Asymmetric Covalent Triazine Framework for Enhanced Visible-Light Photoredox Catalysis via Energy Transfer Cascade

Article abstract of DOI:10.1002/anie.201801112

Complex multiple-component semiconductor photocatalysts can be constructed that display enhanced catalytic efficiency via multiple charge and energy transfer, mimicking photosystems in nature. In contrast, the efficiency of single-component semiconductor photocatalysts is usually limited due to the fast recombination of the photogenerated excitons. Here, we report the design of an asymmetric covalent triazine framework as an efficient organic single-component semiconductor photocatalyst. Four different molecular donor–acceptor domains are obtained within the network, leading to enhanced photogenerated charge separation via an intramolecular energy transfer cascade. The photocatalytic efficiency of the asymmetric covalent triazine framework is superior to that of its symmetric counterparts; this was demonstrated by the visible-light-driven formation of benzophosphole oxides from diphenylphosphine oxide and diphenylacetylene.

Full text of DOI:10.1002/anie.201801112

A Journal of the Gesellschaft Deutscher Chemiker
Angewandte
Chemie
International Edition
www.angewandte.org
Accepted Article
Title: Asymmetric Covalent Triazine Framework for Enhanced Visible
Light Photoredox Catalysis via Energy Transfer Cascade
Authors: Wei Huang, Jeehye Byun, Irina Rörich, Charusheela
Ramanan, Paul W. M. Blom, Hao Lu, Di Wang, Lucas Caire
da Silva, Run Li, Lei Wang, Katharina Landfester, and Kai A.
I. Zhang
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201801112
Angew. Chem. 10.1002/ange.201801112
Link to VoR: http://dx.doi.org/10.1002/anie.201801112
http://dx.doi.org/10.1002/ange.201801112

10.1002/anie.201801112
Angewandte Chemie International Edition
COMMUNICATION
Asymmetric Covalent Triazine Framework for Enhanced Visible
Light Photoredox Catalysis via Energy Transfer Cascade
Wei Huang, Jeehye Byun, Irina Rörich, Charusheela Ramanan, Paul W. M. Blom, Hao Lu, Di Wang,
Lucas Caire da Silva, Run Li, Lei Wang, Katharina Landfester, Kai A. I. Zhang*[a]
Abstract: The construction of complex multiple component
semiconductor photocatalyts allows enhanced catalytic efficiency via
multiple charge and energy transfer, which mimics the nature
photosystems. However, the efficiency of single component
semiconductor photocatalysts is usually inhibited due to the fast
recombination of the photo-generated excitons. Here, we report the
design of an asymmetric covalent triazine framework as efficient
single component organic semiconductor photocatalyst. Four different
molecular donor-acceptor domains are obtained within the network,
leading to an enhanced photogenerated charge separation via
intramolecular energy transfer cascade. The superior photocatalytic
efficiency of the asymmetric covalent triazine framework over its
symmetric counterparts was demonstrated via the visible light-driven
formation of benzophosphole oxides from diphenylphosphine oxide
and diphenylacetylene.
separation and thermodynamically favorable band positions are
of great importance.[14] Indeed, several synthetic strategies have
been recently applied to improve the photocatalytic efficiency of
the organic semiconductors, including copolymerization,
molecular geometry design[15] and heterojunction formation[16]
.
However, the photocatalytic efficiency of the single component
organic semiconductor photocatalysts is usually limited due to the
fast recombination of the photo-generated excitons.[17] New
design strategies are highly needed.
Asymmetric CTF
Symmetric CTFs
(a)
(b)
M4
CTF-Th
M1
Direct use of solar energy to drive photoredox reactions is an
environmentally friendly, non-toxic and highly sustainable
alternative to the traditional thermal reaction conditions.[1] In
nature photosynthesis, a series of stepwise energy and charge
transfer processes is involved to enhance the photogenerated
charge separation and transfer process.[2] Taking the nature
photosystem as a role model, chemists and materials scientists
M3
M2
asy-CTF
CTF-Th-Ph
(c)
have designed
a
wide variety of multiple component
photocatalytic systems in order to increase their photocatalytic
efficiency. For example, the construction of heterojunction metal
semiconductors[3] and bridged transition metal complexes[4] have
been reported to greatly promote the photogenerated charge
separation and transfer. Recently, the state of art metal-free
photocatalyst, carbon nitrides[5] with different metal loadings,[6] or
doping with heteroatoms,[7] conjugated organic dyes,[8] or other
metal semiconductors[9] have been reported as efficient strategy
to overcome the fast recombination of the photogenerated
excitons during the catalytic process.
