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Article Cite This: Chem. Mater. XXXX, XXX, XXX−XXX

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Electrochromic Polymers Processed from Environmentally Benign Solvents Graham S. Collier, Ian Pelse, Anna M. Ö sterholm, and John R. Reynolds* School of Chemistry and Biochemistry, School of Materials Science and Engineering, Center for Organic Photonics and Electronics (COPE), Georgia Tech Polymer Network (GTPN), Georgia Institute of Technology, Atlanta, Georgia 30332, United States

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S Supporting Information *

ABSTRACT: The ability to process conjugated polymers from environmentally benign solvents is essential for making organic electronics commercially viable by reducing costs and enhancing safety in the printing and processing environment. To enhance the solubility of typically alkyl-functionalized redox-active and electrochromic polymers, poly(3,4-propylenedioxythiophenes) with ester-functionalized side chains were synthesized via direct arylation polymerization, resulting in polymers that are processable from 2-methyltetrahydrofuran, ethyl acetate, and propyl acetate. Optical and atomic force microscopy results of spray-processed films indicate that topological features, such as film roughness, can be manipulated via the vapor pressure of the processing solvent. The solvent choice affects the resulting onset of absorbance and relative intensities of vibronic features, which translates into distinctly observable and quantifiable color differences. While the color is sensitive to the casting solvent, the redox properties and onset of oxidation are fairly independent of the processing medium. Most notably, electrochromic properties, such as contrast and switching times, are not drastically affected by the casting solvent or underlying morphologies. Independent of casting solvent, each polymer exhibited a transmittance change greater than 70% at λmax in the oxidized state with switching speeds of ∼2 s for 2 cm2 films in organic electrolytes. This work highlights the synthetic tailorability of the poly(3,4-propylenedioxythiophene) family of materials to introduce functional groups that improve processability without sacrificing electrochromic performance.

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INTRODUCTION Conjugated polymers are attractive for solid-state electronic applications, such as organic photovoltaics (OPVs),1 organic light-emitting diodes (OLEDs),2 and organic field-effect transistors (OFETs),3 as well as redox-active applications such as electrochromism,4,5 charge storage,6 and bioelectronics7,8 due to the potential of simultaneously manipulating photophysical and redox properties through synthetic design. There have been extensive efforts to generate structure− property relationships,4,9 processing methods,10 and morphological characteristics11,12 to improve the efficiency of lab-scale, conjugated polymer-based devices. However, manufacturing cost and environmental impact of reagents, solvents, or purification processes are often not considered which keep many of the “best” materials commercially unviable. For conjugated polymers to achieve commercial scalability, they should be designed to maintain the same performance when processed from environmentally benign or renewable feedstock solvents (so-called “green solvents”) as an alternative to traditional halogenated and nonhalogenated aromatic solvents.13,14 Such solvents include 2-methyltetrahydrofuran (2Me-THF), which is derived from furfural biomass, or polar media such as water, alcohols (methanol), or esters (ethyl acetate, propyl acetate).13,15 While solubility constraints gen© XXXX American Chemical Society

erally hinder processing from green solvents, there are examples of the successful design of conjugated polymers that are soluble in polar media and exhibit respectable performance as the active layer material for OPVs, OFETs, and hole-transporting layers for perovskite solar cells.16−19 The successes exhibited for these solid-state applications set the precedent to find similar solutions for other conjugated polymer technologies, demonstrated here for electrochromic polymers (ECPs). In regards to environmentally benign processing conditions, our group has made a concerted effort to design water-soluble poly(3,4-propylenedioxythiophene)s (PProDOTs) and polythiophenes for electrochromic devices, charge storage applications, and field-effect transistors.14,20−23 This approach has generally consisted of taking advantage of an organic soluble precursor with cleavable side chains, which upon saponification generates a polymer soluble in water. After depositing the polymer on an electrode, the film can be rendered solvent resistant with a mild acid wash22−24 or irradiation of a photocleavable functional group with UV Received: April 27, 2018 Revised: June 22, 2018

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DOI: 10.1021/acs.chemmater.8b01765 Chem. Mater. XXXX, XXX, XXX−XXX

