Screening metal-free photocatalysts from isomorphic covalent organic frameworks for the C-3 functionalization of indoles

Article abstract of DOI:10.1039/d0ta02164d

The visible-light-driven organic transformation using two-dimensional covalent organic frameworks (2D-COFs) as metal-free heterogeneous photocatalysts is a green and sustainable approach, and it has gained a surge of interest by virtue of the photosensitizer's high crystallinity, abundant porosity, outstanding stability, excellent light-harvesting ability and tunable structure. However, the guiding principle for designing, constructing and selecting COF-based photocatalysts has not been put forward so far. Herein, we contribute a fascinating strategy to guide the acquisition of excellent framework photocatalysts, which is to screen them from a series of isomorphic COFs. As a proof of concept, three new isomorphic pyrene-based 2D-COFs (COF-JLU23, COF-JLU24 and COF-JLU25) with variable linkers were successfully synthesized. In addition to having similar crystallinity and porosity with the same pore size and shape, their absorption, emission, bandgap, energy level, transient photocurrent response and photocatalytic activity could be easily adjustedviaconfiguring different linkers in frameworks. Indeed, COF-JLU24 with electron donor-acceptor characteristics exhibited the best photocatalytic activity among the three isomorphic COFs for C-3 functionalization reactions of indoles, even better than that of the metal-free photocatalyst g-C₃N₄. More importantly, the screened COF-JLU24 as a metal-free photocatalyst still displayed extensive substrate adaptability and excellent recyclability. We anticipate that this strategy will become a robust rule of thumb for fast access to COF-based photocatalysts. In addition, we still highlight that the present study broadens the applied frontier of COF-based photocatalysts.

Full text of DOI:10.1039/d0ta02164d

View Article Online
View Journal
Journal of
Materials Chemistry A
Materials for energy and sustainability
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: X. Liu, Z. Li, S.
Han, C. Li, P. Shao, H. Xia, H. Li, X. Chen and X. Feng, J. Mater. Chem. A, 2020, DOI:
10.1039/D0TA02164D.
Volume
Number 12
28 March 2018
Pages 4883-5230
6
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Journal of
Materials Chemistry A
Materials for energy and sustainability
rsc.li/materials-a
Accepted Manuscripts are published online shortly after acceptance,
before technical editing, formatting and proof reading. Using this free
service, authors can make their results available to the community, in
citable form, before we publish the edited article. We will replace this
Accepted Manuscript with the edited and formatted Advance Article as
soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes to the
text and/or graphics, which may alter content. The journal’s standard
Terms & Conditions and the Ethical guidelines still apply. In no event
shall the Royal Society of Chemistry be held responsible for any errors
or omissions in this Accepted Manuscript or any consequences arising
from the use of any information it contains.
ISSN 2050-7488
COMMUNICATION
Zhenhai Wen et al.
An electrochemically neutralized energy-assisted low-cost
acid-alkaline electrolyzer for energy-saving electrolysis
hydrogen generation
rsc.li/materials-a

Please do not adjust margins
Journal of Materials Chemistry A
Page 1 of 11
View Article Online
DOI: 10.1039/D0TA02164D
Journal Name
ARTICLE
Screening metal-free photocatalysts from isomorphic covalent
organic frameworks for C-3 functionalization of indoles
Ziping Li,a Songjie Han,a Chunzhi Li,c Pengpeng Shao,d Hong Xia,b He Li,c Xiong Chen,e Xiao Feng,d
Received 00th January 20xx,
Accepted 00th January 20xx
and Xiaoming Liu*a
DOI: 10.1039/x0xx00000x
Visible-light driven organic transformation using two-dimensional covalent organic frameworks (2D-COFs) as metal-free
heterogeneous photocatalysts is a green and sustainable approach, and that has gathered a surge of interest by virtue of
the photosensitizerʼs high crystallinity, abundant porosity, outstanding stability, excellent light-harvesting ability and tunable
structure. However, the guiding principle for the designing, constructing and selecting COF-based photocatalysts has not
been put forward so far. Herein, we contribute a fascinating strategy to guide the acquisition of excellent framework
photocatalysts, which is to screen them from a series of isomorphic COFs. As a proof of concept, three new isomorphic
pyrene-based 2D-COFs (COF-JLU23, COF-JLU24 and COF-JLU25) with variable linkers were successfully synthesized. In
addition to having similar crystallinity, porosity with same pore size and shape, their absorption, emission, bandgap, energy
level, transient photocurrent response and photocatalytic activity could be easily adjusted via configuring different linker in
frameworks. Indeed, the COF-JLU24 with electron donor-acceptor character exhibited the best photocatalytic activity in
three isomorphic COFs for C-3 functionalization reaction of indoles, even better than that of the metal-free photocatalyst g-
C3N4. More importantly, the screened COF-JLU24 as a metal-free photocatalyst still displayed extensive substrate
adaptability and excellent recyclability. We anticipate that this strategy will become a robust rule of thumb for fast access
to COF-based photocatalysts. In addition, we still highlight current present broadens the applied frontier of COF-based
photocatalyst.
www.rsc.org/
leading to the rapid migration, diffusion and separation of
photogenerated carriers along the periodic columnar π-arrays
and 2D π-conjugated macromolecular layers.24 Thanks to the
Introduction
Covalent organic frameworks (COFs) as a novel kind of porous
crystalline materials, have recently dramatically growing increst
owing to their intriguing characters including extremely light
density, permanent porosity with large surface area, high
crystallinity, outstanding stability, as well as diverse
functionality.1−8 To date, COFs as new functional platforms have
been demonstrated to show tremendous potential applications
in gas adsorption,9−11 chemical sensing,12−14 proton
conductivity,15−17 energy storage,18,19 and heterogeneous
catalysis.20−23 Based on the concept of reticular chemistry,
additionally, the photo/electroactive organic moieties are easy
to be introduced into stable skeletons of two-dimensional (2D)
COFs through specific reversible condensation reactions,
synergistic cooperation of their permanent porosity, superior
stability, high crystallinity, strong harvesting in the visible-light
region, and abundant redox properties in the excited state, the
photo/electroactive 2D-COFs still have very recently emerged
as powerful and metal-free heterogeneous catalysts for light-
induced water splitting,25−31 photocatalytic carbon dioxide
reduction32−34 and photoinduced degradation of pollutants in
water.35,36 For instance, a pioneering study by the Lotsch group
has contributed a 2D hydrazone-linked COF for hydrogen
evolution from water splitting under visible-light illumination.37
More importantly, the photocatalytic organic transformations
by an imine-based COF are still developed successfully, and the
research results proved unequivocally that 2D-COFs possess
potential as excellent heterogeneous photocatalysts for organic
transformations.38 Until now, nevertheless, the strategy for
designing and screening of outstanding COF-based
photocatalysts with high activity and selectivity has not been
explored. Meanwhile, the exploration and development of 2D-
COFs as powerful heterogeneous photocatalysts are in its
infancy, and studied types of organic reactions are also very
rare.39−42
a. College of Chemistry, Jilin University, Changchun, 130012, P.R. China.
