Fluorescent and electrochromic polyamides with pyrenylamine ...

High impact applications, properties and synthesis of exciting new materials

Paper J. Mater. Chem., 2010, 20, 5481 - 5492, DOI: 10.1039/c0jm00495b

Fluorescent and electrochromic polyamides with pyrenylamine chromophore Yi-Chun Kung and Sheng-Huei Hsiao

A series of novel polyamides with a pyrenylamine chromophore in the backbone were prepared from a newly synthesized diamine monomer, N,N-di(4-aminophenyl)-1-aminopyrene, and various dicarboxylic acids via the phosphorylation polyamidation technique. These polyamides were readily soluble in many organic solvents and could be solution-cast into tough and amorphous films. They had useful levels of thermal stability with glass-transition temperatures in the range of 246–326 °C and 10% weight loss temperatures in excess of 500 °C. The dilute NMP solutions of these polyamides exhibited fluorescence maxima around 522–544 nm with quantum yields up to 30.2%. These polyamides also showed remarkable fluorescence solvatochromism in various solvents. The polymer films showed reversible electrochemical oxidation and reduction accompanied by strong color changes from the yellow neutral state to a purple oxidized state and to an orange reduced state. The anodically electrochromic films had high coloration efficiency (up to 172 cm2 C-1 at 834 nm) and good redox stability, which still retained a high electroactivity after long-term redox cycles.

PAPER

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Fluorescent and electrochromic polyamides with pyrenylamine chromophore† Yi-Chun Kunga and Sheng-Huei Hsiao*b Received 24th February 2010, Accepted 7th April 2010 First published as an Advance Article on the web 26th May 2010 DOI: 10.1039/c0jm00495b A series of novel polyamides with a pyrenylamine chromophore in the backbone were prepared from a newly synthesized diamine monomer, N,N-di(4-aminophenyl)-1-aminopyrene, and various dicarboxylic acids via the phosphorylation polyamidation technique. These polyamides were readily soluble in many organic solvents and could be solution-cast into tough and amorphous films. They had useful levels of thermal stability with glass-transition temperatures in the range of 246–326  C and 10% weight loss temperatures in excess of 500  C. The dilute NMP solutions of these polyamides exhibited fluorescence maxima around 522–544 nm with quantum yields up to 30.2%. These polyamides also showed remarkable fluorescence solvatochromism in various solvents. The polymer films showed reversible electrochemical oxidation and reduction accompanied by strong color changes from the yellow neutral state to a purple oxidized state and to an orange reduced state. The anodically electrochromic films had high coloration efficiency (up to 172 cm2 C1 at 834 nm) and good redox stability, which still retained a high electroactivity after long-term redox cycles.

Introduction Pyrene is a prototypical fluorescent molecule with desirable photophysical properties that make it useful as a fluorescence probe.1 Among the attractive properties of pyrene is its ready functionalization, appearance of delayed fluorescence, distinct solvatochromic phenomena, and its high propensity for forming excimers. Pyrene and its derivatives have been widely used as fluorescence probes in many applications.2 In recent years, pyrene derivatives have attracted increasing interest in the fabrication of various optoelectronic devices such as organic light-emitting devices (OLEDs) and organic field-effect transistors (OFETs), due to their emissive properties combined with high charge carrier mobility. There are a vast number of pyrene derivatives that have been reported in the literature, including tetraphenylpyrene derivatives,3 oligothiophenes with pyrenyl side or end groups,4 ethynylene-conjugated pyrene derivatives,5 hexapyrenylbenzene and dipyrenylbenzene derivatives,6 as well as pyrene-carbazole,7 pyrene-fluorene and pyrene-fluorene-carbazole systems.8 Pyrene-cored starbursts and dendrimers have recently been reported in the context of organic electronic applications.9 Furthermore, oligopyrenes, polypyrenes, and polypyrene dendrimers have also been investigated for light-emitting materials.10 Organic-inorganic hybrids based on pyrene functionalized silsesquioxane cores11 or pyrenylamine-functionalized

a Department of Chemical Engineering, Tatung University, 40 Chungshan North Road, 3rd Section, Taipei, 10452, Taiwan b Department of Chemical Engineering and Biotechnology, National Taipei University of Technology, 1 Chunghsiao East Road, 3rd Section, Taipei, 10608, Taiwan. E-mail: [email protected] † Electronic supplementary information (ESI) available: Synthetic details and characterization data of compounds 1, 2 and M1, inherent viscosity and solubility behavior of all polyamides, IR spectra of all the synthesized compounds 1–4 and M1, typical IR spectrum of polymer 6a, NMR spectra of compounds 1, 2, 3 and M1, WAXD patterns of all polyamides. See DOI: 10.1039/c0jm00495b

This journal is ª The Royal Society of Chemistry 2010

cyclic phosphazene cores12 have also been exploited for application in OLEDs. Due to the large planar conjugated aromatic characteristic, pyrene has strong p electron delocalization energy and efficient fluorescence property, and the emission is pure blue to permit ready exploitation as a blue-light emitting material in OLEDs. However, the use of pyrene as emitting material in OLED applications has been limited, due to aggregation between planar pyrene molecules. The high tendency towards p-stacking of the pyrene moieties generally lends the pyrene-containing emitters strong intermolecular interactions in the solid state, which leads to a substantial red shift of their fluorescence emission and a decrease of the fluorescence quantum yields. Through molecular structure design, the close packing/fluorescence quenching effect in pyrene-type materials can be reduced or controlled. A successful effort in the prevention of p-stacking in small molecules was achieved with 1,3,6,8-tetrasubstituted highly sterically hindered pyrenes,3e which can emit blue light in solution as well as in the solid state and with high quantum yield. In addition, diarylamino functionalized pyrene derivatives have been found to perform efficiently as emitters and charge transport materials in OLEDs.13 The emission color of the diarylamino pyrenes can also be tuned by changing the electron-withdrawing and electron-donating nature of the diarylamine substituents.14 The pyrene-containing triarylamines generally exhibit both holetransporting and emitting properties; therefore, they can be used as hole-transporting emitters in the fabrication of OLEDs.13b,13c Triarylamine derivatives are well known for photo and electroactive properties that find optoelectronic applications as photoconductors, hole-transporters, and light-emitters.15 Electron-rich triarylamines can be easily oxidized to form stable radical cations, and the oxidation process is always associated with a noticeable change of coloration. Thus, many triarylaminebased electrochromic polymers have been reported in the literature.16 In recent years, Liou’s and our groups have developed a number of high-performance polymers (e.g., aromatic J. Mater. Chem., 2010, 20, 5481–5492 | 5481

polyamides and polyimides) carrying the triarylamine unit as an electrochromic functional moiety.17 Our strategy was to synthesize the triarylamine-containing monomers such as diamines and dicarboxylic acids that were then reacted with the corresponding comonomers through conventional polycondensation techniques. The obtained polymers possessed characteristically welldefined structure, high molecular weights, and high thermal stability. Because of the incorporation of packing-disruptive, three-dimensional triarylamine units along the polymer backbone, most of these polymers exhibited good solubility in polar organic solvents. They can form uniform, transparent, and amorphous films by solution processes such as spin-coating, inkjet-printing, or spray-coating. This is advantageous for the production of large-area, thin-film devices at low cost. To our knowledge, there has been no report of pyrenylamine-containing condensation polymers. In view of the attractive properties associated with the pyrene and triarylamine units, herein we report the synthesis of N,N-di(4-aminophenyl)-1-aminopyrene, as a new diamine monomer, and its derived polyamides containing pyrenylamine chromophores. The introduction of the pyrenylamine moiety into the polyamide backbone leads to interesting photophysical, redox, and electrochromic properties useful for optoelectronic applications.

