Four Shades of Brown: Tuning of Electrochromic Polymer Blends Toward High-Contrast Eyewear Anna M. O ̈ sterholm,* ,† D. Eric Shen, †,‡ Justin A. Kerszulis, † Rayford H. Bulloch, † Michael Kuepfert, § Aubrey L. Dyer, ∥ and John R. Reynolds* ,† † School of Chemistry and Biochemistry, School of Materials Science and Engineering, Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, Georgia 30332, United States ‡ BASF-SE c/o InnovationLab GmbH, Heidelberg 69115, Germany § Re-synthesis Laboratory, NC/IS, BASF Corporation, Tarrytown, New York 10591, United States ∥ Department of Natural Sciences, Clayton State University, Morrow, Georgia 30260, United States * S Supporting Information ABSTRACT: We report a straightforward strategy of accessing a wide variety of colors through simple predictive color mixing of electrochromic polymers (ECPs). We have created a set of brown ECP blends that can be incorporated as the active material in user-controlled electrochromic eyewear. Color mixing of ECPs proceeds in a subtractive fashion, and we acquire various hues of brown through the mixing of cyan and yellow primaries in combination with orange and periwinkle-blue secondary colors. Upon oxidation, all of the created blends exhibit a change in transmittance from ca. 10 to 70% in a few seconds. We demonstrate the attractiveness of these ECP blends as active materials in electrochromic eyewear by assembling user-controlled, high-contrast, fast-switching, and fully solution-processable electrochromic lenses with colorless transmissive states and colored states that correspond to commercially available sunglasses. The lenses were fabricated using a combination of inkjet printing and blade-coating to illustrate the feasibility of using soluble ECPs for high-throughput and large-scale processing. KEYWORDS: electrochromic polymers, dioxythiophenes, color mixing, electrochromic eyewear, electrochromic devices, organic electronics ■ INTRODUCTION Electrochromics for user-controlled smart wearable electronics target diverse markets, ranging from electrochromic fabrics and lenses for consumer fashion, to military camouflage and visors that require rapid response adaptive technology. In the field of color changing eyewear, the most widespread products are photochromic lenses, which reversibly change between colored states in response to changes in light. These glasses can either transition between a lighter shade and a darker shade while maintaining their color, or switch from one color in low light conditions to a different color in bright light conditions. 1−4 The majority of photochromic lenses are passively activated by UV light, which means that the color transition cannot occur indoors or while driving. The active materials used in photochromic eyewear are evaluated on metrics such as their color in each state, the change in transmittance (Δ%T) upon switching, and the rate at which they switch between states, to name a few. Commercially available photochromic eyewear, often based on compounds such as silver halides, have Δ%T of 18−60% depending on the color of the lens. 1−3 The Δ%T and the switching time of these lenses depend either on the light intensity, the temperature, or a combination of the two. Typically, the clear-to-colored (light-to-dark) transition is faster and occurs in 10−60 s, whereas the colored-to-clear transition can take up to several minutes. 1−3 For certain users (pilots, urban security, drivers, etc.), a more rapid response time, as well as the ability for the transmittance change to be user- controlled, is expected to be highly advantageous, if not crucial. An alternative to photochromic compounds and a route toward fully user-controlled eyewear is to use electrochromic polymers (ECPs). These polymers possess many properties attractive to eyewear applications, with performance on par with or even superior to commercially available products. One attractive feature of the current eyewear market is the range of lens colors. With regard to ECPs, the entire color palette has been completed using solution-processable, cathodically color- ing ECPs that can switch to a highly transmissive state upon oxidation, all within a small voltage window. 5 In addition to Received: October 13, 2014 Accepted: December 19, 2014 Published: January 9, 2015 Research Article www.acsami.org © 2015 American Chemical Society 1413 DOI: 10.1021/am507063d ACS Appl. Mater. Interfaces 2015, 7, 1413−1421