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[Microwave‐Assisted Quick Synthesis of Ru(II)‐Based Metallosupramolecular Polymer for Improved Electrochromic Properties.pdf](https://mdr.nims.go.jp/filesets/c87eabf5-5999-425f-8787-435e7027a609/download)

## Creator

[Utpal Rana](https://orcid.org/0000-0001-5026-1303), [Dines Chandra Santra](https://orcid.org/0000-0002-9292-9524), [Banchhanidhi Prusti](https://orcid.org/0000-0003-4489-2509), [Chanchal Chakraborty](https://orcid.org/0000-0002-4829-1367), [Taichi Ikeda](https://orcid.org/0000-0001-6650-5798), Yuko Saito, Kazuhiko Takeuchi, Ritsuko Nagahata, [Masayoshi Higuchi](https://orcid.org/0000-0001-9877-1134)

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This is the pre-peer reviewed version of the following article: U. Rana, D. C. Santra, B. Prusti, C. Chakraborty, T. Ikeda, Y. Saito, K. Takeuchi, R. Nagahata, M. Higuchi, Microwave-Assisted Quick Synthesis of Ru(II)-Based Metallosupramolecular Polymer for Improved Electrochromic Properties. Macromol. Chem. Phys. 2024, 225, 2300381, which has been published in final form at https://doi.org/10.1002/macp.202300381. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.[In Copyright](http://rightsstatements.org/vocab/InC/1.0/)

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[Microwave‐Assisted Quick Synthesis of Ru(II)‐Based Metallosupramolecular Polymer for Improved Electrochromic Properties](https://mdr.nims.go.jp/datasets/7423e5a7-dbb2-4f20-950b-31e98071f01b)

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1  Microwave-Assisted Quick Synthesis of Ru(II)-Based Metallosupramolecular Polymer for Improved Electrochromic Properties  Utpal Rana,a†Dines Chandra Santra,a Banchhanidhi Prusti,a Chanchal Chakraborty,a‡ Yuko Saito,b Kazuhiko Takeuchi,b Ritsuko Nagahata,b* and Masayoshi Higuchi a*  a U. Rana, D. C. Santra, B. Prusti, C. Chakraborty, M. Higuchi Electronic Functional Macromolecules Group, National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba 305-0044, Japan. E-mail: HIGUCHI.Masayoshi@nims.go.jp  b Y. Saito, K. Takeuchi, R. Nagahata National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8565, Japan. Email: nagahata–ritsuko@aist.go.jp  †Present address: Panipat Naphtha Cracker, Indian Oil Corporation Limited (IOCL), Panipat, Haryana-132140, India.  ‡Present address: Department of Chemistry, BITS Pilani, Hyderabad Campus, Jawahar Nagar, Shameerpet Mandal, Hyderabad-500078, India.  Keywords: metallosupramolecular polymer, microwave assisted synthesis, electrochromic property, redox, metal-to-ligand charge transfer  Metallosupramolecular polymers (MSPs) have reversible electrochromic (EC) characteristics. Transition metal ions and ditopic organic ligands are complexed 1:1 to form MSPs, but the complexation conditions depend on the metal species ions. Herein, we report a microwave-assisted (MWA) quick synthesis of a Ru(II)-based MSP (polyRu–MWA) as a novel preparation method for MSPs. PolyRu–MWA was synthesized under microwave irritation for 60 min using 770 W and 2.45 GHz frequency, whereas a conventionally synthesized Ru(II)-based MSP (polyRu–CS) was obtained using oil-bath at 160 °C for 24 h. PolyRu–MWA was found to show much better EC properties than polyRu–CS. A film of polyRu–MWA prepared on an indium tin oxide glass exhibited higher optical contrast Complete Manuscript 1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65   2  (transmittance change, ΔT: 81.39%) than polyRu–CS (67.73%). Coloration efficiency of polyRu–MWA (425.7 cm2 C–1) was also higher than that of polyRu–CS (318.3 cm2 C–1).  Interestingly, the charge and discharge current ratio for bleaching and coloring in polyRu–MWA was approximately 1.7 times higher than that for polyRu–CS, probably because of the high molecular weight polymer formation in polyRu–MWA. A polyRu–MWA film also displayed a longer EC optical memory than polyRu–CS.  1. Introduction The demand for carbo-neutralization in smart window applications has led to an increased research attention for electrochromic (EC) materials. [1-4] For EC applications, the material must possess a variety of qualities, including excellent redox stability, high contrast ratio and coloration efficiency, controllable switching, and good processability. Various EC materials such as Prussian blue, [5] viologens, [6] conducting polymers [7, 8] metal phthalocyanines, [9] and WO3 [10, 11] have been previously investigated. However, these materials fail to match all of the aforementioned requirements. Instead, new EC materials must be developed, with superior properties to those of already known materials.  