Multistimuli-responsive benzothiadiazole-cored phenylene vinylene derivative with nanoassembly properties

Article abstract of DOI:10.1021/la200382b

A trifluoromethyl-substituted benzothiadiazole-cored phenylene vinylene fluorophore (1) was synthesized and displayed piezo-and vapochromism and thermo-induced fluorescence variation in solid phase. Grinding could disrupt the crystalline compound 1 with o

Full text of DOI:10.1021/la200382b

ARTICLE
pubs.acs.org/Langmuir
Multistimuli-Responsive Benzothiadiazole-Cored Phenylene
Vinylene Derivative with Nanoassembly Properties
Chuandong Dou, Dong Chen, Javed Iqbal, Yang Yuan, Hongyu Zhang,* and Yue Wang*
State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, Changchun 130012,
People’s Republic of China
S Supporting Information
b
ABSTRACT: A trifluoromethyl-substituted benzothiadiazole-cored
phenylene vinylene fluorophore (1) was synthesized and displayed
piezo- and vapochromism and thermo-induced fluorescence variation
in solid phase. Grinding could disrupt the crystalline compound 1 with
orange emission into amorphous compound 1 with green emission,
and heating treatment could change the amorphous compound 1 into
crystalline compound 1. Ultravioletꢀvisible (UVꢀvis) absorption
spectra, 13C nuclear magnetic resonance (NMR), and powder X-ray
diffraction (PXRD) characterizations demonstrated that crystalline
and amorphous compound 1 possess different molecular packing. A
differential scanning calorimetry (DSC) measurement revealed that
the emission switching was due to the exchange between the thermo-
dynamic-stable crystalline and metastable amorphous states. The
ground sample exhibited vapochromic fluorescence property. Further-
more, compound 1 showed interesting supramolecular assembly
characteristics in solution. Slowly cooling the hot N,N-dimethylforma-
mide (DMF) solution of compound 1 resulted in the formation of
orange fluorescent fibers, whereas sonication treatment of the cooling solution led to the generation of organic molecular gel. The
field emission scanning electronic microscope (FESEM) and fluorescent microscopy images revealed smooth nano- or microfiber
and network morphology properties. The PXRD spectra confirmed that these nano- or microstructures had a similar molecular-
packing model with the crystalline state of compound 1. Slow evaporation of the toluene solution of compound 1 could produce
green emissive microrods, which exhibited interesting thermo-induced fluorescence variation.
’ INTRODUCTION
molecular structure was based on the following design principles:
First, the benzothiadiazole group was chosen because it repre-
sents one of the most active luminescent units in various
optoelectronic materials.9 Second, the bulky CF3 groups were
expected to dramatically affect the molecular-packing modes in
solid states.10 Third, the rod-like conformation endowed this
molecule with abundant aggregation modes by noncovalent
πꢀπ interactions and hydrogen-bonding interactions. Com-
pound 1 shows obvious piezochromic luminescence by grinding
stimuli as well as vapochromic emission upon exposure to
organic vapors. With this molecule being responsive to different
environmental stimulus, such as solvent, temperature, and ultra-
sound, it gives interesting supramolecular nanoassembly proper-
ties. The thermal reversible one-dimensional (1D) fibers and
ultrasound-induced organogel11 with a three-dimensional (3D)
fibrous network were generated from N,N-dimethylformamide
(DMF) solution of compound 1. Although the use of ultrasound
The organic piezo-, vapo-, and thermochromic materials that
display reversible stimuli-responsive color and emission switch-
ing in solid phases are attracting considerable attention because
of their important basic science interest and potential applica-
tions in sensors, displays, and memory fields.1ꢀ3 Sagara et al.,4
Kunzelman et al.,5 and Ito et al.6 have reported piezochromic
luminescence behaviors of some small organic compounds by
tuning molecular packing. Takahashi et al.3b recently documented
a vapochromic organic crystal, which exhibited molecular-shape-
dependent color changes upon exposure to organic vapors. We
revealed that trifluoromethyl-substituted aromatic amine deri-
vatives displayed reversible thermo-induced phase transforma-
tion accompanied by luminescence switching.3e Although some
novel molecular systems possessing efficient reversible lumi-
nescence switching behaviors have been reported, it is still an
important issue to develop the fluorophores with multichro-
mism properties.7
In this paper, a trifluoromethyl-substituted benzothiadiazole-
cored phenylene vinylene derivative 1 (Scheme 1) was presented
according to the studies reported by An et al.8 Our proposed
Received: January 28, 2011
Revised:
March 31, 2011
Published: April 13, 2011
r
2011 American Chemical Society
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Scheme 1. Synthesis of Compounds 1 and 2a
Figure 2. (Left) UVꢀvis absorption and (right) emission profile of the
a (I) 4-Formylphenylboronic acid, Pd(PPh3)4, Na2CO3/H2O, and
THF. (II) 3,5-Bis(trifluoromethyl)-phenylacetonitrile or phenylaceto-
nitrile, TBAOH/H2O, tert-butyl alcohol, and THF.