E-mail: xm_liu@jlu.edu.cn
b. State Key Laboratory on Integrated Optoelectronics, College of Electronic Science
and Technology, Jilin University, Changchun, 130012, P.R. China.
c. State Key Laboratory of Catalysis, iChEM, Dalian Institute of Chemical Physics,
Chinese Academy of Sciences, Dalian 116023, China
d. School of Chemistry, Beijing Institute of Technology, Beijing, 100081, P.R. China
e. State Key Laboratory of Photocatalysis on Energy and Environment, College of
Chemistry, Fuzhou University, Fuzhou, 350002, P.R. China
†
Electronic Supplementary Information (ESI) available: Synthesis of monomers and
COFs, material characterization, general photocatalytic process, TGA, and NMR
spectra of catalytic products See DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry A
Page 2 of 11
ARTICLE
Journal Name
View Article Online
DOI: 10.1039/D0TA02164D
Scheme 1. (a) Syntheses of isomorphic pyrene-based COFs. Top (b) and side (c) views of COF-JLU23. Top (d) and side (e) views of COF-JLU24. Top (f) and side
(g) views of COF-JLU25. (light gray, carbon; purple, nitrogen; blue, selenium; green, sulfur; red, oxygen; hydrogen is omitted for clarity).
The indole moiety is a critical component in numerous natural series of isomorphic COFs has some advantages: (a) the
products and pharmaceutical molecules with important isomorphic COFs possess similar crystallinity and the same pore
biological activity.43 Therefore, the synthetic chemistry of indole size and shape, (b) changing the electronic property of building
and its derivatives has gained great interest of chemical units can tailor precisely the photo/electronic characteristics of
researchers over the years. The direct C-3 functionalization of COFs, resulting in the improvement of photocatalytic
indoles such as formylation and thiocyanation is an important performance, (c) it is more conducive to explore the
avenue to obtain a variety of indole derivatives.44−48 In general, relationship between COF structure and photocatalytic
the traditional synthesis method suffered from harsh reaction performance. Herein, we contributed a fascinating strategy to
conditions or toxic noble metal catalysts, leading to low guide the acquisition of excellent framework photocatalysts in
selectivity, weak tolerance of functional groups and this paper, which is to screen them from a series of isomorphic
environment issues.44 In contrast, the light-driven COFs. Along the way, three novel and isomorphic pyrene-based
transformation of 3-substituted indole derivatives is a highly 2D-COFs (Scheme 1, COF-JLU23, COF-JLU24 and COF-JLU25)
selective, mild, and environmentally friendly process. with different linkers have been successfully constructed and
Unfortunately, some drawbacks including high cost and toxicity, their porosity, crystallinity, stability and energy levels, as well as
low recyclability, and tedious purification process of utilized photo/electronic properties were studied in detail. More
photocatalysts like organometallic complexes based on the importantly, the screened COF-JLU24 can work as
a
noble metal and pure organic dyes restrict their application for heterogeneous photocatalyst with high catalytic activity and
large-scale preparation in industry.45−48 Very recently, Yu et al. recyclability in C-3 functionalization of indoles under light-
reported the amorphous conjugated microporous polymers visible illumination. The photocatalysis mechanism of the COF-
(CMPs) catalyzed C-3 functionalization of indoles with good JLU24 to the organic reactions was also researched.
recyclability.49 To the best of our knowledge, however, the
Results and discussion
investigations of crystalline organic frameworks as
heterogeneous photocatalysts for C-3 functionalization of
indoles have not been explored so far.
In the context, to get an outstanding COF-based
photocatalysts for C-3 functionalization of indoles, the design,
construction and screening for framework structure are great
challenges. Screening heterogeneous photocatalysts from a
Selecting 1,3,6,8-tetrakis(4-aminophenyl)pyrene (TTA-Py) as
a knot and dialdehyde of the same size as linker, three new and
isomorphic pyrene-based COFs were prepared through the
imine condensation reaction under solvothermal conditions,
owing to high crystallinity, large surface area, excellent stability
and photo/electronic property of such COFs.50,51 Surprisingly,
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 3 of 11
Journal of Materials Chemistry A
Please do not adjust margins
Journal Name
ARTICLE
the isolation yield 89% for COF-JLU23, 87% for COF-JLU24, and
85% for COF-JLU25 was obtained in same reaction condition,
which is in a mixture of o-DCB/n-BuOH/6M HOAc (5/5/1, by vol.)
View Article Online
DOI: 10.1039/D0TA02164D
o
at 120 C for 3 days (Scheme 1). These isomorphic 2D-COFs
almost didn’t dissolve in H2O and general organic solvents. The
new pyrene-based COFs were well characterized by Fourier
transform infrared (FT-IR), solid state 13C CP/MAS NMR, and
elemental analysis. As shown in Fig. 1a, the stretching peaks at
about 1623 cm−1 were obtained, which indicates the formation
of the imine linkage. In addition, the stretching signals of
carbonyl group nearly disappeared in the FT-IR spectra of the
COFs compared with their corresponding monomer.
Furthermore, more detained connections of three pyrene-
based COFs were studies by solid state 13C CP/MAS NMR as
shown in Fig. 1b, 1c and 1d, respectively. For example, the low-
field signals at ~157.5 ppm and ~150.6 ppm in the spectrum of
COF-JLU23 are attributed to the carbon atoms of the imine
group and benzoselenadiazole unit, respectively. And other
peaks correspond to the signals of the nonsubstituted and
substituted aromatic carbons (Fig. 1b). For COF-JLU25,
particularly, the high-field peak at ~55.2 ppm is generated by
the carbon atom of the methoxy group, while the peak at
~158.5 ppm is assigned to the carbon signal of –C=N– groups. In
addition, elemental analysis of COF-JLU23, COF-JLU24 and
COF-JLU25 revealed that the carbon, hydrogen and nitrogen
contents are close to their calculated values in the
corresponding 2D sheets (Fig. S1†).
