BODIPY-containing porous organic polymers for gas adsorption

Article abstract of DOI:10.1039/c6nj01812b

A series of BODIPY-containing microporous organic polymers was synthesized via a Sonogashira-Hagihara cross-coupling reaction of a BODIPY derivative with triple polymerisable groups and a range of aryl-alkyne monomers. All of the polymers show high isosteric heats of CO₂ adsorption (23.3-27.3 kJ mol^-1) because the incorporation of heteroatoms (N, B, F) from the BODIPY unit into the polymer skeleton enhanced the binding affinity between the pore wall and CO₂ molecules. The aryl-alkyne monomer has a large influence on the surface area and CO₂ adsorption performance of the resulting polymers. The polymer BDPCMP-3 shows a high Brunauer-Emmett-Teller specific surface area of up to 725 m² g^-1, while BDPCMP-2 with a low surface area of 582 m² g^-1 shows a high CO₂ uptake ability of 2.25 mmol g^-1 at 1.13 bar/273 K with a CO₂/N₂ adsorption selectivity of 32.3.

Full text of DOI:10.1039/c6nj01812b

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Page 1 of 23
New Journal of Chemistry
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BODIPY-Containing Porous Organic Polymers for Gas AdsorDpOtI:i1o0n.1039/C6NJ01812B
Yunfeng Xu, Dan Chang, Shi Feng, Chong Zhang, Jia-Xing Jiang*
Key Laboratory for Macromolecular Science of Shaanxi Province, School of Materials Science and
Engineering, Shaanxi Normal University, Xi’an, Shaanxi, 710062, P. R. China.
E-mail: jiaxing@snnu.edu.cn
Abstract
A series of BODIPY-containing microporous organic polymers was synthesized
via Sonogashira-Hagihara cross-coupling reaction from a BODIPY derivative with
triple polymerisable groups and a range of aryl-alkyne monomers. All of the polymers
show high isosteric heats of CO2 adsorption (23.3~27.3 kJ mol−1) because the
incorporation of heteroatoms (N, B, F) from BODIPY unit into the polymer skeleton
enhanced the binding affinity between the pore wall and CO2 molecules. The
aryl-alkyne monomer has a large influence on the surface area and CO2 adsorption
performance of the resulting polymers. The polymer BDPCMP-3 shows a high
Brunauer-Emmett-Teller specific surface area of up to 725 m2 g−1, while BDPCMP-2
with low surface area of 582 m2 g−1 shows a high CO2 uptake ability of 2.25 mmol g−1
at 1.13 bar/273 K with a CO2/N2 adsorption selectivity of 32.3.
Keywords: microporous organic polymers, BODIPY, gas adsorption, isosteric heats
1

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1. Introduction
DOI: 10.1039/C6NJ01812B
Microporous organic polymers (MOPs), owing to their special features such as
high specific surface area, excellent physicochemical and thermal stability, tunable
pore properties, low skeleton density and synthetic diversity, show broad potential in
applications such as gas storage and separation,1, 2 chemical sensors,3 light harvesting
and light emitting devices,4, 5 heterogeneous catalysis,6 photocatalysis,7, 8 and electric
energy conversion and storage.9 Over the past decade, a range of MOPs including
polymers of intrinsic microporosity (PIMs),10 covalent organic frameworks (COFs),11
conjugated microporous polymers (CMPs),12–14 porous polymer networks (PPNs),15
porous aromatic frameworks (PAFs),16 covalent triazine-based frameworks (CTFs),17
and hypercrosslinked porous polymers (HCPs)18 have been developed by using
various polymerization methods, building blocks and synthetic strategies.
