Nitrogen-Containing microporous conjugated polymers via carbazole-based oxidative coupling polymerization: Preparation, porosity, and gas uptake

Article abstract of DOI:10.1002/smll.201301618

Facile preparation of microporous conjugated polycarbazoles via carbazole-based oxidative coupling polymerization is reported. The process to form the polymer network has cost-effective advantages such as using a cheap catalyst, mild reaction conditions, and requiring a single monomer. Because no other functional groups such as halo groups, boric acid, and alkyne are required for coupling polymerization, properties derived from monomers are likely to be fully retained and structures of final polymers are easier to characterize. A series of microporous conjugated polycarbazoles (CPOP-2-7) with permanent porosity are synthesized using versatile carbazolyl-bearing 2D and 3D conjugated core structures with non-planar rigid conformation as building units. The Brunauer-Emmett-Teller specific surface area values for these porous materials vary between 510 and 1430 m² g^-1. The dominant pore sizes of the polymers based on the different building blocks are located between 0.59 and 0.66 nm. Gas (H₂ and CO₂) adsorption isotherms show that CPOP-7 exhibits the best uptake capacity for hydrogen (1.51 wt% at 1.0 bar and 77 K) and carbon dioxide (13.2 wt% at 1.0 bar and 273 K) among the obtained polymers. Furthermore, its high CH₄/N₂ and CO ₂/N₂ adsorption selectivity gives polymer CPOP-7 potential application in gas separation. A series of microporous conjugated polycarbazoles with permanent porosity are synthesized via carbazole-based oxidative coupling polymerization using versatile carbazolyl-bearing 2D and 3D conjugated core structures with non-planar rigid conformation as building units. The Brunauer-Emmett-Teller specific surface areas of obtained polymers range from 510 to 1430 m² g^-1.

Full text of DOI:10.1002/smll.201301618

full papers
Porous Polymers
Nitrogen-Containing Microporous Conjugated Polymers
via Carbazole-Based Oxidative Coupling Polymerization:
Preparation, Porosity, and Gas Uptake
Qi Chen, De-Peng Liu, Min Luo, Li-Juan Feng, Yan-Chao Zhao, and Bao-Hang Han*
Dedicated to the 10th anniversary of the National Center for Nanoscience and Technology of China
F acile preparation of microporous conjugated polycarbazoles via carbazole-based
oxidative coupling polymerization is reported. The process to form the polymer
network has cost-effective advantages such as using a cheap catalyst, mild reaction
conditions, and requiring a single monomer. Because no other functional groups
such as halo groups, boric acid, and alkyne are required for coupling polymerization,
properties derived from monomers are likely to be fully retained and structures
of final polymers are easier to characterize. A series of microporous conjugated
polycarbazoles (CPOP-2–7) with permanent porosity are synthesized using versatile
carbazolyl-bearing 2D and 3D conjugated core structures with non-planar rigid
conformation as building units. The Brunauer–Emmett–Teller specific surface area
values for these porous materials vary between 510 and 1430 m2 g−1. The dominant
pore sizes of the polymers based on the different building blocks are located between
0.59 and 0.66 nm. Gas (H2 and CO2) adsorption isotherms show that CPOP-7 exhibits
the best uptake capacity for hydrogen (1.51 wt% at 1.0 bar and 77 K) and carbon
dioxide (13.2 wt% at 1.0 bar and 273 K) among the obtained polymers. Furthermore,
its high CH4/N2 and CO2/N2 adsorption selectivity gives polymer CPOP-7 potential
application in gas separation.
Microporous conjugated polymers, as the special
microporous polymers with unique functions, have drawn
great attention in recent years. Different types of CϪC cou-
1. Introduction
Microporous polymers with the intrinsic properties including
pling reactions, such as the Suzuki coupling reaction,[4] the
Sonogashira−Hagihara coupling reaction,[5] the Yamamoto
reaction,[6] and the ethynyl trimerization reaction,[7] were
applied to synthesize microporous conjugated polymers.
However, the required preparative conditions such as
expensive catalysts and high reaction temperature limit cost-
effective preparation of the polymers on a large scale. In par-
ticular, effects of unavoidable residues derived from catalysts
and the monomer reactive groups (halo group, boric acid,
and alkyne) on the properties and functions of microporous
polymers are unclear.[8] Therefore, it is necessary to develop
a facile method for the polymer preparation.
large specific surface areas, high chemical stabilities, and
low skeleton density, have potential application in heteroge-
neous catalysis[1] and gas storage and separation.[2] Versatile
microporous polymers have been obtained smoothly through
a template-free chemical process by selection of proper
building blocks and polymerization reactions, which show effi-
cient preparation and high flexibility in the molecular design.[3]
Dr. Q. Chen, D.-P. Liu, M. Luo, L.-J. Feng,
Y.-C. Zhao, Prof. B.-H. Han
National Center for Nanoscience and Technology
Beijing, 100190, China
E-mail: hanbh@nanoctr.cn
FeCl3-promoted oxidative coupling polymerization[9] has
cost-effective advantages in the preparation of microporous
DOI: 10.1002/smll.201301618
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
308 wileyonlinelibrary.com
small 2014, 10, No. 2, 308–315

Nitrogen-Containing Microporous Conjugated Polymers
conjugated backbone of polycarbazole is
beneficial for the formation of a porous
polymer with permanent porosity and high
physicochemical stability. Most impor-
tantly, the nitrogen-containing conjugated
structure makes the polymer electron-
rich, which may enhance the interaction
between specific sorbate molecule and
adsorbent.[10a,15] To deepen insight into
the properties of microporous polycar-
bazole polymers and expand the applica-
tion of carbazole-based oxidative coupling
polymerization to prepare various of
microporous conjugated polymers, in this
article, a series of microporous conjugated
polycarbazoles with permanent porosity
and special functions were synthesized
using versatile carbazolyl-bearing 2D and
3D conjugated core structures with non-
planar rigid conformation as building
units (Scheme 1). Their porosities and gas
adsorption capacities were also studied.
