Abstract
Electron-deficient cyanophenyl side groups decrease the response time and drastically improve the stability of electrochromic polymers.
Highlights
Two novel thieno[3,2-b]thiophene (TT)/3,4-ethylenedioxythiophene (EDOT)-based compounds of 2,5(EDOT–TT–EDOT) type bearing electron-withdrawing side groups (4-cyanophenyl or 4-pyridyl) at 3,6positions of the TT moiety have been synthesized
It has been demonstrated that the polymer obtained from the conjugated 2,5-isomer had a lower band gap (1.82 eV) and showed a better EC performance compared to the 3,6-isomer (2.00 eV), in which the conjugation was interrupted at the TT moiety.[27]
Electron deficient side groups decrease the energies of both the HOMO and LUMO orbitals of the polymers and their somewhat stronger influence on the LUMO results in a band gap contraction of the materials compared to the reference polymer with phenyl side groups, P(Ph-ETTE)
Summary
Two novel thieno[3,2-b]thiophene (TT)/3,4-ethylenedioxythiophene (EDOT)-based compounds of 2,5(EDOT–TT–EDOT) type bearing electron-withdrawing side groups (4-cyanophenyl or 4-pyridyl) at 3,6positions of the TT moiety have been synthesized. Their electropolymerization leads to electroactive conjugated polymers, P(CNPh-ETTE) and P(Py-ETTE), which possess electrochromic properties changing the color from purple to pale grey-blue or from sand brown to pale grey-green, respectively. Cyclic voltammetry and spectroelectrochemical experiments reveal that functionalization with electron-withdrawing side groups decreases the HOMO and LUMO energy levels and contracts the band gap of materials Both new polymers demonstrated extremely short response times of 0.9–1.1 s for bleaching and 0.34–0.35 s for coloring. There are no reports on EC materials based on thieno[3,2-b]thiophene with electron acceptor groups at the 3,6-sites, while this information would be important for deeper understanding of the structure–property relationship and the role of electronic effects in this class of materials on their EC behavior
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