2D sp2 Carbon-Conjugated Porphyrin Covalent Organic Framework for Cooperative Photocatalysis with TEMPO

Article abstract of DOI:10.1002/anie.202000723

2D covalent organic frameworks (COFs) are receiving ongoing attention in semiconductor photocatalysis. Herein, we present a photocatalytic selective chemical transformation by combining sp² carbon-conjugated porphyrin-based covalent organic framework (Por-sp²c-COF) photocatalysis with TEMPO catalysis illuminated by 623 nm red light-emitting diodes (LEDs). Highly selective conversion of amines into imines was swiftly afforded in minutes. Specifically, the π-conjugation of porphyrin linker leads to extensive absorption of red light; the sp² ?C=C? double bonds linkage ensures the stability of Por-sp²c-COF under high concentrations of amine. Most importantly, we found that crystalline framework of Por-sp²c-COF is pivotal for cooperative photocatalysis with (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO). This work foreshadows that the outstanding hallmarks of COFs, particularly crystallinity, could be exploited to address energy and environmental challenges by cooperative photocatalysis.

Full text of DOI:10.1002/anie.202000723

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Accepted Article
Title: 2D sp2 Carbon–conjugated Porphyrin Covalent Organic
Framework for Cooperative Photocatalysis with TEMPO
Authors: Ji-Long Shi, Rufan Chen, Huimin Hao, Cheng Wang, and
Xianjun Lang
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.202000723
Angew. Chem. 10.1002/ange.202000723
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10.1002/anie.202000723
Angewandte Chemie International Edition
RESEARCH ARTICLE
2D sp2 Carbon–conjugated Porphyrin Covalent Organic
Framework for Cooperative Photocatalysis with TEMPO†
Ji-Long Shi, Dr. Rufan Chen, Huimin Hao, Prof. Dr. Cheng Wang, and Prof. Dr. Xianjun Lang*
biological tissues more deeply than light of shorter wavelengths,[8]
Abstract: 2D (two-dimensional) covalent organic frameworks (COFs)
are receiving ongoing attention in semiconductor photocatalysis.
Herein, we present a photocatalytic selective chemical transformation
by combining sp2 carbon-conjugated porphyrin-based covalent
organic framework (Por-sp2c-COF) photocatalysis with TEMPO
catalysis illuminated by 623 nm red light-emitting diodes (LEDs).
Highly selective conversion of amines into imines were swiftly
afforded in minutes. Specifically, the π-conjugation of porphyrin linker
leads to extensive absorption of red light; the sp2 -C=C- double bonds
linkage ensures the stability of Por-sp2c-COF under high
concentration of amine. More importantly, we found that crystalline
framework of Por-sp2c-COF is pivotal for cooperative photocatalysis
with TEMPO. This work foreshadows that the outstanding hallmarks
of COFs, particularly crystallinity, could be exploited to address
energy and environmental challenges by cooperative photocatalysis.
which can extend photocatalysis into biomedical applications.
TEMPO, a small molecule of stable radical, has been used
as a reagent and/or catalyst for a wide range of chemical
transformations.[9] Organic polymers can be successfully used as
supports for TEMPO.[10] However, the cooperative effect between
TEMPO and amorphous polymer was seldom existed.
Immobilization of TEMPO on the COFs turns the original
crystalline framework into a redox active skeleton which in turn
could become feasible strategy to apply TEMPO-COFs for energy
storage, and lithium-ion batteries,[11] highlighting the pivotal role
of crystalline framework for improvement of redox properties of
COFs with TEMPO. TEMPO was widely used a quenching
reagent for radical chain reactions. But it could be transformed
into cocatalysts for photocatalytic chemical transformations.[12] In
them, a ‘hard’ platform of metal oxide semiconductor and a ‘soft’
organic dye were usually needed which scenario is quite like that
of COFs. Thus, we hypothesized that combining TEMPO
catalysis with COF photocatalysis to accomplish red light-induced
selective chemical transformations may be extremely interesting.
To this end, the crystalline framework of Por-sp2c-COF might
provide a unique platform for red light harvesting and cooperative
photocatalysis with TEMPO.
