doi.org/10.26434/chemrxiv.11586510.v1
Single Crystal of a One-dimensional Covalent Organic FrameworkHaisen Xu, Yi Luo, Xing Li, Pei Zhen See, Zhongxin Chen, Tianqiong Ma, Lin Liang, Kai Leng, IbrahimAbdelwahab, Lin Wang, Runlai Li, Xiangyan Shi, Yi Zhou, Xiu Fang Lu, Xiaoxu Zhao, Cuibo Liu, Junliang Sun,Kian Ping Loh
Submitted date: 12/01/2020 • Posted date: 13/01/2020Licence: CC BY-NC-ND 4.0Citation information: Xu, Haisen; Luo, Yi; Li, Xing; See, Pei Zhen; Chen, Zhongxin; Ma, Tianqiong; et al.(2020): Single Crystal of a One-dimensional Covalent Organic Framework. ChemRxiv. Preprint.https://doi.org/10.26434/chemrxiv.11586510.v1
Although polymers have been studied for well over a century, there are few examples of covalently linkedpolymer crystals synthesized directly from solution. One-dimensional (1D) covalent polymers that are packedinto a framework structure can be viewed as a 1D covalent organic framework (COF), but making singlecrystal of this has been elusive. Herein, by combining labile metal coordination and dynamic covalentchemistry, we discovered a strategy to synthesize single-crystal metallo-COF under solvothermal conditions.The single-crystal structure was rigorously solved using single-crystal electron diffraction (SCED) technique.The non-centrosymmetric metallo-COF allows second harmonic generation (SHG). Due to the presence ofsyntactic pendant amine groups along the polymer chains, the metallopolymer crystal can be furthercross-linked into a crystalline woven network.
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1
Single Crystal of a One-dimensional Covalent Organic Framework
Hai-Sen Xu,1† Yi Luo,2,3† Xing Li,1† Pei Zhen See,1 Zhongxin Chen,1 Tianqiong Ma,2 Lin Liang,4
Kai Leng,1 Ibrahim Abdelwahab,1 Lin Wang,1 Runlai Li,1 Xiangyan Shi,5 Yi Zhou,6 Xiu Fang Lu,1
Xiaoxu Zhao,1 Cuibo Liu,1 Junliang Sun,2* Kian Ping Loh1*
1Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 5
117543, Singapore.
2College of Chemistry and Molecular Engineering, Beijing National Laboratory for Molecular
Sciences, Peking University, Beijing 100871, China.
3Department of Materials and Environmental Chemistry Stockholm University, SE-10691
Stockholm (Sweden). 10
4State Key Laboratory of Applied Organic Chemistry, College of Chemistry and Chemical
Engineering, Lanzhou University, Lanzhou, Gansu 730000, China.
5School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang
Link, Singapore 637371.
6School of Physical Science and Technology, Shanghai Tech University, Shanghai 201210, China. 15
† These authors contributed equally to this work.
*Correspondence to: [email protected] (J.S.); [email protected] (K.P.L.)
Abstract: Although polymers have been studied for well over a century, there are few examples
of covalently linked polymer crystals synthesized directly from solution. One-dimensional (1D)
covalent polymers that are packed into a framework structure can be viewed as a 1D covalent 20
organic framework (COF), but making single crystal of this has been elusive. Herein, by
combining labile metal coordination and dynamic covalent chemistry, we discovered a strategy to
synthesize single-crystal metallo-COF under solvothermal conditions. The single-crystal structure
was rigorously solved using single-crystal electron diffraction (SCED) technique. The non-
centrosymmetric metallo-COF allows second harmonic generation (SHG). Due to the presence of 25
syntactic pendant amine groups along the polymer chains, the metallopolymer crystal can be
further cross-linked into a crystalline woven network.
Main Text: Framework solids have been one of the hottest materials over the past 30 years
because they represent mankind’s attempt to control chemical bonding in space versus random
polymerisation1,2. Depending on the nature of the strongest bond (coordination bond, covalent 30
bond, hydrogen bond, etc.) used in constructing the solids, framework materials are categorized
into metal-organic frameworks (MOFs)3-5, covalent organic frameworks (COFs)6-10, and
hydrogen-bonded organic frameworks (HOFs)11,12. The synthesis of framework materials needs to
2
be carried out under conditions where bond formation is highly reversible to facilitate the self-
correction process necessary for crystal growth. In this regard, COFs are among the most difficult
to crystallize, owing to the lesser reversibility of their covalent linkages compared to coordination
bonds and hydrogen bonds in MOFs and HOFs. The ease of encoding functionalities in COFs and
their structural robustness render them potentially useful in wide-ranging applications13-19. 5
However, an in depth understanding of the structure-property correlation in COFs is lacking,
owing to fact that most synthesized COFs are polycrystalline, which hampers structural
determination. Recently, the addition of crystal seeds or modulators have been used to grow single-
crystalline two- or three-dimensional (2D or 3D) COFs20,21. Nevertheless, only a few examples of
3D COFs have their crystal structure rigorously solved21-23. It is generally recognized that single 10
crystalline frameworks of lower dimensionality are more difficult to grow compared to higher
dimensionality ones24.
