Creating Patterned Conjugated Polymer Images Using Water

Jan 5, 2016 - E-mail: [email protected]. ... Although creating patterns of conjugated polymers on paper using common office inkjet printers has been ...
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Creating Patterned Conjugated Polymer Images Using WaterCompatible Reactive Inkjet Printing Seongho Jeon,† Sumin Park,† Jihye Nam,‡ Youngjong Kang,‡,§ and Jong-Man Kim*,†,§ †

Department of Chemical Engineering, Hanyang University, Seoul 133-791, Korea Department of Chemistry, Hanyang University, Seoul 133-791, Korea § Institute of Nano Science and Technology, Hanyang University, Seoul 133-791, Korea ‡

S Supporting Information *

ABSTRACT: The fabrication of patterned conjugated polymer images on solid substrates has gained significant attention recently. Office inkjet printers can be used to generate flexible designs of functional materials on substrates on a large scale and in an inexpensive manner. Although creating patterns of conjugated polymers on paper using common office inkjet printers has been reported, only a few examples exist, such as polyaniline (PANI) and poly(3,4-ethylenedioxythiophene) (PEDOT), because only water-compatible inks can be utilized. Herein, we describe the production of poly(phenylenevinylene) (PPV) patterns on paper by employing a reactive inkjet printing (RIJ) method. In this process, printing of a hydrophilic terephthaldehyde, bis(triphenylphosphonium salt) and potassium t-butoxide using a common office inkjet printer leads to formation PPV patterns as a consequence of an in situ Wittig reaction. In addition, microarrayed PPV patterns are also readily generated on solid substrates, such as glass and PDMS, when a piezoelectric dispenser system is employed. The in situ prepared PPV was found to be insoluble in water and chloroform. As a result, unreacted excess reagents and byproducts can be efficiently removed by washing with these solvents. KEYWORDS: conjugated polymer, reactive inkjet printing, paper substrate, PPV, office inkjet printer

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INTRODUCTION

general use is limited to organic materials that are water incompatible. Our earlier interest in paper-based functional materials led to the development of methods to generate colorimetric conjugated polydiacetylene (PDA) images on paper substrates using a common office inkjet printer.23−26 We were curious if other conjugated polymers could be prepared on paper using inkjet printing. We recognized that several requirements needed to be fulfilled in order to this process to be efficient include (1) the monomers and reagents need to be compatible with water, (2) byproducts and excess reagents need to be readily removed after imaging, and (3) the process needs to form insoluble conjugated polymers. Although several strategies for generating conjugated polymer patterns on paper have been reported, those that enable in situ synthesis of conjugated polymers on this substrate are rare. 13,15,23−26 In the investigation described below, we devised and tested a new strategy for the synthesis of a fluorescent conjugated polymer on a solid substrate employing the RIJ method and a common office inkjet printers.

Reactive inkjet printing (RIJ) technology has emerged as a powerful tool for preparation of patterns of functional organic materials.1−4 The combination of chemical reactions and inkjet printing enables the RIJ method to be employed to fabricate various functional organic materials on solid substrates in a localized and patterned manner. Low reagent consumption and easy processing are additional meritorious features of the RIJ technology. Accordingly, a variety of organic materials including polyacrylated libraries,5−8 poly(9-vinylcarbazole),9 polyurethane,10,11 cross-linked polymer radicals,12 polyaniline,13,14 polypyrrole,14−16 and polythiophene17,18 as well as stimuliresponsive fluorescent materials,19 and polymer matrix assisted quantum dots20 have been prepared by employing this method. Organic solvent based ink systems have been utilized in RIJ printing of a majority of functional organic materials. Meanwhile, generation of patterns of functional organic molecules using common office inkjet printers has gained much attention, because it can be used to produce patterns over large areas on paper substrates.21,22 Printing and deposition of functional materials on paper substrates can be used in flexible, lightweight and disposable devices. Because office inkjet printers are designed to use water based ink materials, their © XXXX American Chemical Society

