3D Covalent Organic Frameworks of Interlocking 1D Square Ribbons

Article abstract of DOI:10.1021/jacs.8b12177

A new mode of mechanical entanglement in extended structures is described where 1D organic ribbons of corner-sharing squares are mutually interlocked to form 3D woven covalent organic framework-500, COF-500. Reaction of aldehyde-functionalized tetrahedral

Full text of DOI:10.1021/jacs.8b12177

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Article
3D Covalent Organic Frameworks of Interlocking 1D Square Ribbons
Yuzhong Liu, Christian S. Diercks, Yanhang Ma, Hao Lyu, Chenhui
Zhu, Sultan A. Alshmimri, Saeed Alshihri, and Omar M. Yaghi
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.8b12177 • Publication Date (Web): 11 Dec 2018
Downloaded from http://pubs.acs.org on December 11, 2018
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3D Covalent Organic Frameworks of Interlocking 1D Square Ribbons
Yuzhong Liu,1 Christian S. Diercks,1 Yanhang Ma,2 Hao Lyu,1 Chenhui Zhu,3 Sultan A. Alshmimri,4
Saeed Alshihri,4 Omar M. Yaghi1,4*
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1Department of Chemistry, University of California-Berkeley; Materials Sciences Division, Lawrence Berkeley National
Laboratory; Kavli Energy NanoSciences Institute, Berkeley, California 94720, USA.
2School of Physical Science and Technology, Shanghai Tech University, Shanghai 201210, China.
3Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.
4UC Berkeley-KACST Joint Center of Excellence for Nanomaterials for Clean Energy Applications, King Abdulaziz City
for Science and Technology, Riyadh 11442, Saudi Arabia.
ABSTRACT: A new mode of mechanical entanglement in extended structures is described where 1D organic
ribbons of corner-sharing squares are mutually interlocked to form 3D woven covalent organic framework-
500, COF-500. Reaction of aldehyde-functionalized tetrahedral Cu(PDB)2PO2Ph2 complexes (PDB = 4,4'-(1,10-
phenanthroline-2,9-diyl)dibenzaldehyde) with rectangular tetratopic ETTBA (4',4''',4''''',4'''''''-(ethene-1,1,2,2-
tetrayl)tetrakis([1,1'-biphenyl]-4-amine)) linkers through imine condensation, yielded a crystalline porous
metalated COF, COF-500-Cu, with pts topology. Upon removal of the Cu(I) ions, the individual 1D square
ribbons in the demetalated form (COF-500) are held together only by mechanical interlocking of rings that
allows their collective movement to produce a narrow-pore form as evidenced by nitrogen adsorption and
solid-state photoluminescence studies. When exposed to tetrahydrofuran vapor, the interlocking ribbons can
dynamically move away from each other to reopen up the structure. The structural integrity of COF-500 is
maintained during its dynamics because the constituent square ribbons cannot part company due to spatial
confinement imparted by their interlocking nature.
INTRODUCTION
of these. In principle, access to the wide range of
these woven framework structures falls within the
realm of reticular chemistry. In this report, we show
how 1D open square ribbons of corner-sharing
squares, entirely composed of covalently linked
organic molecules, can interlock to form extended
3D COFs (Fig. 1d). Specifically, linking tetrahedral
Cu(PDB)2 complexes with rectangular tetratopic
ETTBA linkers yields the woven COF-500-Cu with an
overall structure based on the platinum sulfide (pts)
topology (Fig. 2).
Molecular
weaving
of
covalent
organic
frameworks (COFs)1–3 holds promise for providing
solid state materials capable of dynamics. Such
dynamics would be based on movements of
mechanically entangled4-6 threads rather than
stretching and bending of chemical bonds. In this
context, the term ‘weaving’ is used as a general
denominator for mechanical linkage of 0D and 1D
objects to afford extended 2D and 3D structures. The
key to designing a woven structure is to control the
geometry of the crossing points, the overall
connectivity of the linkers, and the angles these
components make with respect to each other (Fig 1a
and b). Mechanically linked derivatives of almost all
synthetically accessible framework topologies can
be formed by weaving of threads, interlocking of
rings and polyhedra, or in some cases a combination
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Synthesis of Cu(I)-bis[4,4'-(1,10-phenanthroline-2,9-
diyl)dibenzaldehyde] diphenylphosphinate
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[Cu(PDB)2PO2Ph2]. Copper(I) diphenylphosphinate (199
mg, 0.710 mmol) was added to a solution of 4,4'-(1,10-
phenanthroline-2,9-diyl)dibenzaldehyde (500 mg, 1.29
mmol) in CHCl3 (15 mL) and CH3CN (10 mL) in the
glovebox, affording a dark red solution, which was stirred
at room temperature for 30 min. The solution was then
concentrated under vacuum and further purified by silica
column chromatography with a gradient of solvent from
1:100 to 1:10 (v/v) of methanol:dichloromethane.