Fig. 1 (a) FT-IR spectra of TTA-Py (gray line), 4,4'-(benzoselenadiazole-4,7-
diyl)dibenzaldehyde (black point segment), COF-JLU23 (black line), 4,4'-
([1,2,5]thiadiazolo[3,4-c]pyridine-4,7-diyl)dibenzaldehyde
(cyan
point
segment), COF-JLU24 (cyan line), 4-[4-(4-formylmethyl)-2,5-
The crystalline structures of COF-JLU23, COF-JLU24 and COF-
JLU25 were researched using powder X-ray diffraction (PXRD)
measurement coupled with theoretical simulations. The
obtained PXRD pattern for COF-JLU23 showed a strong
diffraction peak at 2.73o, and other relatively weak diffraction
signals 3.62o, 5.46o, 8.28o, and 10.99o, which can be assigned to
the (110), (200), (220), (330) and (440) planes, respectively (Fig.
2a). The relatively broad peak at 23.48o corresponded to the
(001) plane, owing to the existence of π-π stacking between the
layers. The simulation of the PXRD profile indicated the COF-
JLU23 preferably reproduces the AA stacking structure (light
gray line). In this model, the Pawley refinement is in well
agreement with the experimental pattern, as observed from
their negligible difference (Rwp = 6.82% and Rp = 5.66%). For the
other two isomorphic COFs, the most intense peaks at 2.73o for
COF-JLU24 and 2.75o for COF-JLU25 are also ascribed to the 110
reflection (Fig. 2b and 2c). We can found that the positions of
110 reflection peak for three COFs are almost the same, which
is attributed to their isomorphic character. Similarly, both
isomorphic COFs still possess the eclipsed structure (cyan line
for COF-JLU24 and blue line for COF-JLU25). The Pawley refined
patterns display a good match to the experimentally observed
dimethoxyphenyl]benzaldehyde (blue point segment) and COF-JLU25 (blue
line). 13C CP/MAS NMR spectra of COF-JLU23 (b), COF-JLU24 (c) and COF-
JLU25 (d).
The porosity of new isomorphic COFs was further studied via
N2 sorption experiment at 77 K. According to the IUPAC
classification, the sorption curve of three COFs were type IV
isotherm, which indicated that these COFs are mesoporous
materials with one-dimensional open channel (Fig. 2g). The
Brunauer-Emmett-Teller (BET) specifical surface area of COF-
JLU23 was measured to be 791.7 m2 g−1. And the diameter of
diamond pore was estimated as 2.2 nm (Fig. 2h). In contrast,
COF-JLU24 exhibited a lightly increased surface area of 946.3 m2
g−1, whereas its pore diameter also remained at 2.2 nm. The
change was just opposite for COF-JLU25, of which the BET
specific surface area was decreased to 469.6 m2 g−1. And its pore
size is similar to that of other both isomorphic COFs, which is
close to the theoretical pore size based on the refined structure.
In addition, the total pore volumes were calculated based on
nitrogen gas adsorbed at P/Po = 0.99 to be 0.736 cm3 g−1 for
COF-JLU23, 1.210 cm3 g−1 for COF-JLU24 and 0.659 cm3 g−1 for
COF-JLU25, respectively. The high surface, large pore size and
volume of new COFs are beneficial for adsorption, diffusion and
reaction of matters in the heterogeneous catalysis.52−54
result with Rwp = 5.82%, Rp = 4.35% for COF-JLU24 and Rwp
=
5.64%, Rp = 3.88% for COF-JLU25. In addition, the crystalline
morphology of three isomorphic COFs was also researched
through field-emission scanning electron microscopy (FE-SEM).
As shown in Fig. 2d–2f, the FE-SEM images displayed that all
three isomorphic COFs exist in the form of similar block crystal.
Surprisingly, the average size of nanocrystals is different when
the linker in the isomorphic COFs was adjusted.
The stability of COFs is an important character for their
industrial applications. Thermogravimetric analysis (TGA) of
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry A
Page 4 of 11
ARTICLE
Journal Name
position change for PXRD pattern, and the almost same curve in
View Article Online
DOI: 10.1039/D0TA02164D
FT-IR spectrum compared with the corresponding original COFs
(Fig. S3†). Therefore, the control experiments demonstrated
clearly that three new pyrene-based COFs have a superior
thermal and chemical stability.
Fig.
3 (a) Normalized absorption spectra of COF-JLUs, insets: their
photographs. (b) Tauc plot of COF-JLUs. (c) Mott-Schottky plot of COF-JLUs.
(d) Schematic energy band structure of COF-JLUs.
In order to investigate the influence of different linkers on the
photophysical characters, UV-vis diffuse reflectance spectra of
the obtained pyrene-based COFs were first performed. As
shown in Fig. 3a, COF-JLU25 displayed a broad visible-light
absorption with the band edge at 543 nm in solid state (blue
line). In comparison, a red-shifted absorption band for
isomorphic COF-JLU23 (dark line) and COF-JLU24 (cyan line)
with strong electron deficient linker is obtained. The absorption
band edges extended to near infrared region, which may be due
to the establishment of electron donor-acceptor system in both
COF-JLUs. This is still in good agreement with the color change
in COFs, from yellow for COF-JLU25 to brown-red for COF-JLU24
to dark-red for COF-JLU23 (Fig. 3a, insets). Their optical band
gaps were determined to be 1.98 eV for COF-JLU23, 2.00 eV for
COF-JLU24 and 2.44 eV for COF-JLU25, respectively, which was
calculated from the corresponding Tauc plot (Fig. 3b). For
further research the relative positions of valence band (VB) and
conduction band (CB), the electrochemical Mott-Schottky was
performed (Fig. 3c). The results exhibited that the flat band
position (Vfb) of COF-JLU23, COF-JLU24 and COF-JLU25 is
approximately −1.09 V, −1.05 V and −1.00 V (vs. SCE),
respectively. As we known, the flat band potential in n-type
semiconductors is very close to that of CB.55 Therefore, the VB
position at 0.89 V for COF-JLU23, 0.95 V for COF-JLU24 and 1.44
V for COF-JLU25 could be obtained from the corresponding
band gap energy (Fig. 3d).