solution and unground, ground, and heated solids.
Piezochromic Behavior. Recrystallization of compound 1 from
a mixture of chloroform and petroleum ether (1:1, v/v) or
vacuum sublimation resulted in an orange powder with bright
orange luminescence (Figure 1a). Interestingly, after a spatula or
pestle was used for simple grinding, this sample changed into a
yellow solid that emitted a green fluorescence (Figure 1b), and
the ground sample recovered its original orange color and
luminescence by heating at about 100 °C for 1 min. Tempera-
ture-dependent emission spectra of the ground sample indicated
that the fluorescent transition temperature was about 100 °C
(Figure S3 in the Supporting Information). Upon heating to
100 °C, the emission wavelength of the ground sample changed
from 545 to 573 nm, and after cooling to room temperature, the
sample showed an emission peak at 591 nm. The reversible
switching of the emission wavelength can be easily realized by
the repeated performance of grinding and heating processes
(Figure S4 in the Supporting Information).
Figure 1. Stimuli-responsive behaviors of compound 1 upon grinding
and heating treatments (under UV lamp, λex = 365 nm).
waves to trigger the formation of gels has received wide attention
since the groundbreaking work reported by Naota and Koori,
limited compounds with optical and electronic properties have
been fabricated into organogel induced by ultrasound stimuli.12
Moreover, evaporation of the toluene solution generated green
fluorescent microrods, which exhibited pronounced thermo-
induced fluorescence variations. Chung and co-workers have
recently reported many cyano-substituted arylene vinylene-type
compounds and studied their aggregation-induced emission
(AIE) phenomenon, assembly properties, and stimuli-responsive
behaviors.13 These compounds are usually non-emissive in
solution and exhibit bright fluorescence in aggregation states.
The difference between our molecule and the molecule reported
by Chung et al. is that the present molecule has two individual
cyano-substituted phenylene vinylene units, which were bridged
by a fluorescent benzothiadiazole core. The introduced ben-
zothiadiazole unit endows this compound with bright emission
even in dilute solution.
Figure 2 showed ultravioletꢀvisible (UVꢀvis) absorption and
emission spectra of compound 1 in various states. The dilute
chloroform solution (1 ꢁ 10ꢀ5 M) exhibited an absorption
maximum at 402 nm and intensive fluorescence at 488 nm. The
ground sample displayed an absorption maximum at 422 nm and
green fluorescence at 545 nm. The heated sample exhibited a
broad absorption band below 540 nm, the highest intensity at
323 nm, and a shoulder at 430 nm. The unground solid and
heated sample exhibited an orange emission at around 591 nm.