Although the vast choices of COF building units and covalent linkages give rise to diverse
structural motifs in the synthesized product, the produced 2D and 3D COFs tend to crystallize in
high symmetric space groups due to the high symmetries of the building blocks and low freedom 15
of intermolecular packing8,9. As such, conventionally synthesized COFs are mostly
centrosymmetric and do not exhibit second harmonic generation or ferroelectricity25. In this regard,
one dimensional (1D) COFs, which possess a high degree of freedom in molecular packing, can
be a candidate to construct non-centrosymmetric crystals. Conceptually, the framework structure
in 1D COF is constructed from 1D-confined covalent linkages, and non-covalent interactions (such 20
as π-π interactions, hydrogen bonding, etc.) in the other two dimensions help to pack the 1D chains.
However, the extremely high anisotropy and the entropy-driven random packing of organic chains
impose a huge challenge on the synthesis of 1D COFs. Using its covalent analogue, linear
polymers, as examples: since the invention of the first synthetic polymer (Bakelite) in 1907, nearly
all the polymers synthesized are amorphous or poorly crystalline. To obtain a well-defined 1D 25
COF, two basic aspects have to be considered: (i) How to get a framework, not just a densely
packed organic polymer; (ii) how to control the periodic packing of organic chains to get a single
crystalline structure. Although topochemical polymerisation approach has been used to produce
single crystalline polymers from pre-packed molecular crystals, the approach is rather limited in
scope26-28. It is highly desirable to search for a direct crystallization method from solution, which 30
has been so far elusive.
Herein, we demonstrate a strategy to synthesize single crystalline 1D metallo-COFs by
combining metal-ligand coordination29 and dynamic covalent chemistry (DCC)30 (Fig. 1). A one-
pot reaction combining self-assembly31,32 and imine condensation was conducted under
solvothermal conditions. Along with the poly-condensation reaction, the constituents are 35
consumed and regenerated from the reactant “pool”33. An advantage of this method is that building
blocks can evolve into multi-intermediates through reversible reactions or interactions without the
need to synthesize each building block individually, which is distinct from the conventional
methods of making crystalline organic networks using predetermined building blocks34,35. We first
attempt to construct 1D conjugated polymer solely based on DCC without a metal template. Due 40
3
to the absence of secondary interactions, the 1D polymer chains pack randomly to afford a poorly
crystalline polymer (Supplementary Fig. 1). We then introduce AgBF436 to initiate ligand exchange
and provide an additional reversible process for the poly-condensation, which should be beneficial
for the crystal nucleation process. When one of the building units, 4,4'-(1,10-phenanthroline-2,9-
diyl)dianiline (I), is in excessive amount, it can be anchored onto the backbone chains via AgI 5
coordination in a syntactic fashion, thus providing periodic spacers to induce π-π stacking and
hydrogen bonding between the 1D chains (Fig.1). Using this approach, we synthesized single
crystalline 1D metallo-COF (mCOF-Ag) with micrometer-sized particles, allowing the rigorous
characterisation of the crystal structure via single-crystal electron diffraction (SCED)37.
In line with the strategy, a one-pot reaction by combining self-assembly and imine 10
condensation was conducted under solvothermal conditions. In 2,9-bis(4-
(dimethoxymethyl)phenyl)-1,10-phenanthroline (II), an acetal group38 is preferred for its good
solubility which is beneficial for the self-assembly process; besides, the relatively low reactivity
of acetal with amine groups can reduce the crystal nucleation rate to enable good crystals. Once
AgBF4 was added into the suspension of I and II, an immediate colour change was observed 15
indicating the occurrence of self-assembly via coordination. The amount of AgBF4 added has a
strong influence on crystal qualities. According to the strategy, the stoichiometry of I, II, and
AgBF4 is 3:1:2. However, adopting this ratio produces a large number of Ag particles on the
material. The presence of Ag particles is attributed to the reversible nature of imine bond; in situ
formed aldehyde groups can reduce Ag ions into elemental Ag, which then aggregated into 20
particles. When the ratio of AgBF4 is reduced to 1, no Ag particles were detected under the same
reaction conditions. The use of excess I and II can protect Ag ions from being reduced. After
carefully screening the reaction conditions, mCOF-Ag was obtained in a mixture of 1-butanol, 1,2-
dichlorobenzene, and 6 M aqueous acetic acid (1/9/1, v/v/v) at 120 °C for three days with a feeding
ratio of I, II, and AgBF4 equals to 3:1:1. After copiously washing with DMSO and THF, and 25
drying at 100 °C for 8 hours, mCOF-Ag was obtained as a light yellow solid (74% yield, based on
AgBF4).