LUMO
HOMO
M1
M2
M3
M4
Figure 1. (a) Representative repeating unit structure of the asymmetric network
asy-CTF containing different molecular D-A domains (M1-M4), (b) its
symmetric counterparts CTF-Th and CTF-Th-Ph containing only a single D-A
domain, and (c) HOMO and LUMO levels of the 4 different D-A domains within
asy-CTF calculated at the B3LYP/6-31G (d) level.
4
Macromolecular organic semiconductor photocatalysts have
demonstrated their distinct advantage in the ease of tuning the
optoelectronic properties by appropriate choice of donor and
acceptor units as well as their alignment ordering.[10] They have
been employed as a stable and efficient platform for visible light
photoredox reactions as water splitting,[11] selective oxidation of
organic compound,[12] and C-C bond formation reaction[13] etc. To
reach higher photocatalytic efficiency, the enhanced charge
Herein, we report the design of an asymmetric covalent
triazine framework (CTF) as single component organic
semiconductor photocatalyst possessing photogenerated energy
transfer cascade. Four different molecular donor-acceptor
domains were obtained within the backbone, leading to an
enhanced
photogenerated
broad
absorption
range,
intramolecular energy transfer and sufficient photoredox potential.
Here, the alternating and symmetric donor-acceptor structure,
which is characteristic for single organic semiconductor
photocatalysts, is non-existent within the asymmetric network.
Compared to the symmetric CTFs containing similar donor and
acceptor moieties, the superior photocatalytic efficiency of the
asymmetric CTF was demonstrated via the visible light-driven
[a]
Dr. W. Huang, Dr. J. Byun, I. Rörich, Dr. C. Ramanan, Prof. P. W.
M. Blom, Dr. H. Lu, D. Wang, Dr. L. Caire da Silva, Dr. R. Li, Dr. L.
Wang, Prof. K. Landfester and Dr. K. A. I. Zhang
Max Planck Institute for Polymer Research
Ackermannweg 10, 55128 Mainz, Germany
E-mail: kai.zhang@mpip-mainz.mpg.de
Supporting information for this article is given via a link at the end of
the document
This article is protected by copyright. All rights reserved.

10.1002/anie.201801112
Angewandte Chemie International Edition
COMMUNICATION
formation
reaction
of
benzophosphole
oxides
from
can be assigned to the aromatic C-N stretching and breathing
modes in the triazine unit (Figure S4).[19] Solid state 13C cross-
polarization magic-angle-spinning (CP-MAS) NMR spectra of the
symmetric CTFs showed a single sharp peak at 167.3 ppm for
CTF-Th and 170.4 ppm for CTF-Th-Ph, which can be assigned to
the sp2 carbon in the triazine unit (Figure 2a). In contrast, asy-CTF
exhibited a relatively broad signal from 180 to 160 ppm, which is
assigned to the fusion of the sp2 carbons in the triazine units
connected both to the thiophene and phenyl units. This result
clearly indicated the formation of the different D-A combinations
within the asy-CTF backbone. The exact elemental compositions
of CTFs were further confirmed by X-ray photoelectron
spectroscopy (XPS) as displayed in Figure S5. Brunauer-Emmett-
Teller (BET) surface areas were determined to be 78 m2/g for
CTF-Th, 62 m2/g for CTF-Th-Ph, and 52 m2/g for asy-CTF (Figure
S6). The pore sizes of three CTFs were distributed in the
mesoporous range. Additionally, powder X-ray diffraction (PXRD)
patterns indicated the amorphous character of the CTF samples
(Figure S7). It is worth to note that the all three CTF materials
exhibit excellent thermal stabilities up to ca. 500 oC under oxygen
atmosphere (Figure S8).
diphenylphosphine oxide and diphenylacetylene as the model
photoredox reaction.
