Photostimulus-Responsive Large-Area Two-Dimensional Covalent Organic Framework Films

Article abstract of DOI:10.1002/anie.201909613

Using an external stimulus to modulate the electronic structure of covalent organic frameworks (COFs) is very important because such a response will endow them with additional functions. A two-dimensional (2D) COF, constructed from a photo-responsive unit (1,2-bis(5-formyl-2-methylthien-3-yl)cyclopentene), can reversibly switch its electrical conductivity 200 times from low state (the open form) to high state (the closed form) upon irradiation with UV light and reversible with visible light. This reversible phenomenon can be monitored through a circuit containing a light-emitting diode (LED). Photoinduced ring-closing/opening reactions do not destroy the integrity of the frameworks, and both processes follow logarithmic carrier generation with time. Moreover, the correlation between COFs electronic properties and changes in photoinduced kinetics and absorption curves has been demonstrated.

Full text of DOI:10.1002/anie.201909613

Angewandte
Communications
Chemie
International Edition: DOI: 10.1002/anie.201909613
German Edition: DOI: 10.1002/ange.201909613
Covalent Organic Frameworks
Photostimulus-Responsive Large-Area Two-Dimensional Covalent
Organic Framework Films
Fei Yu, Wenbo Liu, Bang Li, Dan Tian, Jing-Lin Zuo,* and Qichun Zhang*
Dedicated to Professor Yunqi Liu, Professor Yongfang Li, and Professor Yuliang Li on the occasion of their 70th birthday
Abstract: Using an external stimulus to modulate the electronic
structure of covalent organic frameworks (COFs) is very
important because such a response will endow them with
additional functions. A two-dimensional (2D) COF, con-
structed from a photo-responsive unit (1,2-bis(5-formyl-2-
methylthien-3-yl)cyclopentene), can reversibly switch its elec-
trical conductivity 200 times from low state (the open form) to
high state (the closed form) upon irradiation with UV light and
reversible with visible light. This reversible phenomenon can
be monitored through a circuit containing a light-emitting
diode (LED). Photoinduced ring-closing/opening reactions do
not destroy the integrity of the frameworks, and both processes
follow logarithmic carrier generation with time. Moreover, the
correlation between COFs electronic properties and changes in
photoinduced kinetics and absorption curves has been dem-
onstrated.
a useful strategy to integrate optical switching, photocatalysis,
[
14]
and evolving memory into one system, the corresponding
phenomena have not been demonstrated in COFs. This gap
strongly encourages us to conduct our research in this
direction.
Herein, for first time, we introduce the concept of
electronic structure modulation into COFs through using
a switchable ligand displaying photoinduced isomerization
(Figure 1). Our results indicate that the photo-responsive
M
any p-conjugated small molecules have been employed
as building units to construct multifunctional covalent organic
framework (COFs) with well-ordered two-/three-dimensional
[
1]
(
2D or 3D) structures. These molecules can be aromatic
Figure 1. Visualization of the on/off state with an LED owing to the
corresponding change in electrical conductivity.
[2]
[3]
[4]
hydrocarbons,
porphyrins,
phthalocyanines,
thio-
[5]
[6]
phenes, and diimides. The resulting COFs possess diverse
physical properties including photoluminescence, high car-
rier mobility in field-effect transistors (FETs), electrocon-
[
7]
[
8]
units in 2D COFs result in tunable electronic properties,
associating with the changes of the conductivity as a function
of the excitation energy. Note that, such switchable electronic
characteristic has little effect on the integrity of the frame-
work. Furthermore, the modulation of electronic structures of
COFs is visualized by the on/off of a light-emitting diode
(LED) owing to the corresponding variation in electrical
conductivity (Figure 1).
[
2a,b,7a,9]
[7b,10]
ductivity,
photoconductivity,
magnetic proper-
[
11]
[12]
ties, and energy storage. However, using external-stim-
ulus-responsive molecules (for example, the dithienylethene
[13]
moiety ) to build external-stimulus-active COFs has rarely
been explored. Such COFs are very important because they
would bring new functions and novel applications such as
switchable devices, sensors, and biosystems. Although using
photons to modulate the electronic structures of metal–
organic frameworks or polymers has been demonstrated to be
The dithienylethene ligand (1,2-bis(5-formyl-2-methyl-
thien-3-yl)cyclopentene, named as DAE-O, O represents
open state), was synthesized (Figure 2) with slight modifica-
[
15]
tion of the reported method.
