Tetrathienoanthracene-functionalized conjugated microporous polymers as an efficient, metal-free visible-light solid organocatalyst for heterogeneous photocatalysis

Article abstract of DOI:10.1039/d1cy00488c

Owing to their advantages of superior inherent porosity, high chemical stability, light weight, and molecularly tunable optoelectronic properties, conjugated microporous polymers (CMPs) have been receiving increasing attention and research interest as pro

Full text of DOI:10.1039/d1cy00488c

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Tetrathienoanthracene-functionalized conjugated
microporous polymers as an efficient, metal-free
visible-light solid organocatalyst for
Cite this: DOI: 10.1039/d1cy00488c
heterogeneous photocatalysis†
*
Chang-An Wang,
Jian-Ping Zhang, Kun Nie, Yan-Wei Li, Qun Li,
*
Guo-Zheng Jiao, Jian-Guo Chang and Yin-Feng Han
Owing to their advantages of superior inherent porosity, high chemical stability, light weight, and
molecularly tunable optoelectronic properties, conjugated microporous polymers (CMPs) have been
receiving increasing attention and research interest as promising alternatives to traditional inorganic
semiconductors for heterogeneous photocatalysis. Herein, we report the concise synthesis of
tetrathienoanthracene-based conjugated microporous polymers (TTA-CMP) via a bottom-up strategy.
TTA-CMP was employed as metal-free visible-light solid organocatalyst for three prototypic organic
reactions: the dehydrogenative coupling reaction, dehydrogenative-Mannich reaction, and photocatalytic
synthesis of benzimidazoles. Indeed, TTA-CMP showed excellent photocatalytic activity (29 examples, 80–
98% yield) and outstanding reusability (10–12 times) in these three reactions. The extended π-conjugation
in TTA-CMP enhances its visible light absorption, therefore, TTA-CMP displays higher catalytic activity than
the corresponding small molecular photocatalyst. This work reveals the bright future of TTA-CMP as an
efficient solid organocatalyst for other photocatalytic syntheses.
Received 20th March 2021,
Accepted 20th April 2021
DOI: 10.1039/d1cy00488c
rsc.li/catalysis
instability under aerobic conditions, and being difficult to
remove after reactions, which impose a significant limit on
Introduction
Organic photochemical synthesis via simulating the
photosynthesis of natural plants has been the dream of
synthetic chemists for more than 100 years.1 In the past
decade, since the pioneering work of MacMillan,2 Yoon,3 and
Stephenson,4 visible-light driven organic photochemical
synthesis has undergone remarkable development.5 Because
organic molecules lack the ability to absorb photons in the
visible region, homogeneous photocatalysts such as
[Ru(bpy)3]2+ (bpy = 2,2,-bipyridine) and [Ir(ppy)2(bpy)]+ (ppy =
2-phenyl-pyridine) are often used to drive organic
transformation due to their rich redox chemistry at the MLCT
(metal-to-ligand charge-transfer) excited states.6 Indeed, in
recent years, many photocatalytic reactions such as direct
C–H functionalizations,7 the synthesis of aromatic aza-
hetereocycles,8 asymmetric photochemical reactions,2,9 and
small molecule activation10 have been studied via different
photoactivation modes. However, Ru and Ir metal ligands
have intrinsic drawbacks, such as high toxicity, high price,
large-scale synthesis.11 From the viewpoints of industrial
application and environmental friendliness, it is highly
desirable to develop efficient photocatalytic solid
organocatalysts with the advantages of being inexpensive,
recyclable, and free of precious metals.12 These solid
organocatalysts can not only eliminate the contamination of
organic products caused by heavy metal ions but can also
reduce the processing costs in large-scale applications.13
Conjugated microporous polymers (CMPs),14 as one of the
typical representatives of porous organic polymers (POPs)
first reported by the Cooper group in 2007, have drawn
considerable scientific attention due to their wide range of
applications. CMPs have been widely used in the field of gas
storage/separation,15 photoelectricity,16 chemosensors,17 and
heterogeneous catalysis.18 Especially in recent years, CMP-
based materials have garnered significant attention as
promising candidates for photocatalytic applications.19
Compared with inorganic semiconductors, the outstanding
features of π-conjugated polymers in the field of
photocatalysis are:19d (i) they consist of lightweight elements
(C, H, O, N, S, etc.) with larger surface areas and they possess
tunable energy levels for oxidation and reduction reactions;
(ii) they can be easily prepared under mild conditions (less
College of Chemistry and Chemical Engineering, Taishan University, Tai'an,
Shandong 271000, P. R. China. E-mail: wangcha@tsu.edu.cn, han@tsu.edu.cn
† Electronic supplementary information (ESI) available. See DOI: 10.1039/
d1cy00488c
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than 100 °C) and possess excellent chemical stability against
photodecomposition; (iii) the skeleton structures of CMPs
can be easily fine-tuned at the molecular level to better utilize
visible light, while traditional inorganic photocatalysts can
only use UV light; (iv) the extension of the π-conjugated
structure of CMPs facilitates the separation of
photogenerated charge carriers and their transport along the
skeleton, which is crucial for driving photoredox reactions.