Experimental Synthesis of monomers 1-Nitropyrene (1) was prepared from the nitration of pyrene using copper nitrate trihydrate, according to a reported procedure.18 Catalytic reduction of nitro compound 1 by means of hydrazine and Pd/C in refluxing ethanol gave 1-aminopyrene (2). The synthetic details and characterization data of compounds 1 and 2 are included in the ESI.† N,N-Di(4-nitrophenyl)-1-aminopyrene (3). In a 250-mL oneneck round-bottomed flask equipped with a stirring bar under air atmosphere, to a solution of 10.2 g (47 mmol) of 1-aminopyrene and 13.4 g (95 mmol) of 4-fluoronitrobenzene in 100 mL of dried dimethyl sulfoxide (DMSO), 14.5 g (95 mmol) of dried caesium fluoride (CsF) was added with stirring all at once, and the mixture was heated at 140  C for 18 h under nitrogen atmosphere. The mixture was poured into 800 mL of stirred methanol slowly, and the precipitated compound was collected by filtration and washed thoroughly by methanol and hot water. The crude product was filtered and recrystallized from DMF–methanol to afford 18.3 g (85% in yield) of brown needles with a mp of 271– 273  C (by DSC at a scan rate of 2  C min1). FT-IR (KBr): 1302, 1579 cm1 (NO2 stretch). 1H NMR (500 MHz, DMSO-d6, d, ppm): 7.24 (d, J ¼ 9.2 Hz, 4H, Hj), 7.96 (d, J ¼ 9.2 Hz, 1H, Ha), 8.04 (d, J ¼ 8.1 Hz, 1H, Hd), 8.13 (t, J ¼ 7.7 Hz, 1H, Hf), 8.15 (d, J ¼ 9.3 Hz, 4H, Hk), 8.20 (d, J ¼ 9.3 Hz, 1H, Hb), 8.28 (d, J ¼ 9.0 Hz, 1H, Hi), 8.32 (d, J ¼ 9.0 Hz, 1H, Hh), 8.32 (d, J ¼ 7.4 Hz, 1H, He), 8.40 (d, J ¼ 7.3 Hz, 1H, Hg), 8.47 (d, J ¼ 8.2 Hz, 1H, Hc). 13C NMR (125 MHz, DMSO-d6, d, ppm): 121.36 (C2), 121.43 (C18), 123.68 (C4), 125.41 (C14), 125.61 (C19), 125.96 (C8), 126.25 (C10), 126.78 (C5), 126.97 (C9), 127.12 (C13), 127.67 (C15), 127.84 (C6), 128.27 (C12), 129.46 (C3), 130.25 (C16), 130.55 (C11), 130.81 (C7), 136.95 (C1), 141.81 (C20), 151.86 (C17). 5482 | J. Mater. Chem., 2010, 20, 5481–5492

N,N-Di(4-aminophenyl)-1-aminopyrene (4). In a 250-mL threeneck round-bottomed flask equipped with a stirring bar under nitrogen atmosphere, 4.0 g (8.7 mmol) of dinitro compound 3 and 0.15 g of 10% Pd/C were dissolved/suspended in 60 mL of ethanol. The suspension solution was heated to reflux, and 2.5 mL of hydrazine monohydrate was added slowly to the mixture, then the solution was stirred at reflux temperature. After a further 16 h of reflux, the solution was filtered to remove the Pd/C, and the filtrate was cooled under a nitrogen flow to grow yellow crystals. The products were collected by filtration and dried in vacuo at 80  C; yield ¼ 2.61 g (75%), mp ¼ 227– 229  C (by DSC at 2  C min1). FT-IR (KBr): 3200–3400 cm1 (N–H stretch). 1H NMR (500 MHz, DMSO-d6, d, ppm) (for the peak assignments, see Fig. 1a): 4.79 (s, 4H, -NH2), 6.48 (d, J ¼ 8.7 Hz, 4H, Hk), 6.66 (d, J ¼ 8.7 Hz, 4H, Hj), 7.63 (d, J ¼ 8.3 Hz, 1H, Ha), 7.94 (d, J ¼ 9.3 Hz, 1H, Hd), 7.99 (t, J ¼ 7.6 Hz, 1H, Hf), 8.03 (d, J ¼ 8.9 Hz, 1H, Hi), 8.06 (d, J ¼ 8.9 Hz, 1H, Hh), 8.12

Fig. 1 (a) 1H and (b) 13C NMR spectra of target diamine monomer 4 in DMSO-d6.

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(two overlapped doublets, J ¼ 9.0 Hz, 2H, Hc + He), 8.16 (d, J ¼ 8.3 Hz, 1H, Hb), 8.19 (d, J ¼ 7.6 Hz, 1H, Hg). 13C NMR (125 MHz, DMSO-d6, d, ppm) (for the peak assignments, see Fig. 1b): 114.88 (C19), 123.70 (C4), 123.81 (C18), 124.19 (C8 + C5), 124.43 (C14), 124.68 (C10), 125.54 (C2), 125.66 (C15), 125.68 (C13), 125.85 (C3), 126.28 (C9), 126.38 (C6), 127.18 (C16), 127.26 (C12), 130.57 (C11), 130.97 (C7), 139.44 (C17), 143.20 (C1), 143.67 (C20). Anal. Calcd (%) for C28H21N3 (399.49): C, 84.18; H, 5.30; N, 10.52. Found: C, 84.02; H, 5.29; N, 10.50. Synthesis of polyamides The synthesis of polyamide 6a was used as an example to illustrate the general synthetic route used to produce the polyamides. A mixture of 0.399 g (1.0 mmol) of diamine 4, 0.166 g (1.0 mmol) of terephthalic acid (5a), 0.1 g of dried calcium chloride, 1.0 mL of triphenyl phosphite (TPP), 0.3 mL of pyridine, and 1.0 mL of N-methyl-2-pyrrolidinone (NMP) was heated with stirring at 120  C for 3 h. The obtained polymer solution was poured slowly into 300 mL of methanol with stirring giving rise to a stringy, fiber-like precipitate that was collected by filtration, washed thoroughly with hot water and methanol, and dried under vacuum at 100  C. Reprecipitations of the polymer by N,Ndimethylacetamide (DMAc)/methanol were carried out twice for further purification. The inherent viscosity of the obtained polyamide 6a was 1.08 dL/g, measured at a concentration of 0.5 g/dL in DMAc at 30  C. IR (KBr): 3290 (amide N–H stretch), 1653 cm1 (amide C]O stretch). 1H NMR (500 MHz, DMSO-

d6, d, ppm) (for the proton assignments, see Fig. 2): 7.00 (d, J ¼ 8.5 Hz, 4H, Hj), 7.69 (d, J ¼ 8.5 Hz, 4H, Hk), 7.86 (d, J ¼ 7.9 Hz, 1H, Ha), 8.05 (s, 4H, Hl), 8.06–8.12 (m, 3H, Hf + Hd + Hc), 8.15– 8.18 (m, 2H, Hh + Hi), 8.22 (d, J ¼ 6.7 Hz, 1H, He), 8.30 (d, J ¼ 7.2 Hz, 1H, Hg), 8.34 (d, J ¼ 7.7 Hz, 1H, Hb), 10.32 (s, 2H, amide N–H). Preparation of the polyamide films A solution of polymer was made by dissolving about 0.5 g of the polyamide sample in 10 mL of hot DMAc. The homogeneous solution was poured into a 9-cm glass Petri dish, which was placed in a 90  C oven for 5 h to remove most of the solvent; then the semidried film was further dried in vacuo at 180  C for 8 h. The obtained films were about 30–50 mm in thickness and were used for X-ray diffraction measurements, solubility tests, and thermal analyses. Fabrication of the electrochromic device Electrochromic polymer films were prepared by dropping solutions of the polyamides (5 mg mL1 in DMAc) onto a ITOcoated glass substrate (20  30  0.7 mm, 50–100 U/square). The polymers were drop-coated onto an active area of letters TTU using a mask. A gel electrolyte based on PMMA (Mw: 120000) and LiClO4 was plasticized with propylene carbonate to form a highly transparent and conductive gel. PMMA (3 g) was dissolved in dry acetonitrile (15 g), and LiClO4 (0.3 g) was added to the polymer solution as supporting electrolyte. Then, propylene carbonate (5 g) was added as plasticizer. The mixture was then slowly heated until gelation. The gel electrolyte was spread on the polymer-coated side of the electrode, and the electrodes were sandwiched. Finally, an epoxy resin was used to seal the device. Measurements

Fig. 2 (a) 1H and (b) H–H COSY NMR spectra of the polyamide 6a in DMSO-d6.

