metric conditions, the polymer was prepared with a 4%
excess of bisphenol to obtain a theoretical average degree
of polymerization (Xn) of 25.
To obtain materials that could be used in sensing or optical
applications, the ratio of comonomers was selected to obtain
soluble polymers with an appropriate number of pyranone
groups, which were subsequently transformed into pyrylium rings.
Functional copolyether V was transformed into pyrylium-
based polymers by reacting the pyranone ring with different
reagents. The synthesis was conducted according to the
optimized conditions, which were obtained through the
modification of polyether model compound 5. Following
this approach, copolyether V was transformed into copo-
lyethers Va, Vb, and Vc (Scheme 5). The chemical modifica-
tion could be followed by NMR, as depicted in Figure 3 for
copolymer Vc.
Properties of the Polymers. Thermal Properties. The
thermal behavior of the polyethers and copolyethers was
evaluated by DSC and TGA. The polyethers possessed high
glass transition temperatures (Tg), from 209 to 238 °C, whereas
the Tg of copolyethers ranged from 181 to 200 °C (Table 3).
The Tg of homopolyethers with a 4-pyranone subgroup in
the polymer backbone was higher than the Tg of related poly-
ethers synthesized by the polycondensation of activated aro-
matic dihalides such as 2,6-dihalobenzonitrile and bisphenol
A or bisphenol AF, which have a Tg of 180 °C.17 On the other
hand, the Tg of copolyether V was less than the Tg of other
homopolyethers, indicating that molecular order and regularity
had a strong effect on the glass transition temperature.

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Gomez-Valdemoro et al.
7116 Macromolecules, Vol. 43, No. 17, 2010
Scheme 4. Synthesis of Copolyethers
Scheme 5. Synthesis of Pyrylium-Based Copolyethers
The transformation of pyranone moieties to pyrylium
rings had little effect on the Tg of the polymer due to the
low molar percent of the pyrylium subunits. Moreover, the
Tg of the copolymers was similar due to two counteracting
effects in the thermal transition. Namely, the pyrylium ring is
more polar and possesses a greater lateral volume than the
pyranone moiety, which impairs interchain interactions.
In DSC experiments, an endothermic peak corresponding to
the melting temperature of the polyethers was not observed,
indicating that the polymers are amorphous. Moreover, in
wide-angle X-ray scattering (WAXS) experiments, all of the
polymers except for polyether IV displayed an amorphous
pattern with a small semicrystalline peak and a dominant
amorphous halo. The WAXS measurements were carried out
with as obtained polymers, meaning that the development or
not of crystalline regions upon annealing was not verified.
The results of thermogravimetric analysis, summarized in
Table 3, confirmed that the aromatic polymers were heat
resistant materials. Thus, the temperature corresponding to
10% weight loss (T10) of the homopolyethers was greater
than 400 °C under a nitrogen and oxygen atmosphere. Figure
4 depicts the TGA degradation pattern of polyether III,
which possessed the highest decomposition temperature, due
to the presence of halide atoms.

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Macromolecules, Vol. 43, No. 17, 2010 7117
Table 3. Thermal DSC and TGA Data of the Polymers and Copolymers
TGA
N2 atmosphere
O2 atmosphere
polymer
DSC Tg (°C)
T5a (°C)
T10b (°C)
char yieldc (%)
T5a (°C)
T10b (°C)
LOId
I
II
III
IV
236
238
209
219
404
410
412
383
437
454
462
425
47
50
55
43
386
396
398
383
422
430
433
420
36.3
37.5
39.5
34.7
TGA
N2 atmosphere
O2 atmosphere
T5a (°C)
T10b (°C)
char yieldc (%)
T5a (°C)
T10b (°C)
LOId
copolymer
DSC Tg (°C)
V
193
200
192
181
383
409
278
263
428
463
390
379
38
46
41
44
362
410
284
271
430
467
410
371
32.7
35.9
33.9
35.1
Va
Vb
Vc
a Temperature at which 5% weight loss was observed. b Temperature at which 10% weight loss was observed. c Residue (wt %) at 800 °C. d Calculated
limiting oxygen index (LOI).