Received: October 13, 2015 Accepted: January 5, 2016

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DOI: 10.1021/acsami.5b09705 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

Research Article

ACS Applied Materials & Interfaces Scheme 1. Synthetic Routes for Preparation of Water Compatible Reactive Ink Componentsa

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Conditions: (a) MsCl, TEA, DCM; (b) p-formaldehyde, HCl, HCHO, dioxane, water; (c) hexamethylenetetramine, CHCl3, H2O, acetic acid; (d) BBr3, DCM; (e) 2, K2CO3, ACN; (f) PPh3, ACN.

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200.0 mmol) was added dropwise at 0 °C under a N2 atmosphere. The mixture was stirred at 20 °C for 3 h. After solvent evaporation, the residue was dissolved in ether (200 mL) and washed with saturated NaCl solution in water. The organic layer was dried over Na2SO4 and concentrated in vacuo to afford the product 2 (22.0 g, 67%) as a colorless liquid. The transparent liquid product was used for the next reaction without further purification. 1H NMR (300 MHz, CDCl3) δ 4.39−4.36 (m, 2H), 3.78−3.74 (m, 2H), 3.67−3.64 (m, 2H), 3.55− 3.52 (m, 2H), 3.37 (s, 3H), 3.06 (s, 3H). 1,4-Bis(chloromethyl)-2,5-dimethoxybenzene (4).28 To a solution of 1,4-dimethoxybenzene (3) (10.0 g, 72.3 mmol) in 1,4-dioxane (30 mL), formaldehyde solution (38% in water, 5 mL) and paraformaldehyde (3.0 g, 99.0 mmol) were added. The resulting mixture was stirred at 90 °C and concentrated HCl (2 × 5 mL) was added during 30 min intervals. Heating was continued for 1 h and a further 30 mL of concentrated HCl was added. The resulting mixture was cooled to room temperature to afford a white precipitate, which was collected by filtration and dried under vacuum. The crude product was recrystallized from hot acetone to give product 4 (4.5 g, 26%) as a white precipitate. 1H NMR (300 MHz, CDCl3) δ 6.93 (s, 2H), 4.64 (s, 4H), 3.86 (s, 6H). 2,5-Dimethoxyterephthalaldehyde (5).28 A solution of 4 (15.0 g, 63.8 mmol) and hexamethylenetetramine (18.0 g, 127.6 mmol) in chloroform (50 mL) was stirred at reflux for 24 h. After cooling to room temperature, the pale yellow precipitate was collected by filtration and redissolved in water (30 mL). The aqueous solution was acidified with acetic acid (10 mL) and stirred at 90 °C for 24 h. The mixture was cooled to room temperature and extracted with DCM (200 mL). The organic phase was washed thrice with water (200 mL) and dried over anhydrous Na2SO4. After solvent evaporation, the residue was recrystallized from ethanol to yield compound 5 (5.5 g, 45%) as a bright yellow solid. 1H NMR (300 MHz, CDCl3) δ 10.50 (s, 2H), 7.26 (s, 2H), 3.95 (s, 6H). 2,5-Dihydroxyterephthalaldehyde (6).28 To a solution of 5 (200.0 mg, 0.9 mmol) in DCM (20 mL), 1.0 M solution of BBr3 in DCM (2.3 mL, 2.3 mmol) was added dropwise at 0 °C under N2 atmosphere. After being stirred for 3 h at 20 °C, the mixture was cooled to 0 °C and water (20 mL) was added in drops to quench excess of BBr3. The organic layer was separated, and aqueous layer was extracted with DCM (3 × 30 mL). The combined organic phases were dried over anhydrous Na2SO4 and evaporated in vacuo. The crude material was subjected to recrystallization from acetone to yield the desired product