Increasing CO2 emission from the rapid consumption of fossil fuels has led to the
global climate change and some environmental issues. Therefore, developing efficient
CO2 capture and separation technologies or CO2 capture materials would be a
potential short-time strategy to solve these issues. The leading CO2 capture
technology of amine-based wet scrubbing technology suffers from the considerable
energy penalty for CO2 release and the regeneration of amine solution.19 MOPs, as a
new class of CO2 capture materials, have attracted much attentions recently because
they adsorb CO2 molecules through relatively weak van der Waals force, which makes
the regeneration of the materials energy efficient. Recent studies demonstrated that
the introduction of heteroatoms and polar functional groups into the skeleton of MOPs
could enhance the binding affinity between the adsorbent and CO2 molecules through
the strong dipole-quadrupole interaction, which leads to a significant increase in the
CO2 capture capacity. For instance, the nitrogen-doped porous polymer framework of
2

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New Journal of Chemistry
20
PPF-1 exhibited a CO2 uptake of 6.1 mmol g−1 at 273 K/1.0 bar, the azo-linked
View Article Online
DOI: 10.1039/C6NJ01812B
nanoporous polymer of ALP-1 showed a remarkable CO2 uptake of up to 5.36 mmol
g−1 at 273 K/1.0 bar with a CO2/N2 adsorption selectivity of 35 at 273 K,21 the
nanoporous covalent organic polymer of TB-COP-1 with tröger’s base functionality
exhibited a CO2 capture capacity of 5.19 mmol g−1 with a CO2/N2 adsorption
selectivity of 79.2 at 273 K,22 the porous covalent triazine polymer network of
PCTP-1 exhibited a high CO2 uptake capacity of up to 4.92 mmol g−1 at 273 K/1.0
bar,23 the microporous polycarbazole of CPOP-1 showed a CO2 capture capacity of
4.82 mmol g−1 with a CO2/N2 adsorption selectivity of 25 at 273 K,1 the covalent
triazine-based framework of CTF-TPC showed a high surface area of 1668 m2 g−1 and
could adsorb CO2 up to 4.25 mmol g−1 with a CO2/N2 adsorption selectivity of 20 at
273 K.24 These results demonstrated that such MOPs with polar functional groups or
heteroatoms have great potential to increase the CO2 capture capacity or CO2/N2
adsorption selectivity. BODIPY is an efficient chromophore that has been studied
widely for light-emitting,25, 26 chemical sensing27 and solar cell.28 Recent studies have
revealed that BODIPY could be an efficient building block for making functional
porous polymers. For example, Liras et al.29 reported the synthesis of luminescent
BODIPY-based porous polymer of CMPBDP, which showed efficient heterogeneous
photocatalytic activity for the oxidation reaction of thioanisole to methylphenyl
sulfoxide. Zhuang et al.30 synthesized a novel nanocarbon (carbon nanosphere, carbon
nanotube, and grapheme) by heating treatment of the BODIPY-based porous polymer
precursors.
In this work, a series of BODIPY-functionalized microporous organic polymers
was synthesized via Sonogashira-Hagihara cross-coupling reaction from a BODIPY
derivative with triple polymerisable groups and a range of aryl-alkyne monomers. We
3

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DOI: 10.1039/C6NJ01812B
expect that the high crosslinked polymer structure formed from the monomers with
high connective sites can substantially increase the surface area of the resulting
BODIPY-containing polymers. On the other hand, BODIPY contains a large number
of heteroatoms (B, N, F), which could enhance the binding affinity between the
polymer and CO2 molecules due to the existence of the C=O polar bonds, and thus we
hypothesized that the introduction of BODIPY segments into the porous polymer
skeleton could lead to the increase of CO2 capture capacity.
2. Experimental section
2.1 Chemicals
2,4-Dimethyl-1H-pyrrole, 4-iodobenzoic acid, SOCl2, 1,4-diethynylbenzene
(DEB), 1,3,5-triethynylbenzene (TEB) and potassium carbonate were purchased from
TCI. Pyrene, tetraphenylthylene and trimethylsilylacetylene (TMSA) were purchased
from Across. Tetrakis(triphenylphosphine)palladium(0), N,N-dimethylformamide and
triethylamine were purchased from J&K Scientific Ltd. All chemicals were used as
received without further purification. 1,1,2,2-tetrakis(4-ethynylphenyl)ethene (TEPE)
32
and 1,3,6,8-tetraethynylpyrene (TEPY) were synthesized by the literature.31,
1,3,5,7-Tetramethyl-2,6-diiodo-8-(4-iodophenyl)-4,4-difluoro-4-bora-3a,4a-diaza-S-in
dacene (TI-BDP) was prepared according to the literature.33
2.2 Synthesis of BODIPY-containing microporous organic polymers
All of the polymer networks were synthesized by palladium(0)-catalyzed
Sonogashira–Hagihara cross-coupling reaction of the aryl-alkyne monomers of DEB,
TEB, TEPE or TEPY with the BODIPY derivative of TI-BDP. The general synthetic
route for the porous polymer networks was shown in Scheme 1. All reactions were
carried out at a fixed reaction temperature and reaction time (100 ºC/48 h).