In this context, combining these features, here we report
the design, synthesis, characterization, and photocatalytic
block (denoted as SBB) and rigid, large-size, planar
functionalized tetrathienoanthracene as the functional building
block (denoted as FBB-TTA). The TTA-CMP framework can be
easily constructed in a high yield through the palladium
catalyzed Sonogashira–Hagihara cross-coupling reaction under
nitrogen atmosphere. The obtained polymeric framework is
insoluble in water and general organic solvents such as MeOH,
DMSO, DMF, THF, acetone and chloroform. It also retains high
chemical stability even in acid or base solutions.
Further, the atomic-level linkages of the TTA-CMP
framework were studied by using Fourier transform infrared
(FT-IR) and 13C solid-state NMR spectroscopy. The FT-IR
spectra of TTA-CMP and their monomers are exhibited in
Fig. 1a. We found that the TTA-CMP polymer still retains
many characteristic vibration signals of the TTA structure.
Compared with the FT-IR spectrum of FBB-TTA and SBB, the
absence of the C–H stretching peak of the –CC–H group
around 3270 cm−1 and the appearance of the characteristic
peak at 2202 cm−1 in the IR spectra of the TTA-CMP
performance of
a
new metal-free visible-light solid
organocatalyst based on an anthra[1,2-b:4,3-b′:5,6-b″:8,7-b‴]
tetrathiophene (TTA) core embedded CMP framework.
Tetrathienoanthracene (TTA) is
a sulfur-rich polycyclic
aromatic hydrocarbon with a flat and rigid π-conjugated
structure, consisting of four thiophene units fused to an
anthracene. It is well known that this structure tends to stack
through strong π–π interactions and leads to excellent hole-
carrier mobilities in organic field-effect transistors (OFETs).20
Although functionalized tetrathienoanthracene molecules are
widely used in the synthesis of organic semiconductors via
π–π stacking interactions,21 they are rarely used in the field
of photocatalysis. Very recently, the An group22 and the Liu
group23 respectively reported the application of CMP
materials based on similar structures of bithiophene and
benzotrithiophene in heterogenous photocatalysis. In this
work, for the first time, we are incorporating
framework indicated the formation of
a carbon–carbon
triple-bond. Additionally, the FT-IR spectra for the TTA-CMP
showed a strong peak for a thiophen ring at 820 cm−1 (Fig. S1
in the ESI†). These results indicate that the polymerization
process is efficient. The 13C solid-state NMR spectra of TTA-
CMP exhibited signals at approximately 132, 128, 125, and
123 ppm, which originate from the carbon atoms of the
tetrathienoanthracene monomer. The signals at 142, 132,
125, and 121 ppm can be attributed to the carbon atoms of
SBB, 1,3,5-tri(4-ethynylphenyl)benzene (the assignments are
shown in Fig. 1b). The signals at 93 and 87 ppm are
tetrathienoanthracene (TTA) into
a
three-dimensional
π-conjugated microporous polymer framework (TTA-CMP),
which could provide a heterogeneous photocatalytic system
for visible light promoted organic transformations.
indicative of the formation of –CAr–CC–Cheter
– sites.
Additionally, the element analysis of the TTA-CMP framework
confirmed the content of sulfur (10.95%) and the TTA
photocatalyst loading could be calculated. All of these data
provided overwhelming evidence that the functional
monomer TTA was successfully embedded in the CMP
skeleton.
Results and discussion
The designed synthesis and characterization of TTA-CMP
Tetrabromo-functionalized
tetrathienoanthracene
was
synthesized via a simple transformation from commercially
available materials.20b As shown in Scheme 1, we selected large-
size 1,3,5-tri(4-ethynylphenyl)benzene as the structural building
The porosity of the TTA-CMP framework was tested by
a nitrogen adsorption–desorption experiment at 77 K. As
Scheme 1 Synthesis of TTA-CMP via a bottom-up strategy.