Table 4. Solubility of the Polymersa
polymer
DMSO
DMF
NMP, DMA
m-cresol
CHCl3
CH
THF
dioxane
AcOH, acetone
I
II
III
IV
þ
þ
þ
þ
þ -
-
þþ
þþ
þþ
þ
þþ
þþ
þþ
þþ
þ -
þþ
-
þ -
þ
þ -
þ -
þ -
þ -
þ -
þ -
þ -
-
þ -
-
þþ
þþ
þ
þ -
þ
DMF
þ -
-
copolymer
DMSO
NMP, DMA
m-cresol
CHCl3
CH
THF
dioxane
AcOH, acetone
V
þþ
þþ
-
þþ
þþ
þ
þþ
þþ
þ
þþ
þþ
-
þþ
þþ
-
þ
þ
-
-
þ -
þ -
-
þ -
þ -
þ -
þ -
þ -
þ -
-
Va
Vb
Vc
-
þ
þ
-
-
-
-
a Key: DMSO = dimethyl sulfoxide; DMF = dimethylformamide; NMP = N-Methyl-2-pyrrolidone; DMA = dimethylacetamide; CH =
cyclohexanone; þþ = soluble at room temperature; þ = soluble upon heating; þ- = partially soluble; - = insoluble
Table 5. Water Absorption of the Polyethers
polymer
water uptake (%)
molecules of H2O/repeating unit
I
II
III
IV
1.6
2.7
5.2
6.1
0.42
0.79
1.67
1.75
copolymer
water uptake (%)
molecules of H2O/repeating unit
V
3.6
4.7
2.9
2.7
--
--
--
--
Va
Vb
Vc
with this equation were greater than 32, indicating that the
polymers can be classified as self-extinguishing (LOI is defined
as the minimum fraction of oxygen in an oxygen and nitrogen
atmosphere that will support combustion after ignition. Air
contains approximately 21% oxygen; thus, a material with a
LOI less than 21 will not burn under open air conditions).
Solubility. The solubility of the copolymers is shown in
Table 4. The polyethers were soluble enough to allow trans-
formations to be conducted in solution (i.e., casting to yield
films, dense membranes or enamels). The solubility of
copolymer V was significantly greater than the solubility
of the homopolyethers because the polymer chains of the
copolymer were asymmetric. Moreover, the use of nonequi-
molecular concentration of comonomers led to a lower mole-
cular weight, which increased the solubility (see Experimen-
tal Section). Surprisingly, the chemical modification of
copolymer V to yield copolymers Vb and Vc dramatically
decreased the solubility; however, this effect was not ob-
served with copolymer Va.
Figure 4. TGA of polyether III under an atmosphere of nitrogen and
oxygen (w.l.: percent weight loss).
The chemical modification of the pyranone subunit to
pyrylium rings slightly increased or drastically decreased the
T10, depending on the substitution on the pyrylium ring. The
T10 displayed a slight increase when small and polar func-
tional groups such as hydroxyl were introduced onto the
pyrylium ring. Alternatively, the latter effect was observed
with bulky organic substituents such as phenoxazin or
phenothiazin moieties.
The char yield at a given temperature is intimately related to
the thermal behavior of the polymers. The results indicated
that the char yield of the polymers was greater than 38% at
800 °C under a nitrogen atmosphere. With the Van Krevelen
equation, the char yield can be used to estimate the limiting
oxygen index (LOI) of the polymers (LOI=17.5 þ 0.4 CR,
where CR is the char yield in % weight).18 The LOI obtained

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Gomez-Valdemoro et al.
7118 Macromolecules, Vol. 43, No. 17, 2010
Figure 5. (a) Solutions of models 6, 7, and 8 (from left to right) in NMP (5 ꢀ 10-3 M); (b) solution of copolyethers Va, Vb, and Vc (from left to right) in
NMP (5 ꢀ 10-3 equivalents of pyrylium per liter of NMP); (c) films of copolymers Va, Vb, and Vc (from left to right).
Table 6. Fluorescence Emission Maxima (nm) of Copolymers and
Models
Polymers and models displayed fluorescence behavior,
where the maximum fluorescence emission was observed
between 476 and 597 nm (Table 6). Figure 6 depicts the
fluorescence spectra of the models and copolymers in solu-
tion, and Figure 7 illustrates the fluorescence behavior of
the copolymers in solution and in the solid state. Moreover,
the batochromic shift and broaden of the emission band
of the films with respect to the solutions, ascribed to the
inter and intrachain interactions in the solid state, is shown
in Figure 7.19 The films, especially polymer Vb, displayed
fluorescence emission maxima at the wavelength of yellow
light, which allows these materials to be combined with a
blue LED pumping source to yield white lighting for lighting
and backlighting applications. Currently, investigations on
the use of pyrylium polymers in LED applications are under-
way. Nevertheless, further improve in the polymer structure
are needed to achieve material with commercial application
in the field of LUCO technologies because the quantum yield
of the polymers and models is lower than 0.1.