The COF thin film was
[
*] Dr. F. Yu, W. Liu, Dr. D. Tian, Prof. Dr. Q. Zhang
School of Materials Science and Engineering
Nanyang Technological University
synthesized in a 100 mL beaker. Briefly, 0.075 mmol (23.7 mg)
of DAE-O was dissolved in 40 mL of CHCl as the bottom
3
Singapore 639798 (Singapore)
E-mail: qczhang@ntu.edu.sg
layer. 0.05 mmol (14.5 mg) of tris(4-aminophenyl)amine
(
TAPA) and 0.15 mmol (28.5 mg) TsOH·H O were dissolved
2
Dr. F. Yu, B. Li, Prof. Dr. J. L. Zuo
in 40 mL of H O and CH CN (v:v = 2:1). The water retains
2
3
State Key Laboratory of Coordination Chemistry, School of Chemistry
and Chemical Engineering, Collaborative Innovation Center of
Advanced Microstructures, Nanjing University
Nanjing, 210023 (China)
the immiscibility of the solvents at the interface during the
film formation while the CH CN helps to increase the
3
solubility of TAPA. The latter solution was then gently
poured onto the surface of chloroform solution over
E-mail: zuojl@nju.edu.cn
2
0 minutes. The as-prepared solution was kept unstirred in
Supporting information and the ORCID identification number(s) for
the author(s) of this article can be found under:
https://doi.org/10.1002/anie.201909613.
the dark at room temperature for 3 days. The targeted COF
films formed at the interface of the two different solutions and
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observed at about 2.8, 5.2, 7.4, and 14.5 (2q), which are
consistent with the patterns of the simulated structure (Fig-
ure 3a). Furthermore, Pawley refinement was used for
analyzing the unit cell (Space group: P1; a = 6.6 and 6.3 ꢀ,
b = 36.1 and 33.7 ꢀ, c = 36.7 and 37.2 ꢀ, a = 64.1 and 63.68,
b = 90.1 and 87.38, g = 88.2 and 88.58 for COF-O and COF-C,
respectively; Figure 3a; Supporting Information, Table S1).
The slight shrinking of the b-axis of the ring-closed hexa-
triene-type structure of dithienylethene indicates the forma-
tion of new CꢀC bonds. The topography of COF-O films was
investigated by microscopy (Supporting Information, Fig-
ure S1). These films exhibited homogeneous topography,
large area, and clean surface. The thickness of COF-O film
was measured to be 0.6 mm by SEM. HRTEM of the thin film
gives clear ordered lines with 6.6 and 6.3 ꢀ distances referring
to the stacking of the COF-O and COF-C layers, which could
provide indirect evidence to confirm the uniformity of the
COFs films (Supporting Information, Figure S2). FTIR
measurement showed the complete disappearance of the
Figure 2. a) Synthetic route to COF-O and COF-C. Simulated struc-
tures: Top and side views of b) COF-O and c) COF-C. (N blue, C gray,
S yellow).
ꢀ1
n(NꢀH) in the range 3406–3000 cm for TAPA and n(C=O)
ꢀ1
of 1654 cm for DAE-O, and the appearance of a new band
ꢀ
1
were collected and washed with H O, N,N-dimethylforma-
at 1600 cm assigned to n(C=N) for COF-O (Supporting
Information, Figure S3). Thermogravimetric analysis (TGA)
showed that the decomposition temperature of COF-O and
COF-C are 400 and 4158C, respectively (Supporting Infor-
mation, Figure S4), suggesting that the close form has a high
stability because the closed state makes the 2D COFs possess
large conjugation in-plane and high p···p interactions vertical
to the plane.
2
mide (DMF), and CH CN, then dried. The yield of the as-
3
obtained COF-O is 5.7 mg (15%), which is variable depend-
ing on the diameter of the beaker as well as the concen-
trations of the starting materials.
