Porous conjugated polymer via metal-free synthesis for visible light-promoted oxidative hydroxylation of arylboronic acids

Article abstract of DOI:10.1016/j.polymer.2017.04.052

Porous conjugated polymers have emerged recently as efficient metal-free and visible light-active photocatalysts. However, the synthesis of this new class of materials usually requires transition metal catalysts such as palladium. A metal-free synthetic route still remains a huge challenge for the chemists. Here we report on a metal-free pathway of a porous conjugated polymer via simple Knoevenagel polycondensation under mild reaction conditions. The obtained polymer exhibited a high surface area and could be applied as a robust and efficient heterogeneous photocatalyst for the oxidative hydroxylation of arylboronic acids under visible light irradiation with a high functional group tolerance of the substrates.

Full text of DOI:10.1016/j.polymer.2017.04.052

Accepted Manuscript
Porous conjugated polymer via metal-free synthesis for visible light-promoted
oxidative hydroxylation of arylboronic acids
Zi Jun Wang, Run Li, Katharina Landfester, Kai A.I. Zhang
PII:
S0032-3861(17)30430-5
10.1016/j.polymer.2017.04.052
JPOL 19633
DOI:
Reference:
To appear in: Polymer
Received Date: 7 February 2017
Revised Date: 19 April 2017
Accepted Date: 20 April 2017
Please cite this article as: Wang ZJ, Li R, Landfester K, Zhang KAI, Porous conjugated polymer via
metal-free synthesis for visible light-promoted oxidative hydroxylation of arylboronic acids, Polymer
(2017), doi: 10.1016/j.polymer.2017.04.052.
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to
our customers we are providing this early version of the manuscript. The manuscript will undergo
copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please
note that during the production process errors may be discovered which could affect the content, and all
legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Porous conjugated polymer via metal-free synthesis for visible light-promoted oxidative
hydroxylation of arylboronic acids
+
+
Zi Jun Wang, Run Li, Katharina Landfester, Kai A. I. Zhang*
Max Planck Institute for Polymer Research, Ackermannweg 10, D-55128 Mainz, Germany.
E-mail: kai.zhang@mpip-mainz.mpg.de
+
[
] These authors contributed equally to this work.
Key words:
Porous conjugated polymer, visible light, photocatalysis, oxidative hydroxylation, metal-free
Abstract
Porous conjugated polymers have emerged recently as efficient metal-free and visible light-
active photocatalysts. However, the synthesis of this new class of materials usually requires
transition metal catalysts such as palladium. A metal-free synthetic route still remains a huge
challenge for the chemists. Here we report on a metal-free pathway of a porous conjugated
polymer via simple Knoevenagel polycondensation under mild reaction conditions. The obtained
polymer exhibited a high surface area and could be applied as a robust and efficient
heterogeneous photocatalyst for the oxidative hydroxylation of arylboronic acids under visible
light irradiation with a high functional group tolerance of the substrates.

ACCEPTED MANUSCRIPT
Introduction
Sunlight is a clean and inexhaustible source of energy. As early as 1912, Ciamician first
envisioned an environmentally conscious chemical industry that would replace energy-intensive
synthetic processes with photochemical transformations driven by sunlight.[1] Inspired by the
2+
3+
nature, numerous transition-metal based homogeneous photocatalysts[2-5] (e.g. Ru or Ir
complexes) and semiconductor-based heterogeneous photocatalysts[6] (e.g. TiO or Nb O )
2
2
5
have been investigated for visible light induced organic transformations. However, due to the
cost, scarcity and potential toxicity associated with these metal-based photocatalysts, the
development of organic, heterogeneous, visible light-active photocatalysts has drawn surging
interests for material chemists in recent years.[7-13]
Since Cooper’s seminal report in 2007,[14] a variety of porous conjugated polymer (PCPs) have
been developed for applications such as gas sorption,[15, 16] molecular separation,[17] green
energy devices,[18] hydrogen production,[8] CO conversion[19] and most recently visible light-
2
promoted heterogeneous photocatalysis.[10, 11, 20-25] Compared to other porous counterparts
such as hypercross-linked polymers (HCPs) or polymers of intrinsic microporosity (PIMs), the
most characteristic feature of PCPs is the
π-conjugated skeleton which leads to their
outstanding light-harvesting/emitting properties, charge transfer/separation, electric energy
storage properties as well as photocatalytic activities.[26]
From a synthetic perspective, an array of protocols has been reported for the preparation of
porous conjugated polymers.[27, 28] Some of the most popular synthetic routes include (a)
metal-mediated cross-coupling reactions (e.g. Suzuki cross-coupling,[22] Sonogashira-
Hagihara-,[14, 29] Yamamoto-,[30] Glaser-,[17] Negishi-,[31] Heck-,[32] Kumada cross-coupling
reactions[33] and oxidative polymerization[34]) and (b) thermally induced ring fusion reactions
such as nitrile cyclization[35] and thermal polycondensation.[8] However, significant amount

