A review of electrochromic (EC) polymers and their applications in absorption/transmission, reflective, and patterned electrochromic devices (ECDs) is presented. Fundamental properties of EC materials such as optical contrast, coloration efficiency, switching speed, and stability are described along with the commonly used characterization methods. The origin of electrochromism in conjugated polymers is explained in terms of the electronic structure changes in the backbone upon doping/dedoping. The ability to tailor the EC properties of conjugated polymers and tune their color states via modification of the polymer structure is demonstrated. Multicolor electrochromic materials can be obtained by substitution of a parent polymer and controlled polymerization of comonomers and with blends and laminates of homopolymers. Absorption/transmission-type ECDs from complementarily colored polymers and reflective-type ECDs on metalized substrates are illustrated with several examples from the literature. Finally, several patterning methods that are promising for ECD applications are discussed. Examples of ECDs constructed from patterned electrodes using line-patterning, screen-printing, and metal vapor deposition techniques are investigated for their possible use in commercial applications.

Four new disubstituted propylenedioxythiophene polymers have been synthesized by Grignard metathesis on the 1−5 g scale. All polymers were found to be soluble in chloroform, methylene chloride, toluene, and tetrahydrofuran and were fully structurally characterized having GPC determined number-average molecular weights ranging from 33000 to 47000 g mol-1. Dilute polymer solutions in toluene exhibited strong red fluorescence with moderate quantum efficiencies from 0.38 to 0.50. Homogeneous thin films were formed by electropolymerization and spray casting polymer solutions onto ITO coated glass slides at thicknesses of ca. 150 nm. The films were electroactive, switching from a dark blue-purple to a transmissive sky blue upon p-doping, often with subsecond switching times, and high electrochromic contrast luminance changes (% ΔY) of 40−70%. These studies revealed that the branched derivatives, [poly(3,3-bis(2-ethylhexyl)-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine)] and [poly(6,8-dibromo-3,3-bis(2-ethylhexyloxymethyl)-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine)], gave an electrochemical response and associated color change over a much smaller voltage range in comparison to the linear chain substituted derivatives, [poly(3,3-dihexyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine)] and [poly(3,3-bis(octadecyloxymethyl)-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine)]. Composite coloration efficiency values were found up to 1365 cm2/C; this was considerably larger than values obtained from previously studied alkylenedioxythiophene based polymers (∼375 cm2/C).

Electrochromic devices (ECDs) utilizing conjugated polymers as electroactive layers have received increased attention owing to their ease-of-color-tuning properties, fast switching times, and high contrast ratios. Our group has recently reported polymer-based ECDs, [1±4] including a transmissive/absorptive-type complimentary colored polymer ECD with an overall colorimetrically determined luminance change of 55 % in the visible region, which can be switched more than 20 000 times between its colored and transmissive states.[4] Throughout the world, a number of groups have utilized electrochromic (EC) polymers as at least one component of an ECD.[5±11]Traditionally, indium tin oxide (ITO) on either glass or plastic has been used as the electrode material in ECDs and electrochromic polymers were deposited electrochemically or cast from solution. While previous workers have claimed all-polymer ECDs, [6±8,12,13] their devices comprised ITO as the electrode material as no suitable highly conducting and transmissive organic polymer was available. Here, we report the construction and characterization of the first truly all-polymer ECD by replacing ITO with a conducting polymer, namely, poly(3,4-ethylenedioxythiopene)±poly(styrene sulfonate) (PEDOT±PSS). Since its discovery in the late 80 s, [14,15] PEDOT has proven to be an outstanding polymer for its electrochromic properties, high conductivity, and high stability in the doped form.[16] It has already found useful applications as antistatic film coatings, [17,18] electrochromic windows, [19] and as a hole-injection material in polymer OLEDs and PLEDs. [20] Further, water-soluble PEDOT derivatives have been used as polyelectrolytes in layer-by-layer assembled systems for electrochromic applications. [21,22] Here, we report on the use of PEDOT±PSS complex as the electrode material for polymer-based ECDs in order to form a device that is fully constructed from organic and polymeric components. We use a PEDOT±PSS aqueous dispersion (Agfa-Gevaert), as the resulting films are highly transmissive in the visible region, have high conductivity, and are unreactive (do not dedope) under the electrochemical conditions employed. Importantly, when used as the electrode material, PEDOT±PSS films do not return to the non-conducting form in the ECD's operating voltage range. In order to evaluate the suitability of PEDOT±PSS films as electrode materials, the films were first subjected to a reductive potential (±1. ) were obtained relative to those that we observe for switching the EC polymers (~3 mA cm ±2 ), indicating that the PEDOT±PSS electrodes are not redox active in this potential window. Once dried, they are well adhered to the plastic substrate and are insoluble in water and the electrolyte solutions used for electrochemical deposition and switching of EC polymers. Using PEDOT±PSS as the electrode material brings about the advantages of making flexible, stable, and truly all-organic ECDs.5The conductivity of the PEDOT±PSS films was determined both from spin-coated films of PEDO...