EXPERIMENTAL SECTION

Materials. Diethylene glycol methyl ether (1), 1,4-dimethoxybenzene (3), hydroquinone (7), triethylamine (TEA), dichloromethane (DCM), hexane, ethyl acetate, 1,4-dioxane, acetonitrile (ACN), diethyl ether, acetone, chloroform, acetic acid, ethanol, methanesulfonyl chloride, anhydrous sodium sulfate (Na2SO4), formaldehyde (38% in water), paraformaldehyde, concentrated hydrochloric acid (37% in water, conc. HCl), boron tribromide (1.0 M of BBr3 in DCM) were purchased from Sigma-Aldrich. Hexamethylenetetramine and triphenylphosphine were purchased from AlfaAesar. Polydimethylsiloxane (PDMS, Sylgard 184) was purchased from Dow Corning. Instruments. Synthesis of ink components were confirmed by using NMR (Mercury Plus 300 MHz) and IR (Thermo Nicolet NEXUS 870 FT-IR equipped with ATR sampling Accessory (ZnSe plate)). Transmission Raman spectra were collected by direct illumination with a laser (785 nm, Invictus, Kaiser Optical, Inc.). Fluorescence dot arrays were obtained by using a Nano-Plotter 2.0 (GeSiM, Germany) with pulse voltage of 75 V, pulse width of 50 μs, and frequency of 100 Hz. Printing was performed with a HP Deskjet Ink Advantage K209a office inkjet printer on a conventional A4 size copy paper (Double A). Optical and fluorescence microscopic images were obtained with an Olympus BX 51W/DP70 microscope. UV− visible absorption spectra were recorded on a Agilent UV−visible Spectroscope. Photoluminescence spectra were recorded with a RF5301PC Spectrofluorophotometer. Molecular weights were estimated with a Waters 717plus Autosampler, equipped with a refractive index detector (Waters 2415) and four series columns (Styragel Column, HR 5, 50K−4M, Styragel Column, HR 4, 5K−600 K, Styragel Column, HR 2, 500−20K, Styragel Column, HR 0.5, 0−1K, columns are packed with 5 μm particles and the size of the column is 7.8 × 300 mm). In GPC measurements, THF was used as the eluent at a flow rate of 1 mL/min. GPC samples were taken at 0.2 wt % concentration and filtered with a 0.2 μm hydrophobic PTFE filter (Advantec Syringe Filters) to remove aggregates. Viscosity was measured with microVISC Viscometer (RheoSense). Synthesis of Ink Components. Synthetic routes for preparation of the water compatible inks EGB-Al (Ink A) and EGB-TPP (Ink B) are shown in Scheme 1. All intermediates and EGB-Al (Ink A) except for EGB-TPP (Ink B) are known and were prepared using literature procedures.27−30 2-(2-Methoxyethoxy)ethylmethanesulfonate (2).27 To a solution of 1 (20.0 g, 166.5 mmol) and TEA (60.0 mL, 332.0 mmol) in dichloromethane (DCM) (250 mL), methanesulfonyl chloride (22.0 g, B

DOI: 10.1021/acsami.5b09705 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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ACS Applied Materials & Interfaces

