Tetraphenylethylene-based fluorescent porous organic polymers: Preparation, gas sorption properties and photoluminescence properties

Article abstract of DOI:10.1039/c1jm11787d

Tetraphenylethylene-based porous organic polymers were synthesized efficiently through a Suzuki coupling polycondensation or oxidative coupling polymerization. According to the obtained nitrogen physisorption isotherms, the Brunauer-Emmett-Teller specific

Full text of DOI:10.1039/c1jm11787d

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PAPER
Tetraphenylethylene-based fluorescent porous organic polymers: preparation,
gas sorption properties and photoluminescence properties†
Qi Chen,a Jin-Xiang Wang,ab Fen Yang,ab Ding Zhou,a Ning Bian,a Xin-Jian Zhang,a Chao-Guo Yanb
a
*
and Bao-Hang Han
Received 23rd April 2011, Accepted 1st July 2011
DOI: 10.1039/c1jm11787d
Tetraphenylethylene-based porous organic polymers were synthesized efficiently through a Suzuki
coupling polycondensation or oxidative coupling polymerization. According to the obtained nitrogen
physisorption isotherms, the Brunauer–Emmett–Teller specific surface area values for these porous
materials vary between 472 and 810 m2 gꢀ1. Using the same linker monomer, the specific surface area of
copolymer materials (TPOP-3 or TPOP-5) prepared by two different core structural monomers
(tetraphenylethylene and spirobifluorene) is higher than those of the respective homopolymers.
Gravimetric hydrogen adsorption isotherms show that the adsorption capacity for hydrogen is up to
1.07 wt% at 1.13 bar and 77 K. Furthermore, incorporation of tetraphenylethylene moieties into these
polymers can induce high photoluminescence (lmax: 530–610 nm) in the solid state. Thanks to the
propeller-like structure and aggregation-induced emission characteristics, tetraphenylethylene is to be
a promising building block for designing porous polymers with special properties.
CMPs, respectively. Nickel-promoted Yamamoto polymeriza-
1. Introduction
tion was used as a novel route to synthesize microporous polymer
materials,9 in which the polymerization can be performed with
only a single monomer. Dioxane formation by polyphenols and
tetrafluoroarylenes was designed for synthesis of a wide variety of
PIMs.4 Some microporous polymers have been prepared by
reactions involving triazine formation10 from aromatic nitriles or
alkyne trimerization.7,8a Meanwhile, using rigid or contorted
building blocks as the cores of polymers often plays an important
role in designing porous materials with high surface areas. It has
been proved that microporous organic polymers containing spiro-
cyclic units,11,8a tetrahedral carbon- and silicon-centred mono-
mers12 usually possess large surface area (greater than 700 m2 gꢀ1).
Recently, the cubic siloxane-cages13 and bulky adamantane14
structures have also been used in preparation of porous polymers.
The monomer structures show a significant influence on the
surface property and porous structure of porous polymers.
Cooper and coworkers6b have demonstrated the feasibility of
systematically controlling the strategy of fine-tuning the average
micropore size and surface area by copolymerization of mono-
mers with different strut lengths.
Porous organic polymers (POPs), exhibiting potential applica-
tions in heterogeneous catalysis1 and gas storage,2 can be cate-
gorized into several classes, such as hyper-crosslinked polymers
(HCPs),3 polymers of intrinsic microporosity (PIMs),4 covalent
organic frameworks (COFs),5 and conjugated microporous
polymers (CMPs).6 Most of the porous organic polymers possess
intrinsic properties of large surface areas, high chemical stabili-
ties, and low skeletal density,7 which have drawn great interests
of scientists in recent years.
By selecting the proper chemical reactions or various building
blocks, versatile porous polymers can be obtained efficiently,
which show high flexibility in the molecular design. For example,
palladium-catalyzed Sonogashira–Hagihara coupling reaction6
and oxidative coupling of thiophenes8 were used for preparation
of poly(aryleneethynylene) CMPs and poly(arylenethiophene)
aNational Center for Nanoscience and Technology, Beijing, 100190, China.
