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A Poly(3,4‐alkylenedioxythiophene) Electrochromic Variable Optical Attenuator with Near‐Infrared Reflectivity Tuned Independently of the Visible Region

Disubstituted poly(3,4‐propylenedioxythiophene)s (PProDOTs) exhibit large electrochromic contrasts in the near infrared (NIR) while showing essentially no color change in the visible region when incorporated into a reflective device platform. The source of this is attributed to a conductive front that propagates through the insulating polymer film, extending from the polymer/electrode interface to the top of the polymer film. A utility of the large contrasts seen in the NIR region is demonstrated with application of the device as an electrochromic variable optical attenuator modulating fiber‐optic signals for optical telecommunications. With bis(ethylhexyloxy)‐substituted PProDOT as the active electrochromic polymer in the device, an optical attenuation of 11 dB at the telecommunications wavelengths of 1.31 and 1.55 μm is achieved with only a 0.1–0.2 dB optical loss in the bleached state. Other favorable properties include optical memory in the absorbing state, switching speeds of under 1 s, a low operating voltage of ±1.2 V, and an improved processability that allows spray‐casting from organic solvents.