Fig. 2 (a)-(c) Observed PXRD pattern (black line), the Pawley refined pattern
(red line), the difference plot (green line) and the simulated pattern (grey line
for COF-JLU23, cyan line for COF-JLU24 and blue line for COF-JLU25) for the
slipped model of COF-JLUs. FE-SEM images of COF-JLU23 (d), COF-JLU24 (e)
and COF-JLU25 (f). N2 sorption isotherms of COF-JLUs at 77 K (g). Pore
distribution of COF-JLUs (h).
three COF samples was firstly performed under a nitrogen
atmosphere (Fig. S2†), the results showed that new framework
materials have excellent thermal stability up to 465 oC for COF-
JLU23, 508 oC for COF-JLU24, and 404 oC for COF-JLU25,
respectively. Furthermore, we still investigated the chemical
stability of the three COFs besides thermal stability. The pyrene-
based COF samples were immersed in tetrahydrofuran (THF),
N,N-dimethylformamide (DMF), water, aqueous HCl (3 M) and
NaOH (3 M) solutions at room temperature for 3 days. Then COF
samples were gathered by filtration, washed with THF and H2O,
and dried in vacuum at 80 oC for 6 h. To our delight, all obtained
samples also displayed strong diffraction signals without
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry A
Page 5 of 11
View Article Online
DOI: 10.1039/D0TA02164D
Journal Name
ARTICLE
Fig. 4 (a) UV-vis absorption spectra and photograph of the cationic radical of TMPD generated by COF-JLU24 in the presence of light and oxygen. (b) ESR spectra
of COF-JLU24 (2.0 mg mL−1) and DMPO (0.1 M) in methanol in dark (black line) and under light illumination for 10 min (cyan line). (c) ESR spectra of COF-JLU24
(2.0 mg mL−1) and TMP (0.1 M) in methanol in dark (black line) and under light illumination for 10 min (cyan line). (d) Transient photocurrent responses of
COF-JLUs upon light illumination. (e) The PL spectra of COF-JLUs in the solid state. (f) The EIS Nyquist plots of COF-JLU24 and COF-JLU25.
To our delight, the isomorphic COF-JLUs have similar redox Under light irradiation by a blue LED lamp (460 nm, 30 W), a
potentials campared with that of classical catalysts such as high yield (62%) was realized by COF-JLU24 in the mixed solvent
*[Ru(bpy)3]2+ (−0.81 V vs. SCE) and [Ru(bpy)3]3+ (+1.29 V vs. of CH3CN/H2O (V/V = 1.5/0.3) (Table 1, entry 1). However,
SCE),56 indicating the great application possibility in changing the ratio of solvent leads to the reduction of yields
photocatalytic organic synthesis.
(Table 1, entries 2-4). As can be seen from Table 1, methanol
Three isomorphic pyrene-based COFs not only possess (MeOH) and THF mixed with H2O did not give a better yield
abundant porosity with the same pore shape and size, high under same conditions than CH3CN (Table 1, entries 5 and 6).
crystallinity and superior stability, but also display an intense When the amount of photocatalyst COF-JLU24 increases to 7.0
absorption in visible-light region and promising photoredox mg, a slightly enhanced yield of 64% was obtained (Table 1,
properties. These characters meet basic requirements of the entry 8). Furthermore, when green LED lamp (520 nm, 30 W) or
heterogeneous photocatalyst. As proof of concept, therefore, white LED lamp (8.0 W) is used as the light source, relatively low
we selected the photocatalytic C-3 functionalization of indoles yields is obtained (Table 1, entries 9 and 10). In addition, no
as a model reaction to screen the best photocatalyst from a target product was detected without light excitation or COF-
series of isomorphic COF-JLUs. Initially, the photocatalytic JLU24 as a photocatalyst in the control experiments (Table 1,
activities of COFs in C-3 formylation reaction were researched, entries 11 and 12). When utilizing nitrogen as gas environment
in which N-methylindole (1a), tetramethyl ethylenediamine instead of molecular oxygen, 1a was uncomfortably converted
(TMEDA), molecular oxygen were selected as a model substrate, to the desired product 2a (Table 1, entry 13). These indicated
a carbon source and a green oxidant, respectively. The influence that light, photocatalyst and molecular oxygen are critical for
of reaction conditions on the yield was investigated in detail. the photocatalytic C-3 formylation process. It is well known that
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry A
Page 6 of 11
ARTICLE
Journal Name
aReaction conditions: photocatalyst (5.0 mg), N-methylindole (25μL, 0.2
the singlet oxygen 1O2 and superoxide radical anion O2•− as two
significant types of active oxygen species undertake an
important task in the aerobic photocatalysis. To further
research the mechanism of this photocatalytic process in deep
level, a series of control experiments were designed and
performed. 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO),
which is a well-known radical scavenger, was added to the
reaction system in the standard conditions, a reduced yield of
16% was obtained (Table 1, entry 14). In addition, by adding
sodium azine (NaN3) as a singlet oxygen 1O2 scavenger, a
reduced yield of 2a was obtained (Table 1, entry 15). On the
contrary, during the photocatalysis process, p-benzoquinone
View Article Online
DOI: 10.1039/D0TA02164D
mmol), TMEDA (61 μL, 0.4 mmol), KI (132.8 mg, 0.8 mmol), solvent (1.5 mL),
H2O (0.3 mL), O2 balloon (~0.1 MPa), 30 W blue LED lamp with 460 nm, 25 oC,
36 h. bIsolated yield. cCOF-JLU24 (3.0 mg). dCOF-JLU24 (7.0 mg). e30 W green
LED lamp 520 nm. f8 W white LED lamp. gDark. hIn N2. iTEMPO as the radical
j
scavenger. NaN3 as the singlet oxygen scavenger. kBQ as the superoxide
scavenger.
On the other hand, it is well known that photosensitive
macromolecular systems could availably mediate the electron
transfer from N,N,N',N'-tetramethylbenzene-1,4-diamine
(TMPD) to molecular oxygen, leading to the formation of
colored cationic radical and superoxide radical anion O2•−. As
expected, the COF-JLU24 with high photooxidative capacity
provided really a strong absorption band (Fig. 4a), which proves
the occurrence of electron transfer process. In addition, we still
research the reactive oxygen species generated by the
representative COF-JLU24 from the electron paramagnetic
resonance (EPR) experiments. Here, DMPO and TMP were
selected and utilized as spin-trapping reagents for active oxygen
species O2•− and 1O2, respectively. We can find from Fig. 4b and
•−
(BQ) was added as superoxide radical anion O2 scavenger,
which achieved the negligible amount of the product (4%)
(Table 1, entry 16). Therefore, we can speculate that both active
oxygen species are important intermediates in this
•−
photocatalytic reaction, while the superoxide radical anion O2
has a more critical mission compared with the singlet oxygen
1O2.