E-mail: hanbh@nanoctr.cn; Fax: +86-10-82545576
bCollege of Chemistry & Chemical Engineering, Yangzhou University,
Yangzhou, 225002, China
Since Tang’s group reported the aggregation-induced emission
(AIE) features of tetraphenylethylene-based luminophors,15 tet-
raphenylethylene (TPE)-based AIE active materials have already
shown practical applications in OLEDs,15 chemo-sensors,16 and
bio-probes,17 owing to their enhanced emission in the aggregate
form or solid state. The AIE effect can greatly improve the
fluorescence quantum yields of the molecules by up to three
orders of magnitude, enhancing the photoluminescence intensity
† Electronic supplementary information (ESI) available: TGA data of
TPOPs; 13C CP/MAS NMR spectra of TPOP-4 and TPOP-5; nitrogen
adsorption–desorption isotherms of TPOP-2 and TPOP-3; BET specific
surface areas of TPOPs calculated over different relative pressure
ranges and corresponding BET specific surface area plots; logarithmic
plots of nitrogen adsorption isotherms and hydrogen adsorption
isotherms of TPOPs measured at 77 K; SEM images of TPOP-1 and
TPOP-2; photos of TPOPs under UV light (365 nm) illumination; 1H
NMR and 13C NMR of M-4. See DOI: 10.1039/c1jm11787d
13554 | J. Mater. Chem., 2011, 21, 13554–13560
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from faint luminophores into strong emitters.16a The steric effect
of the peripheral phenyl rings can prevent TPE from packing via
p–p stacking interactions.15 Therefore, TPE molecules exhibit
propeller-like, nonplanar conformation, which are different from
the contorted spiro-cyclic compounds and the planar p-system
molecules. Thanks to its efficient preparation, propeller-like
structure, and AIE characteristics, tetraphenylethylene is
expected to be a novel building block for the design of porous
polymers with special properties. Herein, preparation and
properties of TPE-based porous organic polymers (TPOPs) are
reported for the first time. The polymer synthesis was facilitated
smoothly by Suzuki coupling polycondensation or oxidative
coupling polymerization. The BET specific surface area data for
these polymers vary between 472 and 810 m2 gꢀ1. Gravimetric
hydrogen adsorption isotherms show that the hydrogen uptake
of the synthetic porous polymer is up to 1.07 wt% at 1.13 bar and
77 K. Incorporation of TPE moieties into these polymers induces
high photoluminescence (lmax: 530–610 nm) in the solid state.
in 30 mL of THF was added a 10 mL saturated solution of
potassium carbonate, and then degassed by bubbling nitrogen
gas for 15 min. After adding Pd(PPh3)2Cl2 (60 mg, 0.085 mmol)
under nitrogen protection, the reaction mixture was refluxed for
48 h and then cooled down to room temperature. The resulting
mixture was extracted with ethyl acetate three times. The
combined organic layer was washed with deionized water and
dried over sodium sulfate. After concentration under reduced
pressure, the remaining oil was purified by column chromatog-
raphy using n-hexane–chloroform (5 : 1) as eluent to give the
1
desired product M-4 (223 mg, 55%) as a light yellow solid. H
NMR (400 MHz, CDCl3): d 7.40 (d, J ¼ 8.4 Hz, 8H, Ar–H), 7.27
(d, J ¼ 3.6 Hz, 4H, Th–H), 7.23 (dd, J ¼ 4.8 Hz, 0.8 Hz, 4H, Th–
H), 7.09 (d, J ¼ 8.4 Hz, 8H, Ar–H), 7.04 (dd, J ¼ 5.2 Hz, 3.6 Hz,
4H, Th–H). 13C NMR (100 MHz, CDCl3): d 144.3, 142.9, 140.4,
132.8, 132.1, 128.1, 125.3, 124.8, 123.2.
2.3. Synthesis of TPOPs by Suzuki coupling polymerization
TPOP-1, TPOP-2, and TPOP-3 were synthesized by palladium-
catalyzed Suzuki coupling condensation between BDBA and
arylbromide. A representative preparation for TPOP-3 is given in
detail as follows.
