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Controlling Charged State Colors in Triphenylamine-Based Anodically Coloring Electrochromes.

Justine S Wagner1, Maxime A Siegler2, Aimée L Tomlinson3

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Advanced Optical Materials
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Researchers developed new electrochromic molecules (EDOT-TPA) with tunable colors. By altering substituents, they precisely controlled oxidation potentials and achieved distinct colors for cation radical and dication states, a first for these systems.

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Area of Science:

  • Materials Science
  • Electrochemistry
  • Organic Electronics

Background:

  • Anodically coloring electrochromic (ACE) molecules are crucial for advanced display and smart window technologies.
  • Controlling the color palette and switching stability of ACE materials remains a key challenge.

Purpose of the Study:

  • To design and synthesize novel EDOT-TPA molecules with systematically varied electronic properties.
  • To investigate the impact of substituent position and electron richness on molecular geometry, electrochemistry, and optoelectronic properties.
  • To demonstrate precise control over successive charge states and their corresponding colors in ACE systems.

Main Methods:

  • Synthesis of thioalkyl-substituted 3,4-ethylenedioxythiophenes coupled to triphenylamine units (EDOT-TPA).
  • Electrochemical characterization (cyclic voltammetry) to determine redox potentials and stability.
  • Spectroscopic analysis (UV-Vis-NIR) of electrochemically generated cation radical and dication states.
  • Density Functional Theory (DFT) and Time-Dependent DFT (TD-DFT) calculations for theoretical validation.

Main Results:

  • Successfully modulated first and second oxidation potentials (0.03–0.18 V and 0.32–0.46 V vs Fc/Fc+).
  • Achieved tunable color generation for cation radical and dication states by controlling electrochemical potential separation.
  • Demonstrated selective control over successive charge states using an optically transparent thin layer electrode (OTTLE).
  • Correlated substituent effects on electron richness and steric interactions with optical transitions using TD-DFT.

Conclusions:

  • The designed EDOT-TPA molecules offer unprecedented control over electrochromic properties.
  • Modulating substituents provides a powerful strategy for tuning redox potentials and color generation in ACE materials.
  • This work advances the development of molecular systems for vibrant and stable electrochromic applications.