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Chemistry of Materials light.14 Notably, there are no drastic differences in photophysical and electrochromic properties of the studied materials. Other groups also have successfully processed conjugated polymers from water by utilizing side chain defunctionalization strategies or by introducing ionic side chains to PProDOT or poly(3,4-ethylenedioxythiophene) (PEDOT) backbones and testing their resulting electrochromic behavior.25−27 While these studies are an important step toward environmentally benign processing conditions, additional postpolymerization treatments and elevated temperatures needed to dry the films after processing from water22 can be undesirable, which has led to a vast majority of conjugated polymers studied for electrochromic applications being deposited from organic solvents such as toluene or chloroform. In order to address the processing restraints of ECPs, a robust design strategy needs to be developed to improve solubility in “green” solvents. In our early efforts to design cleavable side chains for solvent resistant ECPs, we developed ester-functionalized PProDOTs that were found to be readily soluble in a wide range of solvents including ethyl acetate,24 which is a recommended solvent as highlighted by the Innovative Medicines Initiative (IMI)-CHEM21 (a public−private partnership that promotes sustainable biological and chemical methodologies) solvent guide.15 However, multilayer devices were manufactured by spray coating from the aromatic solvent toluene, so the viability of using polar solvent media for deposition remained unknown. This preliminary work motivates us to further study the effect of ester functionalization on the ability to process conjugated polymers from nonaromatic and nonhalogenated solvents. In this vein, we have synthesized two PProDOT polymers: one copolymer with 50% butyloctylester (BOE) and 50% ethylhexyloxy (EtHx) content (BOE-co-EtHx), in an effort to tune solubility without compromising color, and a second butyloctylester-functionalized homopolymer (BOE), both via direct (hetero)arylation polymerization (DHAP), to investigate the effect of ester functionality on processability and electrochromic properties (see Scheme 1 for representa-

logical, absorption, and color properties are sensitive to the processing solvent, switching times and contrast are not drastically affected when processing from the more environmentally benign solvents. This work paves the way for further development of ECPs with functionality that enables processing from environmentally friendly solvents.

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RESULTS AND DISCUSSION Monomer and Polymer Synthesis. Synthesis of esterfunctionalized ProDOT monomers was performed using the strategy described in our previous work and is outlined in Scheme S1.24 Briefly, 2-butyloctanoic acid was synthesized by oxidizing 2-butyl-1-octanol under Jones oxidation conditions. After extraction, the carboxylic acid was isolated with a yield of 75%. The dihydro-ProDOT-BOE monomer (ProDOT-BOEH2) was then synthesized via the esterfication reaction of Br2ProDOT with 2-butyloctanoic acid in the presence of K2CO3 with an 86% yield. Subsequent bromination of ProDOT-BOEH2 with N-bromosuccinimide (NBS) in THF generated the dibromo ProDOT monomer (ProDOT-BOE-Br2) with a 71% yield. Polymerizations were performed via DHAP conditions commonly used to synthesize poly(ProDOT)s, as shown in Scheme 2.28 Reactions were performed in N,N-dimethylScheme 2. Synthesis of BOE-co-EtHx and BOE via Direct Arylation Polymerization

Scheme 1. A Representation of Structure Variations To Enable Processing from Environmentally Benign Solvents acetamide (DMAc) at 140 °C with palladium(II) acetate (Pd(OAc)2) as the catalyst, potassium carbonate (K2CO3) as the base, and pivalic acid (PivOH) as the proton shuttle. As shown in Figures S7 and S8, 1H NMR confirmed the structures of the synthesized polymers. Notably, BOE exhibits a small shoulder at 4.3 ppm, which corresponds to the protons adjacent to the ester moiety experiencing differing proton shielding effects. Polymerizations produced BOE-co-EtHx with Mn = 149.8 kg/mol and dispersity (Đ = Mw/Mn) of 1.7 and BOE with Mn = 81.6 kg/mol and Đ = 1.8, measured via sizeexclusion chromatography (SEC) relative to polystyrene standards using THF as the eluent (see Figures S9 and S10 for SEC elugrams). Each polymer exhibits solubility greater than 50 mg/mL in toluene and 2-Me-THF, while BOE is also soluble in ethyl acetate and propyl acetate at concentrations greater than 50 mg/mL (see Table S1). The solubility exhibited in the respective solvents indicates this family of ProDOT polymers is amenable to a variety of processing techniques such as spray coating, spin coating, or blade coating that all have different viscosity and polymer concentration requirements.

tive structures). DHAP is considered to be a more environmentally viable synthetic approach for conjugated polymers compared to traditional synthetic pathways, such as Stille or Suzuki cross-coupling polymerizations, via decreasing the number of synthetic steps and toxic byproducts, such as trialkyltin halide products from the Stille cross-coupling reaction.28−32 The ester-functionalized polymers’ solubility in green solvents, optical and electrochemical properties, and morphological features are studied and compared to the alkoxy-functionalized analogues. We show that while morphoB