Sensing Behavior of Copolyether Films. Once the charac-
terization of functional polymers was complete, a prelimin-
ary study was conducted to investigate the use of polymer
films as chemosensing materials. Previous research has
shown that pyrylium rings can react with amines to produce
color changes and fluorescence modulations, which may be
useful for the design of optical chemosensors.20 The deter-
mination of toxic substances such as amines has become
relevant in recent years.21-23 For instance, amines are used in
fertilizers and in the pharmaceutical and dye manufacturing
industries. Moreover, amines can be found in industrial
wastewater. Common methods for the detection and deter-
mination of amines include chromatographic methods,24-26
potentiometric techniques,27-30 piezoelectric sensors and quartz
crystal microbalances.31,32 An alternative to these high-cost
techniques is the development of optical sensors for the in situ
and rapid identification of amines.33,34
λemission, nm
models
λexcitation, nm
solution
solid state (film)
6
7
8
362
452
504
476
526
597
--
--
--
λemission, nm
copolymers
λexcitation, nm
solution
solid state (film)
Va
Vb
Vc
364
452
504
469
520
553
514
528
561
Water Sorption. The hydrophilic or hydrophobic charac-
ter of organic molecules arises from the presence or absence
of hydrophilic groups. In the aromatic polyethers, the ether
linkage is not highly polar and water uptake is low, as shown
in Table 5. The water uptake of the polymers can determine
the final application of the materials because absorbed water
decreases the Tg and affects the mechanical, electrical and
dielectrical properties of the material. For instance, mem-
branes with selective chromogenic or fluorogenic groups
can be used as sensing materials in aqueous environments,
where greater water uptake leads to superior performance
because the diffusion of guest molecules or analytes into
a swollen polymer matrix is improved. This effect is signifi-
cant because sensing occurs in the polymer matrix, where
solvated analytes and the sensing moiety of the polymeric
material interact.
The water uptake of copolyether V was 3.6%, which
was greater than the water absorption of polyether I but
less than the uptake of polyether IV. The water uptake
results indicated that substitution on the pyrylium rings
affected the amount of water absorbed by the polymer.
Specifically, polymers containing hydroxypyrylium rings
displayed the greatest water uptake (Va). Dense mem-
branes or films of the copolymers were used to test the
materials as colorimetric sensors for amines, as described
below.
Copolyether Vb was further evaluated in sensing studies.
Changes in the color or fluorescence of this film were tested
in the presence of butylamine, dibutylamine, triethylamine
and aniline, as well as OH-, CO32-, HCO3-, CN-, SCN-,
H2PO4-, F-, Cl-, Br-, I-, acetate, and benzoate, which were
dissolved in solutions of H2O:CH3CN (60:40 v/v). The
chromomeric response of the polymer to the aforementioned
analytes is depicted in Table 7. The color of the film changes
in the presence of primary and secondary amines including
butylamine and dibutylamine, whereas tertiary amines, aro-
matic amines and a number of anions did not induce a color
change. Figure 8 shows the UV-vis spectra of Vb in the
absence and presence of butylamine. Besides the change in
Chromogenic and Fluorescence Behavior. The chromogenic
and fluorescence behavior of high performance polymers is a
fundamental property that is necessary for applications such
as chromogenic and fluorogenic sensing materials and hybrid
LUCO/LED emitting devices.
Solutions of models 6-8 and copolymers Va-Vc in solution
and in the solid state ranged from colorless to deep green
(Figure 5).

Article
Macromolecules, Vol. 43, No. 17, 2010 7119
Figure 6. Fluorescence emission of pyrylium models (left) and pyrylium polyethers in solutions of NMP (right). The sharp fluorescence peak observed
at ca. 500 nm for polymer Vb corresponds to Rayleigh’s diffraction.
Figure 8. UV-vis spectra of copolyether Vb upon soaking the film in
a 5 ꢀ 10-2 M solution of butylamine in H2O:CH3CN (60:40 v/v). The
Figure 7. Fluorescence emission spectra of copolymer Va in solutions
of NMP (continuous lines) and in the solid state (film).
film was immersed in the solution for 24 h, which caused the polymer to
swell by 16% (by weight). Similar spectra were obtained in the presence
of dibutylamine.
Table 7. Chromogenic Response of Copolyether Vb upon Immersing a
Film of the Polymer in Solutions of H2O:CH3CN and Several Amines
or Anions for 30 min (the Images Correspond to Pictures of the Films
Taken with a Digital Camera)
Figure 9. Fluorescence emission spectra of copolyether Vb upon soak-
ing the film in a 5 ꢀ10-2 M solution of butylamine in H2O:CH3CN
(60:40 v/v). The film was immersed in the solution for 24 h, which
caused the polymer to swell by 16%.
the other hand, primary and secondary amines behave as
nucleophiles in aqueous solution, leading to pseudobase for-
mation that, in the case of primary amines, may lead to the
formation of a pyrydinium salt (Scheme 6).35-37
To study the chromogenic response of pyrylium copolyether
Vb to specific amines, the reactivity of model compound 7 was
studied in the presence of butylamine. Upon reacting 7 with
butylamine, a compound containing a pyrydinium ring was
formed (10) (see Scheme 7). The product was isolated and
fully characterized by 1H and 13C NMR. Figure 10 shows the
UV-vis spectra of pyrylium (7) and pyrydinium (10) deriva-
tives in H2O:CH3CN (60:40 v/v). Compound 7 shows a visible
band at 650 nm that is similar to the band observed in polymer
color, a modulation in the fluorescence behavior of the film
(see Figure 9) was observed, where green fluorescence was
transformed into orangish/red emissions.
