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Title

Editing Light Emission with Stable Crystalline
Covalent Organic Frameworks via Wall Surface
Perturbation

Author(s)Li, Zhongping; Geng, Keyu; He, Ting; Tan, Ke Tian;
Huang, Ning; Jiang, Qiuhong; Nagao, Yuki; Jiang,
Donglin

Citation

Angewandte Chemie international edition, 60(35):19419-19427

Issue Date

2021-06-18

Type

Journal Article

Text version

author

URL

http://hdl.handle.net/10119/18091

RightsThis is the peer reviewed version of the following
article: Copyright (C) 2021 Wiley-VCH. Zhongping
Li, Keyu Geng, Ting He, Ke Tian Tan, Ning Huang,
Qiuhong Jiang, Yuki Nagao, Donglin Jiang,
Angewandte Chemie international edition, 60(35),2021, pp.19419-19427, which has been publishedin final form at https://10.1002/anie.202107179.
This article may be used for non-commercial
purposes in accordance with Wiley Terms andConditions for Use of Self-Archived Versions. This
article may not be enhanced, enriched or otherwisetransformed into a derivative work, without express
permission from Wiley or by statutory rights underapplicable legislation. Copyright notices must not
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prohibited.

Description

Japan Advanced Institute of Science and Technology

RESEARCH ARTICLE
Editing Light Emission with Stable Crystalline Covalent Organic
Frameworks via Wall Surface Perturbation
Zhongping Li,+ Keyu Geng,+ Ting He, Ke Tian Tan, Ning Huang, Qiuhong Jiang, Yuki Nagao, andDonglin Jiang*

[a]

[b]

[c]

[+]

Dr. Z. Li, [+] K. Geng,[+] Dr. T. He, K. T. Tan, Dr. N. Huang, Q. Jiang, Prof. Dr. D. Jiang*
Department of Chemistry, Faculty of Science, National University of Singapore
3 Science Drive 3, Singapore 117543, Singapore
E-mail: chmjd@nus.edu.sg
Dr. Z. Li, Prof. Dr. Y. Nagao
Area of Materials Chemistry, School of Materials Science
Japan Advanced Institute of Science and Technology
1-1 Asahidai, Nomi, Ishikawa 923-1292, Japan
Prof. Dr. D. Jiang*
Joint School of National University of Singapore and Tianjin University
International Campus of Tianjin University
Fuzhou 350207, China.
These authors contributed equally to this work.
Supporting information for this article is given via a link at the end of the document.

molecular length of the same π backbones.[3] In this work, weshow an approach to tunable light emission based on anorganic/polymeric system with a two-dimensional (2D) backbone.
Covalent organic frameworks (COFs) are a class of crystalline
porous polymers which enable the integration of chromophores
into well-defined 2D polygonal skeletons connected with different
linkages.[4-6] With the ordered chromophore structures, COFs
could construct light-emitting materials but their limited stability
and tunability have precluded implementation.[7] Herein, we report
COFs as a platform for editing light emission. This is based on ourconcept that surface groups on the pore wall can trigger distinct
electronic effects which can be transmitted to the polygonal
backbone so that the electronic structure of the whole framework
is controlled by the surface sites. Unexpectedly, we observed thatthe framework enables a drastic change in electronic structure toafford RGB emissions by a small perturbation of single surfacesite. Surprisingly, integrating multicomponent surface sites onto
the pore walls yields light-emitting materials and enables to edit
tailor-made emission colors. We emphasize that unlike quantum
dots which must change the particle size for a different emission,
COFs do not need to alter the backbone size but can edit different
colors via surface site perturbation in a predesignable and digitalway. The systems exhibited high luminescence activity, stability,
color tunability, and guest sensibility – a combination of features
highly desired for light-emitting and sensing implementations.
These results demonstrate a new regime for light emission.

Abstract: The ordered π skeletons of covalent organic frameworks
make them viable light-emitting materials but their limited tunability
has precluded further implementation. Here we report the synthesisof hydrazone-linked frameworks which are stable in water, acid, andbase, and demonstrate their utility as a platform for light emission. The
polygonal backbone is designed to be luminescent and partially π
conjugated while the pore wall is docked with single atom or unit toinduce resonance, hyperconjugation, and tautomerization effects.
These effects can be transmitted to the backbone, so that theframework can emit three primary colors of light. The wall can be
perturbated with multiple surface sites, rendering the material able toedit diverse emission colors in a predesignable and digital way. The
systems show high activity, stability, tunability, and sensibility – a setof features attractive for light-emitting and sensing applications.

Introduction
Light emission is necessary for daily life and has broad
applications in cutting-edge science and technology.[1] Red, green,
and blue (RGB) are three primary colors of light and constitute thebasis for organizing various lightening systems. Owing to a big
difference in band gap, RGB emissions are usually obtained withdifferent materials. If a material could systematically shift its band
gap to emit RGB lights upon structural perturbation, this would be
an ideal platform for designing light emission. However, exploringsuch a material is challenging as emission is determined byexcited and ground states which are associated with materials’
inherent electronic structures. An exceptional example is zerodimensional (0D) quantum dot which can trigger size confinement
effect, leading to size-dependent RGB emissions.[2] In contrast,
organic/polymeric materials hardly develop such a system as π
conjugation in polymers tends to saturate within a few repeating
units, precluding the possibility of RGB emissions by tuning

