Novel Starburst Triarylamine-Containing Electroactive Aramids with Highly Stable Electrochromism in Near-Infrared and Visible Light Regions

Abstract

b S Supporting Information ' INTRODUCTIONElectrochromic materials exhibit a reversible optical change in absorption or transmittance upon electrochemically oxidized or reduced, such as transition-metal oxides, inorganic coordination complexes, conjugated polymers, and organic molecules. 1 Despite the fact that the electrochromic devices were mostly based on inorganic oxides, nevertheless, the organic material has several advantages over the former ones, such as processability, high coloration efficiency, fast switching ability, and multiple colors within the same material. Initially, investigation of electrochromic materials has been directed toward optical changes in the visible region (e.g., 400À800 nm), proved useful and variable applications such as E-paper, optical switching devices, smart window, and camouflage materials. 2 Increasingly, attention of the optical changes has been focused extending from the nearinfrared (NIR; e.g., 800À2000 nm) range to the microwave region of the spectrum, which could be exploitable for optical communication, data storage, and thermal control (heat gain or loss) in buildings and spacecrafts. 3 In recent years, NIR electrochromic materials including transition metal oxides WO 3 , organic metal complex (ruthenium dendrimer), and quinonecontaining organic materials have been investigated. 4 Wang and Wan 4cÀg made efforts on the quinone-containing electrochromic materials, which revealed high absorption in the NIR upon electrochemical reduction. Reynold 1i,5a reported color-totransmissive NIR electrochromic conjugated polymers, their devices exhibited multicolor in neutral state and trasmissive in the oxidized state. In addition to conjugated polymers, 5 p-phenylenediamine-containing molecule is an interesting anodic electrochromic system for NIR applications due to its particular intramolecular electron transfer in the oxidized states.Intramolecular electron transfer (ET) processes were studied extensively in the mixed-valence (MV) systems, 6 and usually employed one-dimensional MV compounds contain two or more redox states. According to Robin and Day, 7 the p-phenylenediamine cation radical has been reported as a symmetrical delocalized class III structure with a strong electronic coupling (the electron is delocalized over the two or more redox centers), leading an intervalence charge transfer (IV-CT) absorption band in the NIR region. 8 In order to be useful for electrochromic applications, some key issues such as long-term stability, multiple colors within the same material, rapid redox switching, high coloration efficiency (CE), and high optical transmittance change (Δ%T) during operation are indispensable and are playing important roles. Therefore, to achieve a good combination of the above-mentioned parameters is a crucial and ongoing issue. Reynolds' group 5e studied ABSTRACT: A series of solution-processable near-infrared (NIR) electrochromic aromatic polyamides with starburst triarylamine units in the backbone were prepared by the phosphorylation polyamidation from a n...

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