Ligand Impact on Monolayer Electrochromic Material Properties

Nonconventional Symmetric Double-Side Electrochromic Devices Employing a Nafion Conductive Layer to Unlock Superior Durability

In this work, we present a methodology to create an effective novel double-sided symmetric architecture of solid-state electrochromic devices. This principally new nonconventional configuration provides access to novel electrochromic systems that could be applicable for the creation of smart double-side signage, smart boards, nonemissive displays, and other smart interactive devices that change their color upon application of a voltage. The proposed configuration is based on the assembly of two identical electrochromic materials facing each other through an opaque optical separator. As a proof of concept, we use an electrochromic material based on bis(4'-(pyridin-4-yl)-2,2':6',2″-terpyridine) iron complex, covalently immobilized on screen-printed surface-extended ITO support. The symmetric configuration allows for a drastic enhancement of the overall stability of the device due to both attenuation of the counter electrode polarization and minimization of electrolyte decomposition. A nontransparent ion-permeable separator, in turn, allows observing the color change of only one of the electrodes by cutting off the optical contribution of the electrode located behind it. Further functionalization of the electrochromic material with a thin layer of Nafion is a beneficial strategy to significantly boost up long-term durability of the devices. Applying a layer of Nafion to the electrochromic material results in an increase in ionic conductivity within the device and ensures better retention of electrochromic molecules on the surface, thus minimizing device decomposition during long-term electrochemical cycling. An electrochromic device that bears Nafion-functionalized electrodes can operate (i) in the dual-side mode, where both sides demonstrate effective electrochromic performance; or (ii) in a one-side manner, where only one side of the device changes color. Notably, when operating in the one-side mode, the device withstands 70,000 cycles, after which the performance of the device can be resumed by simply turning the device to the other side (via switching the polarity of the electrodes).

Photoluminescence and Nonlinear Optical Properties of Two Terpyridine-Based Hybrid Zn/Cd Halides

Hybrid metal halides (HMHs) with low-dimensional structures have attracted increasing attention due to their striking optical properties. Herein, two new zero-dimensional HMHs have been fabricated by CdCl2/ZnCl2 and 4'-(4-pyridyl-phenyl)-2,2':6',2″-terpyridine (Tpy), including (TpyH3)[CdCl4][Cl] (Tpy-Cd) and (TpyH3)[ZnCl4][Cl] (Tpy-Zn). Their structures are consisted of a [TpyH3]3+ organic cation, an inorganic [ZnCl4] or [CdCl4] tetrahedron, and one isolated Cl- anion. Tpy-Cd crystallizes to a noncentrosymmetric structure and possesses a moderate second harmonic response of 0.72 × KH2PO4, while Tpy-Zn features a centrosymmetric space group. Though Tpy-Cd and Tpy-Zn crystallize into space groups of completely different symmetry due to distinct connection mode and molecular distortion, they display quite similar photoluminescence of bright green light emission under ultraviolet excitation, nearly identical in Stokes shift, photoluminescence quantum yield, decay lifetime, and energy. The photoluminescence quantum yields of green light emission were measured to be nearly 25%, outperforming most of the Cd/Zn low-dimensional HMHs.

Post-Synthetic Color Tuning of the Ultra-Effective and Highly Stable Surface-Confined Electrochromic Monolayer: Shades of Green for Camouflage Materials

We report here on the strategy for the preparation of a series of electrochromic (EC) materials in green shades designed for camouflage purposes. This top-down post-synthetic modification provides access to new EC materials by fine modulation of the color of the surface-confined metalorganic monolayer pre-deposited on indium tin oxide screen-printed supports. Selective on-surface N-quaternization of the outer pyridine unit of the EC metal complex covalently embedded onto an enhanced surface area electrode results in a bathochromic shift of the absorbance signal as well as visual color change from blue to different shades of green. When assembled into solid-state EC devices (ECDs), the materials demonstrate high color differences between colored and bleached states and significant differences in optical density. Upon electrochemical switching, the ECDs initially featuring different shades of green become yellowish or clay. The accessible gamut of colors, fulfilling the requirements for chameleon-like camouflage materials, is able to mimic conditions of various natural environments including forests and sands. Notably, ECDs demonstrate high long-term durability (95% retention of the performance after 3300 cycles), fast coloration (0.6-1.1 s), and bleaching (1.2-3.3 s) times and outstanding coloration efficiencies of 1018-1513 cm²/C. Importantly, post-synthetic N-quaternization/color tuning does not deteriorate the performance of the resulting EC materials and devices as judged by cyclic voltammetry, spectroelectrochemistry, and electrochemical impedance spectroscopy. This work adds to the limited number of reports that explore color tuning of EC molecular layers via on-surface modification with the aim to access new non-symmetric materials. Notably, the facile and straightforward technology presented here allows the creation of green-colored EC materials that are difficult to prepare in other ways.

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

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.