Scheme 1. Preparation of microporous conjugated polymers CPOP-2∼7 .
conjugated polymers, such as using a cheap catalyst, room
temperature reaction conditions, high yield, and requiring
2. Preparation and Characterization
a single monomer, which are essential for scale-up prepara- It was established that the building units show crucial effects
tion of porous materials. Thiophene-based oxidative cou- on the porosity, specific surface areas, and gas adsorption
pling polymerization has been firstly used in the preparation capacities of the final porous organic polymers. 2D and 3D
of porous poly(arylenethiophene) polymers,[10] in which the conjugated architectures with non-planar rigid conformation,
highest Brunauer–Emmett–Teller (BET) specific surface area such as [2.2]paracyclophan,[16] triphenylamine,[17] triphenylb-
of the obtained microporous polymers is up to 1520 m2 g−1.[11] enzene,[18] and tetraphenylethylene (TPE),[19] have been
Recently, our group reported microporous polycarbazole proven to be good candidates for the monomer core struc-
(CPOP-1) possessing a large specific surface area (above ture to form microporous polymers with permanent porosity
2000 m2 g−1), high gas uptake capacity (2.80 wt% for H2 at and special functions. Carbazolyl groups can be easily intro-
1.0 bar and 77 K, 21.2 wt% for CO2 at 1.0 bar and 273 K), duced into these monomer core structures to afford versatile
good selectivity for CO2 over N2 or CH4 (CO2/CH4 and CO2/ building units for porous polymer preparation. As shown in
N2 adsorption selectivity at 1.0 bar and 273 K is 33 and 25, Scheme 2, monomer Cz-4 was obtained from 4-(9-carbazolyl)
respectively), and intrinsic photoluminescence capacity.[12] phenylboronic acid (1) and 4,16-dibromo[2.2]paracyclophan
CPOP-1 is obtained through carbazole-based oxidative (2) by the Suzuki reaction. The known building block Cz-6
coupling polymerization, in which catalyst FeCl3 can be com- was synthesized by oxo-trimerization of 4-(9-carbazolyl)
pletely removed after easy purification. Because no other phenylethanone (3) rather than the reported palladium-
functional groups such as halo groups, boric acid, or alkyne promoted N-arylation.[20] TPE-containing monomer Cz-7
are required for the coupling polymerization, the effects of can be efficiently prepared through a titanium(0)-catalyzed
the reactive group residues need not be considered. More- McMurry reaction of 4,4′-bis(9-carbazolyl)benzophenone (4).
over, properties derived from monomers are likely to be fully In addition, monomers Cz-2 and Cz-3 are commercially avail-
retained and structures of final polymers are easier to char- able and triphenylamine-based monomer Cz-5 was obtained
acterized. We believe this is a promising method to facilitate according to reported procedure.[21] The chemical structures
preparation of nitrogen-containing microporous polymers.
Our previous studies have shown that the capability
of all monomers were fully confirmed.
Using the aforementioned monomers, carbazole-based
of microporous organic polymers for gas storage and sepa- oxidative coupling polymerization was promoted smoothly
ration is affected by multiple factors such as the material by anhydrous FeCl3 in dry chloroform under nitrogen protec-
nature, specific surface area, pore structure, and material tion at room temperature. Polymers CPOP-2–7 were finally
morphology.[13] It is still a challenge to develop microporous obtained from their corresponding monomers Cz-2–7. All
organic polymers with potential use and good performance polymers are chemically stable, even when exposed to dilute
for the gas storage and separation. Conjugated polycarbazole solutions of acid or base, such as HCl or NaOH. The thermal
with good electroactivity and useful photophysical properties stability of the polymers was characterized by thermogravi-
is a suitable candidate for exploration of porous organic poly- metric analysis (Figure S1, Supporting Information) and 5%
mers possessing special functions and properties.[14] The rigid mass loss was observed from 430 to 610 °C under nitrogen.
www.small-journal.com
309
small 2014, 10, No. 2, 308–315
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Q. Chen et al.
full papers
at 140, 125, 120, and 110 ppm, which are
derived from the signal intensities of the
same repeating units shown in Figure 1.
For example, for CPOP-2, the peak at
140.8 ppm corresponds to the substituted
phenyl carbons binding with nitrogen
atom. The high-intensity peak at 125.5
ppm is ascribed to the signal peak of other
substituted phenyl carbons. The signal
peaks for the unsubstituted phenyl car-
bons are located at 120.3 and 109.7 ppm,
respectively. The solid-state 13C cross
polarizationmagic angle spinning (CP/
MAS) NMR spectra of the other polymers
exhibit similar signal distribution, except
for CPOP-4, in which an additional broad
peak at about 40.0 ppm is corresponding to
the methylene carbons. The 13C CP/MAS
spectra for all the polymers with detailed
assignment of the resonances are shown in
Figures S2a−f (Supporting Information).