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Fig. 1 (a) FT-IR spectra of FBB-TTA (blue line), SBB (red line) and TTA-
CMP (black line). (b) The solid-state 13C NMR spectrum of TTA-CMP
and the assignments of 13C chemical shifts of TTA-CMP are indicated
in the chemical structure (left).
Fig. 2 (a) Nitrogen adsorption–desorption isotherms of TTA-CMP at
77 K. (b) The pore size distribution of TTA-CMP calculated by NL-DFT.
shown in Fig. 2a, TTA-CMP showed a type-IV sorption
isotherm with H2 hysteresis loops, indicating that the
The TTA-CMP polymer is stable up to 300 °C in a nitrogen
atmosphere (Fig. 3a), as revealed by thermogravimetric
analysis (TGA). The SEM image indicates that the polymer
consisted of bulk and spherical nanoparticles with a size of
several hundred nanometers (Fig. 3b). The HR-TEM
measurement displayed the presence of nanopores in the
TTA-CMP network (Fig. 3c and S5†). In addition, energy-
dispersive X-ray spectroscopy (EDX) elemental mapping
images clearly showed that the elements C and S were
homogeneously dispersed in the TTA-CMP network (Fig. 3d).
The element analysis of TTA-CMP also confirmed the content
of S and C in the networks. The PXRD analysis showed that
TTA-CMP is an amorphous polymer, the same as our
previously reported POP polymers13e,25 (Fig. S3 in the ESI†).
The optoelectronic properties of TTA-CMP were studied by
TTA-CMP
polymer
displays
mesoporous
structures
according to the IUPAC classification. Based on the
nitrogen adsorption data, the Brunauer–Emmett–Teller
(BET) surface area of TTA-CMP was calculated to be 461
m2 g−1 and the total pore volume at 0.99P/P0 was
evaluated to be 0.571 cm3 g−1. Using the de Boer
statistical thickness (t-plot) method, the TTA-CMP polymer
displayed
a
micropore volume contribution of 0.105
cm3 g−1 (18%) and a mesopore volume contribution of
0.466 cm3 g−1 (82%). The pore-size distribution (PSD) was
calculated by the nonlocal density functional theory
(NLDFT) model and was found to be centered at 1.3 nm,
2.2 nm and 5.5 nm, respectively (Fig. 2b). The PSD curves
also demonstrated the existence of abundant mesopores
in the TTA-CMP framework. For all we know, most of the
currently reported catalytic POPs are microporous polymers
(the pore size is less than 2 nm), the micropores are not
conducive to mass transfer of the substrate molecule and
the binding of the substrate to the catalytically active
sites, this will reduce the catalytic activity of the porous
catalysts. Therefore, the design and synthesis of CMP-
based materials containing abundant mesopores is
essential to improve the catalytic activity.24
solid-state UV/vis absorption spectroscopy and
a cyclic
voltammetry (CV) experiment. As shown in Fig. 4a, the TTA-
CMP polymer exhibited a broad absorption region and the
band edge extended to 800 nm. In comparison with the UV/
vis absorption spectra of homogeneous FBB-TTA, the large
range indicated that the extended-conjugation structure of
TTA-CMP indeed enhances the visible light absorption
region. The optical band gap (Eg) of TTA-CMP was 2.08 eV
calculated by the Kubelka–Munk function (Fig. 4b). To
evaluate the energy band structures of TTA-CMP, the cyclic
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Fig. 3 (a) TGA curve of TTA-CMP. (b) SEM image of TTA-CMP. (c) HR-TEM image of TTA-CMP. (d) EDS mapping images of C and S for TTA-CMP.
Fig. 4 (a) UV/vis absorption spectra of TTA-CMP (black) and the monomer (blue). (b) Kubelka–Munk plot (to measure the band gap energy) for
solid-state TTA-CMP. (c) Energy band positions of the TTA-CMP and O2/O2˙− measured by CV.
voltammetry (CV) experiment was conducted (Fig. S6†). The
conduction band position (Ec) of TTA-CMP versus SCE was at
−1.20 V, the potential of the conduction band clearly
indicates the reduction of O2 to O2˙− (−0.86 V vs. SCE), which
was negative enough through photoinduced electron transfer
from TTA-CMP to molecular O2 under light illumination
(Fig. 4c).