Powder X-ray diffraction (PXRD) was conducted on the
as-fabricated films of the COF-O and its UV-irradiation-
induced structure COF-C (C represents the close state,
Figure 3a). Note that there is little difference between the
PXRD patterns of COF-O and COF-C. Several distinct
characteristic peaks in the PXRD pattern of COF-O are
Solid-state UV/Vis spectrum of COF-O exhibits two
absorption bands at 292 and 374 nm, which can be assigned to
the n!p* and p!p* transitions of dithienylethene moiety
(Figure 3b), respectively. Upon irradiation with 365 nm UV
light, the photocyclization reaction promotes the p-conjuga-
tion of cyclohexadiene moiety, resulting in the reduced
[
13d–g]
strength of absorption bands at 292 and 374 nm.
At the
same time, the intensity of the absorption band at 640 nm
increases, indicating the formation of the closed state of
cyclohexadiene moiety. Such photocyclization was further
monitored by time-dependent electron absorption spectros-
copy. When COF-C was irradiated with visible light
(> 550 nm), the reversed phenomenon was observed. The
plots of absorbance at 640 nm versus time gave straight lines
ꢀ
3
ꢀ3
ꢀ1
with the slopes of 5.1 ꢁ 10 and 4.2 ꢁ 10 min for the UV
and visible light irradiation, respectively. All of these spectral
changes indicate that under UV irradiation, the open-ring
state of COF-O can transform into the close-ring state of
COF-C, while visible light excitation reverses the process
(Figure 3b; Supporting Information, Figure S5). Cyclic
experiments were carried out under alternate irradiation of
ultraviolet and visible light by monitoring the absorption
changing tendency at 640 nm, which showed that the struc-
tural transformation between open and closed states of COFs
having good cyclability (Supporting Information, Figure S6).
In COF-O and COF-C, the building units creates one-
dimensional (1D) channels along the a-axis, wherein the walls
can serve as an interface for gas adsorption. The walls of the
COF-C are slightly different from those of COF-O owing to
the photocyclization of the dithienylethene moiety. The
Figure 3. a) PXRD patterns of COF-O and COF-C: Observed (blue
line), Pawley refinement (red cross), difference (purple line), eclipsed
AA simulation (green line); b) Solid-state absorption spectrum diversi-
fication of COF-O film upon irradiation at 365 nm and COF-C film
upon irradiation >550 nm (inset: time-dependent profile); c) N2
sorption isotherm of COF-O (blue) and COF-C (red); d) pore size
distribution (PSD) of COF-O. e) Pore size distribution (PSD) of COF-
O.
2
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photoinduced structural transformation is accompanied by
example due to its different known photoinduced switching
the changes in the capacity of gas storage as revealed by
mechanism. Since the formation of covalent bonds between
methylthiophene units occurs in one plane, the dithienyle-
thene derivatives are capable of realizing photoinduced
conversion in the solid state (Figure 2 and Figure 4a).
The photoinduced switching from open to closed state results
isotherm measurements of N sorption at 77 K. Both COF-O
2
and COF-C showed reversible sorption curves. The Bruna-
2
ꢀ1
[13a–g]
uer–Emmett–Teller (BET) surface areas were 477 m g for
2
ꢀ1
COF-O and 330 m g for COF-C; and the pore volumes
3
ꢀ1
were 0.33 and 0.25 cm g , respectively (Figure 3c). Nonlocal
density functional theory (NLDFT) was used for the calcu-
lation of pore size distribution (PSD), and the results showed
that both COF-O and COF-C consist of one type of micro-
pore with the sizes of 1.5 nm and 1.4 nm, respectively
in higher molecular conductance due to the p-conjugation
[
13b–e,16,17]
extension.
The main challenge is to transform the
changes in molecular levels into the overall properties of this
material with the retention of the skeleton.
Specifically, the possible correlation between the photo-
induced conversion process and the electrical conductivity
(Figures 1 and Figure 4) was investigated. The original
electrical conductivity of the COF-O film was examined as
a control experiment. Then, the open-to-closed conversion
induces an increase of electrical conductivity from (1 ꢁ 0.25) ꢁ
(
Figure 3d,e).
