Three-Dimensional Printable Viologen-Based Ionogel for Visible Sensing and Display

Abstract

Open AccessCCS ChemistryRESEARCH ARTICLES16 Aug 2024Three-Dimensional Printable Viologen-Based Ionogel for Visible Sensing and Display Zhikang Han, Huan Yuan, Heng Zhang, Yueyan Zhang, Jian Lv, Xinyi Zhang, Zengrong Wang, Naiyao Li, Chenxu Liang, Ni Yan, Maxim Maximov, YongAn Huang and Gang He Zhikang Han Frontier Institute of Science and Technology, Engineering Research Center of Key Materials for Efficient Utilization of Clean Energy of Shaanxi Province, Future Industrial Innovation Institute of Emerging Information Storage and Smart Sensor, State Key Laboratory for Strength and Vibration of Mechanical Structures, Xi'an Jiaotong University, Xi'an, 710049 Shaanxi , Huan Yuan School of Electrical Engineering, Xi'an Jiaotong University, Xi'an, 710049 Shaanxi , Heng Zhang Frontier Institute of Science and Technology, Engineering Research Center of Key Materials for Efficient Utilization of Clean Energy of Shaanxi Province, Future Industrial Innovation Institute of Emerging Information Storage and Smart Sensor, State Key Laboratory for Strength and Vibration of Mechanical Structures, Xi'an Jiaotong University, Xi'an, 710049 Shaanxi , Yueyan Zhang Frontier Institute of Science and Technology, Engineering Research Center of Key Materials for Efficient Utilization of Clean Energy of Shaanxi Province, Future Industrial Innovation Institute of Emerging Information Storage and Smart Sensor, State Key Laboratory for Strength and Vibration of Mechanical Structures, Xi'an Jiaotong University, Xi'an, 710049 Shaanxi , Jian Lv Frontier Institute of Science and Technology, Engineering Research Center of Key Materials for Efficient Utilization of Clean Energy of Shaanxi Province, Future Industrial Innovation Institute of Emerging Information Storage and Smart Sensor, State Key Laboratory for Strength and Vibration of Mechanical Structures, Xi'an Jiaotong University, Xi'an, 710049 Shaanxi , Xinyi Zhang School of Materials Science & Engineering, Engineering Research Center of Transportation Materials, Ministry of Education, Chang'an University, Xi'an, 710064 Shaanxi , Zengrong Wang Frontier Institute of Science and Technology, Engineering Research Center of Key Materials for Efficient Utilization of Clean Energy of Shaanxi Province, Future Industrial Innovation Institute of Emerging Information Storage and Smart Sensor, State Key Laboratory for Strength and Vibration of Mechanical Structures, Xi'an Jiaotong University, Xi'an, 710049 Shaanxi , Naiyao Li Frontier Institute of Science and Technology, Engineering Research Center of Key Materials for Efficient Utilization of Clean Energy of Shaanxi Province, Future Industrial Innovation Institute of Emerging Information Storage and Smart Sensor, State Key Laboratory for Strength and Vibration of Mechanical Structures, Xi'an Jiaotong University, Xi'an, 710049 Shaanxi , Chenxu Liang School of Electrical Engineering, Xi'an Jiaotong University, Xi'an, 710049 Shaanxi , Ni Yan School of Materials Science & Engineering, Engineering Research Center of Transportation Materials, Ministry of Education, Chang'an University, Xi'an, 710064 Shaanxi , Maxim Maximov Peter the Great Saint-Petersburg Polytechnic University, Saint Petersburg, 195251 , YongAn Huang State Key Laboratory of Digital Manufacturing Equipment and Technology, Huazhong University of Science and Technology, Wuhan, 430074 Hubei and Gang He *Corresponding author: E-mail Address: [email protected] Frontier Institute of Science and Technology, Engineering Research Center of Key Materials for Efficient Utilization of Clean Energy of Shaanxi Province, Future Industrial Innovation Institute of Emerging Information Storage and Smart Sensor, State Key Laboratory for Strength and Vibration of Mechanical Structures, Xi'an Jiaotong University, Xi'an, 710049 Shaanxi Cite this: CCS Chemistry. 