Conducting tetraaniline derivatives with fast switching time, enhanced contrast and coloration efficiency

Pristine tetraaniline and three carboxyl-substituted tetraaniline derivatives, that is, tetraaniline ((Ani)₄), carboxyl-capped tetraaniline ((Ani)₄-COOH), amino/carboxyl-capped tetraaniline (NH₂-(Ani)₄-COOH) and carboxyl-capped star-shaped tetraaniline (Tri-(Ani)₄-COOH) were synthesized, and the influence of substituent and molecular architecture on their electrochromic properties was investigated. Pristine (Ani)₄ shows lowest electrochromic properties while the carboxyl-capped star-shaped Tri-(Ani)₄-COOH possesses the best electrochromic properties with fast bleaching and coloring times of 2.04 s and 1.90 s, respectively, promising optical contrast of 74.2%, and improved coloration efficiency of 133.31 cm²C⁻¹ at 750 nm. This enhanced electrochromic performance can be attributed to the introduction of carboxyl substituent and star-shaped molecular architecture, which are able to improve the interchain charge movement, electron movement between films and substrate and enhanced ion diffusion resulting from loosely packed molecular structure of films, and confirmed by cyclic voltammetry and atomic force microscope results, implying the introduction of special substituent and molecular architecture is an effective strategy to improve the electrochromic properties of aniline oligomers.