The scanning electron microscopy
(SEM) images of the obtained polymers
are shown in Figure S3 (Supporting Infor-
mation). For CPOP-2–4 and CPOP-7, they
exhibit a similar morphology as solid sub-
micrometer spheres with different particle
sizes from 100 to 200 nm. The SEM images
of CPOP-5 and CPOP-6 indicate the
plate-like and rod-like structures, respec-
tively. Small macropores or mesopores in
the polymers can be ascribed mostly to the
interparticulate porosity exists between
agglomerated microgel particles, plates, or
Scheme 2. Synthetic routs to monomers Cz-4, Cz-6, and Cz-7.
It has no evidence for distinct glass transition for these rods. The energy dispersive X-ray (EDX) spectra of all poly-
polymers below the thermal decomposition temperature due mers are shown in Figures S4a−f (Supporting Information)
to the nature of their cross-linking structures. Their struc- and no signal peak for iron element was found. We then ran
tures were cha racterized at the molecular level by 13C CP/ thermogravimetric analysis of all polymers under air. The
MAS NMR spectrum. Figure 1 shows the 13C NMR spectra data (Figure S5a−f, Supporting Information) clearly indicate
for the obtained polymers with assignment of the reso- that the obtained polymers have been completely decom-
nances. Generally, there are four broad peaks approximately posed up to 700 °C and no catalyst residue was found.Among
the prepared polymers, CPOP-2, CPOP-5, and CPOP-7
exhibit intrinsic photoluminescence properties. Based on the
emission spectra (Figure S6a−c, Supporting Information), the
maximum peaks of these polymers range from 460 to 550 nm,
which are assigned to the π−π* transition of the conjugated
backbone.
3. Porosities
The porosity parameters of the polymers were studied by
sorption analysis using nitrogen as the sorbate molecule.
Nitrogen adsorption–desorption isotherms of CPOPs meas-
ured at 77 K are shown in Figure 2, which exhibit a combina-
tion of type I and II nitrogen sorption isotherms according
to the IUPAC classification.[22] The increase in the nitrogen
Figure 1. 13C CP/MAS NMR spectra of CPOP-2–7 (asterisks denote
sorption at a high relative pressure above 0.9, for example
spinning sidebands).
CPOP-7, may arise in part from interparticulate porosity
www.small-journal.com
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
310
small 2014, 10, No. 2, 308–315

Nitrogen-Containing Microporous Conjugated Polymers
Figure 2. Nitrogen adsorption–desorption isotherms of CPOP-2–7
measured at 77 K (the adsorption and desorption branches are labeled
with solid and open symbols, respectively.) For clarity, the isotherms
of CPOP-3–7 were shifted vertically by 150, 450, 500, 800, and
900 cm3 g−1, respectively.
Figure 3. The pore size distribution profiles of CPOP-2∼7 calculated by
NLDFT.
However, the calculated results can give us some related
associated with the meso- and macrostructures of the sam- qualitative information, with which one can make the rela-
ples and interparticular void.[23] Hysteresis can be observed tive comparison of materials synthesized from different
apparently for CPOP-5–7 in the whole range of relative pres- monomers. The PSD profiles of polymers CPOP-2–7 were
sure based on the isotherms due to a linear increase of the calculated from the adsorption branch of the isotherms with
adsorbed volume upon adsorption, which might be attrib- the NLDFT approach. As shown in Figure 3, the dominant
uted to the swelling in a flexible polymer framework induced pore sizes of the obtained polymers range between 0.59 and
by adsorbate molecules dissolved in nominally nonporous 0.66 nm based on different building blocks. For instance,
parts of the polymer matrix after filling of open and acces- bis(carbazoyl)-substituted monomers Cz-2–4 possessing
sible voids or the restricted access of adsorbate to the pores core structures with the increasing length (phenylene, biphe-
blocked by narrow openings.[24]
nylene, 4,16-diphenyl[2.2]paracyclophane) furnish polymers
The specific surface area values calculated in the rela- CPOP-2–4 with the increasing dominant pore sizes. Listed
tive pressure (P/P0) range from 0.01 to 0.1 according to the in Table 1 are the key structural properties of polymers,
previous reports[25] (Figures S7a−f, Supporting Information) which are derived from the corresponding isotherm, such as
show that the BET specific surface area data of CPOP-2–7 the BET specific surface area, micropore surface area, pore
range from 510 to 1430 m2 g−1. Generally, CPOP-2–4 pre- volume, and dominant pore size.
pared from monomers containing two carbazoyl groups
(Cz-2–4) show lower BET specific surface area (below
700 m2 g−1). In contrast, monomers with three or four car-
4. Gas Uptake
bazoyl groups (Cz-5–7) can furnish microporous polymers
(CPOP-5–7) with higher BET specific surface area, in which Microporous conjugated polymers with a narrow pore dis-
CPOP-7 possesses the highest BET specific surface area tribution may interact attractively with small gas molecules
about 1430 m2 g−1. It is reasonable to comprehend that more
reaction sites of the monomer result in higher cross-linking
structure, which endows the polymers with more stable and
permanent pore structure and increasing specific surface area.
Each carbazoyl group in the monomer has two reaction sites
for the oxidative polymerization, which make bis-substituted
monomers such as Cz-2–4 capable to form porous polymers
via the carbazole-based oxidative coupling polymerization.