To correlate the electronic distribution of COFs with the
changes in photoinduced kinetics of photo-switching units, an
[
13b,d,e,16]
electrical circuit was constructed
(Figure 1 and Fig-
ure 4a). Here, a dithienylethene core is selected as an
ꢀ
7
ꢀ1
ꢀ5
ꢀ1
1
0
Scm to (2 ꢁ 0.23) ꢁ 10 Scm , which is a circa 200-
fold increment after irradiation for 6 min at room temper-
ature (Figure 4a). The resistance of samples of different
thicknesses (from 20 nm to 600 nm) has no major difference
(
Supporting Information, Figure S7). Density functional
theory (DFT) calculations showed a decreased band gap
from 1.606 eV for COF-O to 0.543 eV for COF-C) owing to
the transformation of dithienylethene moiety from the open
(
[
18]
to closed state (Figure 4b,c). A transistor amplifier circuit
with an LED was built to visualize the conductivity changes in
COFs under light illumination (Figure 4a; Supporting Infor-
mation, Figure S8). In a common emitter circuit, the COFs
material acted as a resistor (R in the Supporting Information,
2
Figure S8), and the LED is connected to the collector. As we
expected, the LED was illuminated upon the irradiation of
UV light (365 nm), while the irradiation with visible light
(> 550 nm) resulted in the switching-off of the LED. This
result clearly indicates that the open and closed states of
COFs could interconvert upon different light irradiation
without COFs decomposition (Figure 4a).
In conclusion, we have demonstrated that dithienyle-
thene-based COFs can experience photoinduced transforma-
tions without structural destruction; namely, UV light can
switch ON the electrical conductivity while visible light
switches it OFF because the extended p-conjugation through
photocyclization reaction can result in an enhanced conduc-
tivity. This correlation between photophysical variations and
conductivity changes in this crystalline material is explained
by band structure calculations. Furthermore, an electric
circuit with LED-switching performance as a function of
irradiation light is constructed to visualize the conductivity
transformations of the COF films. Our results clearly provide
a novel way to modulate the properties of COF materials by
introducing new external stimulus-responsive building units.
Acknowledgements
Q.Z. acknowledges financial support from AcRF Tier 1 (RG
1
2
11/17, RG 2/17, RG 114/16, RG 113/18) and Tier 2 (MOE
017-T2-1–021 and MOE 2018-T2-1–070), Singapore. As well
Figure 4. a) Changes in the conductivity of COFs illuminated by an
LED. b),c) Band structures and density of states for b) COF-O and
c) COF-C.
as funding support from State Key Laboratory of Supra-
molecular Structure and Materials, Jilin University, P. R.
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China (sklssm2019036). This work was also supported by the
National Basic Research Program of China
2018YFA0306004), the National Natural Science Foundation
of China (No. 21631006, 21875099, and 21601086), and the
Natural Science Foundation of Jiangsu Province
Commun. 2015, 51, 13894 – 13897; b) B. Sun, J. Li, W.-L. Dong,
M.-L. Wu, D. Wang, J. Phys. Chem. C 2016, 120, 14706 – 14711;
c) B. Sun, C.-H. Zhu, Y. Liu, C. Wang, L.-J. Wan, D. Wang,
Chem. Mater. 2017, 29, 4367 – 4374; d) H. Wang, Z. Zeng, P. Xu,
L. Li, G. Zeng, R. Xiao, Z. Tang, D. Huang, L. Tang, C. Lai, D.
Jiang, Y. Liu, H. Yi, L. Qin, S. Ye, X. Ren, W. Tang, Chem. Soc.
Rev. 2019, 48, 488 – 516.
(
(
BK20160994).
[
9] a) X. Ding, L. Chen, Y. Honsho, X. Feng, O. Saengsawang, J.
Guo, A. Saeki, S. Seki, S. Irle, S. Nagase, V. Parasuk, D. Jiang, J.
Am. Chem. Soc. 2011, 133, 14510 – 14513; b) S. Jin, T. Sakurai, T.
Kowalczyk, S. Dalapati, F. Xu, H. Wei, X. Chen, J. Gao, S. Seki,
S. Irle, D. Jiang, Chem. Eur. J. 2014, 20, 14608 – 14613; c) N.
Huang, L. Zhai, D. E. Coupry, M. A. Addicoat, K. Okushita, K.
Nishimura, T. Heine, D. Jiang, Nat. Commun. 2016, 7, 12325.
Conflict of interest
The authors declare no conflict of interest.
Keywords: covalent organic frameworks · electrical switching ·
external stimuli · photostimulus
[10] a) L. Chen, L. Wang, X. Gao, S. Nagase, Y. Honsho, A. Saeki, S.
Seki, D. Jiang, Chem. Commun. 2009, 3119 – 3121; b) D. D.
Medina, T. Sick, T. Bein, Adv. Energy Mater. 2017, 7, 1700387.