Figure 1. Schematic representation for the reactive inkjet printing method and chemical structures of ink components and target conjugated polymer PPV. 6 (110. 0 mg, 72%) as a yellow solid. 1H NMR (300 MHz, CDCl3) δ 10.23 (s, 2H), 9.96 (s, 2H), 7.24 (s, 2H). 2,5-Bis(2-(2-methoxyethoxy)ethoxy)terephthalaldehyde (EGBAl).29 A stirred mixture of 6 (1.0 g, 6.0 mmol), potassium carbonate (6.9 g, 48.0 mmol) and 2 (2.7 g, 14.0 mmol) in acetonitrile (30 mL) was stirred at reflux for 6 h and concentrated in vacuo. The residue was dissolved in diethyl ether (100 mL) and washed with saturated NaCl solution in water. The organic phase was separated, dried over anhydrous Na2SO4 and concentrated in vacuo. The residue was subjected to column chromatography using silica gel (60−120) and hexane/ethyl acetate (v/v = 1/1) as an eluent to obtain EGB-Al (1.1 g, 50%) as a green liquid. 1H NMR (300 MHz, CDCl3) δ 10.51 (s, 2H), 7.45 (s, 2H), 4.29−4.25 (m, 4H), 3.91−3.88 (m, 4H), 3.71−3.68 (m, 4H), 3.57−3.54 (m, 4H), 3.38 (s, 6H). 1,4-Bis(2-(2-methoxyethoxy)ethoxy)benzene (8).30 A mixture of 7 (2.5 g, 23.0 mmol), potassium carbonate (9.5 g, 70.0 mmol), and 2 (10.0 g, 50.4 mmol) in acetonitrile (30 mL) was stirred at reflux for 6 h. Concentration in vacuo gave a residue that was dissolved in diethyl ether (100 mL) and washed with saturated NaCl solution in water. The organic layer was dried over anhydrous Na2SO4, and concentrated in vacuo giving a residue that was subjected to column chromatography using silica gel (60−120) and hexane/ethyl acetate (v/v = 1/1) as an eluent to obtain 8 (6.5 g, 90%) as a colorless oil. 1H NMR (300 MHz, CDCl3) δ 6.83 (s, 4H), 4.09−4.06 (m, 4H), 3.84− 3.81 (m, 4H), 3.72−3.69 (m, 4H), 3.58−3.55 (m, 4H), 3.38 (s, 6H). 1,4-Bis(chloromethyl)-2,5-bis(2-(2-methoxyethoxy)ethoxy)benzene (9).29 To a solution of 8 (6.5 g, 20.7 mmol) in 1,4-dioxane (30 mL) was added formaldehyde solution (38% in water, 10 mL) and paraformaldehyde (3.0 g, 99.0 mmol). The resultant mixture was stirred at 90 °C while adding concentrated HCl (2 × 5 mL) at 30 min intervals. After 1 h, 30 mL of conc. HCl was added and the mixture was cooled to room temperature. Concentration in vacuo gave a residue that was subjected to column chromatography using silica gel (60−120) and hexane/ethyl acetate (v/v = 2/1) as an eluent to give 9 (2.5 g, 30%) as an oily liquid. 1H NMR (300 MHz, CDCl3) δ 6.94 (s, 2H), 4.63 (s, 4H), 4.18−4.15 (m, 4H), 3.88−3.84 (m, 4H), 3.74−3.71 (m, 4H), 3.59−3.55 (m, 4H), 3.40 (s, 6H). ((2,5-Bis(2-(2-methoxyethoxy)ethoxy)-1,4-phenylene)bis(methylene))bis(chlorotriphenyl-l5-phosphane) (EGB-TPP). A mixture of 9 (0.30 g, 0.73 mmol) and triphenylphosphine (0.40 g, 1.52 mmol) in acetonitrile (10 mL) was stirred at reflux for 4 h and concentrated in vacuo. The residue was triturated with acetone to afford a white precipitate. The solid was collected by filtration and dried under vacuum to give the desired product EGB-TPP (4.30 g, 63%) as a white solid; mp 253−254 °C. 1H NMR (300 MHz, CDCl3) δ 7.73−7.60 (m, 30H), 7.03 (s, 2H), 5.32 (d, 4H, J = 12.90 Hz), 3.50−