Metallosupramolecular polymers (MSPs) are a new class of EC material consisting of metal ions and organic ligands. [12-17] MSPs are generally synthesized by the 1:1 complexation of transition metal ions and ditopic organic ligands. The complexation conditions depend on the specific metal species, and temperatures greater than 150 °C are sometimes required to promote polymer formation. For example, Ru(II)-based MSPs are synthesized at high temperatures under reflux conditions for 24 h, which is a time-consuming and energy-intensive procedure. [15, 18-20] Thus, simple, rapid, economical, and environmentally friendly synthetic processes should be developed. To solve these problems, we introduce a microwave-assisted (MWA) complexation process, in which microwave radiation provides the driving force for the reaction. This is a branch of green chemistry because the chemical transformation is pollution-free, eco–friendly, time- and energy-saving, and simple to process and handle. [21-23] The major advantage of this method is that the solvent transforms electromagnetic radiation into heat, which accelerates the chemical reaction. By contrast, heating reactions with classic setups, such as oil baths and sand baths, are not only slow, but also create a heated surface in the reaction vessel where chemicals break down over time. To date, no studies have focused on the synthesis of MSPs using microwave radiation, which we found to be a quick and effective production process.   1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65   3  Herein, we report a facile and rapid synthesis of a Ru(II)-based MSP by a microwave method. The synthesized polymer was characterized by 1H-nuclear magnetic resonance (1H-NMR) spectroscopy and the EC properties were compared with those of a conventionally synthesized Ru(II)-based MSP.   2. Results and discussion The Ru(II)-based MSP, polyRu–MWA, was synthesized under microwave irradiation for 60 min using 770 W and 2.45 GHz frequency (Figure 1), whereas a conventionally synthesized Ru(II)-based MSP, polyRu–CS, was obtained by heating 4’,4’’’’-(1,4-Phenylene)bis(2,2’’:6’,2’’-terpyridine) and dichlorotetrakis(dimethylsulfoxide) ruthenium(II) to 160 °C using an oil-bath for 24 h, in accordance with our previous report. [18] The molecular weights of the obtained polymers were calculated from the 1H NMR spectra (Figure 2) by end group analysis. The peaks at 9.55, 9.07, 8.79, 8.10, 7.69, and 7.40 ppm are assigned to the protons in the positions a, b, c, d, f, and e, respectively. [14, 24, 25] The peak corresponding to the proton in the position b’ was confirmed with the assistance of 1H-1H COSY and 1H-1H NOESY spectra of the model complex (Figure S1 and S2). The proton assigned a’ to the 4’ position of the end terpyridine unit.  End group analysis, with respect to the a’–proton, was conducted to determine the molecular weight of the two polymers. For example, the average degree of polymerization of polyRu-MWA (calculated by the integration ratio of b and b’), was found to be 31, whereas the molecular weight of the repeat unit was determined to be 712.6 g The molecular weight of the polymer was estimated to be 2.2 × 104 Da. A similar approach was conducted for polyRu–CS, providing a molecular weight of 4.4 × 103 Da. Thus, a polymer with higher molecular weight can be produced using microwave synthesis. Moreover, it is significant to note that the conventional synthesis methodology results in the generation of by-products in the form of small metal complexes, even with a 24 h reaction time, resulting in lower yield of target polymer compared to that synthesized using the microwave heating conditions.  