BDPCMP-1: TI-BDP (350 mg, 0.5 mmol), 1,4-diethynylbenzene (DEB) (94.5 mg,
4

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0.75 mmol) tetrakis(triphenylphosphine)palladium(0) (15 mg), copper(I) iodide (10
mg) were dissolved in a mixture of DMF (5.0 mL) and Et3N (5.0 mL). The mixture
was degassed under freeze-pump-thaw, purged with N2 and stirred at 100 °C for 48 h.
The mixture was then cooled down to room temperature and the precipitated polymer
network was filtered and washed with water, methanol, chloroform and acetone,
respectively. Further purification of the polymer was carried out by Soxhlet extraction
with methanol for 48 h. The product was dried under vacuum for 24 h at 70 °C and
obtained as a dark red powder (232 mg, yield: 91%). Elemental combustion analysis
(%) Calcd for (C34H22BF2N2)n: C 80.47, H 4.34, N 5.52; found: C 75.63, H 4.06, N
4.86. The deviation of the elemental analysis from the theoretical value could be
attributed to the unreacted end groups, and trapped gases and water from air in the
porous polymers due to their high microporosities.34
BDPCMP-2: TI-BDP (350 mg, 0.5 mmol), 1,3,5-triethynylbenzene (TEB) (76 mg,
0.5 mmol), tetrakis(triphenylphosphine)palladium(0) (15 mg) and copper(I) iodide (10
mg) were dissolved in DMF (5.0 mL) and Et3N (5.0 mL). The mixture was degassed
under freeze–pump–thaw, purged with N2 and stirred at 100 °C for 48 h. The mixture
was then cooled down to room temperature and the precipitated polymer network was
filtered and washed with water, methanol, chloroform and acetone, respectively.
Further purification of the polymer was carried out by Soxhlet extraction with
methanol for 48 h. The product was dried under vacuum for 24 h at 70 °C and
obtained as a red powder (206 mg, yield: 88%). Elemental combustion analysis (%)
Calcd for (C31H22BF2N2)n: C 78.98, H 4.67, N 5.94; found: C 74.37, H 4.14, N 5.38.
5

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BDPCMP-3: TI-BDP (350 mg, 0.5 mmol), 1,1,2,2-tetrakis(4-ethynylphenyDl)OeI:th10e.1n03e9/C6NJ01812B
(TEPE) (160 mg, 0.375 mmol), tetrakis(triphenylphosphine)palladium(0) (15 mg) and
copper(I) iodide (10 mg) were dissolved in DMF (5.0 mL) and Et3N (5.0 mL). The
mixture was degassed under freeze–pump–thaw, purged with N2 and stirred at 100 °C
for 48 h. The mixture was then cooled down to room temperature and the precipitated
polymer network was filtered and washed with water, methanol, chloroform and
acetone, respectively. Further purification of the polymer was carried out by Soxhlet
extraction with methanol for 48 h. The product was dried under vacuum for 24 h at
70 °C and obtained as a black powder (232 mg, yield: 91%). Elemental combustion
analysis (%) Calcd for (C44.5H31BF2N2)n: C 83.18, H 4.83, N 4.36; found: C 76.73, H
4.27, N 3.94.
BDPCMP-4: TI-BDP (350 mg, 0.5 mmol), 1,3,6,8-tetraethynylpyrene (TEPY) (110
mg, 0.375 mmol), tetrakis(triphenylphosphine)palladium(0) (15 mg) and copper(I)
iodide (10 mg) were dissolved in DMF (5.0 mL) and Et3N (5.0 mL). The mixture was
degassed under freeze–pump–thaw, purged with N2 and stirred at 100 °C for 48 h. The
mixture was then cooled down to room temperature and the precipitated polymer
network was filtered and washed with water, methanol, chloroform and acetone,
respectively. Further purification of the polymer was carried out by Soxhlet extraction
with methanol for 48 h. The product was obtained as a black powder (232 mg, yield:
91%). Elemental combustion analysis (%) Calcd for (C37H23.5BF2N2)n: C 81.54, H
4.32, N 5.14; found: C 75.74, H 3.97, N 4.63.
6

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DOI: 10.1039/C6NJ01812B
Pd(PPh3)4, CuI
Et3N, DMF
BDPCMP-1
Pd(PPh3)4, CuI
Et3N, DMF
BDPCMP-2
BDPCMP-3
I
I
I
+
N
N
Pd(PPh3)4, CuI
Et3N, DMF
B
F
F
TI-BDP
Pd(PPh3)4, CuI
Et3N, DMF
BDPCMP-4
N
N
B
N
N
F
F
B
F
F
BDPCMP-2
BDPCMP-1
N
N
B
N
N
F
F
B
F
F
BDPCMP-3
BDPCMP-4
Scheme 1. Synthetic route to the BODIPY-based microporous organic polymers and the notional
polymer structures.