2. Experimental section
2.1. Materials and characterization
All chemical reagents were commercially available and used as
received unless otherwise stated. Benzene-1,4-diboronic acid
(BDBA) and tetrakis(triphenylphosphine)palladium(0) were
purchased from Acros. Tetrakis(4-bromophenyl) ethylene
(M-1),18 2,20,7,70-tetrabromo-9,90-spirobifluorene (M-2),19 tetra-
kis(4-bromophenyl) methane (M-3),20 and 2,20,7,70-tetrakis(2-
thienyl)-9,90-spirobifluorene (M-5)8 were prepared according to
reported methods, respectively.
A mixture of tetrakis(4-bromophenyl) ethylene (162 mg,
0.25 mmol), 2,20,7,70-tetrabromo-9,90-spirobifluorene (158 mg,
0.25 mmol), and BDBA (163 mg, 1.0 mmol) in dimethylforma-
mide (DMF, 100 mL) was degassed by the freeze–pump–thaw
cycles. To the mixture was added an aqueous solution of
potassium carbonate (2.0 M, 16 mL) and tetrakis(triphenyl-
phosphine)palladium(0) (50 mg, 55 mmol). The resulting solution
was degassed and purged with nitrogen, and stirred at 150 ꢁC for
36 h. The mixture was cooled to room temperature and poured
into water. The insoluble precipitate was filtered and washed
with water, methanol, and acetone to remove any unreacted
monomers or catalyst residues. Further purification of the
polymer was carried out by Soxhlet extraction with water,
methanol, and tetrahydrofuran (THF) for 24 h, respectively, to
give TPOP-3 (240 mg) as a solid.
When 2,20,7,70-tetrabromo-9,90-spirobifluorene was replaced
by the same equivalent of tetrakis(4-bromophenyl) methane,
TPOP-2 can be obtained according to the procedure as described
above. As for TPOP-1, only tetrakis(4-bromophenyl) ethylene
was used as core structural monomer and its amount is a half
equivalent of BDBA.
1
The H and 13C NMR spectra were recorded on a Bruker
DMX400 NMR spectrometer. Solid state cross-polarization
magic angle spinning (CP/MAS) NMR was recorded on a Bruker
Avance III 400 NMR spectrometer. Nitrogen sorption isotherms
were obtained with a Micromeritics ASAP 2020M + C acceler-
ated surface area and porosimetry analyzer at 77 K. The samples
were degassed overnight at 120 ꢁC. The obtained adsorption–
desorption isotherms were evaluated to give the pore parameters,
including Brunauer–Emmett–Teller (BET) specific surface area,
pore size, and pore volume. The pore size distribution was
calculated from the adsorption branch with the nonlocal density
function theory (NLDFT) approach. SEM observations were
carried out using a Hitachi S-4800 microscope (Hitachi Ltd.,
Japan) at an accelerating voltage of 6.0 kV and equipped with
a Horiba energy dispersive X-ray spectrometer. TEM observa-
tions were carried out using a Tecnai G2 20 S-TWIN microscope
(FEI, USA) at an accelerating voltage of 200 kV. The fluores-
cence spectra were measured using a Perkin-Elmer LS55 lumi-
nescence spectrometer. X-Ray diffraction (XRD) patterns of the
samples were acquired from 0.5 to 35ꢁ by a Philips X’Pert PRO
X-ray diffraction instrument. Thermogravimetric analyses
(TGA) were performed on a Pyris Diamond thermogravimetric/
differential thermal analyzer by heating the samples at
2.4. Synthesis of TPOPs by oxidative coupling polymerization
TPOP-4 and TPOP-5 were synthesized through oxidative
coupling polymerization promoted by anhydrous FeCl3. A
representative preparation for TPOP-5 is given in detail as
follows.
To the solution of tetrakis(2-thienyl) ethylene (90 mg,
0.093 mmol) and 2,20,7,70-tetrakis(2-thienyl)-9,90-spirobifluorene
(90 mg, 0.095 mmol) in 50 mL of anhydrous CHCl3 was added
anhydrous FeCl3 (440 mg, 2.72 mmol). The solution mixture was
stirred at room temperature for 2 d under nitrogen protection,
and then 100 mL of methanol was added to the above reaction
mixture. The resulting mixture was kept stirring for another hour
and the precipitate was collected by filtration. After washed with
10 ꢁC minꢀ1 to 800 C in the atmosphere of nitrogen.