2024;0:1–13https://doi.org/10.31635/ccschem.024.202404393 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Viologen has long been explored as an organic electrochromic material. However, conventional viologen (RV2+) often generates free radicals under photo-irradiation, interfering with the polymerization of monomers during digital light processing (DLP) three-dimensional (3D) printing when incorporated into ionogels. In this study, we synthesized a phenyl viologen ( (SPr)2PhMeV) capable of simultaneous two-electron transfer through molecular manipulation, effectively avoiding the formation of photogenerated radicals under illumination. This novel phenyl viologen demonstrated exceptional redox performance and cycle stability and could be seamlessly incorporated into ionogels via 3D printing technology. This innovative approach has facilitated the first-time acquisition of finely structured viologen-based ionogels, featuring high transparency (transmittance: 85%), robust stretchability (17 times), and self-healing capabilities (resistance recovers after contact) simultaneously. Notably, the material demonstrated exceptional visual responses to temperature and strain changes, rendering it ideal for visual temperature (30–90 °C, TCR = 36.09% °C−1) and strain (ΔT = 0 at strains of 300%) sensing applications. Additionally, we have designed a viologen ionogel display device that could independently showcase all 26 letters and 10 numbers within seconds. This breakthrough not only enhances the functionality of electrochromic materials but also paves the way for advanced sensory and display applications in the future. Download figure Download PowerPoint Introduction Various viologens have been developed as color-controllable smart materials, with applications ranging from smart windows, antiglare rearview mirrors, wearable sensors, and smart displays.1–12 However, solution-based viologen electrochromic devices face challenges such as shortened lifespan and circuit corrosion due to electrolyte leakage,13,14 significantly hindering the practical application of electrochromism. In response to this issue, viologen-based ionogels with high ionic conductivity and significant stretchability have emerged. Nevertheless, the challenge of achieving fine structures for exquisite displays persists.15 Previous approaches have primarily relied on polymer addition to increase viscosity and form viologen-based ionogels. Despite their promise, a key obstacle has been the inability of their constituent monomers to polymerize fully, which is crucial for establishing a stable structural framework. This limitation has impeded the creation of ionogels with the required durability and integrity needed for practical applications.16 While recent efforts have involved the photopolymerization of monomers followed by immersion in a viologen solution to create a stretchable and stable ionogel,6 issues like swelling and deformation of crosslinked monomers during soaking hinder the attainment of fine structures.17 The advancement of viologen-based ionogels for high-precision display necessitates the exploration of novel strategies in the gel solidifying process.18 Digital light processing (DLP) three-dimensional (3D) printing technology, which translates digital models into tangible objects through a layer-by-layer transformation process, constitutes an innovative approach to polymer manufacturing. This technology enables the creation of intricate patterns with precision and efficiency.19–21 Recognized for its rapid prototyping capabilities, accurate processing, and extensive design flexibility, DLP technology is commonly employed in manufacturing sensors and creating visually striking displays.22–24 The fundamental principle of 3D printing technology hinges on the photoinitiated free radical polymerization upon exposure to light.25,26 However, when it comes to viologen-based ionogels, the photochromic properties of viologen pose a challenge to the implementation of this technology.27,28 Viologen possesses the property of absorbing photons when exposed to light, leading to a transition into a free radical state. This transition can disrupt the free radical polymerization process, causing complications in the manufacturing process (Figure 1).29–32 To mitigate this issue, the two-electron transfer process of viologen shows promise in avoiding the generation of free radicals under illumination. More recently, it has been reported that introducing a phenyl ring in pyridine units has been shown to facilitate a concerted two-electron transfer