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Infrared spectra were recorded on a Horiba FT-720 FT-IR spectrometer. Elemental analyses were run in a Heraeus VarioEL-III CHNS elemental analyzer. 1H and 13C NMR spectra were measured on a Bruker AVANCE-500 FT-NMR using tetramethylsilane as the internal standard. The inherent viscosities were determined at 0.5 g/dL concentration using Cannon-Fenske viscometer at 30  C. Weight-average molecular weights (Mw) and number-average molecular weights (Mn) were obtained via gel permeation chromatography (GPC) on the basis of polystyrene calibration using Waters 2410 as an apparatus and THF as the eluent. Wide-angle X-ray diffraction (WAXD) measurements were performed at room temperature (ca. 25  C) on a Shimadzu XRD-6000 X-ray diffractometer (40 kV, 20 mA), using graphite-monochromatized Cu-Ka radiation. Thermogravimetric analysis (TGA) was conducted with a PerkinElmer Pyris 1 TGA. Experiments were carried out on approximately 35 mg film samples heated in flowing nitrogen or air (flow rate ¼ 20 cm3 min1) at a heating rate of 20  C min1. DSC analyses were performed on a PerkinElmer Pyris 1 DSC at a scan rate of 20  C min1 in flowing nitrogen (20 cm3 min1). Thermomechanical analysis (TMA) was conducted with a PerkinElmer TMA 7 instrument. The TMA experiments were conducted from 50 to 350  C at a scan rate of 10  C min1 with a penetration probe 1.0 mm in diameter under an applied J. Mater. Chem., 2010, 20, 5481–5492 | 5483

constant load of 10 mN. Softening temperatures (Ts) were taken as the onset temperatures of probe displacement on the TMA traces. Absorption spectra were measured with an Agilent 8453 UV-Visible diode array spectrophotometer. Photoluminescence (PL) spectra were measured with a Varian Cary Eclipse fluorescence spectrophotometer. Fluorescent quantum yield was determined using solutions in NMP and was calculated by comparing emission with that of a standard solution of 9,10diphenylanthracene in cyclohexane (FPL ¼ 90%) at room temperature. Electrochemistry was performed with a CH Instruments 611c electrochemical analyzer. Cyclic voltammetry was conducted with the use of a three-electrode cell in which ITO (polymer film area about 1 cm2, 0.8 cm  1.25 cm) was used as a working electrode. A platinum wire was used as an auxiliary electrode. All cell potentials were taken with the use of a homemade Ag/AgCl, KCl (sat.) reference electrode. Ferrocene was used as an external reference for calibration (+0.44 V vs. Ag/ AgCl). Voltammograms are presented with the positive/negative potential pointing to the right/left with increasing anodic/ decreasing cathodic current pointing upward/downward. Spectroelectrochemistry analyses were carried out with an electrolytic cell, which was composed of a 1 cm cuvette, ITO as a working electrode, a platinum wire as an auxiliary electrode, and a Ag/ AgCl reference electrode. Absorption spectra in the spectroelectrochemical experiments were also measured with an Agilent 8453 UV-Visible diode array spectrophotometer. The DC (direct current) power source was using a model HCPS-030310 laboratory Pulse Power Supply to fix the potential between the two ITO electrodes of the device.

1-aminopyrene (2). According to a well-established procedure,19 the target diamine monomer N,N-di(4-aminophenyl)-1-aminopyrene (4) was prepared by hydrazine Pd/C-catalyzed reduction of N,N-di(4-nitrophenyl)-1-aminopyrene (3) resulting from N,Ndiarylation of 1-aminopyrene with 4-fluoronitrobenzene in the presence of caesium fluoride (CsF). The structures of all the synthesized compounds were confirmed by elemental, IR, and NMR analyses. The FT-IR spectra of compounds 1 to 4 can be seen in the ESI (see Fig. S1†). The nitro groups of compounds 1 and 3 gave two characteristic bands at around 1580–1590 and 1300–1330 cm1, respectively (-NO2 asymmetric and symmetric stretching). After reduction to 2 and 4, the characteristic absorptions of the nitro group disappeared and the primary amino group showed the typical absorption pair at 3400– 3200 cm1 due to N–H stretching. The 1H and 13C NMR spectra of the intermediate compounds 1–3 are also shown in the ESI (Fig. S2 to S7†). 1H NMR and 13C NMR spectra of the target diamine monomer 4 are illustrated in Fig. 1. The complete conversion of the nitro groups to the amino groups was confirmed by the high-field shift of the phenylene protons and by the resonance signals at around 4.81 ppm corresponding to the amino protons. Because of the substitution at the 1-position of the pyrene unit, the NMR spectra of 4 are very complicated. Nevertheless, full assignments of all peaks can be done with the

Results and discussion Synthesis and characterization The pyrene-containing triarylamine-based diamine monomer 4 was synthesized by the synthetic route outlined in Scheme 1. 1-Nitropyrene (1) was synthesized by nitration of pyrene with copper nitrate.18 Catalytic reduction of the nitro group of compound 1 by means of hydrazine and Pd/C gave

Scheme 1 Synthetic route to the target diamine monomer 4.

5484 | J. Mater. Chem., 2010, 20, 5481–5492

Fig. 3 (a) H–H COSY and (b) C–H HMQC NMR spectra of the pyrenyl unit of diamine 4 in DMSO-d6.

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aid of two-dimensional (2D) COSY and HMQC NMR spectra, as shown in Fig. 3. Thus, the results of all the spectroscopic and elemental analyses suggest the successful preparation of the target diamine monomer. The model compound M1 was prepared from the condensation of diamine 4 with two equivalent amounts of benzoic acid as shown in Scheme 2. Its spectroscopic data can be found in the ESI (Fig. S8–S10†). According to the phosphorylation technique described by Yamazaki and coworkers,20 a series of novel polyamides 6a–6j with main-chain pyrenylamine units were synthesized from the diamine monomer 4 with various aromatic or aliphatic dicarboxylic acids (5a–5j) (Scheme 3). The polymerization was carried out via solution polycondensation using triphenyl phosphite and pyridine as condensing agents. All polymerization reactions proceeded homogeneously through the reaction and gave clear, highly viscous polymer solutions. All the polyamides precipitated in a tough fiber-like form when slowly pouring the resulting polymer solutions into stirred methanol (see Fig. S11†). The as-prepared samples, their solutions, and the cast films showed a strong fluorescence upon UV irradiation. The obtained polyamides had inherent viscosities in the range of 0.54–1.23 dL/g (Table S1).† All the polymers could afford transparent and tough films via solution casting, indicating high molecular weights. The GPC measurement of a THF-soluble polyamide 6f showed weight-average molecular weight (Mw) of 49 500 and polydispersity index (Mw/Mn) of 1.87. The structures of the polyamides could be confirmed by IR and NMR spectroscopy. The typical IR spectrum for a representative polyamide 6a is included in the ESI Fig. S12†, which shows the characteristic absorption bands of the amide group at around 1650 cm1 and 3300 cm1.

Scheme 2 Synthesis of model compound M1.

The desired structures of all polymers were confirmed by 1H NMR spectra, as shown in Fig. 2 for polyamide 6a. The resonance peak appearing at 10.3 ppm clearly indicates the formation of amide linkage. As it was mentioned earlier, all the polyamides could be solution-cast into transparent, flexible, and strong films. The WAXD studies of these film samples indicated that all the polymers were essentially amorphous (Fig. S13†). All the polyamides were readily soluble in common organic solvents such as NMP, DMAc, DMF, and m-cresol. Polyamide 6f showed good solubility in less polar solvents like THF because of the additional contribution of the hexafluoroisopropylidene (-C(CF3)2-) fragment in the polymer backbone. The high solubility of these polyamides can be attributed in part to the introduction of bulky, packing-disruptive diphenylpyrenylamine units in the polymer structure. Thus, the excellent solubility makes these polymers potential candidates for practical applications by simple spin- or dip-coating processes to afford high performance thin films for optoelectronic devices. Thermal properties The thermal stability and phase transition temperatures of these polyamides were recorded by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and thermomechanical analysis (TMA), and the thermal behavior data of are summarized in Table 1. A typical set of TGA and DSC curves of polyamide 6a are shown in Fig. S14†. Except for the aliphaticaromatic polyamides 6i and 6j, these polyamides did not show significant weight loss before 500  C in air or nitrogen atmosphere. The decomposition temperatures (Td) at a 10% weightloss of the aromatic polyamides (6a to 6h) in nitrogen and air were recorded in the range of 570–593  C and 543–573  C, respectively. The amount of carbonized residue (char yield) of these polymers was more than 72% at 800  C in nitrogen. The high char yields of these polymers can be ascribed to their high aromatic content. The polyamides 6i and 6j in these series exhibited a lower Td value as compared with 6a–6h obtained from aromatic dicarboxylic acids. This is reasonable when considering the less stable aliphatic segments. Due to the

Scheme 3 Synthesis of pyrenylamine-based polyamides.