The UV–vis spectra of polyRu–MWA and polyRu–CS are comparable (Figure 3a), with both displaying a high-energy absorption peak at 310 nm, assigned to a ligand-centered (1LC) π–π* transition. Additionally, two lower energy bands are observed at 508 and 504 nm in the spectra of polyRu–MWA and polyRu–CS, respectively; these bands are assigned to a metal-to-ligand (dπ–π*) charge transfer (MLCT) transition. [18, 20] The 4 nm red-shift of the low energy band can be attributed to the smaller MLCT energy gap in polyRu–MWA, which is a consequence of the high molecular weight long chain length. The metal complex behaves like  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65   4  an electron-withdrawing group, which typically stabilizes the π system, thus reducing the energy of the π* orbital on the ligand, and consequently red shifts the MLCT transition. [33] The sharper MLCT band observed for polyRu–MWA, along with the longer absorption maxima, indicates that relatively long polymeric chains are formed by the microwave assisted method compared with the conventional synthetic procedure. [26] The room-temperature luminescence properties of polyRu–MWA and polyRu–CS were measured by the excitation of the MLCT band. In MeOH solution, polyRu–MWA exhibited two emission bands at 588 and 675 nm, whereas polyRu–CS showed only one at 588 nm (Figure 3b). The peak at 588 nm can be assigned to the emission from the intra-ligand π–π* and n–π* transition, whereas the peak at 675 nm can be attributed to the 3MLCT transition. Despite the emission from the 3MLCT state being intense and well-resolved for polyRu–MWA, this emission was broadened for polyRu–CS because of the formation of an irregular structure using the conventional synthesis method. [18] X–Ray powder diffraction (XRD) patterns of the polyRu–MWA and polyRu–CS are shown in Figure 4a. The polymer synthesized by the microwave irradiation method exhibited less intense diffraction peaks than the conventionally synthesized polymer. The less intense diffraction peaks of polyRu–MWA suggest a more amorphous nature. Interestingly, for polyRu–MWA, a strong reflection peak was observed in the low angle region with d-spacing of 1.46 nm (2θ = 6.02°), which is consistent with the lateral stacking of polymer chains or lamella structure formation. [27, 28] In the high-angle region, only amorphous peaks were observed, which indicates long-range ordered structure were not formed by polyRu–MWA chains. [29] Thermogravimetric analysis (TGA) of both polymers under N2 at 10 °C min–1 scan rate is shown in Figure 4b. A higher thermal stability for polyRu–MWA was observed relative to polyRu–CS indicating that the former is a high-molecular-weight linear polymer. The weight losses at 600 °C for polyRu–MWA and polyRu–CS were 28% and 36%, respectively. [20]  The cyclic voltammograms (CVs) of the two polymers were measured in acetonitrile using a three-electrode system; the system employed a glassy carbon (GC) working electrode, Pt -flag counter electrode, and Ag/AgCl (KCl) reference electrode in a 0.1 M LiClO4 electrolyte solution. The CV of polyRu–CS and polyRu–MWA (Figure 5a) displayed reversible oxidation peaks at 1.28 and 1.12 V with a 50 mV s–1 scan rate, respectively. For polyRu–CS, the oxidation peak of the Ru(II)/Ru(III) ions was shifted to a lower potential (from 1.28 to 1.26 V). The higher oxidation potential of polyRu–MWA can be explained by the metal–metal interactions in the high-molecular-weight polymer chains. [30, 31] Interestingly, the CV of polyRu–CS at a slower  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65   5  scan rate (10 mV s–1) showed two oxidation peaks at 1.03 and 1.23 V, whereas polyRu–MWA retained only one oxidation peak at 1.25 V (Figure 5b). The appearance of the additional peak in the CV for polyRu–CS is a consequence of the low-molar-mass oligomer mixture in the system. The first peak corresponds to monocomplexes, low-molecular-weight oligomers, or terminates at the metal center of the polymer chain. The second peak indicates that the remaining metal sites are more difficult to oxidize because of their interactions with adjacent oxidized metal ions. [29, 32]  The electron transfer mechanism of both polymer films on ITO glass (1.5 × 1.5 cm2) was investigated using scan-dependent CV studies. For a fair comparison, the thickness of both polymer EC films was carefully controlled by spin-coating under identical conditions. Figure 6 shows the relationship between the anodic peak current (ipa) and the scan rate (ν) or the square root of scan rate (ν1/2) for both polymers. For polyRu–MWA (Figure 6b, c) and polyRu–CS (Figure 6e, f), a linear dependence was observed between ipa and both ν and ν1/2, with the R2 value close to 1.0. This indicates that a diffusion-controlled redox reaction takes place. The higher R2 value obtained for polyRu–CS relative to that for polyRu–MWA from the ipa vs ν plot (0.9682 and 0.9557, respectively) indicates that faster counter anion diffusion occurs in the small chains of the chaotic polymer structure in the polyRu–CS film compared to that of the homogeneous ordered polyRu–MWA film. [17, 33]  The in situ transmittance measurements of polyRu–MWA and polyRu–CS at two applied potentials (0 and 1.8 V) are shown in Figure 7 and S3, respectively. The polymer film was cathodically colored; the spectrum of the as-cast film showed absorbance in the visible region (~510 nm) owing to the MLCT transition which decreased with the applied potential. At 1.8 V of applied potential, the film was found to be colorless owing to the electrochemical oxidation of Ru(II) to Ru(III). A reversible color change occurred upon switching the potential from 0 V to 1.8 V vs Ag/Ag+.  Double-potential-step chronoamperometry was performed to evaluate the response time of the EC films. The potential was stepped between 0 and 1.8 V, with a 5 s interval time, and the transmittance change (ΔT) at MLCT band was recorded.  The transmittance changes for polyRu-MWA (at 510 nm) were recorded to be 81.4% and 22.6% at 5 and 2 s interval time, respectively. In comparison, for polyRu-Cs (at 505 nm), the transmittance changes were lower; 67.7% and 22.2% at 5 and 2 s interval time, respectively. The redox stability of EC devices must also be considered because the deterioration of redox activity reduces the EC contrast and, hence, the performance. Thus, the cycling stability of the devices was measured by non-stop cycling of the applied potential between 0 and 1.8 V for polyRu–MWA and polyRu–CS. As  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65   6  shown in Figure 8, after 200 cycles (100 cycles at intervals of 5 s and 2 s), the devices retained their original electroactivity, indicating adequate redox stability.  The switching speed of an EC material, that is, the time required for the coloring and bleaching process, is another important parameter to consider, especially in applications such as dynamic displays and switchable mirrors. The coloring time (tc) and bleaching time (tb) for the reappearance and disappearance of the MLCT absorption were calculated from Figure 8a and are characterized as the time needed for 95% change of ΔT. For polyRu–MWA, tc and tb were found to be 1.18 and 2.38 s, respectively, whereas for polyRu–CS, these values were 1.07 and 2.43 s, respectively (Table 1). The coloration efficiency () at a given optical density is also an important characteristic for EC films and can calculated using Equation 1, where ΔOD is the optical density change, Qd is the amount of injected/ejected electronic charges in the polymer, and Tc and Tb are the coloring and bleaching transmittance values, respectively.  =∆𝑶𝑫𝑸𝒅= 𝒍𝒐𝒈𝑻𝒃𝑻𝒄/ 𝑸𝒅             (1) Using in–situ electrochemistry-transmittance measurements and Equation 1,  was calculated to be 318.6 cm2 C–1 at 505 nm for polyRu–CS and 425.7 cm2 C–1 at 510 nm for polyRu–MWA. The coloration efficiency of polyRu–MWA was ~1.3 times more than that of polyRu–CS. To the best of our knowledge, the coloration efficiency reported herein is the highest value reported to date for any MSP. The enhancement of the EC contrast and coloration efficiency of the polyRu–MWA film occurred because of the formation of a relatively smooth film owing to the homogeneous distribution of the microwave-synthesized long polymer chains. By contrast, short oligomeric chains were present in the EC film of polyRu–CS, leading to a higher number of nucleation centers and terminated oligomeric chains; the heterogeneous distribution of the oligomeric chains from the chain length distribution point results in the formation of a rougher film. All of these short-chain oligomers cannot be switched under the applied potential, resulting in the poor EC performance of polyRu–CS. [34, 35]    The charge/discharge capacity of the polymer films when switching between 