Iron (II) Metallo-Supramolecular Polymers Based on Thieno[3,2-b]thiophene for Electrochromic Applications

Four new bis(tpy) unimers with different linkers between the thieno[3,2-b]thiophene-2,5-diyl central unit and terpyridine-4′-yl (tpy) end-groups: no linker (Tt), ethynediyl (TtE), 1,4-phenylene (TtPh) and 2,2′-bithophene-5,5′-diyl (TtB) are prepared, characterized, and assembled with Fe²⁺ ions to metallo-supramolecular polymers (Fe-MSPs). The Fe-MSP films prepared by spin-casting on Indium Tin Oxide (ITO) glass are characterized by atomic force microscope (AFM) microscopy, cyclic voltammetry, and UV/vis spectroscopy and studied for their electrochromism and effect of the unimer structure on their electrochromic performance. Of the studied MSPs, Fe-Tt shows the highest optical contrast as well as coloration efficiency (CE = 641 cm² C⁻¹) and the fastest optical response. This makes it an excellent candidate for possible use in electrochromic devices.

Reducing the resistance for the use of electrochemical impedance spectroscopy analysis in materials chemistry

Electrochemical impedance spectroscopy (EIS) is a highly applicable electrochemical, analytical, and non-invasive technique for materials characterization, which allows the user to evaluate the impact, efficiency, and magnitude of different components within an electrical circuit at a higher resolution than other common electrochemical techniques such as cyclic voltammetry (CV) or chronoamperometry. EIS can be used to study mechanisms of surface reactions, evaluate kinetics and mass transport, and study the level of corrosion on conductive materials, just to name a few. Therefore, this review demonstrates the scope of physical properties of the materials that can be studied using EIS, such as for characterization of supercapacitors, dye-sensitized solar cells (DSSCs), conductive coatings, sensors, self-assembled monolayers (SAMs), and other materials. This guide was created to support beginner and intermediate level researchers in EIS studies to inspire a wider application of this technique for materials characterization. In this work, we provide a summary of the essential background theory of EIS, including experimental design, signal responses, and instrumentation. Then, we discuss the main graphical representations for EIS data, including a scope of the foundation principles of Nyquist, Bode phase angle, Bode magnitude, capacitance and Randles plots, followed by detailed step-by-step explanations of the corresponding calculations that evolve from these graphs and direct examples from the literature highlighting practical applications of EIS for characterization of different types of materials. In addition, we discuss various applications of EIS technique for materials research.

This manuscript highlights a beginner-to-intermediate level scope of electrochemical impedance spectroscopy (EIS), which is an indispensable, non-destructive electrochemical technique that can be applied for materials characterization.

Multichromic Monolayer Terpyridine-Based Electrochromic Materials

The article describes novel electrochromic materials (ECMs) that are based on a monolayer consisting of two or three isostructural metal complexes of 4'-(pyridin-4-yl)-2,2':6',2''-terpyridine simultaneously deposited on surface-enhanced support. The support was made by screen printing of indium tin oxide (ITO) nanoparticles on ITO-glass and has a surface area sufficient for a monolayer to give color visible to the naked eye. The ability to separately electrochemically address the oxidation state of the metal centers on the surface (i.e., Co²⁺/Co³⁺, Os²⁺/Os³⁺, and Fe²⁺/Fe³⁺) provides an opportunity to achieve several distinct color-to-color transitions, thus opening the door for constructing monolayer-based multicolor ECMs.

Constructing Alternated Heterobimetallic [Fe(II)/Os(II)] Supramolecular Polymers with Diverse Solubility for Facile Fabrication of Voltage-Tunable Multicolor Electrochromic Devices

Metallo-supramolecular polymer (MSP)-based electrochromic devices (ECDs) have drawn much attention because of their variable colors and attractive electrochromic (EC) properties. However, fabrication of voltage-tunable multicolor ECDs using single MSP is yet hard to realize. We anticipated alternate introduction of two different redox-active metal ions in an MSP combined with the adjustment of counteranions could be a solution to fabricate multicolor ECDs. The heterometals will induce color variability upon voltage alteration, and counteranions will help to tune the solubility of MSP in different solvents. In an attempt to fulfill this target, we have synthesized four heterobimetallic supramolecular polymers (HBPs) having different counteranions (BF₄^-, Cl^-, PF₆^-, and OAc^-), in which Fe(II) and Os(II) are alternately complexed by two terpyridine units. To apply as EC material, the HBPs should be soluble in methanol and insoluble in acetonitrile for the preparation of EC film as well as ECDs. However, among the HBPs, only HBP-OAc is found to meet this requirement. The EC behaviors of the spray-coating film of HBP-OAc on an indium tin oxide (ITO)-coated glass substrate are investigated in terms of maximum transmittance contrast, coloration voltage, response time, coloration efficiency, and operational stability, which exhibits reversible multicolor electrochromism (the initial purple color of the film is changed to violet followed by greenish-yellow) upon alteration of the voltage from 0.0 to 0.7 V [required to oxidize the Os(II) ion] and to 1.0 V [required to oxidize the Fe(II) ion]. The film is also integrated into a laminated ECD by using lithium-based gel electrolyte. Finally, as a proof-of-concept, a prototype voltage-tunable multicolor EC display (6 cm × 2.5 cm) is fabricated by using a designed image containing a flower, leaves, and a flower pot, which exhibits six different types of multicolor image upon application of tunable voltages.

