Fluorescent temperature sensing using triarylboron compounds and microcapsules for detection of a wide temperature range on the micro- and macroscale

Article abstract of DOI:10.1002/adfm.201201712

Fluorescent temperature sensing has received increasing interest in a wide range of fields, including fluid dynamics, micromechanics, and molecular cell biology. Here, a novel series of triarylboron compounds with significant thermosensitive hue transformation and high fluorescent quantum efficiency in wide temperature range is described. It is then demonstrated that fluorescent core/shell microcapsules based on one of the compounds exhibit outstanding temperature response. The microcapsules, dispersed in different liquid or solid media, can serve as highly robust, reliable, and sensitive fluorescent temperature sensors. The sensors are the first example containing a single organic luminophor with a self-reference feature that can detect on the micro- and macroscale from -30 to 140 °C. This finding may open a new avenue to the development of novel fluorescent temperature sensors. Single luminophore microcapsules are fabricated to detect temperature with a yellow-green to orange luminescence change over a wide temperature range (-30 to +140 °C). The microcapsules are demonstrated to be novel, reliable, and absolute luminescent microthermometers. Copyright

Full text of DOI:10.1002/adfm.201201712

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Fluorescent Temperature Sensing using Triarylboron
Compounds and Microcapsules for Detection of a Wide
Temperature Range on the Micro- and Macroscale
Jiao Feng, Lei Xiong, Shuangqing Wang, Shayu Li,* Yi Li,* and Guoqiang Yang*
optical methods have been developed
to limit the impact of measurement.[6]
Fluorescent temperature sensing has received increasing interest in a wide
Infrared (IR) and thermochromic liquid
range of fields, including fluid dynamics, micromechanics, and molecular cell
biology. Here, a novel series of triarylboron compounds with significant ther-
mosensitive hue transformation and high fluorescent quantum efficiency in
crystals (TLC) are the most used tech-
niques for optical thermosensors.[2b,7] The
IR measurement is fairly rapid but can
wide temperature range is described. It is then demonstrated that fluorescent
core/shell microcapsules based on one of the compounds exhibit outstanding
temperature response. The microcapsules, dispersed in different liquid or
solid media, can serve as highly robust, reliable, and sensitive fluorescent
temperature sensors. The sensors are the first example containing a single
organic luminophor with a self-reference feature that can detect on the micro-
and macroscale from −30 to 140 °C. This finding may open a new avenue to
the development of novel fluorescent temperature sensors.
only probe the temperature at the surface,
and the transparent media which could
absorb the radiation would cause errors in
the measurements. TLC is capable to give
high precision measurement results, but
one kind of liquid crystal can only be used
in a comparatively narrow temperature
range.
Luminescence is one of the most sensi-
tive and easy-observable detection signals.
Some temperature-sensitive luminescence
materials, such as organic dyes, nanotube-based systems,
quantum dots, inorganic phosphors and organic-inorganic
hybrid materials, have been used to measure temperature in
a relatively wide range.[8] Most of the approaches detected the
luminescence intensity to calculate the temperature, which is
so-called ratiometric fluorescence thermometry (RFT).[9] By
addition of a temperature-insensitive luminescent material as
reference into a temperature-dependent luminophore, the RFT
method could provide a good accuracy for the measurement
of the temperature.[8h,10] However, no common luminescence
system could be used in both organic and aqueous system due
to the solubility of the probes. Meanwhile, for the combination
system, it required careful calibration because of the different
physicochemical features between two or more luminophores,
especially in a wide temperature range.[11] There exists a need
for developing novel luminophore systems which are suitable
for the temperature measurement in diverse situations.