This journal is ª The Royal Society of Chemistry 2010

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Table 1 Thermal properties of polyamides Td d/ C Polymera Tgb/ C 6a 6b 6c 6d 6e 6f 6g 6h 6i 6j

321 (295)f 298 (290) 326 (302) 296 (273) 317 (296) 319 (295) 307 (288) 313 (307) 277 (259) 246 (208)

Ts c/ C in N2 318 294 309 292 314 315 306 311 267 233

593 (546) f 570 (554) 580 (573) 582 (571) 576 (515) 577 (544) 572 (564) 582 (569) 486 (431) 442 (393)

in air

Char yielde (%)

573 (526) f 559 (513) 554 (528) 559 (523) 537 (504) 543 (525) 556 (532) 557 (535) 470 (436) 448 (413)

81 80 80 78 75 72 79 80 52 52

a

The polymer film samples were heated at 300  C for 1 h prior to all the thermal analyses. b The sample were heated from 50 to 400  C at a scan rate of 20  C min1 followed by rapid cooling to 50  C at 200  C min1 in nitrogen. The midpoint temperature of baseline shift on the subsequent DSC trace (from 50 to 400  C at heating rate 20  C min1) was defined as Tg. c Softening temperature measured by TMA using a penetration method. d Decomposition temperature at which a 10% weight loss was recorded by TGA at a heating rate of 20  C min1. e Residual weight percentages at 800  C under nitrogen flow. f Values in parentheses are data of analogous polyamides 60 having the corresponding diacid residue as in the 6 series.

Fig. 4 Absorption and emission spectra of selected polyamides in NMP solution (1  105 M). 9,10-Diphenylanthracene (DPA) dissolved in cyclohexane (1  105 M) was used as the standard (FF ¼ 90%). Photographs were taken under illumination of a 365 nm UV light.

incorporation of thermally stable pyrene unit, all the polymers exhibited higher Td values compared to their corresponding 60 series counterparts derived from 4,40 -diaminotriphenylamine. These polyamides not only showed good thermal stability but also possessed high glass-transition temperatures (Tg) of 246– 326  C. The lowest Tg value of 6j is expected and can be explained in terms of the flexible polymethylene segments in its backbone. As compared to the 60 series analogs, the present series polyamides exhibit a remarkably increased Tg as a result of the presence of rigid pyrene segments. The softening temperatures (Ts) (may be referred as apparent Tg) of the polyamide films determined by the TMA method using a loaded penetration probe are also listed in Table 1. They were read from the onset temperature of the probe displacement on the TMA trace. In most cases, the Ts values of the polyamides obtained by TMA are comparable to the Tg values measured by the DSC experiments. Thus, the thermal analysis results revealed that these polyamides, especially for the aromatic ones, exhibited excellent thermal stability, which in turn is beneficial to increase the service time in device application and enhance the morphological stability to the spin-coated film. Optical properties All the polyamides were examined by UV-Vis absorption and photoluminescence (PL) spectroscopy in both solution and the solid state. Fig. 4 shows representative examples of the 5486 | J. Mater. Chem., 2010, 20, 5481–5492

absorption and emission profiles of the selected polyamides in NMP, together with their PL images on exposure to an UV light in both solution and solid states. The relevant absorption and PL data are collected in Table 2. In the absorption spectra all the polyamides display two to three prominent bands with unsymmetrical shape and adjoining shoulders. The most bathochromically shifted transitions may be ascribed to that originating from the amine to pyrene and amine to amide intramolecular charge-transfer (ICT) states. The strong highenergy absorption bands at ca. 325 nm are assigned to that arising from pyrene based p–p* transitions. These absorption bands are relatively insensitive to the solvent compared with the corresponding emission bands. Solid film absorption spectra of these polyamides were similar to those in solution, with a very slight red-shift of ca. 1–6 nm. All the polyamides exhibit similar emission profiles in NMP solutions with emission maxima in the range 522–544 nm. This clearly indicates that the emission originates from a similar excited state in this class of polymers. We believe that the emission mainly comes from the diphenylpyrenylamine core because it has a lower energy gap. As shown in Fig. 4, the emission color of the NMP solutions of these polyamides is greenish yellow, whereas that of the solid films is green or yellowish green. As shown in Table 2, the fluorescence quantum yields (FF) of these polyamides in NMP solution were found to vary from 0.7% to 30.2% relative to the This journal is ª The Royal Society of Chemistry 2010

Table 2 Photophysical properties of polyamides a

As solid film

In solution Polymer lmaxabs/nm 6a 6b 6c 6d 6e 6f 6g 6h 6i 6j

335, 385 335, 412 302, 335, 371 336, 417 320, 334, 392 335, 412 320, 334, 387 302, 334, 387 321, 331, 421 321, 331, 421

lmaxPL/nmb FF (%)c

lonsetabs lmaxPL lmaxabs/nm /nme /nmb

525 (425)d 533 (429) 533 (433) 536 (416) 538 (454) 531 (452) 524 (438) 522 (430) 544 (387) 543 (385)

335, 388 336 308, 384 336 323, 403 334 321, 384 308, 394 321, 411 324, 412

1.2 (0.2)d 25.0 (0.5) 1.3 (0.2) 26.1 (0.3) 0.7 (0.2) 8.8 (0.4) 1.1 (0.2) 0.8 (0.3) 29.7 (5.7) 30.2 (5.6)

469 465 470 467 474 461 465 476 466 469

—f 509 — 509 — 513 — — 516 519

a The polymer concentration was 1  105 mol L1 in NMP. b Excited at the absorption maximum for both solution and the solid film states. c Fluorescent quantum yield estimated using 9,10-diphenylanthracene in cyclohexane (1  105 M) as standard (FF ¼ 90%). d Values in parentheses are data of analogous polyamides 60 having the corresponding diacid residue (see footnote in Table 1) as in the 6 series. e Wavelength of the low energy absorption band edge. f Difficult to be defined due to low PL intensity.

9,10-diphenylanthracene standard (in cyclohexane solution, FF ¼ 90%).21 The low FF of most aromatic polyamides such as 6a, 6c, 6e, 6g, and 6h may be attributed to the quenching effect arising from intra- and interchain charge transfer (CT) complexing between the triarylamine donor and the aryl amide (or aroyl) acceptor. Polyamides derived from aromatic dicarboxylic acids such as isophthalic acid (5b), 4,40 -dicarboxydiphenyl ether (5d), and 2,2-bis(4-carboxyphenyl)hexafluoropropane (5f) seemed to have reduced CT interactions and showed a higher FF. It is worth noting that CT-inhibited polyamides 6i and 6j derived from aliphatic dicarboxylic acids also showed a relatively higher FF of ca. 30%. When compared with the corresponding 60 series counterparts, the higher quantum efficiency of the present series polyamides could be attributable to the presence of rigid, highly fluorescent pyrene chromophore. In contrast to absorption spectra, a strong medium effect is observed in the fluorescence spectra of these polyamides. For

Fig. 5 The normalized UV-Vis absorption and PL spectra of polyamide 6f in dilute NMP and THF solutions (1  105 M), as well as in the solid film.

