Black-to-transmissive electrochromism of azulene-based donor-acceptor copolymers complemented by poly(4-styrene sulfonic acid)-doped poly(3,4-ethylenedioxythiophene)

A series of azulene-carbazole-2,1,3-benzothiadiazole (BTD) conjugated terpolymers were synthesized and their electrochemical and electrochromic properties were studied. The terpolymer containing a small amount of BTD units exhibits significantly higher electrochromic contrast and faster switching speed than azulene-carbazole alternating copolymer under low potentials because the BTD units act as electron acceptors, facilitating electron removal from azulene and carbazole units (electron donors) upon oxidation and hence leading to a lower oxidation potential. A complementary electrochromic device (ECD) was fabricated using the terpolymer as the anodically coloring layer and poly(4-styrene sulfonic acid)-doped poly(3,4-ethylenedioxythiophene) (PEDOT:PSS) as the cathodically coloring layer. The ECD exhibits black-to-transmissive electrochromism as the absorption bands of the two polymers are complementary to each other in covering the whole visible region and they can be switched simultaneously under relatively low potentials.