ꢁ
2.2. Synthesis of tetrakis(2-thienyl) ethylene (M-4)
To the solution of tetrakis(4-bromophenyl)ethylene (400 mg,
0.617 mmol) and 2-thiopheneboronic acid (395 mg, 3.086 mmol)
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methanol, the obtained solid was stirred vigorously in 37% HCl
solution for 2 h. The suspension was then filtered and washed
with water and methanol. After extraction in a Soxhlet extractor
with methanol for 24 h, and then with THF for another 24 h, the
desired polymer was collected (81% in yield) and dried in
140 and 127 ppm, which are assigned to the substituted vinyl and
phenyl carbons (140 ppm) and the unsubstituted phenyl carbons
(127 ppm), respectively. As to TPOP-2, there are two other peaks
at 146.1 and 64.9 ppm corresponding to substituted phenyl
carbons and quaternary carbons in tetraphenylmethane moieties,
respectively. For TPOP-3, besides the two broad peaks at 140
and 127 ppm aforementioned, two other signal peaks at 150.0
and 120.9 ppm can be ascribed to part of substituted and
unsubstituted phenyl carbons of spirobifluorenes, respectively.
In addition, the signal peak of quaternary carbons in spirobi-
fluorenes is also observed at 67.1 ppm. As for TPOP-4 and
TPOP-5 prepared by oxidative coupling polymerization, their
13C CP/MAS NMR spectra are shown in Fig. S2† with similar
signal distribution.
ꢁ
a vacuum oven at 110 C overnight.
When only tetrakis(2-thienyl) ethylene was used as the core
structural monomer, TPOP-4 was obtained according to the
procedure as described above in a yield of 77%.
3. Results and discussion
2,20,7,70-Tetrabromo-9,90-spirobifluorene and tetrakis(4-bromo-
phenyl) methane, as two types of monomers with spiral and
tetrahedral core structures, have been commonly selected for
constructing intrinsic porosity within the polymers by several
groups.12 In this work, tetrakis(4-bromophenyl) ethylene was
first used as one of the non-planar building blocks for prepara-
tion of porous polymers, owing to its propeller-like structure and
AIE characteristics. It can be obtained quantitatively from 4,40-
The porosity and porous structure of the polymers were
studied by sorption analysis using nitrogen as the sorbate
molecule. Typical nitrogen adsorption–desorption isotherms of
these polymers are shown in Fig. 2 and S3†. According to the
physisorption isotherms measured at 77 K, all polymers are
microporous and show a combination of type I and II nitrogen
gas sorption isotherms according to the IUPAC classification.22
The isotherms display a continuous increase after the adsorption
at low relative pressure, indicating an adsorption on the outer
surface of small particles. The increase in the nitrogen uptake at
a high relative pressure above 0.9 could be explained by
condensation of nitrogen in the meso- and macrostructures of the
samples and interparticular voids, respectively.12b In addition,
hysteresis was observed for the whole range of relative pressure
based on the isotherms, which is attributed to the swelling in
a flexible polymer framework or the restricted access of adsor-
bate to pores blocked by narrow openings, especially for non-
ordered nanoporous materials.12b,23
dibromobenzophenone through
a
titanium(0)-catalyzed
McMurry reaction.18 As shown in Scheme 1, the porous homo-
polymers TPOP-1 and TPOP-4 were synthesized efficiently by
a Suzuki coupling polycondensation and oxidative coupling
polymerization promoted by anhydrous FeCl3, respectively.
Considering that the different types of contorted or non-planar
core structures with similar reactivities would have different
impact on the surface areas of polymers, three copolymers
(TPOP-2, TPOP-3, and TPOP-5) containing two different types
of core structures were also prepared using the same methods.
All the polymers are chemically stable even when exposed to
dilute solutions of acid and base, such as HCl and NaOH.