0 and 1.8 V were measured from the chronoamperometry curve and are shown in Figure 8a. Charge required when the EC material is bleached from 0 to 1.8 V and discharged when it is darkened from 1.8 to 0 V. The charge densities required for bleaching (charging) polyRu–MWA and polyRu–CS were 7.37 and 4.33 mC cm–2, respectively, whereas, the charge densities required for coloring (discharge) were 6.77 and 4.29 mC cm–2, respectively. Higher charge density value were observed during charge/discharge for polyRu–MWA for two reasons: first, the formation  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65   7  of an ordered structure by long polymer chains [36] and second, insolubility in the electrolyte.[37]. Open-circuit memory, the time during which the material retains its color state after the electric field is removed, is an important parameter in EC devices because it is directly related to its utilization and energy consumption. To test this property for the EC devices based on polyRu–MWA and polyRu–CS, a 1.8 V potential was applied for 10 s. After charging, the device was maintained under open-circuit conditions for 600 s. The percentage change in transmittance was monitored using the MLCT of the EC devices. The EC memory spectra of both polymers are shown in Figure 8b. T The change was ca. two times higher for the polyRu–CS film than that for the polyRu–MWA film. A significant level of EC memory was observed for polyRu–MWA because the electrons were trapped in the high-molecular-mass polymer film, preventing them from reverting to their equilibrium state. Faster mass transport to polyRu–CS can lead to a lower optical memory owing to the existence of more contacts among the oligomer chains in the chaotic structure of the polymer film. [38, 39]  3. Conclusion We present a fast and facile microwave-assisted synthesis of high-molecular-weight Ru(II)-based MSP (polyRu–MWA) and characterize its photophysical and EC properties. For comparison, the same polymer (polyRu–CS) was synthesized using the oil-bath method. The molecular weights of polyRu–MWA and polyRu–CS were estimated through end group analysis by 1H NMR spectroscopy, and the obtained values were 11 × 104 Da and 4.4 × 103 Da, respectively. Changes in molecular weight significantly affect solubility, photophysical properties, and EC properties. The polyRu–MWA film showed better reversible electrochemical processes and stable color changes with good coloration efficiency (425.7 cm2 C–1 at 510 nm) and optical contrast (81.4% at 510 nm) than the polyRu–CS film (67.7% optical contrast with 318.6 cm2 C–1 efficiency at 510 nm), when the EC device was switched between the neutral (red at 0 V) and oxidized states (transparent at 1.8 V). Furthermore, polyRu–MWA exhibited better optical memory and long-term stability. In particular, the high optical contrast, remarkable coloration efficiency, significantly fast switching, good open-circuit stability, and tremendous redox stability make polyRu–MWA a good candidate for commercial applications.  4. Experimental Section/Methods  Materials   1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65   8  Unless otherwise noted, all reagents were of reagent grade and were used without purification. 4′,4′′′′-(1,4-Phenylene)bis(2,2′:6′,2′′-terpyridine) (96%) was purchased from Sigma-Aldrich co. Ltd. Dichlorotetrakis(dimethyl sulfoxide) ruthenium(II) was purchased from Tokyo Chemical Industry Co., Ltd., and used as received. Dehydrated ethylene glycol and tetrahydrofuran (THF) were used as the reaction solvents. Methanol for the UV–vis and acetonitrile for the CV measurements were of spectroscopic grade. These solvents were purchased from Wako or Kanto Chemical Co. Inc., and used as received.   Instrumentation Microwave irradiation was carried out using SMW-087 (μ Reactor®, Shikoku Instrumentation, Co. Ltd). The reaction temperature was measured using a fiber-optic thermometer (AMOTH FL-2000; Anritsu). UV−vis spectra were obtained using a Shimadzu UV-2550 UV-visible spectrophotometer. 