In the absorption spectrum of the solution, the low-energy
absorption bands below 540 nm, which were very similar to that
of the reported benzothiadiazole-cored phenylene vinylene
derivatives, are assigned to π f π* transitions.15 The experi-
mental and theoretical works16 have demonstrated that, in the
aggregated states, the different aggregation models of aromatic
π systems may result in different changes of the absorption and
emission bands; in general, strong intermolecular πꢀπ interac-
tions commonly induce obvious red-shift absorption and fluo-
rescence because of exciton delocalization. In comparison to the
monomer state, the red-shift absorption bands of the ground and
heated samples suggested that different aggregation modes were
possibly formed in these two samples. More red-shift fluores-
cence of the heated sample should be induced by much stronger
’ RESULTS AND DISCUSSION
Synthesis and Characterization of Compound 1. Com-
pound 1 was synthesized from the precursor dibromobenzothiadia-
zole via Suzuki coupling with 4-formylphenylboronic acid and then
followed by the Knoevenagel reaction with 3,5-bis(trifluoromethyl)-
phenylacetonitrile.14 The obtained compounds were characterized
by 1H nuclear magnetic resonance (NMR), 13C NMR, mass spectra,
and element analyses. 1H NMR spectra revealed that their molecular
geometries are all centrosymmetric in solution (Figures S1 in the
Supporting Information).
πꢀπ interactions and closer chromophoric packing.17 The 13
C
NMR measurements were performed on the solution and solid
states (Figure 3). As shown, the signal of the carbon atom that
connects the cyano group appeared at 109.4 ppm in solution and
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Figure 3. Solution and solid-state 13C NMR spectra at different states.
Figure 5. Vapochromism of the ground sample under different organic
vapors (excited at 365 nm): (a) ether (1 min or even longer), (b) THF
(0.5 h), (c) THF (1 min), and (d) THF (0.5 h).
To obtain insight into the solid-state molecular packing as well
as phase transition of the present compound, powder X-ray
diffraction (PXRD) and differential scanning calorimetry (DSC)
experiments were performed. As shown in Figure 4a, the diffrac-
tion pattern of the unground solid clearly exhibited sharp and
intense reflections, indicating a microcrystalline-like structure.4,6
In contrast, the ground solid did not give any noticeable
diffraction in the XRD profile, reflecting its amorphous feature
in this state. A reversion from the amorphous to original crystal-
line state took place, because the diffraction peaks of the heated
sample appeared similar to those before grinding. Thus, the
transformations between the orange and green fluorescent
samples might be accomplished by the change of molecular
packing between a well-defined state and a poorly organized
phase through treatments of grinding (disruption of molecular
packing) and heating (self-reparation of molecular packing). The
ground and heated samples have similar melting points at 305 °C
(Figure 4b). When the amorphous ground sample was heated, it
first experienced an exothermic recrystallization process at
relatively low temperature (about 95 °C) and then melted at
the temperature identical to the melting point of the heated
sample. These observations suggest that the grinding could
convert the thermodynamically stable crystalline sample to a
metastable state, which could be restored to the original crystal-
line state through an exothermic process.20
Figure 4. (a) PXRD and (b) DSC profiles of compound 1 at solid
phases.
shifted to 106.5 ppm in the heated sample. Such an upfield shift
could be considered to reflect the πꢀπ interactions in the
aggregated state.18 Grinding this solid sample resulted in broa-
dened 13C NMR signals; notably, the signal corresponding to the
carbon atom mentioned above downfield-shifted to that of the
solution sample, which was possibly due to the destruction of
πꢀπ interactions by grinding treatment.19 Another possibility
regarding the color and luminescence change is that the grinding
treatment leads to the variation of molecular conformation,
hence, the change of color and fluorescence.