This journal is ª The Royal Society of Chemistry 2010

instance polyamide 6f displays a blue-shifted emission profile in solid film (lmax ¼ 513 nm) when compared to that observed for NMP solution (lmax ¼ 531 nm), as shown in Fig. 5. This latter observation suggests that the polarity in the solid film is less than that in NMP solution. This may be accounted for by the planarity violation of the diphenylpyrenylamine segment in the solid state due to the more restricted bond rotation. As can be seen from Fig. 5, the dilute solution of polyamide 6f in less polar THF exhibited an emission profile (lmax ¼ 511 nm) similar to that in the solid film. Therefore, the emission maximum or color of these pyrenylamine-based polyamides is dependent upon the solvent polarity, i.e., they display a solvatochromic behavior. The expressed solvatochromism is typical to pyrene derivatives, as well as to triarylamine-containing compounds22 and polymers23 with donor–acceptor architecture. It is well known that pyrene derivatives exhibit environment sensitive solvatochromic behavior in which the relative intensity of emission bands is dependent on the solvent polarity.24 In order to further investigate the solvatochromic properties, we investigated the absorption and fluorescence of model compound M1 in solvents with different polarity. The model compound was chosen for study because it exhibits better solubility than the polyamides; it can dissolve in less polar solvents like toluene, chloroform, and dichloromethane. Fig. 6 showed the normalized PL spectra of M1 in dilute solution in various solvents, together with fluorescence images of its solutions. The absorption and PL emission data are collected in Table 3. The solution absorption spectra of M1 are similar, with little shift in the peak maximum (absorption lmax  334 nm). This clearly indicates that the solvent polarity exerts little effect on its ground-state electronic transition. In contrast, the PL emission spectra of M1 show strong solvent-polarity dependence, revealing a dominant broad emission band that undergoes remarkable bathochromic shifts with an increase of the solvent polarity. The emission color

Fig. 6 Normalized PL spectra the dilute solutions of M1 (ca. 1  105 M) in solvents of various polarity. Photographs were taken under illumination of a 365 nm UV light.

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Table 3 Photophysical properties of M1 in different solvents Solvent

3a

lmaxabs/nmb

lmaxPL/nmc

FF (%)d

Toluene CHCl3 THF CH2Cl2 NMP MeCN DMSO

2.4 4.8 7.5 9.1 32.2 37.0 47.0

334 334 334 334 335 334 336

480 492 507 510 531 533 544

45.1 42.9 42.0 41.6 30.2 28.6 24.1

a Dielectric constant of the solvent. b Concentration of the solution ¼ 1  105 M. c Excited at the absorption maximum. d Fluorescent quantum yield estimated using 9,10-diphenylanthracene in cyclohexane (1  105 M) as standard (FF ¼ 90%).

changes from blue in toluene (PL lmax ¼ 480 nm) to greenish yellow in DMSO (lmax ¼ 544 nm). A decreased fluorescence quantum yield and an increased band width were also observed in the solvent of higher polarity. The solvatochromism could be attributed to the fast intramolecular charge-transfer process resulting in a large change of dipole moment in the excited state.25 Such solvatochromic behavior is associated with the stabilization of the polar emissive excited states by the polar solvents.

Electrochemical properties Cyclic voltammetry (CV) experiments were conducted to investigate the electrochemical properties of the polyamides. The oxidation and reduction cycles of the film samples were measured in acetonitrile and DMF, respectively, using tetrabutylammonium perchlorate, Bu4NClO4, as the electrolyte. Samples were coated on the surface of the ITO-glass by a solution-casting process. Typical CV curves of polyamide 6d are shown in Fig. 7. All the polyamides displayed reversible oxidation and reduction processes, indicating their high electrochemical stability for both p- and n-doping. These reversible waves also represent the formation of stable radical cation and radical anion originating from electrochemical redox reactions of the diphenylpyrenylamine core (Scheme 4). The onset potential of the reduction process was recorded in the range from 1.86 to 1.77 V. From the positions of the redox couple peaks of the reduction process, the n-doping half-wave potentials, Ered1/2, for polyamides 6a–6j were determined, and these values range from 2.05 to 1.96 V (Table 4). These potentials are similar to those found in related pyrene derivatives.26 The color of the polyamide films changed

Fig. 7 Cyclic voltammograms of the polyamide 6d film on an ITOcoated glass substrate in 0.1 M Bu4NClO4 acetonitrile (for the oxidation process) and DMF (for the reduction process) solutions at a scan rate of 50 and 100 mV s1, respectively. The arrows indicate the film color change during CV scan. E1/2 values are indicated by dashed lines.

from yellow to pale orange due to electrochemical reduction of the polymers. The onset and half-wave potentials (Eox1/2) of the oxidation process were found to be around 0.66–0.70 V and 0.81–0.83 V, respectively. The oxidation potentials are relatively insensitive to the structure of the dicarboxylic acid component in these polyamides. Variations of less than 0.04 V were observed in the 6a–6j series, and this indicates that the diacid residue does not significantly disturb the electronic nature of the oxidizable triarylamine core. The color of the polyamide films turned from yellow to purple upon oxidation. In comparison to the corresponding 60 analogs, the 6 series polyamides displayed a slightly lower oxidation potential. This suggests that the presence of electron-rich pyrene moiety in the latter case is responsible for the decrease in the oxidation potential. On the basis of the oxidation and reduction onset potentials, the bandgaps for polyamides 6a–6j were calculated, and were found to vary from 2.45 to 2.56 eV. The bandgaps calculated from the CV measurements are somewhat lower (by 0.11– 0.22 eV) than those obtained from the absorption spectra. By using the oxidation and reduction onset potentials, the highest occupied molecular orbital (HOMO) levels for these polyamides were calculated and found to be between 5.02 and 5.06 eV (relative to the vacuum energy level), whereas the values for the lowest unoccupied molecular orbital (LUMO) levels lay between 2.50 and 2.59 eV (Table 4). When the calculations are based on

Scheme 4 Postulated redox chemistry of polyamides.

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This journal is ª The Royal Society of Chemistry 2010

Table 4 Redox potentials and energy levels of polyamides Oxidation potential/Va

Reduction potential/Vb

Polymer

Eox nset

Eox1/2

Eredonset

Ered1/2

from Eonset

from E1/2

Egopt/eVd

from Eonset

from E1/2

6a 6b 6c 6d 6e 6f 6g 6h 6i 6j

0.69 0.68 0.68 0.68 0.70 0.70 0.70 0.68 0.66 0.67

0.82 (0.84)f 0.82 (0.86) 0.82 (0.84) 0.82 (0.85) 0.83 (0.86) 0.83 (0.86) 0.82 (0.85) 0.82 (0.84) 0.81 (0.84) 0.81 (0.84)

1.82 1.80 1.77 1.84 1.77 1.77 1.86 1.80 1.84 1.85

2.02 1.98 2.05 1.96 2.02 2.04 2.04 2.04 1.96 1.96

2.51 2.48 2.45 2.52 2.47 2.47 2.56 2.48 2.50 2.52

2.84 2.80 2.87 2.78 2.85 2.87 2.86 2.86 2.77 2.77

2.64 2.67 2.64 2.66 2.62 2.69 2.67 2.61 2.66 2.64

5.05/2.54 5.04/2.56 5.04/2.59 5.04/2.52 5.06/2.59 5.06/2.59 5.06/2.50 5.04/2.56 5.02/2.52 5.03/2.51

5.18/2.34 5.18/2.38 5.18/2.31 5.18/2.40 5.19/2.34 5.19/2.32 5.18/2.32 5.18/2.32 5.17/2.40 5.17/2.40

EgCV/eVc

HOMO/LUMO/eVe

a

vs. Ag/AgCl in CH3CN. E1/2 ¼ average potential of the redox couple peaks. b vs. Ag/AgCl in DMF. c Bandgaps calculated from CV measurements. Bandgaps calculated from absorption edge of the polymer films: Egopt ¼ 1240/lonset. e The HOMO energy levels were calculated from Eonset or E1/2 values of CV curves and were referenced to ferrocene (4.8 eV relative to the vacuum energy level). f Values in parentheses are data of analogous polyamide 60 having the corresponding R as that of the 6 series. d

the E1/2 values, the HOMO and LUMO energy levels are estimated to be in the range of 5.17–5.19 eV and 2.31–2.40 eV, respectively, which are similar to those reported for the pyrenecontaining triarylamines.13c The closeness of the HOMO of these polyamides to the work function of ITO (Ef ¼ 4.7 eV) indicates that hole injection into the molecular layer of these polymers will be effective if they are employed as hole-transporters in OLEDs.