The chemical bonding in mCOF-Ag was assessed by Fourier-transform infrared
spectroscopy (FT-IR) (Supplementary Figs. 3 and 4) and 13C cross-polarization magic-angle
spinning (CP/MAS) NMR (Supplementary Fig. 5). mCOF-Ag exhibits sharp powder X-ray 30
diffraction (PXRD) peaks, indicating its high crystallinity (Supplementary Fig. 2). Scanning
electron microscopy (SEM) image reveals that mCOF-Ag exhibits a uniform rod-like morphology
with the crystal size larger than 2 μm (Fig. 2b). Ordered lattice fringes in the high-resolution
transmission electron microscopy (HRTEM) image (Fig. 2c) and selected-area electron diffraction
(SAED) pattern (Fig. 2c, inset) confirm its single-crystal nature. 35
The single-crystal structure of mCOF-Ag is determined directly from the SCED data39,40
(Fig. 2a). From the observed electron density maps (Fig. 2d and Supplementary Fig. 8), all
positions of the non-hydrogen atoms (C, N, and Ag) on the framework structure and the locations
of the guests (BF4‾ anions) are identified. The SCED data was collected on a typical rod-like
4
crystal, with a resolution of ~0.95 Å, which reflects the single-crystal nature of mCOF-Ag. A C-
centered monoclinic cell with a = 15.66 Å, b = 31.00 Å, c = 10.87 Å, and β = 123.31° is identified
by indexing the SCED data using the program XDS (Supplementary Table S1). As indicated by
the reflection conditions (hkl: h+k; 0kl: k = 2n; hk0: h+k; h00: h = 2n; and 0k0: k = 2n), the
possible space groups are deduced to be C2/c (No.15), Cc (No. 9), C2/m (No. 12), Cm (No. 8), or 5
C2 (No. 5). Based on this SCED data, the structure model of mCOF-Ag was solved directly in the
space group C2/c using the program SHELXT (dual-space method). In the determined structure
model, it is found that the C and N atoms on the connection bonds (–C=N–) are symmetry related.
In order to make them symmetry independent, the symmetry of the structure model was reduced
into its subgroup C2. The determined structure model of mCOF-Ag was further confirmed and 10
refined against its synchrotron powder X-ray diffraction (SPXD) data (Supplementary Fig. 11).
Using the SVD-index method implemented in the software Topas, the SPXD data of mCOF-Ag is
indexed by a C-centered monoclinic cell of a = 15.83 Å, b = 29.97 Å, c = 10.69 Å, and β = 123.96°,
which is consistent with the unit cell obtained from the SCED data. The final agreement residuals
for the Rietveld refinement are RI = 0.075, Rwp = 0.108, with Rexp = 0.049. 15
Further analysis of the crystal structure reveals more insights about the packing of the 1D
chains. The adjacent phenanthroline chains are arranged in a parallel fashion to generate a 2D
corrugated layer (Supplementary Fig. 10), and the 2D layers are further stabilized by the
interactions of amines with BF4‾ anions (Supplementary Fig. 9), as well as the π-π stacking of
interlayer phenanthroline rings (Supplementary Fig. 10), to form a permanent structure (Fig. 3a). 20
The Ag and pendant groups I are arranged in a syntactic version, favouring ordered packing of the
polymer chains. mCOF-Ag belongs to the C2 space group, which is non-centrosymmetric. This is
validated by second harmonic generation (SHG)41 at 425 nm when the crystal is excited by
fundamental laser wavelength of 850 nm (Fig. 3b and Supplementary Fig. 16). Polarization-
dependent SHG was recorded on an isolated crystal. Using polarized laser excitation, a SHG map 25
of the COF-Ag crystal could be obtained (Fig. 3b, inset). The strongest SHG response was
observed under parallel polarized excitation, this means that the maximum SHG response
originates from the longitudinal direction of the mCOF-Ag crystal.
Due to the packing of zigzag chains, the orientation and rotation of amine groups in
building block I are spatially well defined and the two diagonally positioned –NH2 groups are 30
separated by ~3.9 Å (Fig. 4a). mCOF-Ag is an ideal scaffold for crystalline state polymerisation
because the adjacent amine groups can be linked by bi-functional compounds. Glyoxal, a molecule
with two aldehyde groups, was chosen for its suitable molecular size and good reactivity with
amine groups. mCOF-Ag was reacted with glyoxal solution (40 wt. % in H2O) at 70 °C in 1,4-
dioxane. After incubation for five days and washing, the product was collected and dried to yield 35
a cross-linked woven network, termed as wCOF-Ag (Fig. 4a). The crystalline-state polymerisation,
which occurs via “stitching” of the inter-chain amine groups by the aldehyde molecules, was
verified using a range of techniques. In the FT-IR spectra, the characteristic bands at 3361 cm-1,
3301 cm-1, and 3197 cm-1 for N-H stretching, and at 1618 cm-1 for N-H bending, have almost
vanished after cross-linking, indicating the near-complete consumption of amine groups in mCOF-40
5
Ag (Supplementary Fig. 17). The polymerisation process was further verified by the CP/MAS
NMR spectrum of wCOF-Ag, where the peak corresponding to the aldehyde carbon in glyoxal at
190 ppm is absent (Supplementary Fig. 18), indicating the full connection of amine and aldehyde
groups. The PXRD pattern appears very similar with mCOF-Ag except for slight differences at
high angles (Fig. 4b). These results affirm that cross-linking process did not affect the major part 5
of the crystal structure. One evidence that the cross-linked solid is different from the pristine
structure is provided by the photoluminescence (PL) spectroscopy, where the PL of wCOF-Ag
showed a dramatic six-fold enhancement in intensity compared to that of mCOF-Ag
(Supplementary Fig. 23). We have also examined the mechanical properties of the crystals before
and after cross-linking using nano-indentation. By indenting on an isolated micron-sized crystal 10
of each of these two samples, the Young’s moduli of mCOF-Ag and wCOF-Ag were determined
to be 9.0 (Supplementary Fig. 24) and 19.1 GPa (Supplementary Fig. 25), respectively (Fig. 4c).