To interpret the chromo-fluorogenic behavior of copo-
lyether Vb, one must consider that the R or γ position of the
pyrylium ring reacts with nucleophiles to afford a variety of
acyclic or cyclic products. Attack at the R position is preferred
because this site is more electron deficient than the γ position.
Under basic or acidic conditions, nucleophilic attack in aqu-
eous solution leads to the diketone, as shown in Scheme 6. On

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Gomez-Valdemoro et al.
7120 Macromolecules, Vol. 43, No. 17, 2010
Scheme 6. Reaction of Pyrylium Rings with Nucleophiles
of pyrylium rings to pyrydinium moieties. Moreover, the chro-
mogenic response of the polymer to secondary amines leads to
similar UV-vis spectra. Primary amines and pyrylium groups
present in the polymer film react to form a divinylogous amide,
which also occurs with secondary amines.
Conclusion
In this study, the synthesis and characterization of eight new
fluorescent polyethers, copolyethers and polyether models was
achieved. The pyranone ring in the polymers could be chemically
transformed into substituted pyrylium groups, which can be used
as chromogenic and fluorogenic receptors in supramolecular
chemistry.
Figure 10. UV-vis spectra of a 2.5 ꢀ 10-5 M solution of pyrylium
model 7 and pyrydinium 10 in H2O:CH3CN (60:40 v/v).
The parent copolyether can be easily modified to yield pure,
high performance polyethers with “a la carte” fluorescent and
chromogenic properties. The inherent difficulty associated with
clean and high yielding chemical modifications of polymers was
overcome by optimizing the reaction conditions with polyether
models. Upon determining the optimal conditions, the reactions
were applied to functional polymers, and the desired chemical
modifications were effected. The influence of the pyranone and
pyrylium rings was evaluated, and the thermal properties, solu-
bility and water uptake of the polymers was determined.
In short, a clean and easy preparation of functional polymers
was achieved, and the synthesis of high value, high performance
materials was attained by subsequent modification of parent poly-
mers. The results of this study suggested that the characteristics of
these materials are applicable to innovative technologies associated
with the fluorescence and chromogenic characteristics of the pyry-
lium moiety. Moreover, the host behavior of pyrylium rings can be
applied to the fluorescent and chromogenic-naked eye-sensing of
amines or hybrid luminescent converter (LUCO) and LED systems.
Further investigations on the applications of the polymers are cur-
rently in progress.
Scheme 7. Synthesis of the Pyrydinium Model
Vb (see Figure 8). In the presence of butylamine, this band
disappears due to the formation of pyrydinium derivative 10.
Similar behavior (i.e., the disappearance of the visible band at
650 nm) was observed for Vb in the presence of butylamine,
suggesting that the chromogenic response of the polymer was
due to the transformation of the pyrylium ring to a pyrydinium
moiety. Finally, the color of polymer Vb changed in the presence
of dibutylamine. As shown in Scheme 2, the reaction between
a pyrylium ring and a diamine is expected to result in the
formation of a divinylogous amide. Moreover, the rupture of
the pyrylium ring is expected to cause the band at 680 nm to
disappear; thus, the formation of the divinylogous amide is in
agreement with the observed color change. The reactivity of the
pyrylium ring is also in agreement with the lack of reaction in the
presence of triethylamine, a tertiary amine.
Acknowledgment. The authors gratefully acknowledge finan-
cial support provided by the Spanish Ministerio de Ciencia
ꢀ
e Innovacion (MICINN);Feder (MAT2008-00946/MAT and
MAT2009-14564-C04-01), the Caja de Burgos, and the General-
itat Valencia (project PROMETEO/2009/016).
Supporting Information Available: Text giving synthetic
details and characterization of the monomer, polyether models, amine
sensing related molecules, polymers, and copolymers. This material
is available free of charge via the Internet at http://pubs.acs.org.
The results indicated that the chromogenic response of pyryli-
um films toward primary amines was due to the transformation

Article
Macromolecules, Vol. 43, No. 17, 2010 7121
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