Results
Design principle. We selected COFs as the platform for lightemission as they enable the construction of extended polygonal
backbones with well-defined structures. The COF architecturedevelops ordered π backbones and orientated one-dimensional(1D) channels via π-π stacking.[5a, 5b] One distinct feature is that1

RESEARCH ARTICLE

Figure 1. a) Schematic of TMHzcB-TFB-COF. b) Schematic of TMHzcB-TFPB-COF. c) Schematics of hydrazone-linked light-emitting COFs perturbated withdifferent wall surface sites for editing light emission. d) Schematics of model compounds.

the 2D polygonal backbone can be easily engineered at molecularlevel to decorate different single atoms or units on pore walls. The
surface site can trigger different π electronic interplays andtransmits the effect to the backbone, offering a way to control theelectronic structure of the whole framework. These features pave
the chemical basis for editing light emission via simple wall
surface perturbation. Integrating intra- or inter-layer hydrogenbonding interactions could tune π distance, which however has alimited influence on the band gap and emission color.[8]Distinct from non- or fully-conjugated linkage, hydrazone isunique as it allows p–π conjugation between the partiallyconjugated aryl amide bond and lone pair of linked nitrogen site,
so that the knot and linker units are partially conjugated.[9] In thiscase, the surface site on the pore wall would have a chance toaffect the p–π conjugation of the polygonal backbone and change
its π electronic structure. We introduced single chlorine, methyl,
methoxy, and hydroxy sites onto the pore wall (Figure 1), which
are designed to trigger different interplays with the polygonal

backbonevia
resonance,
hyperconjugation,andphototautomerization effects. Dramatically, the polygonal
backbones with different surface atom or site can emit three
primary colors of light. More importantly, this strategy enables thewall surface perturbation with multiple atoms and sites to achieve
tailor-made emission colors in a predesignable and digital way
while retaining the same backbone.
Synthesis and characterization. We synthesized a set of newly
designed hydrazone-linked COFs (Figures 1a–c), bypolycondensationof
1,3,5-tris(3’-methoxy-4’hydrazinecarbonylphenyl)benzene (TMHzcB) as a knot with
1,3,5-triformylbenzene (TFB), 1,3,5-tris(4-formylphenyl) benzene(TFPB), terephthalaldehyde (TA), 2,5-dichloroterephthalaldehyde(DCTA),
2,5-dimethylterephthalaldehyde(DMeTA),2,5dimethoxyterephthalaldehyde(DMeOTA),or
2,5dihydroxyterephthalaldehyde (DHTA) as a linker undersolvothermal conditions (for details see Supporting Information,
Experimental Procedures). These reactions produce TMHzcB-

2

RESEARCH ARTICLE
TFB-COF (Figure 1a), TMHzcB-TFPB-COF (Figure 1b),
TMHzcB-TA-COF, TMHzcB-DCTA-COF, TMHzcB-DMeTA-COF,
TMHzcB-DMeOTA-COF, and TMHzcB-DHTA-COF (Figure 1c) in
87%, 89%, 85%, 90%, 92%, 93%, and 89% yield, respectively.
Among the series, TMHzcB-TFB-COF and TMHzcB-TFPB-COF
serve as controls with only one hydrazone linkage at each edge,
to see how the polygonal backbone itself affects light emission.
The TMHzcB-TA-COF, TMHzcB-DCTA-COF, TMHzcB-DMeTACOF, TMHzcB-DMeOTA-COF, and TMHzcB-DHTA-COF (Figure1c) possess two hydrazone linkages at each edge, and they are
identical in the polygonal backbone but have different wall surface
sites (R), i.e. hydrogen, chlorine, methyl, methoxy, and hydroxy,
respectively (Figure 1c). Moreover, five model compounds, i.e.
model compound-H, model compound-Cl, model compound-Me,model compound-OMe, and model compound-OH were used to
distinguish the knot and linker effects (Figure 1d).