The value of wCOF-Ag is comparable with that of COF-505 (~12.5 GPa)34. The distinct increase
in Young’s modulus of wCOF-Ag is in line with its covalently connected structure in a 3D space,
which imbues greater rigidity on the resulting material. 15
In this study, by combining metal-ligand coordination and dynamic imine bond formation,
a single crystalline material, mCOF-Ag, was successfully constructed via solvothermal conditions;
its crystal structure was rigorously solved with SCED. Due to its non-centrosymmetric structure,
mCOF-Ag shows an obvious SHG signal, demonstrating its potential as nonlinear optical
materials. Moreover, due to the presence of interlaced pendant amine groups along the polymer 20
chains, a high degree of control on the polymer backbone is obtained by crystalline-state
polymerisation to form a woven network. From a synthetic perspective, the strategy we developed
combines the powerful templating effect of metal ions and cooperative organization of building
blocks to maximize the number of secondary bonds in solution, thus it can be a promising method
for the solution-phase synthesis of single-crystal covalent metallopolymers with unique topologies 25
and functionalities.
6
Fig. 1 | Strategy of synthesizing single crystalline 1D metallo-COF. Colour scheme: C on
organic chains, blue; C on pendants, grey; N, purple; Ag, yellow; B, pink; F, green. Hydrogen
atoms are omitted for clarity.
7
Fig. 2 | Structure characterisation and analysis of mCOF-Ag. a, 3D reciprocal lattice of mCOF-
Ag reconstructed from the SCED data (left) and 2D slices cut from the reconstructed reciprocal
lattice (right). b, SEM image of mCOF-Ag with uniform rod-like morphology. Scale bar: 1 µm. c,
HRTEM image of mCOF-Ag and SAED pattern (inset) confirmed the single crystalline nature of 5
the material. Scale bar: 20 nm. d, Observed electron density map of the initial structure model
determined from SCED data along the c-axis.
8
Fig. 3 | Single-crystal structure and nonlinear optical measurements of mCOF-Ag. a, Crystal
view of mCOF-Ag along the c-axis. Colour scheme: C on organic chains, blue; C on pendants,
grey; N, purple; Ag, yellow. Hydrogen atoms and BF4‾ anions are omitted for clarity. b, The SHG
spectrum of an isolated crystal of mCOF-Ag. The excitation wavelength is 850 nm, the peak at 5
425 nm is the SHG signal. Inset: polarization dependent SHG response. Red curve is the fitting
result of experimental data (blue dots). The units are in degree.
9
Fig. 4 | Crystalline-state polymerisation and characterisation. a, Confined environments of
mCOF-Ag (left) and the ideal structure of the cross-linked framework, wCOF-Ag (right). One of
the cross-linked parts is highlighted with a red circle. Colour scheme: C on organic chains, blue;
C on pendants, grey; N, purple; Ag, yellow. Hydrogen atoms and BF4‾ anions are omitted for 5
clarity. b, PXRD patterns of mCOF-Ag and wCOF-Ag. c, The Young’s moduli of mCOF-Ag and
wCOF-Ag.
10
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Acknowledgments
K.P.L. acknowledges NRF-CRP grant “Two Dimensional Covalent Organic Framework:
Synthesis and Applications”. Grant number NRF-CRP16-2015-02, funded by National Research
Foundation, Prime Minister’s Office, Singapore. J.S. and Y.L. acknowledge National Natural
Science Foundation of China and Swedish Research Council. H.-S.X. and K.P.L. thank Q. Zhang 10
(National University of Singapore) for help with PL tests, Z. Zhu, X. Wu, Q. Guo (National
University of Singapore) for help with SHG tests, and L. Zhang, P. Chen (Peking University) for
help with single-crystal structure analysis.
Author contributions
K.P.L. supervised the project. J.S. supervised the crystal structures analysis. H.-S.X. designed and 15
performed the experiments. Y.L. conducted SCED characterisation and Rietveld Refinement.
X.L., Z.C., T.M., L.L., K.L., X.F.L. and C.L. discussed the synthesis and characterisation. I.A.
conducted the SHG test. L.W. conducted the AFM test. R.L. helped to analyze the nano-
indentation data. X.S. conducted CP/MAS NMR characterisation. Y.Z. conducted HRTEM
characterisation. X.Z. helped to analyse the HRTEM data. K.P.L., H.-S.X., X.L., P.Z.S. and Y.L. 20
wrote the manuscript.
Competing interests
The authors declare no competing interests.
download fileview on ChemRxivSingle-crystal 1D COF.pdf (1.14 MiB)
1
Supplementary Materials for
Single Crystal of a One-dimensional Covalent Organic Framework
Hai-Sen Xu,† Yi Luo,† Xing Li,† Pei Zhen See, Zhongxin Chen, Tianqiong Ma, Lin Liang, Kai
Leng, Ibrahim Abdelwahab, Lin Wang, Runlai Li, Xiangyan Shi, Yi Zhou, Xiu Fang Lu, Xiaoxu
Zhao, Cuibo Liu, Junliang Sun,* Kian Ping Loh*
†These authors contributed equally to this work.
*Correspondence to: [email protected] (J.S.); [email protected] (K.P.L.)
This PDF file includes:
Materials and Methods
Supplementary Text
Supplementary Figures 1-25
Supplementary Table 1
Supplementary References
2
Materials and Methods
Reagent
All commercially available starting compounds and solvents were purchased from commercial
sources and used without further purification. 2-(4-(dimethoxymethyl)phenyl)-4,4,5,5-
tetramethyl-1,3,2-dioxaborolane was synthesized through a two-step reaction as reported in
literature1.
