Violet Anthraquinone for Expanding the Color Palette of Electrochromes with Three Discrete Colors and Full Color...

An anthraquinone chromophore displaying a vivid violet color in solution was synthesized and it was thoroughly characterized both spectroscopically and electrochemically, along with its X-ray crystallography. Single crystal X-ray analysis of the chromophore revealed a nearly planar π-conjugated framework with short intermolecular contacts. Cyclic voltammetry revealed two consecutive one-electron reductions, corresponding to the formation of its radical anion and dianion. The spectroelectrochemistry of the chromophore confirmed two distinct and reversible color changes with the stepwise electrochemical reduction. These were quantified via the CIE L a* b* color space. Large optical differences (98%) between the bleached and colored states were observed along with a coloration efficiency of 698 cm²/C. These parameters confirm the anthraquinone is an ideal electrochrome: capable of reversibly switching its colors with applied potential. The three color changes and color bleaching associated with the neutral, radical anion, dianion, and cation, respectively, are also of interest for extending the palette of colors of molecular electrochromes toward panchromatic color tuning with molecular structure for use in smart windows and displays.