If using some other coupling polymerization methods such
as the Suzuki coupling reaction, the Sonogashira−Hagihara
coupling reaction, or the Yamamoto reaction, bis-substituted
monomers generally give linear polymers.
Table 1. Porosity Properties and Gas Uptake Capacities of CPOP-2∼7.
a)
b)
c)
d)
Polymers
SBET
Smicro
Vtotal
Dpore
CO2 Uptake e) H2 Uptakef)
(m2 g−1
510
)
(m2 g−1
230
)
(cm3 g−1
0.352
0.530
0.361
0.940
0.772
1.512
)
(nm)
0.59
0.60
0.63
0.60
0.63
0.66
(wt%)
(wt%)
1.29
0.91
0.93
1.26
1.23
1.51
CPOP-2
CPOP-3
CPOP-4
CPOP-5
CPOP-6
CPOP-7
7.8
630
280
8.4
660
470
9.0
1050
980
390
11.8
11.5
13.2
440
1430
360
a)Specific surface area calculated from the adsorption branch of the nitrogen adsorption−des-
orption isotherm using the BET method; b) Micropore surface area calculated from the adsorp-
The pore size distribution (PSD) analysis based on
the nonlocal density function theory (NLDFT) approach
has been used extensively to characterize a wide variety of
porous materials although it does have some limitations.[23b]
c)
tion branch of the nitrogen adsorption−desorption isotherm using the t -plot method; Total
pore volume at P/ P 0 = 0.97; d) Data calculated from nitrogen adsorption−desorption isotherms
with the NLDFT method; e)Data were obtained at 1.0 bar and 273 K; f)Data were obtained at
1.0 bar and 77 K.
www.small-journal.com
311
small 2014, 10, No. 2, 308–315
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Q. Chen et al.
full papers
also play crucial roles in the hydrogen uptake capacity of the
porous polymers.
To investigate the impact of microporosity and the chem-
ical nature of pore surfaces of obtained polymers on the
hydrogen uptake, we further measured hydrogen adsorption
isotherms of CPOP-2, CPOP-5, and CPOP-7 at 87 K and cal-
culated their isosteric heat of hydrogen adsorption based on
adsorption isotherms at different temperatures (77 and 87 K)
from 0 to 1.13 bar through the Clausius−Clapeyron equation.
As shown in Figure S8 (Supporting Information), it can be
observed that, at zero coverage, the isosteric heat of CPOP-2
is surprisingly high, up to 7.5 kJ mol−1, which is not only higher
than CPOP-5 (6.4 kJ mol−1), CPOP-7 (6.8 kJ mol−1), and some
reported porous polymers such as PAF-1 (4.6 kJ mol−1),[27] and
polyimide network PI-1 (5.3 kJ mol−1),[28] but also comparable
to adamantine-based PPNs (5.51−7.59 kJ mol−1)[29] and poly-
benzimidazole BILP-1 (7.9 kJ mol−1).[30] The higher heat of
adsorption implies the presence of enhanced affinity between
hydrogen molecules and CPOP-2. Therefore, CPOP-2 with
a low BET specific surface area shows an unusual hydrogen
uptake capacity. As for CPOP-7 with relatively lower isos-
teric heat of hydrogen adsorption, its higher specific surface
area and pore volume play the dominant roles in hydrogen
uptake. As a result, CPOP-7 exhibits the highest hydrogen
uptake capacity at 1.0 bar and 77 K among the obtained
polymers. From the hydrogen physisorption isotherms (Figure
4a), the uptaking capacity of CPOP-2 enhances apparently
when the absolute pressure is up to 200 mmHg and exceeds
the uptaking capacities of CPOP-3–6 with increasing pres-
sures. Probably, conformation changes of the polymer with
the randomly packed network has taken place with released
heat by H2 adsorption, due to rotation and stretching of the
building units, which may provide some “hidden” micropores
Figure 4. Gas adsorption isotherms of CPOP-2–7: a) H2 at 77 K; b) CO2
at 273 K.
through improved molecular interaction. Furthermore, and surface area in the polymer for hydrogen to continually
electron-rich polycarbazole network and high charge den- permeate into this material.
sity at the nitrogen sites of the polymer might facilitate more
The uptake capacity of CPOP-2–7 for carbon dioxide is
favorably the interaction between sorbate molecule and also studied. From the carbon dioxide physisorption isotherms
adsorbent.[12] Therefore, as the nitrogen-containing micropo- measured at 273 K and a pressure up to 1.13 bar (Figure 4b),
rous conjugated polymers, CPOP-2–7 inspired us to investi- we can find an increasing trend in the carbon dioxide loading
gate their gas (H2 and CO2) uptaking capacities.