Introduction
COFs, which comprise topologically repeating units based on
covalent bonds, are becoming increasingly important for
photovoltaic and optoelectronic applications due to advantages
such as aligned pore structures and tunable functionality.[1] In
particular, COFs with linkages that facilitate
π electron
Visible-light-induced selective aerobic oxidation of amines
into imines has become one of the most representative chemical
transformations in organic semiconductor photocatalysis since a
seminal work.[13] Later, conjugated microporous polymers (CMPs)
were also explored for this reaction.[14] Most photocatalysts – i.e.,
wide-band gap semiconductor systems such as TiO2, CdS,
ZnIn2S4, ZrO2, BiVO4, and Nb2O5 – remain limited in terms of
visible light sensitivity.[15] While organic dyes such as alizarin red
S and 5(6)-carboxyfluorescein can be used as photosensitizers to
extend the visible light response of these semiconductors, they
do not absorb light substantially beyond the green light region.[16]
Herein, we present a novel, facile and efficient strategy that
combines visible light photocatalysis of Por-sp2c-COFs with
TEMPO catalysis for efficiently selective oxidation of amines into
valuable imines illuminated by 623 nm red LEDs. To the best of
our knowledge, this is the first report of red light-induced selective
chemical transformation by semiconductor photocatalysis.
Besides, the title protocol is suitable for a wider range of
substrates with shorter reaction time and higher turnover numbers.
delocalization between the linked units possess favorable
electronic properties, but tended to be plagued by difficulty in
synthesis and poor stability.[2] Therefore, sp2 carbon-conjugated
COFs with optimal π-electron delocalization along both the x and
y directions received much attention [3]. The formation of -C=C-
linkage with desired conjugation and refined crystallinity for COFs
from reversible coupling reactions is hugely challenging. There
were two elegant examples applied in semiconductor
photocatalysis.[4] However, these two COFs were based on either
pyrene or triazine, which has limited absorption in visible region
even though π-conjugation could extend it to some extent.
Previously, we reported a 2D porphyrin-based COF (Por-sp2c-
COF) which exhibit excellent stability during photocatalytic
chemical transformations under white light illumination.[5]
However, the extensive absorption of Por-sp2c-COF in visible light
was unexploited to date. The utility of the Por-sp2c-COF can be
further extended to red light illumination due to sp2 carbon–
conjugation. From the perspective of sustainability, extending the
light absorption of photocatalysts from ultraviolet to visible or even
near-infrared regions can achieve greater sunlight utility.[6]
Moreover, red light has low energy of excitation. It is difficult to
activate other sensitive bonds.[7] Besides, red light can penetrate
[*] J. L. Shi,[a] Dr. R. F. Chen,[a] H. M. Hao, [a] Prof. Dr. C. Wang,[a] and
Prof. Dr. X. J. Lang[a]
[a] Sauvage Center for Molecular Sciences, College of Chemistry and
Molecular Sciences, Wuhan University, Wuhan 430072 (China).
E-mail: xianjunlang@whu.edu.cn.
† TEMPO, (2,2,6,6-tetramethylpiperidin-1-yl)oxyl.
Figure 1. The schematic representations of Por-sp2c-COF and
Por-COF
Supporting information for this article is given via a link at the end of
the document.
1
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10.1002/anie.202000723
Angewandte Chemie International Edition
RESEARCH ARTICLE
-
The Por-sp2c-COF was synthesized by Knoevenagel
spatial separation of ecb -hvb+ pairs in the ordered frameworks will
be beneficial to the oxidation of benzylamine. Meanwhile, the CV
experiments revealed that the addition of TEMPO decreased the
oxidation potential of Por-sp2c-COF, thus enhancing the reduction
ability of Por-sp2c-COF, which is also in favor of oxidation of
benzylamine.
condensation
benzaldehyde)porphyrin
reaction
of
5,10,15,20-tetrakis(4-
with 1,4-
(p-Por-CHO)
phenylenediacetonitrile (PDAN) in optimized ratio.[5] As a control,
Por-COF, which is based on -C=N- linkage, was also prepared
according to reported procedure (See supporting information).