25.71°, which were assigned to the (100), (110), (200), (210), and(001) facets (Figure 2a, black curve), respectively. On the other
hand, TMHzcB-TFPB-COF with a slightly bigger lattice displayed
PXRD peaks at 3.65°, 6.31°, 7.25°, 9.54°, and 25.43°, which wereassigned to the (100), (110), (200), (210), and (001) facets,
respectively (Figure 2d, black curve).
The TMHzcB-TA-COF (Figure 3a, black curve), TMHzcBDCTA-COF (Figure 3d, black curve), TMHzcB-DMeTA-COF(Figure 3g, black curve), TMHzcB-DMeOTA-COF (Figure 3j,
black curve), and TMHzcB-DHTA-COF (Figure 3m, black curve)
exhibited similar PXRD patterns to each other, to have peak setsof [2.34° (100), 4.08° (110), 6.42° (210), and 25.53° (001)], [2.36°(100), 4.09° (110), 4.74° (200), 6.26° (210), 8.40° (310), and26.02° (001)], [2.40° (100), 4.26° (110), 4.94° (200), 6.49° (210),
8.68° (310), and 26.24° (001)], [2.56° (100), 4.98° (110), 6.70°(210), 8.94° (310), and 26.76° (001)], and [2.38° (100), 4.90°(110), 8.26° (210), and 26.30° (001)], respectively. Pawley
refinements of these seven COFs (Figures 2a, 2d, 3a, 3d, 3g, 3j,
and 3m, green curves) confirmed the peak assignments asevidenced by negligible differences (Figures 2a, 2d, 3a, 3d, 3g, 3j,
and 3m, orange curves).
Structural simulations using density function tight binding(DFTB+) revealed that the AA stacking mode (for atomistic
coordinates see Supporting Information, Tables S2–S8)
reproduced the experimentally observed PXRD patterns (Figures
2a, 2d, 3a, 3d, 3g, 3j, and 3m, red curves). In contrast, the AB
stacking mode does not match the experimental results (Figures
2a, 2d, 3a, 3d, 3g, 3j, and 3m, blue curves). Therefore, these
COFs constituted extended 2D hexagonal lattices (Figures 2b, 2e,3b, 3e, 3h, 3k, and 3n), which further stack to form layer
frameworks (Figures 2c, 2f, 3c, 3f, 3i, 3l, and 3o). Moreover, the(001) facets at 25.43°–26.76° correspond to small interlayerintervals of 3.50–3.33 Å, suggesting that the surface sites aredense aligned on the pore wall. The well-defined organization of
surface sites is unique, which can hardly be achieved inconventional organic/polymeric materials.
Porosity. The TMHzcB-TFB-COF is microporous to exhibit typeI N2 sorption isotherm (Figure S4a) and possesses a Brunauer–
Emmett–Teller (BET) surface area of 471 m2 g–1 with a pore sizeof 1.6 nm and a pore volume of 0.23 cm3 g–1 (Figure S4b). The
TMHzcB-TFPB-COF has a BET surface area of 1116 m2 g–1, apore size of 2.1 nm, and a pore volume of 0.52 cm3 g–1 (Figures
4c and 4d). The TMHzcB-TA-COF (Figures 4e and 4f), TMHzcBDCTA-COF (Figures 4g and 4h), TMHzcB-DMeTA-COF (Figures
4i and 4j), TMHzcB-DMeOTA-COF (Figures 4k and 4l), andTMHzcB-DHTA-COF (Figures 4m and 4n) are mesoporous andexhibit a BET surface area of 470, 1082, 932, 799, and 342 m2 g–
1, respectively. Their pore sizes are 3.7, 3.7, 3.7, 3.2, and 3.6 nm,
while pore volumes are 0.26, 0.72, 0.56, 0.39, and 0.21 cm3 g–1,
respectively (Figure S4).
Stability. We investigated stability by dispersing COFs intetrahydrofuran (THF), water, hydrochloric acid (HCl, 1 M), andaqueous sodium hydroxide solution (NaOH, 1 M or 0.1 M),
respectively, at 25 °C for 24 h. These COFs retained PXRD peaks,
suggesting the robustness of the polygonal backbone (Figure S5).
Electronic abstraction features. We measured diffuse
reflectance Kubelka−Munk (K–M) spectra of COFs, building units
and model compounds in the solid state (Table 1, Figure S6, andTable S9) to reveal their electronic absorption features. Modelcompound-H, model compound-Cl, model compound-Me, modelcompound-OMe, and model compound-OH exhibited absorption

Figure 2. Crystal structures of blue light-emitting COFs. a) PXRD patterns ofexperimentally observed (black curve), Pawley refined (green curve) and theirdifference (orange curve), and simulated from the eclipsed AA-stacking mode
(red curve) and staggered AB-stacking mode (blue curve) of TMHzcB-TFB-COF.
b) Unit cell of TMHzcB-TFB-COF. c) Reconstructed 10 layers of TMHzcB-TFBCOF (seven pores are shown). d) PXRD patterns of experimentally observed(black curve), Pawley refined (green curve), and their difference (orange curve),and simulated from the eclipsed AA-stacking mode (red curve) and staggered
AB-stacking mode (blue curve) of TMHzcB-TFPB-COF. e) Unit cell of TMHzcBTFPB-COF. f) Reconstructed 10 layers of TMHzcB-TFPB-COF (seven poresare shown).

Fourier transform infrared (FT IR) spectroscopy revealed thestretching vibrations of the C=N bond in the hydrazone linkage at
1665–1686 cm–1, which are close to those of their corresponding
model compounds (Figure S1). Field emission scanning electron
microscopy showed polymeric morphologies (Figure S2).
Elemental analysis confirmed that the C, H, and N contents areclose to the theoretical values (Table S1). Thermogravimetricanalysis revealed that these COFs do not lose weight up to 300 °C
under N2 (Figure S3).
Crystal structures. The TMHzcB-TFB-COF exhibited powder Xray diffraction (PXRD) peaks at 4.78°, 8.32°, 9.56°, 12.71°, and3

RESEARCH ARTICLE

Figure 3. Crystal structures of surface-perturbated COFs for RGB emissions. (a, d, g, j, and m) PXRD patterns of experimentally observed (black curves), Pawley
refined (green curves) and their difference (orange curves), and simulated from the eclipsed AA-stacking mode (red curves) and staggered AB-stacking mode (bluecurves), of (a) TMHzcB-TA-COF, (d) TMHzcB-DCTA-COF, (g) TMHzcB-DMeTA-COF, (j) TMHzcB-DMeOTA-COF, and (m) TMHzcB-DHTA-COF, respectively. (b,e, h, k, and n) Unit cell of (b) TMHzcB-TA-COF, (e) TMHzcB-DCTA-COF, (h) TMHzcB-DMeTA-COF, (k) TMHzcB-DMeOTA-COF, and (n) TMHzcB-DHTA-COF,
respectively. (c, f, i, l, and o) Reconstructed 10 layers of (c) TMHzcB-TA-COF, (f) TMHzcB-DCTA-COF, (i) TMHzcB-DMeTA-COF, (l) TMHzcB-DMeOTA-COF, and(o) TMHzcB-DHTA-COF, respectively (seven pores are shown).