Table 1. Photocatalytic C-3 formylation of N-methylindole by COF-JLUsa
•−
4c (cyan lines), the characteristic signal peaks of O2 and
N
Photoatalyst/KI
N
2,2,6,6-tetramethylpiperidine-1-oxyl (TMPO) nitroxide radical
originated from the reaction between 1O2 and TMP, were
distinctly determined under visible-light irradiation. On the
basis of previous reports48,49 and our observations, therefore, a
plausible photocatalytic process for C-3 formylation with COF-
JLU24 is proposed (Fig. 5a). Upon light illumination, the COF-
JLU24 is firstly excited, and the photogenerated electrons can
activate molecular oxygen O2 through a single electron transfer
(SET) or energy transfer process, producing two reactive oxygen
species O2•− and 1O2. Simultaneously, the photogenerated holes
of COF-JLU24 are transferred to TMEDA, which results in the
formation of radical cations A. Subsequently, a hydrogen atom
+
TMEDA
solvent
light RT
O
1a
2a
Entry
1
Catalyst
Solvent (mL)
Yield (%)b
62
COF-JLU24
CH3CN/H2O (1.5/0.3)
CH3CN/H2O (0.9/0.9)
H2O (1.8)
2
3
COF-JLU24
COF-JLU24
COF-JLU24
COF-JLU24
COF-JLU24
COF-JLU24
COF-JLU24
COF-JLU24
COF-JLU24
COF-JLU24
~
54
25
31
34
29
52
64
26
15
0
4
CH3CN (1.8)
•−
5
CH3OH/H2O (1.5/0.3)
THF/H2O (1.5/0.3)
of the intermediate A migrated to superoxide radical anion O2
to form iminium ion B. Then electrophilic addition of B to 1a
affords indole iminium ion C. The C-3 substituted indole
intermediate D is formed upon rearomatization by releasing a
hydrogen ion. The another iminium ion E is formed after a
second photocatalytic cycle. Finally, the target product 2a is
obtained via the hydrolysis of intermediate E.
Furthermore, the photocatalytic activity of two other
isomorphic COFs for the C-3 formylation reaction was also
investigated as a comparison. Under the optimized reaction
conditions, the relatively lower yield of 51% for COF-JLU23 and
48% for COF-JLU25 was detected (Table 1, entries 17 and 18),
which demonstrates the importance of precise adjustment for
the isomorphic COFs structure. On the basis of basic theory, the
structure of matters determines their nature. For
heterogeneous photocatalysis, the efficient generation,
6
7c
CH3CN/H2O (1.5/0.3)
CH3CN/H2O (1.5/0.3)
CH3CN/H2O (1.5/0.3)
CH3CN/H2O (1.5/0.3)
CH3CN/H2O (1.5/0.3)
CH3CN/H2O (1.5/0.3)
CH3CN/H2O (1.5/0.3)
CH3CN/H2O (1.5/0.3)
CH3CN/H2O (1.5/0.3)
CH3CN/H2O (1.5/0.3)
CH3CN/H2O (1.5/0.3)
CH3CN/H2O (1.5/0.3)
8d
9e
10f
11g
12
13h
14i
15j
16k
17
18
0
COF-JLU24
COF-JLU24
COF-JLU24
COF-JLU24
COF-JLU23
COF-JLU25
6
16
41
4
separation, and migration of photogenerated electron-hole
pairs in
a photocatalyst are still crucial for improving
photocatalytic performances, besides their photoelectric
properties, optical band gap and energy level. Consequently, we
further explored the transient photocurrent response,
photoluminescence and electrochemical impedance of COFs to
gain insight into them. As shown in Fig. 4d, three isomorphic
51
48
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 7 of 11
Journal of Materials Chemistry A
Please do not adjust margins
Journal Name
ARTICLE
COFs gave fast photocurrent responses under visible-light
irradiation, which offered distinct evidence on the
both electron-donating and electron-withdrawing substituents
View Article Online
and proceed smoothly with yields rangiDnOgI:f1r0o.m103m9/Do0dTeAr0a2t1e64tDo
good. For instance, N-methylindole with a methyl at C-2 or C-7
position, yield of 58% and 61% for the corresponding product
2b and 2c were obtained, respectively (Table 2, entries 2 and 3).
And the results are similar to that of the unsubstituted N-
methylindole, indicating that the increased steric hindrance of
substrates did not significantly affect the reaction. For the
electron-withdrawing group (-Br, -Cl) at the C-5 or C-6 position
of N-methylindole, the reactions projected the moderated
yields of 40~55% (Table 2, entries 5 and 6). However, a longer
reaction time is needed compared with the electron-donating
substituted substrate (Table 2, entry 4). To our delight, the
photocatalytic formylation of 1H-indole also achieved the
desired product 2g in a 35% yield.
a
photogenerated carries transfer within COFs. We can also find
that COF-JLU24 displayed the highest transient photocurrent
responses in three isomorphic COFs, suggesting the more
efficient separation of the photoinduced electron-hole pairs. In
addition, the photoluminescent intensity of COF-JLU24
exhibited more poorer than that of two other COFs (Fig. 4e),
implying that the recombination of the photogenerated carrier
is more difficult for COF-JLU24. Surprisingly, we found that COF-
JLU24 and COF-JLU23 always possess similar performance on
optical and electrical properties, which can be attributed to the
formation of the similar electron donor-acceptor structure in
both COF-JLUs. For a deeper insight, EIS of COF-JLU24 and COF-
JLU25 was studied to demonstrate the transfer of their
photoinduced charge carriers. The arc radius of COF-JLU24 on
the EIS Nyquist plot presented to be smaller than that of COF-
JLU25 (Fig. 4f), indicating the COF-JLU24 has lesser interface
layer and charge transfer resistances. In the context, the whole
experiments demonstrated that the photocatalytic
performance of isomorphic COFs for C-3 formylation are
consistent with their photo/electrochemical properties.
