A Porous and Solution-Processable Molecular Crystal Stable at 200 °c: The Surprising Donor-Acceptor Impact

Article abstract of DOI:10.1021/acs.cgd.9b01488

We report a curious porous molecular crystal that is devoid of the common traits of related systems. Namely, the molecule does not rely on directional hydrogen bonds to enforce open packing, and it offers neither large concave faces (i.e., high internal f

Full text of DOI:10.1021/acs.cgd.9b01488

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Article
A porous and solution-processable molecular crystal
stable at 200 °C: the surprising donor-acceptor impact
Shengxian Cheng, Xiaoxia Ma, Yonghe He, Jun He, Matthias Zeller, and Zhengtao Xu
Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.9b01488 • Publication Date (Web): 13 Nov 2019
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Crystal Growth & Design
A porous and solution-processable molecular crystal stable at 200 °C:
the surprising donor-acceptor impact
Shengxian Cheng†, Xiaoxia Ma‡, Yonghe He⊥, Jun He⊥*, Matthias Zeller§, and Zhengtao Xu†*
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†Department of Chemistry, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Hong Kong, China
‡Department of Mechanical Engineering, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Hong Kong, China
⊥School of Chemical Engineering and Light Industry, Guangdong University of Technology, Guangzhou, China
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Department of Chemistry, 560 Oval Drive, Purdue University, West Lafayette, Indiana, 47907, United States.
ABSTRACT: We report a curious porous molecular crystal that is devoid of the common traits of related systems. Namely, the
molecule does not rely on directional hydrogen bonds to enforce open packing; and it offers neither large concave faces (i.e., high
internal free volume) to frustrate close packing, nor any inherently built-in cavity like in the class of organic cages. Instead, the
permanent porosity (as unveiled by the X-ray crystal structure and CO2 sorption studies) arises from the strong push-pull units
built into a Sierpinski-like molecule that features four symmetrically backfolded (SBF) side arms. Each side arm consists of the
1,1,4,4-tetracyanobuta-1,3-diene acceptor (TCBD) coupled with the dimethylaminophenyl donor, which is conveniently installed
by a cycloaddition-retroelectrocyclization (CA-RE) reaction. Unlike the poor/fragile crystalline order of many porous molecular
solids, the molecule here readily crystallizes and the crystalline phase can be easily deposited into thin films from solutions.
Moreover, both the bulk sample and thin film exhibit excellent thermal stability with the porous crystalline order maintained even
at 200 °C. The intermolecular forces underlying this robust porous molecular crystal likely include the strong dipole interactions
and the multiple C···N and C···O short contacts afforded by the strongly donating and accepting groups integrated within the rigid
molecular
scaffold.
INTRODUCTION
The discovery here bears closely on the topical porous molecular materials,1-10 even though the backdrop is a curiosity-driven
study to synergize shape and functionality in molecular design. The shape concerns a type of symmetrically backfolded (SBF)
structure related to the famous fractal of the Sierpinski triangle (see molecules M1 and M2 in Figure 1), which contrasts the
starburst branching motifs of more commonly studied dendrimers. The functionality arises from the versatile [2+2] cycloaddition-
retroelectrocyclization (CA-RE) reaction (Figure 2):11-18 this occurs between electron-rich alkynes and electron-deficient alkenes, to
form strong push-pull units in 3D nonplanar conjugated systems, and to afford intense redox activities and optoelectronic
properties.14, 18, 19
Compared with other alkyne reactants (including starburst molecules20) of the CA-RE reaction, the backfolded Sierpinski
scaffold offers unique possibilities. For example, the backfolded side arms bend toward the interior of the molecule, and tend to
block free rotation of the backbone. Building extra atoms of the push-pull units into the side chains increases steric repulsion,
further reducing the flexibility of the overall conformation. The resultant 3D, rigid and branched molecule, with its rugged surface,
is likely to leave significant voids in the solid state—without the need for strong directional hydrogen bonds3, 4, 21-24 to impose
open packing of the molecules.
Figure 1. The Sierpinski triangle and the backfolded molecules M1 and M2.
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Figure 2. The CA-RE reaction of M2 and TCNE for preparing the molecule SBF-16.
This design therefore recalls the use of so-called awkward shapes to frustrate close packing (as in the triptycene-based
systems,25-27 with the distinct concave surface imparting large internal free volume).7, 28-30 Further exploration of this strategy,
however, is needed, as awkward is a subjective term, and non-porous, energetically favored polymorphs are often hard to avoid.
Moreover, the inefficient packing tends to defuse crystalline order, resulting in ill-defined, amorphous phases.9, 26, 31 For example,
few single crystal structures are known from this class of open-packed molecules (aka organic molecules with intrinsic
microporosity, OMIMs), and solution deposition of crystalline thin-films, a low-cost processing of industrial importance, remains
unknown for such molecules.9
By contrast, the 3D conjugated molecule SBF-16 stands out not only for its lack of distinct internal free volume (i.e., no large
concave surface), but also for its persistent crystalline porous phase—both as single crystals and as thin films readily deposited
from organic solutions. Indeed, a solution-processed crystalline thin film of a porous molecular solid is still considered a rare
feat,9, 32 even among the broader class of organic macrocycles22, 33-35 and cages36-41 (these latter cases derive porosity from the
intrinsic cavity of the individual molecules, instead of open packing motifs). Compared with the high dilution and dynamic
covalent chemistry42, 43 often entailed in assembling organic cages (e.g., to avoid polymeric side products), SBF-16 also offers the
ease of synthesis by a near-quantitative CA-RE reaction between M2 and TCNE (tetracyanoethene). Moreover, the porous
crystalline phase of SBF-16 is highly stable to heat, water and air, with no need for delicate activation procedures often required
of the generally fragile porous molecular crystals.
We will also discuss two notable features of molecule SBF-16. First, the rigid molecular backbone together with bulky side arms
results in distinct axial chirality features on different hierarchy levels of the Sierpinski scaffold. Second, the strong push-pull units
extensively integrated to the conjugated scaffold achieve an extremely high extinction coefficient for visible light, providing
opportunities for interfacing optical and electronic processes in the porous media (e.g., as in solar cells).
EXPERIMENTAL DETAILS
General procedure. Starting materials, reagents, and solvents were purchased from commercial sources (Aldrich and J&K) and
used without further purification. Elemental analysis was obtained using a Vario EL III CHN elemental analyzer. Infrared spectra
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were recorded on a Nicolet Avatar 360 FT-IR spectrophotometer. Solution H NMR and 13C NMR spectra were recorded on 300
MHz or 400 MHz Bruker superconducting-magnet high-field NMR spectrometers at room temperature with tetramethylsilane
(TMS) as the internal standard. Chemical shifts (δ) are expressed in ppm relative to the residual non-deuterated solvents.