Spectroelectrochemical and electrochromic properties The electro-optical properties of the polymer films were investigated using the changes in electronic absorption spectra at various applied voltages. For these investigations, the polyamide film was cast on an ITO-coated glass slide (a piece that fit in the commercial UV-visible cuvette), and a homemade electrochemical cell was built from a commercial UV-visible cuvette. The cell was placed in the optical path of the sample light beam in a commercial diode array spectrophotometer. This procedure allowed us to obtain electronic absorption spectra under potential control in a 0.1 M Bu4NClO4/acetonitrile solution. The result of the 6d film upon oxidation is presented in Fig. 8a as a series of UV-vis absorbance curves correlated to electrode potentials. Fig. 9 shows the surface plot diagram for the % transmittancewavelength-applied potential correlations of this sample. In the neutral form, at 0 V, the film exhibited strong absorption at wavelength around 336 nm, characteristic for triarylamine, but it was almost transparent at wavelengths > 450 nm. Upon oxidation of the 6d film (increasing applied voltage from 0 to 1.00 V), the intensity of the absorption peak at 336 nm gradually decreased while new peaks at 403, 550, and 597 nm and a broadband having its maximum absorption wavelength at 834 nm gradually increased in intensity. Meanwhile, the color of the film changed from yellow to purple. We attribute this spectral change to the formation of a stable radical cation of the diphenylpyrenylamine moiety. For a comparative study, the spectral changes of the analogous triphenylamine-based polyamide 6d0 are presented in Fig. 8b. The spectral changes in the region of 500–600 nm of polyamide 6d0 upon oxidation are slightly different from those of 6d, and the film of 6d0 appeared a greenish This journal is ª The Royal Society of Chemistry 2010

Fig. 8 Spectral changes of (a) polyamide 6d and (b) 6d0 thin film on an ITO-coated glass substrate (in CH3CN with 0.1 M Bu4NClO4 as the supporting electrolyte) along with increasing of the applied voltage up to 1.00 V (vs. Ag/AgCl couple as reference). The inset shows the color changes of the polymer films between neutral and oxidized states.

blue color at its fully oxidized state. The observed UV-vis absorption changes in the film of 6d at various potentials are fully reversible and are associated with strong color changes; indeed, they even can be seen readily by the naked eye. From the photographs shown in Fig. 9, it can be seen that the film of 6d switches from a transmissive neutral state (yellow) to a highly J. Mater. Chem., 2010, 20, 5481–5492 | 5489

Fig. 9 Electronic absorption spectra of the cast film of polyamide 6d on ITO in 0.1 M Bu4NClO4/CH3CN at various applied potentials between 0.0 and 1.0 V (vs. Ag/AgCl couple as reference). The photo shows the color change of the film on an ITO electrode at indicated potentials.

absorbing oxidized state (purple). The film colorations are distributed homogeneously across the polymer film and survive for more than hundreds of redox cycles. Moreover, coloration changes were also observed in these polyamides upon reduction. However, the color change is not strong as that observed in the anodic scanning. In general, the polyamide films changed from yellow neutral form to a pale orange reduced form. Typical electronic absorption changes of the 6d film upon reduction are illustrated in Fig. S15†. Upon oxidation, the polyamide films exhibited a strong coloration change between redox states. The stability, response time, and color efficiency are the key parameters for an electroactive polymer film to be amenable for usage in optical and electrochromic devices. For optical switching studies, polymer films were cast on ITO-coated glass slides in the same manner as described above, and each film was potential stepped between its bleaching (0.0 V) and coloring (+1.00 V) state. While the films were switched, the absorbance at 834 nm was monitored as

Fig. 11 Optical transmittance changes at l ¼ 834 nm for a solution-cast film of polyamide 6d (with an optical density of 0.44 a.u.) in 0.1 M Bu4NClO4/CH3CN between the potentials of 0 and 1.0 V.

a function of time with UV-vis-NIR spectroscopy. The switching time was calculated at 90% of the full switch because it is difficult to perceive any further color change with the naked eye beyond this point. The polyamides switch rapidly (within three seconds) between the highly transmissive neutral state and the colored oxidized state. As depicted in Fig. S16†, the thin film of polyamide 6d required only 2.9 s at 1.00 V for coloring and 1.0 s for bleaching. As shown in Fig. 10, the absorbance changes at 834 nm reflect the switch in current, and the kinetics of the charge transport process can be referenced to the coloration response time. Fig. 11 shows the change in transmittance measured as the rate of switching the polymer film of 6d, between oxidized and neutralized, is increased. As the polymer is switched between 0 and 1.0 V with a 10 s hold at each potential, the percent transmittance (DT) contrast for 834 nm is 65.0%. As the time the oxidizing and reducing potentials are held is decreased to 5 s, the optical contrast decreases only slightly to 61.4%, and subsequently to 46.6% for a 2 s hold. The electrochromic coloration efficiencies (h ¼ DOD834/Q)27 after various switching steps of the film of polyamide 6d are summarized in Table 5. The Table 5 Coloration efficiency of polyamide 6d

Fig. 10 Dynamic changes of (a) the transmittance and (b) current upon switching the potential between 0 and 1.0 V (vs. Ag/AgCl) with a pulse width of 10 s applied to the cast film of polyamide 6d on the ITO-glass (active area  1 cm2) in CH3CN containing 0.1 M Bu4NClO4. The absorption was recorded at 597 and 834 nm.

5490 | J. Mater. Chem., 2010, 20, 5481–5492

Cyclesa

DOD834b

Qc/mC cm2

hd/cm2 C1

Decaye (%)

1 50 100 150 200 250 300 350 400 450 500

0.400 0.395 0.389 0.383 0.374 0.367 0.358 0.352 0.345 0.337 0.328

2.322 2.348 2.351 2.357 2.348 2.358 2.356 2.344 2.339 2.321 2.319

172 168 165 162 159 156 152 150 147 145 141

0.0 2.3 4.1 5.9 7.6 9.3 11.6 12.8 14.5 15.7 18.0

a Number of cyclic switching by applying potential steps between 0 and 1.00 V (vs. Ag/AgCl), with a pulse width of 10 s. b Optical density change at 834 nm. c Ejected charge, determined from the in situ experiments. d Coloration efficiency is calculated by the equation: h ¼ DOD834/Q. e Decay of coloration efficiency after cyclic scans.

This journal is ª The Royal Society of Chemistry 2010

under atmospheric condition. To prevent leakage, an epoxy resin was applied to seal the device. As a typical example, an electrochromic cell based on polyamide 6d was fabricated. When a voltage of 0.0 V is applied, the polymer is neutral and yellow. When the voltage applied was increased (to a maximum of 2.4 V), the color changed from yellow to purple, the same as was already observed for the solution spectroelectrochemistry experiments. The color change is uniform, as can be seen in Fig. 13a where the letters TTU were written by spray-coating 6d solution over a stencil. The neutral state is yellow, while the oxidized state is purple. We believe that optimization could further improve the device performance and fully explore the potential of these electrochromic polyamides.

Conclusions Fig. 12 The PL images (upon excitation with a 365-nm UV light) of the cast film of polyamide 6d on ITO-coated slide before and after redox cycling between 0 and 1.0 V.

A series of novel pyrenylamine-functionalized polyamides have been prepared from a newly synthesized diamine monomer, N,Ndi(4-aminophenyl)-1-aminopyrene, with various aromatic and aliphatic dicarboxylic acids via the phosphorylation polyamidation reaction. All the polymers could form morphologically stable and uniform amorphous films using solution-casting techniques. In addition to high Tg, high thermal stability, notable fluorescence and solvatochromism, the polymers also revealed interesting electrochromic characteristics with color change from yellow neutral state to purple oxidized state and orange reductive state. Thus, these polyamides have great potential for use in optoelectronic applications as new charge-transporting, lightemitting, and electrochromic materials. Further development of materials of this type would seem to be warranted by the very encouraging initial results presented here.

Acknowledgements Fig. 13 (a) Photos of sandwich-type ITO-coated glass electrochromic cell, using polyamide 6d as active layer. (b) Schematic illustration of the structure of the electrochromic cell.

The authors are grateful to the National Science Council of Taiwan (Republic of China) for financial support of this work.