capacity (from 7.8 to 13.2 wt%) with increasing specific sur-
Hydrogen uptake capacities of CPOP-2–7 based on the face area. Polymers CPOP-5–7 show higher carbon dioxide
hydrogen physisorption isotherms measured at 77 K and a uptake capacities than other obtained materials. CPOP-7
pressure up to 1.13 bar are shown in Figure 4a. Except for exhibits the highest carbon dioxide storage of 13.2 wt% at
CPOP-2, an increase in the hydrogen loading capacity with 1.0 bar and 273 K. The isosteric heat of CPOP-5–7 for CO2
increasing specific surface area is observed. CPOP-7, pos- adsorption (Figure S9, Supporting Information) was esti-
sessing the highest BET specific surface area and total pore mated based on adsorption data collected at different tem-
volume, exhibits the highest hydrogen uptake of 1.51 wt% at peratures (273 and 293 K) from 0 to 1.13 bar. Compared
1.0 bar and 77 K among the obtained polymers, which indi- with CPOP-6 (29.8 kJ mol−1) and CPOP-7 (26.9 kJ mol−1),
cate that the specific surface area of porous polymer has a the heat of adsorption in CPOP-5 is highest and up to
significant effect on the hydrogen uptake. CPOP-2 with a 31.5 kJ mol−1 at zero coverage. Most importantly, they remain
low BET specific surface area (510 m2 g−1) shows a compa- almost constant over the whole gas loading range. These
rable hydrogen uptake (1.29 wt% at 1 bar, 77 K) with some values are higher than those for other porous polymer ana-
porous polymers possessing high specific surface area (more logs, such as HCP materials (20−24 kJ mol−1),[31] polybenzi-
than 1000 m2 g−1), such as CPOP-5 (1.26 wt% at 1 bar, 77 K, midazole BILP-1 (26.5 kJ mol−1),[30] polycarbazole CPOP-1
SBET = 1050 m2 g−1), the element organic framework EOF-6 (27 kJ mol−1),[12] and can be comparable to some CMP mate-
(1.29 wt% at 1 bar, 77 K, SBET = 1380 m2 g−1)[23a] and covalent rials with or without functional groups (25−33 kJ mol−1).[15,32]
organic framework COF-102 (1.20 wt% at 1 bar, 77 K, SBET
=
The high adsorption heat may imply the presence of the
3620 m2 g−1).[26] These results prove that, besides the specific affinity with the polarizable CO2 molecules through local-
surface area, structure and chemical nature of the polymer dipole/quadrupole interactions facilitated more favorably by
www.small-journal.com
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
312
small 2014, 10, No. 2, 308–315

Nitrogen-Containing Microporous Conjugated Polymers
monomers easy to form porous polymers via the carba-
zole-based oxidative coupling polymerization. Due to the
high cross-linking structure, the pores in the polymer are
more stable and permanent. Among the obtained polymers,
CPOP-7 exhibits the best uptake capacity for hydrogen (1.51
wt% at 1.0 bar and 77 K) and carbon dioxide (13.2 wt% at
1.0 bar and 273 K). Furthermore, its high CH4/N2 and CO2/
N2 adsorption selectivity makes polymer CPOP-7 possess
potential application in gas separation.
6. Experimental Section
Materials: All chemical reagents were commercially avail-
able and used as received unless otherwise stated. 1,4-Bis(9-
carbazolyl)benzene
(Cz-2),
4,4′-bis(9-carbazolyl)biphenyl
Figure 5. Gas adsorption isotherms (CO2, CH4 and N2) of CPOP-7 at
273 K.
(Cz-3), and 4,16-dibromo[2.2]paracyclophan (2) were pur-
chased from Acros company. Titanium trichloride complex and
tetrakis(triphenylphosphine)palladium(0) were purchased Alfa
Aesar company. 4-(9-Carbazolyl)phenylboronic acid (1),[33]
4-(9-carbazolyl)phenylethanone (3),[34] 4,4′-bis(9-carbazolyl)ben-
zophenone (4),[35] and triphenylamine-based monomer Cz-5[21]
were prepared according to reported methods, respectively.
electron-rich polycarbazole network and high charge density
at the nitrogen sites of polymer. From the CO2 sorption iso-
therms, CPOP-5–7 exhibit similar loading capacity at a lower
pressure range (less than 200 mmHg) mainly due to the
higher affinity of CPOP-5 and CPOP-6. In the higher pres-
sure range, where the surface area and pore volume become
dominant, CPOP-7 exhibits the highest uptake capacity.
Besides gas storage, the selectivity is very important
for potential application in gas separation. Considering the
best gas adsorption performance and the highest porosity
of CPOP-7 among the obtained polymers, the gas selective
adsorption behavior of CPOP-7 is measured and evidenced
by the pure component isotherm data presented in Figure 5.
The CO2 or CH4 uptake shows a nearly linear increase with
the pressure whereas that of nitrogen has no apparent
increase trend. At 273 K and 1.0 bar, the CO2 or CH4 uptake
capacity is nearly same (3.0 mmol g−1). In comparison, the
nitrogen uptake of CPOP-7 under the same conditions is
0.1 mmol g−1. The data show that CPOP-7 has no significant
CO2/CH4 adsorption selectivity due to the similar saturation
capacity. However, the estimated ideal CH4/N2 or CO2/N2
adsorption selectivity is up to 30/1.
Measurements: The 1H and 13C NMR spectra were recorded
on a Bruker DMX400 NMR spectrometer. Solid-state CP/MAS NMR
spectra were recorded on a Bruker Avance III 400 NMR spectro-
meter. The samples were spun at MAS rate of 5 KHz in all experi-
ments. 13C NMR spectra were acquired using a cross polarization
pulse sequence with total suppression of side bands (CPTOSS)
and a pulse length of 7.5 μs. The contact time (ct) is 3.0 ms.