[
11] S. Wu, M. Li, H. Phan, D. Wang, T. S. Herng, J. Ding, Z. Lu, J.
Wu, Angew. Chem. Int. Ed. 2018, 57, 8007 – 8011; Angew. Chem.
2
018, 130, 8139 – 8143.
12] X. Zhan, Z. Chen, Q. Zhang, J. Mater. Chem. A 2017, 5, 14463 –
4479.
13] a) J. Park, D. Feng, S. Yuan, H. C. Zhou, Angew. Chem. Int. Ed.
015, 54, 430 – 435; Angew. Chem. 2015, 127, 440 – 445; b) E. A.
[
[
[
1] a) A. P. Cꢂtꢃ, A. I. Benin, N. W. Ockwig, M. OꢄKeeffe, A. J.
Matzger, O. M. Yaghi, Science 2005, 310, 1166 – 1170; b) H. M.
El-Kaderi, J. R. Hunt, J. L. Mendoza-Cortꢃs, A. P. Cꢂtꢃ, R. E.
Taylor, M. OꢄKeeffe, O. M. Yaghi, Science 2007, 316, 268 – 272;
c) N. Huang, P. Wang, D. Jiang, Nat. Rev. Mater. 2016, 1, 16068.
2] a) E. Jin, M. Asada, Q. Xu, S. Dalapati, M. A. Addicoat, M. A.
Brady, H. Xu, T. Nakamura, T. Heine, Q. Chen, D. Jiang, Science
1
2
Dolgopolova, V. A. Galitskiy, C. R. Martin, H. N. Gregory, B. J.
Yarbrough, A. M. Rice, A. A. Berseneva, O. A. Ejegbavwo,
K. S. Stephenson, P. Kittikhunnatham, S. G. Karakalos, M. D.
Smith, A. B. Greytak, S. Garashchuk, N. B. Shustova, J. Am.
Chem. Soc. 2019, 141, 5350 – 5358; c) F. Meng, Y. M. Hervault,
Q. Shao, B. Hu, L. Norel, S. Rigaut, X. Chen, Nat. Commun.
[
2
017, 357, 673 – 676; b) S. Dalapati, M. Addicoat, S. Jin, T.
Sakurai, J. Gao, H. Xu, S. Irle, S. Seki, D. Jiang, Nat. Commun.
015, 6, 7786; c) E. Jin, J. Li, K. Geng, Q. Jiang, H. Xu, Q. Xu, D.
2
2
2
1
2
014, 5, 3023; d) T. Kawai, Y. Nakashima, M. Irie, Adv. Mater.
005, 17, 309 – 314; e) E. Kim, H. W. Lee, J. Mater. Chem. 2006,
6, 1384 – 1389; f) Q. Luo, H. Cheng, H. Tian, Polym. Chem.
011, 2, 2435 – 2443; g) S.-L. Huang, T. S. A. Hor, G.-X. Jin,
Jiang, Nat. Commun. 2018, 9, 4143.
3] a) L. Chen, Y. Yang, D. Jiang, J. Am. Chem. Soc. 2010, 132,
[
9
138 – 9143; b) X. Feng, L. Liu, Y. Honsho, A. Saeki, S. Seki, S.
Irle, Y. Dong, A. Nagai, D. Jiang, Angew. Chem. Int. Ed. 2012,
1, 2618 – 2622; Angew. Chem. 2012, 124, 2672 – 2676; c) S.
Coord. Chem. Rev. 2017, 346, 112 – 122; h) Y. Jiang, J. Park, P.
Tan, L. Feng, X. Q. Liu, L. B. Sun, H. C. Zhou, J. Am. Chem. Soc.
2
5
Kandambeth, D. B. Shinde, M. K. Panda, B. Lukose, T. Heine, R.
Banerjee, Angew. Chem. Int. Ed. 2013, 52, 13052 – 13056; Angew.
Chem. 2013, 125, 13290 – 13294.
019, 141, 8221 – 8227.
[
14] a) I. Stassen, N. Burtch, A. Talin, P. Falcaro, M. Allendorf, R.
Ameloot, Chem. Soc. Rev. 2017, 46, 3185 – 3241; b) A. Kirchon,
L. Feng, H. F. Drake, E. A. Joseph, H. C. Zhou, Chem. Soc. Rev.
[
4] a) L. Chen, K. Furukawa, J. Gao, A. Nagai, T. Nakamura, Y.
