4-Methoxytriphenylamine15 (1) and 4-hydroxytriphenylamine16 (2) were prepared according to the literature. 2-Amino-anthraquinone (ACROS), [6,6]-C61-butyric acid methyl ester (PCBM), iodobenzene (TCI), potassuim carbonate (ACROS), N,N-dimethylformamide (DMF) (ACROS), dimethyl sulfoxide (DMSO) (TEDIA), chloroform (ECHO), and tetrahydrofuran (THF) (TEDIA) were used without further purification. Tetrabutylammonium perchlorate (TBAP) (ACROS) was recrystallized twice by ethyl acetate under nitrogen atmosphere and then dried in vacuo prior to use.
All other reagents were used as received from commercial sources.
2.2.2 Monomer Synthesis
2-diphenylaminoanthracene-9,10-dione (3)
A mixture of 6.69 g (30.00 mmol) 2-amino-anthraquinone, 10.36 g (75.00 mmol) potassium carbonate, 4.82 g (75.00 mmol) copper at room temperature. 7.86 g (30.00 mmol), 15.30 g (75.00 mmol) of iodobenzene and 18-crown-6-ether 1.99 g (7.53 mmol) in 30 mL o-dichlorobenzene was added in 250 ml three-neck round-bottomed flask in sequence. The mixture was heated with stirring at 180 oC for 27 h under nitrogen atmosphere then poured slowly into 150 mL of stirred methanol, and the precipitated brown powders was collected by filtration and dissolved in toluene then filtrated for removing copper. The product was collected by concentration to afford
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8.3902 g (74.5 % in yield) of brown powders. Mp: 190–193 oC measured by DSC at a scan rate of 10 oC/ min. IR (KBr): 1674 cm-1 (C=O stretch). 1H NMR (500 MHz, DMSO-d6, δ, ppm): 8.14-8.12 (d, 1H, Hf), 8.07-8.05 (d, 1H, Hi), 8.01-7.99 (d, 1H, He), 7.88-7.80 (m, 2H, Hg + Hh), 7.47-7.44 (t, 1H, Ha), 7.40-7.39 (d, 4H, Hc), 7.30-7.24 (m, 6H, Hj + Hb) , 7.14-7.11 (dd, 1H, Hd) .Anal. C26H17NO2 (375.42): C, 83.18 %; H, 4.56
%; N, 3.73 %. Found: C, 83.21 %; H, 4.46 %; N, 3.70 %.
2-(4-diphenylaminophenoxy)anthracene-9,10-dione (4)
A mixture of 3.18 g (23.00 mmol) of potassium carbonate in 40 mL dimethyl sulfoxide (DMSO) was stirred at room temperature. To the mixture 3.82 g (15.70 mmol) of 2-chloroanthracene-9,10-dione and 3.96 g (15.00 mmol) of 2 were added in sequence. The mixture was heated with stirring at 120 oC for 20 h and slowly poured into 300 mL methanol/water (2:1). The product was purified by THF/ methanol to afford 5.56g (79.3 % in yield) of yellow powders with a mp of 177–179 oC (by Melting Point System at a scan rate of 5 oC /min). FT-IR (KBr): 1673 cm-1 (C=O stretch). 1H NMR (500 MHz, DMSO-d6, δ, ppm): 8.24-8.21 (d, H, He), 8.20-8.15 (m, 2H, Ha + Hb), 7.95-7.88 (m, 2H, Hb+ Hc), 7.56-7.55 (s, 1H, Hg), 7.52-7.49 (d, 1H, Hf), 7.34-7.30 (m, 4H, Hh + Hi), 7.16-7.03 (m, 10H, Hj + Hk + Hl). Anal. Calcd (%) for C32H21NO3 (467.51): C, 82.21 %; H, 4.53 %; N, 3.00 %. Found: C, 81.87 %; H, 4.31
%; N, 2.62 %. ESI-MS: calcd for (C32H21NO3)+: m/z 467.5; found: m/z 468.2.
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2.2.3 Polymer Synthesis
The polymerization procedure of the studying materials were synthesized via oxidative coupling reaction according to the previous literature.17 P-TPAOAQ was used as an example to illustrate the general synthetic route of this kind of the oxidative coupling reaction. To a two-necked 50 mL flask equipped with a magnetic stirrer were placed 2-(4-diphenylaminophenoxy)anthracene-9,10-dione (1 mmol) and chloroform (3 mL) under nitrogen atmosphere. A quarter portion of FeCl3 (1 mmol;
total is 4 mmol) was added to the reaction mixture at the interval of 1 h. The solution was stirred at 45 oC for 48 h then poured into a mixture of methanol containing 10%
hydrochloric acid to recover the product. Collected powder was washed in dilute ammonia aqueous solution. The resulting polymer was filtrated and dried in vacuo at 120 oC for 12 h (yield: 94%).