Instrumentation and characterization
Liquid 1H and 13C NMR spectra were recorded on a Bruker AVANCE I 300 MHz or a Bruker
AVANCE I 500 MHz NMR spectrometer and chemical shifts (δ-scale) were reported in parts per
million (ppm). Solid-state NMR experiments were performed on a Bruker Avance III HD 600
MHz wide-bore NMR spectrometer. The 13C cross-polarization magic-angle spinning (CP/MAS)
NMR spectra were recorded with a 4 mm double-resonance MAS probe. High-resolution mass
spectrometry (HRMS) data were obtained on a Finnigan/MAT 95XL-T spectrometer. Fourier-
transform infrared spectroscopy (FTIR) was carried out on a Bruker VERTEX 80V spectrometer
in transmission mode under vacuum. Photoluminescence (PL) spectra were obtained with a laser
confocal microscope (NT-MDT, NTEGR Spectra) with 532 nm (continuous wave (cw)) excitation
lasers under ambient conditions. H, C and N contents were determined via elemental analysis
performed on an Elementar vario MICRO cube. Thermogravimetric analysis (TGA) was carried
out on a Discovery TGA within the temperature range of 30 °C to 800 °C with a heating rate of 10
°C/min.
Powder X-ray diffraction (PXRD) data were collected on a Bruker D8 Focus Powder X-ray
Diffractometer using Cu Kα radiation (40 kV, 40 mA) at room temperature. Synchrotron powder
X-ray diffraction (SPXD) data were collected on the sample in a 0.5 mm capillary on the BL14B1
beamline (λ = 0.69005 Å) at the Shanghai Synchrotron Radiation Facility in Shanghai, China. The
collected data were ranging from 2.0 to 20.0° with 0.004° data binning.
Scanning electron microscopy (SEM) images were obtained with a JEOL JSM-6701F microscope.
A JEM-2100Plus (LaB6 filament) operated at 200 kV was used for high resolution transmission
electron microscopy (HRTEM) imaging. Single-crystal electron diffraction (SCED) data were
collected using a JEOL JEM2100 TEM (LaB6 filament) operating at 200 kV. The reciprocal space
reconstruction was carried out using the RED software, and the reflection intensity extraction was
conducted by the program XDS2,3.
For the second harmonic generation (SHG) characterization, a Yb:KGW femtosecond PHAROS
laser system was used as the pump of a collinear optical parametric amplifier ORPHEUS with a
LYRA wavelength extension option (Light Conversion Ltd, pulse duration of 150 fs, tunable
excitation wavelength of 310 nm – 2700 nm, and repetition rate of 100 Hz –100 kHz). The laser
beam was focused onto the COF samples with a 100x (NA = 0.9) air objective from Nikon (1 μm2
spot size). The nonlinear emission was collected in a back-scattering configuration via the same
3
objective and detected by a spectrograph (PI Acton SP2300 by Princeton Instruments) for spectral
measurements. The power of the collected SHG emission was measured using a calibrated silicon
photodetector (Newport), while the excitation power was measured using a germanium
photodetector (Thorlabs). For polarization dependent SHG measurements, a half-wave plate was
used to vary the orientation of the linearly polarized laser pulses.
X-ray photoelectron spectroscopy (XPS) was performed using PHI Quantera II with a
monochromatic Al-Kα source (energy = 1486.6 eV).
Atomic force microscopy (AFM) nano-indentation experiments were performed using the
Dimension Icon instrument operating under the indentation mode, equipped with a Bruker
Tap525A probe. Its spring constant and contact sensitivity have been calibrated as 156.760 N/m
and 83.01 nm/volt, respectively.
4
Supplementary Text
Synthesis of 4,4'-(1,10-phenanthroline-2,9-diyl)dianiline (I)
Compound S2. To a two-necked round bottom flask were added S1 (1.014 g, 3.0 mmol), tert-
butyl (4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)carbamate (2.490 g, 7.8 mmol),
K2CO3 (1.242 g, 9.0 mmol), Pd(PPh3)4 (347 mg, 0.3 mmol), 1,4-dioxane (48 mL), and H2O (12
mL). The reaction mixture was deaerated by slow bubbling of N2 for 30 min, and then heated to
reflux at 100 °C for 8 h. After cooling to room temperature, the solvent was removed under reduced
pressure, the residue was treated with H2O (60 mL), extracted with CH2Cl2 (4 × 40 mL), the
combined organic phase was washed with brine, dried over Na2SO4, and concentrated. The crude
product was purified by silica gel column chromatography using CH2Cl2/CH3OH = 100/0.5 as the
eluent to give the product S2 (1.204 g, 71% yield) as a white solid. 1H NMR (300 MHz, CDCl3):
δ = 8.48-8.39 (m, 4H), 8.26 (d, J = 8.5 Hz, 2H), 8.10 (d, J = 8.5 Hz, 2H), 7.75 (s, 2H), 7.64-7.53
(m, 4H), 6.65 (s, 2H), 1.57 (s, 18H). 13C NMR (125 MHz, CDCl3): δ = 156.1, 152.5, 139.7, 136.8,
134.1, 128.4, 127.7, 125.7, 119.4, 118.4, 80.8, 28.4. HRMS: m/z calcd for C34H35N4O4 [M + H]+:
563.2653, found: 563.2664.