Mass spectra were recorded with a Microflex LRF MALDI-TOF mass
spectrometer. SEM observations were carried out using a Hitachi
S-4800 microscope (Hitachi Ltd., Japan) at an accelerating voltage
of 20.0 kV without sputter coating and equipped with a Horiba
energy dispersive X-ray spectrometer. The fluorescence spectra
were measured using a Perkin−Elmer LS55 luminescence spec-
trometer. Thermogravimetric analysis was performed on a Pyris
Diamond thermogravimetric/differential thermal analyzer by
heating the samples at 10 °C min−1 to 800 °C in the atmosphere
of nitrogen or air. Gas sorption isotherms were obtained with
Micromeritics TriStar II 3020 and Micromeritics ASAP 2020 M+C
accelerated surface area and porosimetry analyzers at certain
temperature. The samples were degassed overnight at 120 °C.
The obtained adsorption−desorption isotherms were evaluated to
5. Conclusion
A
series of nitrogen-containing microporous polymers give the pore parameters, including BET specific surface area, pore
have been prepared via carbazole-based oxidative coupling size, and pore volume. The pore size distribution was calculated
polymerization method with cost-effective advantages. 2D from the adsorption branch with the NLDFT approach. Total pore
and 3D conjugated architectures with non-planar rigid con- volume was calculated from nitrogen adsorption−desorption iso-
formation have been proven to be good candidates for the therms at P/P0 = 0.97.
monomer core structure and carbazolyl groups can be easily
Synthesis of Cz-4: 4-(9-Carbazolyl)phenylboronic acid (1)
introduced into these monomer core structures to afford (896.0 mg, 3.4 mmol) and 4,16-dibromo[2.2]paracyclophan (2)
versatile building units polymer preparation. The BET spe- (366.0 mg, 1.0 mmol) were dissolved in dimethylformamide (DMF,
cific surface area values for obtained porous materials vary 40 mL). To the mixture were added aqueous solution of potassium
between 510 to 1430 m2 g−1. The dominant pore sizes of the carbonate (2.0 M, 10 mL) and then tetrakis(triphenylphosphine)
polymers based on different building blocks are located palladium(0) (30 mg, 33 μmol) under nitrogen atmosphere after
between 0.59 and 0.66 nm. No other functional groups such being degassed by the freeze−pump−thaw cycles. The reaction
as halo groups, boric acid, or alkyne are required for coupling solution was stirred at 120 °C for 8 h, and TLC showed that the
polymerization. Each carbazoyl group in the monomer has reaction was completed. The resulting mixture was cooled to room
two reaction sites, which make multi(carbazoyl)-substituted temperature, poured into water and extracted with ethyl acetate.
www.small-journal.com
313
small 2014, 10, No. 2, 308–315
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Q. Chen et al.
full papers
The combined organic layer was dried over anhydrous sodium sul-
fate and concentrated under reduced pressure. The crude product
was purified by column chromatography on silica gel (petroleum
ether) to give the product Cz-4 (350 mg, 51%) as a white solid. 1H
NMR (400 MHz, CDCl3, δ): 8.19 (d, 4H, J = 6.0 Hz), 7.82−7.77 (m,
4H), 7.72 (d, 4H, J = 8.4 Hz), 7.58 (d, 4H, J = 8.4 Hz), 7.48 (t, 4H,
J = 7.2 Hz), 7.33 (t, 4H, J = 7.2 Hz), 6.84−6.82 (m, 2H), 6.79−6.74
(m, 4H), 3.75−3.57 (m, 2H), 3.20−3.10 (m, 2H), 3.05−2.80 (m,
4H). 13C NMR (100 MHz, CDCl3, δ): 141.3, 140.9, 140.4, 140.1,
137.0, 136.5, 135.0, 132.5, 131.1, 129.6, 127.1, 126.0, 123.5,
120.4, 120.0, 109.9, 34.9, 33.9. MS (MALDI-TOF) m/z: calculated
for C52H38N2: 690.30 [M]; found: 690.45 [M].
Synthesis of Cz-6: 4-(9-Carbazolyl)phenylethanone (3) (1.0 g,
1.0 mmol) was suspended and stirred in dried ethanol (20 mL)
and tetrahydrofuran (THF, 10 mL). Thionyl chloride (1.5 mL) was
added gradually to the solution with caution at 0 °C. After 1 h, the
temperature was allowed to rise to room temperature, and then
the mixture was refluxed overnight. After cooling to room tempera-
ture, the precipitate was collected by filtration and then washed
with ethanol and recrystallized from dichloromethane to afford
Cz-6 (300 mg, 38%) as a white powder, which was further charac-
terized as reported.[20] 1H NMR (400 MHz, CDCl3, δ): 8.19 (d, 6H,
J = 8.0 Hz), 8.05 (s, 3H), 8.03 (d, 6H, J = 8.4 Hz), 7.76 (d, 6H, J
= 8.4 Hz), 7.54 (d, 6H, J = 8.0 Hz), 7.46 (t, 6H, J = 7.6 Hz), 7.33
(t, 6H, J = 7.4 Hz). MS (MALDI-TOF) m/z: calculated for C60H39N3:
801.31 [M]; found: 802.04 [M+1].
Supporting Information
Supporting Information is available from the Wiley Online Library
or from the author.
Acknowledgements
The financial support of the National Science Foundation of China
(Grants 91023001, 21002017, and 21274033) and the Chinese
Academy of Science (Grant KJCX2-YW-H21) is acknowledged.
[1] a) Y. Zhang, S. N. Riduan, Chem. Soc. Rev. 2012, 41, 2083;
b) P. Kaur, J. T. Hupp, S. B. T. Nguyen, ACS Catal. 2011, 1, 819;
c) R. Palkovits, M. Antonietti, P. Kuhn, A. Thomas, F. Schüth,
Angew. Chem., Int. Ed. 200 9, 48, 6909; d) J. Roeser, K. Kailasam,
A . T h o m a s , ChemSusChem 2012, 5, 1793.
[2] a) R. Dawson, A. I. Cooper, D. J. Adams, Prog. Polym. Sci. 2012,
37, 530; b) N. B. McKeown, P. M. Budd, Macromolecules 2010,
43, 5163; c) J. Germain, J. M. J. Frechét, F. Svec, Small 2009, 5,
1098; d) C. G. Bezzu, M. Carta, A. Tonkins, J. C. Jansen,
P. Bernardo, F. Bazzarelli, N. B. McKeown, Adv. Mater. 2012,
24, 5930; e) N. Du, H. B. Park, G. P. Robertson, M. M. Dal-Cin,
T. Visser, L. Scoles, M. D. Guiver, Nat. Mater. 2011, 10, 372.
[3] a) D. Wu, F. Xu, B. Sun, R. Fu, H. He, K. Matyjaszewski, Chem. Rev.
2012, 112, 3959; b) J. X. Jiang, A. I. Cooper, Top. Curr. Chem.
2010, 293, 1; c) S. Ren, M. J. Bojdys, R. Dawson, A. Laybourn,
Y. Z. Khimyak, D. J. Adams, A. I. Cooper, Adv. Mater. 2012, 24,
2357.
Synthesis of Cz-7: To a mixture of 4,4′-bis(9-carbazolyl)benzo-
phenone (4) (773 mg, 1.5 mmol), Zn (784 mg, 12.0 mmol) and 30 mL
of dry THF was added TiCl3-AlCl3 (3.0 g) under nitrogen atmos-
phere. The mixture was stirred for 30 min at room temperature
and then refluxed overnight. After cooling to room temperature,
triethylamine (5 mL) was added and the mixture was filtrated. The
filtrates were extracted with dichloromethane and dried over anhy-
drous sodium sulfate. After removal of the solvents under reduced
pressure, the crude product was recrystallized from acetone and
dichloromethane co-solvent to give Cz-7 (250 mg, 33%) as a white
[4] J. Weber, A. Thomas, J. Am. Chem. Soc. 2008, 130, 6334.
[5] J. X. Jiang, F. Su, A. Trewin, C. D. Wood, N. L. Campbell, H. Niu,
C. Dickinson, A. Y. Ganin, M. J. Rosseinsky, Y. Z. Khimyak,
A. I. Cooper, Angew. Chem., Int. Ed. 2007, 46, 8574.
[6] J. Schmidt, M. Werner, A. Thomas, Macromolecules 2009, 42,
4426.
[7] S. Yuan, B. Dorney, D. White, S. Kirklin, P. Zapol, L. Yu, D. J. Liu,
Chem. Commun. 2010, 46, 4547.
1
solid. H NMR (400 MHz, CDCl3, δ): 8.16 (d, 8H, J = 7.6 Hz), 7.54
(s, 16H), 7.45 (d, 8H, J = 8.4 Hz), 7.36 (t, 8H, J = 7.4 Hz), 7.30
(t, 8H, J = 7.4 Hz). 13C NMR (100 MHz, CDCl3, δ): 142.0, 141.2,
140.7, 136.7, 132.9, 126.6, 126.1, 123.5, 120.4, 120.1, 109.7.
MS (MALDI-TOF) m/z: calculated for C74H48N4: 992.39 [M]; found:
993.30 [M+1].
[8] H. Lim, J. Y. Chang, Macromolecules 2010, 43, 6943.
[9] M. Ueda, T. Abe, H. Awano, Macromolecules 1992, 25, 5125.
[10] a) S. Yuan, S. Kirklin, B. Dorney, D. J. Liu, L. Yu, Macromol-
ecules 2009, 42, 1554; b) J. Schmidt, J. Weber, J. D. Epping,
M. Antonietti, A. Thormas, Adv. Mater. 2009, 21, 702.
[11] J. Xia, S. Yuan, Z. Wang, S. Kirklin, B. Dorney, D. J. Liu, L. Yu, Mac-
romolecules 2010, 43, 3325.
Synthesis of CPOP-2–7 by Carbazole-Based Oxidative Coupling
Polymerization: CPOP-2–7 were prepared through FeCl3-promoted
oxidative coupling polymerization from corresponding monomers
Cz-2–7. A representative procedure for preparation of CPOP-7 from
Cz-7 is given in details: Cz-7 (150 mg, 0.15 mmol) was dispersed
in anhydrous chloroform (25 mL), and then transferred dropwise
to a suspension of ferric chloride (585 mg, 3.6 mmol) in anhy-
drous chloroform (15 mL). The mixture was stirred for 1 day under
nitrogen at room temperature, and then 50 mL of methanol was
added to the reaction mixture. The resulting mixture was kept stir-
ring for another hour and the precipitate was collected by filtration.
After being washed with methanol, the obtained solid was stirred
vigorously in hydrochloric acid solution (37%) for 2 h. The suspen-
sion was then filtered and washed with water and methanol. After
extracted in a Soxhlet extractor with methanol for 24 h, and then
with THF for another 24 h, the desired polymer CPOP-7 was col-
lected and dried in vacuum oven at 110 °C overnight (yield: 98%).