bands at 366, 364, 368, 367, and 370 nm, respectively (Figures
S6a–g, black curves, Table S9). The small difference suggeststhat the surface site has a limited effect on the model compounds.
The TMHzcB-TFB-COF (Table 1, Figure S6a, red curve) andTMHzcB-TFPB-COF (Table 1, Figure S6b, red curve) exhibitedabsorption bands at 380 and 390 nm, respectively, which areclearly redshifted from those of TMHzcB (blue curves, 327 nm),
TFB (green curves, 357 nm), and model compound-H (black
curves, 366 nm; Table S9). These redshifts suggest the extensionof conjugation in the polygonal backbone.
The TMHzcB-TA-COF with surface H atom exhibited anabsorption band at 387 nm (Table 1, Figure S6c, red curve). The
TMHzcB-DCTA-COF with surface Cl atom (Table 1, Figure S6d,
red curve) exhibited an adsorption band at 406 nm, which isgreatly redshifted by 42 nm from model compound-Cl and by 19
nm from TMHzcB-TA-COF. The Cl atom triggers inductive effectowing to its electronegativity which reduces the π density of p–π
conjugated edge while the lone pairs of Cl donate electrons to theedge to increase the π density. The progressed redshift reflectsthat the p–π conjugation in TMHzcB-DCTA-COF is extended by
the Cl atom. Thus, the resonance effect of Cl atom is predominant
in the framework (Figure 4a).

The TMHzcB-DMeTA-COF with methyl surface site exhibitedan absorption band at 414 nm (Table 1, Figure 6e, red curve),
which is redshifted by 46 and 8 nm from model compound-Me and
TMHzcB-DCTA-COF, respectively. These redshifts indicate afurther progressed p–π conjugation compared to those of
TMHzcB-DCTA-COF with surface Cl atom and TMHzcB-TA-COF
bearing surface H atom. The methyl group can trigger
hyperconjugation via its C–H bonds, which donate electron to theedge to enhance its p–π conjugation (Figure 4b). More explicitly,
integrating methoxy site onto the wall further induces progressed
redshift of absorption band because of improved p–π conjugation
driven by the resonance effect of lone pairs of O atoms (Figure4c). Indeed, TMHzcB-DMeOTA-COF (Table 1, Figure S6f, red
curve) exhibited the absorption band at 441 nm, which is 74- and27-nm redshifted from those of model compound-OMe and
TMHzcB-DMeTA-COF, respectively.
Similarly, TMHzcB-DHTA-COF with hydroxy unit exhibited anabsorption band at 453 nm (Table 1, Figure 6g, red curve), which
is 83- and 12-nm redshifted from those of model compound-OH
and TMHzcB-DMeOTA-COF, respectively. The progressed
redshifts originate from a two-fold effect: one is the resonanceeffect of the O atom, and another is the improved planarity of

4

RESEARCH ARTICLE

Figure 4. Perturbation of surface site and their effects. (a–d) Electronic effects of (a) Cl atom via induction and resonance (inset: p–π conjugation of hydrazone
linkage), (b) methyl site via hyperconjugation, (c) methoxy site via resonance, and (d) hydroxyl site via hydrogen bond and phototautomerization, on the backbone.
e) Progress of light emission via perturbation of wall surface site, enabling to emit three primary colors and to edit different light emissions (scale bar = 20 μm).

linker via hydrogen bond interaction between the hydroxy unit andhydrazone linkage (Figure 4d).
The drastic changes in the absorption band of these COFs
reveal that the surface sites play a key role in controlling the p–π
conjugation of the polygonal backbone (Figures 4a–d). Eachmacrocycle possesses six surface sites which are aligned along
the z direction to form six single file chains in each channel(Figures 3c, 3f, 3i, 3l, and 3o). Therefore, the effect of thesesurface chains can be transmitted to the polygonal backbone to
influence the p–π conjugation and electronic structure.
Emission of RGB lights. The distinct electronic effects attracted
us to investigate light emission behavior of COFs, upon excitation
at their absorption bands. Model compound-H, model compoundCl, model compound-Me, model compound-OMe, and modelcompound-OH emitted at 406, 435, 442, 445, and 528 nm,
respectively (Figure S7, Table S9). Both COFs with one
hydrazone linkage at each edge emitted blue light. For example,
TMHzcB-TFB-COF emits at 447 nm (Figure 5a) with an absolute
fluorescence quantum yield of 5.1% (Figure 5b) and the standard
Commission Internationale de l’Eclairage (CIE) coordinate of(0.15, 0.03) (Table 1, Figure 5c). The TMHzcB-TFPB-COF
emitted at 469 nm (Figure 5a) with a quantum yield of 10.5%(Figure 5b) and a CIE coordinate of (0.12, 0.12) (Figure 5c).
The TMHzcB-TA-COF with surface H atom also emitted a blue
light at 463 nm (Figure 5a) with a quantum yield of 11.7% (Figure5b) and a CIE coordinate of (0.14, 0.06) (Table 1, Figure 5c). On
the other hand, TMHzcB-DCTA-COF with surface Cl atom emitted
a sky-blue light at 482 nm (Figure 5a) with an absolute quantum
yield of 6% (Figure 5b) and a CIE coordinate of (0.11, 0.20) (Table
1, Figure 5c). Interestingly, TMHzcB-DCTA-COF exhibited asimilar redshift by 19 nm in both absorption and emission bands
compared to those of TMHzcB-TA-COF. This result suggests that
the Cl atom controls the emission via its resonance effect.

