Effects of N-Substitution Group on Electrochemical, Electrochromic and Optical Properties of Dithienyl Derivative

This paper describes the easy syntheses of a new conjugated monomer namely 4,4′-((1E,1′E)-ethane-1,2-diylidenebis(azanylylidene))bis(N-(2,5-di(thiophen-2-yl)-1H-pyrrol-1-yl)benzamide) (NPB2) and its derived polymer containing bi-functional imine bridged dithienyl group, along with their electrochemical and electrochromic properties. The electrochemical properties of the two monomers containing single-side polymerizable (NPB1) and double-sided polymerizable (NPB2) groups have been investigated comparatively. For electrochemical polymerization, NPB2 have four thiophene sites in the peripheral part in the molecular structure. The presence of four thiophene sites is thought to cause the cross-linked structure. For this reason, in the electropolymerization process of NPB2, the NPB2 units are inclined to couple with itself at the low potential because of cross-linked structure according to NPB1. The results showed that the polymer has excellent optical and electrical properties because of the highly-branched structure in comparison with its linear counterparts. The bi-functional electroactive polymer film possessed low optical bandgap (Eg < 2.02 eV), high optical contrast (%ΔT:54 at 935 nm), low switching time (1.5 s at 935 nm). The polymer film presents a stable and well-defined reversible redox process as well as multicolor electrochromic change from yellowish (in the neutral state) to blue (in the oxidized state) making it a suitable candidate for optoelectronic applications.