photocatalytic reactions were proposed. We first chose the
dehydrogenative coupling reaction of N-aryl-
tetrahydroisoquinolines and nitroalkanes to examine the
photocatalytic activity of the TTA-CMP polymer. The reaction
of 2-phenyl-1,2,3,4-tetrahydroisoquinoline and nitromethane
as a model reaction was first investigated to screen the
conditions, and the results are shown in Table S1 in the ESI.†
We found that TTA-CMP showed the best reactivity with 2.0
mol% catalyst loading in the presence of air with a common
fluorescent lamp (24 W) as the light source at room
temperature, giving the product in high yield (96%) after 12
h (Table S1,† entries 1–3). A number of control experiments
were also conducted to demonstrate the photocatalytic nature
of TTA-CMP. Natural light gave a low yield and the reaction
did not work in the dark (Table S1,† entries 4–5), which
indicated that light is necessary to promote the photoinduced
Photocatalytic application
The good photoredox properties, excellent stability, high BET
surface and abundant mesopores of TTA-CMP ensured its
excellent photocatalytic activity in visible-light driven organic
transformations. Based on this, we selected three prototypic
organic reactions to determine its photocatalytic activity, the
scope of the substrates and the reusability of TTA-CMP were
studied and the plausible mechanism of heterogeneous
electron transfer. The TTA-CMP polymer played
a
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heterogenous catalytic role in the reaction, which was
demonstrated by the background reaction in the absence of
TTA-CMP (Table S1,† entry 6) and the non-photoactive CMP-1
as the heterogeneous catalyst (Table S1,† entry 7). In addition,
O2 played a critical role, which was demonstrated by the fact
that the reaction proceeded much more slowly in nitrogen
gas (Table S1,† entry 8). Importantly, it should be noted that
the monomer FBB-TTA as the catalyst did not give a good
yield (35%), implying that the extended π–π conjugated
structure of CMP was advantageous for photocatalytic activity
(Table S1,† entry 9). Under the established conditions, the
substrate scope of the dehydrogenative coupling reaction
catalyzed by TTA-CMP was examined. We evaluated the
performance of different N-aryl-tetrahydroisoquinolines 1a–g
with nitroalkanes 2a–b in the presence of 2.0 mol% TTA-CMP
(Table 1). Both CH3NO2 (Table 1, 3a–3g) and C2H5NO2
(Table 1, 3h–3j) as the nucleophile provided the desired
products with good to excellent yields (90–98%). The results
are comparable to those using the reported Ir- or Ru-loaded
CMP,26 RB-CMP,27 EY-CMP,25a and the homogeneous
photocatalysts.7a,28 This demonstrates that the TTA-CMP
framework can be used as an efficient heterogeneous organo-
photocatalyst for this class of dehydrogenative coupling
reaction.
iminium ions. In the dual catalytic Mannich-type reaction,
we also evaluated the performance of different N-aryl-
tetrahydroisoquinolines with the ketone in the presence of
2.0 mol% TTA-CMP and 20 mol% L-proline (Table 2). Various
tetrahydroisoquinoline derivatives were reacted with acetone
(Table 2, 5a–5g) and butanone (Table 2, 5h–5j) to provide the
desired products in good to excellent yields (80–96%). To the
best of our knowledge, the use of recyclable heterogeneous
photocatalysts for dual-catalytic reactions has rarely been
reported.13d,30
A possible reaction mechanism is proposed (Scheme 2).
The excited state species TTA-CMP* is generated under
visible light irradiation, which is reductively quenched by the
tertiary amine 1 via a single electron transfer (SET) process to
obtain a tertiary amine radical cation and a TTA-CMP˙−
radical anion. The photoredox cycle is completed by the
oxidation of TTA-CMP˙− back to the ground state TTA-CMP by
molecular oxygen. The key intermediate iminium comes from
the tertiary amine radical cation, which donates one
hydrogen atom to the O2˙−, it can be trapped by nucleophiles
2 or 4 under mild conditions to release the target product 3
or 5. This plausible mechanism is also the most widely
reported reaction mechanism in other groups.7a,28b
The third reaction tested was the photocatalytic synthesis
of benzimidazoles by TTA-CMP under visible light. The
We next investigated the dehydrogenative-Mannich
reaction29 occurring between a tertiary amine and a ketone
catalyzed by TTA-CMP. Whereas the TTA-CMP was once again
shown to be a good photocatalyst for the oxidation of tertiary
amine to generate the iminium ions in situ under light
illumination, L-proline was used to generate the enamine
nucleophiles from the ketone, which can easily react with the
photosynthesis of 2-phenyl-benzimidazole as
a
model
reaction was investigated to screen the conditions, and the
results are shown in Table S2.† After screening the amount of
catalyst and different solvents, we found that the use of 2.0
mol% TTA-CMP and ethanol as the solvent give the desired
product in an excellent yield (see ESI,† Table S2, entries 1–11).