ACCEPTED MANUSCRIPT
(
e.g. 5-20 mol%) of metal catalysts (e.g. Pd, Cu, Mo, Ni, Fe) are often required for the metal
mediated cross-coupling reactions.[36] Meticulous efforts have to be applied to remove the
metal catalyst residuals from the resulted polymer to avoid potential interference and
detrimental contamination for the intended applications. Moreover, traditional metal-free routes,
such as nitrile cyclization, thermal polycondensation or phenazine ring fusion reaction, demand
0
0
2
harsh reaction conditions (e.g. molten ZnCl at 400 C or calcination at 550 C), which greatly
limit the tenability of the functionalities that can be incorporated into these PCPs. Despite the
widespread application and promising potentials of PCPs, there have been few reports on the
metal-free synthetic pathways of PCPs under mild reaction conditions.[37, 38]
Herein, we report on a metal-free synthetic pathway of porous conjugated polymer (PCP) via
simple polycondensation method under mild reaction conditions. We also demonstrate that the
resulted PCP could serve as a reusable and efficient visible light heterogeneous photocatalyst
for light-induced oxidative hydroxylation of arylboronic acids using molecular oxygen as green
oxidant.[39, 40]
Results and discussion
The PCP was prepared using base-promoted Knoevenagel condensation of 4,7-bis(4,4'-
benzaldehyde)benzo[c][1,2,5]-thiadiazole (BT-BA) and 1,3,5-benzenetriacetonitrile (BAN) in
THF at 80 °C. The synthetic route of the polymer PCP-MF is displayed in Scheme 1. The
experimental synthetic details and polymer characterization data are described in the ESI. The
1
3
cross-linked polymer was insoluble in all common organic solvents tested. Solid state C/MAS
NMR spectroscopy showed that quaternary and tertiary aromatic carbons give rise to the broad
signals between 122 ppm and 148 ppm (Figure S1 in ESI). The signals at
δ
= 153 ppm can be
2
assigned to the carbon of the –C=N- groups in the benzothiadiazole units. In addition, the sp
carbon of double bonds in cyanostilbene unit should be at ca. 110 ppm and ca. 141 ppm which

ACCEPTED MANUSCRIPT
was likely molten to the main broad aromatic carbon bands. The carbon signal on cyano group
appeared at 118.7 ppm.
2
The Brunauer-Emmett-Teller (BET) surface area of PCP-MF was found to be 130 m /g with a
3
pore volume of 0.291 cm /g. The N
2
sorption isotherms are shown in Figure S2 in ESI. It can be
noted that the polymer PCP-MF doses not only possess micropores (<2 nm), but also contains
a significant amount of mesopores (2-10 nm). This could be attributed to the relatively long strut
length and the rigidity of the alkenyl groups, which favor a planar configuration than 3-D
networks. Thermogravimetric analysis (TGA) (Figure S4) showed that PCP-MF is thermally
0
stable up to around 350 C with less than 5% weight loss. The SEM and TEM images illustrated
a fused particle-like morphology of PCP-MF (Figure 1a and 1b).The FTIR spectra of the starting
-
1
compound and the polymer are displayed in Figure 1c. The signal at 1660 cm was attributed to
characteristic stretching vibration of –C=C bond in the cyanostilbene unit and signal at ca. 2360
-
1
-1
cm was typical for -C
≡N stretching bands. The absence of stretching band at 1695 cm , which
was attributed to the carbonyl group originally from aldehydes indicated the high polymerization
−
1
degree. In addition, the signals at 1348, 1377, 1567, and 1577 cm are characteristic for the -
C=N and -N−S stretching modes of benzothiadiazole unit. The FTIR spectra, consistent with
solid state NMR, confirmed that photoactive benzothiadiazole moiety and cyanostilbene have
been successfully combined via knoevenagel polymerization.[41]
The UV/vis DR spectrum of PCP-MF showed broad absorption of PCP-MF from the visible light
to near infrared range (Figure 1d). The polymer also showed a yellowish green fluorescence
with a maximum at 542 nm (Figure 1d). The electron paramagnetic resonance (EPR) displayed
a remarkable increase in signal intensity under light irradiation compared to the one taken in
dark, indicating the generation of long-lived photo-induced electron-hole pairs inside the
polymer (Figure 1e). The results confirmed that the special structural design containing the
photoactive benzothiadiazole units could enhance the light-induced charge separation and