1H NMR spectra were recorded on a 300 MHz JEOL AL 300/BZ instrument (Tokyo, Japan). Mass spectra were measured using a Shimadzu/Kratos time-of flight mass spectrometer (Kyoto, Japan). High-resolution mass spectrometry was performed on a Shimadzu LCMS-ITTOF spectrometer. Wide angle XRD was measured by using a RINT ULTIMA III device with Cu Kα radiation (λ= 1.54 Å), a generator voltage of 40 kV, and a current of 40 mA. CV and amperometric experiments were performed by spin-coating the polymer solution onto an ITO electrode. The experiments were performed in an electrochemical analyzer (ALS/H CH instruments) using an anhydrous acetonitrile solution containing 0.1 M lithium perchlorate (LiClO4) as the supporting electrolyte. A platinum flag was used as the counter electrode and Ag/AgCl was used as the reference electrode.  Synthesis of polyRu-MWA 4’,4’’’’-(1,4-Phenylene)bis(2,2’:6’,2’’-terpyridine) (0.05 g, 0.09 mM) and dichlorotetrakis(dimethylsulfoxide)ruthenium(II) (0.04 g, 0.09 mM) were placed in a two-neck round-bottom flask. Dry ethylene glycol (50 mL) was added, and the reaction mixture was irradiated with microwave at 770 W and 2.45 GHz frequency along with constant stirring for 60 min. After completion of the reaction, the solvent was removed and concentrated to approximately 10 mL. The reaction mixture was then added to 200 mL THF. The polymer was precipitated in THF, collected by filtration, washed with THF, and dried in a vacuum oven overnight. Finally, polyRu-MWA was obtained as red powder (0.08 g, 80% yield).   1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65   9  Preparation of a polymer film on ITO The polyRu-MWA and polyRu-CS films were prepared on ITO-coated glass using a spin-coating technique. First, the polymer was dissolved (5 mg mL-1) in dry methanol. Then, 100 µL of the polymer solution was spin-coated on an ITO glass (1.5 × 1.5 cm2) for 180 s at 100 rpm. The prepared films were dried for 30 min at room temperature.  Supporting Information  Supporting Information is available from the Wiley Online Library or from the author. 1H NMR spectra of polyRu-MWA and polyRu-CS, electrochromism of polyRu-CS, and 1H-1H COSY and 1H-1H NOESY NMR spectra of the model complex.   Acknowledgements This research was financially supported by the Mirai project (grant number: JPMJMI21I4) from the Japan Science and Technology Agency (JST) and the Environment Research and Technology Development Fund (ERTDF) (JPMEERF20221M02) from the Environmental Restoration and Conservation Agency (ERCA).  Received: ((will be filled in by the editorial staff)) Revised: ((will be filled in by the editorial staff)) Published online: ((will be filled in by the editorial staff))  References [1] P. Yang, P. Sun, W. Mai, Mater. Today 2016, 19, 394. [2] B. A. Korgel, Nature 2013, 500, 278. [3] G. Cai, J. Wang, P. S. Lee, Acc. Chem. Res. 2016, 49, 1469. [4] S. Zhao, B. Wang, N. Zhu, Y. Huang, F. Wang, R. Li, Y. Zhao, Q. Jiang, X. Wu, R. Zhang, Carbon Neutralization 2023, 2, 4. [5] A. Paolella, C. Faure, V. Timoshevskii, S. Marras, G. Bertoni, A. Guerfi, A. Vijh, M. Armand, K. Zaghib, J. Mater. Chem. A 2017, 5, 18919. [6] K. Madasamy, D. Velayutham, V. Suryanarayanan, M. Kathiresan, K.-C. 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(a) Microwave synthesis of polyRu, (b) an illustration of the microwave synthesis, and (c) the power and temperature profiles.                    1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65   13   Figure 2. 1H-NMR spectra of polyRu-MWA and model complex (solvent: CD3OD at room temperature).                1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65   14   Figure 3. (a) UV–vis and (b) emission spectra of polyRu-MWA and polyRu-CS in MeOH (concentration: 2.5 × 10-5 M).                   1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65   15   Figure 4. (a) Powder XRD analysis and (b) TGA data (heating rate: 10 °C /min) of polyRu-MWA and polyRu-CS.                 1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65   16    Figure 5. Cyclic voltammograms of polyRu-MWA and polyRu-CS (scan rate: (a) 50 mV s-1 and (b) 10 mV s-1) in 0.1 M LiClO4/ACN electrolyte solution.                        1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65   17   Figure 6. (a) CVs of a polyRu-MWA film with different scan rates (10–500 mV/s), (b) a graph of the peak current vs. the scan rate, and (c) a graph of the peak current vs. the square root of the scan rate. (d) CVs of a polyRu-CS film with different scan rates (10–500 mV/s), (e) a graph of the peak current vs. the scan rate, and (f) a graph of the peak current vs. the square root of the scan rate. The electrolyte solution is 0.1 M LiClO4/ACN.                  