2.3 Characterization
The FT-IR spectra were measured in transmission mode on a Tensor 27 FT-IR
spectrometer (Bruker) using KBr disks. The thermal properties of the polymer
networks were evaluated using thermogravimetric analysis (TGA) with a differential
thermal analysis instrument (Q1000DSC + LNCS + FACS Q600SDT) over the
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DOI: 10.1039/C6NJ01812B
temperature range from 30 to 800 ºC under a nitrogen atmosphere with a heating rate
of 10 ºC min−1. Powder X-ray diffraction measurement was carried out on an X-ray
Diffractometer (D/Max-3c). Elemental analysis was performed on a EURO EA3000
Elemental Analyzer. The morphologies of the polymer networks were obtained using
a field emission scanning electron microscope (SEM, JSM-6700F, JEOL, Japan).
Surface areas and pore size distributions were measured by nitrogen adsorption and
desorption at 77.3 K using an ASAP 2420-4 (Micromeritics) volumetric adsorption
analyzer. The surface areas were calculated in the relative pressure (P/Po) range from
0.05 to 0.20. Pore size distributions and pore volumes were derived from the N2
adsorption branch of the isotherms using non-local density functional theory
(NL-DFT). The samples were degassed at 120 ºC for 12 h under vacuum (10−5 bar)
before analysis. The gas sorption isotherms were measured on an ASAP 2420-4 as
well.
3. Results and discussion
All of the polymer networks are insoluble in common organic solvents because
of their highly crosslinked structures, and they are also chemically stable. The
resulting polymer networks exhibit high thermal stability in nitrogen atmosphere, as
revealed by TGA (Fig. S1). It was found that BDPCMP-3 has the best thermal
stability among the four polymers, which could be possibly attributed to the high
crosslinking degree and molecular weight of BDPCMP-3 because of more
polymerizable functional groups of TEPE than DEB and TEB, and smaller steric
hindrance of TEPE than TEPY due to the C-C bond rotation in TEPE. The FT-IR
spectra of the polymer networks (Fig. 1) are consistent with the expected network
structure showing the alkyne of C≡C band at 2190 cm−1, the stretching vibration
band of C-N-C at 1636 cm−1, and the characteristic vibration of C=C bond at ∼1530
8

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−1
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cm . The -CH3 stretching vibration from the BODIPY segment was also obsDeOrvI:e10d.10a3t9/C6NJ01812B
around 2925 cm−1 for the polymers. The C-I bands of the monomer of TI-BDP at
∼743 cm−1 and ∼520 cm−1 were disappeared, and a new vibration peak around 833
cm−1 was observed for the polymers, indicating that the polymerization reaction was
almost complete. Powder X-ray diffraction measurements indicated that the polymer
networks are amorphous in nature without showing any clear diffraction peaks (Fig.
S2). The broad peak indicated the formation of an amorphous random polymer
network. The different 2 values and different sharpness of the broad peaks could be
derived from the different molecular size of the four aryl-alkyne monomers and the
imparity of the short-range length. Scanning electron microscopy (SEM) images
revealed that the resulting polymer networks show very similar morphology with
relatively uniform solid nanoparticles (Fig. 2).
1636
833 520
BDPCMP-4
BDPCMP-3
BDPCMP-2
BDPCMP-1
2190
TI-BDP
2925
1530
743
4000 3500 3000 2500 2000 1500 1000 500
Wavenumber / cm-1
Fig. 1 FT-IR spectra of the BDPCMPs
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DOI: 10.1039/C6NJ01812B
Fig. 2. Scanning electron microscopy images of the BDPCMPs with a scale bar of 5.0 μm.
350
300
250
200
150
100
50
2.0
1.5
1.0
0.5
0.0
(a)
(b)
BDPCMP-4
BDPCMP-3
BDPCMP-2
BDPCMP-1
BDPCMP-2
BDPCMP-3
BDPCMP-4
BDPCMP-1
10
0
0.0
0.2
0.4
0.6
0.8
1.0
1
P / Po
Pore Dimeter (nm)
Fig. 3. (a) Nitrogen adsorption (filled symbols) / desorption (empty symbols) isotherms for the
polymer networks collected at 77.3 K; (b) Pore size distribution curves calculated by NL-DFT.
