Poly(thieno[3,4‑<i>b</i>]‑1,4-oxathiane):\nMedium Effect on Electropolymerization and Electrochromic Performance

Abstract

The\nasymmetrical sulfur analog of 3,4-ethylenedioxythiophene (EDOT),\nthieno­[3,4-<i>b</i>]-1,4-oxathiane (EOTT), was synthesized,\nand its electropolymerization was comparatively investigated by employing\ndifferent solvent–electrolyte systems (room temperature ionic\nliquid 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF₆), CH₂Cl₂–Bu₄NPF₆, and CH₂Cl₂–BmimPF₆). Further, the effect of solvents and supporting electrolytes on\nthe structure, morphology, electrochemical, electronic, and optical\nproperties and electrochromic performance of the obtained poly­(thieno­[3,4-<i>b</i>]-1,4-oxathiane) (PEOTT) films were minutely studied. PEOTT\nfilm with a band gap (<i>E</i>_g) of about 1.6\neV could be facilely electrodeposited in all the solvent-electrolytes\nand displayed excellent electroactivity, outstanding redox stability\nin a wide potential window, and improved thermal stability. Cyclic\nvoltammetry showed that EOTT could be electropolymerized at a lower\noxidation potential in BmimPF₆ (∼1.0 V vs Ag/AgCl)\ndue to several advantanges of RTIL BmimPF₆ itself, such\nas high intrinsic conductivity and mild chemical conditions, etc.,\nand the resulting PEOTT film exhibited compact morphology with better\nelectroactivity and stability and higher electrical conductivity.\nOn the other hand, PEOTT films from all the sovent-electrolytes also\nshowed the electrochromic nature by color changing from gray blue\nto green, and further kinetic studies revealed that PEOTT had decent\ncontrast ratios (36%), higher coloration efficiencies (212 cm²/C in BmimPF₆), low switching voltages, moderate\nresponse time (1.2 s), excellent stability, and color persistence.\nFrom these results, PEOTT provides more plentiful electrochromic colors\nand holds promise for display applications.