A fast-switching electrochromic device with a surface-confined 3D metallo-organic coordination assembly

Demonstrated herein is a fast (<1 s)-switching solid-state electrochromic device (t = 0.49 s for coloration and 0.90 s for bleaching), fabricated with a novel imidazolium-linked [Fe(terpyridine)2]2+ chromophore-based surface-confined three dimensional metallo-organic coordination assembly. The device also exhibits promising electrochromic attributes such as high coloration efficiency (η = 275 cm2 C-1), moderate operating voltage (from -2 V to +3.2 V) and transmittance contrast (ΔT = 40%), and high cycling stability (up to 4500 cycles).

Integrated Molecular Logic Using a Multistate Electrochromic Platform

Herein, we present an approach that integrates molecular logic functions using surface-confined metallo-organic assemblies. These assemblies are electrochromic and mimic the behaviour of logic elements. The logic elements are addressed individually by electrochemical methods, and their outputs are simultaneously read-out optically by UV/Vis absorption spectroscopy. The versatility of our setup is demonstrated by the integration of two multi-component assemblies; each acting as ternary logic elements. We used also a laminated cell configuration to demonstrate color-to-color and color-to-transparent transitions. This concept offers a route for the future development of devices with multiple logic states.

Synthesis and Characterization of Novel Triarylamine Derivatives with Dimethylamino Substituents for Application in Optoelectronic Devices

Two novel triphenylamine-based derivatives with dimethylamino substituents, N, N'-bis(4-dimethylaminophenyl)- N, N'-bis(4-methoxyphenyl)-1,4-phenylenediamine (NTPPA) and N, N'-bis(4-dimethylaminophenyl)- N, N'-bis(4-methoxyphenyl)-1,1'-biphenyl-4,4'-diamine (NTPB), were readily prepared for investigating the optical and electrochromic behaviors. These two obtained materials were introduced into electrochromic devices accompanied with heptyl viologen (HV), and the devices demonstrate a high average coloration efficiency of 287 cm²/C and electrochemical stability. Besides, NTPB/HV was further used to fabricate electrofluorochromic devices with a gel type electrolyte, and exhibit a controllable and high photoluminescence contrast ratio ( I_off/ I_on) of 32.12 from strong emission to truly dark by tuning the applied potential in addition to a short switching time of 4.9 s and high reversibility of 99% after 500 cycles.

Dual-colored 4,4′,4′′,4′′′-(cyclobutane-1,2,3,4-tetrayl)-tetrabenzoate electrochromic materials with large optical contrast and coloration efficiency

This paper reports novel ester-containing electrochromic materials, 4,4′,4′′,4′′′-(cyclobutane-1,2,3,4-tetrayl)tetrabenzoate derivatives, with dual-colored electrochromism, high color contrast and coloration efficiency.

Where Are the tpy Embraces in [Zn{4′-(EtO)2OPC6H4tpy}2][CF3SO3]2?

In this paper, the bromo- and phosphonate-ester-functionalized complexes [Zn(1)2][CF3SO3]2 and [Zn(2)2][CF3SO3]2 (1 = 4′-(4-bromophenyl)-2,2′:6′,2″-terpyridine, 2 = diethyl (4-([2,2′:6′,2″-terpyridin]-4′-yl)phenyl)phosphonate) are reported. The complexes have been characterized by electrospray mass spectrometry, IR and absorption spectroscopies, and multinuclear NMR spectroscopy. The single-crystal structures of [Zn(1)2][CF3SO3]2.MeCN.1/2Et2O and [Zn(2)2][CF3SO3]2 have been determined and they confirm {Zn(tpy)2}2+ cores (tpy = 2,2′:6′,2″-terpyridine). Ongoing from X = Br to P(O)(OEt)2, the {Zn(4′-XC6H4tpy)2}2+ unit exhibits significant “bowing” of the backbone, which is associated with changes in packing interactions. The [Zn(1)2]2+ cations engage in head-to-tail 4′-Phtpy...4′-Phtpy embraces with efficient pyridine...phenylene π-stacking interactions. The [Zn(2)2]2+ cations pack with one of the two ligands involved in pyridine...pyridine π-stacking; steric hindrance between one C6H4PO(OEt)2 group and an adjacent pair of π-stacked pyridine rings results in distortion of backbone of the ligand. This report is the first crystallographic determination of a salt of a homoleptic [M{4′-(RO)2OPC6H4tpy}2]n+ cation.

High-Precision and Low-Cost Wireless 16-Channel Measurement System for Malachite Green Detection

Focusing on the issue of the malachite green traditional test methods such as large volume, high cost and high complex, this paper proposed a novel multi-channel electrochemical malachite green detection system. Specific recognition properties of malachite green DNA adapter is employed to realize accurate sensing of concentration of malachite green, which can achieve precise detection of malachite green concentration with low noise and high precision. The maximum measurement capability of multi-channel acquisition system is 16 samples in a batch. According to the experimental results, malachite green could be detected quantitatively in the range from 10⁻³ μg/mL to 10 μg/mL, which performs well in the test of malachite green residues in aquatic product transportation.