Recrystallization from acetone afforded the analytically
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1
pure compound as red crystals (490 mg, 72%). H NMR
(400 MHz, dmso-d6) δ 9.68 (s, 4H), 8.83 (d, 3J = 7.9 Hz, 4H),
8.19 (d, 3J = 7.9 Hz, 4H), 8.15 (s, 4H), 7.72 (m, 4H), 7.62 (d,
3J = 8.0 Hz, 8H), 7.43 (m, 6H), 7.07 (d, 3J = 8.0 Hz, 8H). ESI-
MS for [C52H32CuN4O4]+ (Calcd. 839.17): m/z =839.17
([M]+, 100%).
Figure 1 Modes of mechanical entanglement in
woven COFs. (a) Combination of tetrahedral
building
blocks
encoding
for
mechanical
entanglement with linear struts. (b) Tetrahedral and
square shaped tetratopic linkers encoding for
mechanical entanglement. (c) Weaving of 1D
threads that cross at regular intervals. (d)
Interlocking square ribbons that are held together
by entanglement of rings.
Synthesis and activation of COF-500-Cu. A Pyrex tube
measuring 10 × 8 mm (o.d × i.d) was charged with
Cu(PDB)2PO2Ph2 (17.6 mg, 0.0160 mmol), ETTBA (12.0 mg,
0.0160 mmol), 1 mL of 1:1 (v/v) 1,2-dichlorobenzene:1-
butanol mixture, and 0.1 mL of 9 M aqueous acetic acid.
The tube was flash frozen at 77 K (liquid N2), evacuated to
an internal pressure of 50 mTorr and flame sealed. Upon
sealing, the length of the tube was reduced to 18-20 cm.
The reaction was heated at 180 °C for 72 h yielding a
brown solid at the bottom of the tube which was isolated
by centrifugation and washed by Soxhlet extraction with
anhydrous THF for 12 h. The sample was activated at 85
°C under reduced pressure (50 mTorr) for 12 h. Yield: 21.2
mg, 75.7% based on Cu(PDB)2PO2Ph2. Elemental analysis:
Calcd. for C114H74CuN8O2P·6H2O: C, 76.47; H, 4.84; N,
6.25%. Found: C, 76.43; H, 5.26; N, 6.11%. ICP-AES of Cu
content: Calcd.: 3.55%; Found: 3.5%.
The copper ions serve as points of registry that bring
together square ribbons in a controlled manner such
that they interlock with other ribbons to form a 3D
woven framework. We show that COF- -Cu can be
demetalated to produce the purely organic woven
form, COF-500, where the individual ribbons are
held together only by mechanical interlocking, and
that it is possible to remetalate the structure
reversibly with full retention of its crystalline order.
It is worthy of note that the specific mode of
interlocking reported here has not been conceived
prior to this report. In COF-500, large degrees of
motional freedom, without unzipping of the
structure, are observed by vapor sorption and
photoluminescence studies. This is attributed to the
fact that the individual ribbons of COF-500 can move
freely with respect to each other within the
confinement of the interlocking rings.
RESULTS AND DISCUSSION
The synthetic strategy to make COF-500 is depicted
in Fig. 1. Tetrahedral tetratopic Cu(I)-bis[4,4'-(1,10-
phenanthroline-2,9-diyl)dibenzaldehyde]
diphenylphosphinate
[Cu(PDB)2PO2Ph2],
an
aldehyde functionalized
copper(I)-
bisphenanthroline complex salt, was linked with
square planar tetratopic 4',4''',4''''',4'''''''-(ethene-
1,1,2,2-tetrayl)tetrakis(([1,1'-biphenyl]-4-amine))
(ETTBA)
EXPERIMENTAL SECTION
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Figure 2. Synthetic strategy for the design and synthesis of interlocking 1D square ribbons. COF-500-
Cu was constructed from (a) Cu(PDB)2PO2Ph2 and ETTBA to yield interlocking 1D corner-sharing square
ribbons connected to each other through copper(I) ions. (b) Upon demetalation an entirely organic extended
woven 3D framework, COF-500, with underlying pts topology is formed.