ACCEPTED MANUSCRIPT
further introduce a potential redox activity of the materials.[42] The highest occupied molecular
orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) were determined to be +1.67
V and -0.75 V vs. SCE via cyclic voltammetry (Figure 1f, S5 and S6). The photoredox potentials
of PCP-MF are slightly lower compared to the oxidative and reductive potentials of some well-
+
3
2+
established homogeneous visible light photocatalysts, for example the Ru(bpy) /Ru(bpy)
3
couple with -0.86 V and 1.29 V, respectively.[2, 4]
The photocatalytic oxidative hydroxylation of phenylboronic acid was chosen as the model
reaction using PCP-MF as the photocatalyst under visible light irradiation. The reaction occurred
to give the desired phenol as product in 94% yield after 10 hours (entry 1 in Table 1).
Encouraged by the result, we then conducted a series of screening and control experiments as
listed in Table 1. It was found that little or only trace conversion was observed if any one of the
reaction components was absent, indicating that the photocatalyst PCP-MF, amine, oxygen and
light are all indispensable components for this reaction (entries 2-4).
●−
Previous studies reported that the two active oxygen species, superoxide (O2 ) and singlet
1
oxygen ( O
2
) could be generated by using conjugated porous polymers under visible light
irradiation.[29, 43] Here, spin trap EPR measurements were conducted using 5,5-dimethyl-1-
pyrroline N-oxide (DMPO) and 2,2,6,6-tetramethylpiperidinyloxyl (TEMPO) as superoxide and
singlet oxygen trapping agents, respectively. Interestingly, as shown in Figure S7 in ESI, only
●−
one oxygen species, O2 could be determined by using PCP-MF as photocatalyst. It indicates
●−
2
that O
played a major role for the hydroxylation of boronic acid in this study, similar to
previous report,[39] To fully understand the specific role of the photogenerated electron-hole
pairs during the photocatalytic hydroxylation reaction, we then added benzoquinone (BQ) as
●
−
2
O
scavenger into the reaction mixture, a yield of 45% was determined (entry 6). Both results
indicate that superoxide radical anion took a vital part in the hydroxylation reaction of
phenylboronic acid. Fluorescence quenching experiment showed that the fluorescence of PCP-

ACCEPTED MANUSCRIPT
MF could be effectively quenched in the presence of O
2
and phenylboronic acid, indicating an
oxidative quenching process (Figure S8 and S9 in ESI). Based on our observations from the
screening and control experiments, we propose a modified reaction mechanism similar to the
literature.[40, 43]
The proposed mechanism of the hydroxylation of arylboronic acids is illustrated in Figure 2.
Upon light exposure, the photoexcited electron is quenched by oxygen, forming the superoxide
●
−
2
●−
2
radical anion O
. As the reduction potential of the O
2
/O
lies at -0.57 V vs SCE,[44-47] the
LUMO level of PCP-MF (-0.75 V vs. SCE) was indeed sufficient to activate the molecular
oxygen species. The superoxide radical anion then reacts with the boronic acid to form the
peroxide radical A as intermediate. Meanwhile, triethylamine is oxidized by losing an electron to
the photogenerated hole in the excited state of PCP-MF, which returns to its ground state and
complete the photoredox cycle. The intermediate A then abstracts one H atom from the cationic
radical of triethylamine to form intermediate peroxide B, which rearranges to form phenyl
dihydrogen borate C. The final product is obtained after hydroxylation of C.
The scope of the visible light-induced oxidative hydroxylation of arylboronic acids is summarized
in Table 2. With PCP-MF as photocatalyst, various arylboronic acids, bearing either electron-
donating group such as methoxy, biphenyl and naphthalenyl or electron withdrawing groups
such as cyano, fluoride, bromide, nitro and cyanomethyl, were effectively oxidized to the
corresponding aryl alcohols in good to excellent yields. Notably, the electron-deficient
arylboronic acids reacted slightly faster than that of electron-rich ones. A possible explanation is
that phenylboronic acids with electron-withdrawing substituents had a higher electron affinity
than the ones with electron-donating substituents. This makes them thermodynamically more
favorable to complex with superoxide radical, as indicated in the reaction mechanism.
Hydroquinone could also be obtained from the relevant p-phenylenediboronic acid with a
moderate yield (table 2, entry 15). Moreover, repeating experiments for hydroxylation of