Thermogravimetric analyses (TGA) were carried out in a nitrogen stream using PerkinElmer Thermal analysis equipment (STA
6000) with a heating rate of 3 °C/min. The porosity and surface area analysis was performed using a Quantachrome Autosorb iQ
gas sorption analyzer. The sample was outgassed at 0.03 torr with a 2 °C/min ramp to 120 °C and held at 120 °C for 12 hours. The
sample was then held at vacuum until the analysis was run. Powder X-ray diffraction data were collected in reflection mode at
room temperature on an Inel Equinox 1000 X-ray diffractometer (Inel, France) equipped with a CPS 180 detector using
monochromated Cu-Kα (λ = 1.5418 Å) radiation. The X-ray tube operated at a voltage of 30 kV and a current of 30 mA. Single
crystal X-ray diffraction data were collected on a Bruker Quest CMOS diffractometers with Mo-K (λ = 0.71073 Å) or Cu -K (λ =
1.54178 Å) radiation. See the single crystal X-ray diffraction section in the SI for details.
Synthesis of SM1. M1 was synthesized based on a modified reported method.44 A mixture of 4-bromo-dimethylaniline (2.0 g,
10 mmol), bis(triphenylphosphine)palladium(II) chloride (351 mg, 0.5 mmol), triphenylphosphine (262 mg, 1.0 mmol) and
copper(I) iodide (190 mg, 1.0 mmol) were added to a 50-mL Schlenk tube and the tube was connected to a nitrogen manifold.
Triethylamine (10.0 mL) and THF (10.0 mL), each previously purged by bubbling nitrogen gas for 5 minutes, were then transferred
into the tube. After trimethylsilylacetylene (4.1 mL, 30 mmol) was injected, the tube was screw-capped and the reaction mixture
was stirred and heated to reflux under nitrogen protection for 12 hours. After cooling to room temperature, the solvents were
removed by rotary evaporation and the resulting residue was purified by column chromatography (eluent: hexanes/DCM, 12:1 by
volume) to yield SM1 as a yellow solid (1.95 g, 90% yield based on 4-bromo-dimethylaniline). 1H NMR (300 MHz, CDCl3): δ = 7.34
(d, J = 8.7 Hz, 2H, CHAr), 6.59 (d, J = 8.8 Hz, 2H, CHAr), 2.97 (s, 6H, NCH3), 0.23 (s, 9H, SiCH3). 13C{1H} NMR (75 MHz, CDCl3) δ =
150.1, 133.1, 111.5, 109.8, 106.5, 91.1, 40.1, 0.2.
Synthesis of SM2. M2 was synthesized based on a modified reported method.44 A mixture of SM1 (1.95 g, 8.9 mmol) and
anhydrous potassium carbonate (2.48 g, 17.9 mmol) in a solution of DCM (20.0 mL) and methanol (20.0 mL) was stirred at room
temperature for one hour. Then the reaction mixture was filtered to remove the undissolved K2CO3, and the resulting organic
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filtrate was extracted with DCM (3 × 80 mL), washed with distilled water (3 × 100 mL) and dried over anhydrous MgSO4. After
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solvent removal, the orange solid obtained was used directly in the next step (1.26 g, 98% based on SM1). H NMR (300 MHz,
CDCl3) δ = 7.37 (d, J = 8.8 Hz, 2H, CHAr), 6.62 (d, J = 8.8 Hz, 2H, CHAr), 2.98 (s, 6H, NCH3). 13C{1H} NMR (75 MHz, CDCl3) δ = 150.3,
133.2, 111.6, 108.7, 84.8, 74.8, 40.2.
Synthesis of SM3. Methyl 4-amino-3,5-dibromobenzoate (SM3) was prepared based on a literature method.45 Methyl 4-
aminobenzoate (10.0 g, 66.2 mmol) was added to a round-bottom flask charged with a magnetic stirring bar and dissolved in
acetic acid (30 mL). A mixture of acetic acid (30 mL) and bromine (23 g, 146 mmol) was added dropwise into the flask. After
stirring at room temperature for 12 hours, the reaction mixture was poured into deionized water (500 mL). The precipitate was
collected by filtration and re-dissolved in dichloromethane (DCM) and dried over anhydrous MgSO4. After solvent removal, the
residue was purified by column chromatography (silica gel, 1:1 n-hexane/DCM as the eluent) to provide SM3 as a white powder
(18.0 g, yield 90% based on methyl 4-aminobenzoate). 1H NMR (400 MHz, DMSO-d6): δ = 8.07 (s, 2H, CHAr), 5.00 (s, 2H, NH2), 3.86
(s, 3H, CH3).
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Synthesis of SM4. SM4 was synthesized according to the reported method.45 After a stirred mixture of methyl 4-amino-3,5-
dibromobenzoate (8.0 g, 26 mmol), 98% H2SO4 (10 mL) and glacial acetic acid (50 mL) was cooled below 5 °C by an ice-salt bath, a
solution of NaNO2 (2.0 g, 29 mmol) in water (25 mL) was added dropwise over a period of one hour (with the reaction mixture
kept below 5 °C). A solution of KI (43 g, 260 mmol) in water (30 mL) was then added, and the mixture was stirred at room
temperature for an additional 30 min. After neutralization with saturated aqueous NaOH, the resulted mixture was extracted with
CH2Cl2 (70 ml × 3), and the organic phase obtained was washed with an aqueous solution of Na2SO3 and dried over MgSO4. After
removal of the solvent on a rotary evaporator, an orange solid was obtained (9.6 g, 88% yield based on SM3). 1H NMR (400 MHz,
CDCl3): ): δ = 8.16 (s, 2H, CHAr), 3.93 (s, 3H, CH3).
Synthesis of SM5. SM5 was prepared according to the reported method.45 A mixture of SM4 (4.0 g, 9.8 mmol),
bis(triphenylphosphine)palladium(II) chloride (344 mg, 0.49 mmol), triphenylphosphine (256 mg, 0.98 mmol) and copper(I) iodide
(186 mg, 0.98 mmol) were added to a 50-mL Schlenk tube which was then connected to a nitrogen manifold. Anhydrous
triethylamine (12.0 mL) and THF (12.0 mL), each previously purged by bubbling with nitrogen gas for 5 minutes, were then
transferred into the tube. After trimethylsilylacetylene (2.7 mL, 19.6 mmol) was injected, the tube was screw-capped and the
reaction mixture was stirred at the temperature of refluxing under nitrogen protection for 12 hours. After cooling to room
temperature, the solvents were removed by rotary evaporation and the resulting residue was purified by column chromatography
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(silica gel, 2:1 hexanes/EA as the eluent) to yield SM5 as an orange solid (3.0 g, 80% yield based on SM4). H NMR (400 MHz,
DMSO-d6): δ = 8.18 (s, 2H, CHAr), 3.92 (s, 3H, CH3).