Table 1 Dehydrogenative coupling catalysed by TTA-CMP with visible lighta
3a, 5 h, 96% yield
3b, 12 h, 94% yield
3c, 4 h, 96% yield
3f, 24 h, 95% yield
3i, 5 h, 92% yield
3d, 5 h, 98% yield
3g, 5 h, 90% yield
3e, 5 h, 94% yield
3h, 5 h, 96% yield
3j, 5 h, 93% yield
a
Reaction conditions: 0.2 mmol tertiary amine; 1.0 mL nitroalkane; TTA-CMP (4.7 mg, 2.0 mol%); room temperature; 24 W household bulb, in
air. Isolated yields after silica gel column chromatography.
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Table 2 Dehydrogenative-Mannich reaction catalysed by TTA-CMP under visible lighta
5a, 5 h, 94% yield
5d, 12 h, 82% yield
5g, 24 h, 85% yield
5b, 12 h, 82% yield
5e, 12 h, 96% yield
5h, 12 h, 80% yield
5c, 12 h, 83% yield
5f, 24 h, 88% yield
5i, 12 h, 80% yield
5j, 12 h, 85% yield
a
Reaction conditions: 0.1 mmol tertiary amine; 1.0 mL ketone; L-proline (2.3 mg, 20 mol%); TTA-CMP (2.4 mg, 2.0 mol%); room temperature;
24 W household bulb, in air. Isolated yields after silica gel column chromatography.
Scheme 2 The proposed mechanism for TTA-CMP catalyzed dehydrogenative coupling.
Furthermore, some control experiments were carried out to
determine whether visible light and the photocatalyst are
necessary for the reaction (Table S2,† entries 12–16). The
desired product was obtained in trace amounts or low yields
when the reaction was performed in natural light, dark, and
in the absence of TTA-CMP or the non-photoactive CMP-1 as
the catalyst. It should also be noted that the monomer FBB-
TTA as the catalyst did not give a good yield (72%), once
again implying that the extended π–π conjugated structure of
CMP was advantageous for photocatalytic activity (Table S1,†
entry 17). Again, molecular O2 played a critical role in the
reaction (Table S1,† entry 18). The optimized reaction
conditions were determined as: 2.0 mol% TTA-CMP as the
photocatalyst, ethanol as the solvent, irradiation with a 24 W
blue bulb at ambient temperature in air. With the optimal
photocatalytic conditions in hand, we next investigated the
substrate scope of different aldehydes for the photocatalytic
reaction catalyzed by the TTA-CMP polymer. As shown in
Table 3, all the substrates of the aromatic aldehydes with
different substituent groups, including benzaldehyde
possessed –Br, –OH, –NO2, –CN in the p-position (8a–8e), –Cl
in the o-position (8h) and –CH3 in the m-position (8i),
2-naphthaldehyde (8f), and 1-naphthaldehyde (8g), could
furnish the corresponding benzimidazole derivatives
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Table 3 Photocatalytic synthesis of benzimidazoles by TTA-CMP under visible lighta
8a, 2 h, 98% yield
8d, 5 h, 83% yield
8b, 3 h, 98% yield
8e, 5 h, 88% yield
8c, 8 h, 90% yield
8f, 4 h, 94% yield
8h, 9 h, 87% yield
8g, 5.5 h, 98% yield
8i, 6 h, 91% yield
a
Reaction conditions: 1,2-phenylenediamine (0.25 mmol), benzaldehyde (0.25 mmol), EtOH (3.0 mL), TTA-CMP catalyst (5.8 mg, 2.0 mol%),
irradiation with 24 W blue bulb, room temperature, in air. Isolated yields after silica gel column chromatography.
smoothly in 2–9 h with good to excellent yields (Table 3, 83–
98%). The geometries of the reactants and product of this
photocatalytic reaction were optimized with the Gaussian 09
package at the B3LYP/6-31G(d) level in combination with
frequency calculations (Fig. S8 in the ESI†). The three-
dimensional sizes of 1,2-phenylenediamine, benzaldehyde
and 2-phenyl-benzimidazole were estimated to be 7.8 Å × 7.4
Å × 2.5 Å, 8.5 Å × 6.7 Å × 2.4 Å, and 13.3 Å × 7.4 Å × 2.4 Å,
compared with the pore-size distribution (∼5.5 nm) of TTA-
CMP, it was clearly demonstrated that the reactants and
product can be freely transported in the nanopores. Based on
the synthesis of benzimidazoles catalyzed by other reported
losing hydrogen peroxide (Fig. S14 in the ESI†), the target
product was obtained through the dehydrogenation process
of III.