Vapochromic Behavior. Another notable feature of the
present compound is that the ground sample shows pronounced
vapochromic luminescence. As shown in Figure 5, after exposure
of the ground solid i to saturated ether vapor for about 1 min or
even longer, the fluorescence changed from green to orange
(a process, sample ii). Exposing this in-situ-formed orange sample
to tetrahydrofuran (THF) vapor for over 0.5 h generated an
intensive green emissive powder (b process, sample iv). Exposure
of the ground solid to THF vapor for about 1 min also led the
fluorescence to orange (c process, sample iii), and the color of
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Figure 6. Emission wavelength of the repeated vapochromic behavior
by grinding (around 545 nm) and exposing to ether (around 592 nm)
treatments (excited at 365 nm).
the formed orange sample further converted to green when the
exposure time was long enough (over 0.5 h, d process). After the
produced green emissive sample iv was ground, the conversion of
vapochromic luminescence could be readily repeated. The
reversibility of emission changes was confirmed by the repeated
grindingꢀvapor exposing processes (Figure 6 and Figures S5 and
S6 in the Supporting Information). The emission peaks of the
orange and green states appeared at 592 and 545 nm, respec-
tively, and the two emissive states could be easily and mutually
switched. XRD and thermogravimetric analysis (TGA) experi-
ments have been performed on the samples exposed to the
solvent vapors. As shown in the XRD spectra (Figures S7 in the
Supporting Information), the samples obtained after exposure to
ether and THF vapors are two crystalline states with obviously
different diffraction patterns. The orange material from ether
vapor exhibited the same XRD pattern as the heated solid,
suggesting that they have similar molecular-packing structures.
TGA curves (Figures S8 in the Supporting Information) showed
that the green sample from THF vapor lost 4.40% in weight
between 129 and 156 °C, while the orange sample did not exhibit
such a transition process. The lost weight can be attributed to the
loss of THF vapor molecules, and the mole ratio (THF/
compound 1) calculated from the weight is about 1:2. Thus,
the vapochromic behavior is actually a molecular-repacking
process that, in ether, the ground solid assembled into an orange
crystalline state. In THF vapor, the ground sample first as-
sembled into an orange crystalline state and then adsorbed
solvent molecules to generate a green emissive crystalline solid.
The vapochromic experiments have been performed using differ-
ent organic solvents. Toluene, dichloromethane, and chloroform
gave similar results to THF, while acetic acid, triethylamine,
methanol, ethanol, ethyl acetate, and petroleum ether showed
similar phenomenon to ether. Comparing these two groups of
solvents, we found that compound 1 has better solubility in the
former set of solvents and this set of solvents probably provides
similar vapor environments with THF.
Figure 7. (i) Stimuli-responsive gelation properties of compound
1 in DMF solution upon heating and ultrasound treatments (under
UV light, λ = 365 nm). FESEM and fluorescent microscopy images
of the assembled structures: (a and b) xerogel from DMF gelation,
(cꢀe) fibers from DMF solution, and (f) emission spectra of two
superstructures.
building block to construct organic fibers and gel with a stimuli-
responsive characteristic. When the hot solution of compound 1
in DMF (80 °C, 0.85 wt %) was left at room temperature for over
0.5 h, some organic fibers were gradually formed in the solution,
suggesting that compound 1 has 1D assembly abilities based on
noncovalent intermolecular interactions. Interestingly, after the
DMF solution was quickly cooled to room temperature in the
water bath (25 °C, 1 min) and then sonication (0.45 W/cm2, 40kHz,
30 s) was exerted, the homogeneous solution turned into an opaque
viscous state and formed a stable organogel, immediately (Figure 7i).
Upon excitation with UV light, the sol and gel states exhibit strong
bright green and yellow fluorescence, respectively.
A fluorescence microscope and field emission scanning elec-
tronic microscope (FESEM) were used to study the morpholo-
gies of the fibers and xerogel in this study (panels aꢀe of
Figure 7). FESEM images clearly showed that the width of the
formed fibers was about 2ꢀ5 μm, and these fibers were hier-
archically assembled from many thinner fibers with the diameter
of about 100 nm, as shown in the amplified image (Figure 7e).24
The xerogel gave a smooth fibrous network, with the width in the
range of 500ꢀ1000 nm. As shown in Figure 7f, the fibers and
xerogel gave an intensive orange emission, with the peak
centered at 583 nm. The PXRD spectra (Figure 8) of the fibers
and xerogel show an identical diffraction pattern, which is similar
to that recorded for the unground and heated samples. There-
fore, the fibers and xerogel have a similar molecular-packing
Supramolecular Assembly of Fibers and Gelation. Molec-
ular fibers and gels as classes of important supramolecular system
have been intensively studied because of their potential applica-
tions as functional materials.21ꢀ23 Compound 1 displayed novel
supramolecular assembly properties and could be employed as
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Figure 8. XRD measurements of the assembled fibers and xerogel
from DMF.