Synthesis of SM6. A mixture of SM5 (500 mg, 1.3 mmol), SM2 (580 mg, 4.0 mmol), bis(triphenylphosphine)palladium(II)
chloride (45.6 mg, 0.065 mmol), triphenylphosphine (34 mg, 0.13 mmol) and copper(I) iodide (25 mg, 0.13 mmol) were added to
a 20-mL Schlenk tube and the tube was connected to a nitrogen manifold. Anhydrous triethylamine (4.0 mL) and THF (2.0 mL),
each previously purged by bubbling with nitrogen gas for 5 minutes, were then transferred into the tube. The tube was screw-
capped and the reaction solution was stirred at the temperature of refluxing in an oil bath under nitrogen protection for 16 hours.
After cooling to room temperature, the solvents were removed by a rotary evaporation and the residue was purified by column
chromatography (silica gel, 1:1 hexanes/DCM as eluent) to yield SM6 as an orange red solid (525 mg, 78% yield based on SM3). 1H
NMR (300 MHz, CDCl3) δ = 8.03 (s, 2H, CHAr), 7.46 (d, J = 8.8 Hz, 4H, CHAr), 6.67 (d, J = 8.8 Hz, 4H, CHAr), 3.93 (s, 3H, COOCH3),
3.01 (s, 12H, NCH3), 0.35 (s, 9H, SiCH3). 13C{1H} NMR (75 MHz, CDCl3) δ = δ 165.8, 150.3, 132.9, 130.6, 129.9, 129.2, 127.66, 111.7,
109.5, 105.5, 102.2, 96.0, 85.8, 52.4, 40.1, 0.1.
Synthesis of SM7. A mixture of SM6 (280 mg, 0.54 mmol) and anhydrous potassium carbonate (149 g, 1.08 mmol) in a solution
of DCM (2.0 mL) and methanol (2.0 mL) was stirred at room temperature for one hour. The solid was then filtered off, and the
organic filtrate was extracted with DCM (3 × 20 mL), washed with distilled water (3 × 50 mL) and dried over anhydrous MgSO4.
After removal of the solvent by a rotary evaporation at room temperature, the orange solid thus obtained was used directly in the
next step (236 mg, 98% based on SM6). 1H NMR (400 MHz, CDCl3) δ = 8.04 (s, 2H, CHAr), 7.45 (d, J = 8.6 Hz, 4H, CHAr), 6.67 (d, J =
8.5 Hz, 4H, CHAr), 3.93 (s, 3H, COOCH3), 3.77 (s, 1H, C≡CH), 3.01 (s, 12H, NCH3).13C{1H} NMR (75 MHz, CDCl3) δ = δ 165.7, 150.4,
133.1, 130.6, 129.6, 129.1, 128.1, 111.7, 109.3, 96.2, 87.2, 85.5, 81.1, 52.4, 40.2.
Synthesis of M2. SM7 (236 mg, 0.53 mmol) and copper(II) acetate monohydrate (298 mg, 0.48 mmol) were placed in a round-
bottom flask, into which methanol (5.0 mL) and pyridine (5.0 mL) were then added. The reaction mixture was stirred overnight at
60 °C in an oil bath. Afterwards, the solvents were removed by filtration, and the residue was purified by column chromatography
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(silica gel, 25:1 chloroform/ethyl acetate as eluent) to provide M2 as a red powder (191 mg, 88% based on SM7). H NMR (300
MHz, CDCl3): δ = 8.04 (s, 4H, CHAr), 7.42 (d, J = 8.6 Hz, 8H, CHAr), 6.46 (d, J = 8.7 Hz, 8H, CHAr), 3.95 (s, 6H, COOCH3), 2.87 (s, 24H,
NCH3). Solution 13C NMR was not obtained, because of the limited solubility; but X-ray-quality single crystals can be obtained by
heating M2 (5.0 mg) with CuCN (2.0 mg,) in acetonitrile at 80 °C for 48 hours (see SI for the crystal structure; no CuCN included
therein).
Synthesis of SBF-16. A mixture of M2 (191 mg, 0.21 mmol), tetracyanoethylene (TCNE, 113 mg, 0.88 mmol) and THF (1 ml) was
stirred at 50 °C for 2 hours. The solvent was then removed by a rotary evaporation and the residue purified by column
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chromatography (silica gel 5:2 chlorform/ethyl acetate as eluent) to afford SBF-16 as a black powder (yield 98%). H NMR (300
MHz, CDCl3): δ 8.10 (s, 4H, CHAr), 7.70 (d, J = 8.9 Hz, 8H, CHAr), 6.71 (d, J = 8.0 Hz, 8H, CHAr), 3.99 (s, 6H, CH3COOH), 3.06 (s, 24H,
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NCH3). 13C{1H} NMR (101 MHz, CDCl3): δ = 164.0, 162.9, 154.8, 138.3, 136.5, 132.8, 132.2, 129.9, 129.6, 128.9, 128.2, 126.0, 125.8,
114.3, 113.1, 111.2, 110.5, 96.2, 82.5, 53.7, 40.3.
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Preparation of single crystals of SBF-16. A THF solution of SBF-16 (3.0 mM, 100 µL) and an acetonitrile solution of CuI (0.016 M,
100 µL) were mixed and then transferred into a glass tube (ID 3 mm). The tube was capped by an aluminum foil with fine holes to
allow slow evaporation of the solvents. Black, plate-like single crystals (e.g., 0.5 x 0.2 x 0.1 mm3) suitable for X-ray diffraction were
obtained after 3 days. Similar setups without the use of CuI yielded crystals that are much smaller and less well suited for X-ray
diffraction studies.
Large-scale preparation of crystalline powder. SBF-16 (30 mg) was dissolved in acetonitrile (2 ml) in a small open vial, and then
heated at 60 °C to evaporate the solvent until a precipitate started to form on the wall. The saturated solution thus obtained was
allowed to naturally cool to room temperature, and the remaining solvent was allowed to evaporate to dryness (e.g., overnight)
to afford a black powder of high crystallinity.
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Preparation of thin films. SBF-16 (10 mg) was dissolved in acetonitrile (0.5 ml), and was heated to 60 °C to evaporate the
solvent until near saturation was reached. Several drops of the solution were then cast onto a glass slide that was placed on a hot
plate and pre-heated to 60 °C. The solvent quickly evaporated, and a thin film of high crystallinity was deposited as a result.