The porous properties of the polymer networks were investigated by nitrogen
adsorption analyses at 77.3 K. As shown in Fig. 3a, all of the polymer networks gave
rise to Type I nitrogen gas sorption isotherms with a steep nitrogen gas uptake at low
relative pressure (P/P0 < 0.001) according to IUPAC classification,35 indicating the
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abundant micropores in the polymer networks. A steep rise in the nitrogen adDsoOrI:p10ti.1o0n39/C6NJ01812B
isotherms was also observed at high relative pressures (P/P0 > 0.9), indicating the
presence of some mesopores and/or macropores in the polymers that are probably due
to inter-particle porosity or void.36 Hysteresis was observed upon desorption branch of
the isotherm for the polymer networks, which is consistent with elastic deformations
or swelling as a result of gas sorption.37 Fig. 3b shows the pore size distribution (PSD)
curves for the polymer networks as calculated using nonlocal density functional theory
(NL-DFT). All of the polymer networks exhibit abundant microporous structure with
the main pore size around 1.0 nm, and BDPCMP-4 shows the smallest micropore pore
size around 0.91 nm among the four polymers. The apparent Brunauer-Emmet-Teller
(BET) specific surface area varies between 482 m2 g−1 for BDPCMP-1 and 725 m2 g−1
for BDPCMP-3 (Table 1), indicating that the aryl-alkyne monomers with different
number of polymerisable groups and different geometries have a large influence on
the surface area of the polymer networks. The high surface area of 725 m2 g−1 for
BDPCMP-3 could be attributed to the high degree of crosslinking because of the four
polymerisable groups of 1,1,2,2-tetrakis(4-ethynylphenyl)ethene and the relative
flexible backbone of the polymer. The surface area is much higher than that of
reported BODIPY-based microporous organic polymers, such as the CMPBDP (299
m2 g−1)29 and the dimensionality controlled CMPs with BODIPY segment (593–622
m2 g−1).30 All of the polymer networks show high microporous surface area ratio over
74% and microporous volume ratio over 55%, and BDPCMP-2 shows the highest
microporous surface area ratio of 87.28% and microporous volume ratio of 75.00%
among the four polymers (Table 1), again suggesting that the pores of the polymer
networks are dominated by microporous, which is in agreement with the character of
the nitrogen sorption isotherms.
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DOI: 10.1039/C6NJ01812B
Table 1. Summary of pore properties for the polymer networks
a
b
c
d
SBET
SMicro
VMicro
VTotal
SMicro / SBET
[%]
VMicro / VTotal
Polymer
[m2 g-1]
[m2 g-1]
[cm3 g-1]
[cm3 g-1]
[%]
BDPCMP-1
BDPCMP-2
BDPCMP-3
BDPCMP-4
482
390
0.18
0.28
80.91
64.28
75.00
55.55
68.96
582
508
0.24
0.32
87.28
725
539
0.25
0.45
74.34
501
422
0.20
0.29
84.23
a
Surface area calculated from N2 adsorption isotherm in the relative pressure (P/Po) range from
b
0.05 to 0.20; Microporous surface area calculated from the N2 adsorption isotherm using t-plot
c
method based on the Harkins Jura Equation. The microporous volume derived from the t-plot
method; d Total pore volume at P/Po = 0.90.
2.5
2.0
1.5
1.0
0.5
0.0
120
100
80
60
40
20
0
(a)
(b)
BDPCMP-1
BDPCMP-2
BDPCMP-3
BDPCMP-4
BDPCMP-1
BDPCMP-2
BDPCMP-3
BDPCMP-4
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Pressure (bar)
Pressure (bar)
0.8
0.6
0.4
0.2
0.0
30
25
20
15
10
5
(c)
(d)
BDPCMP-1
BDPCMP-2
BDPCMP-3
BDPCMP-4
BDPCMP-1
BDPCMP-2
BDPCMP-3
BDPCMP-4
0
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Quantity adsorbed (mmol/g)
Pressure (bar)
Fig. 4. (a) Volumetric H2 sorption curves for the polymer networks at 77.3 K up to 1.13 bar; (b)
CO2 adsorption isotherms collected at 273 K (solid point) and 298 K (empty point) up to 1.13 bar;
(c) Isosteric heats of adsorption for CO2 calculated from the adsorption isotherms collected at 273
K and 298 K; (d) CH4 adsorption isotherms collected at 273 K.