Figure 10. PXRD measurements of the different superstructures.
does not form fibers or gel in the test solvents. A fluorescence
microscope image showed that the solid of compound 2 pro-
duced by slowly evaporating the CHCl3 solution was composed
of short green emissive microcrystals, while that of compound 1
was constructed by many long orange fluorescence fibers (Figure
S10 in the Supporting Information). In addition, the ground solid
of compound 2 cannot respond to organic vapors. All of these
results suggested thatthe introduced CF3 groups play an important
role in impacting the manner of assembly and stimuli-responsive
behaviors of compound 1.
Thermo-induced Fluorescence Variation. Upon natural
evaporation of the solution of compound 1 in toluene (6 ꢁ
10ꢀ4 M) on the glass substrates at room temperature, some
green fluorescent microrods were gradually formed (Figure 9a).25
The microrods exhibited thermo-induced fluorescence variation
behavior, as shown in Figure 9b. The heating treatment of the
microrods at 220 °C for 10 min resulted in remarkable fluores-
cence transition from green (550 nm) to orange (592 nm)
(Figure 9d). The orange microsolids exhibited a similar XRD
pattern to that of the unground or heated sample and also
possessed piezochromic fluorescence property (Figure 9c). The
XRD patterns of the green microrods and orange microsolids
gave obviously different diffraction patterns, suggesting that
two kinds of molecular-packing modes existed in the green and
orange crystalline microstructures (Figure 10). In the DSC profile
of the microrods, a broad endothermic band at around 145 °C
was observed, consisting with the observation of the phase transition
temperature at 150 °C (Figure S11 in the Supporting Information).
As shown in the TGA curve (Figure S7 in the Supporting Infor-
mation), the microrods lost 5.60% in weight between 150 and
167 °C, which can be attributed to the loss of toluene molecules, and
the mole ratio (toluene/compound 1) calculated from the weight is
about 1:2. These microrods are crystalline, but they certainly contain
toluene molecules, which are inserted within the molecular stacks.
The observed thermo-induced microstructure and emission varia-
tions are due to the departure of solvent molecules from the green
microrods.
Figure 9. Fluorescent microscopy images: (a) microrods, (b) heated
microrods, (c) microsolids upon grinding, and (d) emission spectra.
model to that of unground and heated samples. For the slow
coolingprocessofhot solution, the molecular nuclei shouldappear
at the supersaturation state and the molecules stacked with each
other to form the thin fiber units that hierarchically assembled into
largerdimensionalfibers. Sonication ofthe solution could drivethe
molecules to contact each other more quickly and induced a large
amount of nuclei, which spontaneously aggregated into a fibrous
network, immediately. Thus, the ultrasound stimulus played an
important role in the instant formation of gelation. The formed
fibers and xerogel film also showed that the piezochromism
accompanied by fluorescence changes between orange and green
(Figure S9 in the Supporting Information).
As reported by An et al., this type of molecule is likely packed
in a J-packing fashion in the aggregation state by an intermole-
cular πꢀπ interaction, which was further stabilized by a Cꢀ
H
FꢀC hydrogen bond.8b To illuminate the influence of the
3 3 3
’ CONCLUSION
CF3 groups on the assembled structures as well as the stimuli-
responsive behaviors, we have synthesized an analogue com-
pound 2 by replacing CF3 with H and tested its self-assembly
properties as well as stimuli-responsive behaviors. This molecule
In conclusion, we have designed and synthesized a CF3-
substituted benzothiadiazole-cored phenylene vinylene fluoro-
phore (1) with pronounced stimuli-responsive fluorescence
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behaviors. The piezochromic luminescence can be reversibly
switched by tuning molecular packing in the solid states.