Scheme 1. Synthetic route of M2
RESULTS AND DISCUSSION
Molecular synthesis and characterization. The Sierpinski molecule M2 was synthesized using the well-established (e.g.,
Sonogashira and Glaser coupling) protocol (Scheme 1). The four secondary branches were terminated with the strongly electron-
donating dimethylamino group, in order to promote the CA-RE reaction with the electron-poor alkene molecule of TCNE: the
reaction proceeds near-quantitatively in THF at 50 °C within 2 hours to form a dark solution of the product SBF-16. Elemental
analyses on the obtained product found [C (68.69%), H (4.07%), N (18.06%)]; a fitting formula can be determined to be SBF-
16·4H2O (mw 1505), which gives a calculated profile as [C (68.61%), H (4.28%), N (18.61%)]. Mass spectra (Figure S2) also shows
the expected molecular weight and isotopic distribution. The thermal stability of SBF-16 was investigated by thermogravimetric
anal differential scanning calorimetry analysis (TG-DSC) (Figure S3), which displays an onset decomposition around 250 °C. The FT-
IR spectrum (Figure S4) features a strong and sharp peak around 2210 cm-1 consistent with the carbonitrile stretching in the
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Figure 3. UV-vis spectra of THF solutions of SBF-16 at different concentrations. The inset is the
photograph of the solutions denoted with the concentrations.
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molecule of SBF-16. The redox properties of SBF-16 were investigated by cyclic voltammetry (CV) in CH3CN (+0.1M nBu4NPF6).
Four reversible cathodic peaks from 0.67 V to -0.27 V (versus Fc+/Fc) were observed (Figure S5), which may correspond to the
consecutive reduction of four 1,1,4,4-tetracyanobuta-1,3-diene (TCBD) units. The oxidization wave, however, shows poor
reversibility, with two irreversible and unresolved peaks centered at -1.87 V and -1.02 V respectively.
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In spite of its highly conjugated and rigid structure, compound SBF-16 is readily soluble in various organic solvents (e.g., THF,
chloroform, ethyl acetate and acetonitrile), but sparingly soluble in methanol or ethanol. The solid of SBF-16 is nearly black in
color, consistent with its conjugated strong donor-acceptor components giving rise to broad and intense absorbance in the visible
region (Figure 3). Solution UV-vis spectra feature a wavelength of maximum absorption (λmax) at 472 nm, with a corresponding
molar extinction coefficient (ε) of 4.8x104 M-1cm-1, which compares well with similar donor-acceptor systems (e.g., as sensitizers
for photochemical applications),46-51 even though porphyrins chromophores with ε > 105 M-1cm-1 are also known.52, 53 In general,
strongly-absorbing molecules are of interest in dye-sensitized solar cell fabrication because of their efficient photon capturing and
charge injection (e.g., onto a semiconductive layer of TiO2).46-51
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Crystallization and crystal structure. Single crystals or polycrystalline solid of the SBF-16 molecule can be obtained by
evaporation from an acetonitrile solution, depending on the rate of evaporation. Interestingly, the presence of CuI in the solution
was found to significantly enhance the crystal size; even though CuI was not incorporated into the crystal, it can coordinate to
the SBF-16 nitrile groups in solution, and help dissolve the nuclei: the impedance of nucleation thus promotes the growth of
fewer yet larger individual crystals. On the other hand, amorphous solid of SBF-16 can also be obtained, e.g., simply by rotary-
evaporating from a 5:2 chloroform/ethyl acetate solution (e.g., as obtained from column chromatography).
The X-ray single crystal structure of SBF-16 (see Table S1) reveals the molecular connectivity as well as the overall packing
motif, even though the weak diffraction data significantly lowers the resolution of the atomistic positions. The lack of diffraction
at medium and high angles can be ascribed to intrinsic disorder of the porous molecular crystal, with ill-defined solvate molecules
making up around 17% of the total volume. The torsional angles and contact/bond distances herein are consequently associated
with high errors; nevertheless, they do allow for a qualitative description of the stereochemistry of the rigid molecular scaffold of
SBF-16 and the packing motif in the solid state.
The branched, rigid 3D molecule of SBF-16 adopts the lowest point-group symmetry 1 (identity group); while the unit cell
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(space group: P ) contains an enantiomeric pair of SBF-16. The complex conformation of the SBF-16 molecule is underlain by the
four backfolded side arms of the donor-substituted TCBD units (see the green and magenta bonds in Figures 4a and 4b), with the
donor being the 4-dimethylaminophenyl group. The TCBD units are all non-planar due to rotation around the central single bond
(colored magenta). Each non-planar TCBD unit contains two stereogenic elements associated with the central single bond: the s-
trans or s-cis configuration and the axial chirality (P or M; clockwise or counterclockwise), generating four theoretical possibilities:
(s-trans, P), (s-trans, M), (s-cis, P) and (s-cis, M).
The four stereochemical possibilities are defined by the torsion angle θ between the two dicyanovinyl planes: If |θ|< 90o, the
TCBD is in the s-cis conformation, and if |θ|> 90o, the s-trans; If θ is positive, the axially chiral configuration is P, and if θ is
negative, M. The torsional angles obtained in the current crystal structure, in spite of the uncertainty due to weak diffraction, are
useful for identifying the stereochemical configurations of the TCBD units: i.e., θ(C26-C14-C13-C23)= -136o (s-trans, M); θ(C42-C30-C29-
C39)=-51o (s-cis, M); θ(C82-C70-C69-C79)=134o (s-trans, P) and θ(C66-C54-C53-C63)=58o (s-cis, P); see Figures 4a and 4b for the atom
Figure 4. Single-crystal X-ray structure of molecule SBF-16: a) A complete molecule, with dashed lines indicating the short contacts
(i.e., N···C contacts shorter than 3.5 Å), and the four butadiene units highlighted by green/magenta bonds and selected atom
labeling; b) A partial structure with the dimethylaminophenyl groups omitted to highlight the non-planarity of the four side arms and
the main backbone; c) A space-filling model highlighting the compact fitting of the side-chain atoms.
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labeling. As is also seen in the space-filling model (Figure 4c), the snug fitting of the side arm atoms around the backbone does not
allow free rotation of the TCBD units to effect configuration changes within the molecule.