3.47 (m, 8H), 3.35−3.30 (m, 10H), 3.19−3.17 (m, 4H), 13C NMR (300 MHz; CDCl3) δ 150.3, 134.7, 134.3, 129.9, 118.5, 117.3, 117.0, 116.7, 71.7, 70.1, 68.8, 67.2, 58.9. FT-IR (ZnSe, cm−1): 3041, 3000, 2936, 1507, 1436, 1215, 1107, 1044, 996, 957, 934, 861, 834, 751, 686. Solution-Phase Synthesis of PPV Derivative. The PPV derivative was synthesized using the literature procedure.31 To a stirred solution of EGB-Al (16.2 mg, 43.7 mmol) and EGB-TPP (40.9 mg, 43.7 mmol) in water (0.8 mL), was added a solution of t-BuOK (9.8 mg, 87.4 mmol) in water (0.4 mL) in drops at 20 °C. After being stirred for 12 h at 20 °C, the mixture was extracted with chloroform (5 mL) and the organic phase was dried over anhydrous Na2SO4. The solid obtained after concentration in vacuo was triturated with methanol to afford PPV (14.0 mg, 45%) as a red solid. Synthesis of PPV Derivatives by Reactive Inkjet Printing. Three ink solutions were prepared in deionized water (Ink A: EGB-Al, 110 mM; Ink B: EGB-TPP, 110 mM; Ink C: t-BuOK, 220 mM). A piezoelectric dispensing system (GeSiM Nanoplotter, Germany) was used to print the reactive inks on glass or a PDMS coated glass substrate. Owing to its high reproducibility and accuracy, three prepared reactive inks can be dropped (10 nL) at the same location on the substrate. The inkjet printing was carried out in a high humidity chamber (relative humidity = 80%) to prevent fast evaporation of water after printing. An HP Deskjet Ink Advantage K209 a-z printer was used for printing on paper. The commercial black cartridge (HP 703, CD887AA) was used after washing with methanol, sonication in water (30 min) and drying by N2 purging. Ink solutions were loaded into the black cartridges (200 uL) and printed using default standard settings. Inkjet printing was conducted on the paper in the order of Ink A, Ink B, and Ink C, respectively. The three inks were overprinted at the same location on the paper to induce polymerization.

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RESULTS AND DISCUSSION To explore the feasibility of in situ synthesis of a conjugated polymer by using the RIJ method, we selected poly(phenylenevinylene) (PPV) as the target conjugated polymer because it can be readily prepared through Wittig reaction between a dialdehyde and a bis(triphenylphosphonium salt) in the presence of base. Several meritorious features of using the Wittig reaction include (1) mild reaction conditions and room temperature, (2) no need for metal catalysts, and (3) large reaction rate in aqueous media.32 Synthetic routes for preparation of the dialdehyde and bis(triphenylphosphonium salt) monomers are displayed in Scheme 1. To increase water compatibility, hydrophilic C

