Chasing the black electrochromism: A new electrochromic copolymer based on 4,7-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)benzo[c][1,2,5]thiadiazole and ProDOT

Absorbing all the visible light, in other words, neutral state black electrochromics has a great importance for certain applications such as smart windows, electronic papers, car rear views or displays. In this study, it was focused on a combination of monomers that can absorb entire the visible region. Poly(4,7-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)benzo[c][1,2,5]thiadiazole) (PEDAD) is a neutral state green polymer and has a dual absorption band before and after 500 nm, corresponding red and blue regions of the visible spectrum. On the other hand, polymer of dihexyl-3,4-propylenedioxythiphene (PProDOT) has an 400–700 nm optical absorption band with having a maximum at 584 nm. In the light of this information, a new copolymer, consisting of 4,7-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)benzo[c][1,2,5]thiadiazole and ProDOT, was synthesized via electrochemical techniques, to trap the entire visible region. 1:1 eq. of monomer feed was used and a neutral state very-dark copolymer was obtained. The copolymer showed enhanced optical contrast coming from PProDOT, (of having 44% transmittance) and lower band gap coming from PEDAD (of having 1.32 eV). In the oxidized state, the copolymer exhibited transmissive blue, coming from both homopolymers. © 2022 Elsevier Ltd.