The asymmetric CTF (asy-CTF) was synthesized via
trifluoromethanesulfonic acid (TfOH) catalyzed trimerization[18] of
5-(4-cyanophenyl)thiophene-2-carbonitrile in its solid state
(Figure 1a). For comparison, two symmetric CTFs containing
thiophene and phenylthiophene with triazine core were prepared
as reference materials, referring to CTF-Th and CTF-Th-Ph,
respectively (Figure 1b). The synthetic details and
characterization data are described in the Supporting Information
(SI). The structure of asy-CTF suggested the formation of four
different combinations containing triazine unit as electron
acceptor and thiophene or phenyl units as electron donor. The
observation was confirmed by the control reaction of a 1:1 mixture
of benzonitrile and thiophene-2-carbonitrile, which led to the
formation of the 4 model D-A combinations (M1-M4) (Figure S1).
Theoretical simulations of the 4 different D-A combinations
calculated at the B3LYP/6-31G* level showed different electron
densities on the HOMO and LUMO levels (Figure 1c and Figure
S2).
UV/Vis diffuse reflection spectra (DRS) of the three CTFs
showed a broad absorption range up to 800 nm (Figure 2b).
Optical band gaps of 2.48 eV for CTF-Th, 2.42 eV for CTF-Th-Ph
and 2.30 eV for asy-CTF could be derived from the Kubelka-
Munk-transformed reflectance spectra (Figure S10).[20] Cyclic
voltammetry (CV) measurement further revealed the lowest
unoccupied molecular orbital (LUMO) of asy-CTF at -1.30 V vs
SCE, which is higher than that of CTF-Th-Ph at -1.24 V and that
of CTF-Th at -1.02 V vs. SCE (Figure S11). The corresponding
HOMO levels could be observed to be +1.0 V, +1.18 V and +1.46
V for asy-CTF, CTF-Th-Ph and CTF-Th, respectively (Figure 2c).
Time-resolved photoluminescence (TRPL) spectroscopy at
the excitation wavelength at 400 nm revealed a fluorescence
lifetime of 1.27 ns for asy-CTF, which was shorter than that of
CTF-Th and CTF-Th-Ph with 1.66 ns and 1.57 ns, respectively
(Figure 2d). The slightly shorter fluorescence lifetime of asy-CTF
compared to CTF-Th and CTF-Ph-Th might indicate an improved
delocalization and thereby more non-radiative recombination of
the excitons within asy-CTF, which led to a reduction of the
lifetime. To get a deeper insight, we then recorded the TRPL
spectra of asy-CTF and CTF-Th for a select time traces between
0.5-7.5 ns as a direct comparison (Figure S12a). Asy-CTF
exhibited a broader and higher energy emission peak than
steady-state PL as shown in Figure S9. The resulting decay-
associated spectra (DAS) via global analysis scheme[21] (Figure
S12b) showed a longer lifetime of asy-CTF at longer emission
wavelength (see detailed note for Figure S12), suggesting rather
a possible excitation energy transfer than charge transfer within
asy-CTF. To reveal the multiple successive energy transfer steps
from higher to lower energy moieties along a broad spectral range
for asy-CTF, we conducted fluorescence quenching experiments
with the model molecules M1 and M4 in steady states. The
quenched fluorescence of M1 by M4 confirmed the energy
transfer mechanism inside asy-CTF (Figure S13). The
photocurrent measurements (Figure 2e) showed that asy-CTF
exhibited an enhanced photocurrent compared to its symmetric
counterparts, which revealed the improved light-induced charge
mobility within asy-CTF.
Figure 2. (a) Solid state 13C CP NMR spectra, (b) UV/Vis DR spectra, (c) HOMO
and LUMO levels, (d) time-resolved photoluminescence spectra, and (e)
photocurrent of all three CTFs.
Transmission electron microscopy (TEM) images of CTFs
showed a similar fused particle-like morphology (Figure S3).
Fourier transform infrared (FT-IR) spectra of the CTFs showed
the characteristic bands around 1438, 1348 and 800 cm-1, which
This article is protected by copyright. All rights reserved.