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Chemistry of Materials

Figure 1. Film appearance and morphology of BOE films spray cast from (row 1) toluene, (row 2) 2-Me-THF, (row 3) ethyl acetate, and (row 4) propyl acetate. Physical scale decreases from left to right, starting with a photograph, to large and small optical micrographs, and finally an AFM micrograph. The films were cycled using CV 10 times in 0.5 M TBAPF6/PC before recording the images.

respectively, while films cast from toluene and propyl acetate are more homogeneous. Contact angle measurements were performed, and it was found that films cast from 2-Me-THF and ethyl acetate have slightly larger contact angles (109.9 ± 3.0° and 104.5 ± 2.0°, respectively) compared to films cast from toluene and propyl acetate (94.9 ± 2.4° and 84.7 ± 2.0°, respectively), indicating that the films with higher surface roughness are more hydrophobic35,36 (see Figure S11 and Table S2). Atomic force microscopy was then used to probe the topography of the films cast from each of the four solvents. The AFM images in Figure 1 confirm that as the evaporation rate of the solvent increases, the roughness of the polymer films also increases on the micrometer scale. The topography of films cast from toluene and propyl acetate (vapor pressures of 22 mmHg vs 25 mmHg at 20 °C for toluene and propyl acetate, respectively) appear homogeneous and exhibit roughness (Rq) values of ∼11 nm. Films processed from 2-Me-THF and ethyl acetate, on the other hand, are slightly rougher with Rq values of ∼36 and ∼63 nm, respectively. As shown in Figure S12, upon additional investigation of the films on the 500 nm scale, the rougher films exhibit pitlike features while the

Effects of Casting Solvent on Film Morphology. Because of the favorable solubility of BOE in all of the target solvents, the solid-state features of the resulting BOE films cast from toluene, 2-Me-THF, ethyl acetate, and propyl acetate were studied using contact angle measurements, optical microscopy, and atomic force microscopy (AFM) to determine the effect of casting solvent on surface energy and film topography. The first characteristic noticed was that films cast from solvents with lower boiling points and higher vapor pressures have a higher degree of haze. These observations were confirmed by measuring the diffuse transmittance using various sample configurations with an integrating sphere.33 For example, films cast from ethyl acetate (bp = 77 °C, vapor pressure = 73 mmHg at 20 °C) have haze values of ∼6% while films cast from propyl acetate (bp = 102 °C, vapor pressure = 25 mmHg at 20 °C) exhibit haze values of ∼2%. The increased haze for films cast from lower boiling point solvents indicates that these films are more heterogeneous with larger domain sizes compared to films cast from toluene, which can be confirmed by comparing the optical micrographs in Figure 1.12,34 Specifically, films cast from 2-Me-THF and ethyl acetate (Figure 1b,c) possess aggregate features of 10 and 5 μm, C


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Figure 2. UV−vis spectra of (a) EtHx and (b) BOE spray cast from toluene (black), 2-Me-THF (red), ethyl acetate (blue), and propyl acetate (green). Solid lines correspond to as-cast films while dashed lines represent films that have been cycled 10 times between −0.5 and 0.8 V in 0.5 M TBAPF6/PC at 50 mV/s.

Table 1. Electrochromic Properties of ProDOT Polymers as Electrochemically Conditioned Films L*, a*, b* polymer EtHx BOE-co-EtHx BOE

casting solvent

Eox onset (V)

ΔTa (%)

bleaching t95 (s)

coloration t95 (s)

toluene 2-Me-THF toluene 2-Me-THF toluene 2-Me-THF ethyl acetate propyl acetate

0.10 0.08 0.07 0.08 0.11 0.11 0.11 0.09

73 71 76 74 76 75 79 79

1.3 1.2 1.9 1.6 1.8 1.8 1.2 2.2

3.4 2.0 1.4 1.9 1.9 2.1 1.8 2.6

neutral state 48, 47, 40, 39, 42, 43, 44, 39,

56, 50, 68, 51, 41, 46, 53, 60,

−38 −41 −50 −50 −52 −53 −54 −55

oxidized state 90, 91, 94, 90, 92, 91, 93, 92,

−1, −5 −2, 5 −1, −3 −1, −4 −0.4, −4 −0.3, −4 −0.8, −3 −0.9, −3

a

Films were initially sprayed to transmittances of 5−10 %T. After electrochemical conditioning, transmittance values of 2−6 %T were measured.

