Design Rules for High Contrast Mid-Infrared Electrochromism in Conjugated Polymers
D. Eric Shen, Callie L. Goins, Austin L. Jones, Anna M. Österholm, John R. Reynolds
Abstract
High Resolution Image Download MS PowerPoint Slide The ability to modulate absorption in the mid-infrared on-demand has broad applications ranging from camouflage to thermal management. While the ability of conjugated polymers to modulate mid-IR is known through tuning of the oxidation state, the specific structure–property relationships that govern the modulation amplitude remain largely unexplored. Our study introduces a series of dioxythiophene-based copolymers, where we adjust backbone planarity, electron-richness, and side chain polarity to investigate their effects on spectral traits. We find a clear correlation between higher conductivity and larger optical modulations attained through a broadening of the charge carrier bands and an intensification of specific vibrational modes. As thin films, our top-performing copolymer attains an 85% IR-contrast between its doped and undoped states. To probe their performance under electrochemical control, we fabricated and tested electrochromic cells with the best cells reaching a mid-IR contrast of nearly 60%. These findings enhance our understanding of design rules impacting mid-IR spectral features for conjugated polymers.