Ortho-chloranil—a new electrochromic material

Abstract

Under certain experimental conditions, the electrochemical reduction of ortho-chloranil yields electrode-adherent blue films which can be bleached by oxidation. The chemical and electrochemical parameters likely to be involved in the electrochromic process have been studied with metal electrodes; spectroelectrochemical analyses have been conducted with transparent indium tin oxide (ITO) electrodes. Particular attention was paid to counter-ions conducive to ortho-CA ⨪ M + association. While several alkaline and alkaline-earth ions yield blue precipitates, only sodium yields true electrode-adherent films. Films with an excellent contrast are obtained at −300 mV and can be bleached at +400 mV. For long-lasting (lifetime > 10 5 cycles) electrochromic behaviour, the formation of ortho-CA 2− dianions must be avoided.