Electrochromic materials have the ability to switch between two colored states, or transmissive states, upon the application of an electrochemical potential. They have prospective uses in full color passive displays, energy saving tinted windows, and dimmable visors for military and/or recreational use. Organic polymer electrochromes are solution processable, lightweight, and flexible. The current state of the art electrochromic materials are cathodically coloring, with broadly absorbing charged states that trail into the visible. In this project, a family of pi-conjugated chromophores was designed to be UV absorbing and switch to a vibrantly colored state upon electrochemical oxidation. Through collaboration, synthesis and theoretical calculations have worked in tandem to design materials to have electron rich, discrete chromophores with have wide optical gaps absorbing in the UV in their neutral state and are anodically coloring.<br/>We show that using a divergent synthetic approach allows for creating a series of polymers with discrete chromophores of various lengths with a consistent alkyl bridge. Increasing conjugation by increasing the number of dioxythiophenes in the chromophore has the hypothesized effect of red-shifting the neutral and radical cation absorptions; however, the introduction of a sterically demanding dimethoxybenzene unit has the effect of blue-shifting the neutral absorbance relative to a shorter and more electron rich chromophore. This steric effect is further extended to confining the radical cation absorption to an unusually high energy and sharp absorption focused inside the visible. This absorption confinement manifests itself in creating a very saturated chromophore in this oxidation state giving a broadly absorbing black colored state. Upon moving to wider gap systems we use a small molecule model to show that this method has the ability to make materials with contrasts exceeding what is possible in traditional cathodically coloring conjugated polymers.

Discrete chromophores as a path towards high contrast anodically coloring electrochromic polymers

253rd National Meeting (2017)

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