Thermal analysis (Fig. S1†) shows that the material is stable up
to 300 ꢁC in all cases under nitrogen and there has been no
evidence for distinct glass transition for these polymers below the
thermal decomposition temperature due to the nature of their
cross-linking structures, which is consistent with good physico-
chemical robustness for most of the porous organic polymers.21
In order to confirm their structures, all polymers were charac-
terized at the molecular level by 13C CP/MAS NMR spectros-
copy. The 13C NMR spectra for the porous polymers with
assignment of the resonances are shown in Fig. 1. For polymers
TPOP-1, TPOP-2, and TPOP-3 prepared by Suzuki coupling
polymerization, there are two broad peaks approximately at
Listed in Table 1 are the key structural properties derived from
the isotherm, such as BET and Langmuir surface areas, micro-
pore surface areas and volumes. The BET specific surface areas
for these polymers range from 472 m2 gꢀ1 (TPOP-1) to 810 m2 gꢀ1
(TPOP-5), which are calculated over the relative pressure (P/P0)
range from 0.01 to 0.1 according to the previous report, which
gives a better fit than using the relative pressure range of 0.05–0.2
(see Fig. S5–9 and Table S1†).24 It should be noted that when
tetrakis(4-bromophenyl) ethylene (M-1) was used as the only one
core structural monomer, the obtained homopolymer (TPOP-1)
shows a low BET specific surface area. Similar result was found
for homopolymer P1 (450 m2 gꢀ1) obtained using the same
Scheme 1 Preparation of TPOPs by Suzuki coupling polymerization and oxidative coupling polymerization.
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Fig. 1 Selected 13C CP/MAS NMR spectra of prepared TPOPs.
method by Weber and Thomas,11a in which only tetra-
bromospirobifluorene (M-3) is a core structural monomer.
However, when the same amount of M-1 and M-3 were used as
core constructing monomers together, the BET specific
surface area of the synthetic copolymer (TPOP-3) increases to
765 m2 gꢀ1. When M-3 was replaced by tetrakis(4-bromophenyl)
methane (M-2), another copolymer (TPOP-2) can be obtained
through the same procedure, and its BET specific surface area is
673 m2 gꢀ1, which is also higher than that of TPOP-1. Using the
method of oxidative coupling of thiophenes, synthetic polymer
TPOP-5 containing two different core structural monomers
possesses a higher BET specific surface area (810 m2 gꢀ1) than
TPOP-4 (681 m2 gꢀ1). Cooper’s group6b has reported preparation
and physisorption properties of poly(aryleneethynylene) (PAE)
homopolymers and copolymers. Using a same core structural
building block, the micropore size and surface area of PAE
polymers can be fine-tuned by systematic variation of the
monomer strut length. Additionally, both the BET specific
surface area and the Langmuir surface area of the series of
copolymers fall between the related homopolymers. In light of
some cases in our work, keeping the length of the linker mono-
mer (BDBA) same, the surface area of copolymers prepared by
two different core structural monomers is higher than that of the
corresponding homopolymers. These results might provide some
new clues for the design and synthesis of porous organic
polymers.
For the non-ordered porous materials, accurate determination
of the pore size distribution (PSD) is very difficult. Different
results are usually obtained according to different calculation
methods. Furthermore, the pronounced hysteresis indicates that
porous polymers are swelling during the nitrogen sorption
measurement, which suggests that the pore structure probably
changes during the measurement. PSD analysis based on the
NLDFT approach has been used extensively to characterize
a wide variety of similar porous materials, although it does have
limitations.12a,24b However, the calculated results can give some
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Fig. 3 Pore size distribution of TPOPs calculated by the NLDFT
approach.