The schematic representations of Por-sp2c-COF and Por-COF
are listed in Figure 1. Powder X-ray diffraction (PXRD)
measurement shows three different diffraction peaks at 3.62°,
Having established that Por-sp2c-COF can work with
TEMPO from a perspective both in pore size and in redox
potentials, we performed the photocatalytic oxidation of four
different representative amines: electron-deficient benzylamine
1a, benzylamine 1b, electron-rich benzylamine 1c, and
dibenzylamine 1d for 12 min illuminated by red LEDs in
acetonitrile (CH3CN). Figure 3 shows the photocatalytic activity of
5,10,15,20-tetraphenylporphyrin (Por), Por-sp2c-COF and Por-
sp2c-COF plus 2 mol% TEMPO cocatalyst. There were only slight
conversions of these four amines with Por photocatalyst due to
limited red light absorption of Por. The sp2 carbon–conjugation of
Por into Por-sp2c-COF led to significant better yields of imines due
to extension of visible light absorption. More importantly, the yield
of imines could be more than twice to that of Por-sp2c-COF with
7.12°, and 7.52°, which could be assigned to the (100), (220), and
(310) facets, respectively (Figure S1 and S3). Fourier transform
infrared (FTIR) spectrum revealed the presence of the stretching
vibration peak of the cyano group at 2210 cm-1 for both PDAN
monomer and Por-sp2c-COF (Figure S4). A peak at 1697 cm-1
attributed to the C=O stretching vibration was observed in
monomer p-Por-CHO and it was broadly weakened in Por-sp2c-
COF, which illustrated that a high degree of polymerization
existed in the frameworks. The newly formed peak at 3018 cm-1
in Por-sp2c-COF was attributable to the CH=C stretch, which
clearly manifested the C=C linkages in the frameworks. The
morphology of Por-sp2c-COF, as inspected by scanning electron
microscopy (SEM) and transmission electron microscopy (TEM),
comprises uniform particles with a honeycomb-like internal
structure, where the bright spots correspond to the pores (Figure
S5 and S6). N2 sorption isotherm curves revealed a high
Brunauer-Emmett-Teller (BET) surface area of 714 m2 g–1 (Figure
S7a), and a pore size of 1.91 nm (Figure S7b). The optoelectronic
properties of Por-sp2c-COF was investigated by diffuse
reflectance UV-visible spectra, revealing a broad absorption band
in the visible light region that spans the spectrum distribution of
different LEDs including violet, blue, green, yellow and red ones
the introduction of
2 mol% of TEMPO, suggesting the
establishment of cooperative photocatalysis with unprecedented
reaction efficiency. Excellent conversions and selectivities could
be completed in minutes illuminated by 623 nm red LEDs. Our
cooperative photocatalytic system comprising 0.005 mmol Por-
sp2c-COF and 2 mol% TEMPO produced nearly twice the yields
(73%-84%) of the corresponding imines 2a-c compared to that of
Por-sp2c-COF only (32-43%) (Figure 2). The cooperative Por-
sp2c-COF photocatalysis and TEMPO catalysis is also capable of
achieving high yields of 2b in 7 minutes illuminated by different
LEDs (Figure S8b). This indicates good solar utility around all the
visible light region, which is special realm reserved for π-
conjugated COFs rather than molecular dyes or inorganic
semiconductors.
(Figure S8a).
Figure 3. Control experiments for selective oxidation of amines
into imines by cooperative Por-sp2c-COF photocatalysis with
TEMPO catalysis.
Reaction conditions: (a) primary amine (0.5 mmol), Por-sp2c-COF (0.005
mmol), TEMPO (0.01 mmol), red LEDs (623 ± 8 nm, 3 W × 4), air (1 atm),
CH3CN (1 mL), 12 min. (b) secondary amines (0.25 mmol), Por-sp2c-COF
(0.005 mmol), TEMPO (0.005 mmol), red LED illumination (623 ± 8 nm, 3
W × 4), air (1 atm), CH3CN (1 mL), 15 min. Yield of imine was determined
by GC-FID using chlorobenzene as the internal standard.
Figure 2. Cyclic voltammetry tests for different conditions in
CH3CN.
The pore size for Por-sp2c-COF is 1.91 nm and the molecular
dimension of TEMPO is 0.9 nm × 0.5 nm × 0.5 nm [17]. Therefore,
TEMPO can easily penetrate into the pore of Por-sp2c-COF, a
necessary condition for cooperative interaction. Next,
electrochemical characterization was used to study the possibility
of cooperative photocatalysis between Por-sp2c-COF and
TEMPO through cyclic voltammetry (CV) measurement (Figure 2).
The curve of Por-sp2c-COF recorded one oxidation peak,
manifesting the ability to oxidize benzylamine. The addition of
TEMPO, results in the obvious improvement of the intensity of
oxidation peak current, reasoning that the higher efficiency of the
When
visible-light-induced
selective
oxidation
of
benzylamine 1b was conducted by organic dye photocatalysts
such as Por, eosin Y, erythrosin Y and rose Bengal, negligible
yields of 2b were obtained. The addition of TEMPO did not
improve the conversion of 1b. Even though the excitation
wavelength of these dyes is within the range of red LED, its lack
2
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10.1002/anie.202000723
Angewandte Chemie International Edition
RESEARCH ARTICLE
of stability and weak electron delocalization detracts from the
cooperative effect with TEMPO (Table S1, entries 1-10).
conversion, suggesting the Por-COF imine linkage was destroyed
by exchange with benzylamine.