5Interestingly, TMHzcB-DMeTA-COF with surface methyl site
exhibited a further redshifted luminescence to emit green at 499
nm (Figure 5a) with a quantum yield of 20% (Figure 5b) and a CIE
coordinate of (0.13, 0.45) (Table 1, Figure 5c). This redshift
originates from the hyperconjugation effect of the methyl site
(Figure 4c). The high fluorescence quantum yield is compatible tothe state-of-the-art COFs represented by TPE-Ph COF (32%),[10a]sp2c-COF (14%),[10b] and 3D-TPE-COF (20%).[10c] Notably,
distinct from aggregation-induced emission of backbones in these
COFs, the emission of our newly designed COFs is controlled by
the surface site on the pore wall (Figure 4d).
The TMHzcB-DMeOTA-COF with surface methoxy site also
emitted a green light with a redshifted band at 526 nm (Figure 5a)and exhibited an absolute quantum yield of 19% (Figure 5b) anda CIE coordinate of (0.17, 0.74) (Table 1, Figure 5c). These
results indicate that the resonance effect of methoxy site drives
the redshift of both absorption and emission bands (Figure 4c).
Surprisingly, TMHzcB-DHTA-COF with surface hydroxyl site
emitted a red light centered at 635 nm (Figure 5a) to achieve aquantum yield of 3.1% (Figure 5b) and a CIE coordinate of (0.69,0.31) (Table 1, Figure 5c). At the ground state, TMHzcB-DHTACOF exists in the stable enol form.[11] Photoexcitation induces theredistribution of electron density to increase the acidity of thehydrogen bond donor (−OH) and the basicity of the hydrogenbond acceptor (=N−). As a result, phototautomerization occurs totransform enol to keto form, yielding an exited keto form (Figure4d).[11] This phototautomerization effect makes TMHzcB-DHTACOF distinct from red emissive porphyrin COFs as the surfacesite of new COFs induces a red emission (Figure 4d).[8a, 12]Compared to model compounds, the emission band of COFs isgreatly redshifted by 60–100 nm (Table 1), suggesting theimportance of surface site on the polygonal backbone. The dense
yet aligned surface sites form multipoint and multichain on the

RESEARCH ARTICLE

Figure 5. Editing light emission via surface perturbation. a) Fluorescence spectra of TMHzcB-TFB-COF, TMHzcB-TA-COF, TMHzcB-TFPB-COF, TMHzcB-DCTACOF, TMHzcB-DMeTA-COF, TMHzcB-DMeOTA-COF, and TMHzcB-DHTA-COF at solid state (normalized peak top from left to right). b) Absolute fluorescencequantum yield (red bar) and lifetime (blue bar) of TMHzcB-X-COF (X = TFB, TFPB, TA, DCTA, DMeTA, DMeOTA, and DHTA). c) CIE coordinates of COFs
perturbated with single surface site (white dots), two surface sites (yellow and green dots), and three surface sites (blue dots).

six walls of each channel, so that the resonance,
hyperconjugation, and phototautomerization effects arecollectively and sensitively transmitted to the photoexcited state.
These features render the backbone able to emit different lights(Table 1, Figures 4e and 5c).
Stokes shift. To probe how the surface site influences vibrational
states, we evaluated Stokes shift to show the energy differences
between the absorption and emission bands of the COFs. As aresult, the Stokes shift follows an order of TMHzcB-DHTA-COF(6327 cm–1) > TMHzcB-TFPB-COF (4319 cm–1) > TMHzcB-TACOF (4241 cm–1) > TMHzcB-DMeTA-COF (4114 cm–1) >TMHzcB-TFB-COF (3944 cm–1) > TMHzcB-DCTA-COF (3883
cm–1) > TMHzcB-DMeOTA-COF (3664 cm–1). We further
measured time-resolved fluorescence spectra to evaluate thefluorescence lifetime (Figure 5b, Figure S8). Indeed, TMHzcBDHTA-COF with the largest Stokes shift exhibited the shortest
fluorescence lifetime (0.21 ns, Figure 5b, Figure S8), while
TMHzcB-DMeOTA-COF with the resonance effect and TMHzcBDMeTA-COF with hyperconjugation effect displayed much longer
lifetimes of 1.71 and 2.71 ns, respectively (Figure 5b, Figure S8).
According to Perrin-Jablonski diagram and Frank-Cotton principle,
the difference in Stokes shifts and fluorescence lifetimes are selfconsistent and reflect that the surface site plays a critical role inphonon relaxation, which triggers the difference of light emission.