10.1002/anie.201801112
Angewandte Chemie International Edition
COMMUNICATION
Benzophosphole oxide derivatives have recently attracted
much attention in the field of material chemistry due to their
unique photophysical and electronic properties.[22] Common
synthetic approaches to generate benzophosphole oxides usually
involve the utilization of transition metal catalysts and elevated
temperature.[23] Very few reports on the photocatalytic method
have been reported. Here, to investigate the photocatalytic
activities of the CTF materials and confirm the superior catalytic
performance of asy-CTF for organic photoredox reactions, the
visible light-promoted formation of 1,2,3-triphenylphosphindole 1-
oxide (3a) from diphenylphosphine oxide (1a) and
diphenylacetylene (2a) was chosen as a model reaction in the
paramagnetic resonance (EPR) experiments with α-phenyl-N-
tert-butylnitrone (PBN) as a radical trapping agent (Figure
S19a).[25] Remarkably, the phosphinoyl radial could be identified
along with the disappearance of the ethoxyl radical signals
followed by the addition of diphenylphosphine oxide into the
mixture (Figure S19b).[26] These results clearly demonstrated that
the electron transfer from the photocatalyst to the oxidant ought
to be the initial step of the photocatalytic cycle. Moreover, the
slope of the Stern-Volmer curve of the oxidant to quench asy-CTF
was determined to be 127.4, which was 2.6 and 6.3 times higher
than those of CTF-Th-Ph (49.7) and CTF-Th (20.3). This indicates
a considerably more efficient electron transfer between asy-CTF
and the oxidant in comparison to the cases of the symmetric
polymer networks. The reason is most likely the highest
overpotential (E= 0.52 V) between the LUMO of asy-CTF (-1.30
V vs SCE) and the reduction potential of the oxidant (-0.78 V vs.
SCE) (Figure S20), combined with the superior photo-induced
electron conductivity as demonstrated by the photocurrent
measurement.
presence of
a
base and N-ethoxy-2-methylpyridinium
tetrafluoroborate as an oxidant.[24] As shown in Figure 3a, the
reaction catalyzed by asy-CTF reached a conversion of 93% after
24 hours, which was significantly higher than those catalyzed by
the symmetric conjugated polymers CTF-Th (22%) and CTF-Th-
Ph (63%). In the absence of the photocatalyst, light or oxidant, no
product was obtained (Table S1, entries 4-6), indicating the
indispensable role of the three components. Additionally, the
effect of the solvents and bases were also studied. DMF and
NaHCO3 appeared to be the most suitable reagents to achieve
the high reaction conversion (Table S1, entries 7-12). Asy-CTF
exhibited the higher catalytic efficiency than CTF-Th and CTF-Ph-
Th under single wavelengths (420 nm and 495 nm), implying the
synergetic effect of broader light absorption and enhanced energy
transfer cascade within the asymmetric network (Figure S14).
Repeating experiment of the model reaction demonstrated that
asy-CTF could be reused up to five cycles without losing its
catalytic efficiency (Figure S15) and physicochemical properties
(Figure S16).
On the basis of the above observations, we proposed a
plausible mechanism similar to the literature,[24] as displayed in
Figure S21. Under visible light irradiation, the reaction is first
initiated by a single electron transfer (SET) event from the LUMO
of
the
photocatalyst
to
N-ethoxy-2-methylpyridinium
tetrafluoroborate to form the ethoxyl radical. The ethoxyl radical
subsequently undergoes via hydrogen abstraction from the
secondary phosphine oxide to obtain the phosphinoyl radical. The
phosphinoyl radical then adds to the alkyne to form the alkenyl
radical. Then intermolecular cyclization between the alkenyl
radical and the phenyl ring of the phosphine oxide leads to the
cyclohexadienyl radical, which can be readily oxidized by the
photogenerated holes of the photocatalyst to generate a cation
intermediate. Finally, after deprotonation in the presence of base,
the desired final product is obtained.
To investigate the general feasibility of asy-CTF as an efficient
photocatalyst, we then extended the scope of the substrates. As
summarized in Figure 4, the symmetric diaryl-substituted alkynes
with both electron-rich and electron-withdrawing groups can react
smoothly with DPPO to afford the corresponding products in
excellent yields (3b-f). The symmetric alkyl alkyne 4-octyne can
also be employed in current reaction with moderate yield (3g).
Remarkably, all the asymmetric phenylacetylenes tested here
could react with DPPO in a regioselective manner to form the 2-
substituted 1,3-diphenyl-1H-phosphindol-1-ones with moderate
yields (3h-k). The high regioselectivity can be attributed to the
stabilizing effect for the formed alkenyl radical by the adjacent of
the phenyl rings.[27] Furthermore, the scope of phenylphosphine
oxides with various substituted groups was also examined. The
monophenylphosphine oxides bearing alkyl groups could be
coupled with diphenylacetylene to afford the corresponding
products with moderate to good yields (3l-o). For the
diphenylphosophine oxide derivatives bearing electron-rich or
electron-poor groups at the aromatic rings, regioisomers were
obtained (3p-f), which was probably caused by the new C-P bond
formation via aryl migration.[23a, 28]
Figure 3. (a) Reaction dynamics in photosynthesis of 1,2,3-
triphenylphosphindole 1-oxide catalyzed by asy-CTF, CTF-Th-Ph and CTF-Th;
b) Stern-Volmer quenching measurements with CTFs and oxidant (I0 and I are
the integrated emission intensities of photocatalysts in DMF in the absence and
presence of the oxidant, respectively).
