Dual-Branched Dense Hexagonal Fe(II)-Based Coordination Nanosheets with Red-to-Colorless Electrochromism and Durable Device Fabrication

Fabrication and Photovoltaic Conversion Performances of Imidazolyl and Fumaric Acid Composite Langmuir-Blodgett Membranes

Novel organic small molecule structures have received increasing attention in the preparation of multifunctional thin film materials and have become the subject of research in many cutting-edge directions. In this work, imidazolyl and transbutylene glycolic acid molecules and dye molecules were designed and prepared as composite films by supramolecular self-assembly in the LB technique, and their morphological features and spectral properties were analyzed. The results showed that the prepared LB films presented different aggregation states. In addition, their photoelectrochemical properties, on ITO sheets were tested, all of which showed good optoelectronic properties, and their binding energies, structure optimization, and electrostatic potentials were theoretically calculated by DFT simulations, which proved that the prepared films have good optoelectronic properties, and have the potential to become optoelectronic multifunctional ultrathin film devices.

Near-IR Electrochromic Film with High Optical Contrast and Stability Prepared by Oxidative Electropolymerization of Triphenylamine Modified Terpyridine Platinum(II) Chloride

Terpyridine (TPY) platinum(II) chloride with a triphenylamine (TPA) group was successfully synthesized. The strong intramolecular Donor(TPA)-Acceptor(TPY) interaction induced the low-energy absorption band, mixing the spin-allowed singlet dπ(Pt)→π*(TPY) metal-to-ligand charge transfer (MLCT) with the chloride ligand-to-metal charge transfer (LMCT) and chloride ligand-to-ligand (TPY) charge transfer (LLCT) transitions, to bathochromically shift to λmax = 449 nm with significant enhancement and broadening effects. Using the cyclic voltammetry method, its oxidative electropolymerization (EP) films on working Pt disk and ITO electrodes were produced with tunable thickness and diffusion controlled redox behavior, which were characterized by the SEM, EDS, FT-IR, and AC impedance methods. Upon applying +1.4 V voltage, the sandwich-type electrochromic device (ECD) with ca. 290 nm thickness of the EP film exhibits a distinct color transformation from red (CIE coordinates: L = 50.75, a = 18.58, b = 5.69) to dark blue (CIE coordinates: L = 45.65, a = -1.35, b = -12.49). Good electrochromic (EC) parameters, such as a large optical contrast (ΔT%) of 78%, quick coloration and bleaching response times of 2.9 s and 1.1 s, high coloration and bleaching efficiencies of 278.0 and 390.5 C-1·cm2, and good cycling stability (maintains 70% of the initial ΔT% value after 3200 voltage switching cycles), were obtained.

Recent progress in electrochromic energy storage materials and devices: a minireview

Integration of several functionalities into one isolated electrochemical body is necessary to realize compact and tiny smart electronics. Recently, two different technologies, electrochromic (EC) materials and energy storage, were combined to create a single system that supports and drives both functions simultaneously. In EC energy storage devices, the characteristic feature of EC materials, their optical modulation depending on the applied voltage, is used to visually identify the stored energy level in real time. Moreover, combining energy-harvesting and EC storage systems by sharing one electrode facilitates the realization of further compact multifunction systems. In this minireview, we highlight recent groundbreaking achievements in EC multifunction systems where the stored energy levels can be visualized using the color of the device.

Investigation of electrochemistry and electrochromic performance of metallopolymer formed by electropolymerization of Fe(II) complex with triphenylamine-hydrazone ligand

The complex of Fe(II) ions of general formula [FeL2](BF4)2 with triphenylamine-hydrazone ligand L has been synthesized and characterized. Oxidative electropolymerization of the complex proceeded smoothly on the working electrode producing homogenous thin film of metallopolymer. The film thickness and morphology of the layer was investigated by microscopy techniques such as SEM and AFM, and the composition of the film was confirmed by XPS analysis. It was found that after fifty successive oxidation/reduction cycles the film of thickness 120 nm was formed on the electrode surface. The metallopolymer was also characterized using cyclic voltammetry and spectroelectrochemical methods. The film was found to change its color from yellow to green-blue, high change in transmittance of 60% at 770 nm and good electrochemical stability during 375 cycles of switching of the potential between -0.1 V and +1.5 V, due to the presence of metal ions that link two ligand molecules resulting in formation of highly cross-linked film. The switching times (coloration and bleaching) were calculated to be 34.2 s and 7.3 s, respectively. Coloration efficiency of the formed film of polymeric complex was found to be 144 cm 2 /C.

Electrochromic behavior of fac-tricarbonyl rhenium complexes

Tricarbonyl rhenium complex shows good electrochromic performance with a colored stage of green, rapid response and good switching stability.

Construction of a pillararene-based supramolecular polymer network and its application in efficient removal of dyes from water

An AB-type monomer based on a pillar[5]arene host and an imidazolium salt guest was successfully synthesized through a facile way. This monomer can self-assemble into linear supramolecular polymers in chloroform. After the addition of silver ions, the imidazolium salt group coordinated with silver ions to crosslink the linear supramolecular polymers at their ends, resulting in the formation of supramolecular polymer networks. Meanwhile, after further adding iodide ions, the supramolecular polymer network changed back to the linear supramolecular polymer. As a result, the topological structure of the system can be reversibly tuned. Furthermore, this supramolecular polymer network can be applied to remove organic dyes in water, suggesting its great potential in the treatment of waste water.

Reductive Electropolymerization and Electrochromism of Iron(II) Complex with Styrene-Based Ligand

The benzimidazole-based ligand containing polymerizable styrene group has been prepared via condensation of picolinaldehyde derivative containing styrene moiety and benzimidazole-based hydrazine. The ligand reacted with iron(II) tetrafluoroborate and iron(II) trifluoromethanesulfonate giving red-brown complexes of Fe(II) ions of formula [FeL₂]X₂, where X = CF₃SO₃⁻ (1) or BF₄⁻ (2). Reductive electropolymerization was used to obtain a thin layer of the polymeric complex, poly-1. Further investigation of electrochemical properties of the compound by cyclic voltammetry showed two quasi-reversible redox processes assigned to electrooxidation and electroreduction of the polymer. Spectroelectrochemical measurements confirmed that the polymer undergoes the color changes during oxidation and reduction process. The polymer in its neutral state (Fe(II)) is yellow and it exhibits absorption band at 370 nm, after oxidation to Fe(III) state absorption band shifts to 350 nm and the polymer is almost colorless. While the metal ions are reduced to Fe(I) absorption band at around 410 nm has been observed and the polymer changed its color to intense yellow. The stability of the polymer during multiple oxidation/reduction cycles has also been investigated.

Transmissive to blackish-green NIR electrochromism in a Co(II)-based interfacial co-ordination thin film

Herein, a Co(ii)-based metallo-polymer (Co-tpy-L) with a three armed non-conjugated terpyridine ligand is synthesized using solvent-solvent interfacial polymerization. The thin film exhibits durable transmissive-to-blackish green electrochromism, selectively covering both the visible and NIR regions with a moderate voltage range of -1.4 to 0 V.

Ligand-Controlled Electrochromic Diversification with Multilayer Coated Metallosupramolecular Polymer Assemblies

Designing surface-confined molecular systems capable of expressing changes in functional properties as a result of slight variations in chemical structure under the influence of an external stimulus is of contemporary interest. In this context, we have designed three tetraterpyridine ligands with variations in their core architecture (phenyl vs tetraphenylethynyl vs bithiophene) to create spray-coated electrochromic assemblies of iron(II)-based metallosupramolecular polymer network films on transparent conducting oxide substrates. These assemblies exhibited molecular permeability and spectroelectrochemical properties that are in turn dictated by the ligand structure. Electrochromic films with high coloration efficiencies (up to 1050 cm²/C) and superior optical contrast (up to 76%) with a concomitant color-to-color redox transition were readily achieved. These functional switching elements were integrated into sandwich-type electrochromic cells (CE up to 641 cm²/C) that exhibited high contrast ratios of up to 56%, with attractive ON-OFF ratios, fast switching kinetics, and high operational stability. Every measurable spectroelectrochemical property of the films and devices is an associated function of the ligand structure that coordinates the same metal ion to different extents. While exhibiting a ligand-structure induced differential metal coordination leading to porosity and spectroelectrochemical diversification, these assemblies allow the creation of electrochromic patterns and images by a simple spray-coating technique.

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.

Dual-Redox System of Metallo-Supramolecular Polymers for Visible-to-Near-IR Modulable Electrochromism and Durable Device Fabrication

Dual-redox metallo-supramolecular polymers with a zigzag structure (polyFe-N and polyRu-N) were successfully synthesized by 1:1 complexation of a redox-active Fe(II) or Ru(II) ion and 4,4-bis(2,2:6,2-terpyridinyl)phenyl-triphenylamine (L_TPA) as a redox-active ligand. The polymers had high solubility in methanol, and the polymer solutions showed dark brown (polyFe-N) or orange-red (polyRu-N) coloration. UV-vis spectra of the polymers displayed a strong metal-to-ligand charge transfer (MLCT) absorption in the visible region. Cyclic voltammograms of the polymer films exhibited two pairs of reversible redox waves. The first redox at ∼0.5 V versus Ag/Ag⁺ was assigned to the redox in the triphenylamine (TPA) moiety of L_TPA, and the second redox at 0.8 V versus Ag/Ag⁺ (polyFe-N) or 0.9 V versus Ag/Ag⁺ (polyRu-N) was given to the redox of Fe(II)/(III) or Ru(II)/(III), respectively. Upon applying a positive potential of more than 0.5 V versus Ag/Ag⁺ to the polymer films, a new absorption at ∼820 nm in the near-infrared (NIR) region appeared with wide tailing to the longer wavelength. It is considered that the new absorption in the NIR region is caused by the polaron band of the oxidized ligand in the polymers. When the applied potential was increased to 1.0 V versus Ag/Ag⁺ (polyFe-N) or 1.1 V versus Ag/Ag⁺ (polyRu-N), the maximum wavelength of the new absorption in the NIR region shifted to 885-900 nm and the absorbance was further enhanced with disappearance of the MLCT absorption. Eventually, the original colors of the polymers were faint to light green. This visible-to-NIR electrochromism was reversible, and maximum optical contrast (ΔT) reached 52% in the visible region and 80% in the NIR region. A prototype solid-state device with the polymer was fabricated for practical utilization, exhibiting excellent cycle stability of >4000 cycles with maintaining high optical contrast from the visible-to-NIR range.