Table 2. Photocatalytic aerobic C-3 formylation of indole derivatives by COF-
JLU24a
R1
R1
COF-JLU24/KI
N
N
R3
R2
R3
TMEDA
R2
+
CH3CN/H2O
light, RT
O
1
2
Entry
Substrate
Product
Time (h) Yield (%)b
N
N
36
62
1
O
2a
N
N
36
36
36
58
61
55
2
3
O
2b
N
N
O
2c
N
N
4
5
6
7
MeO
MeO
O
2d
2e
2f
N
N
72
72
36
40
45
35
Br
Cl
Br
Cl
O
N
N
O
H
N
H
N
O
2g
aReaction conditions: photocatalyst COF-JLU24 (5.0 mg), TMEDA (61 μL, 0.4
mmol), substrate (0.2 mmol), KI (132.8 mg, 0.8 mmol), CH3CN (1.5 mL), H2O
(0.3mL), O2 balloon (~0.1 MPa), 30 W blue LED lamp with 460 nm, 25 oC.
bIsolated yield.
Fig. 5 Proposed mechanism for photocatalytic C-3 formylation (a) and
thiocyanation (b) of indoles by COF-JLU24.
In order to research the general feasibility of COF-JLU24 as a
heterogeneous photocatalyst, then we extended the C-3
formylation reaction with a series of indole derivatives. As
expected, this photocatalytic formylation reaction tolerated
Recently, the synthesis of organosulfur compounds have
attracted huge attention due to their widely biological and
pharmaceutical activity. The introduction of sulfur fragments
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry A
Page 8 of 11
ARTICLE
Journal Name
into carbon skeletons by thiocyanation is a convenient strategy. COF-JLU25 were next performed. Stern-Volmer analysis clearly
View Article Online
DOI: 10.1039/D0TA02164D
To further evaluate the photocatalytic performance of screened showed that the emission intensity of COF-JLU25* was
COF-JLU24, the C-3 thiocyanation reaction of indole derivatives obviously reduced in the presence of NH4SCN, while there is no
was still investigated. Utilizing 1H-indole 1g as a model similar effect for indole (Fig. S4†). Based on the previous
substrate, the conditions of photocatalytic C-3 thiocyanation literatures48,49 and above results, a plausible process is
were firstly optimized. Selecting 2 equiv of ammonium proposed (Fig. 5b). Under light irradiation, COF-JLU24 is
thiocyanate (NH4SCN) as the SCN agent and molecular oxygen converted to its excited state COF-JLU24*. And a single electron
as a green oxygen source, the reaction was performed with a transfer (SET) from thiocyanate anion SCN− to COF-JLU24*
moderate yield of 53% under illumination with 30 W blue LED forms a radical •SCN and a radical anion COF-JLU24•−. Then the
lamp at 25 oC in CH3CN (Table S1, entry 1). Inspired by this result, generated COF-JLU24•− is subsequently reacted with molecular
•−
we also screened other organic solvent such as THF, CH3OH and oxygen to generate the superoxide anion O2
and
DMF. To our delight, the desired product 3g with an excellent simultaneously to form the ground state COF-JLU24. Meanwhile,
yield of 95% was obtained in THF after 7 h (Table S1, entry 2), the produced radical •SCN attacked substrate indole to
while in CH3OH and DMF, the yields were relatively low (34% generate intermediate F. Subsequently, intermediate F was
and 24%, Table S1, entries 3 and 4). When NH4SCN was replaced oxidized to give cation intermediate H, which afforded the final
with potassium thiocyanate (KSCN) or sodium sulfocyanate 3-thiocyanoindole compound 3g via deprotonation.
Table 3. Photocatalytic C-3 thiocyanation of indoles by COF-JLU24a
(NaSCN), 1H-indole was unsatisfactory converted to the target
product (58% and 50%, Table S1, entries 5 and 6). Increasing the
amount of NH4SCN afforded 3g with similar yield (97%, Table
S1, entry 7). On the contrary, decreasing the amount of NH4SCN
leaded to the sharp drop for yield (57%, Table S1, entry 8).
Beyond that, under the illumination of white or green LED lights,
the yield is relatively poor (Table S1, entries 9 and 10). In
addition, the photocatalytic thiocyanation in the control
experiments only obtained 0, 33 and 20% yields, in the absence
of light, photocatalyst COF-JLU24 or molecular oxygen (Table S1,
entries 11−13), which proves all of the components are
essential. The metal-free g-C3N4, a state of art photocatalyst,
was also researched for C-3 thiocyanation of 1g, a relatively
inferior yield of 79% was obtained (Table S1, entry 14), proving
the structural rationality of screened COF-JLU24. When COF-
JLU23 as a photocatalyst this reaction achieved the similar yield
compared with COF-JLU24 (93%, Table S1, entry 15). However,
a relatively low yield of 86% was obtained by COF-JLU25 under
optimized conditions (Table S1, entry 16). In the context, the
trend in photocatalytic results of three isomorphic COFs is same
for both formylation and thiocyanation processes.
In order to prove the generality of the photocatalytic system,
a lot of C-3 thiocyanation between NH4SCN and indole
derivatives were performed. For indoles with either an
electron-donating or electron-withdrawing group, the
corresponding C-3 thiocyanation products were obtained in
excellent yield, as shown in Table 3. In addition, the
photocatalytic activity of COF-JLU24 is more superior than that
of the previously reported CMP-CSU649 and Rose Bengal48
systems, which needs more photocatalyst and longer reaction
time. To gain more insight into the reaction mechanism, a series
of control experiments were conducted. For the optimized
condition, the addition of a radical scavenger, 2,6-di-tert-butyl-
aReaction conditions: photocatalyst COF-JLU24 (3.0 mg), NH4SCN (45.7 mg,
0.6 mmol), substrate (0.3 mmol), THF (2.0 mL), O2 balloon (~0.1 MPa), 30 W
blue LED lamp with 460 nm, 25 oC.
Besides the excellent activity and broad substrate
applicability, the recycling performance of catalyst is the most
critical virtue of heterogeneous reactions from the perspective
of practical application. Thus we further explored the reusability
and stability of screened COF-JLU24 in the photocatalytic C-3
thiocyanation of 1H-indole under visible-light illumination. The
photocatalyst COF-JLU24 was separated from the reaction
system through a centrifugation. The obtained COF-JLU24 was
4-methylphenol, had
a clear negative impact on the
photocatalytic C-3 thiocyanation, and the yield for disired
product 3g reduced to 59% (Table S1, entry 17). By introducing
N,N-diisopropylethylamine (DIPEA) as
a hole scavenger,
similarly, the yield of 3g declined to 40% (Table S1, entry 18). On
the other hand, a poor yield of 26% and 35% was achieved in
the present of BQ and NaN3, respectively (Table S1, entries 19
and 20). In addition, the fluorescence quenching experiments of
8 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 9 of 11
Journal of Materials Chemistry A
Please do not adjust margins
Journal Name
ARTICLE
cleaned by washing with THF and H2O to remove the residual delight, the COF-JLU24 after recycling still maintained the initial
View Article Online
DOI: 10.1039/D0TA02164D
substrate and product, dried by heating in vacuum, and then framework connectivity (Fig. 6b), high crystallinity (Fig. 6c), and
reused in the next photocatalytic process. It was found that the aggregated morphology (Fig. 6d and 6e), as well as large surface
COF-JLU24 can be recycled for 5 repeating cycle without area (Fig. 6f), which is mainly attributed to its excellent stability.