Besides the excellent photocatalytic activity and substrate
tolerance, the reusability of TTA-CMP and its stability after
reuse were studied. First, the catalytic recyclability of TTA-
CMP was assessed by examining the photocatalytic
dehydrogenative coupling reaction of 2-phenyl-1,2,3,4-
tetrahydroisoquinoline and nitromethane (see ESI,† Table
S4), the photocatalytic dehydrogenative-Mannich reaction of
2-phenyl-1,2,3,4-tetrahydroisoquinoline and acetone (Table
S5†) and the photocatalytic synthesis of 2-substituted
benzimidazole of 1,2-phenylenediamine and benzaldehyde
(Table S6†). After each cycle, the TTA-CMP polymer can be
easily separated from the reaction solution by centrifugation.
As shown in Fig. 5, no sign of significantly decreasing
reactivity was observed after reusing TTA-CMP 10 times for
the dehydrogenative coupling reaction (92–96%) and
dehydrogenative-Mannich reaction (89–94%) and 12 times for
the third reaction (92–98%). Second, after 12 cycles, the FT-IR
spectra (see ESI,† Fig. S10), UV-visible spectra (Fig. S11†),
SEM (Fig. S12†), and EDX elemental mapping (Fig. S13†) of
the recovered TTA-CMP indicate no apparent change in the
skeleton structure. The BET surface area of TTA-CMP
photocatalytic
photocatalysts,31,32
CMPs22,23
possible reaction mechanism is
and
the
homogeneous
a
proposed in Scheme 3. First, the excited state species TTA-
CMP* is generated under visible light irradiation, which is
reductively quenched by intermediate I via a single electron
transfer (SET) process to obtain the intermediate II radical
cation and the TTA-CMP˙− radical anion. The photoredox
cycle is completed by the oxidation of TTA-CMP˙− back to the
ground state TTA-CMP by molecular oxygen, and in this
process O2˙− is produced. The intermediate II radical cation
donates one hydrogen proton to O2˙− and then intermediate
III is generated via intramolecular cyclization. Finally, after
Scheme 3 The proposed mechanism for the photocatalytic synthesis of benzimidazole catalyzed by TTA-CMP under visible light.
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Acknowledgements
This work was supported by the National Natural Science
Foundation of China (No. 21502136 and 81803835) and the
Shandong Outstanding Youth Innovation Team Program (No.
2019KJC032).
Notes and references
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Fig. 5 Reusability of TTA-CMP in the photocatalyzed dehydrogenative
coupling reaction of 2-phenyl-1,2,3,4-tetrahydroisoquinoline and
nitromethane (blue), the dehydrogenative-Mannich reaction of
2-phenyl-1,2,3,4-tetrahydroisoquinoline and acetone (black), and the
synthesis of 2-substituted benzimidazole of 1,2-phenylenediamine and
benzaldehyde (red).
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Scheme 4 The gram-scale photocatalytic synthesis of 2-phenyl-1H-
benzo[d]imidazole.
decreased to 159 m2 g−1 after the 10th recycled used, possibly
due to the substrates or the products blocking the partial
micropores of TTA-CMP (Fig. S9†). Pleasingly, as shown in
Scheme 4, a gram scale experiment was carried out under
optimal conditions without difficulty, attesting to the
practicality of TTA-CMP in industry (Fig. S7†).
Conclusions
In summary, we used a bottom-up strategy to construct a
metal-free solid porous organo-photocatalyst (TTA-CMP) for
robust heterogeneous photocatalysis. Thanks to its excellent
photoelectric properties, high BET surface area, mesoporous
structure, and outstanding stability, the synthesized TTA-
CMP was shown to be a highly active, recyclable and reusable
heterogeneous photocatalyst in three different types of
photoreactions. Compared with the photocatalytic activity of
the monomer molecule, the unique extended π–π conjugation
of the CMP materials is very important for improving the
catalytic efficiency. Now, the exploration of CMP-based
photocatalysts in asymmetric reactions is underway in our
laboratory.
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