To better understand the photo-induced electron transfer
between the CTFs and substrates, and explain the superior
photocatalytic activity of asy-CTF, we further conducted
fluorescence quenching experiments (Figure S17, S18). The
fluorescence intensity of CTFs was gradually attenuated by
adding the oxidant, while the addition of DPPO did not
significantly affect the fluorescence intensity. Meanwhile, the
formed ethoxyl radical intermediate was also detected by electron
This article is protected by copyright. All rights reserved.

10.1002/anie.201801112
Angewandte Chemie International Edition
COMMUNICATION
Romero, D. A. Nicewicz, Chem. Rev. 2016, 116, 10075-10166; d) C. K.
Prier, D. A. Rankic, D. W. MacMillan, Chem. Rev. 2013, 113, 5322-5363;
e) J. M. Narayanam, C. R. Stephenson, Chem. Soc. Rev. 2011, 40, 102-
113; f) X. Lang, W. Ma, C. Chen, H. Ji, J. Zhao, Acc. Chem. Res. 2013,
47, 355-363; g) J. Liu, Q. Liu, H. Yi, C. Qin, R. Bai, X. Qi, Y. Lan, A. Lei,
Angew. Chem. 2014, 126, 512-516; h) M. Neumann, S. Füldner, B. König,
K. Zeitler, Angew. Chem. Int. Ed. 2011, 50, 951-954.
[2]
[3]
Y. Tachibana, L. Vayssieres, J. R. Durrant, Nat. Photonics 2012, 6, 511.
J. Low, J. Yu, M. Jaroniec, S. Wageh, A. A. Al-Ghamdi, Adv. Mater. 2017,
29, 1601694.
[4]
[5]
[6]
a) M. Wang, K. Han, S. Zhang, L. Sun, Coord. Chem. Rev. 2015, 287, 1-
14; b) M. Yamamoto, L. Wang, F. Li, T. Fukushima, K. Tanaka, L. Sun,
H. Imahori, Chem. Sci. 2016, 7, 1430-1439; c) M. F. Kuehnel, K. L.
Orchard, K. E. Dalle, E. Reisner, J. Am. Chem. Soc. 2017.
a) X. Wang, K. Maeda, A. Thomas, K. Takanabe, G. Xin, J. M. Carlsson,
K. Domen, M. Antonietti, Nat. Mater. 2009, 8, 76-80; b) S. Guo, Z. Deng,
M. Li, B. Jiang, C. Tian, Q. Pan, H. Fu, Angew. Chem. Int. Ed. 2016, 55,
1830-1834.
a) K. Maeda, X. Wang, Y. Nishihara, D. Lu, M. Antonietti, K. Domen, J.
Phys. Chem. C 2009, 113, 4940-4947; b) X.-H. Li, M. Antonietti, Chem.
Soc. Rev. 2013, 42, 6593-6604.
[7]
[8]
[9]
Y. Zhang, T. Mori, J. Ye, M. Antonietti, J. Am. Chem. Soc. 2010, 132,
6294-6295.
J. Zhang, X. Chen, K. Takanabe, K. Maeda, K. Domen, J. D. Epping, X.
Fu, M. Antonietti, X. Wang, Angew. Chem. Int. Ed. 2010, 49, 441-444.
Y. Hou, A. B. Laursen, J. Zhang, G. Zhang, Y. Zhu, X. Wang, S. Dahl, I.
Chorkendorff, Angew. Chem. Int. Ed. 2013, 52, 3621-3625.
[10] a) J.-S. Wu, S.-W. Cheng, Y.-J. Cheng, C.-S. Hsu, Chem. Soc. Rev.
2015, 44, 1113-1154; b) N. Chaoui, M. Trunk, R. Dawson, J. Schmidt, A.