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through imine bond formation (Supplementary
Section S2). In Cu(PDB)2PO2Ph2, the copper centers
pre-organize two PDB ligands such that their
appended aldehyde functional groups approximate
a tetrahedral geometry. The 60 angles between the
two points of extension (i.e. aldehyde functionalities)
of each phenanthroline ligand are complementary
to the 120 angles between the points of extension
(i.e. amino functionalities) of ETTBA thus leading to
the formation of 4-membered macrocycles (Fig. 2a).
These macrocycles are covalently linked through the
double bonds of ETTBA to yield corner-sharing 1D
square ribbons. In each individual ribbon, the
phenanthroline ligands comprising the corners of
the macrocycles are linked together by copper(I)
ions in an embracing manner. The second set of
phenanthroline ligands forms part of an adjacent
interlocking ribbon (blue and red, Fig. 2a). The
entangled ribbons are orthogonal to each other
because of the dihedral angle the two
phenanthroline ligands of the complex assume, thus
yielding a woven 3D framework with an underlying
pts net  the default net for the linking of
tetrahedral and square planar building units.7,8
The synthesis of COF-500-Cu was carried out
based on reversible imine bond formation:
Equimolar amounts of Cu(PDB)2PO2Ph2 and ETTBA
were reacted in a 1:1 (v/v) mixture of 1,2-
dicholorobenzene and 1-butanol in the presence of
aqueous acetic acid as a catalyst. The reaction
mixture was sealed in a Pyrex tube and heated at
180°C to increase solubility of the starting materials
and enhance the reversibility of the reaction. After
three days, the resulting precipitate was collected
and washed by Soxhlet extraction with anhydrous
tetrahydrofuran to yield a dark brown crystalline
solid, which was found to be insoluble in common
organic solvents and water (Supplementary Section
S2).
The formation of imine linkages in COF-500-Cu
was confirmed by Fourier-transform infrared (FT-IR)
spectroscopy and 13C cross-polarization magic angle
spinning (CP-MAS) solid-state nuclear magnetic
resonance (NMR) spectroscopy (Supplementary
Sections S3 and S4). A molecular analog of COF-500-
Cu with a tetraphenylethylene core, (1E,1'E,1''E,1'''E)-
N,N',N'',N'''-(ethene-1,1,2,2-tetrayl-tetrakis([1,1'-
biphenyl]-4',4-diyl))tetrakis(1-phenylmethan-imine)
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(ETTP) was used as
a
model compound
distances of 26 Å (highlighted in the inset). (c)
Indexed PXRD pattern of the activated sample of
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(Supplementary Section S2). The disappearance of
the C=O stretching vibration at 1695 cm−1 of the
aldehyde functional groups in the FT-IR spectra, as
well as the absence of peaks at a chemical shift
above 200 ppm in the 13C CP-MAS NMR solid-state
spectrum demonstrate full conversion of the
COF-500-Cu (red) and Pawley refinement (blue) of
the unit cell from the modeled structure. (d) Selected
area electron diffraction pattern acquired from the
crystal confirms the single-crystalline nature of the
particles.
Cu(PDB)2PO2Ph2
aldehyde
starting
material
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Scanning electron microscopy (SEM) micrographs
of COF-500-Cu show a homogeneous morphology
of rod-shaped crystals with dimension of
approximately 1 m  0.2 m  0.2 m (Fig. 3a and
Supplementary Section S5). After ultrasonic
oscillation of the sample in ethanol, individual
crystals of COF-500-Cu were dispersed on a copper
sample grid for transmission electron microscopy
(TEM) studies. 3D electron diffraction tomography
(3D-EDT)11 data of COF-500-Cu was collected by
combining specimen tilt and electron-beam tilt in
the range of –34.3° to +33.0° with a beam-tilt step
of 0.3°. From the acquired data set the 3D reciprocal
lattice of COF-500 was constructed and found to
have unit-cell parameters of a = 21 Å, b = 52 Å, c =
21 Å, and V = 22932 Å3, which were used to index
reflections observed in both the powder X-ray
diffraction (PXRD) pattern and Fourier diffractogram
of high-resolution transmission electron microscopy
(HRTEM) images (Fig. 3b to d and Supplementary
Section S6). The unit-cell parameters were optimized
further by Pawley refinement of the PXRD pattern to
be a = 20.0 Å, b = 51.9 Å, c = 20.0 Å, and V = 20760
Å3. A structure model of COF-500-Cu was built in
Materials Studio 8.012 in the orthorhombic space
group C222. The calculated PXRD pattern of the
modeled structure was found to be in good
agreement with the experimental pattern of
activated COF-500-Cu.