significant loss of photocatalytic performance (Fig. 6a). To out Finally,
Fig. 6 (a) Reusability of COF-JLU24 in the C-3 thiocyanation of 1H-indole. (b) FT-IR spectra of photocatalyst COF-JLU24 before and after five cycles. (c) Powder
XRD spectra of photocatalyst COF-JLU24 before and after five cycles. FE-SEM images of photocatalyst COF-JLU24 before (d) and after (e) five cycles. (f) N2
sorption isotherm of COF-JLU24 after five cycles at 77k (SABET = 450 m2 g−1).
we still studied the possibility the large scale synthesis utilizing isomorphic COFs, even better than that of state-of-the-art
1g as a substrate. A high yield of 94% was afforded in the scaled- metal-free photocatalyst g-C3N4. Moreover, COF-JLU24 as a
up preparation reaction. The excellent performances of metal-free photocatalyst still displayed extensive substrate
screened COF-JLU24 including high activity, broad substrate adaptability and excellent recyclability. The current work not
applicability and fine reusability make it promising scaffold for only present a robust rule of thumb for fast access to COF-based
commercial application.
photocatalysts, but still expands the applied frontier of COFs for
sustainable development.
Conflicts of interest
Conclusions
In summary, we have dedicated the guiding principle for fast
access to COF-based photocatalysts, that is to screen them from
a series of isomorphic COFs. We synthesized three new
isomorphic pyrene-based 2D-COFs with different linkers
through the imine condensation reaction under solvothermal
conditions. These isomorphic COFs possess similar crystallinity
and same topology. On the other hand, the photoelectric
properties, bandgaps, energy levels, and transient photocurrent
response of obtained isoform COF-JLUs were conveniently
adjusted. The incorporation of 4,4'-([1,2,5]Thiadiazolo[3,4-
c]pyridine-4,7-diyl)-based electron-deficient building block into
COF can induce strong visible-light harvesting and
photogenerated carrier transfer, which facilitates the electron
and energy transfer processes to generate the active oxygen
species. The screened COF-JLU24 has the best photocatalytic
activity for C-3 functionalization reaction of indoles in three
There are no conflicts to declare
Acknowledgements
This work was supported by the Natural Science Foundation of
China (21774040, 21805110 and 61435005).
Notes and references
1
A. P. Cote, A. I. Benin, N. W. Ockwig, M. O`Keefe, A. J. Matzger,
O. M. Yaghi, Science 2005, 310, 1166−1170.
X. Feng, X. Ding, D. Jiang, Chem. Soc. Rev. 2012, 41,
6010−6022.
2
3
4
S. Ding, W. Wang, Chem. Soc. Rev. 2013, 42, 548−568.
P. J. Waller, F. Gandara, O. M. Yaghi, Acc. Chem. Res. 2015, 48,
3053−3063.
5
N. Huang, P. Wang, D. Jiang, Nat. Rev. Mater. 2016, 1, 16068.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 9
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry A
Page 10 of 11
ARTICLE
Journal Name
6
J. L. Segura, M. J. Mancheno, F. Zamora, Chem. Soc. Rev. 2016, 39 Z. Li, Y. Zhi, P. Shao, H. Xia, G. Li, X. Feng, X. Chen, Z. Shi, X. Liu,
View Article Online
45, 5635−5671.
Appl. Catal. B: Environ. 2019, 245, 334−342.
DOI: 10.1039/D0TA02164D
7
8
Y. Jin, Y. Hu, W. Zhang, Nat. Rev. Chem. 2017, 1, 0056.
S. Kandambeth, K. Dey, R. Banerjee, J. Am. Chem. Soc. 2019,
141, 1807−1822.
40 P. Wei, M. Qi, Z. Wang, S. Ding, W. Yu, Q. Liu, L. Wang, H.
Wang, W. An, W. Wang, J. Am. Chem. Soc. 2018, 140,
4623−4631.
41 R. Chen, J. L. Shi, Y. Ma, G. Lin, X. Lang, C. Wang, Angew. Chem.
Int. Ed. 2019, 58, 6430–6434.
42 S. Liu, W. Pan, S. Wu, X. Bu, S. Xin, J. Yu, H. Xu, X. Yang, Green.
Chem. 2019, 21, 2905–2910.
43 A. J. K. Karamyan, M. T. Hamann, Chem. Rev. 2010, 110, 4489–
4497.
44 L. Zhang, C. Peng, D. Zhao, Y. Wang, H. J. Fu, Q. Shen, J. X. Li,
Chem. Commun. 2012, 48, 5928−5930.
45 J. Chen, B. Liu, D. Liu, S. Liu, J. Cheng, Adv. Synth. Catal. 2012,
354, 2438−2442.
46 F. Stanek, R. Pawlowski, J. Mlynarski, M. Stodulski, Eur. J. Org.
Chem. 2018, 47, 6624−6628.
9
Y. Zeng, R. Zou, Y. Zhao, Adv. Mater. 2016, 28, 2855−2873.
10 Z. Li, X. Feng, Y. Zou, Y. Zhang, H. Xia, X. Liu, Y. Mu, Chem.
Commun. 2014, 50, 13825−13828.
11 X. Guan, H. Li, Y. Ma, M. Xue, Q. Fang, Y. Yan, V. Valtchev, S.
Qiu, Nat. Chem. 2019, 11, 587−594.
12 S. Dalapati, S. Jin, J. Gao, Y. Xu, A. Nagai, D. Jiang, J. Am. Chem.
Soc. 2013, 135, 17310−17313.
13 Z. Li, Y. Zhang, H. Xia, Y. Mu, X. Liu, Chem. Commun. 2016, 52,
6613−6616.
14 Y. Zhang, X. Shen, X. Feng, H. Xia, Y. Mu, X. Liu, Chem.
Commun. 2016, 52, 11088−11091.