1. Introduction
Temperature is a basic physical parameter that can be meas-
ured quantitatively with thermometers based on various kinds
of temperature-dependent physical properties, such as volume,
electric conductance and resistance, etc.[1] Currently, in situ
characterizations for temperature become continuing trend in
analysis and diagnostics fields because of their apparent advan-
tages.[2] From a practical point of view, these in situ observation
should have little impact on its analytes. This criterion poses a
serious challenge to classical intrusive thermometers, such as
measurements in microelectromechanical systems (MEMS),[3]
marine research,[4] and shipbuilding and aircraft industries.[5]
Several non-intrusive measurement techniques based on
J. Feng, L. Xiong, Dr. S. Q. Wang, Dr. S. Y. Li,
Prof. G. Q. Yang
In general, the performance of a luminescent material is
also affected by its microenvironments other than tempera-
ture.[12] To avoid the disturbance from the surroundings, an
appropriate approach involving microencapsulation tech-
nology has been proved to be effective.[13] Acting as barrier
walls of liquids, microcapsules can protect the inside sub-
stances from external affected factors, such as oxidization,
acidity, alkalinity, moisture and evaporation, which makes
liquid materials possibly used in various environments with
high performance.[14] Herein, we describe a novel lumines-
cent microcapsule containing one kind of temperature sensi-
tive dye with self-reference characteristic, which can be dis-
persed in different media (e.g., organic solvents, water and
Beijing National Laboratory for Molecular Sciences
Key Laboratory of Photochemistry
Institute of Chemistry
Chinese Academy of Sciences
Beijing 100190, China
E-mail: shayuli@iccas.ac.cn; gqyang@iccas.ac.cn
Prof. Y. Li
Key Laboratory of Photochemical Conversion
and Optoelectronic Materials
Technical Institute of Physics and Chemistry
Chinese Academy of Sciences
Beijing 100190, China
E-mail: yili@mail.ipc.ac.cn
DOI: 10.1002/adfm.201201712
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Scheme 1. Structures of a) DPTB, b) MPTB, and c) TBBD.
polymers). The microcapsules can be used as a luminescent
thermosensors in broad applied fields with a wide tempera-
ture range from −30 to 140 °C.
2. Results and Discussion
For MPTB, two methoxy groups are as the electron-donating
groups and the characteristics of intramolecular charge transfer
are enhanced. The absorption and fluorescence spectra in dif-
ferent solvents are shown in Figure S1 (Supporting Informa-
tion). It can be seen that both the absorption and fluorescence
maximum are located at longer wavelength, compared to DPTB.
When the MPTB molecules were dissolved in MOE, significant
temperature effects were observed from −50 to 100 °C, similar
with the results of DPTB (see Figure S2a, Supporting Informa-
tion). However, when the MPTB molecules were dissolved in a
solvent with low polarity, 1,2,3,4-tetrahydronaphthalene (THN),
the fluorescence maximum was slightly shifted only 10 nm,
from 494 nm to 484 nm, when the temperature was from −30
to 100 °C (see Figure S2b, Supporting Information). It indicates
that more polar molecules are needed for the reliable fluores-
cence shift with the temperature changing in the low polarity
solvent.
The TBBD is a more polar molecule and two pyrrolidine
groups are as the electron-donating groups. The THN with
5 wt% polystyrene (THN-PS), was chosen as the solvent to dis-
solve TBBD for its low polarity and relatively wide temperature
range of liquid phase. Polystyrene is added into the system
to increase the viscosity of the solvent for the fabrication of
the microcapsule. As expected, TBBD shows a temperature-
dependent color changing luminescence from orange-red
to green-yellow in THN-PS with high quantum yields over a
wide temperature range (Table 1). The absorption spectra and
corrected emission spectra of TBBD in THN-PS at various tem-
peratures are shown in Figure S3 (Supporting Information). In
accord with previous results, the absorbance is temperature-
insensitive while the emission band shows a significant hyp-
sochromic shift with increasing temperature. To fabricate the
microcapsules, cross-linked poly(urea–formaldehyde) (PUF)
Luminescent dye is the core component of the microcapsule
for temperature measurement. Although numerous dyes have
been reported with intense luminescence, few of them present
high quantum yield at the temperature over 100 °C because
of the inevitable thermal activation of radiationless proc-
esses.[15] The requirements of temperature sensitivity and self
reference cause further difficulties for luminescent molecular
design. Recently, we proposed a novel strategy involved triaryl-
boron compound, dipyren-1-yl(2,4,6-triisopropylphenyl)borane
(DPTB), to circumvent the challenge.[16] The strategy exploited
the intense luminescence of triarylboron compounds and
temperature-sensitive population of luminescent excited states
with different conformations. The triarylboron compound shows
an intrinsic dual fluorescence originated from two luminescent
excited states, local excited state (LE) and twisted intramolecular
charge-transfer (TICT) state. Generally, microenvironment with
higher polarity and lower viscosity leads to larger population of
TICT state.[17] To obtain significant thermosensitive hue trans-
formation, the reported system unfortunately must be used in
polar organic solvents, e.g., 2-methoxyethyl ether (MOE), which
is difficult to form microcapsules.[13,18] Taking the advantage for
the attractive temperature-dependent luminescent color change,
the introduction of an electron-donating group in the pyrene
groups should render the luminescence with stronger intramo-
lecular charge-transfer characteristic, which would reduce the
requirement of solvent polarity.[19] This should get easier way
to fabricate microcapsules. Following this idea, two new lumi-
nescent triarylboron molecules, di-6-methoxylpyren-1-yl-(2,4,6-
triisopropylphenyl)borane (MPTB) and 1,1′-(6,6′-((2,4,6-triiso-
propylphenyl)boranediyl)bis(pyrene-6,1-diyl))dipyrrolidine
(TBBD) (shown in Scheme 1 with DPTB), were designed and
synthesized.
