Towards multichromatic electrochromes from ambipolar conjugated azomethines

Abstract

A series of conjugated azomethines end-capped with phenylamides and consisting of different aromatic cores of varying π-donor strength were prepared. Their optical and electrochemical properties were investigated to assess the suitability of the azomethines as electrochromic materials. The azomethines were found to undergo both electrochemical oxidation and reduction in the window of −1.60 and +1.35 V vs. Ag/Ag⁺. The color of the ambipolar compounds could be dramatically changed when switched between their reduced, neutral, and oxidized states. The color of the different states was contingent on the π-donor strength of the central aromatic unit. The largest spectral difference of 350 nm between the reduced and oxidized states was observed when the central aromatic group was 3,4-ethylenedioxythiophene (EDOT). The colors detectable by the eye for this EDOT derivative were blue, red, and bleached for the reduced, neutral, and oxidized states, respectively. The multichromatic azomethine was used as an electrochromic layer in a functioning device. The proof-of-concept ambipolar electrochromic device could be repeatedly switched between its orange (neutral) and purple (reduced) states. The device could also be switched to its oxidized (bleached) state.