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Moreover, axial chirality also exists on a higher level of the Sierpinski hierarchy of molecule SBF-16. Because the two TCBD units
on each moiety are different (in stereochemistry), the axial chirality of M can be identified along the primary backbone of the
diacetylene bridge in the same molecule. This axial chirality is also underpinned by the backfolded geometry of the four side arms,
which are crowded toward the central region of the molecule (i.e., wrapping closely around the diacetylene bridge) to restrict
rotation around the diacetylene backbone. The corresponding torsion angle θ(C10-C5-C45-C46) along the diacetylene unit is found to
be -99o, with the two associated benzene units being twisted almost perpendicular to each other. Close contacts are observed
across the TCBD units (see Figure 4a), consistent with the rigid conformation of the conjugated, self-similar scaffold.
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The above description is for a single molecule; for the enantiomer observed in the crystal structure, apparently, the axial
chirality configurations (P or M) along the side arm as well as the primary backbone are inverted; while the cis or trans forms in
the side arms remain unchanged (by reflection). Overall, only two stereoisomers are observed in the crystal structure--out of the
large number of mathematical combinations (4x4x4x4x2=512; 4 side arms, each giving 4 possible spatial forms, and 2 axial chiral
forms on the primary level). The selectivity of 2/512=1/256 is impressive.
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Figure 5. The packing of SBF-16 molecules in the X-ray single-crystal structure: a) View (along the b axis) of three layers (these are
stacked along the a axis), with inter-layer contacts indicated by green dashed lines, and selected intra-layer contacts (e.g., N···C, O···C
contacts shorter than 3.4 Å) indicated by magenta dashed lines; b) An individual layer viewed along the a axis, with the central
molecule and its four close neighbors shaded in orange color: two of the neighbors are aligned along the b axis, and the short
contacts thereof are colored blue, while the contacts with the other two neighbors are marked in magenta.
The rigid and rugged molecules of SBF-16 leave significant voids in the crystal structure, with solvent accessible regions
calculated to be 17% of the cell volume. The void regions can been readily seen along the b axis direction, i.e., these occur
between distinct layers parallel to the a plane (Figure 5a); by comparison, the packing of the molecules appears to be more dense
within the individual layer (Figure 5b, Figure S6), suggesting stronger intermolecular interactions therein. The anisotropy of the
layer-like character is also reflected in the thin-platelet-like morphology of the crystallites (see Figure S7 for the SEM images), and
the orientational preference of the crystallites observed in the intensity profiles of the PXRD patterns (see Figure S8 for an
exemplary parameter for the preferred orientation). For example, the 001 peak was observed to be relatively weak relative to the
100 peak, consistent with the lamellar domains parallel to the 100 plane.
The interatomic distances in the current crystal structure, in spite of the modest data quality, are also suggestive of the
lamellar character. For example, intermolecular interactions across the layers appear to be limited, with each molecule forming
only three inter-layer short contacts under 3.4 A (i.e., N···C 3.28, N···C 3.34, N···N 3.17 Å; marked by the green dashed lines in
Figure 5a). The molecules within the individual layer, by comparison, featuring more extensive intermolecular short contacts
(Figure 5b), with each molecule forming a total of 46 short contacts with four close neighbors: two of these are aligned along the
b axis, and each contributes 11 short contacts (colored blue in Figure 5b), while the other two each contributes 12 shorts contacts
(colored magenta in Figure 5a). Even though the specific numbers and values of these short contacts may be better refined in a
more resolved structure, their disparate distributions observed here serve to further illustrate the anisotropic, lamellar feature.
Porosity, stability and processing. The permanent porosity of SBF-16 crystals was demonstrated by gas sorption studies. As is
often observed in (ultra)microporous materials, SBF-16 solid samples exhibit no significant N2 uptake at 77 K (Figure S9), while the
CO2 sorption at 195 K was substantial. The CO2 uptake here is facilitated by the smaller kinetic diameter of CO2, its quadruple
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Figure 6. CO2 (195 K) adsorption and desorption isotherms for a crystalline powder of SBF-16
activated at 120 °C (blue graph) and 180 °C (red graph), respectively.
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moment (enhancing interaction with the host), and the stronger thermal motion at 195 K (relative to 77 K for N2). Specifically, the
as-made molecular solid of SBF-16, after being heated/activated under vacuum at 120 °C for 18 hours, revealed highly
reproducible type-I gas sorption isotherms for CO2 (Figure 6 and Figure S10a), with a significant hysteresis observed being
attributable to the narrow slit-like pores, and the diverse/irregular voids as revealed in the crystal structure of SBF-16. For
example, the sorbed CO2 guests interact with and c ontract the porous host (breathing effect), making it significantly harder to
escape from the very tight pores in the desorption cycle. The Langmuir surface area thus obtained is 317 cm2/g. The remarkable
thermal stability of the porous molecular host of SBF-16 was further demonstrated: even after being heated at 180 °C for 12
hours, significant CO2 uptake capability was maintained (Figure 6 and Figure S10b), although the Langmuir surface area slightly
decreased to 263 cm2/g.
The stability of the crystalline sample of SBF-16 was also verified by powder X-ray diffraction (PXRD) studies. The above-
mentioned 180 °C-activated sample retains its crystallinity after the CO2 adsorption and desorption tests (Figure 7c); even after
being heated at 200 °C, distinct diffraction peaks consistent with the original lattice continued to be observed (Figure 7d, see also
the indexing results), even though the peak broadening indicates somewhat degraded crystallinity. In addition, the SBF-16 crystals
are stable to water at room temperature, and even after being heated in water at 60 °C for 3 hours, the sample remains highly
crystalline as shown in Figure 7e. The long-term stability of SBF-16 is also excellent: for example, a sample stored in air for over six
months shows a PXRD profile identical with that of the fresh sample (Figure 7f). A molecular porous crystal with such stability
properties is rare.
Molecules of SBF-16 can be easily deposited into thin films from solution with no need for high vacuum and a high temperature
apparatus (inset of Figure 7). Among the rapidly growing class of molecular crystals, this represents a rare case in which highly
reproducible solution processability is achieved.9 Moreover, both bulky sample and thin film exhibit excellent thermal stability
with the porous structure remaining intact even when heated at 180-200 °C. The robust crystalline thin films, combined with the
Figure 7. X-ray powder patterns (Cu Kα, λ=1.5418 Å): (a) calculated from the single crystal structure of SBF-16; (b) as-
made crystalline powder of SBF-16; (c) as-made sample heated at 180 °C for 12 h and after CO2 sorption study; (d) as-
made sample heated at 200 °C for 2 h; (e) as-made sample heated in water at 60 °C for 3 h; (f) as-made sample exposed
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in air over half a year; (g) thin film drop-casted from hot THF solution of SBF-16.
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strong push-pull units generating high optical absorptivity, provide opportunities for interfacing optical and electronic process in
the porous media.
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CONCLUSIONS
To sum up, we have discovered a molecule (SBF-16) that readily crystallizes into a robust microporous solid state material
which is stable even when heated to 200 °C. The robust open packing of the molecules can be ascribed to the strong dipole
interactions and intermolecular short contacts afforded by the strongly electron-withdrawing ester/cyano groups and donating
amino groups integrated within a rigid and conjugated 3D scaffold. Two instructive comparisons can be made here. Firstly, the
lack of either directional hydrogen bonds or pre-assembled cage-like cavity distinguishes SBF-16 from these two common classes
of porous molecular materials. The second contrast refers to the rarer organic molecules with intrinsic microporosity (OMIMs,
e.g., the triptycenes), which depend on rigid, large concave surfaces (to forge internal free volume), but such irregular shapes
often lead to amorphous solids.
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The persistent crystallinity observed in both the bulk sample and the solution-cast thin films points to a new avenue to porous
molecular materials. Namely, the multiple, densely arrayed donor-acceptor units serve to impose strong intermolecular
interactions, while the rigid side arms locked in the backfolded shape forge cavities in the solid state. The versatile CA-RE reaction,
as used in installing the push-pull units here, is suited for exploring other molecular scaffolds, in order to further implement this
design strategy for porous molecular materials.
ASSOCIATED CONTENT
Supporting Information.
MS spectrum, TG-DSC plot, FT-IR spectrum, Cyclic Voltammogram for SBF-16, morphology image, powder patterns, N2 (77K) sorption
isotherm, CO2 (195K) sorption isotherm for SBF-16 crystalline powder, single crystal data, powder XRD index details and NMR spectra.
This material is available free of charge via the Internet at http://pubs.acs.org
CCDC 1908275 and CCDC 19082765 contain the supplementary crystallographic data for this paper.
AUTHOR INFORMATION
Corresponding Author
* zhengtao@cityu.edu.hk
* junhe@gdut.edu.cn
Author Contributions
All authors have given approval to the final version of the manuscript.
Funding Sources
This material is based upon work supported by the National Science Foundation through the Major Research Instrumentation Program
under Grant No. CHE 1625543. (Funding for the single crystal X-ray diffractometer).
Notes
The authors declare no competing financial interest
ACKNOWLEDGMENT
The work was supported by a GRF grant from the Research Grants Council of HKSAR (CityU 11306018), the National Natural Science
Foundation of China (21871061), Local Innovative and Research Teams Project of Guangdong Pearl River Talents Program and Science
and Technology Program of Guangzhou (201807010026). The single crystal X-ray diffractometer were funded by the US National Science
Foundation through the Major Research Instrumentation Program under Grant No. CHE 1625543.
REFERENCES
(1) Hasell, T.; Cooper, A. I., Porous organic cages: soluble, modular and molecular pores. Nat. Rev. Mater. 2016, 1, 16053.
(2) Chen, L.; Reiss, P. S.; Chong, S. Y.; Holden, D.; Jelfs, K. E.; Hasell, T.; Little, M. A.; Kewley, A.; Briggs, M. E.; Stephenson, A.; Thomas, K. M.;
Armstrong, J. A.; Bell, J.; Busto, J.; Noel, R.; Liu, J.; Strachan, D. M.; Thallapally, P. K.; Cooper, A. I., Separation of rare gases and chiral molecules
by selective binding in porous organic cages. Nat. Mater. 2014, 13, 954-960.
(3) MacGillivray, L. R.; Atwood, J. L., A chiral spherical molecular assembly held together by 60 hydrogen bonds. Nature 1997, 389, 469-472.
(4) Hashim, M. I.; Le, H. T. M.; Chen, T.-H.; Chen, Y.-S.; Daugulis, O.; Hsu, C.-W.; Jacobson, A. J.; Kaveevivitchai, W.; Liang, X.; Makarenko, T.;
Miljanic, O. S.; Popovs, I.; Tran, H. V.; Wang, X.; Wu, C.-H.; Wu, J. I., Dissecting Porosity in Molecular Crystals: Influence of Geometry,
Hydrogen Bonding, and [π···π] Stacking on the Solid-State Packing of Fluorinated Aromatics. J. Am. Chem. Soc. 2018, 140, 6014-6026.
(5) Chen, T.-H.; Popov, I.; Kaveevivitchai, W.; Chuang, Y.-C.; Chen, Y.-S.; Jacobson, A. J.; Miljanic, O. S., Mesoporous Fluorinated Metal-Organic
Frameworks with Exceptional Adsorption of Fluorocarbons and CFCs. Angew. Chem., Int. Ed. 2015, 54, 13902-13906.
(6) Bezzu, C. G.; Helliwell, M.; Warren, J. E.; Allan, D. R.; McKeown, N. B., Heme-Like Coordination Chemistry Within Nanoporous Molecular
Crystals. Science 2010, 327, 1627-1630.
(7) Baroncini, M.; d'Agostino, S.; Bergamini, G.; Ceroni, P.; Comotti, A.; Sozzani, P.; Bassanetti, I.; Grepioni, F.; Hernandez, T. M.; Silvi, S.;
Venturi, M.; Credi, A., Photoinduced reversible switching of porosity in molecular crystals based on star-shaped azobenzene tetramers. Nat.
Chem. 2015, 7, 634-640.
8
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Page 9 of 11
Crystal Growth & Design
(8) Cullen, W.; Misuraca, M. C.; Hunter, C. A.; Williams, N. H.; Ward, M. D., Highly efficient catalysis of the Kemp elimination in the cavity of a
cubic coordination cage. Nat. Chem. 2016, 8, 231-236.
(9) Wuttke, S.; Medina, D. D.; Rotter, J. M.; Begum, S.; Stassin, T.; Ameloot, R.; Oschatz, M.; Tsotsalas, M., Bringing Porous Organic and Carbon-
Based Materials toward Thin-Film Applications. Adv. Funct. Mater. 2018, 28, 1801545.
(10) Bassanetti, I.; Comotti, A.; Sozzani, P.; Bracco, S.; Calestani, G.; Mezzadri, F.; Marchio, L., Porous molecular crystals by macrocyclic
coordination supramolecules. J. Am. Chem. Soc. 2014, 136, 14883-95.
1
2
3
4
(11) Michinobu, T.; Diederich, F., The [2+2] Cycloaddition-Retroelectrocyclization (CA-RE) Click Reaction: Facile Access to Molecular and
Polymeric Push-Pull Chromophores. Angew. Chem., Int. Ed. 2018, 57, 3552-3577.
(12) Kato, S.-i.; Diederich, F., Non-planar push-pull chromophores. Chem. Commun. 2010, 46, 1994-2006.