conduct polycondensation reaction enables the perturbation ofwall surface with different sites while retaining the same polygonal
backbone. This approach would produce emission colors that are
distinct from those with single surface site.
We first challenged to edit light emission between green andred by synthesizing TMHzcB-DMeOTAX/DHTAY-COFs with two
surface sites, i.e. methoxy and hydroxy sites at different molar
ratios (X/Y = 2/1, 1/1, and 1/2 in mol) by polycondensation of
TMHzcB as knot with a mixture of DMeOTA and DHTA as linker(for details see Supporting Information, Experimental Procedures).
The TMHzcB-DMeOTAX/DHTAY-COFs were characterized by FT
IR spectroscopy (Figure S9), elemental analysis (Table S1),PXRD (Figure S10), and nitrogen sorption isotherm
measurements (Figure S11). The TMHzcB-DMeOTAX/DHTAYCOFs exhibited absorption bands at 450, 450, and 440 nm as the
X/Y ratio was changed from 2/1 to 1/1 and 1/2 (Table 1, Figures
S12a–c). Interestingly, upon excitation at their absorption bands,
TMHzcB-DMeOTAX/DHTAY-COFs showed dual emission bands
at 517 and 640 nm; each band is close to that of TMHzcBDMeOTA-COF and TMHzcB-DHTA-COF, respectively (Table 1,
Figures
S12a–c).
The
TMHzcB-DMeOTA2/DHTA1-COF,
andTMHzcBTMHzcB-DMeOTA1/DHTA1-COF,
DMeOTA1/DHTA2-COF exhibited a CIE coordinate of (0.22, 0.66),(0.37, 0.54), and (0.60, 0.39), respectively (Table 1, Figure 5c,yellow spots). Clearly, the emission colors are distinct from the
COFs with single surface site. Looking closely at the CIE plot, wefound that the spots of these COFs with two surface sites arealigned between the spots of green shining TMHzcB-DMeOTACOF and red emissive TMHzcB-DHTA-COF (Figure 5c).
We then edited the emission color between blue and red byengineering the wall surface with proton and hydroxyl sites to
produce TMHzcB-TA2/DHTA1-COF (Table S1, Figures S9-S11),

Discussion
With the development of three primary colors of light, we
scrutinized the possibility of editing light emission. As linker units
have different surface sites, developing multicomponent linkers to

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Table 1. Absorption and emission features of COFs.
Single surfacesite COFs

Abs. (nm)Em. (nm)CIE
coordinate

TMHzcB-TFBCOF

380

447

(0.15, 0.03)

TMHzcBTFPB-COF

390

469

(0.12, 0.12)

TMHzcB-TACOF

387

463

(0.14, 0.06)

TMHzcBDCTA-COF

406

482

(0.11, 0.20)

TMHzcBDMeTA-COF

414

499

(0.13, 0.45)

TMHzcBDMeOTACOF

441

526

(0.17, 0.74)

TMHzcBDHTA-COF

453

635

(0.69, 0.31)

Multiplesurface site
COFs

TMHzcBDMeOTAX/DH
TAY-COFs

TMHzcBTAX/DHTAYCOF

TMHzcBTAX/DMeOTA
Y/DHTAZCOFs

as TMHzcB-TA-COF and TMHzcB-DHTA-COF emit blue and red,respectively. The TMHzcB-TA2/DHTA1-COF upon excitation at
440 nm affords a dual luminescence at 468 and 638 nm (Table 1,
Figure S12d), which is again close to the emission band of
TMHzcB-TA-COF and TMHzcB-DHTA-COF, respectively. The
TMHzcB-TA2/DHTA1-COF exhibited a CIE coordinate of (0.42,0.18) (Table 1, Figure 5c, green spot), which is spotted between
TMHzcB-TA-COF and TMHzcB-DHTA-COF. These results areindicative as the emission color can be predesigned by solely
tuning the ratio of surface sites on the pore wall.
We further perturbate the frameworks with three surface sites.
For this purpose, we selected TMHzcB as knot and three linkers
of TA, DMeOTA, and DHTA for the polymerization. We tuned themolar ratio of TA/DMeOTA/DHTA at 3/1/2, 2/1/2, and 4/1/4 tosynthesize three COFs, i.e. TMHzcB-TA3/DMeOTA1/DHTA2-COF,
andTMHzcBTMHzcB-TA2/DMeOTA1/DHTA2-COF,
TA4/DMeOTA1/DHTA4-COF, respectively (Table S1, Figures S9–
S11). All TMHzcB-TA3/DMeOTA1/DHTA2-COF, TMHzcBand
TMHzcBTA2/DMeOTA1/DHTA2-COF,
TA4/DMeOTA1/DHTA4-COF exhibited three emission bands at
468, 533, and 640 nm (Table 1, Figure S13), which is close to theblue, green, and red luminescence of TMHzcB-TA-COF,
TMHzcB-DMeOTA-COF, and TMHzcB-DHTA-COF (Table 1),
respectively. Interestingly, the intensity of three emissions isdifferent from each other, so that the emission color of these
COFs is finely controlled by the molar ratio of surface sites.
TMHzcBIndeed,
TMHzcB-TA3/DMeOTA1/DHTA2-COF,
andTMHzcBTA2/DMeOTA1/DHTA2-COF,
TA4/DMeOTA1/DHTA4-COF exhibited different CIE coordinates of(0.29, 0.46), (0.34, 0.46), and (0.42, 0.38), respectively (Table 1,
Figure 5c, blue spots).
As demonstrated above, our strategy can edit light emission ina predesignable and digital way by tuning the component andratio of surface sites. Synthetically, any colors in the CIE diagram
surrounded by these five COFs can be predesigned byengineering the surface sites. Such an editing capability isunprecedented in both organic and inorganic systems. We

Molecular
Ratio

Abs. (nm)X/Y = 2/1

450

X/Y = 1/1

450

X/Y = 1/2

440

X/Y = 2/1

440

X/Y/Z = 3/1/2

448

X/Y/Z = 2/1/2

456

X/Y/Z = 4/1/4

442

Em. (nm)CIE
coordinate(0.22, 0.66)