(Supplementary Section S4). Furthermore, the FT-IR
spectrum of COF-500-Cu features characteristic
C=N stretching vibrations at 1622 and 1171 cm−1
(1625 and 1170 cm−1 for ETTP) corroborating the
formation of imine bonds.1,9,10 These observations
support completeness of the reaction and formation
of imine bonds between the building blocks to form
an extended framework.
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Figure 3. Electron microscopy and PXRD studies
of COF-500-Cu. (a) Only rod-shaped crystals are
observed by SEM indicating the formation of COF-
500-Cu in pure phase. (b) HRTEM image of a single
crystal of COF-500-Cu showing lattice fringes with
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Figure 4. Crystal structure of woven COF-500-Cu. (a) One woven framework of COF-500-Cu is constructed
from interlocking blue and red 1D square ribbons. The ribbons are entangled through the use of copper(I)
ions represented as pink spheres. (b) Representation of the structural model with two entangled woven
frameworks viewed along the crystallographic [001] direction reveals that the copper ions are aligned in the 0
¼ 0 and 0 ¾ 0 lattice planes separated by 26 Å. (c) The structural model overlaid with a 2D projected potential
map of COF-500-Cu shows good agreement. Color code: Individual 1D ribbons are depicted in blue, red, cyan,
and yellow, respectively. Copper(I) ions are depicted in pink. All counterions are omitted for clarity.
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According to the refined model, COF-500-Cu
crystallizes in a pts net with tetrahedral building
units Cu(PDB)2PO2Ph2 and square planar ETTBA
connected through imine bonds (Fig. 4a). Covalently
linked 1D square ribbons propagate along the
crystallographic a (highlighted in blue and cyan) and
c directions (red and yellow) and are mechanically
entangled along the crystallographic b axis (Fig. 4b).
The Cu-Cu distance within each macrocycle is half of
the b parameter, 26 Å, which allows for another
identical net to reside within the pore (blue/red and
cyan/yellow represent the two independent pts
nets). As the copper centers sit in the 0 ¼ 0 and 0 ¾
0 lattice planes in the crystal structure, they are
separated by 26 Å viewed along the c axis (Fig. 4b),
in good agreement with the striped pattern of the
lattice fringes observed in the HRTEM image shown
in Fig. 3b. Overlaying of the derived structure model
with the experimentally observed TEM micrograph
shows good agreement (Fig. 4c). Additional electron
density in the pore could be attributed to the
presence of counterions.
disappeared and COF-500 showed a pale yellow
color. The crystallinity of COF-500 decreased
drastically as compared to its metalated progenitor,
indicating spatial rearrangement of the structure
and concomitant loss of long-range periodicity. This
is expected as the ribbons in COF-500 experience
large degrees of freedom to move about without the
need for breaking or flexing of chemical bonds. The
integrity of the overall structure is retained because
of the constraints imposed by the mechanical
interlocking of the constituents: The FT-IR imine
stretching vibrations at 1623 and 1171 cm−1 are
consistent with those of the metalated COF-500-Cu
(1622 and 1171 cm−1, respectively). In COF-500, the
1D square ribbons are held together by interlocking
such that the overall structure remains unaltered.
Indeed, upon remetalation of the material by stirring
in
Cu(CH3CN)4BF4, crystalline COF-500-Cu was
recovered. The crystallinity and chemical
a
solution of acetonitrile/chloroform and
composition of this remetalated framework are
identical to the original as-synthesized COF-500-Cu,
as evidenced by the complete recovery of the
intensity and positions of the reflections in the PXRD
pattern as well as the presence of identical vibration
bands in the FT-IR spectrum (Supplementary Section
S7). The facile demetalation process indicates that
the copper centers in COF-500-Cu are readily
accessible due to openness of the structure. N2 gas
The copper ions were removed to yield woven
COF-500 by heating in a 1M KCN methanol solution
at 75 °C.1,13 Inductively coupled plasma analysis
revealed that more than 99% of the copper ions
were removed upon demetalation. The dark color of
COF-500-Cu, which arises from the copper-
phenanthroline metal-to-ligand charge transfer,14
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adsorption isotherms of evacuated samples of both
To obtain additional structural information for
COF-500, fluorescence emission spectra before and
after demetalation were recorded. The
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COF-500-Cu and COF-500 were recorded to
examine their porosity. The nitrogen isotherm of
COF-500-Cu [at 77 K from 0 to 1 bar (1 bar = P0)]
shows a sharp uptake between P/P0 = 10-5 to 10-1, a
signature feature of microporous materials. The
Brunauer-Emmett-Teller (BET) model15 was applied
to the isotherm for P/P0 between 0.05 and 0.1 to give
an apparent surface area of SBET = 352 m2g-1. In
contrast, COF-500 exhibited decreased porosity with
a SBET of only 155 m2g-1 (Fig. 5a). Calculation of the
pore size obtained from fitting of the two respective
isotherms using a non-linear density functional
theory slit pore equilibrium model16 yielded a
definitive pore size of 12.66 Å for COF-500-Cu, which
is in good agreement with the pore size of the crystal
structure. In contrast a wider distribution of the pore
size from 10-16 Å with a maximum centered at 12.30
Å was observed for COF-500 indicating a less well-
defined pore system (Fig. 5b). This is attributed to
the added degrees of freedom and concomitant
motional dynamics of the 1D square ribbons upon
demetalation.
