An electrochromic behavior of novel polythiophenes obtained from unsymmetrical monomers- a comprehensive study

Abstract

The paper contains a comprehensive study regarding the synthesis and properties of novel polythiophenes, where bithiophene units are linked by phenylene bridges. In this work, four tetrasubstituted benzene monomers were synthesized with yields ranging from 41% to 69% by the cycloaddition reaction of [2 + 2 + 2]. 5-ethynyl-2,2′-bithiophene and appropriate β-ketoester were used as the substrates. Obtained compounds were designed so that the molecule was asymmetric, i.e. possessing electron-withdrawing substituent (COOEt) in position 2, whereas in the 3rd position there were acceptor substituents. This provides a non-uniform electron density distribution within the molecule, which in turn should provide for the difference in oxidation potential of the individual bithiophene fragments. The influence of this architecture on the stability, electrochemical and electrochromic behavior was thoroughly studied. The polymers present a good stability during multiple p-doping. The experimental results were also investigated theoretically, using DFT approach. Calculations of the frontier orbital energies and the corresponding Eg value were done for each polymer, by means of periodic boundary conditions. Furthermore, obtained polymers exhibit multistep electrochromism.