517 and 640(0.37, 0.54)(0.60, 0.39)

468 and 638(0.42, 0.18)(0.29, 0.46)468, 533, and
640(0.34, 0.46)(0.42, 0.38)

highlight that distinct from 0D quantum dots which must change
the particle size, the 2D COFs do not need to alter the backbone
but can emit various lights by simply decorating different surface
sites. Therefore, our strategy offers a new regime in light-emitting
materials.
Hydrazone serves as a hydrogen-bond acceptor owing to thepresence of N and O atoms with lone pairs. We observed that thehydrazone linkages endow these light-emitting COFs withexceptional sensing capability. We proved the concept by using
TMHzcB-DMeTA-COF with the highest fluorescence quantum
yield to probe 2,4,6-trinitrophenol (TNP) in THF. A drastic andquick drop of fluorescence was observed (Figure S14a and inset).
Noticeably, the detection limit is as low as sub ppm level; this highsensitivity is much superior to the reported COFs.[13] The
TMHzcB-DMeTA-COF is highly selective in sensing and shows a
low quenching degree by other aromatic compounds even atmuch higher concentrations (Figure S14b), including 2,4dinitrophenol (DNP, quenching degree = 16%), 2,4-dinitrotoluene(DNT, quenching degree = 7%), 2-nitrophenol (NP, quenchingdegree = 5%), and 2-nitrotoluene (NT, quenching degree = 4%).
From the fluorescence quenching profile, the Stern–Volmer
constant (kSV) was evaluated to be 3.7 × 105 M–1 (Figure S14c).
Time-resolved fluorescence decay measurements revealed thatthe lifetime of TMHzcB-DMeTA-COF in THF was 2.10 ns (Figure
S14d, black curve) which decreased to 1.49 ns upon addition of
TNP (10 ppm) (Figure S14d, blue curve). This result indicates thatphotoinduced electron transfer proceeds at a rate of 1.9 × 108 s–1
and controls the sensing process. The fluorescence quenchingrate constant kq (= kSV / τ ) was evaluated to be as high as 2.5 ×
1014 M−1 s−1. Therefore, the hydrazone-linked COF merges
selectivity, sensitivity, and sensibility into one material, which ishighly desired for sensors and detectors.

Conclusion

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RESEARCH ARTICLE
In summary, we have developed COFs as a molecular platform
for editing light emission. This is possible by integrating hydrogen,chlorine, methoxy, methyl, and hydroxy surface sites onto thepore wall, which are designed to trigger various π electronic
effects
includingresonance,
hyperconjugation,andphototautomerization. The surface site transmits the effect to thepolygonal backbone, so that the ground and excited states can
induce a drastic change to emit three primary colors of light. The
multiple surface site perturbation approach greatly increases thescope of emission colors and enable to edit diverse lightemissions in a predesignable and digital way. The frameworks
combine luminescence activity, stability, color tunability, andsensibility in one material which is highly desired for light-emitting
and sensing applications. With the diversity of polygonal topology
as well as the broad scope of backbone and surface site, we
envision that our strategy shapes a new regime in light-emittingorganic/polymeric materials.

[8]

[9]

[10]

Acknowledgements[11]This work is supported by the MOE tier 1 grant (R-143-000-A71114) and NUS start-up grant (R-143-000-A28-133).

[12]

Conflict of interest[13]

The authors declare no conflict of interests
Keywords: covalent organic framework • hydrazone linkage •luminescence • color design • RGB
[1]
[2]
[3]
[4]

[5]

[6]

[7]

C.R. Ronda, Luminescence: from theory to applications. John Wiley &Sons, 2007.
a) D.J. Norris, M.G. Bawendi, Phys. Rev. B 1996, 53, 16338; b) T.
Takagahara, K. Takeda, Phys. Rev. B 1992, 46, 15578.
A. Haque, R. A. Al-Balushi, I. J. Al-Busaidi, M.S. Khan, P.R. Raithby,
Chem. Rev. 2018, 118, 8474−8597.
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 2017, 357, 673–
676; b) T. Ma, E. A. Kapustin, S. Yin, L. Liang, Z. Zhou, J. Niu, L. Li, Y.
Wang, J. Su, J. Li, X. Wang, W. Wang, W. Wang, J. Sun, O. M. Yaghi,
Science 2018, 361, 48–52; c) A. M. Evans, L. R. Parent, N. C. Flanders,R. P. Bisbey, E. Vitaku, M. S. Kirschner, R. D. Schaller, L. X. Chen, N. C.
Gianneschi, W. R. Dichtel, Science 2018, 361, 52–57.
a) K. Geng, T. He, R. Liu, K. T. Tan, Z. Li, S. Tao, Y. Gong, Q. Jiang, D.
Jiang, Chem. Rev. 2020, 120, 8814–8933; b) N. Huang, P. Wang, D.
Jiang, Nat. Rev. Mater. 2016, 1, 16068; c) D. Rodríguez-San-Miguel, C.
Montoro, F. Zamora, Chem. Soc. Rev. 2020, 49, 2291−2302; d) W. K.
Haug, E. M. Moscarello, E. R. Wolfson, P. L. McGrier, Chem. Soc. Rev.
2020, 49, 839–864.
a) M. S. Lohse, T. Bein, Adv. Funct. Mater. 2018, 28, 1705553; b) R. Liu,
K.T. Tan, Y. Gong, Y. Chen, Z. Li, S. Xie, T. He, Z. Lu, H. Yang, D. Jiang,
Chem. Soc. Rev. 2021, 50, 120-242; c) S. Xu, Q. Zhang, Mater. Today
Energy 2021, 20, 100635; d) H. Vardhan, A. Nafady, A.M. Al-Enizi, S.
Ma, Nanoscale 2019, 11, 21679-21708; e) L. Ma, X. Feng, S. Wang, B.
Wang, Mater. Chem. Front. 2017, 1, 2474-2486.
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) Z. Li, Y. Zhang,
H. Xia, Y. Mu, X. Liu, Chem. Commun. 2016, 52, 6613–6616; c) A. M.
Evans, I. Castano, A. Brumberg, L. R. Parent, A. R. Corcos, R. L. Li, N.
C. Flanders, D. J. Gosztola, N.C. Gianneschi, R. D. Schaller, W. R.
Dichtel, J. Am. Chem. Soc. 2019, 141, 19728–19735; d) F. Yu, W. Liu,
S.-W. Ke, M. Kurmoo, J.-L. Zuo, Q. Zhang, Nat. Commun. 2020, 11, 16. e) J. W. Crowe, L. A. Baldwin, P. L. McGrier, J. Am. Chem. Soc. 2016,