Supramolecular self-assembly microstructures based on this
compound have been obtained and display thermo-induced
fluorescence variation accompanied with fluorescence switching
from green to orange. Vapochromism was observed in this
system, and organic vapors could result in fluorescence changes
between orange and green. Compound 1 showed interesting
supramolecular assembly characteristics in solution. Lumines-
cent nanofibers and organic gel have been achieved by naturally
cooling the hot DMF solution of compound 1 and sonication
treatment of the quickly cooled solution, respectively. Slow
evaporation of the toluene solution of compound 1 could lead
to the formation of green emissive microrods that exhibited
interesting thermo-induced fluorescence variation. The example
of organic fluorophores that simultaneously exhibit piezo-, vapo-,
and thermochromic luminescence behaviors and stimuli-respon-
sive nanoassembly properties has been developed.
(d, 4H, J = 8.2 Hz, CH), 8.07 (d, 4H, J = 8.2 Hz, CH), 7.91 (s, 2H, CH).
MS (m/z): 345.0 [M]þ. Anal. Calcd (%) for C20H12N2O2S (344.1): C,
69.75; H, 3.51; N, 8.13; O, 9.29; S, 9.31. Found: C, 69.66; H, 3.39; N,
8.20; S, 9.48.
A mixture of the obtained green powder (300 mg) and 3,5-bis-
(trifluoromethyl)-phenylacetonitrile (654 mg) in tert-butyl alcohol
(20 mL) and THF (80 mL) was stirred at 50 °C for 0.5 h in dark, and
then tetrabutylammonium hydroxide (TBAOH) (1 M solution in H2O,
1 mL) was slowly dropped into the mixture. This brown mixture was
stirred at 50 °C for over 12 h, poured into water, and extracted with
chloroform. After the solvents were removed, purification on a silica
column (dichloromethane/n-hexane = 2:1) afforded the product com-
pound 1 as orange powder (525 mg, 74% yield), which was further
purified using vacuum sublimation. 1H NMR (CDCl3) δ: 8.18 (m, 12H,
CH), 7.94 (s, 4H, CH), 7.75 (s, 2H, CH). MS (m/z): 814.6 [M]þ. Anal.
Calcd (%) for C40H18F12N4S (814.1): C, 58.97; H, 2.23; F, 27.99; N,
6.88; S, 3.94. Found: C, 58.97; H, 2.10; N, 6.86; S, 4.15.
Compound 2 was synthesized by the same procedure as that for
1
compound 1. Yield: 78%. H NMR (CDCl3) δ: 8.16ꢀ8.09 (m, 8H,
CH), 7.91 (s, 2H, CH), 7.75ꢀ7.73 (d, 4H, CH), 7.63 (s, 2H, CH),
7.51ꢀ7.43 (m, 6H, CH). MS (m/z): 542.5 [M]þ. Anal. Calcd (%) for
C36H22N4S (542.1): C, 79.68; H, 4.09; N, 10.32; S, 5.91. Found: C,
79.49; H, 4.15; N, 10.21; S, 6.15.
’ EXPERIMENTAL SECTION
1
Instrumentation. H NMR spectra were recorded on a Bruker
Gelation, Assembled Fibers, and Microrods. Compound 1
and solvent DMF (0.85 wt %) were put into a septum-capped test tube
and heated at 80 °C until the solid was completely dissolved into the
solvent. The resulting solution was left to cool to room temperature for
0.5 h or sonicated using an ultrasonic cleaner (0.45 W/cm2, 40 kHz, 30 s)
after quick cooling. The gelation state was confirmed if the two criteria
were met: (1) by visual observation and (2) when the sample did not
flow perceptibly. Evaporation of the solution of compound 1 in toluene
(6 ꢁ 10ꢀ4 M) on the glass substrates at room temperature produced
many green fluorescent microrods.