ACCEPTED MANUSCRIPT
phenylboronic acid showed a slight decrease with a generally high conversion of more than 80
%
during the whole repeating cycles (Figure S10 in ESI). The small decrease of conversion is
possibly due to the recovery problem because the polymer demonstrated a very fine powder-
like shape, which made some unavoidable loss during the collecting process. Nevertheless, the
SEM image of PCP-MF after the fifth cycle barely showed any change compared with the
pristine one (Figure S11 in ESI), indicating the stability of the PCP-MF during the photocatalytic
reaction.
Conclusion
In summary, a porous conjugated polymer was synthesized via a simple metal-free
Knoevenagel condensation reaction at mild conditions. The photocatalytic activity of the porous
polymer as heterogeneous photocatalyst was demonstrated by the hydroxylation of a series of
arylboronic acids to the corresponding phenols under visible light. High functional group
tolerance of the substrates was demonstrated during the photocatalytic reaction. We hope this
work can present a new alternative metal-free synthetic route of pure organic and
heterogeneous photocatalyts based on porous conjugated polymers at mild conditions and
stimulate further discussions in the field.
Acknowledgement
The Max Planck Society is acknowledged for financial support. R.L. thanks the China
Scholarship Council (CSC) for funding. Z.J.W. is a recipient of a fellowship through funding of
the Excellence Initiative (DFG/GSC 266) of the graduate school of excellence “MAINZ”
(
Materials Science in Mainz).

ACCEPTED MANUSCRIPT
Scheme 1. Synthetic route of the porous conjugated polymer PCP-MF via a simple metal-free
Knoevenagel polycondensation reaction.

ACCEPTED MANUSCRIPT
Figure 1. (a) SEM and (b) TEM images, (c) FT-IR spectra, (d) UV/vis DR and fluorescence
spectra, (e) EPR spectra in dark and under light irradiation, and (f) HOMO and LUMO band
positions of PCP-MF.

ACCEPTED MANUSCRIPT
Figure 2. Proposed mechanism of the photocatalytic hydroxylation of arylboronic acids using
PCP-MF.
Table 1. Screening and control experiments of the photocatalytic hydroxylation of phenylboronic
a
acid

ACCEPTED MANUSCRIPT
b
Entry
1
Reaction condition variations
Light
Yield (%)
-
-
+
-
94
<5
c
2
3
no Et
3
N
+
+
+
+
Trace
Trace
Trace
45
d
4
no O2
5
no photocatalyst
radical scavenger
e
6
a
Reaction conditions: phenylboronic acid (0.5 mmol), Et N (1.5 mmol),
3
photocatalyst (10 mg), 3 mL CH
3
CN, 1 atm O
2
, 10 hr, white LED lamp
2
b
c
(
1.2 W/cm ). Isolated yield after chromatography over silica. In dark.
d
e
Under N2 environment. Benzoquinone (BQ) used as radical
scavenger
Table 2. Photocatalytic hydroxylation of various arylboronic acids using PCP-MF as
a
photocatalyst

ACCEPTED MANUSCRIPT
b
Entry
7
Arylboronic acid
Product
Time (h)
20
Yield (%)
96
92
88
8
9
20
23
1
1
1
1
0
1
2
3
19
24
24
24
95
85
93
95
1
1
4
5
20
24
83
76
a
Standard reaction conditions: arylboronic acid (0.5 mmol), Et N (1.5
3
mmol), PCP-MF (10 mg), 3 mL CH CN, 1 atm O , white LED lamp (1.2
3
2
2
b
W/cm ). Isolated yield after chromatography over silica.
References:
[
1] G. Ciamician, The Photochemistry of the Future, Science 36(926) (1912) 385-94.

