Polyarylether‐Based 2D Covalent‐Organic Frameworks with In‐Plane D–A Structures and Tunable Energy Levels for Energy Storage

Abstract The robust fully conjugated covalent organic frameworks (COFs) are emerging as a novel type of semi‐conductive COFs for optoelectronic and energy devices due to their controllable architectures and easily tunable the highest occupied molecular orbital (HOMO) and the lowest occupied molecular orbital (LUMO) levels. However, the carrier mobility of such materials is still beyond requirements due to limited π‐conjugation. In this study, a series of new polyarylether‐based COFs are rationally synthesized via a direct reaction between hexadecafluorophthalocyanine (electron acceptor) and octahydroxyphthalocyanine (electron donor). These COFs have typical crystalline layered structures, narrow band gaps as low as ≈0.65 eV and ultra‐low resistance (1.31 × 10−6 S cm−1). Such COFs can be composed of two different metal‐sites and contribute improved carrier mobility via layer‐altered staking mode according to density functional theory calculation. Due to the narrow pore size of 1.4 nm and promising conductivity, such COFs and electrochemically exfoliated graphene based free‐standing films are fabricated for in‐plane micro‐supercapacitors, which demonstrate excellent volumetric capacitances (28.1 F cm−3) and excellent stability of 10 000 charge–discharge cycling in acidic electrolyte. This study provides a new approach toward dioxin‐linked COFs with donor‐acceptor structure and easily tunable energy levels for versatile energy storage and optoelectronic devices.


S1. Model reaction
Synthesis of molecular analog 1: Following a modified procedure from reference [1] . 1,2,3,4tetrafluorobenzene (3.3 g mL, 22 mmol), catechol (2.20 g, 20.0 mmol), potassium carbonate (8.30 g, 60.0 mmol) and N,N-dimethylformamide (DMF) (60 mL) were placed into a flask under nitrogen atmosphere. The reaction mixture was stirred at 120 o C for 10 h, and then cooled to room temperature. The mixture was acidified with 1M HCl aq. to pH 4 and extracted with ethyl acetate (EtOAc). The organic layer was washed with water, dried over MgSO4, and filtered. The filtrate was evaporated and the crude product was purified by a short pad of silica gel column chromatography (EtOAc) to yield the product (1)  1,2-Dicyano-4,5-dimethoxybenzen: 1,2-Dibromo-4,5-dimethoxybenzene (25 g, 1 eq) was heated under reflux (bath temperature 165 ℃) for 5 h with 22.7 g (3 eq) of CuCN in 350 mL of DMF. After being cooled, the reaction mixture was stirred in 1 L of concentrated ammonium hydroxide under air atmosphere overnight. The blue solution was suction filtered (sintered glass), and the solid residue was washed with a little dilute ammonium hydroxide and then with copious amounts of water until the filtrates were neutral. The dry, crude olive-green product was placed in the thimble of a Soxhlet extractor and extracted for 3 days with acetone. The white crude powder isolated from the acetone was purified through the silica gel column with dichloromethane and petroleum ether. Finally, the product was further crystallized from methanol: yield 6.84 g, 43 %; colorless small needles. 1 2,3,9,10,16,17,23,24-octamethoxyphthalocyaninato) (ZnPcOMe8): 1,2-Dicyano-4,5-dimethoxybenzen (4.00 g, 1 eq) and zinc(Ⅱ) acetate (1.17 g, 0.25 eq) together with 1.28 g urea were stirred in N,N-dimethylacetamide (DMAC) (40 mL) at 140 o C for 3 days under the argon atmosphere. After cooling to room temperature, the reaction mixture was treated with a mixture of methanol and water (3/1in vol.; 100 mL), and the resulting solid obtained was filtered, washed with methanol and acetone. The obtained green sample was vacuum dried in     After sonication for about 20 minutes to disperse evenly, the tube was flash-frozen at 77 K (liquid N2 bath) and degassed through three freeze-pump-thaw cycles by evacuated through an oil pump and then sealed under vacuum. After the temperature recovers to room temperature, the mixture was heated at 180 ºC and left undisturbed for 7 days. A black precipitate was isolated by filtration and washed with N-methyl-2-pyrrolidone (NMP), DMF, deionized water, dichloromethane, methanol and acetone until the filtrate was colorless. Finally, the product was evacuated at 60 ºC under vacuum overnight to yield activated samples (~40 mg).

S3. Electrochemical measurement for energy Levels
Cyclic voltammetry (CV) was performed on a CHI 650E electrochemical analyzer in anhydrous CH3CN containing recrystallized tetra-n butylammoniumhexafluorophosphate (TBAPF6, 0.1 M) as supporting electrolyte at 298 K. A conventional three electrode cell was used with a glassy carbon working electrode (surface area of 0.3 mm 2 ) and a platinum wire as the counter electrode. The glassy carbon working electrode was routinely polished with a polishing alumina suspension and rinsed with acetone before use. The measured potentials were recorded with respect to Ag/AgCl reference electrode. The sample was wet-transferred onto the surface of a glassy carbon working electrode and let the solvent evaporate at room temperature for 30 min.