DOI: 10.1021/acsami.5b09705 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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ACS Applied Materials & Interfaces oligoethylene oxide moieties were incorporated into each of the monomers. The oligoethylene oxide containing terephthaldehyde monomer EGB-Al, used as Ink A, was readily prepared by employing known synthetic procedures starting from 1,4dimethoxybenzene (3). By employing a similar strategy, the phosphonium salt EGB-TPP (Ink B) was prepared. Owing to the hydrophilic ethylene oxide moieties, the terephthaldehyde derivative EGB-Al (Ink A) and the phosphonium salt EGB-TPP (Ink B) form stable dispersions in deionized water. The results of dynamic light scattering (DLS) measurements indicate that EGB-Al (Ink A) and EGBTPP (Ink B) have particle sizes of 136 and 301 nm, respectively (Figure S1). Water-soluble potassium t-butoxide (t-BuOK) was used as Ink C because it is needed to initiate the Wittig reaction. As displayed in Figure 1, it is expected that the desired PPV derivative will be generated when the three reactive inks are printed at the same spot. Accordingly, the three reactive inks were prepared in the following concentration in deionized water; Ink A (110 mM), Ink B (110 mM), and Ink C (220 mM). The viscosities of Ink A and Ink B were found to be 0.94 and 1.23 cP, respectively (Table S1). The contact angles obtained after printing with the individual inks were determined to be approximately 30° on glass and 60° on PDMS substrate (Table S2). With the desired ink solutions in hand, our attention next turned to the generation of PPV derivatives on glass and PDMS substrates. For this purpose, a piezoelectric dispensing system (GeSiM Nanoplotter, Germany) was employed owing to the fact that it has a high reproducibility and accuracy and that 10 nL of the three prepared reactive inks can be dropped at the same location on the substrate. To prevent fast water evaporation, we carried out inkjet printing in a humid chamber (relative humidity: 80%). Utilizing this procedure, three ink solutions were dispensed in the form of aligned dot arrays on glass and PDMS substrates at room temperature. Figure 2a shows fluorescence microscopic images obtained 2 h after inkjet printing of three inks on the glass substrate. The red fluorescence (excitation: 510−550 nm) emitted from the microarrayed dots arises from the formed conjugated polymer PPV because Ink A and Ink B do not emit red fluorescence. Interestingly, no coffee ring effect was observed in the microarray, a likely result of the increased viscosity that occurs during formation of polymer and the slow evaporation of water in the high humidity chamber. Synthesis of the microarray composed on the PPV derivative can be also performed on the soft surface of the PDMS substrate. In this case, the microarray dots have a much smaller size than those on the glass substrate even when the same amounts of the inks are used for printing (Figure 2b). This phenomenon is related to the hydrophobic nature of PDMS substrate, which prevents spreading of the water-based ink droplets and confines the droplets near to the printing location. UV−visible absorption spectroscopy was employed to demonstrate that the RIJ process does indeed form PPV. Samples, collected from the microarray after designated time periods, were washed with aqueous 1 M HCl. The residues were dissolved in chloroform and the resulting solutions were analyzed by using UV−visible absorption spectroscopy. Inspection of the spectra (Figure 2c) shows that a decrease in the band at 395 nm associated with wavelength maximum of EGB-Al (green line) takes place. At the same time, a new band (red line) with a maximum absorption wavelength of 420 nm arises within 1 min after printing the three inks on the glass

Figure 2. Fluorescence microscope images of PPV arrays obtained by in situ inkjet synthesis on glass (a) and PDMS (b) substrates. (c) UV− visible absorption spectra of (green) EGB-Al, (black) independently prepared PPV, and extracted reaction mixtures which are sampled after (red) 1 min, (purple) 1 h, and (blue) 2 h after plotting on glass.

substrate. The new peak at 420 nm, associated with oligomeric PPV, disappears within 1 h following printing while a band corresponding to polymeric PPV is generated (purple line). At longer reaction times (2 h) an increase of the conjugation length of the polymer does not occur (blue line) as demonstrated by the fact that the absorption spectrum remains the same as that of the PPV derivative independently prepared using solution phase method (black line). Thus, the reaction appears to reach completion within 1 h after printing the inks serving as the reactants. The use of paper as the substrate would increase the flexibility of the new strategy for fabrication of PPV on a largescale and in an inexpensive manner. As a result, we explored the possibility of generating PPV on paper using the RIJ approach. A partially overlapped three-circle pattern was printed on conventional paper using reactive Inks A, B, and C (Figure 3a). Only the central part of the image displays an orange color as well as red fluorescence. Moreover, the circle printed with Ink A has a pale yellow color arising from the terephthaldehyde derivative. In addition, printing of Ink B and Ink C does not result in the generation of colored images because the substances in these inks do not absorb visible light. These observations support the conclusion that all three inks are necessary in order to generate PPV on the paper (see also Figure S2 in the Supporting Information). The generation of the desired PPV by using the RIJ method was also demonstrated by employing Raman spectroscopy (Figure S3). Characteristic Raman bands for the PPV derivative include those for vinyl group C−C stretching (1625 cm−1), phenyl ring C−C stretching (1583 cm−1), C−H bending of the phenyl ring (1312 cm−1) and CC stretching of the phenyl group (1121 cm−1).33 Importantly, the PPVs, prepared by utilizing a conventional solution-phase synthesis procedure and by the RIJ method on glass and paper substrates, have nearly identical spectra. D

DOI: 10.1021/acsami.5b09705 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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ACS Applied Materials & Interfaces

Figure 4. Photograph and (inset) fluorescence microscopic image of printed text formed from in situ synthesized PPV on paper.

program (font size: 7) created text printed with three reactive inks. The orange color of the text indicates that it is comprised of the conjugated polymer, PPV. In addition, the fluorescence microscope image shown in Figure 4 also demonstrates that the text is composed the PPV derivative.