Without illumination, the photocatalytic reaction did not occur
(Figure S12). Besides, the light intensity was considered and the
results were listed in Table S2 in which the conversions of
benzylamine is light dependent. Therefore, the dark reaction and
light intensity dependent results affirm an authentic photocatalytic
reaction. The stability and reusability of Por-sp2c-COF was
demonstrated by the high yields of 2b achieved from
photocatalytic oxidation of 1b in all 3 consecutive runs (Figure
S13). After that, PXRD pattern of Por-sp2c-COF showed its
structural integrity and stability (Figure S14).
Table 1: Visible-light-induced selective oxidation of primary
amines into imines with air by cooperative Por-sp2c-COF
photocatalysis with TEMPO catalysis [a]
.
Por-sp2c-COF
N
NH2
R
R
2
R
Red LEDs, air, RT
It is notable that all substrates exhibit high conversion to
produce imines. The reaction time for complete conversion within
30 min. The conversion of benzylamine 1b reaches 94%
conversion and 99% selectivity for imine 2b. Moreover, we
isolated pure product of imine 2b with 91% yield (see S9 for
details), which is in a good agreement with GC-FID result. The
reaction of benzylamines substituted by electron-donating groups
preserved slightly higher conversions as compared to
benzylamine (Table 1, entries 2-4 vs. entry 1). While the
substitution of benzylamines by electron-withdrawing groups
needed slightly longer time for comparable conversions (Table 1,
entries 5-7 vs. entry 1). 3-Methoxybenzylamine was relatively
similar to conversion compared with 2-methoxybenzylamine
(Table 1, entries 8-9), which reveals the presence of small steric
effects. Heterocyclic amines can also be oxidized to
corresponding imines (Table 1, entries 10-11). And it was clearly
that selectivity of imine for conversion of pyridine methylamine
was lower than others.
[a] Reaction conditions: primary amine (0.5 mmol), Por-sp2c-COF (0.005
mmol), TEMPO (0.01 mmol), red LEDs (623 ± 8 nm, 3 W × 4), air (1 atm),
CH3CN (1 mL). [b] Determined by GC-FID using chlorobenzene as the
internal standard, conversion of primary amine, and selectivity of imine.
To further confirm the oxidative ability of Por-sp2c-COF with
TEMPO cooperative photocatalysis system under red light
illumination at room temperature, different substituted secondary
amines were investigated (Table 2). Dibenzyl amine,
a
One can conclude that molecular photocatalysts are too
flexible to allow for cooperative effect to mature. Thus, the
crystallinity of Por-sp2c-COF might accounts for cooperative
photocatalysis. To this end, we controlled the reaction conditions
to synthesize amorphous counterpart (Por-sp2c-CMP, see
supporting information for details) of Por-sp2c-COF with the same
starting materials. There was also no promoting effect of TEMPO
representative of the secondary amines, is transformed to the
corresponding imine in 97% conversion (Table 2, entry 1). Most
of photocatalytic oxidation dibenzyl amines reactions with more
than 90% conversion, whether the substituent is electron-rich
(Table 2, entries 2-4) or electron-deficient (Table 2, entries 5-7)
on either phenyl ring. In the oxidation of N-tert-butyl benzylamine,
the product N-tert-butyl benzalimine is obtained in 15 min (Table
2, entry 8). These photocatalytic selective oxidation reactions are
weakly affected by substituent groups on the N-tert-butyl
substituted benzylamine. N-tert-butyl benzylamine with an
electron-donating group such as –CH3 and –OCH3 or an electron
withdrawing group such as –F and –Cl on the phenyl ring were
found to react at similar rate (Table 2, entries 9-12). The
differences of conversion were within 5% because of the wide
adaptability of the reaction system. Since N-tert-butyl
benzylamine with methyl (CH3) substituted at different position of
phenyl ring displayed reaction rate in the order of para- < ortho-
substituted, indicating the existence of the minor steric hindrance
(Table 2, entry 10). N-isopropyl benzylamine could be
successfully oxidized into corresponding imine with slightly low
conversion and selectivity result of the Cα–H bond is away from
the benzene ring (Table 2, entry 14).
for Por-sp2c-CMP, further suggesting the crystalline framework is
pivotal to cooperative photocatalysis with TEMPO.