15 S. Chandra, T. Kundu, S. Kandambeth, R. BabaRao, Y. Marathe,
S. Kunjir and R. Banerjee, J. Am. Chem. Soc. 2014, 136, 47 W. Fan, Q. Yang, F. Xu, P. Li, J. Org. Chem. 2014, 79,
6570−6573.
10588−10592.
48 X. Li, X. Gu, Y. Li, P. Li, ACS Catal. 2014, 4, 1897−1900.
16 H. Xu, S. Tao and D. Jiang, Nat. Mater. 2016, 15, 722−726.
17 Z. Xie, B. Wang, Z. Yang, X. Yang, X. Yu, G. Xing, Y. Zhang, L. 49 W. Zhang, J. Tang, W. Yu, Q. Huang, Y. Fu, G. Kuang, C. Pan, G.
Chen, Angew. Chem. Int. Ed. 2019, 58, 15742–15746.
18 C. R. DeBlase, K. E. Siberstein, T. T. Truong, H. D. Abruna, W. 50 D. Bessinger, L. Ascherl, F. Auras, T. Bein, J. Am. Chem. Soc.
R. Dichtel, J. Am. Chem. Soc. 2013, 135, 16821−16824. 2017, 139, 12035−12042.
19 S. Wang, Q. Wang, P. Shao, Y. Han, X. Gao, L. Ma, S. Yuan, X. 51 Z. Li, N. Huang, K. Lee, Y. Feng, S. Tao, Q. Jiang, Y. Nagao, S.
Yu, ACS Catal. 2018, 8, 8084−8091.
Ma, J. Zhou, X. Feng, B. Wang, J. Am. Chem. Soc. 2017, 139,
4258−4261.
20 S. Ding, J. Gao, Q. Wang, Y. Zhang, W. Song, C. Su, W. Wang, J.
Am. Chem. Soc. 2011, 133, 19816−19822.
21 X. Wang, X. Han, J. Zhang, X. Wu, Y. Liu, Y. Cui, J. Am. Chem.
Soc. 2016, 138, 12332−12335.
22 H. Xu, J. Gao, D. Jiang, Nat. Chem. 2015, 7, 905−912.
Irle, D. Jiang, J. Am. Chem. Soc. 2018, 140, 12374−12377.
52 Y. Zhi, K. Li, H. Xia, M. Xue, Y. Mu, X. Liu, J. Mater. Chem. A
2017, 5, 8697−8704.
53 Y. Zhi, S. Ma, H. Xia, Y. Zhang, Z. Shi, Y. Mu, X. Liu, Appl. Catal.
B: Environ. 2019, 244, 36–44.
54 Y. Zhi, Z. Yao, W. Jiang, H. Xia, Z. Shi, Y. Mu, X. Liu, ACS Appl.
Mater. Inter. 2019, 11, 37578−37585.
23 Y. Zhi, P. Shao, X. Feng, H. Xia, Y. Zhang, Z. Shi, Y. Mu, X. Liu, J. 55 W. Jiang, Q. Ruan, J. Xie, X. Chen, Y. Zhu, J. Tang, Appl. Catal.
Mater. Chem. A 2018, 6, 374−382.
B: Environ. 2018, 236, 428–435.
24 D. D. Medina, T. Sick, T. Bein, Adv. Energy Mater. 2017, 7, 56 J. M. Narayanam, C. R. Stephenson, Chem. Soc. Rev. 2011, 40,
1700387.
102−113.
25 V. S. Vyas, F. Haase, L. Stegbauer, G. Savasci, F. Podjaski, C.
Ochesenfeld, B. V. Lotsch, Nat. Commun. 2015, 6, 8508.
26 P. Pachfule, A. Acharjya, J. Roeser, T. Langenhahn, M.
Schwarze, R. Schomäcker, A. Thomas, J. Schmidt, J. Am. Chem.
Soc. 2018, 140, 1423−1427.
27 M. Liu, Q. Huang, S. Wang, Z. Li, B. Li, S. Jin, B. Tan, Angew.
Chem. Int. Ed. 2018, 57, 11968–11972.
28 S. Bi, C. Yang, W. Zhang, J. Xu, L. Liu, D. Wu, X. Wang, Y. Han,
Q. Liang, F. Zhang, Nat. Commun. 2019, 10, 2467.
29 X. Wang, L. Chen, S. Y. Chong, M. A. Little, Y. Wu, W. H. Zhu,
R. Clowes, Y. Yan, M. A. Zwijnenburg, R. S. Sprick, A. I. Cooper,
Nat. Chem. 2018, 10, 1180−1189.
30 J. Chen, X. P. Tao, C. Z. Li, Y. H. Ma, L. Tao, D. Y. Zheng, J. F.
Zhu, H. Li, R. G. Li, Q. H. Yang, Appl. Catal. B: Environ. 2020,
262, 118271.
31 E. Jin, Z. Lan, Q. Jiang, K. Geng, G. Li, X. Wang, D. Jiang, Chem
2019, 5, 1632-1647.
32 S. Lin, C. S. Diercks, Y. B. Zhang, N. Kornienko, E. M. Nichols, Y.
Zhao, A. R. Paris, D. Kim, P. Yang, O. M. Yaghi, C. J. Chang,
Science 2015, 349, 1208−1213.
33 Y. Fu, X. Zhu, L. Huang, X. Zhang, F. Zhang, W. Zhu, Appl. Catal.
B: Environ. 2018, 239, 46–51.
34 M. Lu, Q. Li, J. Liu, F. M. Zhang, L. Zhang, J. L. Wang, Z. H. Kang,
Y. Q. Lan, Appl. Catal. B: Environ. 2019, 254, 624–633.
35 S. He, B. Yin, H. Niu, Y. Cai, Appl. Catal. B: Environ. 2018, 239,
147–153.
36 W. Chen, Z. Yang, Z. Xie, Y. Li, X. Yu, F. Lu, L. Chen, J. Mater.
Chem. A 2019, 7, 998−1004.
37 L. Stegbauer, K. Schwinghammer, B. V. Lotsch, Chem. Sci.
2014, 5, 2789–2793.
38 Y. Zhi, Z. Li, X. Feng, H. Xia, Y. Zhang, Z. Shi, Y. Mu, X. Liu, J.
Mater. Chem. A 2017, 5, 22933–22938.
10 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 11 of 11
Journal of Materials Chemistry A
View Article Online
An excellent framework photocatalyst was screened from a series of isoDmOoI: r10p.h10i3c9/D0TA02164D
COFs. The photocatalytic properties of C-3 functionalization of indoles by the
COF-based photocatalyst was first reported.