Synthesis of electrochemically exfoliated graphene:
The electrochemically exfoliated graphene (EG) sheets were prepared according to previously reported method [4] . Typically, the natural graphite foil, a Pt wire, and 0.1 M (NH4)2SO4 solution were acted as working electrode, counter electrode, and electrolyte, respectively. The distance between the graphite foil and the Pt electrode was about 2 cm during the electrochemical process. The electrochemical exfoliation of graphite was carried out by applying positive voltage at 10 V. After the graphite exfoliation was completed, the product was collected through a cotton fiber membrane filter with ~0.2 µm pore size and washed several times with deionized water by vacuum filtration.
The resultant EG was then dispersed in NMP by sonication for 60 min. The dispersion was maintained for 2 days to precipitate un-exfoliated graphite flakes or particles. The supernatant dispersion of EG nanosheets could be directly used for device fabrication.

PAE-M1M2PcF8/graphene hybrid and device fabrication:
Typically, EG (~1 mg mL -1 ) and PAE-M1M2PcF8 (~0.3 mg mL -1 ) were dispersion in NMP and mixed them with different volume ratios. After sonication for another 60 min, the mixture solution was stirred overnight to form a homogeneous suspension. Subsequently, the film was obtained by the suspension through vacuum filtration of with a polypropylene filter membrane (pore size of 0.22 µm) and washed with ethanol and deionized water respectively. After drying at room temperature, PAE-M1M2PcF8/EG hybrid film was transferred to rigid glass slide substrate, then a thin Au layer was deposited these film surface. The interdigital electrode was fabricated by directly laser scribing. Then, 1 M PVA/H2SO4 gel electrolyte was drop-casted onto the surface of interdigital electrode and solidified overnight. Finally, all solid-state hybrid film-based in-plane microsupercapacitors (MSCs) were manufactured. For further discussion, the PAE-M1M2PcF8/EG hybrid film MSCs were prepared based on different EG and PAE-NiNiPcF8 weight ratios that were denoted as PAE-NiNiPcF8/EG-3 (EG: PAE-NiNiPcF8=3), PAE-NiNiPcF8/EG-5 (EG: PAE-NiNiPcF8=5) and PAE-NiNiPcF8/EG-7 (EG: PAE-NiNiPcF8 =7).
For comparison, the pure EG film-based MSC also was prepared under the same experimental condition. The PVA/H2SO4 gel electrolyte was prepared by mixing PVA (6 g) (molecular weight 85,000-124,000, Sigma-Aldrich) and H2SO4 (6 mL) in 60 ml deionized water, and heated at 85 °C under magnetic stirring until forming a clear solution. Finally, cooled naturally to room temperature. The H2SO4/PVA gel electrolyte was obtained for the experiment. If no otherwise specified, the PAE-M1M2PcF8/EG hybrid film or PAE-M1M2PcF8 hybrid film is Electrochemical characterization: All the electrochemical measurements including cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) measurements, and electrochemical impedance spectroscopy (EIS) were conducted using an electrochemical workstation (CHI660E).
The specific capacitance values of the device are calculated from the CV data according to the equation (1) and (2): where is donated as specific areal capacitance (mF cm -2 ) of PAE-M1M2PcF8 /EG MSCs, The specific areal capacitance ( , mF cm -2 ) and specific volume capacitance ( , F cm -3 ) of the entire MSCs on the basis of GCD curves can be obtained according to the following equation (3) and (4): where is the current density (A m -2 ) of charge/discharge, ∆ is the discharged time (s), ∆ is voltage output window (V), and is the thickness of PAE-M1M2PcF8/EG film.
The electrochemical performance of the whole device showed in the Ragone plot is based on the volumetric stack capacitance from the CV data. The specific areal ( , Wh·cm -2 ) and volumetric ( , Wh·cm -3 ) energy densities are calculated from the equation (5) and (6): The ∆ is the discharge potential range (in volts).

Capacitance contribution calculation methods
The Trasatti method is used to differentiate the capacitance contribution from EDL capacitance between them. Specifically, the correlation can be described by the following equation (9): where C is experimental areal capacitance, v is the scan rate and CT was the total capacitance, respectively. The "total capacitance" equals the sum of EDL capacitance and pseudocapacitance.
Plotting the areal capacitances (C) against the reciprocal of the square root of scan rates (v 0.5 ) should also give a linear correlation described by the following equation (10) (if assuming a semi-infinite diffusion of ions): Linear fit the plot and extrapolate the fitting line to the y-axis gives the maximum EDL capacitance (Cdl). Subtraction of Cdl from CT yield the maximum Cp.

Electrochemical quartz crystal microbalance analysis:
The mass sensitivity of electrochemical quartz crystal microbalance (EQCM) originates from the relationship between the oscillation frequencies, as shown below equation (11): where the EQCM sensor with the fundamental frequency of 7.946 MHz, is the area of active surface (0.196 cm 2 ), is the AT-cut quartz constant (2.947 × 10 11 g cm -1 s -2 ), is the quartz crystal density (2.84 g cm -3 ), and then the sensitivity factor is 1.42 ng Hz -1 .