T a b le 1 . Fluorescence quantum yield Φ of TBBD in THN-PS at different temperatures.
0
10
20
30
0.5
40
50
T [°C]
Φ
−30
0.30
60
−20
0.34
70
−10
0.39
80
0.41
90
0.44
100
0.64
0.46
110
0.65
0.53
130
0.64
0.56
140
0.60
120
0.65
T [°C]
Φ
0.59
0.60
0.62
0.63
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excellent candidate for a novel reliable and absolute lumines-
cent temperature sensor.
The microcapsules can be dispersed in water and common
organic media. No significant change on the morphology
is observed after long time soaking, indicative of a great
mechanical stability of the microcapsules. The normalized
luminescent spectra of the microcapsules and TBBD in several
common solvents are provided in Figure S7 (Supporting Infor-
mation). All spectra of the microcapsules in different solvents
show perfect matching regardless of whether water or organic,
nonpolar or high polar solvents, which is entirely different from
those of TBBD in homogeneous solutions. The results indicate
that the THN-PS solution of TBBD with temperature sensitivity
is encapsulated by the microcapsules. The excellent characters
of the microcapsules on dispersion and solvent-insensitive
luminescence fulfill the requirement of widespread use for in
situ thermosensors.
Two kinds of data processing based on intensity and color are
executed on luminescence spectra to determine the calibration
curve. For the intensity-based procedure, the function of tem-
perature versus the fluorescence intensity ratio of 530/650 nm
is depicted (Figure 3a), which can be fitted by a fifth-order
polynomial (solid curve; the inset of Figure 3a). The slope of
calibration curve gives temperature sensitivities dI/dT ranging
from 0.011 °C−1 at T = −30 °C−1 to 0.059 °C−1 at T = 140 °C,
suggesting the outstanding sensitivity in such wide tempera-
ture range.[8n] The microcapsule was used to measure the melt
points of ice and 1-octadecanol to test its practical applicability.
The intensity ratios were 0.6818 and 3.303, respectively, which
corresponded to 0.3 °C and 58.4 °C that compared well with
the reported results.[21] For color-based procedure, the temper-
ature-dependent spectra are transformed to the Commission
Internationale de l’Eclairage (CIE) 1931 coordinates (Figure
3b). The color-based approach is suitable for direct observation
of temperature gradient with the naked eye while it is not sen-
sitive as ratiometric method because the spectral transforma-
tion lost intensity information. Both processes eliminate the
errors due to non-uniform excitation and fluctuation of exci-
tation power, which guarantee a high-precision measurement
for temperature, while the accuracies are strongly instrument
dependent.