Fig. 2 Nitrogen adsorption–desorption isotherms of TPOPs measured
at 77 K. (The adsorption and desorption branches are labeled with filled
and open symbols, respectively.) See the ESI for a logarithmic plot of
adsorption isotherms (Fig. S4†).
hydrogen physisorption isotherms, we can see that TPOP-1 and
TPOP-2 seem to follow a linear increasing uptake at higher
pressures, while the others are inclined to level off. This suggests
that, as the randomly packed networks, conformation changes of
some polymers have probably taken place with enhancing pres-
sure, due to rotation and stretching of the building units, which
may provide some ‘‘hidden’’ micropores and surface area in the
polymers for hydrogen to continually permeate into these
materials.
related qualitative information, with which one can make
a relative comparison of materials synthesized from different
monomers. The PSDs of TPOPs were calculated from the
NLDFT approach. As shown in Fig. 3, for TPOPs prepared by
the Suzuki coupling polycondensation, pore widths are mainly
centered at 0.58 nm. Meanwhile, polymers TPOP-4 and TPOP-5
exhibit a similar pore size distribution with a dominant pore
width at 0.67 nm. Fig. S4† indicates that there is no big difference
in the nitrogen uptake behavior of TPOPs at the low relative
pressure (P/P0 < 0.1). On account of the good capacity in
hydrogen adsorption for many porous materials, we investigated
their hydrogen uptake based on the hydrogen physisorption
isotherms measured at 77 K up to a pressure of 1.13 bar (Fig. 4).
An increase in the total hydrogen capacity with increasing
surface area is observed. TPOP-5, possessing the highest micro-
pore volume and highest BET specific surface area, exhibits the
largest hydrogen uptake of 1.07 wt% at 1.13 bar and 77 K. The
hydrogen uptake capacity of TPOP-5 is not only higher than
some previously obtained porous organic polymers with similar
surface areas14,25 but also comparable to the reported element
organic framework, EOF-7, with a higher BET specific surface
area (1.14 wt% at 1 bar and 77 K, SBET ¼ 1083 m2 gꢀ1).12b As
shown in Fig. S10†, the hydrogen uptake behaviors of TPOPs are
similar at the low pressure range (P < 100 mmHg). From the
As expected, all TPE-based nanoporous organic polymers
show a non-ordered, amorphous structure proved by the X-ray
diffraction (XRD) measurements, due to the kinetic control of
the polymerization. Fig. 5 and S11† show the scanning electron
microscopy images and high-resolution transmission electron
microscopy images of the obtained polymers, respectively. They
exhibit a similar morphology with different particle sizes. The
typical SEM images of TPOP-3 (Fig. 5a and b) indicate that the
polymer consists of relatively uniform solid submicrometre
spheres with particle sizes from 100 to 150 nm. Whereas the
particle sizes of spheres in TPOP-4 are generally above 200 nm
(Fig. 5d and e). Small macropores or mesopores in the polymers
can be ascribed mostly to the interparticulate porosity that exists
between agglomerated microgel particles.26 The TEM images
(Fig. 5c and f) are indicative of porous structures of the materials,
which are similar to some reported amorphous microporous
organic polymers.6a
As aforementioned, TPE-based luminophor possesses the AIE
features. In the aggregate form or solid state, its
Table 1 Porosities and hydrogen uptake capacities of TPOPs
Hydrogen uptakee (wt%)
a
b
c
d
TPOPs
Monomer(s)
SBET /m2 gꢀ1
Smicro /m2 gꢀ1
Vtotal /cm3 gꢀ1
Vmicro /cm3 gꢀ1
TPOP-1
TPOP-2
TPOP-3
TPOP-4
TPOP-5
M-1
472 (533)
673 (760)
765 (851)
681 (768)
810 (912)
297
368
369
422
445
0.330
0.462
0.491
0.380
0.479
0.119
0.150
0.153
0.170
0.181
0.83
0.91
1.00
0.96
1.07
M-1 + M-2
M-1 + M-3
M-4
M-4 + M-5
a
Specific surface area calculated from the nitrogen adsorption isotherm using the BET method. The number in parentheses is the Langmuir surface area
calculated from the nitrogen adsorption isotherm by application of the Langmuir equation. Micropore surface area calculated from the nitrogen
b
c
d
adsorption isotherm using the t-plot method. Total pore volume at P/P0 ¼ 0.97. Micropore volume derived using the t-plot method based on the
e
Halsey thickness equation. Data were obtained at 1.13 bar and 77 K.