(13) Bruce, M. I.; Low, P. J.; Skelton, B. W.; White, A. H., Reaction of {Ru(PPh3)2Cp}2(μ-C4) with tetracyanoethene: macrocycle formation by
intermolecular CN coordination. New J. Chem. 1998, 22, 419-422.
5
6
7
8
9
(14) Wu, X.; Wu, J.; Liu, Y.; Jen, A. K. Y., Highly Efficient, Thermally and Chemically Stable Second Order Nonlinear Optical Chromophores
Containing a 2-Phenyl-tetracyanobutadienyl Acceptor. J. Am. Chem. Soc. 1999, 121, 472-473.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(15) Bruce, M. I.; Rodgers, J. R.; Snow, M. R.; Swincer, A. G., Cyclopentadienylruthenium and -osmium chemistry. Cleavage of tetracyanoethylene
under
mild
conditions.
X-ray
crystal
structures
of
[Ru{η3-C(CN)2CPhC=C(CN)2}(PPh3)(η-C5H5)]
and
[Ru{C[=C(CN)2]CPh=C(CN)2}(CNCMe3)(PPh3)(η-C5H5)]. J. Chem. Soc., Chem. Commun. 1981, 271-272.
(16) Onitsuka, K.; Takahashi, S., Synthesis and structure of s-cis- and s-trans-μ-butadiene-2,3-diyldiplatinum complexes by the reaction of μ-
ethynediyldiplatinum complexes with tetracyanoethylene. J. Chem. Soc., Chem. Commun. 1995, 2095-2096.
(17) Morioka, Y.; Yoshizawa, N.; Nishida, J.; Yamashita, Y., Novel donor-π-acceptor compounds containing 1,3-dithiol-2-ylidene and
tetracyanobutadiene units. Chem. Lett. 2004, 33, 1190-1191.
(18) Michinobu, T.; May, J. C.; Lim, J. H.; Boudon, C.; Gisselbrecht, J.-P.; Seiler, P.; Gross, M.; Biaggio, I.; Diederich, F., A new class of organic
donor-acceptor molecules with large third-order optical nonlinearities. Chem. Commun. 2005, 737-739.
(19) Cai, C.; Liakatas, I.; Wong, M.-S.; Boesch, M.; Bosshard, C.; Guenter, P.; Concilio, S.; Tirelli, N.; Suter, U. W., Donor-Acceptor-Substituted
Phenylethenyl Bithiophenes: Highly Efficient and Stable Nonlinear Optical Chromophores. Org. Lett. 1999, 1, 1847-1849.
(20) Kivala, M.; Boudon, C.; Gisselbrecht, J.-P.; Seiler, P.; Gross, M.; Diederich, F., Charge-transfer chromophores by cycloaddition-retro-
electrocyclization: multivalent systems and cascade reactions. Angew. Chem., Int. Ed. 2007, 46, 6357-6360.
(21) Simard, M.; Su, D.; Wuest, J. D., Use of hydrogen bonds to control molecular aggregation. Self-assembly of three-dimensional networks with
large chambers. J. Am. Chem. Soc. 1991, 113, 4696-8.
(22) Venkataraman, D.; Lee, S.; Zhang, J.; Moore, J. S., An organic solid with wide channels based on hydrogen bonding between macrocycles.
Nature 1994, 371, 591-593.
(23) Cullen, D. A.; Gardiner, M. G.; White, N. G., A three dimensional hydrogen bonded organic framework assembled through antielectrostatic
hydrogen bonds. Chem. Commun. 2019, 55, 12020-12023.
(24) Lee, Y.-L.; Lu, M.-C.; Shao, P.-L.; Lu, P.-L.; Chen, Y.-H.; Cheng, S.-H.; Ko, W.-C.; Lin, C.-Y.; Wu, T.-S.; Yen, M.-Y.; Wang, L.-S.; Liu, C.-P.; Lee,
W.-S.; Shi, Z.-Y.; Chen, Y.-S.; Wang, F.-D.; Tseng, S.-H.; Lin, C.-N.; Chen, Y.-H.; Sheng, W.-H.; Lee, C.-M.; Liao, M.-H.; Hsueh, P.-R., Nationwide
surveillance of antimicrobial resistance among clinically important Gram-negative bacteria, with an emphasis on carbapenems and colistin:
Results from the Surveillance of Multicenter Antimicrobial Resistance in Taiwan (SMART) in 2018. International Journal of Antimicrobial Agents
2019, 54, 318-328.
(25) Taylor, R. G. D.; Bezzu, C. G.; Carta, M.; Msayib, K. J.; Walker, J.; Short, R.; Kariuki, B. M.; McKeown, N. B., The Synthesis of Organic
Molecules of Intrinsic Microporosity Designed to Frustrate Efficient Molecular Packing. Chem. - Eur. J. 2016, 22, 2466-2472.
(26) Kohl, B.; Rominger, F.; Mastalerz, M., Crystal Structures of a Molecule Designed Not To Pack Tightly. Chem. - Eur. J. 2015, 21, 17308-17313.
(27) Abbott, L. J.; McKeown, N. B.; Colina, C. M., Design principles for microporous organic solids from predictive computational screening. J.
Mater. Chem. A 2013, 1, 11950-11960.
(28) Couderc, G.; Hertzsch, T.; Behrnd, N. R.; Kraemer, K.; Hulliger, J., Reversible sorption of nitrogen and xenon gas by the guest-free zeolite
tris(o-phenylenedioxy)cyclotriphosphazene (TPP). Microporous Mesoporous Mater. 2006, 88, 170-175.
(29) Barrer, R. M.; Shanson, V. H., Dianin's compound as a zeolitic sorbent. J. Chem. Soc., Chem. Commun. 1976, 333-334.
(30) Sozzani, P.; Comotti, A.; Simonutti, R.; Meersmann, T.; Logan, J. W.; Pines, A., A porous crystalline molecular solid explored by
hyperpolarized xenon. Angew. Chem., Int. Ed. 2000, 39, 2695-2698.
(31) Tian, J.; Thallapally, P. K.; Dalgarno, S. J.; McGrail, P. B.; Atwood, J. L., Amorphous Molecular Organic Solids for Gas Adsorption. Angew.
Chem., Int. Ed. 2009, 48, 5492-5495.
(32) Song, Q.; Jiang, S.; Hasell, T.; Liu, M.; Sun, S.; Cheetham, A. K.; Sivaniah, E.; Cooper, A. I., Porous Organic Cage Thin Films and Molecular-
Sieving Membranes. Adv. Mater. 2016, 28, 2629-2637.