ACCEPTED MANUSCRIPT
[
2] D.A. Nagib, D.W.C. MacMillan, Trifluoromethylation of arenes and heteroarenes by means of
photoredox catalysis, Nature 480(7376) (2011) 224-228.
3] T.P. Yoon, M.A. Ischay, J.N. Du, Visible light photocatalysis as a greener approach to photochemical
synthesis, Nature Chem. 2(7) (2010) 527-532.
4] J.M.R. Narayanam, C.R.J. Stephenson, Visible light photoredox catalysis: applications in organic
synthesis, Chem. Soc. Rev. 40(1) (2011) 102-113.
5] C.H. Dai, J.M.R. Narayanam, C.R.J. Stephenson, Visible-light-mediated conversion of alcohols to
halides, Nature Chem. 3(2) (2011) 140-145.
6] X.J. Lang, X.D. Chen, J.C. Zhao, Heterogeneous visible light photocatalysis for selective organic
transformations, Chem. Soc. Rev. 43(1) (2014) 473-486.
7] S. Ghosh, N.A. Kouame, L. Ramos, S. Remita, A. Dazzi, A. Deniset-Besseau, P. Beaunier, F. Goubard,
[
[
[
[
[
P.H. Aubert, H. Remita, Conducting polymer nanostructures for photocatalysis under visible light, Nat.
Mater. 14(5) (2015) 505-511.
[
8] X.C. Wang, K. Maeda, A. Thomas, K. Takanabe, G. Xin, J.M. Carlsson, K. Domen, M. Antonietti, A
metal-free polymeric photocatalyst for hydrogen production from water under visible light, Nat. Mater.
(1) (2009) 76-80.
9] J. Liu, Y. Liu, N.Y. Liu, Y.Z. Han, X. Zhang, H. Huang, Y. Lifshitz, S.T. Lee, J. Zhong, Z.H. Kang, Metal-free
efficient photocatalyst for stable visible water splitting via a two-electron pathway, Science 347(6225)
8
[
(2015) 970-974.
[
10] N. Kang, J.H. Park, K.C. Ko, J. Chun, E. Kim, H.W. Shin, S.M. Lee, H.J. Kim, T.K. Ahn, J.Y. Lee, S.U. Son,
Tandem synthesis of photoactive benzodifuran moieties in the formation of microporous organic
networks, Angew. Chem. Int. Ed. 52(24) (2013) 6228-32.
[
11] K. Zhang, D. Kopetzki, P.H. Seeberger, M. Antonietti, F. Vilela, Surface Area Control and
Photocatalytic Activity of Conjugated Microporous Poly(benzothiadiazole) Networks, Angew. Chem. Int.
Ed. 52(5) (2013) 1432-1436.
[
12] C. Yang, B.C. Ma, L. Zhang, S. Lin, S. Ghasimi, K. Landfester, K.A.I. Zhang, X. Wang, Molecular
Engineering of Conjugated Polybenzothiadiazoles for Enhanced Hydrogen Production by Photosynthesis,
Angew. Chem. Int. Ed. 55(32) (2016) 9202-9206.
[
13] C. Su, R. Tandiana, B. Tian, A. Sengupta, W. Tang, J. Su, K.P. Loh, Visible-Light Photocatalysis of
Aerobic Oxidation Reactions Using Carbazolic Conjugated Microporous Polymers, ACS Catal. 6(6) (2016)
594-3599.
14] J.X. Jiang, F. Su, A. Trewin, C.D. Wood, N.L. Campbell, H. Niu, C. Dickinson, A.Y. Ganin, M.J.
3
[
Rosseinsky, Y.Z. Khimyak, A.I. Cooper, Conjugated microporous poly (aryleneethynylene) networks,
Angew. Chem. Int. Ed. 46(45) (2007) 8574-8578.
[
15] R. Dawson, D.J. Adams, A.I. Cooper, Chemical tuning of CO2 sorption in robust nanoporous organic
polymers, Chem. Sci. 2(6) (2011) 1173-1177.
16] Q. Chen, M. Luo, P. Hammershøj, D. Zhou, Y. Han, B.W. Laursen, C.-G. Yan, B.-H. Han, Microporous
Polycarbazole with High Specific Surface Area for Gas Storage and Separation, J. Am. Chem. Soc. 134(14)
[
(2012) 6084-6087.
[
17] A. Li, H.X. Sun, D.Z. Tan, W.J. Fan, S.H. Wen, X.J. Qing, G.X. Li, S.Y. Li, W.Q. Deng, Superhydrophobic
conjugated microporous polymers for separation and adsorption, Energy Environ. Sci. 4(6) (2011) 2062-
065.
18] X. Zhuang, Gehrig, D., Forler, N., Liang, H., Wagner, M., Hansen, M., Laquai, F., Zhang, F., Feng, X.3,
2
[
Conjugated Microporous Polymers with Dimensionality-Controlled Heterostructures for Green Energy
Devices, Adv. Mater. 27(25) (2015) 3789-3796.
[
19] Y. Xie, T.T. Wang, X.H. Liu, K. Zou, W.Q. Deng, Capture and conversion of CO2 at ambient conditions
by a conjugated microporous polymer, Nat. Commun. 4 (2013) 1960.