The microporous nature of the BODIPY-containing polymer networks inspired
us to investigate their gas uptake capacity. Fig. 4a shows the hydrogen sorption curves
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of the polymer networks measured at 77.3 K up to a pressure of 1.13 bar. BDPCMP-2
exhibits the largest hydrogen uptake capacity of 115 cm3 g−1 (1.02 wt%) among the
four polymer networks, which is comparable to that of some other porous polymers at
the same conditions, such as the nitrogen-rich CMP of DA-CMP1 (1.01 wt%, SBET
=
662 m2 g−1),38 the borazine-linked porous polymer of BLP-1 (0.68 wt%, SBET = 503
m2 g−1),39 the isoindigo-based microporous organic polymer of TBMIDM (0.95 wt%,
SBET = 763 m2 g−1),40 the nitrogen-rich azo-bridged porphyrin conjugated microporous
network of Azo-1 (0.86 wt%, SBET = 571 m2 g−1),41 and the phthalazinone-based
covalent triazine framework of PHCTF-1b (0.66 wt%, SBET = 955 m2 g−1),42 although
it is still lower than that of the carbazole-based CPOP-1 with the hydrogen uptake
capacity of 2.80 wt% at 1.13 bar/77.3 K,1 the copolymerized conjugated microporous
polymer of CP-CMP5 (2.24 wt%, SBET = 2241 m2 g−1),43 and the nanoporous organic
framework of NPOF-2 (1.45 wt%, SBET = 3127 m2 g−1).44
The CO2 uptakes of the polymer networks were measured up to 1.13 bar at 273 K
and 298 K, respectively. As shown in Fig. 4b, all of the polymers show high CO2
uptake since the microporous nature of the polymers and the heteroatoms (B, N, F)
from BODIPY unit enhanced the binding affinity between the polymer and CO2
molecules. It is noteworthy that the CO2 adsorption capacity of these polymers
persistently increases with increasing the pressure, and has not reached saturation at
1.13 bar, indicating that higher CO2 uptake ability can be achieved at higher pressures.
The polymer networks of BDPCMP-2 shows the highest CO2 uptake ability of 2.25
mmol g−1 at 1.13 bar/273 K among the four polymers, which could be attributed to its
higher micropore surface area ratio (87.28%) and micropore volume ratio (75.00%) as
discussed above. In addition, the elemental analysis showed that the BDPCMP-2 has
the highest nitrogen containing (5.38%) among the four polymers, which could be
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another important reason as reported for other nitrogen-rich porous polymers.38, 41, 45
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DOI: 10.1039/C6NJ01812B
The CO2 uptake capacity of 2.25 mmol g−1 for BDPCMP-2 is higher than that of many
other reported CMPs produced from Sonogashira-Hagihara coupling reaction under
the same conditions (Table 2), such as the amide-functionalized CMP of
CMP-1-AMD1 (1.51 mmol g1, SBET = 316 m2 g1),46 the pyrene-based porous
aromatic framework of PAF-20 (1.16 mmol g−1, SBET = 702 m2 g−1),47 and the
hexabenzocoronene-based porous organic polymer of HBC-POP-1 (2.05 mmol g−1,
SBET = 668 m2 g−1).48 It is also much higher than that of some other type of porous
materials with much higher BET surface area under the same conditions, such as
PAF-1 (2.1 mmol g−1, SBET = 5460 m2 g−1),49 COF-102 (1.56 mmol g−1, SBET = 3620
m2 g−1),50 the tetraphenylmethane-based HCPs (1.66 mmol g−1, SBET = 1679 m2 g−1),51
and the spirobifluorene-based porous organic polymer of POP-1 (1.92 mmol g−1, SBET
= 983 m2 g−1).52 It has been proved that the electron-rich porous polymers networks
can yield strong dipole-quadrupole interaction with polarizable CO2 molecules, and
thus leading to a significant increase in the CO2 capture capacity. Therefore, the high
CO2 uptake ability of these BODIPY-based polymer networks could be mainly
attributed to the nature of the heteroatom-rich (N, B, F) porous polymers, which
enhanced the interactions between the polymer networks and CO2 molecules.