process in viologen molecules.33,34 Nonetheless, the study of the phenyl viologen (PhV2+) has been primarily focused on charge transfer during the redox process, lacking exploration of the photochemistry-related reactions. It is envisioned that leveraging the advantages of PhV2+ with its two-electron transfer process alongside a conductive ionogel could effectively overcome the challenges associated with polymerized conductive ionogels for DLP 3D technology. This innovation could pave the way for the development of novel visible sensors and display devices. Figure 1 | The technical route of one-step preparation of electrochromic ionic gel (compared with previous work) and the synthesis route of (SPr)2PhMeV. Download figure Download PowerPoint Based on these considerations, we have successfully achieved the 3D printing of viologen-based ionogels through molecular manipulation, resulting in ionogels with finely structured architectures. The phenyl viologen (3,3′-(1,4-phenylenebis(2,6-dimethylpyridine-1-ium-4,1-diyl))bis(propane-1-sulfonate) [ (SPr)2PhMeV]) was synthesized by introducing a phenyl ring into parent viologen skeletons. The incorporation of a phenyl ring effectively prevented the generation of free radicals, thus avoiding interference by photopolymerization of the monomers. Additionally, PhV2+ acted as an internal salt through the introduction of propanesulfonate groups, enhancing steric hindrance and inhibiting the formation of by-products during the redox process.35,36 To address the issue of liquid leakage, deep eutectic solvents (DES) (composed of choline chloride and urea) were utilized as conductive media.37,38 Through 3D printing, successfully obtained PhV2+-based ionogels with superior mechanical performance, intricate structures, and excellent electrochromic functionality. These ionogels are well-suited for visible temperature and strain-sensing applications. Moreover, we have developed an innovative display device capable of independently showcasing all 26 alphabets and 10 digits, broadening viologens' applicability in high-resolution sensory and display technologies. Experimental Methods Materials and instrumentation All reactions were conducted utilizing standard Schlenk and glovebox (Vigor) techniques under an argon atmosphere. All chemicals were purchased from Energy Chemical Inc. (Anhui, China), and stored in an Argon glovebox. Toluene was distilled from sodium/benzophenone prior to use, and other chemicals were used as commercially available without further purification. Deionized water was purged overnight using Ar before use. Nuclear magnetic resonance (NMR) spectroscopy was performed using a Bruker 400 MHz NMR spectrometer (Bruker, Massachusetts, USA). UV–vis measurements were conducted using a DH-2000-BAL Scan spectrophotometer (OceanOptics, Florida, USA). The cyclic voltammetry (CV) and differential pulse voltammetry in solution were measured using the electrochemical workstation CHI660E B157216 (Chen Hua, Shang Hai, China). High-resolution mass spectra (HRMS) were performed on a Bruker maxis UHR-TOF mass spectrometer (Bruker, Massachusetts, USA) in positive electrospray ionization (ESI) mode. All photographs were taken using a Nikon D5100 digital camera (Nikon, Tokyo, Japan). Single crystal X-ray diffraction data collection of the compounds were recorded on Bruker D8 Venture photon II diffractometer (Bruker, Massachusetts, USA). Electron paramagnetic resonance (EPR) was measured using a Bruker EMXPLUS6/1 instrument (Bruker, Massachusetts, USA) at room temperature in their aqueous solution. Thermogravimetric analysis (TGA) measurements were conducted using a Mettler-Toledo TGA1 thermal analyzer (Mettler Toledo, Zurich, Switzerland) in air, at a heating rate of 10 °C min−1 in the temperature range of 30–800 °C. The morphology and chemical elements of the samples were characterized using a scanning electron microscope (SEM, MAIA3 LMH; TESCAN, Prague, Czech) equipped with an energy dispersive X-ray spectroscopy (EDX) Analyzer (Aztec X-max 50, Oxford, Oxfordshire, UK). Synthesis of 1,4-bis(2,6-dimethylpyridin-4-yl)benzene (PhDMeP) To a mixture of 1,4-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzene (1.00 g, 3.03 mmol), 4-bromo-2,6-dimethylpyridine (1.41 g, 7.57 mmol), Pd(PPh3)4 (0.140 g, 0.121 mmol), K3PO4 (3.22 g, 15.51 mmol), and 25 mL N,N-dimethylformamide were added. The solution was sealed in a pressure vial with a Teflon bushing and heated at 100 °C for 2 days. Upon completion, the reaction mixture was allowed to cool to room temperature and filtered to remove the catalyst. The filtrate was subjected to three extractions with water and chloroform, dried over Na2SO4, and filtered. The addition of ethyl ether (50 vol %) led to the precipitation of a faint yellow solid, which was filtered off and washed with hexane, ethanol, and ether. The solid was dried in a vacuum oven overnight to obtain a needle crystal of 1,4-bis(2,6-dimexthylpyridin-4-yl)benzene (0.68 g, 82% yield). 1H NMR (400 MHz, CDCl3, δ): 7.71 (d, J = 2.2 Hz, 4H, ArH), 7.22 (s, 4H, ArH), 2.61 (d, J = 2.0 Hz, 12H, CH3). 13C NMR (101 MHz, CDCl3, δ): 158.34 (s), 148.17 (s), 139.07 (s), 127.59 (s), 118.23 (s), 24.62 (s). Synthesis of 3,3′-(1,4-phenylenebis(2,6-dimethylpyridine-1-ium-4,1-diyl))bis(propane-1-sulfonate) [(SPr)2PhMeV] The dry N,N-dimethylformamide solution of 1,4-bis(2,6-dimethylpyridin-4-yl)benzene (PhDMeP; 1.00 g, 3.47 mmol) and 1,3-Propanesultone (4.24 g, 34.67 mmol) was heated at 155 °C for 24 h under an inert atmosphere. After the reaction was complete, the mixture was cooled to room temperature and filtered. The orange precipitate was washed with acetone and dried in a vacuum oven overnight to obtain a needle crystal of (SPr)2PhMeV (1.67 g, 90% yield). 1H NMR (400 MHz, D2O, δ): 8.07 (s, 4H, ArH), 8.04 (s, 4H, ArH), 4.69–4.64 (m, 4H, CH2), 3.13 (t, J = 6.9 Hz, 4H, CH2), 2.90 (s, 12H, CH3), 2.32–2.26 (m, 4H, CH2). 13C NMR (101 MHz, D2O, δ): 155.53 (s), 153.65 (s), 136.82 (s), 128.73 (s), 125.11 (s), 50.75 (s), 47.36 (s), 23.08 (s), 20.51 (s). HRMS (ESI) m/z: [M+Na]+ calcd for C26H32N2O6S2 555.1594; found 555.1595. Synthesis of ionogels based on deep eutectic solvent First, choline chloride and urea were weighed according to the molar ratio of 1:2 to form a deep eutectic solvent. Subsequently, acrylamide was introduced as the monomer, comprising 30% of the solvent's mass. To initiate the polymerization process, 2,4,6-trimethylbenzoyldiphenyl phosphine oxide (TPO) was added as a photoinitiator at a concentration of 5/10,000 of the monomer's mass, while methylene-bis-acrylamide (MBAA) served as the crosslinker at 2/1000 of the monomer's mass. Further, the electrochromic elastomer was synthesized through free radical polymerization, augmented by the addition of (SPr)2PhMeV as a discoloration material at a ratio of 1/1000 of the monomer's mass. The above substances were mixed at 70° and heated and stirred in an argon atmosphere to form a yellowish transparent solution, that was the precursor solution of ionogels. The subsequent 3D printing process was executed using an Elegoo printer equipped with a UV projector (405 nm) as the light source. Firstly, the designed 3D structure was sliced by the software to form the corresponding 2D images of each layer, and then the patterned ultraviolet light was irradiated on the elastomer precursor solution by the projector, and the electrochromic ionogel was solidified layer by layer. The electrochemical characterization Redox potential was referenced to the normal hydrogen electrode (NHE). The glassy carbon electrode (d = 3 mm) was used for the working electrode, which was polished using Al2O3 suspended in deionized H2O, then rinsed with deionized H2O, and dried with airflow. The platinum sheet (1 cm2) was used for the counter electrode. The reference electrode consisted of a silver wire coated with a layer of AgCl and suspended in a solution of 3 M KCl electrolyte (Ag/AgCl, vs NHE). Density functional theory (DFT) calculations The geometries for the ground state of these compounds were optimized at the B3LYP hybrid functional and 6-311+G(d) basis set for all atoms.39 The calculated molecular orbitals involved in the main transitions were reported in this work. It should be pointed out that the structures of all stationary points were fully optimized; frequency calculations were performed at the same level, which confirmed the nature of all revealed equilibrium geometries without imaginary