Figure 1. Corrected emission spectra of TBBD in THN-PS microcapsules
recorded from −30 to 140 °C. Excitation wavelength: 365 nm.
was chosen as shell material to coat the THN-PS solution of
TBBD. This is the first attempt to coat low polarity solvent
with PUF and only nonpolar solvents (e.g., paraffin) were
coated by PUF before. The procedures of encapsulation are
similar to those of Fan et al. and provided in the supporting
information.[20]
The microcapsules were characterized by fluorescence
spectroscopy (FL), scanning electron microscopy (SEM),
transmission electron microscopy (TEM), dynamic light scat-
tering (DLS) and fluorescent microscopy (FM). The corrected
emission spectra of the microcapsules are very close to that
of TBBD in THN-PS solution (slight difference at shorter
wavelength edge), indicative of a very low scattering of the
microcapsules, as shown in Figure 1. Meanwhile, the appar-
ently luminescent difference (Figure S4, Supporting Informa-
tion) between microcapsules and the neat TBBD suggests that
the microcapsules possess liquid-core/solid-shell structure.
The surface of these microcapsules is fairly smooth and inte-
grated, revealing that the PUF fraction is dense without pores
(see Figure 2a). The transmission view indi-
Because this is a one-to-one correspondence between tem-
perature and luminescence, the accuracy and the precision
cates that the microspheres are hollow and
indeed are microcapsules (Figure 2b). The
diameter of the microcapsules is about 3
1 μm from the observations of the electron
microscopy, which is consistent with the
DLS result (Figure S5, Supporting Informa-
tion). Furthermore, the coating formation
efficiency (or coating formation rate) of the
encapsulation is determined by counting
the number of emissive microcapsules in
FM image, which is as high as ≈70% using
our fabrication conditions (Figure S6, Sup-
porting Information). The intense and wide-
range thermosensitive emission suggests
the easy-prepared microcapsule to be an
Figure 2. a) SEM and b) TEM images of microcapsules.
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simulated and measured. The hot and cold
salt aqueous solutions containing 5% (w/w)
microcapsules were injected into two end
ports of a T-shaped square tube with width
1 mm, respectively, and then outflowed
from the third port. Upon irradiation of
the tube, a color pattern of the temperature
gradient was observed in the fast moving
fluid. The orange-red and green-yellow are
corresponding to cold fluid and hot fluid,
respectively. It is interesting that two flows in
opposite directions do not interfere with each
other until they outflow from the third exit
(Figure 4a). When one of the injecting ports
was exchanged with the outflowing one, the
luminescent pattern showed a different fea-
ture, and an instantaneous of flow is clearly
Figure 3. a) Temperature dependence of the ratio of fluorescence intensity (I = I530nm/I650nm) of
TBBD-THN-PS microcapsules. b) CIE chromaticity diagram showing the temperature depend-
ence of the (x,y) color coordinates of TBBD-THN-PS microcapsules.
(repeatability) of the microcapsule thermometry will be
determined by the quality of the observation equipments and
the stability of the microcapsules. The shell of cross-linked
PUF is dense and greatly chemically inert with high resist-
ance against swelling, dissolution and degradation, therefore,
a high stability of the microcapsules is expected. The heating
and irradiation tests were conducted to evaluate the lumines-
cent stability within the microcapsules. The luminescence
spectra are changeless before and after heating at 140 °C for
30 min (Figure S8, Supporting Information). Additional ther-
mogravimetric analysis reveals that TBBD does not dissociate
upon heating to 320 °C (Figure S9, Supporting Information).
In irradiation test, a 1000 W medium pressure mercury
lamp was placed 50 mm distant from the microcapsule dis-
persed solution, and a filter was used to cut-off the light
below 340 nm. The shape of the emission spectrum of the
microcapsules exhibits exactly same and only 5% decrease
of intensity after 10 min irradiation (Figure S10, Supporting
Information).
Moreover, response speed to the changes in temperature
and spatial resolution must be considered for evaluating the
luminescence thermosensor systems. Considering that the
conformation reversal between LE state and TICT state is in a
time range of pico- or nanoseconds, the probe response time
is determined just by the thermal diffusion distance and the
coefficient of the conductive media (e.g., PUF and THN). The
thermal diffusion distance is the radius of the microcapsules
which is about 1 to 2 μm. The thermal diffusion coefficient of
the media is assumed as ≈100 μm2/ms, just like other organic
polymers (e.g., nylon 90 μm2/ms, rubber 130 μm2/ms). Hence,
the response time is estimated less than 1 ms, which can be
considered as a real-time measurement. The spatial resolution
of the approach is limited by the size of microcapsules. With
these microcapsules, the spatial resolution is as high as 4 μm.