However, due to the moderate surface area, the CO2 uptake capacities of these
BODIPY-based polymers are still low in comparison with those of the leading CO2
adsorbents (Table 2), such as the imine-linked porous polymer network of PPF-1 (6.1
mmol g−1, SBET = 1740 m2 g−1),20 the porous pyridine-functionalized polymer of
P-PCz (5.57 mmol g−1, SBET = 1647 m2 g−1),53 the fluorinated polycarbazole covalent
triazine framework of FCTF-1-600 (5.5 mmol g−1, SBET = 752 m2 g−1),54 and the
porous covalent triazine polymer network of PCTP-1 (4.92 mmol g−1, SBET = 1200 m2
14

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g−1).23 Therefore, one could expect to get high surface area porous polymers with
View Article Online
DOI: 10.1039/C6NJ01812B
enhanced gas adsorption ability by using some non-planar three-dimensional
comonomers (such as tetraphenylmethane, tetraphenyl adamantine and triptycene) for
polymerization with BODIPY since these three-dimensional building blocks are
efficient to produce high surface area porous organic polymers.24, 55–58
Table 2. Summary of the CO2 uptake capacity of some reported porous materials
SBET
[m2 g-1]
582
CO2 uptake a
[mmol g-1]
2.25
Porous materials
Ref.
BDPCMP-2
CMP-1-AMD1
PAF-20
this work
46
316
1.51
702
1.16
47
HBC-POP-1
PAF-1
668
2.05
48
5460
3620
1679
983
2.1
49
COF-102
HCPs
1.56
50
1.66
51
POP-1
1.92
52
PPF-1
1740
1647
752
6.1
20
5.57
53
P-PCz
FCTF-1-600
PCTP-1
5.5
54
1200
4.92
23
a data obtained at 1.13 bar and 273 K.
The isosteric heat of adsorption (Qst) of the polymers was calculated from the
Clausius-Clapeyron equation using the CO2 adsorption data collected at 273 K and
298 K. As shown in Fig. 4c, all of the polymer networks show high isosteric heats of
CO2 adsorption over 23 kJ mol−1, indicating that the incorporation of BODIPY unit
into the framework of the porous polymers enhanced the binding affinity between the
porous polymer and CO2 molecules. BDPCMP-4 shows a slight higher Qst (27.3 kJ
mol−1) than the other three polymers at the zero-coverage, which could be attributed to
the smaller micropore size of BDPCMP-4 as discussed above, and small pore sizes
known to increase the heat of adsorption. All of the polymers show nearly constant
Qst over a wide range of CO2 loading, which suggests that a significantly higher CO2
15

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uptake could probably be achieved by increasing the micro-surface area and
micropore volumes of the adsorbent. The Qst values of these polymer networks are
comparable to those of many known porous polymers, such as the porous
benzimidazole-linked polymers (26.7-28.8 kJ mol−1),34 the carbazole-based CMPs
(27.1-30.8 kJ mol−1),59 and the tetraphenylethylene-based HCPs (23.3-28.2 kJ
mol−1),60 although they are lower than those of some porous polymers with strong
polar groups, such as PAF-26-COONa (35 kJ mol−1),61 PPN-6-SO3Li (35.7 kJ
mol−1),62 PPN-6-SO3NH4 (40 kJ mol−1),62 and TBMID (33.5 kJ mol−1).40 The CH4
uptake of the polymer networks was measured up to 1.13 bar at 273 K (Fig. 4d).
BDPCMP-2 exhibits the largest methane uptake capacity of 0.70 mmol g−1 among the
four polymer networks, which is comparable to that of some other reported porous
polymers, such as PMETBC (0.65 mmol g−1, SBET = 540 m2 g−1),59 CP-CMP7 (0.74
mmol g−1, SBET = 699 m2 g−1),43 InCz-HCP1 (0.84 mmol g−1, SBET = 750 m2 g−1),63
and TBMID (0.75 mmol g−1, SBET = 688 m2 g−1),40 although it is still low in
comparison with that of the benzimidazole-linked polymer of BILP-2 (0.87 mmol
g−1)34 and the nanoporous azo-linked polymer of ALP-4 (0.89 mmol g−1).21
In order to investigate the gas adsorption selectivity of the microporous polymer
networks, CO2, N2, and CH4 sorption properties were measured by volumetric
methods at the same conditions. The selectivity of the polymer networks was first
estimated using the ratios of the Henry’s law constant calculated from the initial
slopes of the single-component gas adsorption isotherms collected at 273 K at the low
pressure coverage less than 0.10 bar (Fig. S3-6). All of the polymers show very
similar CO2/CH4 adsorption selectivity of around 5.1:1 at 273 K (Table 3), which is
comparable to that of most other reported porous polymers, such as the phosphine