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2.2.4 Measurements
The inherent viscosities were determined at 0.5 g/dL concentration using Tamson TV-2000 viscometer at 30 oC. Gel permeation chromatographic (GPC) analysis was carried out on a Waters chromatography unit interfaced with a Waters 2410 refractive index detector. Two Waters 5 μm Styragel HR-2 and HR-4 columns (7.8 mm I. D. × 300 mm) were connected in series with NMP as the eluent at a flow rate of 0.5 ml/min at 40 oC and were calibrated with polystyrene standards. DSC analyses were performed on a PerkinElmer Pyris 1 DSC in flowing nitrogen (20 cm3/min).
Thermogravimetric analysis (TGA) was conducted with a PerkinElmer Pyris 1 TGA.
Experiments were carried out on approximately 6-8 mg samples heated in flowing nitrogen or air (flow rate = 20 cm3/min) at a heating rate of 20 oC/min. Cyclic voltammetry (CV) was performed with a Bioanalytical System Model CV-27 and conducted with the use of a three-electrode cell in which ITO (polymer films area about 0.5 cm x 1.2 cm) was used as a working electrode and a platinum wire as an auxiliary electrode at a scan rate of 100 mV/s against a Ag/AgCl reference electrode in anhydrous DMF and CH3CN, using 0.1 M of TBAP as a supporting electrolyte in nitrogen atmosphere. All cell potentials were taken by using a homemade Ag/AgCl, KCl (sat.) reference electrode. The ITO-coated glass slide was used as the working electrode, a platinum wire as the counter electrode, and a Ag/AgCl cell as the reference electrode. Fourier transform infrared (FT-IR) spectra were recorded on a PerkinElmer Spectrum 100 Model FT-IR spectrometer. 1H spectra were measured on a JEOL JNMAL 300 MHz spectrometer in DMSO- d6.The microstructure of the prepared films was examined by using a JOEL JEM-1230 transmission electron microscope (TEM). Photoluminescence (PL) spectra was measured with Fluorolog-3 spectrofluorometer.
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2.2.5 Fabrication and Measurement of the Memory Device
The memory device was fabricated with the configuration of ITO/thin film/Al as shown in Figure 2.1. The ITO glass used for memory device was precleaned by ultrasonication with water, acetone, and isopropanol each for 15 min. The hybrid thin film was prepared by the chloroform solution of P-TPA containing calculated PCBM, which was stirred to form homogeneous solutions then filtrated by 0.45 μm pore size of PTFE membrane syringe filter and spin-coated at 1000 rpm for 30 seconds onto the ITO substrate and kept at 70 oC for 10 mins under nitrogen. The other thin films were prepared by 250 μl chloroform solution of P-TPAAQ or P-TPAOAQ (5 mg/ml) by above procedure. The film thickness was determined to be around 50 nm. Finally, a 300-nm-thick Al top electrode was thermally evaporated through the shadow mask (recorded device units of 0.5 × 0.5 mm2 in size) at a pressure of 10-7 torr with a uniform depositing rate of 3-5 Å /s. The electrical characterization of the memory device was performed by a Keithley 4200-SCS semiconductor parameter analyzer equipped with a Keithely 4205-PG2 arbitrary waveform pulse generator. ITO was used as the cathode (maintained as common), and Al was set as the anode during the voltage sweep. The probe tip used 10 μm diameter tungsten wire attached to a tinned copper shaft with a point radius <0.1 μm (GGB Industries, Inc.).
2.2.6 Theoretical Calculation
The theoretical calculation in this study was performed by Gaussian 09 program package. The results of value and distributions of the corresponding energy levels within each basic unit of P-TPAAQ and P-TPAOAQ were investigated via density functional theory (DFT) method at the B3LYP level of theory (Beckesstyle three-parameter density functional theory using the Lee-Yang-Parr correlation functional) with the 6-31G(d) basic set.
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I-V
Al
ITO glass P-TPA:PCBM hybrid films
P-TPAAQ P-TPAOAQ PCBM P-TPA
Figure 2.1. The schematic diagram of the memory device consisting of a polymeric active layer sandwiched between an ITO bottom electrode and an Al top electrode.
The thickness of polymeric thin film is about 50 nm and the thickness of electrode is 300nm.
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2.3 RESULTS AND DISCUSSION