References electrochromic film of 6d was found to exhibit good coloration efficiencies up to 172 cm2 C1 at 834 nm. It was confirmed that the polymer film does not lose its electro-optical activity significantly and retains about 80% of its optical response after 500 coloring/bleaching cycles. Therefore, the electrochromic switching behavior appears to be a highly reversible process. Moreover, the film fluorescence properties after of the electrochemical treatment were also evaluated. The PL spectra of the polyamide 5d film display almost no change after 100 repeated electrochemical cycling, indicating high oxidation stability and little change in the molecular structure after redox cycling. The PL images of the polymer film of 5d before and after redox cycling are reproduced in Fig. 12. Based on the foregoing results, it can be concluded that these polyamides can be used in the construction of electrochromic devices and optical display due to the fast response time and the robustness of the polymers. Therefore, we fabricated as preliminary investigations single layer elecrochromic cells (Fig. 13). The polymer films were spray-coated onto ITO-coated glass and then dried. Afterwards, the gel electrolyte was spread on the polymercoated side of the electrode and the electrodes were sandwiched This journal is ª The Royal Society of Chemistry 2010

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5492 | J. Mater. Chem., 2010, 20, 5481–5492

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This journal is ª The Royal Society of Chemistry 2010

Supplementary Material (ESI) for Journal of Materials Chemistry This journal is (c) The Royal Society of Chemistry 2010

Supplementary Information For Fluorescent and electrochromic polyamides with pyrenylamine chromophore

By

Yi-Chun Kung, Sheng-Huei Hsiao* E-mail: [email protected]

List of Contents for Supplementary Material: page Materials and synthesis of compounds 1, 2, and M1…………………………. Inherent viscosity and Solubility behavior of polyamides……………………. IR spectra of compounds 1-4…………………………………………………. 1 H and 13C NMR spectra of 1-nitropyrene (1)………………………………... H-H COSY and C-H HMQC NMR spectra of the 1-nitropyrene (1)………… 1 H and 13C NMR spectra of 1-aminopyrene (2)………………………………. H-H COSY and C-H HMQC NMR spectra of the 1-aminopyrene (2)……….. 1 H and 13C NMR spectra of dinitro compound 3……………………………... H-H COSY and C-H HMQC NMR spectra of dinitro compound 3………….. IR spectra of model compound M1…………………………………………... 1 H and 13C NMR spectra of model compound M1…………………………… H-H COSY and C-H HMQC NMR spectra of M1…………………………… IR spectra of polyamide 6a…………………………………………………… WAXD patterns of polyamides 6a-6j………………………………………… TGA and DSC curves of polyamide 6a………………………………………. Spectral changes of polyamide 6d thin film along with increasing of the applied voltage………………………………………………………………………… Calculation of optical switching time for polyamide 6d………………………

1

2-4 5 6 7 8 9 10 11 12 13 14 15 16 17 17 18

18

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Materials. Pyrene (Acros), 4-fluoronitrobenzene (Acros), copper(II) nitrate trihydrate (Showa), 10% palladium on charcoal (Pd/C) (Lancaster), cesium fluoride (CsF) (Acros), acetic anhydride (Tedia), triphenyl phosphite (TPP) (Acros), and hydrazine monohydrate (TCI) were used without further purification. N,N-Dimethylacetamide (DMAc) (Tedia), N,N-dimethylformamide (DMF) (Tedia), pyridine (Py) (Wako), N-methyl-2-pyrrolidone (NMP) (Tedia), and acetonitrile (Tedia) were dried over calcium hydride for 24 h, distilled under reduced pressure, and stored over 4 Å molecular sieves in a sealed bottle. The aromatic dicarboxylic acids such as terephthalic acid (5a) (Wako), isophthalic acid (5b) (Wako), 4,4’-biphenyldicarboxylic acid (5c) (TCI), 4,4’-dicarboxydiphenyl ether (5d) (TCI), bis(4-carboxyphenyl)

sulfone

(5e)

(New

Japan

Chemicals

Co.),

2,2-bis(4-carboxyphenyl)hexafluoropropane (5f) (TCI), 1,4-naphthalenedicarboxylic acid (5g) (Wako), 2,6-naphthalenedicarboxylic acid (5h) (TCI), 1,4-dicarboxycyclohexane (5i) (TCI), and adipic acid (5j) (TCI) were used as received. Commercially obtained anhydrous calcium chloride (CaCl2) was dried under vacuum at 180 oC for 8 h prior to use. Tetrabutylammonium perchlorate (TBAP) (TCI) was recrystallized twice by ethyl acetate under nitrogen atmosphere and then dried in vacuo prior to use. Poly(methyl methacrylate) (PMMA) (MW 120,000) and propylene carbonate (PC) were used as received from Aldrich and Acros Organic, respectively. Synthesis of 1-Nitropyrene (1): In a 500-mL three-neck round-bottomed flask equipped with a stirring bar under nitrogen atmosphere. To a mixture of pyrene (20.2 g, 100 mmol) and Ac2O (26 mL, 277 mmol) in 200 mL of dried EtOAc was added Cu(NO3)2 (36 g, 150 mmol). The mixture was stirred at 55 oC for 24 hr and a thick yellow precipitate formed during nitration. The reaction was cooled to room temperature and inorganic materials were filtered off. The crude product obtained on evaporation of solvent was purified by recrystallized from amount of ethanol to afford 22.6 g (92 % in yield) of fluffy, amber, fine needles with a mp of 151-152 oC (by DSC 2 oC/ min). FT-IR (KBr): 1331, 1593 cm-1 (NO2 stretch). 1H NMR (500 MHz, DMSO-d6, δ, ppm): 8.20 (t, J = 7.7 Hz, 1H, Hf), 8.26 (d, J = 8.9 Hz, 1H, Hh), 8.37 (d, J = 9.1 Hz, 1H, Hb), 8.39 (d, J = 9.3 Hz, 1H, Hi), 8.37 (d, J = 9.1 Hz, 1H, Hb), 8.39 (d, J = 9.3 Hz, 1H, Hi), 8.44 (d, J = 9.5 Hz, 1H, Hc), 8.45 (d, J = 7.5 Hz, 1H, He), 8.47 (d, J = 7.7 2

Supplementary Material (ESI) for Journal of Materials Chemistry This journal is (c) The Royal Society of Chemistry 2010

Hz, 1H, Hg) , 8.65 (d, J = 9.4 Hz, 1H, Hd) , 8.68 (d, J = 8.5 Hz, 1H, Ha).

13

C NMR (125 MHz,

DMSO-d6, δ, ppm): 120.83 (C6), 122.62 (C2), 123.58 (C14), 123.71 (C1), 124.69 (C3), 126.90 (C12), 127.30 (C8), 127.44 (C9), 127.96 (C10), 129.45 (C16), 130.36 (C15), 130.78 (C13), 131.59 (C5), 134.56 (C7+C11), 142.25 (C16). 15 12 h 10 g 9f

13 NO2 i 14 1

a2

11

e 7 d 8 6

4 c5

b3

16

Synthesis of 1-Aminopyrene (2): In a 250-mL three-neck round-bottomed flask equipped with a stirring bar under nitrogen atmosphere, 12.4 g (50 mmol) of nitro compound 1 and 0.15 g of 10 % Pd/C were dissolved/suspended in 80 mL of ethanol and 40 mL of THF. The suspension solution was heated to reflux, and 6.5 mL of hydrazine monohydrate was added slowly to the mixture, then the solution was stirred at reflux temperature. After a further 12 h of reflux, the solution was filtered to remove Pd/C, and the filtrate was evaporated under reduced pressure to dryness. The crude product was recrystallized by ethanol/water and dried in vacuo at 80 oC to give 9.23 g (85 % in yield) of greenish yellow crystals with a mp of 115-116 oC (by DSC 2 oC/ min). FT-IR (KBr): 3200-3400 cm-1 (N-H stretch). 1H NMR (500 MHz, DMSO-d6, δ, ppm): 6.34 (s, 2H, -NH2), 7.40 (d, J = 8.3 Hz, 1H, Ha), 7.71 (d, J = 8.8 Hz, 1H, Hd), 7.86 (t, J = 7.7 Hz, 1H, Hf), 7.88 (d, J = 8.8 Hz, 1H, Hc), 7.92 (d, J = 9.3 Hz, 1H, Hi), 7.97 (d, J = 8.4 Hz, 1H, Hb), 7.98 (d, 1H, He), 7.99 (d, 1H, Hg), 8.29 (d, J = 9.2 Hz, 1H, Hh). 13C NMR (125 MHz, DMSO-d6, δ, ppm): 113.13 (C2), 114.72 (C4), 121.39 (C14), 121.76 (C6), 122.13 (C12), 122.37 (C8), 122.91 (C10), 124.14 (C13), 125.14 (C15), 125.70 (C16), 125.85 (C9), 126.52 (C3), 127.70 (C5), 131.67 (C11), 132.02 (C7), 144.36 (C1). 15 12 h 10 g 9f