AVANCE 300 MHz spectrometer with tetramethylsilane as the internal
standard. Mass spectra were measured on a GC/MS mass spectrometer.
Element analyses were performed on a Flash EA 1112 spectrometer.
Absorption spectra were obtained using a Shimadzu UV-2550 spectro-
meter. Photoluminescence spectra were recorded on a Perkin-Elmer LS
55 spectrophotometer. DSC experiments were recorded on a NETZSCH
DSC 204 instrument at a scanning rate of 10 K minꢀ1. Ultrasound
irradiation was performed on a Kun Shan KQ-300 DE ultrasound
cleaner (maximum power, 200 W, 40 kHz, Kunshan Ultrasound
Instrument Co, Ltd., China). The fluorescence microscopy images were
obtained from Olympus BX51 fluorescence microscopy. FESEM images
were obtained from a JSM 6700F field emission scanning electronic
microscope. PXRD data were recorded with a Siemens D5005 diffract-
ometer with Cu KR radiation (λ = 1.5418 Å). The 13C solid-state
NMR spectra were recorded on a Bruker AVANCE III 400 WB
spectrometer equipped with a 4 mm standard bore cross-polarization
magic angle spinning (CPMAS) probehead, whose X channel was tuned
to 100.62 MHz for 13C and the other channel was tuned to 400.18 MHz
for broad-band 1H decoupling, using a magnetic field of 9.39 T at 297 K.
The dried and finely powdered samples were packed in the ZrO2 rotor
closed with a Kel-F cap, which were spun at a 12 kHz rate. The
experiments were conducted at a contact time of 1 ms. A total of 8000
scans were recorded with a 2 s recycle delay for each sample. All 13C
CPMAS chemical shifts are referenced to the resonances of Adamantine
standard (δ = 29.5).
Synthesis. All reagents and solvents (standard grade) were used as
received, unless otherwise stated. THF was distilled from sodium/
benzophenone ketyl under a nitrogen atmosphere immediately prior
to use. 3,5-Bis(trifluoromethyl)-phenylacetonitrile and Pd(PPh3)4 were
obtained from the Aldrich Chemical Company.
The Na2CO3/H2O solution (1.27 g/6 mL) in a 100 mL three-necked
flask was degassed for over 20 min with N2. Then, distilled THF
(30 mL), 4,7-dibromo-2,1,3-benzothiadiazole (500 mg), 4-formylphe-
nylboronic acid (765 mg), and Pd(PPh3)4 (120 mg) were added to the
flask, which was degassed twice again. After reflux for over 36 h, the
mixture was poured into water and extracted with chloroform 3 times
and the organic solvents in the obtained solution were removed
with a rotary evaporator. The resulting greenish solid was purified
through column chromatography (silica gel, dichloromethane) to afford
a formyl-substituted benzothiadiazole molecule as green powder
(477 mg, 81% yield). 1H NMR (CDCl3) δ: 10.13 (s, 2H, CHO), 8.17
Preparation of Xerogel and Fiber Samples for FESEM,
Fluorescent Microscopy, DSC, and XRD Measurements.
The sample was obtained by freezing and pumping the fibers or gels
prepared by slow cooling or sonication of solutions.
’ ASSOCIATED CONTENT
S
Supporting Information. Additional emission spectra,
b
TGA and DSC profiles, and vapochromism images. This material
is available free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*Fax: þ86-431-85193421. E-mail: hongyuzhang@jlu.edu.cn (H.Z.);
yuewang@jlu.edu.cn (Y.W.).
’ ACKNOWLEDGMENT
This work was supported by the National Natural Science
Foundation of China (50733002, 20921003, and 50903037)
and the Major State Basic Research Development Program
(2009CB939700).
’ REFERENCES
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