4,4'-(1,10-phenanthroline-2,9-diyl)dianiline (I). To a round bottom flask were added S2 (562.3
mg, 1.0 mmol) and 4 M HCl/1,4-dioxane (10 mL). The mixture was stirred at room temperature
for 2 h, and then filtered to get a dark red solid. The solid was dissolved in deionized water (50
mL), and then neutralized with KOH solution. The resulting suspension was extracted with CH2Cl2
(3 × 40 mL), the combined organic phase was washed with brine, dried over Na2SO4, and
concentrated to afford the product I (335 mg, 92% yield) as a light yellow solid. 1H NMR (300
MHz, DMSO-d6): δ = 8.36 (d, J = 8.5 Hz, 2H), 8.24 (d, J = 8.6 Hz, 4H), 8.16 (d, J = 8.5 Hz, 2H),
7.81 (s, 2H), 6.77 (d, J = 8.6 Hz, 4H), 5.57 (s, 4H). 13C NMR (125 MHz, DMSO-d6): δ = 155.6,
150.4, 145.2, 136.5, 128.3, 126.7, 126.3, 124.9, 118.3, 113.8. HRMS: m/z calcd for C24H19N4 [M
+ H]+: 363.1604, found: 363.1611.
5
Synthesis of 2,9-bis(4-(dimethoxymethyl)phenyl)-1,10-phenanthroline (II)
2,9-bis(4-(dimethoxymethyl)phenyl)-1,10-phenanthroline (II). To a two-necked round bottom
flask were added S1 (676 mg, 2.0 mmol), 2-(4-(dimethoxymethyl)phenyl)-4,4,5,5-tetramethyl-
1,3,2-dioxaborolane (1.45 g, 5.2 mmol), K2CO3 (828 mg, 6.0 mmol), Pd(PPh3)4 (231 mg, 0.2
mmol), 1,4-dioxane (32 mL), and H2O (8 mL). The reaction mixture was deaerated by slowly
bubbling N2 for 30 min, and then heated to reflux at 100 °C for 8 h. After cooling to room
temperature, the solvent was removed under reduced pressure. The residue was treated with H2O
(60 mL), extracted with CH2Cl2 (4 × 40 mL), the combined organic phase was washed with brine,
dried over Na2SO4, and concentrated. The crude product was purified by silica gel column
chromatography using hexane/ethyl acetate = 3/1 as the eluent to give the product II (758 mg, 79%
yield) as a white solid. 1H NMR (300 MHz, CDCl3): δ = 8.51-8.40 (m, 4H), 8.33 (d, J = 8.4 Hz,
2H), 8.16 (d, J = 8.4 Hz, 2H), 7.81 (s, 2H), 7.68 (d, J = 8.3 Hz, 5H), 5.54 (s, 3H), 3.39 (s, 11H). 13C NMR (125 MHz, CDCl3): δ = 156.5, 146.1, 139.6, 139.2, 136.9, 127.9, 127.6, 127.3, 126.0,
120.1, 102.8, 52.5. HRMS: m/z calcd for C30H29N2O4 [M + H]+: 481.2122, found: 481.2131.
Synthesis of the conjugated polymer
I (11.6 mg, 0.032 mmol) and II (15.4 mg, 0.032 mmol) were weighed into a 10 mL Schlenk tube.
To the mixture were added 1-butanol (0.1 mL), 1,2-dichlorobenzene (0.9 mL) and 6 M aqueous
acetic (0.1 mL). The Schlenk tube was frozen in a liquid nitrogen bath, evacuated to an internal
pressure of 0 mbar and sealed. After warming to room temperature, the Schlenk tube was placed
into an oven and heated at 120 °C for 3 days yielding a yellow orange solid at the bottom of the
tube. The Schlenk tube was opened when the mixture was still warm and the solid was transferred
into a vial, separated by centrifugation, washed copiously with DMSO, THF, and EtOH. After
drying at room temperature, the resulting solid was dried under vacuum at 100 °C for 12 h to obtain
the conjugated polymer.
Crystallization of single-crystalline mCOF-Ag
I (17.4 mg, 0.048 mmol) and II (7.7 mg, 0.016 mmol) were weighed into a 10 mL Schlenk tube.
To the mixture, a solution of AgBF4 (3.1 mg, 0.016 mmol) in 1-butanol (0.1 mL) and 1,2-
6
dichlorobenzene (0.9 mL) was added. After sonicating at room temperature for 10 min, 0.1 mL 6
M aqueous acetic was added into the suspension. The Schlenk tube was frozen in a liquid nitrogen
bath, evacuated to an internal pressure of 0 mbar and sealed. After warming to room temperature,
the Schlenk tube was placed into an oven and heated at 120 °C for 3 days yielding a light yellow
solid at the bottom of the tube. The Schlenk tube was opened when the mixture was still warm and
the solid was transferred into a vial, separated by centrifugation, washed copiously with DMSO,
THF, and EtOH. After drying at room temperature, the resulting solid was dried under vacuum at
120 °C for 8 h to obtain mCOF-Ag as a light yellow solid (10.8 mg, 74% yield, based on AgBF4).
Anal. Calcd for (C49H33N7AgBF4)n: C 64.35; H 3.64; N 10.72. Found: C 64.29; H 3.61; N 10.67.
