Effect of electrolytes on the electropolymerization and optoelectronic properties of poly(3-methylselenophene)

Abstract

Polyselenophenes exhibit several special properties and potential advantages over polythiophenes and have been extensively employed in organic electronics recently. Yet, electrosynthesized polyselenophene derivatives have attracted surprisingly scant attention. In this work, 3-methylselenophene (3MeS) was synthesized by a simple procedure, and its electropolymerization was comparatively investigated by employing different electrolyte systems, namely, CH₂Cl₂–Bu₄NPF₆, CH₂Cl₂–BFEE (boron trifluoride diethyl etherate), and ionic liquid BmimPF₆. Further, the effect of electrolytes on the structure and morphology, electrochemical, electronic and optical properties, and the electrochromic performances of the as-obtained poly(3-methylselenophene) (P3MeS) films were minutely studied. Surprisingly, we find a very significant electrolyte effect on the electropolymerization behavior of 3MeS and also on the structure, morphology, redox activity and stability, and optoelectronic and electrochromic properties of the electrosynthesized P3MeS material. The 3MeS monomer could be successfully electropolymerized in all the electrolytes, mainly through the coupling at the α-sites of the selenophene ring, and the as-formed P3MeS films from all three electrolytes displayed several mutual characteristics, such as similar chain structures, insolubility in common solvents, electrical conductivity of 10⁻⁴ to 10⁻² S cm⁻¹, good redox activity and stability superior to polyselenophene, and electrochromic nature from yellow brown in the reduced form to dark gray upon oxidation, but with poor kinetic performances. We also show that the high intrinsic conductivity and viscosity of ionic liquid BmimPF₆ provide milder polymerization conditions for 3MeS, leading to the facile electrodeposition of a homogeneous and continuous P3MeS film with less structural defects and better chain arrangement. Further, P3MeS from BmimPF₆ exhibited uniform and compact morphology, higher electrical conductivity, better electroactivity and stability, and also a lower band gap of 1.83 eV.