oxide-based conjugated microporous polymer of TEPO-1 (12.6:1),64 the nitrogen-rich
16

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conjugated microporous polymer of Azo-CMP2 (5.3:1)36 and the isoindigo-based
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DOI: 10.1039/C6NJ01812B
microporous organic polymer of TBMID (9.7:1).40 The calculated CO2/N2 adsorption
selectivity for the polymers varies between 31.1:1 and 38.6:1 (Table 3). Though the
CO2/N2 adsorption selectivities are moderate compared with those of some other
reported MOPs with the CO2/N2 adsorption selectivity higher than 100, such as the
tetraphenylethylene-based HCPs (119 for Network-7),60 the porous covalent
electron-rich organonitridic frameworks (109 for PECONF-1),65 and the
tri(4-ethynylphenyl) amine-based porous aromatic framework (251 for
PAF-33-NH2),66 BDPCMP-2 shows higher CO2 adsorption capacity than those
adsorbents (Network-7: 1.92 mmol g−1, PECONF-1: 1.86 mmol g−1, and PAF-33-NH2:
1.19 mmol g−1) under the same conditions. Ideally, high uptake and selectivity are
both required for practical applications. As such, the good CO2 adsorption
performance by these polymer networks make them potential candidates for
applications in post-combustion CO2 capture and sequestration technology. The gas
adsorption selectivities were also predicted for CO2:N2 (15:85) and CO2:CH4 (5:95)
mixtures by using ideal adsorbed solution theory (IAST) (Table 3), which is widely
used to predict binary gas mixture adsorption selectivity in many porous
materials.67–69 The calculated IAST selectivities are higher than the values obtained
from Henry's constant ratios as observed for most reported porous organic polymers.70,
71
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Table 3. Summary of gas uptakes for the polymer networks
Henry Law
IAST
H2 uptakea CH4 uptakebCO2uptakeb CO2 uptakec
Selectivityd
Selectivitye
Polymer
[wt%]
[mmol g-1] [mmol g-1] [mmol g-1]
CO2/N2 CO2/CH4 CO2/N2 CO2/CH4
BDPCMP-1
BDPCMP-2
0.80
1.02
0.48
0.70
1.68
2.25
1.03
1.45
38.6
32.3
5.4
5.1
65.2
55.3
8.4
8.4
BDPCMP-3
BDPCMP-4
0.96
0.84
0.60
0.56
2.03
1.91
1.24
1.23
31.1
34.1
5.1
5.4
50.2
58.2
9.1
9.9
a Data obtained at 77.3 K and 1.13 bar; b Data collected at 273 K and 1.13 bar; c Data collected at
298 K and 1.13 bar; d Selectivity was calculated by initial slope method at 273 K; e Selectivity was
calculated by IAST method at the molar ratio of 15:85 for CO2/N2 and 5:95 for CO2/CH4 at 273 K.
4. Conclusion
In conclusion, BODIPY-functionalized microporous organic polymer networks
have been synthesized via Sonogashira-Hagihara cross-coupling reaction. These
polymer networks are stable in various solvents tested and thermally stable in nitrogen
atmosphere. All of the polymers show high isosteric heats of CO2 adsorption
(23.327.3 kJ mol−1) because the incorporation of electron-rich BODIPY unit into the
skeleton of the porous polymers enhanced the binding affinity between the porous
polymer and CO2 molecules. The polymer BDPCMP-2 shows a high CO2 uptake
ability of 2.25 mmol g−1 and a CO2/N2 adsorption selectivity of 32.3. These results
demonstrated that these BODIPY-containing microporous organic polymers are
promising candidates for potential applications in post-combustion CO2 capture and
sequestration technology.
Acknowledgements
This work was supported by the National Natural Science Foundation of China
(21304055 & 21574077), Shaanxi Innovative Team of Key Science and Technology
(2013KCT-17), the Fundamental Research Funds for the Central Universities
(GK201501002), and the Open Fund of the State Key Laboratory of Luminescent
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Materials and Devices (2015-skllmd-04).
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Table of Contents
BODIPY-containing microporous organic polymers were synthesized via
Sonogashira-Hagihara coupling reaction from a BODIPY derivative and a range of
aryl-alkyne monomers.
2.5
CO2
CH4
2.0
N2
1.5
1.0
N
N
0.5
B
F
F
BDPCMP-2
0.0
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Pressure (bar)
Yunfeng Xu, Dan Chang, Shi Feng, Chong Zhang, Jia-Xing Jiang*
BODIPY-Containing Porous Organic Polymers for Gas Adsorption