Crystalline-state polymerization
wCOF-Ag. To a 10 mL pressure tube were added mCOF-Ag (5.0 mg), 1,4-dioxane (1.0 mL), and
glyoxal solution (40 wt. % in H2O) (5.0 μL). The tube was sealed and placed in an oven at 70 °C
for 5 days. After cooling to room temperature, the solid was transferred into a vial, and washed
with THF, H2O, EtOH, and Et2O in sequence. The resulting solid was dried at room temperature
to afford the polymerized material, wCOF-Ag. Anal. Calcd for (C51H31N7AgBF4)n: C 65.41; H
3.34; N 10.47. Found: C 65.92; H 3.26; N 10.35.
Temperature is an important factor to obtain a high quality material. Increasing the temperature
from 70 °C to 80 °C will generate Ag particles on the surface of the crystal. The Ag particles are
attributed to the labile nature of Ag ions, which can be reduced to elemental Ag by glyoxal at a
higher temperature.
7
Supplementary Figure 1 | Experimental PXRD patterns of the conjugated polymer (black) and
mCOF-Ag (red). The synthesized conjugated polymer has a semi-crystalline feature, which is
attributed to the π-π stacking in the rigid and conjugated structure of phenanthroline backbones;
besides, the reversibility in imine bond formation can impart self-correction during the
hydrothermal conditions.
8
Supplementary Figure 2 | Experimental PXRD patterns of mCOF-Ag (black), building block a
(red), and building block b (blue).
9
Supplementary Figure 3 | FT-IR spectra of mCOF-Ag (black), building block a (red), and
building block b (blue).
10
Supplementary Figure 4 | FT-IR spectra of mCOF-Ag before (black) and after (red) drying the
KBr pellet at 100 °C to eliminate the influence of water. In the red curve, the characteristic peaks
of N–H stretches and N–H bending vibration are apparent.
11
Supplementary Figure 5 | 13C CP/MAS NMR spectra of mCOF-Ag. The asterisks denote the
spinning sidebands.
12
Supplementary Figure 6 | TGA curve of mCOF-Ag. The decomposition temperature is about 320
ºC. The ~1.4% weight loss below 320 °C is attributed to the small amount of solvents trapped in
the crystal.
13
Supplementary Figure 7 | Nitrogen adsorption (filled symbols) and desorption (empty symbols)
isotherms of mCOF-Ag. The low uptake in the isotherm line is in line with its crystal structure,
whereby the pores are occupied by BF4– anions.
14
Supplementary Table 1 | SCED: Experimental and Crystallographic parameters of mCOF-Ag.
Tilt range (°) -41.40 ~ 39.96
Tilt step (°) 0.23
Wave length (Å) 0.0251
No. of frames 336
Exposure time per image (s) 0.5
Crystal system Monoclinic
Possible space group C2/c, Cc, C2/m, Cm, C2
Unit cell parameters a = 15.66 Å, b = 31.00 Å, c = 10.87 Å,
α = 90°, β = 123.3°, γ = 90°
Resolution (Å) 0.95
I/σ(I) 4.90
Completeness (%) 56
CC1/2 98.8
Rmeas (%) 11.8
No. of total reflections 4024
No. of unique reflections 1522
15
Supplementary Figure 8 | Observed electron density map of the structure of mCOF-Ag
determined from SCED data along the a-axis. All positions of the non-hydrogen atoms (C, N, and
Ag) on the framework and the locations of the guests (BF4‾ anions) are resolved.
16
Supplementary Figure 9 | Crystal view along the c-axis, in which the H∙∙∙F hydrogen bond
interactions between amine and BF4‾ anions are highlighted with a red square. Colour scheme: C
on organic chains, blue; C on pendants, grey; N, purple; Ag, yellow; B, pink; F, green; H of amine
groups, white.
17
Supplementary Figure 10 | Tilted side view of the crystal structure, in which a single
phenanthroline chain is highlighted in bright yellow. The corrugated layer and the π-π stacking of
interlayer phenanthroline rings are also identified. C on organic chains, blue; C on pendants, grey;
N, purple; Ag, yellow. Hydrogen atoms and BF4‾ anions are omitted for clarity.
18
Supplementary Figure 11 | Structure refinement of mCOF-Ag against the SPXD data (Rietveld
refinement). Experimental (red), Rietveld refined (blue), as well as difference profiles (black) are
presented. The positions of Bragg reflections under the patterns are shown in green.
19
Supplementary Figure 12 | Experimental SPXD pattern and the simulated profile from the single
crystal structure of mCOF-Ag. The simulated data is highly consistent with the experimental data,
indicating the very high quality of the synthesized crystals.
20
Supplementary Figure 13 | Uv-vis spectra of mCOF-Ag, building block I, and building block
II.
21
Supplementary Figure 14 | PL spectra of mCOF-Ag, building block I, and building block II
excited by 532 nm laser.
22
Supplementary Figure 15 | SHG spectra of an isolated mCOF-Ag crystal at different pump
wavelengths.
23
Supplementary Figure 16 | Pump power dependent SHG spectra of an isolated mCOF-Ag crystal
at 850 nm. Inset shows the linear relationship between SHG intensity and pump power, the fitting
curve (red line) has a slope of 1.94, confirming the second-order nature of the nonlinear process.