blue-shifted as the temperature increases from 25 to 100 °C (Figures S15−S17). The absorbance spectra of spray cast films were also investigated (see Figure S18); all three polymers display two well-defined peaks and are red shifted compared to their respective solution spectra. The change in optical properties of the films compared to solution is attributed to increased π−π interactions in the solid state. As the ester content increases, the intensity of the lower energy transition at ∼600 nm also increases, which is indicative of the ester-functionalized polymers having closer interchain interactions compared to EtHx-functionalized ProDOTs. This characteristic is further observed when comparing electrochemically conditioned films to pristine films. As shown in Figure 2a, the absorbance profiles of EtHx films cast from toluene and 2-Me-THF are essentially identical, both in their as-cast and in their electrochemically conditioned forms. In contrast, while the absorbance properties for films of BOE-co-EtHx cast from toluene and 2-MeTHF are identical in the as-cast state (Figure S19), films cast from toluene exhibit a larger increase in absorbance after being electrochemically conditioned. The difference in the relative intensity of the vibronic peaks after electrochemical conditioning for BOE-co-EtHx and EtHx indicates that the ester functionality promotes larger changes in intermolecular interactions in the solid state upon electrochemical conditioning. The absorbance properties of BOE show clear differences based on the casting solvent (Figure 2b). First, the films cast from 2-Me-THF, ethyl acetate, and propyl acetate exhibit a

homogeneous films have less distinct features. These findings demonstrate that green solvents can be substituted for aromatic solvents and generate similar morphologies by choosing solvents with comparable vapor pressures, which may be advantageous for applications that have specific requirements for the level of haze that is acceptable. Furthermore, varying the vapor pressure of the processing solvent allows for manipulation of the appearance of films deposited via spray coating, which will be helpful in fine-tuning the aesthetic features of application specific ECP films. Effects of Casting Solvent on Optical and Electrochemical Properties. In addition to differences observed in the large-scale morphology, the hue of the films varied depending on the casting solvent as shown in the photographs in Figure 1. To understand these differences, the optical absorbance properties of BOE were investigated in solution, and as thin films, using UV−vis spectroscopy. As shown in Figure S13, the λmax of BOE in solution varies from ∼530 to ∼550 nm, and there is also a shoulder peak at ∼570 nm in ethyl acetate and propyl acetate solutions due to varying degrees of aggregation in the different solvents.24,28,37 Notably, the intensity of the shoulder peak increases from BOE, to BOE-co-EtHx, to EtHx when we compare the three polymers in toluene (see Figure S14), indicating that BOE is the most solvated due to the ester functionalities present on each repeat unit. Thermochromic measurements verified the presence of aggregates due to the distinct changes in the spectra, specifically the disappearance of the 570 nm shoulder and formation of a broad, featureless absorbance profile that is D


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Figure 3. Cyclic voltammograms of (a) films as-cast and (b) films cycled 10 times between −0.5 and 0.8 V of BOE spray cast from toluene, 2-MeTHF, ethyl acetate, and propyl acetate in 0.5 M TBAPF6/PC at 50 mV/s.

Figure 4. (a) Color coordinates of ProDOT polymer films cast from toluene obtained as a function of potential in 0.5 M TBAPF6/PC and (b) L* of the ProDOT polymer films spray cast from toluene as a function of potential in 0.5 M TBAPF6/PC. (c) Photographs of EtHx (top), BOE-coEtHx (middle), and BOE (bottom) films cast from toluene.

agreement with the blue-shifted absorbance spectra and vibronic peak ratios observed in the UV−vis absorbance spectra of the as-cast films in Figure 2b. However, after electrochemical conditioning, the onset of oxidation is almost identical (0.07−0.11 V vs Ag/Ag+) regardless of the casting solvent. Furthermore, as shown in Figure 3, for BOE, the CV traces are nearly identical in shape and current density after electrochemical conditioning, independent of the processing solvent. As shown in Figure S20, both EtHx and BOE exhibit a large oxidation of ∼0.2 V when cast from toluene, but EtHx exhibits a second oxidation at ∼0.4 V. The most notable difference seen in the cyclic voltammograms is the current density: while BOE and EtHx have similar CV traces, the current density measured for BOE-co-EtHx is significantly lower when processed from toluene (see Figure S20). However, when all three polymers are cast from 2-Me-THF to a transmittance (%T) ≈ 3−6%, ’each polymer exhibits a peak current density of ∼0.3 mA/cm2. The similarity of the current density for each polymer when cast from 2-Me-THF, in contrast to the varied current density when cast from toluene, indicates the processing solvent generates differences in the underlying morphologies that determine the redox capacity of a film. This is related to similar variations in the