The excellent thermo- and photostability, fast response and high
spatial resolution provide possible applications of the microcap-
sules as high performance thermometer for in situ microarea
and large-area temperature measurement.
observed (Figure 4b). The cold and hot flows met in a T-shaped
junction perpendicularly to generate turbulence, resulting in
a half-moon distribution. This visualized observation provides
an approach to map real-time temperature distribution of a
dynamic fluid system conveniently.
The microcapsules can also be used in macrosize systems.
The amphiphilic PUF shell makes the microcapsules to be
easily sprayed on the surface of objects or placed in polymer
as temperature sensitive paints (TSP) for aerodynamics
mechanics and heat transfer experiments. To simulate TSP for
mapping the full-field temperature distributions of the large
surface, the CH2Cl2 solution of 10% polystyrene containing
20% (w/w) microcapsules were sprayed on a square aluminum
plate. When the center of the surface was cooled by a stream of
cold nitrogen gas, a color changing pattern of the temperature
gradient was observed upon irradiation (Figure 5). The tem-
perature distribution can be readily estimated or measured by
comparing with the temperature dependent CIE chromaticity
diagram. This simulation result demonstrates the feasibility of
using the microcapsules to map the surface temperature distri-
bution of macroscale objects.
3. Conclusions
Two new triarylboron compounds were synthesized and the
temperature sensitivity behaviors of the compounds were
As mentioned earlier, determining transient temperature of
the fast flowing system is very important in MEMS and other
fluid dynamics research fields. To demonstrate the availability
of the microcapsules in these fields, a fast flowing system was
Figure 4. Fluorescence microscopy images of fluids with different tem-
perature. Fluid flow a) in opposite directions and b) in perpendicular
directions.
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mixture products as colorless solid (2.76 g, yield 89%). The mixture
products were used without further purification.
Synthesis of the Di-6-methoxylpyren-1-yl-(2,4,6-triisopropylphenyl)borane
(MPTB): n-BuLi (4.4 mmol, 1.60 M solution in n-hexane) was added
at −78 °C to a Et2O (30 mL) solution of the mixture of 1-bromo-6-
methoxypyrene/1-bromo-8-methoxypyrene (1.24 g, 4.0 mmol); after one
hour, the temperature was allowed to naturally rise to room temperature.
Stirring was then continued for an additional hour. The mixture was then
cooled again to −78 °C and 2,4,6-triisopropylphenylboronate[21] (0.56 g,
2.0 mmol) in Et2O (5 mL) was added by injection, then was stirred for
1 h at this temperature, allowed slowly to reach room temperature,
and stirred overnight. All the solvents were removed under reduced
pressure. The residue was hydrolyzed and the product was extracted
with ethyl acetate. The crude product obtained after evaporation of
solvent was purified by column chromatography (silica gel, eluent: 15%
dichloromethane in petroleum ether), followed by crystallization from
ethanol to obtain MPTB as a yellow powder (0.35 g, yield 26%). 1H NMR
(400 MHz, CDCl3, δ): 8.55 (d, J = 9.1 Hz, 2H; Ar H), 8.19 (d, J = 9.7 Hz,
2H; Ar H), 8.09 (dd, J = 8.7 Hz, 4H; Ar H), 7.95 (d, J = 8.4 Hz, 2H; Ar H),
7.84 (d, J = 9.2 Hz, 2H; Ar H), 7.50 (dd, J = 8.9 Hz, 4H; Ar H), 7.07 (s,
2H, Ar H), 4.16 (s, 6H, CH3), 2.98-2.87(m, 3H, CH), 1.36 (d, J = 9.0 Hz,
6H; CH3), 0.93 (d, J = 8.2 Hz, 6H; CH3), 0.79 (d, J = 8.0 Hz, 6H; CH3);
MALDI-TOF m/z (%): 676.5 [M+]; Anal. calcd for C49H45BO2: C 86.97, H
6.70; found: C 87.03, H 6.90.
Figure 5. Fluorescence photograph of TSP.