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65   18    Figure 7. (a) In-situ UV–vis spectra of a polyRu-MWA film in 0.1 M LiClO4/ACN at 0 and 1.8 V. (b) The color changes of a polyRu-MWA film (2.5 × 2.5 cm) at 0 and 1.8 V.                1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65   19   Figure 8. (a) Transmittance change (ΔT %) at 510 nm of a polyRu-MWA film switched between 0 and 1.8 V with 10, 5, and 2 s interval times. (b) The magnified view of the ΔT% for interval time of 5 s. (c) ΔT% at 505 nm of a polyRu-CS film switched between 0 and 1.8 V with 10, 5, and 2 s interval times. (d) The magnified view of the ΔT% for interval time of 5 s. All measurements were performed in 0.1 M LiClO4/ACN electrolyte solution.            1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65   20   Figure 9. (a) Chronoamperometry plots of polyRu-MWA. (b) Open circuit memory of polyRu-MWA and polyRu-CS electrochromic devices monitored at 510 and 505 nm, respectively (the initial applied potential: 1.8 V).        Table 1. EC properties of a polyRu-MWA and polyRu-CS film when switched between 0 and 1.8 V with an interval of 5 s.  Bleaching time (tb, s) Darkening time (td, s) Transmittance Change (ΔT, %) Charge/discharge amount  (Q, mC cm-2) Coloration efficiency  (, cm2 C-1 ) PolyRu-MWA  2.38 1.18 81.39 7.37/6.77 425.7 PolyRu-CS  2.43 1.07 67.73 4.33/4.29 318.6      1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65   21  A Ru(II)-based metallosupramolecular polymer was successfully synthesized by the 1:1 complexation of bis(terpyridyl)benzene and Ru(II) in ethylene glycol at 180 ⁰ C under microwave-irradiation (2.4 GHz, 770 W) for 60 min. An exceptional quality polymer with a high molecular weight (2.2 × 104 Da) was obtained in this reaction. The polymer film exhibited improved electrochromic properties with large optical contrast (81.4%) and high coloration efficiency (ƞ) (425.7 cm2/C) compared to the polymer synthesized using conventional methods.   Utpal Rana, Dines Chandra Santra, Banchhanidhi Prusti, Chanchal Chakraborty, Yuko Saito, Kazuhiko Takeuchi, Ritsuko Nagahata*, and Masayoshi Higuchi*  Microwave-Assisted Quick Synthesis of Ru(II)-Based Metallosupramolecular Polymer for Improved Electrochromic Properties   TOC         1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65   22  Supporting Information    Microwave-Assisted Quick Synthesis of Ru(II)-Based Metallosupramolecular Polymer for Improved Electrochromic Properties  Utpal Rana,a Dines Chandra Santra a, Banchhanidhi Prusti,a Chanchal Chakraborty,a Yuko Saito,b Kazuhiko Takeuchi,b Ritsuko Nagahata,*b and Masayoshi Higuchi*a   aElectronic Functional Macromolecules Group, National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan bNational Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8565, Japan.    Contents  1. 1H-1H COSY NMR spectrum of the model complex……………………..23 2. 1H-1H NOESY NMR spectrum of the model complex…………………..24 3. Electrochromism of polyRu-CS………………………………………25                      1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65   23  b' acd f e9.5            9.0            8.5             8.0            7.5    9.5              9.0            8.5             8.0             7.5         d (ppm)d(ppm)bb'acdfeb b' acd f e1. 1H-1H COSY NMR spectrum of the model complex                                      Figure S1. 1H-1H COSY NMR spectrum of the model complex in CD3OD at room temperature.         1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65   24  2. 1H-1H NOESY NMR spectrum of the model complex                   Figure S2. 1H-1H NOESY NMR spectrum of the model complex in CD3OD at room temperature.            1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65   25  3. Electrochromism of polyRu-CS                              Figure S3. (a) In situ UV–vis spectra of a polyRu-CS film in 0.1 M LiClO4/ACN at switching potentials of 0 and 1.8 V. (b) Corresponding color switching of a polyRu-CS film operated at 0 and 1.8 V (2.5 × 2.5 cm).          (a) (b)  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65