Dong, D. Jiang, J. Am. Chem. Soc. 2014, 136, 9806 – 9809; b) S.
Jin, X. Ding, X. Feng, M. Supur, K. Furukawa, S. Takahashi, M.
Addicoat, M. E. El-Khouly, T. Nakamura, S. Irle, S. Fukuzumi,
A. Nagai, D. Jiang, Angew. Chem. Int. Ed. 2013, 52, 2017 – 2021;
Angew. Chem. 2013, 125, 2071 – 2075.
5] G. H. Bertrand, V. K. Michaelis, T. C. Ong, R. G. Griffin, M.
Dinca, Proc. Natl. Acad. Sci. USA 2013, 110, 4923 – 4928.
6] a) S. Jin, M. Supur, M. Addicoat, K. Furukawa, L. Chen, T.
Nakamura, S. Fukuzumi, S. Irle, D. Jiang, J. Am. Chem. Soc.
2
018, 47, 8611 – 8638.
[
15] a) L. N. Lucas, J. J. D. de Jong, J. H. van Esch, R. M. Kellogg,
B. L. Feringa, Eur. J. Org. Chem. 2003, 155 – 166; b) Z. Zhou, Y.
Chang, S. Shimizu, J. Mack, C. Schutt, R. Herges, Z. Shen, N.
Kobayashi, Angew. Chem. Int. Ed. 2014, 53, 6563 – 6567; Angew.
Chem. 2014, 126, 6681 – 6685; c) H. Dong, M. Luo, S. Wang, X.
Ma, Dyes Pigm. 2017, 139, 118 – 128.
16] T. Kudernac, N. Katsonis, W. R. Browne, B. L. Feringa, J. Mater.
Chem. 2009, 19, 7168 – 7177.
17] M. Irie, T. Fukaminato, K. Matsuda, S. Kobatake, Chem. Rev.
[
[
[
[
[
2015, 137, 7817 – 7827; b) F. Xu, S. Jin, H. Zhong, D. Wu, X.
Yang, X. Chen, H. Wei, R. Fu, D. Jiang, Sci. Rep. 2015, 5, 8225.
7] a) S. Wan, J. Guo, J. Kim, H. Ihee, D. Jiang, Angew. Chem. Int.
Ed. 2008, 47, 8826 – 8830; Angew. Chem. 2008, 120, 8958 – 8962;
b) S. Wan, J. Guo, J. Kim, H. Ihee, D. Jiang, Angew. Chem. Int.
Ed. 2009, 48, 5439 – 5442; Angew. Chem. 2009, 121, 5547 – 5550;
c) Y. Xu, L. Chen, Z. Guo, A. Nagai, D. Jiang, J. Am. Chem. Soc.
2
014, 114, 12174 – 12277.
18] a) F. Yu, M. Kurmoo, G.-L. Zhuang, J.-L. Zuo, Chem. Sci. 2018,
, 7498 – 7504; b) F. Yu, J. Li, Z.-H. Cao, M. Kurmoo, J.-L. Zuo,
Inorg. Chem. 2018, 57, 3443 – 3450.
[
9
2011, 133, 17622 – 17625; d) S. Dalapati, E. Jin, M. Addicoat, T.
Manuscript received: July 30, 2019
Heine, D. Jiang, J. Am. Chem. Soc. 2016, 138, 5797 – 5800.
8] a) J. I. Feldblyum, C. H. McCreery, S. C. Andrews, T. Kurosawa,
E. J. Santos, V. Duong, L. Fang, A. L. Ayzner, Z. Bao, Chem.
Revised manuscript received: August 21, 2019
Accepted manuscript online: September 4, 2019
Version of record online: && &&, &&&&
[
4
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Covalent Organic Frameworks
Two-dimensional COFs that are photo-
stimulus-responsive exhibit a change of
electrical conductivity as a function of the
photon energy. The modulation of elec-
tronic structures of COFs, associated with
ring closing and opening, is visualized by
the on/off of a light-emitting diode (LED)
owing to the corresponding variation in
electrical conductivity.
F. Yu, W. Liu, B. Li, D. Tian, J. L. Zuo,*
Q. Zhang*
&&&& — &&&&
Photostimulus-Responsive Large-Area
Two-Dimensional Covalent Organic
Framework Films
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