Thomas, Chem. Soc. Rev. 2017, 46, 3302-3321.
Figure 4. Scope of substrates for photocatalytic synthesis of benzophosphole
oxides using asy-CTF as a photocatalyst.
[11] a) K. Schwinghammer, M. B. Mesch, V. Duppel, C. Ziegler, J. r. Senker,
B. V. Lotsch, J. Am. Chem. Soc. 2014, 136, 1730-1733; b) C. Yang, B.
C. Ma, L. Zhang, S. Lin, S. Ghasimi, K. Landfester, K. A. Zhang, X. Wang,
Angew. Chem. Int. Ed. 2016, 55, 9202-9206; c) R. S. Sprick, J.-X. Jiang,
B. Bonillo, S. Ren, T. Ratvijitvech, P. Guiglion, M. A. Zwijnenburg, D. J.
Adams, A. I. Cooper, J. Am. Chem. Soc. 2015, 137, 3265-3270; d) L. Li,
Z. Cai, Q. Wu, W.-Y. Lo, N. Zhang, L. X. Chen, L. Yu, J. Am. Chem. Soc.
2016, 138, 7681-7686; e) L. Wang, R. Fernández-Terán, L. Zhang, D. L.
A. Fernandes, L. Tian, H. Chen, H. Tian, Angew. Chem. 2016, 128,
12494-12498; f) P. B. Pati, G. Damas, L. Tian, D. L. A. Fernandes, L.
Zhang, I. B. Pehlivan, T. Edvinsson, C. M. Araujo, H. Tian, Energy
Environ. Sci. 2017, 10, 1372-1376.
In summary, a simple structural design of asymmetric
covalent triazine framework as an efficient visible light-active
photocatalyst for photoredox reactions has been introduced. By
incorporating the asymmetric building block, four different
molecular donor-acceptor domains were obtained within the
backbone structure. The asymmetric donor-acceptor structure led
to enhanced photogenerated charge separation, intramolecular
electron transfer and sufficient photoredox potential. The
asymmetric CTF demonstrated its superior photocatalytic
efficiency compared to the symmetric CTFs containing similar
donor and acceptor moieties, proven by the photocatalytic
[12] a) Z. J. Wang, S. Ghasimi, K. Landfester, K. A. Zhang, Chem. Commun.
2014, 50, 8177-8180; b) Y. Chen, J. Zhang, M. Zhang, X. Wang, Chem.
Sci. 2013, 4, 3244-3248; c) C. Su, R. Tandiana, B. Tian, A. Sengupta, W.
Tang, J. Su, K. P. Loh, ACS Cat. 2016, 6, 3594-3599.
formation
reaction
of
benzophosphole
oxides
from
[13] Z. J. Wang, S. Ghasimi, K. Landfester, K. A. Zhang, Chem. Mater. 2015,
27, 1921-1924.
diphenylphosphine oxide and diphenylacetylene derivatives. We
believe that this study could establish a simple but new design
strategy of organic semiconductor photocatalysts for a broader
range of applications such as water splitting and CO2 reduction
etc.
[14] a) R. Marschall, Adv. Funct. Mater. 2014, 24, 2421-2440; b) H. Kisch,
Angew. Chem. Int. Ed. 2013, 52, 812-847.
[15] Z. J. Wang, S. Ghasimi, K. Landfester, K. A. Zhang, Adv. Mater. 2015,
27, 6265-6270.
[16] J. Chen, C. L. Dong, D. Zhao, Y. C. Huang, X. Wang, L. Samad, L. Dang,
M. Shearer, S. Shen, L. Guo, Adv. Mater. 2017.
[17] a) S. Melissen, T. Le Bahers, S. N. Steinmann, P. Sautet, J. Phys. Chem.
C 2015, 119, 25188-25196; b) J. Chen, C. L. Dong, D. Zhao, Y. C. Huang,
X. Wang, L. Samad, L. Dang, M. Shearer, S. Shen, L. Guo, Adv. Mater.
2017, 29.
Acknowledgements
The authors thank the Max Planck Society for financial support.
J.B. thanks the Alexander von Humboldt Foundation for the
postdoctoral research fellowship. W. H. thanks the China
Scholarship Council (CSC) for the fellowship.
[18] a) S. Ren, M. J. Bojdys, R. Dawson, A. Laybourn, Y. Z. Khimyak, D. J.