For crystalline frameworks like COFs, stability under reaction
condition of high concentration of benzylamine which is a much
strong nucleophile than anilines, should be seriously considered.
Previously, imine-linked porphyrin COF were observed to be
efficient for size-selective photocatalysis.[18] However, imine-
linked COFs are plagued by the dynamic nature of imine bonds,
formed from benzaldehyde moiety and aniline, under high
concentration of benzylamine (0.5 mol/L). Thus, we applied Por-
COF instead of Por-sp2c-COF as a photocatalyst. The use of Por-
COF provided no yields of imines (Table S1, entries 11-12),
further proving the advantage of sp2 C=C double bonds in this
specific transformation. A series of characterizations between
Por-sp2c-COF and Por-COF had been carried out
comprehensively (Figures S9-S11). One could conclude that Por-
sp2c-COF should in principle possess better activity than Por-
COF. However, for oxidation of benzylamine, Por-sp2c-COF had
remarkably good conversion and in contrast Por-COF had no
To evaluate the mechanism of the oxidation reactions,
kinetically relevant elementary steps in the reaction pathways
were measured (Figure S15a). Time-dependent experiment on
the oxidation of benzylamine was conducted to study the reaction
kinetic. Moreover, benzyl-α, α-d2-amine changing the benzylic H
3
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10.1002/anie.202000723
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RESEARCH ARTICLE
to D in benzylamine was used to study the reaction kinetic. The
obtained kinetic isotope effect (KIE) was 1.67 by kH/kD, indicating
the reaction belongs to primary KIE. We could surmise that the
cleavage of Cα–H played the core role in the photocatalytic
selective oxidation of benzylamine. This also indirectly illustrates
that 2,2,6,6-tetramethylpiperidin-1-ol (TEMPOH) was generated
by 2,2,6,6-tetramethylpiperidine-1-oxoammonium (TEMPO+)
seizured the hydrogen of the amines. We used equal amount of
TEMPOH to substitute TEMPO, affording same conversion of
benzylamine, circumstantially prove TEMPOH was involved in the
reaction pathway.
benzylamine (Figure S15b, C). It is well known that CD3CN is
advantageous to the lifetime of singlet oxygen (1O2). However,
when the CD3CN solvent was added to the reaction system for
photocatalytic oxidation of benzylamine instead of CH3CN, the
conversion of benzylamine did not increase (Figure S15b, E). The
p-BQ and CD3CN results displayed the central ROS in
photocatalytic oxidation of amine should be O2•−. The AgNO3 was
added into the reaction for the electron quencher. The result was
consistent with p-BQ condition, revealing the presence of electron
transfer in the photocatalytic selective oxidation of benzylamine
(Figure S15b, D).
Table 2: Visible-light-induced selective oxidation of secondary
amines into imines with air by cooperative Por-sp2c-COF
photocatalysis with TEMPO catalysis[a]
Figure 4. (a) EPR detection of O2•− generation over Por-sp2c-COF
and TEMPO trapped by DMPO. (b) EPR detection of the TEMPO
transformation process in photocatalytic oxidation of amine.
Electron paramagnetic resonance (EPR) measurement was
utilized to confirm the existence of O2•−. Application of 5,5-
dimethyl-pyrroline-N-oxide (DMPO) as a sensitive trapping agent
•−
manifested the formation of O2
over Por-sp2c-COF in
photocatalytic oxidation amines. EPR signals for DMPO captured
with the O2•−. The signals evidently increased under light
illumination for 2 min, and the signal continued to increase as the
illumination time was extended to 4 minutes, demonstrating that
•−
O2 indeed participates in the reaction (Figure 4a). TEMPO,
which is a stable radical and EPR active species, could act as the
cocatalyst in photocatalysis. We also studied the probable
synergistic effect of TEMPO in the reactions by EPR trapping
experiments (Figure 4b). Upon the addition of light illumination,
the signal intensity of TEMPO evidently decreases from 2 min to
4 min, suggesting TEMPO took part in the reaction. Without light,
the signal of TEMPO bounced back with some time (Figure 4b).
The redox catalytic cycle of TEMPO could be combined with the
photocatalytic cycle to create a cooperative photocatalysis to
promote selective chemical transformations.
Based on the above results, a plausible mechanism for
photocatalytic oxidation of amines were illustrated in Figure 5.