tetraphenylethylene core of ETTBA is known to
exhibit aggregation-induced emission17-19. When
rotation of the phenyl rings along the =C–Ar axes
and torsional motions of the C=C bond are
unrestricted, both can serve as non-radiative
relaxation channels for the decay of the excited
state, thus rendering the molecule non-emissive.
Once such molecular motion becomes restricted,
photoluminescence activity is effectively turned
on17. Based on the crystal structure of COF-500-Cu
there is an ETTBA linker of an adjacent 1D chain
located at the center of each macrocycle. Spatial
segregation between this ETTBA linker and the
phenanthroline corners of the surrounding
macrocycle (3.4 Å for the closest H-H distance)
allows for free rotation of the ETTBA’s phenyl rings
and thus for quenching of fluorescent emission.
Upon demetalation, the phenanthroline corners of
neighboring 1D ribbons are free to move about
within the
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Figure 5. Adsorption and solid-state photoluminescence studies of COF-500-Cu and COF-500. (a)
Comparison of N2 sorption isotherms of COF-500-Cu before and after demetalation. Solid and open circles
represent the adsorption and desorption branches, respectively. Data of COF-500-Cu and the demetalated
framework in this figure are depicted in blue and red, respectively. (b) Pore size distribution calculated from
the N2 sorption isotherms using a non-linear density functional theory slit pore equilibrium model. (c) Upon
excitation at 375 nm, the demetalated framework exhibits an intense emission while metalated COF-500-Cu
is non-emissive. (d and e) THF vapor sorption isotherms of COF-500-Cu and COF-500. (f) Within the boundary
of each rigid covalently linked macrocycle, the phenanthroline corners (highlighted in cyan) are free to move
towards the tetraphenylethylene core (blue) upon demetalation. As a result, the motion of the phenyl rings of
the tetraphenylethylene core is restricted thus causing aggregation induced emission.
constraints of the rigid covalently linked macrocycle
of the surrounding ribbons. We believe that, upon
removal of the copper(I) ions, the ribbons move
closer to the central ETTBA linker in order to
maximize van der Waals interactions, thereby
restricting the rotation of the phenyl rings and thus
affecting aggregation induced emission. This implies
that these ribbons become more packed along the
crystallographic c direction when the material is
demetalated, which is consistent with the decrease
in uptake observed in N2 adsorption studies (Fig. 5a).
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Based on the described sorption and intensity was retained for at least 10 minutes even
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photoluminescence experiments we know that upon
demetalation of COF-500-Cu, there is a pronounced
structural rearrangement to yield COF-500. To test
whether this motion between adjacent ribbons that
yields COF-500 is dynamic we carried out
tetrahydrofuran (THF) vapor adsorption studies.20
THF vapor adsorption isotherms were collected for
both COF-500-Cu and COF-500 at 283 K. COF-500-
Cu shows an uptake with a major step at low partial
pressure. The maximum uptake reached at P/P0 =
0.97 is 90.5 cm3g−1 (Fig. 5d).21 For COF-500-Cu, the
initial steep uptake saturates at P/P0 = 0.06 with 32.0
cm3g−1 (vs. P/P0 = 0.06 with 21.9 cm3g−1 for COF-
500, Fig. 5e). This is expected as this uptake is due to
filling of the pore that is expected to be partially
collapsed in the case of COF-500, thus decreasing its
accessible surface area. However, subsequently the
adsorption curve of the demetalated framework
exhibits a steady linear increase, which suggests
opening up of the pores until the maximum uptake
of 103.6 cm3g−1 is reached at P/P0 = 0.97. By taking
the density difference between the two materials
(1680 and 1400 gmol−1 for each repeating unit of
COF-500-Cu and COF-500, respectively) into
consideration, we can roughly approximate the THF
adsorption per unit volume. We conclude that in the
presence of THF vapor, the demelatated framework
opens up to possess 95.3% of the accessible porosity
of COF-500-Cu. Thus, upon exposure of COF-500 to
THF, the structure adopts an open conformation that
likely resembles the structure of COF-500-Cu. The
proposed motion in which the 1D ribbons move
away from each other in the process of the
reopening in the presence of THF can further be
after surrounding THF evaporated, suggesting
strong interactions of THF with the framework.