Adams, A. I. Cooper, Adv. Mater. 2012, 24, 2357-2361; b) J. Bi, W. Fang,
L. Li, J. Wang, S. Liang, Y. He, M. Liu, L. Wu, Macromol. Rapid Commun.
2015, 36, 1799-1805; c) W. Huang, Z. J. Wang, B. C. Ma, S. Ghasimi, D.
Gehrig, F. Laquai, K. Landfester, K. A. Zhang, J. Mater. Chem. A 2016,
4, 7555-7559.
Keywords: Asymmetric organic semiconductor • Photocatalysis
• Covalent triazine framework • Donor acceptor • Metal-free
[19] M. J. Bojdys, J. Jeromenok, A. Thomas, M. Antonietti, Adv. Mater. 2010,
22, 2202-2205.
[20] H. Sun, G. Zhou, S. Liu, H. M. Ang, M. O. Tadé, S. Wang, Chem. Eng. J.
2013, 231, 18-25.
[1]
a) M. Oelgemöller, C. Jung, J. Mattay, Pure Appl. Chem. 2007, 79, 1939-
1947; b) N. Hoffmann, Chem. Rev. 2008, 108, 1052-1103; c) N. A.
This article is protected by copyright. All rights reserved.

10.1002/anie.201801112
Angewandte Chemie International Edition
COMMUNICATION
[21] J. Snellenburg, S. Laptenok, R. Seger, K. Mullen, I. Van Stokkum, J. Stat.
Softw. 2012, 49, 1-22.
[22] a) T. Baumgartner, Acc. Chem. Res. 2014, 47, 1613-1622; b) N. M.-W.
Wu, M. Ng, W. H. Lam, H.-L. Wong, V. W.-W. Yam, J. Am. Chem. Soc.
2017, 139, 15142-15150.
[23] a) Y.-R. Chen, W.-L. Duan, J. Am. Chem. Soc. 2013, 135, 16754-16757;
b) Y. Unoh, K. Hirano, T. Satoh, M. Miura, Angew. Chem. Int. Ed. 2013,
52, 12975-12979; c) P. Zhang, Y. Gao, L. Zhang, Z. Li, Y. Liu, G. Tang,
Y. Zhao, Adv. Synth. Cat. 2016, 358, 138-142.
[24] V. Quint, F. Morlet-Savary, J.-F. o. Lohier, J. Lalevꢀe, A.-C. Gaumont, S.
Lakhdar, J. Am. Chem. Soc. 2016, 138, 7436-7441.
[25] C. Jenkins, D. Murphy, C. Rowlands, T. Egerton, J. Chem. Soc., Perkin
Trans. 2 1997, 2479-2486.
[26] a) F. Morlet‐Savary, J. E. Klee, F. Pfefferkorn, J. P. Fouassier, J.
Lalevée, Macromol. Chem. Phys. 2015, 216, 2161-2170; b) J. Lalevꢀe,
F. Morlet-Savary, M. A. Tehfe, B. Graff, J. P. Fouassier, Macromolecules
2012, 45, 5032-5039.
[27] U. Wille, Chem. Rev. 2013, 113, 813-853.
[28] Z.-M. Chen, X.-M. Zhang, Y.-Q. Tu, Chem. Soc. Rev. 2015, 44, 5220-
5245.
This article is protected by copyright. All rights reserved.

10.1002/anie.201801112
Angewandte Chemie International Edition
COMMUNICATION
Entry for the Table of Contents (Please choose one layout)
Layout 1:
COMMUNICATION
The molecular design of an
asymmetric covalent triazine
framework as efficient single
component semiconductor
photocatalyst is presented. Enhanced
photocatalytic efficiency can be
achieved via light-induced multiple
intramolecular energy transfer
cascade.
W. Huang, J. Byun, I. Rörich, C.
Ramanan, P. W. M. Blom, H. Lu, D.
Wang, L. Caire da Silva, R. Li, L. Wang,
K. Landfester, K. A. I. Zhang*
Page No. – Page No.
Asymmetric Covalent Triazine
Framework for Enhanced Visible
Light Photoredox Catalysis via
Energy Transfer Cascade
Asymmetric Covalent Triazine Framework
Layout 2:
COMMUNICATION
Author(s), Corresponding Author(s)*
((Insert TOC Graphic here))
Page No. – Page No.
Title
Text for Table of Contents
This article is protected by copyright. All rights reserved.