Multicolored electrochromism in 4,4 '-biphenyl dicarboxylic acid diethyl ester

We investigated the properties of 4,4'-biphenyl dicarboxylic acid diethyl ester (PCE). The PCE underwent a 2-step reduction at -1.5 V and -2.2 V. The color of the PCE changed from colorless to yellow in the first step and consequently to red in the second reduction step. A PCE based EC cell using an NiO-modified electrode was also fabricated. The NiO electrode worked as a counter reaction material for PCE reduction. The PCE-NiO cell achieved multi-coloration ranging from colorless to yellow and red, and also achieved high coloration efficiency and long term switching stability.