8

138, 10120−10123; f) T. Jadhav, Y. Fang, W. Patterson, C.-H. Liu, E.
Hamzehpoor, D. F. Perepichka, Angew. Chem. Int. Ed. 2019, 58, 13753–
13757; Angew. Chem. 2019, 131, 13891–13895; g) S. Haldar, D.
Chakraborty, B. Roy, G. Banappanavar, K. Rinku, D. Mullangi, P. Hazra,
D. Kabra and R. Vaidhyanathan, J. Am. Chem. Soc. 2018, 140, 13367–
13374; h) S. Ding, M. Dong, Y. Wang, Y. Chen, H. Wang, C. Su, W.
Wang, J. Am. Chem. Soc. 2016, 138, 3031–3037; i) Z. Li, N. Huang, K.
H. Lee, Y. Feng, S. Tao, D. Jiang, Y. Nagao, S. Irle, D. Jiang, J. Am.
Chem. Soc. 2018, 140, 12374−12377.
a) X. Chen, M. Addicoa, E. Jin, L. Zhai, H. Xu, N. Huang, Z. Guo, L. Liu,
S. Irle, D. Jiang, J. Am. Chem. Soc. 2015, 137, 3241–3247; b) X. Li, Q.
Gao, J. Wang, Y. Chen, Z. Chen, H. Xu, W. Tang, K. Leng, G. Ning, J.
Wu, Q. Xu, S. Y. Quek, Y. Lu, K. P. Loh, Nat. Commun. 2018, 9, 2335.
a) F. J. Uribe-Romo, C. J. Doonan, H. Furukawa, K. Oisaki, O. M. Yaghi,
J. Am. Chem. Soc. 2011, 133, 11478−11481; b) L. Stegbauer, K.
Schwinghammer, B. V. Lotsch, Chem. Sci. 2014, 5, 2789–2793.
a) S. Dalapati, E. Jin, M. Addicoat, T. Heine, D. Jiang, J. Am. Chem. Soc.
2016, 138, 5797−5800; b) E. Jin, J. Li, K. Geng, Q. Jiang, H. Xu, Q. Xu,
D. Jiang, Nat. Commun. 2018, 9, 4143; c) H. Ding, J. Li, G. Xie, G. Lin,R. Chen, Z. Peng, C. Yang, B. Wang, J. Sun, C. Wang, Nat. Commun.
2018, 9, 5234.
A. C. Sedgwick, L. Wu, H.-H. Han, S. D. Bull, X.-P. He, T. D. James, J.
L. Sessler, B. Z. Tang, H. Tian, J. Yoon, Chem. Soc. Rev. 2018, 47, 88428880.
B. P. Biswal, S. Valligatla, M. Wang, T. Banerjee, N. A. Saad, B. M. K.
Mariserla, N. Chandrasekhar, D. Becker, M. Addicoat, I. Senkovska, R.
Berger, D. N. Rao, S. Kaskel, X. Feng, Angew. Chem. Int. Ed. 2019, 58,
6896-6900; Angew. Chem. 2019, 131, 6970-6974.
a) S. Dalapati, S. Jin, J. Gao, Y. Xu, A. Nagai, D. Jiang, J. Am. Chem.
Soc. 2013, 135, 17310−17313; b) G. Lin, H. Ding, D. Yuan, B. Wang, C.
Wang, J. Am. Chem. Soc. 2016, 138, 3302−3305; c) G. Das, B. P. Biswal,
S. Kandambeth, V. Venkatesh, G. Kaur, M. Addicoat, T. Heine, S. Verma,
R. Banerjee, Chem. Sci., 2015, 6, 3931–3939.

RESEARCH ARTICLE
Entry for the Table of Contents

Neon lights: Topology-directed polymerization enables the construction of highly emissive stable covalent organic frameworks linked
by hydrazone bond. Perturbation of pore wall surface site can tune the emission to achieve three primary colors of light, rendering thematerials able to edit various emission colors by organizing different surface sites onto the pore wall.
Institute and/or researcher Twitter usernames: @jiang_donglin

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