Under red LEDs illumination, the linker-to-linkage charge transfer
process, mostly from the lowest unoccupied molecular orbital
(LUMO) to the highest occupied molecular orbital (HOMO) in Por-
sp2c-COF gave rise to effective e--h+ separation. Moreover, owing
to suitable molecular dimension of TEMPO, it could be flexibly
positioned as outside or inside the pore space of Por-sp2c-COF,
favoring the spatial separation of e--h+ pairs. The O2•−, generated
from O2 by reacting with e- from e--h+ pairs, could combine with
TEMPOH to produce H2O2. Then, TEMPOH was restored to
TEMPO to join into the photocatalytic cycle again. TEMPO was
oxidized TEMPO+ by extra h+ come from e--h+ pairs. Meanwhile,
TEMPO+ captured the hydrogen of the benzylamine and was
reduced to the TEMPOH. At the same time, benzylamine was
converted to benzylideneamine which further reacted with
benzylamine to produce the desired imine 2b.
[a] Reaction conditions: secondary amine (0.25 mmol), Por-sp2c-COF
(0.005 mmol), TEMPO (0.005 mmol), red LED illumination (623 ± 8 nm, 3
W × 4), air (1 atm), CH3CN (1 mL). [b] Determined by GC-FID using
chlorobenzene as the internal standard, conversion of secondary amine,
selectivity of imine.
Furthermore, we performed
a
series of quenching
experiments to recognize reactive oxygen species (ROS). Owing
to O2 is a relatively stable molecule, environmentally friendly, it
was widely used in photocatalytic selective chemical
transformations. As for the oxidation of benzylamine, quenching
experiments suggest the important effect of O2 in the reaction.
The conversion of benzylamine decreased sharply to 7% under
N2 atmosphere instead of 1 atm of air condition (Figure S15b, A
and B). Judging by previous reports, p-BQ (p-benzoquinone) is a
universal scavenger for the superoxide anion radical (O2•−). The
addition of p-BQ did significantly quench the conversion of
4
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10.1002/anie.202000723
Angewandte Chemie International Edition
RESEARCH ARTICLE
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Figure 5. A plausible mechanism of visible-light-induced selective
aerobic oxidation of benzylamine by cooperative Por-sp2c-COF
photocatalysis and TEMPO catalysis.
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In summary, 2D sp2 carbon–conjugated porphyrin covalent
organic framework photocatalysis meets with TEMPO catalysis to
push forward visible-light-induced selective oxidation of a wide
range of amines illuminated of red LEDs. This is the first example
of red light-induced chemical transformation illuminated by 623
nm red light by semiconductor photocatalysis. Unprecedentedly,
both primary amines and secondary amines could be oxidized to
corresponding imines with remarkably high conversions and
selectivities within 30 min. Importantly, the large π-conjugation of
2D COF leads to 623 nm red light absorption; and the sp2 C=C
double bonds linkage ensures the stability of the 2D COF under
high concentration of benzylamines. More importantly, the
crystalline framework of 2D COF underpins cooperative
photocatalysis with TEMPO which is unavailable for either
amorphous polymers or molecular dyes. This work not only
provides a protocol to optimize charge transfer and separation of
COFs photocatalysis in cooperation with TEMPO catalysis, but
also stimulates further discoveries on selective chemical
transformations by cooperative photocatalysis.
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Acknowledgements
[18] Y. Meng, Y. Luo, J. L. Shi, H. M. Ding, X. J. Lang, W. Chen, A. M. Zheng,
J. L. Sun, C. Wang, Angew. Chem. Int. Ed. 2020, 59, 3624-3629.
Financial support from the National Natural Science
Foundation of China (grant number 21773173) and the start-up
fund of Wuhan University is gratefully acknowledged.
Conflict of interest
The authors declare no conflict of interest.
Keywords: covalent organic frameworks • TEMPO • red LEDs •
cooperative photocatalysis • amines to imines
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This article is protected by copyright. All rights reserved.

10.1002/anie.202000723
Angewandte Chemie International Edition
RESEARCH ARTICLE
Entry for the Table of Contents
RESEARCH ARTICLE
Red, Go! An effective
protocol for selective
oxidation of amines into
imines was unveiled by
cooperative photocatalysis
of Por-sp2c-COF and
TEMPO illuminated by 623
nm red LEDs.
Ji-Long Shi, Dr. Rufan Chen,
Huimin Hao, Prof. Dr. Cheng
Wang, and Prof. Dr. Xianjun
Lang*
Page No. – Page No.
((Insert TOC Graphic here))
2D sp2 Carbon–conjugated
Porphyrin Covalent Organic
Framework for Cooperative
Photocatalysis with TEMPO
6
This article is protected by copyright. All rights reserved.