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]thia-diazole 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 elec-trochemical 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.

Automated summary

Black electrochromics have great importance for applications such as smart windows, electronic papers, car rear views or displays, as they can absorb all visible light. In this study, a copolymer was synthesized to trap the entire visible region, showing enhanced optical contrast and a lower band gap.