Synthesis of the 1-(6-Bromopyren-1-yl)pyrrolidine: Tris(dibenzylidene-
acetone)dipalladium-chloroform adduct (Pd2(dba)3•CHCl3) (100 mg,
0.1 mmol), sodium t-butoxide (NaOtBu) (1.5 g, 15.6 mmol), and (R)-(+)-
2,2′-Bis(diphenylphosphino)-1,1′-binaphthyl (BINAP) (120 mg, 0.2 mmol)
were placed in a three-neck round-bottom flask equipped with a reflux
condenser under argon atmosphere. Degassed toluene (50 mL) was
added to the flask, and stirred for 15 min. Then, 1,6-dibromopyrene
(1.80 g, 5 mmol) was added and stirred for 15 min. Pyrrolidine
(0.5 mL, 6 mmol) was added and the mixture was slowly heated to 90 °C
over 1.5 h. After stirring for a further 3 h at 90 °C, the hot mixture was
filtered though Celite. The Celite layer was washed with hot toluene (ca.
50 mL). The combined filtrate was concentrated. The residual mixture
was separated by column chromatography (silica gel, eluent: 50%
dichloromethane in petroleum ether). Recrystallization from ethanol
gave 1-(6-bromopyren-1-yl)pyrrolidine as yellow crystals (910 mg, yield
52%). 1H NMR (400 MHz, CDCl3, δ): 8.41 (d, J = 9.1 Hz, 1H; Ar H),
8.19 (d, J = 9.1 Hz, 1H; Ar H), 8.14 (d, J = 8.2 Hz, 1H; Ar H), 8.07 (d, J =
8.4 Hz, 1H; Ar H), 8.02 (d, J = 9.1 Hz, 1H; Ar H), 7.88 (t, J = 9.6 Hz,
2H), 7.60 (d, J = 8.3 Hz, 1H; Ar H), 3.60 (s, 4H, CH2), 2.07 (s, 4H, CH2);
EIMS m/z (%): 351(100) [M+], 350(33) [M+], 349(100) [M+], 200(45)
[C16H8+]; Anal. calcd for C20H16BrN: C 68.58, H 4.60, N 4.00; found:
C 68.47, H 4.55, N 3.96.
studied. Based on the luminescent properties of the compounds,
a novel thermosensitive microcapsule has been developed by
encapsulation of the TNH-PS solution of TBBD into an cross-
linked poly(urea–formaldehyde) microshell. This luminescent
microcapsule can map transient temperature in fast flowing
systems and gradient temperatures of objects with large areas,
and works under a wide range of −30 to 140 °C with high sta-
bility and a 4 μm spatial resolution. The temperature values are
transformed to the luminescence spectra or the luminescence
color, which can be observed directly by the naked eye or with
a camera. This thermosensitive microcapsule can serve a wide
variety of temperature monitoring functions in industries and
scientific researches.
4. Experimental Section
General: All chemicals and reagents were used as received from
commercial sources. Solvents for chemical synthesis were purified
or freshly distilled prior to use according to standard procedures. All
chemical reactions were carried out under an inert atmosphere. 1H NMR
spectra were recorded on a Bruker Avance 400 spectrometer. MALDI-
TOF-MS spectra were measured by a Bruker BIFLEX III spectrometer.
EI mass spectra were recorded on a Waters Micromass GCT mass
spectrometer. UV-vis absorption spectra were recorded on a Hitachi
U-3010 spectrophotometer. Photoluminescence spectra were carried
out on a Hitachi F-4500 spectrophotometer. Elemental analyses were
performed by a Carlo Erba 1106. Fluorescence microscopy images were
taken using an Olympus IX81 fluorescence microscope. The microscopic
images were captured by transmission electron microscopy (TEM, JEOL
JEM-1011) and field emission scanning electron microscopy (FE-SEM,
Hitachi-S4300). Thermogravimetric analysis (TGA) was carried out with
a Seiko TG/DTA 6300 instrument.
Synthesis of the 1-Bromo-6-methoxypyrene/1-Bromo-8-methoxypyrene:
Bromine (1.6 g, 10 mmol) at 0 °C was gradually added to a CH2Cl2
(25 mL) solution of 1-methoxypyrene (2.32 g, 10 mmol). After 30 min, the
temperature was allowed to naturally rise to room temperature. Stirring
was then continued for a further 3 h. All the solvents were removed
under reduced pressure. The residue was extracted with ethyl acetate.
