A series of alkyl-substituted and unsubstituted poly(3,4-alkylenedioxythiophene)s were synthesized electrochemically using 3,4-alkylenedioxythiophene derivative monomers where either the size of the alkylenedioxy ring or the nature of the pendent group was varied. The specific systems studied include 3,4-ethylenedioxythiophene (EDOT), 2-methyl-2,3dihydrothieno [3,4-b][1,4] (BuDOT-Xyl). Optoelectrochemical experiments revealed that the nature of the substitution on the polymers had little effect on the extent of conjugation of the backbone as evidenced by electronic band gaps for all polymers of approximately 1.7 eV (730 nm). These electrochromic polymers switch from a relatively transmissive light green in the oxidized form to an opaque dark blue in the reduced form, with the highest electrochromic contrast ratios accessible for PBuDOT and PEDOT-C 14 H 29 . Multiple switching studies monitoring the electrochromic contrast showed that ca. 300 nm thick polymer films could be fully switched between their reduced and oxidized forms in 0.8-2.2 s with ∆%T of 44-63%. In situ conductivity studies carried out on relatively thick polymer films (2.7-9.5 µm) deposited between large gap (200 µm) lateral growth electrodes demonstrated the lowpotential turn-on for these materials, and maximum conductivities of 0.2-12.1 S/cm were attained.

We report a method to measure the composite coloration efficiency of organic electrochromic polymers at 95% of the total optical density change measured at λmax. This practical method is useful for the comparison of organic polymers as well as inorganic electrochromic oxides and for gaining insights into the reasons for increased efficiencies in organic polymer systems. Three polymers from the family of the poly(3,4-alkylenedioxythiophenes) (PXDOTs) were chosen, due to their well-behaved electrochromic properties, to develop the tandem chronoabsorptometry/chronocoulometry method. Coloration efficiencies were measured by monitoring the amount of injected/ejected charge as a function of the change in optical density of the polymer film. The results of these experiments revealed a significant relationship between structure and coloration efficiency determined at λmax in organic polymers. Poly(3,3-dimethyl-3,4-dihydro-2H-thieno[3,4-b]dioxepine) (PProDOT-Me2) possessed the highest coloration efficiency (375 cm2/C) compared to poly(3,4-ethylenedioxythiophene) (PEDOT) (183 cm2/C) and poly(3,4-propylenedioxythiophene) (PProDOT) (285 cm2/C), due to a combination of larger changes in optical density at λmax and higher doping levels.

Electrochromics (ECs) are materials that exhibit varying colors when held at various potentials. [1] In order to be useful for applications, these materials must exhibit long-term stability, rapid redox switching, and large changes in transmittance between states (large D%T values). Many inorganic materials have been used as EC materials, but difficulties in processing and slow response times have created the need for different types of EC materials. Conjugated, redox-active polymers offer a different approach to EC materials. [1] These polymers are inherently electrochromic, and they can be switched electrochemically or chemically between different colored states. [2] Most of the well-studied conjugated polymers are anodically coloring, meaning they are more deeply colored in their oxidized form. Poly(thiophene) (PT) and its 3-substituted derivatives fall into this category. These polymers are red to purple in their reduced or neutral form, and dark blue to black in their oxidized form. Although this type of color change can be useful, a more desirable color change would be one where the polymer switches from a highly colored state to a highly transmissive state.Of the conducting polymers available, poly(3,4-ethylenedioxythiophene) (PEDOT) and its derivatives exhibit the most promising EC properties. When compared to PT, PEDOT exhibits more rapid switching, lower oxidation potentials, and greater stability at ambient and elevated temperatures. [3,4] In addition, PEDOT is a cathodically coloring polymer that is a dark opaque blue in its reduced form, and a very transmissive light blue in its oxidized form. [5±7] In our laboratory, we have successfully exploited the advantages of EDOT to synthesize many EC polymers. [8±10] We have shown that PEDOT can be used as a cathodically coloring polymer in dual-polymer EC devices with a D%T of 45 % at 620 nm. [11] Although other laboratories have studied PEDOT and other alkylenedioxythiophene derivatives, [7,12] our laboratory recently published the first exhaustive study of electrical, optical, and conductive properties of a large series of alkylenedioxythiophene derivatives. [13] We found that the D%T value of PEDOT can be improved significantly by increasing the alkylenedioxythiophene ring size or by incorporating substituents.Of the derivatives synthesized, poly(3,4-propylenedioxythiophene) (PProDOT) exhibited the greatest maximum in-situ conductivity, and because of its structure, it can be symmetrically disubstituted on the central carbon of the propylene bridge. [13] Our previous synthetic route did not allow for this disubstitution, but now we report the first disubstituted derivative, PProDOT±Me 2 . PProDOT±Me 2 exhibits an extremely high D%T value of 78 % at l max (578 nm), in fact the highest reported to date. We report here its optical properties, and compare them to PProDOT and the mono-substituted derivative, PProDOT±Me.The monomer synthesis is shown in Schemes 1a and 1b. ProDOT and ProDOT±Me were synthesized using the route illustrated in Scheme 1a, with ...

The ability to match two complementary polymers constitutes an important step forward in the design of electrochromic devices (ECDs). Here we show that the necessary control over the color, brightness, and environmental stability of an electrochromic window can be achieved through the careful design of anodically coloring polymers. For this purpose, we have constructed ECDs based on dimethyl substituted poly(3,4-propylenedioxythiophene) (PProDOT-Me 2 ) as a cathodically coloring layer, along with poly[3,6-bis(2-ethylenedioxythienyl)-N-methyl-carbazole] (PBEDOT-NMeCz) and N-propane sulfonated poly(3,4-propylenedioxypyrrole) (PProDOP-NPrS) as anodically coloring polymers. Comparison of the results shows that using PProDOP-NPrS as the high band gap polymer has several advantages over the carbazole counterpart. The main benefit is the opening of the transmissivity window throughout the entire visible spectrum by moving the π-π* transition of the neutral anodically coloring material into the ultraviolet region. Another advantage of the PProDOPNPrS based device is the noticeable increase in the optical contrast as evidenced by an increase in the transmittance change of the device (∆%T) from 56% to 68%, as measured at 580 nm. These devices exhibit a 60% change in luminance along with half-second switching times for full color change. Moreover, they were found to retain up to 86% of their optical response after 20 000 double potential steps, opening up new directions in optical technology.