ACCEPTED MANUSCRIPT
[
20] J.X. Jiang, Y.Y. Li, X.F. Wu, J.L. Xiao, D.J. Adams, A.I. Cooper, Conjugated Microporous Polymers with
Rose Bengal Dye for Highly Efficient Heterogeneous Organo-Photocatalysis, Macromolecules 46(22)
(2013) 8779-8783.
[
21] Z.J. Wang, S. Ghasimi, K. Landfester, K.A.I. Zhang, Photocatalytic Suzuki Coupling Reaction Using
Conjugated Microporous Polymer with Immobilized Palladium Nanoparticles under Visible Light, Chem.
Mater. 27(6) (2015) 1921-1924.
[
22] Z.J. Wang, S. Ghasimi, K. Landfester, K.A.I. Zhang, Highly porous conjugated polymers for selective
oxidation of organic sulfides under visible light, Chem. Commun. 50(60) (2014) 8177-8180.
23] Z.J. Wang, S. Ghasimi, K. Landfester, K.A.I. Zhang, A conjugated porous poly-benzobisthiadiazole
network for a visible light-driven photoredox reaction, J. Mater. Chem. A 2(44) (2014) 18720-18724.
24] Z.J. Wang, S. Ghasimi, K. Landfester, K.A.I. Zhang, Molecular Structural Design of Conjugated
[
[
Microporous Poly(Benzooxadiazole) Networks for Enhanced Photocatalytic Activity with Visible Light,
Adv. Mater. 27(40) (2015) 6265-6270.
[
25] Z.J. Wang, K. Garth, S. Ghasimi, K. Landfester, K.A.I. Zhang, Conjugated Microporous
Poly(Benzochalcogenadiazole)s for Photocatalytic Oxidative Coupling of Amines under Visible Light,
ChemSusChem 8(20) (2015) 3459-3464.
[
26] Y.H. Xu, S.B. Jin, H. Xu, A. Nagai, D.L. Jiang, Conjugated microporous polymers: design, synthesis and
application, Chem. Soc. Rev. 42(20) (2013) 8012-8031.
27] F. Vilela, K. Zhang, M. Antonietti, Conjugated porous polymers for energy applications, Energ
Environ. Sci. 5(7) (2012) 7819-7832.
[
[
(
[
28] R. Dawson, A.I. Cooper, D.J. Adams, Nanoporous organic polymer networks, Prog. Polym. Sci. 37(4)
2012) 530-563.
29] K. Zhang, D. Kopetzki, P.H. Seeberger, M. Antonietti, F. Vilela, Surface Area Control and
Photocatalytic Activity of Conjugated Microporous Poly(benzothiadiazole) Networks, Angew. Chem. Int.
Ed. 52(5) (2013) 1432-1436.
[
30] J. Schmidt, M. Werner, A. Thomas, Conjugated Microporous Polymer Networks via Yamamoto
Polymerization, Macromolecules 42(13) (2009) 4426-4429.
31] G.L. Lu, H.S. Yang, Y.L. Zhu, T. Huggins, Z.J. Ren, Z.N. Liu, W. Zhang, Synthesis of a conjugated porous
[
Co(II) porphyrinylene-ethynylene framework through alkyne metathesis and its catalytic activity study, J.
Mater. Chem. A 3(9) (2015) 4954-4959.
[
32] L.B. Sun, Z.Q. Liang, J.H. Yu, R.R. Xu, Luminescent microporous organic polymers containing the
1
1
,3,5-tri(4-ethenylphenyl)benzene unit constructed by Heck coupling reaction, Polym. Chem. 4(6) (2013)
932-1938.
[
33] V. Senkovskyy, I. Senkovska, A. Kiriy, Surface-Initiated Synthesis of Conjugated Microporous
Polymers: Chain-Growth Kumada Catalyst-Transfer Polycondensation at Work, ACS Macro Lett. 1(4)
(2012) 494-498.
[
34] J. Schmidt, J. Weber, J.D. Epping, M. Antonietti, A. Thomas, Microporous Conjugated
Poly(thienylene arylene) Networks, Adv. Mater. 21(6) (2009) 702-705.
35] P. Kuhn, M. Antonietti, A. Thomas, Porous, covalent triazine-based frameworks prepared by
ionothermal synthesis, Angew. Chem. Int. Ed. 47(18) (2008) 3450-3453.
[
[
[
36] F.o. Diederich, P.J. Stang, Metal-catalyzed cross-coupling reactions, Wiley-VCH, New York, 1998.
37] C. Xu, N. Hedin, Synthesis of microporous organic polymers with high CO2-over-N-2 selectivity and
CO2 adsorption, J. Mater. Chem. A 1(10) (2013) 3406-3414.
38] M.G. Schwab, M. Hamburger, X.L. Feng, J. Shu, H.W. Spiess, X.C. Wang, M. Antonietti, K. Mullen,
[
Photocatalytic hydrogen evolution through fully conjugated poly(azomethine) networks, Chem.
Commun. 46(47) (2010) 8932-8934.