13 NH2 i 14 1

a2

11

e 7 d 8 6

3

4 c5 16

b3

Supplementary Material (ESI) for Journal of Materials Chemistry This journal is (c) The Royal Society of Chemistry 2010

Synthesis of Model Compound, N,N-Di(4-benzamidophenyl)-1-aminopyrene (M1): A 50 mL round-bottom flask with a magnetic stirrer was charged with 0.400 g (1.0 mmol) of diamine monomer 4, 0.244 g (2.0 mmol) of benzoic acid, 0.5 mL of triphenyl phosphite (TPP), 0.4 mL of NMP, and 0.3 mL of pyridine. The reaction mixture was heated with stirring at 120 oC for 3 hr. The reaction solution was poured into 150 mL of stirring cold methanol giving rise to a greenish precipitate that was collected by filtration, washed thoroughly with hot water and methanol, and dried in vacuo at 80 oC. Yield = 0.595 g (98%). IR (KBr): 3282 (amide N-H stretch), 1647 cm-1 (amide C=O stretch). 1H NMR (500 MHz, DMSO-d6, δ, ppm): 6.99 (d, J = 9.0 Hz, 4H, Hj), 7.51 (t, J = 7.1 Hz, 4H, Hm), 7.57 (t, J = 7.4 Hz, 2H, Hn), 7.68 (d, J = 9.0 Hz, 4H, Hk), 7.86 (d, J = 8.2 Hz, 1H, Ha), 7.94 (d, J = 7.2 Hz, 4H, Hl), 8.07 (t, J = 7.7 Hz, 1H, Hf), 8.12 (d, J = 9.3 Hz, 1H, Hd), 8.17 (d, J = 9.2 Hz, 1H, Hh), 8.19 (d, J = 9.2 Hz, 1H, Hi), 8.23 (d, J = 7.5 Hz, 1H, He), 8.30 (d, J = 7.8 Hz, 1H, Hg), 8.34 (d, J = 8.2 Hz, 1H, Hb) 10.19 (s, 2H, amide N-H). 13C NMR (125 MHz, DMSO-d6, δ, ppm): 121.73 (C18), 121.89 (C19), 122.85 (C6), 124.01 (C4), 125.13 (C8), 125.37 (C10), 125.58 (C14), 126.35 (C3), 126.57 (C9), 126.88 (C15), 127.03 (C13), 127.20 (C2), 127.23 (C12), 127.53 (C22), 127.76 (C5), 128.31 (C23), 128.86 (C16), 130.46 (C11), 130.78 (C7), 131.39 (C21), 133.49 (C24), 134.97 (C20), 140.69 (C1), 144.31 (C17), 165.15 (amide, C=O). m n

l

O H N

19

k j 18

17 N 15 13 i 14 1 a 2 12 h 11 b3 10 g 4 c5 9f e 7 d 16 8 6

4

H O 20 N 21 22

24 23

Supplementary Material (ESI) for Journal of Materials Chemistry This journal is (c) The Royal Society of Chemistry 2010

Table S1 Inherent viscositya and solubility behaviorb of polyamides Polymer ηinh Code (dL/g)

Various Solvent c NMP

DMAc

DMF

DMSO

m-Cresol THF

6a

1.08

++ (++)

++ (++)

++ (+)

++ (+)

++ (+)

6b

0.54

++ (++)

++ (++)

++ (+)

++ (+)

++ (+)

6c

1.23

++ (++)

++ (++)

++ (+)

++ (+)

++ (+)

6d

0.95

++ (++)

++ (++)

++ (++)

++ (++)

++ (+)

6e

1.02

++ (++)

++ (++)

++ (++)

++ (++)

++ (+)

6f

0.95

++ (++)

++ (++)

++ (++)

++ (++)

++ (+)

6g

0.76

++ (++)

++ (++)

++ (+)

++ (+)

++ (++)

6h

1.13

++ (++)

++ (++)

++ (+)

++ (+)

++ (+)

6i

0.73

++ (++)

++ (++)

++ (++)

++ (++)

++ (+)

6j

0.70

++ (++)

++ (++)

++ (++)

++ (++)

++ (+)

－ (－) － (－) － (－) － (－) － (－) ++ (－) － (－) － (－) － (－) － (－)

a

Inherent viscosity measured at a concentration of 0.5 dL/g in DMAc – 5 wt % LiCl at 30 oC. b Solubility: ++: soluble at room temperature; +－: partially soluble; +: soluble on heating; －: insoluble even on heating. c Solvent: NMP: N-methyl-2-pyrrolidone; DMAc: N,N-dimethylacetamide; DMF: N,N-dimethylformamide; DMSO: dimethyl sulfoxide; THF: tetrahydrofuran. Values in parentheses are data of analogous polyamides 6’ having the corresponding diacid residue as in the 6 series. H

H O

N

N N

O R

n

6'

5

Supplementary Material (ESI) for Journal of Materials Chemistry This journal is (c) The Royal Society of Chemistry 2010

Fig. S1 IR spectra of compounds 1-4.

6

Supplementary Material (ESI) for Journal of Materials Chemistry This journal is (c) The Royal Society of Chemistry 2010

Fig. S2 (a) 1H and (b) 13C NMR spectra of 1-nitropyrene (1) in DMSO-d6.

7

Supplementary Material (ESI) for Journal of Materials Chemistry This journal is (c) The Royal Society of Chemistry 2010

Fig. S3 (a) H-H COSY and (b) C-H HMQC NMR spectra of 1-nitropyrene (1) in DMSO-d6.

8

Supplementary Material (ESI) for Journal of Materials Chemistry This journal is (c) The Royal Society of Chemistry 2010

Fig. S4 (a) 1H and (b) 13C NMR spectra of 1-aminopyrene (2) in DMSO-d6.

9

Supplementary Material (ESI) for Journal of Materials Chemistry This journal is (c) The Royal Society of Chemistry 2010

Fig. S5 (a) H-H COSY and (b) C-H HMQC NMR spectra of 1-aminopyrene (2) in DMSO-d6.

10

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Fig. S6 (a) 1H and (b) 13C NMR spectra of dinitro compound 3 in DMSO-d6.

11

Supplementary Material (ESI) for Journal of Materials Chemistry This journal is (c) The Royal Society of Chemistry 2010

Fig. S7 (a) H-H COSY and (b) C-H HMQC NMR spectra of dinitro compound 3 in DMSO-d6. 12

Supplementary Material (ESI) for Journal of Materials Chemistry This journal is (c) The Royal Society of Chemistry 2010

Fig. S8 IR spectra of amide-type model compound M1.

13

Supplementary Material (ESI) for Journal of Materials Chemistry This journal is (c) The Royal Society of Chemistry 2010

Fig. S9 (a) 1H and (b) 13C NMR spectra of model compound M1 in DMSO-d6.

14

Supplementary Material (ESI) for Journal of Materials Chemistry This journal is (c) The Royal Society of Chemistry 2010

Fig. S10 (a) H-H COSY and (b) C-H HMQC NMR spectra of M1 in DMSO-d6.

15

Supplementary Material (ESI) for Journal of Materials Chemistry This journal is (c) The Royal Society of Chemistry 2010

Fig. S11 (a) The as-prepared sample of polyamide 6i; (b) Photoluminescence of the as-prepared sample, its DMAc solution, and its cast film irradiated by a laboratory UV lamp.

Fig. S12 IR spectra of polyamide 6a.

16

Supplementary Material (ESI) for Journal of Materials Chemistry This journal is (c) The Royal Society of Chemistry 2010

Fig. S13 WAXD patterns of polyamides 6a-6j.

Fig. S14 TGA and DSC curve of polyamide 6a with a heating rate of 20 oC/min.

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Supplementary Material (ESI) for Journal of Materials Chemistry This journal is (c) The Royal Society of Chemistry 2010

Fig. S15 Spectral changes of polyamide 6d thin film on an ITO-coated glass substrate (in DMF with 0.1 M NBu4ClO4 as the supporting electrolyte) along with increasing of the applied voltage up to -2.20 V (vs. Ag/AgCl couple as reference). The inset shows the color changes between neutral and reductive states.

Fig. S16 Calculation of optical switching time for polyamide 6d thin film at λmax = 834 nm as the applied voltage was stepped between 0 and 1.00 V (vs. Ag/AgCl couple as reference) with cycle time = 10 s.

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