blue-shift in the absorbance spectra in the as-cast state when compared to films cast from toluene as well as differences in the intensity ratio of the vibronic features (see inset of Figure 2b). After electrochemical conditioning for 10 cyclic voltammetry (CV) cycles, the spectra red shift, and the intensity ratio between the 600 nm and the 550 nm peaks (λ600/λ550) change from λ600/λ550 ≈0.9−1.0 to ≈1.1− 1.3. The differences observed in the spectra are due to the varying evaporation rates of the four solvents that lead to the morphological differences in Figure 1, since the evaporation rate of the solvent affects the polymer organization in the solid state.12,34 This demonstrates that while these ProDOT polymers exhibit varying degrees of aggregation in solution based on the choice of solvent, the differences in the underlying film morphology and the optical properties are dependent on the vapor pressure of the casting solvent and not polymer conformation in solution. Next, the redox properties of the polymers were evaluated by CV. As shown in Table 1 and Figure 3a as well as Figures S20−S22 (for EtHx and BOE-co-EtHx) the onset of oxidation for the films cast from 2-Me-THF, ethyl acetate, and propyl acetate, in the case of BOE, is slightly higher (∼0.05 V vs. Ag/ Ag+) when compared to films cast from toluene, which is in E


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Figure 5. (a) Color coordinates and (b) L* as a function of potential in 0.5 M TBAPF6/PC for BOE films spray cast from toluene, 2-Me-THF, ethyl acetate, and propyl acetate. (c) Photographs of films cast from toluene (top), 2-Me-THF (top-middle), ethyl acetate (bottom-middle), and propyl acetate (bottom).

underlying morphology of films prepared using different processing techniques that leads to a different number of accessible redox-active sites.10 The changes in absorbance as a function of potential from −0.5 to 0.8 V were evaluated for the polymers cast from the various solvents. At ∼ 0.1 V, which corresponds to the onset of oxidation measured by CV, the neutral state absorption band in all three polymers begins to decrease in intensity, which is accompanied by the formation of cation radicals (polarons) around 800−1000 nm and ultimately the formation of dications (bipolarons) at wavelengths greater than 1400 nm, for each polymer regardless of casting solvent, as seen in Figures S23−S25. As shown in Figure S26, for BOE films cast from the four different solvents, each film transitions from a colored state at −0.5 V to a highly transmissive, color neutral state at 0.8 V. However, as shown in Figures S23−S25, there are slight differences in spectra from 400 to 650 nm, specifically in the vibronic peak ratios during oxidation, that manifest themselves in the color properties. Colorimetric analysis of the polymer films based on the “Commission Internationale de l’Eclairage” 1976 L*a*b* color standards was used to evaluate the effect of casting solvent on the perceived color of EtHx, BOE-co-EtHx, and BOE.21 As shown in Table 1, Figure 4a, and Figures S27−S28, each polymer exhibits a large a* value (∼60) as a pristine film that decreases to ∼40 for BOE after 10 CV cycles. In an effort to benchmark the three polymers, the L*a*b* values of neutral state films cast from toluene were compared. The polymers follow a trend of decreasing a* and b* values going from EtHx > BOE-co-EtHx > BOE. This decrease results in the films appearing bluer as the ester content in increased, as shown in Figure 4c. This is in good agreement with the UV−vis spectra in Figure S18, where the low-energy absorbance transition increases with increasing ester content. The quantitative difference in color between the films, ΔE*ab, was calculated according to eq S1. A ΔE*ab value larger than 2.3 means that two colors are noticeably different to the human eye.38,39 As shown in Table S3, the quantified color difference for films cast from toluene is significantly larger than 2.3. BOE-co-EtHx and BOE exhibit ΔE*ab = 19.0 and ΔE*ab = 21.3 compared to EtHx, respectively, while BOE-co-EtHx and BOE have a ΔE*ab = 27.0.

