Electrochromism Through Redox Regulation of a Nearly Colorless Dynamic Covalent Radical Equilibrium

Area of Science:

• Materials Science
• Organic Chemistry
• Electrochemistry

Background:

• Radical-based dynamic covalent systems offer potential for stimuli-responsive materials.
• Reversible radical dimerization-cleavage reactions can induce significant property changes, including color and magnetism.

Purpose of the Study:

• To demonstrate reversible electrochromism controlled by redox modulation of a radical-based dynamic covalent equilibrium.
• To investigate a system utilizing the monomer-dimer equilibrium of a phenoxyl radical and its σ-dimer.

Main Methods:

• Synthesis of a phenoxyl radical conjugated with an indandione skeleton.
• Electrochemical measurements to study redox behavior and monomer-dimer equilibrium.
• TD-DFT calculations to understand electronic transitions and absorption properties.
• Spectroelectrochemical measurements to observe color changes.

Main Results:

• The phenoxyl radical (3•) is nearly colorless, while its reduced form (3-) is strongly colored.
• Electrochemical reduction of 3• shifts the equilibrium, favoring monomer dissociation.
• Reversible color changes from nearly colorless to deep red were observed upon electrochemical reduction and oxidation.
• Variable-temperature electrochemical studies confirmed the influence of the dynamic equilibrium on electrochemical behavior.

Conclusions:

• A rare electrochromic system driven by redox modulation of a radical-based dynamic covalent equilibrium was established.
• The system utilizes the colorless dimer/radical equilibrium as an OFF state and the colored monoanion as an ON state.
• This work provides insights into designing advanced electrochromic materials based on radical chemistry.