Ru(II)-Based Metallo-Supramolecular Polymer with Tetrakis(N-methylbenzimidazolyl)bipyridine for a Durable, Nonvolatile, and Electrochromic Device Driven at 0.6 V

Abstract

Low-voltage operation, high durability, and long memory time are demanded for electrochromic (EC) display device applications. Metallo-supramolecular polymers (MSPs), composed of a metal ion and ditopic ligand, are one of the recently developed EC materials, and the ligand modification is expected to tune the redox potential of MSP. In order to lower the redox potential of MSP, tetrakis­(N-methylbenzimidazolyl)­bipyridine (L Bip ) was designed as an electronically rich ligand. Ru-based MSP (polyRu-L Bip ) was successfully synthesized by 1:1 complexation of RuCl2(DMSO)4 with L Bip . The molecular weight (M w) was high (8.8 × 106 Da) enough to provide a simple 1H NMR spectrum, of which the proton peaks could be assigned by the comparison with the spectrum of the corresponding mono-Ru complex. The redox potential (E 1/2) between Ru­(II/III) was 0.51 V versus Ag/Ag+, which was much lower than the redox potential of previously reported Ru-based MSP with bis­(terpyridyl)­benzene (0.95 V vs Ag/Ag+). The polymer film exhibited reversible, distinct color changes between violet and light green-yellow upon applying very low potentials of 0 and 0.6 V vs Ag/Ag+, respectively. The appearance and disappearance of the metal-to-ligand charge transfer absorption by the electrochemical redox between Ru­(II/III) were confirmed using in situ spectro-electrochemical measurement. A solid-state EC device with polyRu-L Bip was revealed to have large optical contrast (ΔT 54%), fast response time (1.37 s for bleaching and 0.67 s for coloration), remarkable coloration efficiency (571 cm2/C), and high durability for the repeated color changes more than 20,000 cycles. The device also showed a long optical memory time of up to 19 h to maintain 40% to the initial contrast under the open circuit conditions. It is considered that the stabilization of the Ru­(III) state by L Bip suppressed the self-coloring to Ru­(II) inside the device.

Nanocomposites of Fe(II)-Based Metallo-Supramolecular Polymer and a Layered Inorganic–Organic Hybrid for Improved Electrochromic Materials

“…Electrochromic (EC) materials have received considerable attention as an important material used in electrochemical glass tinting, i.e., smart windows and antiglare rearview mirrors in cars [ 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 ]. Many types of EC materials have been reported and are often categorized as follows.…”

“…Metal oxides, such as tungsten oxide, are the first generation of EC materials; transition metal complexes, such as Prussian blue, are the second generation of EC materials; and organic molecules and π-conjugated polymers are the third generation of EC materials [ 3 , 4 , 7 , 8 , 9 , 10 , 11 , 12 ]. Recently, metallo-supramolecular polymers (MSPs), composed of metal ions with multi-topic organic ligands, such as bis-terpyridine, were reported as the fourth generation of EC materials [ 13 , 14 , 15 , 16 , 17 , 18 , 19 ]. MSPs demonstrate absorption in the visible region because of the metal-to-ligand charge transfer (MLCT) (d → π*) from the metal ion center to the organic ligand.…”

“…The appearance/disappearance of MLCT absorption is switched by the electrochemical redox of the metal ion in MSPs because the enhanced d–d splitting width is too large to allow the MLCT in the visible region for oxidized MSPs. The colors and redox potential of MSPs are tunable by changing metal ions (such as Fe(II), Ru(II), and Os(II)) or the substituents and spacer of organic ligands [ 13 , 14 , 15 , 16 , 17 , 18 , 19 ]. Three-dimensional hyperbranched MSPs show better EC properties than linear MSPs [ 17 ].…”

Synthesis and characterization of novel Al(III)‐metallopolymer and its application as a non‐volatile resistive memristive material

“…So, the properties of the metallopolymers can be tuned by tuning the functional group in the organic structure and the change in metal ion in the inorganic part, which changes the electronic, magnetic, and optical properties of functional materials 5–10 . These metallopolymers contain various metals as metal centers from main groups; such as Sn, Pb, a large variety of transition‐metal ions like Fe, Zn, Cu, Co, Pt, Ru, Os, Cr, and lanthanides like Eu and Tb 11–22 . Different non‐covalent interactions are often observed in these materials, like host‐guest interaction, π‐π stacking, and hydrogen‐bonding interactions, either in the backbone or side‐chain functional group present in the ligand with metal ions 23–25 .…”

“…Therefore, demand‐based manipulation of the different properties of the metallopolymers can be done easily either by changing the interaction strength in terms of the HOMO‐LUMO bandgap through the introduction of the new metal centers or by the modification in the π‐conjugated ligand 26 . Recently, different research groups have tried to explore tailorable metallopolymers' properties by choosing different metal ions with the same ligand 12,18,21 . The change in the properties of tailorable metallopolymers having the same organic moiety and different metal ions is observed because of differences in size, charge density, and variable oxidation state of the metal ion.…”