Star polymers with globular architecture and multiple arms are among the simplest forms of polymers with branched topologies. The combination of their unique architecture and high local densities of active functional groups makes star polymers unique candidates for a diverse range of applications. In this article, we describe the synthesis of star polymers with precisely controlled structures via atom transfer radical polymerization (ATRP) using the one-pot arm-first method. Specifically, two types of highly defined, high charge density star polymers with oppositely charged arm structures were prepared: poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) star and poly(acrylic acid) (PAA) star polymers with cross-linked cores. By exploiting the electrostatic interactions between the polyelectrolyte arms, we have integrated the PDMAEMA star and PAA star polymers within alternating multilayer thin films using layer-by-layer (LbL) assembly to generate all-star polyelectrolyte LbL films. The prepared star/star multilayer films illustrate nonuniform and nanoporous structures, which result from the characteristic architecture of star polymers. The thickness, porosity, and refractive index of star/star multilayer films are precisely tunable by assembly pH conditions. Furthermore, as-assembled star/star multilayer films exhibit distinct morphological changes by undergoing extensive structural reorganization upon post-treatment under different pH conditions that do not lead to any changes with their linear compositional counterparts; it is hypothesized that these differences are due to the star polyelectrolyte's compact structure and decreased extent of entanglement and interpenetration, which lead to a low degree of ionic cross-linking compared to their linear counterparts. The pH-responsive structural changes of the films are characterized by AFM, SEM, and FTIR. Finally, we have observed an enhanced ionic (proton) conductivity of star/star multilayers following the pH-induced structural reorganization.

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Layer-by-layer (LbL) assembly has recently attracted great attention as a promising method to form defect-free and highly conformal coatings. 1,2 The technique has advantages in chemically controlling the nanoscale local structure, film morphology, and thickness and incorporating a wide range of functional materials. LbL assembly can be driven by either electrostatic or hydrogen bonding. In the first case, the multilayer coating is created by alternatively dipping the substrate into solutions of oppositely charged polyelectrolytes. Assembly by hydrogen bond is applied for compounds of which hydrogen-donor and hydrogen-acceptor groups are available. Control of film growth can be obtained through adjustment of the assembling parameters, such as solution pH for "weak" polyelectrolytes 3,4 or solution ionic strength for "strong" polyelectrolytes, 5,6 and deposition temperature. 7 A wide range of applications utilizing LbL assembly as a fabrication technique has been reported, such as electrochromic devices, 8 solid-state ionic electrolytes, 9,10 proton-exchange membranes for fuel cells, 11 loading/delivery vehicles for biological compounds, 12,13 adhesive layers for cells, 14 humidity sensors, 15 and other nanostructure and microstructure materials. 16,17 Of these applications, electrochromic (EC) devices can benefit most from the LbL assembly, because both electrochromic and electrolyte layers have been successfully formed via this method. 8À10 Currently, high-performance electrochromic devices have been dependent on the use of gel or liquid electrolytes. Although a great

The emergence of electroactive and conducting polymers offers new opportunities for the design of materials for electrochromic devices (ECDs). Of these, poly(3,4-alkylenedioxythiophene)s (PXDOTs) and their derivatives exhibit the most promising electrochromic (EC) properties. Here, we report the use of highly porous metallized membranes which allow the production of patterned, rapid-switching, reflective ECDs. Using poly(3,4-ethylenedioxithiophene) (PEDOT), poly(3,4-propylenedioxythiophene) (PProDOT), and the dimethyl-substituted derivative PProDOT-Me2 as the active EC materials, we have obtained switching times of 0.1−0.2 s (5−10 Hz) to achieve full EC contrast. These polymers yield reflective contrast values of up to 90% in the NIR and ∼60% in the visible regions. In addition, the ECDs were switched repetitively 180 000 times with less than 10% contrast loss. We have also demonstrated a 2 × 2 pixelated display device built using shadow mask patterning. Two cathodically coloring polymers which exhibit two distinct colors in their neutral states (blue and red) are patterned on a porous metallized electrode to yield a highly contrasted surface. Upon simultaneous oxidation of these polymers, the bi-color surface is rapidly bleached presenting a uniform shiny gold surface.