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Figure 3. (a) Photograph of a partially overlapped three circle image obtained by inkjet printing of individual ink on paper. (b,c) Photographs and fluorescence microscope images (inset) of in situ synthesized PPV derivative on paper before (b) and after (c) washing with water and chloroform. (d) Photoluminescence spectra of PPV derivatives obtained by conventional solution-phase synthesis (black line), by RIJ method on glass (red line) and paper (blue line) (excitation wavelength: 450 nm).

CONCLUSIONS In the investigation described above, we developed a watercompatible reactive ink system that can be employed to generate luminescent conjugated polymers on solid substrates. Inkjet printing of inks composed individually of terephthaldehyde, bis(triphenyl phosphonium salt), and sodium t-butoxide on identical locations on a glass or PDMS substrate using a piezoelectric dispenser leads to efficient formation of poly(phenylenevinylene) (PPV). The results of monitoring the progress of this reaction by using UV−visible absorption spectroscopy indicate that PPV is produced within 1 h at 20 °C. Because the hydrophilic inks are compatible with a common office inkjet printer, a large area of PPV patterned images is easily produced. Because the in situ synthesized PPV on paper is insoluble in water and chloroform, excess reagents and byproducts can be readily removed by washing with these substances. The new strategy, which utilizes Wittig-reactionbased generation of conjugated polymers by using the RIJ method, should serve as a useful addition to the ever increasing areas in which conjugated polymers are used advantageously.

Interestingly, the PPV prepared on paper substrate is insoluble in water and organic solvents. As a result, the color and fluorescence intensities of the printed area remain after washing the printed paper with water and chloroform (Figure 3b,c). Moreover, the insolubility of the conjugated polymer can be advantageously utilized to remove excess starting materials and some water/organic soluble byproducts. We attempted to determine the molecular weight of the PPV prepared on paper but were unsuccessful owing to the highly insoluble nature of the polymer. Also, the molecular weight (Mw) of the material obtained by washing the printed paper with chloroform was found to be in the range of 15 000−20 000 (GPC analysis). This finding suggests that the molecular weight of insoluble PPV immobilized on paper is over 20 000. The formation of the PPV derivative on paper by using the inkjet printing method was confirmed by utilizing photoluminescence spectroscopy. As can be seen by viewing the spectra in Figure 3d, PPV derivatives obtained through inkjet printing on paper and on a glass substrate, and independent chemical synthesis have similar photoluminescence spectra. A major advantage of using a common office inkjet printer for generating conjugated polymer images is that large area patterning can be readily achieved on paper. In more classical approaches, conjugated polymers are deposited on paper using office inkjet printers by either printing precursor monomers on catalyst-precoated paper or by exposing monomer printed paper to catalysts. Direct printing of water compatible conjugated polymers such as polyaniline (PANI) or poly(ethylene dioxythiophene) (PEDOT) on paper substrate have also been reported.21,34 However, large area patterning of conjugated polymer on paper using an in situ chemical reaction such as Wittig type reaction has not been explored previously. The images displayed in Figure 4 shows are of Microsoft Word

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.5b09705. DLS diagrams and viscosities of inks, contact angles for printed surface, fluorescence microscopic images of printed areas with each ink, Raman spectra of PPVs. (PDF)

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AUTHOR INFORMATION

Corresponding Author

* E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This study was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government E

DOI: 10.1021/acsami.5b09705 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

Research Article

ACS Applied Materials & Interfaces

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(MSIP) (No. 2014R1A2A1A01005862, 2012R1A6A1029029, 2012M3A7B4035286, and 2013M3C8A3075845).

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DOI: 10.1021/acsami.5b09705 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX