Thienylmethylene Oxindole Based Conjugated Polymers via Direct Arylation Polymerization and Their Electrochromic Properties

Direct arylation methods have been used to polymerize thienylmethylene oxindoles(TEIs) and 3,3-bis[[(2-ethylhexyl)oxy]methyl]-3,4-dihydro-2 H-thieno-[3,4-b][1,4]dioxepin(ProDOT) for new donor-acceptor conjugated polymers. The polymers exhibited blue hues in neutralstate with distinct color-to-transmissive reversible electrochromic switching under applied potentials from 0 V to +1.5 V, and showed high coloration efficiencies(436-438 cm~2·C~(-1)) in near-infrared regions with high switching speeds around 1-2 s under ambient conditions.     

Prototype electrochromic device and dye sensitized solar cell using spray deposited undoped and ‘Li’ doped V2O5 thin film electrodes

Lithium (Li) (0–5 wt%) doped V₂O₅ thin films were spray deposited at 450 °C onto ITO substrates. Structural analysis using X-ray diffraction and Raman spectroscopy revealed orthorhombic phase of the films. In addition to the V₂O₅ phase, presence of VO₂ peaks due to high deposition temperature is also evident from structural and optical characterization. The non-stoichiometric nature of the films due to loss of the terminal O atom was confirmed from Raman spectroscopy. The direct band gap, indirect bandgap, and phonon energies were also calculated from optical studies. Different charge states of vanadium ions present in the film were identified from X-ray photoelectron spectroscopy study. Results from cyclic voltammetry experiments reflected significant differences between the undoped and Li doped V₂O₅ samples. Transport properties by Hall-effect measured at room temperature indicated significant increase in conductivity, carrier concentration and mobility of V₂O₅ thin films on doping with Li. A Dye Sensitized Solar Cell (DSSC) was fabricated using mobility enhanced 5 wt% Li doped V₂O₅ film as photoanode and its efficiency was found to be 2.7%. A simple electrochromic cell is fabricated using undoped V₂O₅ thin film to demonstrate the colour change.     

Spectroelectrochemical Studies on Silicate Sol‐Gel Matrix‐supported Sub‐10 nm Prussian Blue Nanostructures‐based Electrochromic Device

In this study, spectroelectrochemical (SPE) studies to monitor the electrochromic properties of electrochemically synthesized sub‐10 nm sized Prussian blue (PB) nanostructures (NSs) are employed. At the beginning the dark blue coloured device, shifts reversibly between translucent and dark‐blue while applying an applied bias between +1 to ?1 V with an opposite polarization. Amine functionalized silicate sol‐gel matrix (SSG) is used as a solid support and stabilizer for electrodepositing highly uniform sub‐10 nm PB NSs. The SSG's film thickness is suitably optimized through suitable controlled experiments. It is found that the SPE behaviour of sub‐10 nm sized PB NSs, suitably followed a colour modulation of PB into Prussian white (PW) and vice‐versa. SPE studies are used to investigate the redox switching between the PB and PW and which are responsible for an electrochromic function of a fabricated electrochromic device (ECD). Fabricated ECD has demonstrated an optical modulation at 680 nm with the moderate coloration efficiency of 115.8 cm²/C. Present study validates the SPE feature of sub‐10 nm PB NSs as an active electrochromic nanomaterial and demonstrating the applicability of SPE technique to investigate the variety of electrochromic nanomaterials, with consequences in both spectral and electrochemically active nanomaterials for electrochromic device applications.     

Urea Biosensor Based on Electrochromic Properties of Prussian Blue

Prussian blue (PB) is an electrochromic material, which can be used as a signal transducer in the formation of optical urea biosensors. The previous researches in electrochromic properties of PB demonstrated the optical PB response to ammonium ions, which occurs when ammonium ions are interacting with PB layer at a constant 0.2 V vs Ag|AgCl|KCl_sat potential. In this work PB optical dependence on ammonium ions concentration was applied in the formation of electrochromic urea biosensor. Biosensor was formed by modifying the optically transparent indium tin oxide (ITO) coated glass electrode (glass/ITO) with Prussian blue layer and immobilizing urease (glass/ITO/PB‐urease). Calibration curve showed the linear dependency (R²=0.995) between the change of maximal absorbance (ΔA) and urea concentration in concentration range varying from 3 mM to 30 mM. The highest sensitivity (4 ΔA M^?1) of glass/ITO/PB‐urease biosensor is in the concentration range from 7 mM to 30 mM. It was determined that working principle of the glass/ITO/PB‐urease biosensor is not related to pH changes occurring during enzymatic hydrolysis of urea.     

Design,synthesis, photochromism and electrochemistry of a novel material with pendant photochromic units

In the present work, the synthesis, photochromism and electrochemistry of a novel material 1, 1-(4-[3,4-bis(2,5-dimethyl-3-thienyl)cyclopent-3-en-1-yl]phenyl)-2,5-di-2-thienyl-1H-pyrrole, with pendant dithienylethene (DTE) photochromic units are described. It should be noted that the system 1 can be reversibly and efficiently switched between open (1o) and closed (1c) states by light in both solution and in the solid poly(methyl methacrylate) matrix. It is also noteworthy that the two isomers (1o and 1c) of this novel system 1 can be smoothly polymerized on ITO by electrochemical means. Surprisingly, the DTE unit in 1 does not retain its photochemical switching properties after immobilization onto ITO. The morphology of the polymer film was investigated by AFM analysis. Furthermore, it was found that the polymer exhibited remarkable electrochromic features that can be switched from green in the neutral state to violet state under applied external potentials without disturbing the photochromic units.     

Effects of film structure on electrochromic properties of the multilayer films containing polyoxometalates

Multilayer films of tungstophosphate anion (P₂W₁₈) and poly(allylamine hydrochloride) (PAH) were fabricated on quartz and ITO substrates by layer-by-layer self-assembly method. These films were characterized by UV–vis spectroscopy, cyclic voltammetry (CV), chronoamperometric (CA), chronocoulometry (CC) and atomic force microscopy (AFM). The effects of film structure on multilayer electrochromic properties were investigated. The electrochromic responses of the composite films were related to the surface coverage of anion and multilayer thickness. It was found that higher concentration of polycation and anion, or adding salt to the polycation solution used for multilayer film preparation led to thicker and denser film structure which improved optical contrast and coloration efficiency whereas prolonged response time.     

High throughput screening and measurements of proton conductivity of newly developed PEM materials based on proton transport visualization

An electrochemical method for proton transport visualization was developed and applied to the investigation of proton-conducting membrane materials. The method employs the change in the visual appearance of chemo-chromic tungsten oxide WO₃ in the presence of atomic hydrogen. An all-solid electrochemical cell arranged by substituting a fuel cell cathode with a thin film of WO₃-electrode was built and shown to generate both optical and electrical response to hydrogen gas exposure. The design of the cell was extended to a high throughput screening system that was utilized to characterize proton transport properties of samples, including a number of new compounds synthesized in-house by sol–gel wet chemistry. Non-destructive introduction of superacidic groups promoting proton hopping in the membrane materials was achieved by photodecomposition of a photoacid generator just after membrane casting. A model quantitatively describing current–voltage relation in the cell was developed and successfully applied to derive area-specific resistance of proton-conductive membranes from the experimental results. Area-specific resistances of membranes are derived from the slopes of optically reconstructed voltage–current curves. Sensitivity and dynamic range of the screening method are discussed.     

Ferrocene clicked poly(3,4-ethylenedioxythiophene) conducting polymer: Characterization, electrochemical and electrochromic properties

The “click” chemistry, Cu(I)-catalyzed azide–alkyne cycloaddition reaction, was applied to covalently functionalize the poly(3,4-ethylenedioxythiophene) (PEDOT) conducting polymer film with an excellent electron transfer mediator (ferrocene). Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and Raman spectroscopy were used to characterize the ferrocene-grafted PEDOT conducting polymer film, and it was proved that the grafting procedure via click reaction had a high efficiency. The ferrocene groups covalently grafted in the polymer films turned out to own a relatively fast electron transfer rate and show multi-color states via adjusting applied potential.     

苯/二联苯为桥的噻吩-吡咯-噻吩结构:分子构型及电致变色性质

A series of multi-branched dithienylpyrrole (SNS) monomers with rigid phenyl (PhSNS) and biphenyl rings (BPhSNS) as bridges were designed and synthesized, and were fabricated to form cross-linked polymers (pPhSNS, pBPhSNS) by electrochemical polymerization. Cyclic voltammetry (CV) results showed that PhSNS and BPhSNS exhibited similar oxidative properties except for one new higher-potential oxidative peak appearing in the curves of PhSNS. Theoretical calculations indicated that it should be attributed to the different steric configuration between the two dithienylpyrrole (SNS) units in PhSNS. One SNS unit possessed a larger twist angle (40.2°) between thiophene and pyrrole rings than the other one (21.2°), which indicated that PhSNS possessed a relatively larger energy gap (~0.4 eV) between HOMO-1 and HOMO than BPhSNS, for which HOMO and HOMO-1 levels were of almost the same energy. However, both PhSNS and BPhSNS showed similar onset oxidation potentials. The CV curves of pPhSNS and pBPhSNS showed that they presented similar oxidative properties, which enabled their corresponding electrochemical polymers to exhibit similar electrochromic properties. The UV-vis spectra of the corresponding polymers showed that both pPhSNS and pBPhSNS possessed similar optical absorption and similar multicolor switching between yellow (-0.8 V), greyish-green (0.9 V) and gray (1.1 V) colors. Besides, pPhSNS and pBPhSNS showed fast switching times of 0.57 s and 0.93 s at 1100 nm, respectively and reasonable contrasts of 46% and 31% at 1100 nm, respectively. These investigations may help understand the relationship between structural configuration and the electrochemistry/electrochromic properties for polymer electrochromic (PEC) materials research.     

A soluble and multichromic conducting polythiophene derivative

A new soluble polythiophene derivative was synthesized by both chemical and electrochemical oxidative polymerization of 1-4-nitrophenyl-2,5-di(2-thienyl)-1H-pyrrole (SNSNO₂). Chemical method produces a polymer which is completely soluble in organic solvents. The structures of both the monomer and the soluble polymer were elucidated by ¹H and ¹³C-NMR and FTIR. The average molecular weight has been determined by GPC to be Mn = 6.3 × 10³ for the chemically synthesized polymer. P(SNSNO₂) was also synthesized via potentiostatic electrochemical polymerization. Characterizations of the resulting polymer were performed by cyclic voltammetry CV, FTIR and UV-Vis spectroscopy. Four-probe technique was used to measure the conductivities of the samples. Moreover, the spectroelectrochemical and electrochromic properties of the polymer film were investigated. In addition, dual type polymer electrochromic devices ECDs based on P(SNSNO₂) with poly3,4-ethylenedioxythiophene (PEDOT) were constructed. Spectroelectrochemistry, electrochromic switching and open circuit stability of the devices were studied. They were found to have good switching times, reasonable contrasts and optical memories.