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Fig. 4 Gravimetric hydrogen adsorption isotherms for TPOP-1 (dia-
monds), TPOP-2 (down triangles), TPOP-3 (circles), TPOP-4 (squares),
and TPOP-5 (up triangles) at 77 K. See the ESI for a logarithmic plot of
adsorption isotherms (Fig. S10†).
Fig. 6 Fluorescent spectra of the polymers in the solid state (excitation
wavelength is 365 nm).
emission maximum peak at 530 nm (green emission, Fig. 6),
probably ascribed to the decreased extent of p-orbital overlap
owing to the tetraphenylmethane moieties. Furthermore,
compared to copolymers TPOP-2 and TPOP-3, polymer TPOP-1
displays an emission maximum peak at 560 nm (yellow emission,
Fig. 6). The red shift could be owing to the relatively enhanced
planar conformation of polymer backbone for TPOP-1 in the
solid state, considering that two different contorted core struc-
tural monomers are used to construct the network structure of
TPOP-2 and TPOP-3. Moreover, due to the electron-rich thio-
phene moieties with efficient charge carrier transport property,
the polymers of TPOP-4 and TPOP-5 show emission maximum
peaks at 590 and 610 nm, respectively. Photos of selected poly-
mers under UV light (365 nm) illumination are shown in
Fig. S12†. Weber and Thomas have also reported the emission
spectrum of the similar spirobifluorene-based polymer P1 with
a maximum peak at 460 nm (blue emission).11a Based on our
studies, the photoluminescence properties of porous polymers
can be tuned significantly by substituting a half amount of spi-
robifluorene building blocks with tetraphenylethylene, which
implies that the optical properties of the porous organic poly-
mers can also be controlled by using proper constructing
monomers.
photoluminescence intensity can be greatly enhanced. Because of
the network structure of the prepared porous polymers, intra-
molecular rotations of the TPE moieties are restricted. There-
fore, we can expect that TPE-based porous polymers shall exhibit
strong photoluminescence properties. Fig. 6 summarizes the
fluorescent properties of the polymers. Based on the emission
spectra, the maximum peaks of all polymers range from 530 to
610 nm, which are assigned to the p–p* transition of the
conjugated backbone. TPOP-3 exhibits an emission maximum
peak at 540 nm in the solid state. Compared with TPOP-3, the
blue shift in emission is observed for TPOP-2 which shows an
4. Conclusion
TPE-based porous organic polymers were prepared successfully
through palladium-catalyzed Suzuki coupling polymerization
and oxidative coupling polymerization, respectively. BET
specific surface areas for these polymers vary between 472 and
810 m2 gꢀ1, based on different core structural building blocks.
Incorporation of tetraphenylethylene moieties into these poly-
mers induced high photoluminescence (lmax: 530–610 nm) in the
solid state. Because of the propeller-like structure and AIE
characteristics, tetraphenylethylene is proved to be a novel
building block for the design of porous polymers with special
properties. Different types of contorted or non-planar core
structures with similar reactivity would have great impact on the
gas sorption and photoluminescence properties of polymers. By
selecting proper building units, both surface area and optical
property of porous organic polymers can be fine-tuned.
Fig. 5 SEM images of TPOP-3 (a and b) and TPOP-4 (d and e) and
TEM images of TPOP-3 (c) and TPOP-4 (f).
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11 (a) J. Weber and A. Thomas, J. Am. Chem. Soc., 2008, 130, 6334–
6335; (b) J. Weber, M. Antonietti and A. Thomas, Macromolecules,
2008, 41, 2880–2885.
€
12 (a) E. Stockel, X. Wu, A. Trewin, C. D. Wood, R. Clowes,
N. L. Campbell, J. T. A. Jones, Y. Z. Khimyak, D. J. Adams and
Acknowledgements
The financial supports of the Ministry of Science and Technology
of China (Grant 2011CB932502), National Science Foundation
of China (Grants 20972035, 91023001, and 21002017), and the
Chinese Academy of Science (Grant KJCX2-YW-H21) are
acknowledged.
A. I. Cooper, Chem. Commun., 2009, 212–214; (b) M. Rose,
€
N. Klein, W. Bohlmann, B. Bohringer, S. Fichtner and S. Kaskel,
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