(33) Xu, Y.; Smith, M. D.; Geer, M. F.; Pellechia, P. J.; Brown, J. C.; Wibowo, A. C.; Shimizu, L. S., Thermal Reaction of a Columnar Assembled
Diacetylene Macrocycle. J. Am. Chem. Soc. 2010, 132, 5334-5335.
(34) Dawn, S.; Dewal, M. B.; Sobransingh, D.; Paderes, M. C.; Wibowo, A. C.; Smith, M. D.; Krause, J. A.; Pellechia, P. J.; Shimizu, L. S., Self-
Assembled Phenylethynylene Bis-urea Macrocycles Facilitate the Selective Photodimerization of Coumarin. J. Am. Chem. Soc. 2011, 133, 7025-
7032.
(35) Schlutter, F.; Rossel, F.; Kivala, M.; Enkelmann, V.; Gisselbrecht, J. P.; Ruffieux, P.; Fasel, R.; Müllen, K., pi-Conjugated heterotriangulene
macrocycles by solution and surface-supported synthesis toward honeycomb networks. J. Am. Chem. Soc. 2013, 135, 4550-7.
(36) Zhang, G.; Mastalerz, M., Organic cage compounds - from shape-persistency to function. Chem. Soc. Rev. 2014, 43, 1934-1947.
(37) Ding, H.; Yang, Y.; Li, B.; Pan, F.; Zhu, G.; Zeller, M.; Yuan, D.; Wang, C., Targeted synthesis of a large triazine-based [4+6] organic molecular
cage: structure, porosity and gas separation. Chem. Commun. 2015, 51, 1976-1979.
(38) Ding, H.; Wu, X.; Zeller, M.; Xie, Y.; Wang, C., Controllable Synthesis of Covalent Porphyrinic Cages with Varying Sizes via Template-
Directed Imine Condensation Reactions. J. Org. Chem. 2015, 80, 9360-9364.
(39) MacGillivray, L. R., Design Rules: A Net and Archimedean Polyhedra Score Big for Self-Assembly. Angew. Chem., Int. Ed. 2012, 51, 1110-1112.
(40) Burgun, A.; Valente, P.; Evans, J. D.; Huang, D. M.; Sumby, C. J.; Doonan, C. J., Endohedrally functionalised porous organic cages. Chem.
Commun. 2016, 52, 8850-8853.
(41) M. Adam, V. E., H. J. Räder, J. Rohrich, K. Müllen,, A Donor Cage with Two Tetrathiafulvene Units. Angew. Chem. Int. Ed. 1992, 31, 309-310.
(42) Jin, Y.; Wang, Q.; Taynton, P.; Zhang, W., Dynamic Covalent Chemistry Approaches Toward Macrocycles, Molecular Cages, and Polymers.
Acc. Chem. Res. 2014, 47, 1575-1586.
(43) Jin, Y.; Jin, A.; McCaffrey, R.; Long, H.; Zhang, W., Design Strategies for Shape-Persistent Covalent Organic Polyhedrons (COPs) through
Imine Condensation/Metathesis. J. Org. Chem. 2012, 77, 7392-7400.
9
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Page 10 of 11
(44) K. A. Leonard, M. I. N., L. T. Anderson, S. L. Gibson, R. Hilf, and M. R. Detty, 2,4,6-Triarylchalcogenopyrylium Dyes Related in Structure to
1
2
3
4
the Antitumor Agent AA1 as in Vitro Sensitizers for the Photodynamic Therapy of Cancer. J. Med. Chem. 1999, 42, 3942-3952.
(45) Hou, Y.-L.; Li, M.-Q.; Cheng, S.; Diao, Y.; Vilela, F.; He, Y.; He, J.; Xu, Z., Dramatic improvement of stability by in situ linker cyclization of a
metal-organic framework. Chem. Commun. 2018, 54, 9470-9473.
(46) Zhang, X.; Xu, Y.; Giordano, F.; Schreier, M.; Pellet, N.; Hu, Y.; Yi, C.; Robertson, N.; Hua, J.; Zakeeruddin, S. M.; Tian, H.; Gratzel, M.,
Molecular Engineering of Potent Sensitizers for Very Efficient Light Harvesting in Thin-Film Solid-State Dye-Sensitized Solar Cells. J. Am. Chem.
Soc. 2016, 138, 10742-10745.
5
(47) Farre, Y.; Raissi, M.; Fihey, A.; Pellegrin, Y.; Blart, E.; Jacquemin, D.; Odobel, F., A Blue Diketopyrrolopyrrole Sensitizer with High Efficiency
in Nickel-Oxide-based Dye-Sensitized Solar Cells. ChemSusChem 2017, 10, 2618-2625.
(48) Zhong, C.; Gao, J.; Cui, Y.; Li, T.; Han, L., Coumarin-bearing triarylamine sensitizers with high molar extinction coefficient for dye-sensitized
solar cells. J. Power Sources 2015, 273, 831-838.
(49) Chen, D.-Y.; Hsu, Y.-Y.; Hsu, H.-C.; Chen, B.-S.; Lee, Y.-T.; Fu, H.; Chung, M.-W.; Liu, S.-H.; Chen, H.-C.; Chi, Y.; Chou, P.-T., Organic dyes
with remarkably high absorptivity; all solid-state dye sensitized solar cell and role of fluorine substitution. Chem. Commun. 2010, 46, 5256-5258.
(50) Lee, C.-P.; Lin, R. Y.-Y.; Lin, L.-Y.; Li, C.-T.; Chu, T.-C.; Sun, S.-S.; Lin, J. T.; Ho, K.-C., Recent progress in organic sensitizers for dye-
sensitized solar cells. RSC Adv. 2015, 5, 23810-23825.
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(51) Wu, Y.; Zhu, W., Organic sensitizers from D-π-A to D-A-π-A: effect of the internal electron-withdrawing units on molecular absorption,
energy levels and photovoltaic performances. Chem. Soc. Rev. 2013, 42, 2039-2058.
(52) Dahlstedt, E.; Collins, H. A.; Balaz, M.; Kuimova, M. K.; Khurana, M.; Wilson, B. C.; Phillips, D.; Anderson, H. L., One- and two-photon
activated phototoxicity of conjugated porphyrin dimers with high two-photon absorption cross sections. Org Biomol Chem 2009, 7, 897-904.
(53) Jia, H.-L.; Chen, Y.-C.; Ji, L.; Lin, L.-X.; Guan, M.-Y.; Yang, Y., Cosensitization of porphyrin dyes with new X type organic dyes for efficient
dye-sensitized solar cells. Dyes and Pigments 2019, 163, 589-593.
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