frequencies. All of the above computational calculations reported in this work were performed using the Gaussian 09 code ( https://gaussian-09w.software.informer.com/). Results and Discussion Synthesis and structural characterization of (SPr)2PhMeV The synthesis method was detailed in the supporting information.34,40–42 2,5-di(pyridin-4-yl)thiophene (TDP), 2,5-di(pyridin-4-yl)furan (FDP), 1,4-di(pyridin-4-yl)benzene (PhDP), and PhDMeP were synthesized via the Suzuki coupling reaction. Subsequently, they were ionized using iodomethane to produce diiodide. Tetrabutylammonium chloride was used to exchange anions to obtain 4,4′-(thiophene-2,5-diyl)bis(1-methylpyridin-1-ium) dichloride (MTV)Cl2, 4,4′-(furan-2,5-diyl)bis(1-methylpyridin-1-ium) dichloride (MFV)Cl2, 4,4′-(1,4-phenylene)bis(1-methylpyridin-1-ium) dichloride (MPhV)Cl2. (SPr)2PhMeV was obtained by the reaction of 1,3-Propanesultone with PhDMeP. The structures were confirmed through NMR ( Supporting Information) and HRMS ( Supporting Information). The molecular structure was further characterized by a single-crystal X-ray diffraction analysis ( Supporting Information Figure S1 and Table S1). The single crystal was prepared by heating and dissolving (SPr)2PhMeV in water until the solution reached saturation, followed by cooling and precipitation at room temperature. The supplementary crystallographic data was deposited at the Cambridge Crystallographic Data Centre (CCDC 2333264) and can be obtained free of charge from the CCDC via www.ccdc.cam.ac.uk/data_request/cif. The angle between the pyridine plane and the phenyl ring in (SPr)2PhMeV was 176.61°, indicating that these three groups were not coplanar. The linear structure nature of the molecule was attributed to the stabilizing influence of the four methyl groups. As an internal salt, the molecules carried the negative charges after reduction, with the linear configuration promoting charge repulsion. This effectively mitigated the likelihood of side reactions.35,36 The thermal stability of four viologens was characterized by TGA. The decomposition occurred above 270 °C, underscoring their capability for applications in high temperatures ( Supporting Information Figure S2). The UV–vis spectra of the four viologens were tested in H2O to evaluate their light absorption characteristics ( Supporting Information Figure S3). The concentration of viologen was 10−4 mol/L. The absorption maxima of (SPr)2PhMeV and (MPhV)Cl2 were at 322 and 321 nm, respectively, and (MTV)Cl2 and (MFV)Cl2 exhibited peaks at 370 nm. This indicated that the light absorption characteristics of viologen were mainly affected by the bridging group. The electrochromic ability of (SPr)2PhMeV was investigated by spectroelectrochemistry at a voltage of 2.8 V ( Supporting Information Figure S4). The molecule showed strong absorption at 474, 554, and 900 nm, with the solution color changing from colorless to purplish red. This result proved the capability of (SPr)2PhMeV in electrochromic applications. Electrochemical characterization and electron paramagnetic resonance of viologens To underscore the distinctive redox capabilities of (SPr)2PhMeV, three commonly encountered methylated conjugated viologen ( (MPhV)Cl2, (MTV)Cl2, and (MFV)Cl2) were selected and subjected to CV in a 0.5 M sodium chloride solution. (MTV)Cl2 and (MFV)Cl2exhibited two sets of redox peaks, while (SPr)2PhMeV and (MPhV)Cl2 displayed a single peak (Figure 2a and Supporting Information Figure S5). This indicated that (SPr)2PhMeV and (MPhV)Cl2 could two-electron transfer at (MTV)Cl2 and (MFV)Cl2 required an increase in voltage to the The capability of (SPr)2PhMeV to two-electron transfer was attributed to the of the phenyl ring in The phenyl ring electron between two pyridine electron Figure 2 | of 2.0 (SPr)2PhMeV and (MTV)Cl2 with 1 in 0.5 M solution. CV of (SPr)2PhMeV at and of and The spectra of (MTV)Cl2 and (SPr)2PhMeV after of illumination. the and energy of (MTV)Cl2, and (MFV)Cl2, (MPhV)Cl2 and (SPr)2PhMeV. Download figure Download PowerPoint To further the redox capabilities of phenyl viologen ( (SPr)2PhMeV, their were measured at scanning ( Supporting Information and The redox peaks for (SPr)2PhMeV and (MPhV)Cl2 were at and The redox of (SPr)2PhMeV were significantly that of (MPhV)Cl2. This was attributed to the of four methyl groups on the pyridine as electron groups, with the propanesulfonate groups on the electron ability the methyl group. This led to a redox potential for The peak of the redox process of (SPr)2PhMeV and (MPhV)Cl2 were to the of the indicating the and process of the redox reaction. The of (SPr)2PhMeV = and (MPhV)Cl2 = were calculated according to the method ( Supporting Information Table S2). The electron transfer of (SPr)2PhMeV was that of (MPhV)Cl2, which indicated that the electrochromic of (SPr)2PhMeV was under the same The cyclic stability of the two phenyl viologens was in a 0.5 M sodium chloride solution at a scanning rate of (SPr)2PhMeV showed cyclic performance (Figure while (MPhV)Cl2 exhibited a significant with and peaks at the cycle ( Supporting Information Figure This from the steric hindrance of the four methyl and propanesulfonate groups in (SPr)2PhMeV, effectively side reactions during the redox was measured in their aqueous solution. can be found in the Supporting The of (MTV)Cl2 and (MFV)Cl2 were after of while (MPhV)Cl2 and (SPr)2PhMeV showed ( Supporting Information Figure After the light exposure to (MTV)Cl2 and (MFV)Cl2 exhibited a (SPr)2PhMeV and (MPhV)Cl2 to (Figure and Supporting Information Figure This showed that (MPhV)Cl2 and (SPr)2PhMeV prevented free radicals under and they can be used for DLP 3D printing to ionogels with fine calculations of four viologens calculations for the four viologens were to the of electrochemical characterization ( Supporting Information Figure with a phenyl the of (SPr)2PhMeV was to the phenyl ring to a as by (MPhV)Cl2, which the at while (MTV)Cl2 and (MFV)Cl2 displayed of 3.47 the methyl and propanesulfonate groups of (SPr)2PhMeV the and the of the phenyl The energy between the molecular of the state and the molecular of the ground state served as an of the for a molecule to a electron (Figure the introduction of the phenyl ring in a of this for the phenyl viologen exhibited a single redox It is that the two energy of (SPr)2PhMeV was the This was attributed to the high of in the free radical The structure of the (SPr)2PhMeV after was the to the energy state all potential structures ( Supporting Information Table S3). the of their electron the potential of (SPr)2PhMeV were shown by color ( Supporting Information Figure The potential pyridine was indicating that pyridine was the of the reaction. Additionally, the study indicated that the molecule a linear with the from the single-crystal It is that the molecular structure after electron with the ring and the two in a and characterization of ionogels as the as the acrylamide as the monomer, and (SPr)2PhMeV as the electrochromic discoloration the mixture was by the UV This indicated that (SPr)2PhMeV the generation of free radicals under ultraviolet light and the to the polymerization of the the DLP 3D printing of ionogel based on this viologen could The viologen-based ionogels with fine structures and strong were prepared (Figure which exhibited high transparency and exceptional properties (Figure analysis revealed a of and elements on the the of and viologen in the ionogel ( Supporting Information Figure Figure 3 | Ionogel prepared by three-dimensional (3D) printing technology. photographs of of ionogels prepared by the 3D printing method and the previous soaking of the and ionogels °C, 1 of the and ionogels. Electrical properties of the and ionogels. Download figure Download PowerPoint To the mechanical properties of the its properties were tested at a strain rate of 10 It could be its without Upon and subsequent heating to °C for 1 the ionogel demonstrated the ability to to of its and of its showcasing excellent self-healing capabilities (Figure This was attributed to the of and groups in the ionogel that a robust As a the hydrogen were after The ionogel attributed to the of choline 25 °C and the water of the ionogel to ( Supporting Information Figure the of the ionogel 10 1 mm) exhibited a and stable ( Supporting Information Figure was for sensors to of the ionogel at revealed a of before 100 °C, corresponding to the of The decomposition of the ionogel at °C, its for

Topics & Concepts