Conclusion
We report
a
novel mode of mechanical
entanglement in extended structures — interlocking
of 1D corner-sharing square ribbons in COF-500-Cu
and its demetalated analogue, COF-500. The
structure of COF-500-Cu was solved by X-ray
powder diffraction and electron microscopy. Upon
removal of the copper(I) ions the 1D ribbons in COF-
500 experience large degrees of freedom that allow
for their collective movement with respect to one
another. The concomitant structural rearrangement
is evidenced by decreased nitrogen adsorption and
turned-on solid-state photoluminescence. Vapor
sorption and photoluminescence studies further
showed that exposure to tetrahydrofuran vapor
affects dynamic reopening of the framework. The
structural integrity of COF-500 is maintained during
such dynamic motion, which is credited to
constrictions imposed on the movement by the
interlocking of its constituents. We anticipate the
modular synthesis of COFs combined with the
prospect of framework dynamics based on
mechanical entanglement to instigate further
research on interlocking frameworks.
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ASSOCIATED CONTENT
Supporting Information
Synthetic protocols, powder X-ray diffraction analysis,
structural modeling, and porosity evaluation of the COFs, as
well as details concerning the solid-state NMR and
photoluminescence studies.
supported
by
additional
solid-state
AUTHOR INFORMATION
photoluminescence studies. After careful dosing of
COF-500 with THF on a glass slide, a decrease in
emission intensity of approximately 20% as
compared to the dry sample is observed. While this
result can only give qualitative information due to
limitations in the experimental setup, the decreased
intensity nonetheless gives credence to the notion
that solvent molecules can diffuse into the less open
framework leading to reopening of the structure and
separation of the ribbons such that they are far
enough apart from each other to again allow for
molecular motion of the phenyl rings of the
tetraphenyl ethylene centers. The low emission
Corresponding Author
* E-mail: yaghi@berkeley.edu
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENT
Financial support for COF research in the O.M.Y. laboratory
was provided by King Abdulaziz City for Science and
Technology as part of
collaboration (Center of Excellence for Nanomaterials and
Clean Energy Applications). Y.L. was supported by the
Philomathia Graduate Student Fellowship in the
Environmental Sciences. C.S.D. would like to acknowledge the
a joint KACST−UC Berkeley
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Porous Covalent Organic Framework. J. Am. Chem. Soc.
2009, 131, 4570–4571.
KAVLI foundation for funding through a KAVLI ENSI graduate
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student fellowship. Y.M. acknowledges funding support from
National Science Foundation of China (NSFC grant no.
21875140). The Advanced Light Source is supported by the
Director, Office of Science, Office of Basic Energy Sciences, of
the U.S. Department of Energy under Contract No. DE-AC02-
05CH11231. The authors acknowledge Ye Zhang and
Professor Peidong Yang for solid-state photoluminescence
measurement, Dr. Nanette Jarenwattananon and Dr. Hasan
Celik for assistance with solid-state NMR studies.
(10) Zhang, Y.-B.; Su, J.; Furukawa, H.; Yun, Y.; Gandara, F.;
Duong, ́ A.; Zou, X.; Yaghi, O. M. Single-crystal Structure
of a Covalent Organic Framework. J. Am. Chem. Soc.
2013, 135, 16336− 16339.
(11) Gemmi, M.; Oleynikov, P. Scanning Reciprocal Space for
Solving Unknown Structures: Energy Filtered Diffraction
Tomography and Rotation Diffraction Tomography
Methods. Zeitschrift fur Krist. 2013, 228, 51–58.
(12) Dassault Systèmes BIOVIA, Materials Studio 8.0, San
Diego: Dassault Systèmes, 2014.
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