While the ability to reach a highly transmissive oxidized state was not affected by the casting solvent, the film color revealed a dependence on the choice of solvent. As shown in Figures S27 and S28, films of EtHx and BOE-co-EtHx have slightly larger a* values (a redder color) when processed from toluene compared to 2-Me-THF, which is attributed to the onset of absorbance (λonset) beginning at lower energy for films cast from 2-Me-THF. As shown in Figure 5a, the a* value for BOE increases when cast from 2-Me-THF, ethyl acetate, and propyl acetate. This is also observed in Figure 5c which shows a clear progression of the color change going from toluene (top) to propyl acetate (bottom). However, the b* and L* values (Figure 5b) do not drastically differ while varying the casting solvent for any of the ProDOT polymers. The differences of the a* values for this family of polymers are due to the slight differences in the λonset and λmax ∼ 600 nm as measured with UV−vis absorbance spectroscopy (Figure 2). As shown in Table S4, the BOE films have ΔE*ab values larger than 2.3 when changing the casting solvent. The large calculated differences are in good agreement with the qualitative observations and quantitative analysis described above. The brightness of the ProDOT polymers was investigated by evaluating the L* value as a function of potential. As highlighted in Figures 4b and 5b, each polymer achieves a fully transmissive state around 0.4 V. While the films range from 2%T to 6%T in the colored state, they are all able to reach L* values ≥90 and Δ%T values ∼70% across the visible spectrum. The switching rate of the ProDOT polymers was studied by monitoring the change in transmittance (ΔT (%)) at a single wavelength as a function of time by applying square-wave potential steps (−0.5 to 0.8 V vs Ag/Ag+ in 0.5 M TBAPF6/ PC) to polymer films spray cast onto ITO electrodes (see Supporting Information for area and resistance details) for periods of 10, 5, 2, 1, 0.5, and 0.25 seconds (s). As shown in Figures S29−S31, at switching times above 2 s each polymer exhibits ΔT values >70%. As the switching time is decreased to 0.25 s, the measured ΔT values also decrease, as expected. Furthermore, as shown in Table 1, each ProDOT polymer exhibits a bleaching time of less than 2 s and a coloration time of 2−3 s to reach 95% of a full-contrast switch (t95). The similar ΔT and t95 values for this family of ProDOT polymers F


Chemistry of Materials are an indication that although the photophysical and color properties of the polymers vary depending on the casting solvent, the electrochromic properties such as contrast and switching speed are minimally affected.

CONCLUSIONS Introducing polar functionalities to the side chains of conjugated polymers used for electrochromic applications is a promising route for increasing their solubility in and processing from more environmentally benign solvents. For conjugated polymers to find commercial viability, it will be useful to have them designed so that processing from nonaromatic and nonhalogenated solvents is achievable to increase safety and decrease environmental impacts. In an effort to address this problem, ester-functionalized PProDOTs were synthesized via direct (hetero)arylation polymerization conditions, yielding the polymer BOE that was readily soluble in ethyl acetate and propyl acetate. Studies of the materials cast from the various solvents revealed minimal differences in electrochemical properties, but distinct changes in the UV−vis absorbance and color properties, ostensibly due to variations in polymer organization in the solid state brought on by the different evaporation rates of the casting solvents. However, the electrochromic switching properties, such as transmittance and switching speed, were found to be independent of the casting solvent, as the polymers maintained ΔT values greater than 70% and switching speeds of ∼2 s on 2 cm2 sized electrodes. These results set the precedent for designing, through thoughtful side chain engineering, electrochromic polymers that are processable from environmentally benign solvents without postpolymerization modifications. Furthermore, by showing that the redox properties are not affected by changing the side chain, it stands to reason ester-functionalized ProDOT monomers can be used for a variety of redox-active applications, such as supercapacitors, to improve processability without sacrificing redox properties.

ACKNOWLEDGMENTS

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REFERENCES

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.chemmater.8b01765.

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Funding from NxN Licensing Inc. for this work is acknowledged. We gratefully acknowledge Dr. James F. Ponder, Jr., for helpful discussions regarding the synthesis and SEC measurements. Ian Pelse was supported by the Department of Defense (DoD) through the National Defense Science & Engineering Graduate Fellowship (NDSEG) Program.

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Materials and methods, synthetic procedures, 1H and 13 C of monomers and polymers, UV−vis and thermochromic measurements of polymer solutions, spectroelectrochemistry plots, switching kinetics, cyclic voltammetry traces, and contact angle data (PDF)

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (J.R.R.). ORCID

John R. Reynolds: 0000-0002-7417-4869 Notes

The authors declare the following competing financial interest(s): Electrochromic polymer technology developed at the Georgia Institute of Technology has been licensed to NXN Licensing. J.R.R. and A.M.O. serve as consultants to NXN Licensing. G


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