Abstract
Fe-based metallo-supramolecular polymer (polyFe), composed of Fe(II) ions and bis(terpyridyl)benzene, is known as a good electrochromic (EC) material. For the first time, to improve the EC properties, we prepared nanocomposites comprising polyFe and a layered inorganic–imidazoline covalently bonded hybrid (LIIm) by simply mixing them in methanol and then examined the effect of the nanocomposition on EC properties. The obtained blue/purple-colored composites (polyFe/LIIm composites) were demonstrated by scanning electron microscopy (SEM) to comprise a structure of LIIm nanoparticles coated with amorphous polyFe. Interestingly, X-ray diffraction (XRD) measurements suggested that there was no intercalation of polyFe in the interlayer space of LIIm. Ultraviolet-visible (UV-vis) spectroscopy measurements demonstrated that light absorption close to 600 nm was attributed to metal-to-ligand charge transfer (MLCT) from the Fe(II) ion to the bisterpyridine ligand and was influenced by LIIm in the composites. The composites exhibited a pair of redox waves, assigned to the redox between Fe(II) and Fe(III), in the cyclic voltammograms; moreover, the composites were estimated to be diffusion controlled. Thin composite films demonstrated reversible EC changes, triggered by the redox reaction of the metal. Furthermore, the results show that the nano-scale composition of the metallo-supramolecular polymers with LIIm can effectively improve the memory properties without reducing the contrast in transmittance (ΔT) of 70–76% in EC changes after applying 1.2 V vs. Ag/Ag+. The EC properties varied with varying ratios (3/0.1, 0.5, 1, and 5) of the polyFe/LIIm, and the ratio of 3/1 exhibited the longest memory and largest MLCT absorption peak among composites. The results show that the polyFe/LIIm composites are useful EC materials for dimming glass applications, such as smart windows.
Highlights
Introduction published maps and institutional affilElectrochromic (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 [1–29]
The blue-purple-colored polyFe/layered inorganic– imidazoline covalently bonded hybrid (LIIm) composite thin films showed a pair of redox waves at 0.86–0.89 V vs. Ag/Ag+, which were attributed to the electrochemical redox of Fe(II/III)
The appearance/disappearance of metal-to-ligand charge transfer (MLCT) absorption was triggered by the electrochemical redox
Summary
Introduction published maps and institutional affilElectrochromic (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 [1–29]. 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 [3,4,7–12]. 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 [13–19]. 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 iations
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