24
Supplementary Figure 17 | FT-IR spectra showing time evolution of vibrational bands when
mCOF-Ag was cross-linked with glyoxal. With longer reaction time, the characteristic peaks of
N−H stretches (blue band) and N−H bending vibration (pink band) decrease, indicating the
consumption of amine groups, while the peak at 1600 cm-1 (green band) due to newly formed
imine bond increases gradually. The red curve corresponds to the control experiment without
glyoxal, which was heated in 1,4-dioxane at 70 °C for five days. All KBr pellets were dried at 100
°C before testing to eliminate background signals due to water.
25
Supplementary Figure 18 | 13C CP/MAS NMR spectra of mCOF-Ag and wCOF-Ag. The
asterisks denote the spinning sidebands.
26
Supplementary Figure 19 | SEM image of wCOF-Ag.
27
Supplementary Figure 20 | 3D reciprocal lattice of wCOF-Ag reconstructed from the SCED data.
As wCOF-Ag was synthesized via post-synthesis, the local bonding is not very order. It is difficult
to directly observe the new formed bonds via SCED data.
28
Supplementary Table 2 | SCED: Experimental and Crystallographic parameters of wCOF-Ag.
Tilt range (°) -53.22 ~ 50.17
Tilt step (°) 0.23
Wave length (Å) 0.0251
No. of frames 401
Exposure time per image (s) 0.5
Crystal system Monoclinic
Possible space group C2/c, Cc, C2/m, Cm, C2
Unit cell parameters a = 15.74 Å, b = 31.11 Å, c = 11.00 Å,
α = 90°, β = 122.6°, γ = 90°
Resolution (Å) 1.15
I/σ(I) 2.54
Completeness (%) 72.4
CC1/2 95.6
Rmeas (%) 27.2
No. of total reflections 2775
No. of unique reflections 1145
29
Supplementary Figure 21 | Pawley fitting of wCOF-Ag. Experimental (red), calculated (blue),
as well as difference profiles (black) are presented. The position of Bragg reflections under the
patterns are shown in green. The refined unit cell parameters are a = 15.6958 Å, b = 29.9200 Å, c
= 10.6661 Å, and β = 123.31° (space group: C2), which are in good agreement with those of
mCOF-Ag, indicating the parent structure of mCOF-Ag has been well inherited by wCOF-Ag. The
final residuals for the Pawley fitting are Rwp = 0.135, Rexp = 0.123.
30
Supplementary Figure 22 | X-ray photoelectron spectroscopy (XPS) Ag3d data of mCOF-Ag
and wCOF-Ag. The XPS Ag3d spectrum of wCOF-Ag is nearly identical with that of mCOF-Ag,
indicating that Ag ions in both materials have similar chemical environment.
31
Supplementary Figure 23 | PL spectra of mCOF-Ag (before crosslinking) and wCOF-Ag (after
crosslinking) excited by 532 nm laser.
32
Supplementary Figure 24 | AFM nano-indentation force−displacement curve of an isolated
crystal of mCOF-Ag. Following the standard analysis of nano-indentation, the Young’s modulus
is related to the indentation curve by Equation 1: Hertzian model 𝐹 = 4
3
𝐸
(1−𝑣2)√𝑅𝛿3/2, where F =
force (from force curve), E = Young's modulus (fit parameter), ν = Poisson's ratio (sample
dependent, 0.3), R = radius of the indenter (30.0 nm), δ = indentation.
33
Supplementary Figure 25 | AFM nano-indentation force−displacement curve of an isolated
crystal of wCOF-Ag. Following the standard analysis of nano-indentation, the Young’s modulus
is related to the indentation curve by Equation 1: Hertzian model 𝐹 = 4
3
𝐸
(1−𝑣2)√𝑅𝛿3/2, where F =
force (from force curve), E = Young's modulus (fit parameter), ν = Poisson's ratio (sample
dependent, 0.3), R = radius of the indenter (30.0 nm), δ = indentation.
34
Supplementary Figure 26 | 1H-NMR spectrum of compound S2 (25 °C, 300 MHz, CDCl3).
Supplementary Figure 27 | 13C-NMR spectrum of compound S2 (25 °C, 125 MHz, CDCl3).
35
Supplementary Figure 28 | 1H-NMR spectrum of I (25 °C, 300 MHz, DMSO-d6).
Supplementary Figure 29 | 13C-NMR spectrum of I (25 °C, 125 MHz, DMSO-d6).
36
Supplementary Figure 30 | 1H-NMR spectrum of II (25 °C, 300 MHz, CDCl3).
Supplementary Figure 31 | 13C-NMR spectrum of II (25 °C, 125 MHz, CDCl3).
37
Supplementary References:
1. Clary, J. W. et al. Hydride as a leaving group in the reaction of pinacolborane with halides under
ambient Grignard and Barbier conditions. One-pot synthesis of alkyl, aryl, heteroaryl, vinyl, and
allyl pinacolboronic esters. J. Org. Chem. 76, 9602-9610 (2011).
2. Kabsch, W. XDS. Acta Crystallogr. Sect. D. 66. 125-132 (2010).
3. Wan, W., Sun, J., Su, J., Hovmöller, S. & Zou, X. Tree-dimensional rotation electron difraction:
sofware RED for automated data collection and data processing. J. Appl. Crystallogr. 46, 1863-
1873 (2013).
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