The crude product obtained after evaporation of solvent. Recrystallization
from ethanol gave 1-bromo-6-methoxypyrene/1-bromo-8-methoxypyrene
Synthesis of the 1,1′-(6,6′-((2,4,6-triisopropylphenyl)boranediyl)-
bis(pyrene-6,1-diyl))dipyrrolidine (TBBD): n-BuLi (2.2 mmol, 1.60
M
solution in n-hexane) was added at −78 °C to a Et2O (20 mL) solution of
1-(6-bromopyren-1-yl)pyrrolidine (700 mg, 2.0 mmol); after one hour, the
temperature was allowed to naturally rise to room temperature. Stirring
was then continued for an additional hour. The mixture was then cooled
again to −78 °C and 2,4,6-triisopropylphenylboronate (278 mg, 1.0 mmol)
in Et2O (5 mL) was added by injection, then was stirred for 1 h at this
temperature, allowed slowly to reach room temperature, and stirred
overnight. All the solvents were removed under reduced pressure. The
residue was hydrolyzed and the product was extracted with ethyl acetate.
The crude product obtained after evaporation of solvent was purified
by column chromatography (silica gel, eluent: 30% dichloromethane in
petroleum ether), followed by crystallization from THF to obtain TBBD
as a red powder (500 mg, Yield 66%). 1H NMR (400 MHz, CDCl3, δ):
8.50 (d, J = 9.1 Hz, 2H; Ar H), 8.14 (d, J = 6.8 Hz, 2H; Ar H), 8.00 (t, J =
8.0 Hz, 4H; Ar H), 7.85 (q, J = 8.3 Hz, 4H; Ar H), 7.56 (s, 2H, Ar H),
7.43 (d, J = 8.5 Hz, 2H; Ar H), 7.06 (s, 2H, Ar H), 3.61 (s, 8H, CH2), 2.98
(t, J = 6.7 Hz, 1H; CH), 2.91 (t, J = 5.7 Hz, 2H; CH), 2.11 (s, 8H, CH2),
1.35 (d, J = 6.8 Hz, 6H; CH3), 0.94 (d, J = 5.9 Hz, 6H; CH3), 0.78 (d, J =
6.0 Hz, 6H; CH3); MALDI-TOF m/z (%): 754.5 [M+]; Anal. calcd for
C55H55BN2: C 87.51, H 7.34, N 3.71; found: C 87.10, H 7.26, N 3.57.
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Fabrication of Microcapsules: Water (30 mL), urea (0.5 g),
resorcinol (0.05 g), ammonium chloride (0.05 g), sodium chloride
(1.00 g), sodium dodecylbenzene sulfuric (0.038 g), gum Arabic
[8] a) H. S. Peng, M. I. J. Stich, J. B. Yu, L. N. Sun, L. H. Fischer,
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(0.035 g), 37 wt% formalin solution (1.5 mL), and 2 × 10−5
M
1,2,3,4-tetrahydronaphthalene (containing 5 wt% polystyrene) solution
of 1,1′-(6,6′-((2,4,6-triisopropylphenyl)boranediyl)bis(pyrene-6,1-diyl))
dipyrrolidine) (TBBD) (0.8 mL) were mixed in a beaker. O/W emulsions
were formed using a high-speed homogeniser at the rotation speed of
10000 rpm for 10 min. O/W emulsions were transferred to a three-neck
round-bottom flask equipped with mechanical agitation. Stirring at the
rotation speed of 1000 rpm for 4 min and the emulsions were slowly and
carefully adjusted to pH = 3.5 using diluted aqueous citric acid solutions.
Then, stirring speed was reduced to 300 rpm and the emulsions were
heated at a rate of 2 °C min−1 to 60 °C. After 4 h, the reaction was ended.
The microcapsules that formed were separated from aqueous solution
with suction filtration and the microcapsules were collected.
Supporting Information
Supporting Information is available from the Wiley Online Library or
from the author.
Acknowledgements
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The authors are grateful to the National Natural Science Foundation of
China (Grant Nos. 21073206, 20733007, 20873165, 50973118) and the
National Basic Research Program (2007CB808004, 2009CB930802) and
Chinese Academy of Sciences.
Received: June 24, 2012
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2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Funct. Mater. 2012,
DOI: 10.1002/adfm.201201712