ACCEPTED MANUSCRIPT
[
39] Y.Q. Zou, J.R. Chen, X.P. Liu, L.Q. Lu, R.L. Davis, K.A. Jorgensen, W.J. Xiao, Highly Efficient Aerobic
Oxidative Hydroxylation of Arylboronic Acids: Photoredox Catalysis Using Visible Light, Angew. Chem.
Int. Ed. 51(3) (2012) 784-788.
[
40] S.P. Pitre, C.D. McTiernan, H. Ismaili, J.C. Scaiano, Mechanistic Insights and Kinetic Analysis for the
Oxidative Hydroxylation of Arylboronic Acids by Visible Light Photoredox Catalysis: A Metal-Free
Alternative, J. Am. Chem. Soc. 135(36) (2013) 13286-13289.
[
41] Y. Wei, W. Chen, X. Zhao, S. Ding, S. Han, L. Chen, Solid-state emissive cyanostilbene based
conjugated microporous polymers via cost-effective Knoevenagel polycondensation, Polym. Chem. 7(24)
(2016) 3983-3988.
[
42] L. Wang, W. Huang, R. Li, D. Gehrig, P.W. Blom, K. Landfester, K.A. Zhang, Structural Design Principle
of Small-Molecule Organic Semiconductors for Metal-Free, Visible-Light-Promoted Photocatalysis,
Angew. Chem. Int. Ed. 55(33) (2016) 9783-7.
[
43] J. Luo, X. Zhang, J. Zhang, Carbazolic Porous Organic Framework as an Efficient, Metal-Free Visible-
Light Photocatalyst for Organic Synthesis, ACS Catal. 5(4) (2015) 2250-2254.
[
[
44] P.M. Wood, The potential diagram for oxygen at pH 7, Biochem. J 253(1) (1988) 287-289.
45] P.S. Rao, E. Hayon, Experimental determination of the redox potential of the superoxide radical
•
O2−, Biochem. Biophys. Res. Commun. 51(2) (1973) 468-473.
46] P.S. Rao, E. Hayon, Redox potentials of free radicals. IV. Superoxide and hydroperoxy radicals . O2-
and . HO2, J. Phys. Chem. 79(4) (1975) 397-402.
47] S. Ghosh, N.A. Kouamé, L. Ramos, S. Remita, A. Dazzi, A. Deniset-Besseau, P. Beaunier, F. Goubard,
[
[
P.-H. Aubert, H. Remita, Conducting polymer nanostructures for photocatalysis under visible light,
Nature Mater. 14(5) (2015) 505-511.

ACCEPTED MANUSCRIPT
Highlights
•
•
•
•
metal-free preparation of porous conjugated polymers
photocatalytic oxidative hydroxylation of arylboronic acids
visible light photocatalysis
high functional group tolerance of the substrates