[12] Q. Chen, M. Luo, P. Hammershφj, Y. Han, B. W. Laursen, C. G. Yan,
B. H. Han, J. Am. Chem. Soc. 2012, 134, 6084.
[13] a) Q. Chen, J.-X. Wang, Q. Wang, N. Bian, Z.-H. Li, B.-H. Han,
Macromolecules 2011, 44, 7987; b) Y.-C. Zhao, D. Zhou,
Q. Chen, X.-J. Zhang, N. Bian, A.-D. Qi, B.-H. Han, Macromolecules
2011, 44, 6382; c) Q. Chen, M. Luo, T. Wang, J.-X. Wang, D. Zhou,
Y. Han, C.-G. Yan, B.-H. Han, Macromolecules 2011, 44, 5573;
d) Q. Chen, Q. Wang, M. Luo, L.-J. Mao, C.-G. Yan, Z.-H. Li,
B.-H. Han, Polymer 2012, 53, 2032.
[14] a) J. F. Morin, M. Leclerc, D. Ades, A. Siove, Macromol. Rapid
Commun. 2005, 26, 761; b) N. Blouin, M. Leclerc, Acc. Chem.
Res. 2008, 41, 1110.
[15] R. Dawson, E. Stockel, J. R. Holst, D. J. Adams, A. I. Cooper, Energy
Environ. Sci. 2011, 4, 4239.
[16] Y. Morisaki, M. Gon, Y. Tsuji, Y. Kajiwara, Y. Chujo, Tetrahedron
Lett. 2011, 52, 5504.
[17] J. X. Jiang, A. Trewin, F. Su, C. D. Wood, H. Niu, J. T. A. Jones,
Y. Z. Khimyak, A. I. Cooper, Macromolecules 2009, 42, 2658.
www.small-journal.com
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
314
small 2014, 10, No. 2, 308–315

Nitrogen-Containing Microporous Conjugated Polymers
[18] J. X. Jiang, F. Su, A. Trewin, C. D. Wood, H. Niu, J. T. A. Jones, [28] Z. Wang, B. Zhang, H. Yu, L. Sun, C. Jiao, W. Liu, Chem. Commun.
Y. Z. Khimyak, A. I. Cooper, J. Am. Chem. Soc. 2008, 130, 7710.
2010, 46, 7030.
[19] Q. Chen, J.-X. Wang, F. Yang, D. Zhou, N. Bian, X.-J. Zhang, [29] W. Lu, D. Yuan, D. Zhao, C. I. Schilling, O. Plietzsch, T. Muller,
C.-G. Yan, B.-H. Han, J. Mater. Chem. 2011, 21, 13554.
[20] K. S. Kim, S. Jeong, C. Kim, J. Y. Ham, Y. Kwon, B. D. Choi,
Y. S. Han, Synth. Met. 2009, 159, 1870.
[21] J. Ding, Q. Wang, L. Zhao, D. Ma, L. Wang, X. Jing, F. Wang, J.
Mater. Chem. 2010, 20, 8126.
S. Bräse, J. Guenther, J. Blümel, R. Krishna, Z. Li, H.-C. Zhou,
Chem. Mater. 2010, 22, 5964.
[30] M. G. Rabbani, H. M. El-Kaderi, Chem. Mater. 2011, 23,
1650.
[31] C. F. Martín, E. Stöckel, R. Clowes, D. J. Adams, A. I. Cooper,
J. J. Pis, F. Rubiera, C. Pevida, J. Mater. Chem. 2011, 21, 5475.
[32] R. Dawson, D. J. Adams, A. I. Cooper, Chem. Sci. 2011, 2, 1173.
[22] K. S. W. Sing, D. H. Everett, R. A. W. Haul, L. Moscou, R. A. Pierotti,
J. Rouquérol, T. Siemieniewska, Pure Appl. Chem. 1985, 57, 603.
[23] a) M. Rose, N. Klein, W. Böhlmann, B. Böhringer, S. Fichtner, [33] F. Liang, T. Kurata, H. Nishide, J. Kido, J. Polym. Sci., Part A: Polym.
S. Kaskel, Soft Mater. 2010, 6, 3918; b) J. Weber, J. Schmidt,
A. Thomas, W. Böhlmann, Langmuir 2010, 26, 15650.
[24] M. Rose, W. Böhlmann, M. Sabo, S. Kaskel, Chem. Commun.
2008, 44, 2462.
[25] K. S. Walton, R. Q. Snurr, J. Am. Chem. Soc. 2007, 129, 8552.
[26] H. Furukawa, O. M. Yaghi, J. Am. Chem. Soc. 2009, 131, 8875.
[27] T. Ben, H. Ren, S. Ma, D. Cao, J. Lan, X. Jing, W. Wang, J. Xu,
F. Deng, J. M. Simmons, S. Qui, G. Zhu, Angew. Chem., Int. Ed.
2009, 48, 9457.
Chem. 2005, 43, 5765.
[34] J. Xu, Y. Q. Zhan, X. Y. Hou, F. Xiao, Chin. J. Chem. 2005, 23,
454.
[35] Z. Yang, Z. Chi, T. Yu, X. Zhang, M. Chen, B. Xu, S. Liu, Y. Zhang,
J. Xu, J. Mater. Chem. 2009, 19, 5541.
Received: May 24, 2013
Revised: June 26, 2013
Published online: August 5, 2013
www.small-journal.com
315
small 2014, 10, No. 2, 308–315
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim