Effect of terminal groups on the microscopic morphologies and electrochromic properties of pentaaniline derivatives

Abstract

Pristine pentaaniline ((Ani)5) and three derivatives, carboxyl-capped pentaaniline ((Ani)5COOH), amino/carboxyl-capped pentaaniline (NH2(Ani)5COOH) and carboxyl/carboxyl-capped pentaaniline (COOH(Ani)5COOH) were synthesized, and the influence of terminal groups on their microscopic morphologies and electrochromic properties was investigated in detail. It was found that, when more terminal groups with hydrogen bonding ability were attached to pentaaniline, their molecular arrangements became denser with smoother surface morphology, which led to slower ion conduction and longer switching time. The doping effects of carboxyl terminal group accelerated the bleaching process, while its hydrophilicity reduced the cycle stability of electrochromic films in aqueous solution. Combined with moderate doping, (Ani)5COOH presented the highest ion diffusion rate, shortest switching time (4.68/3.40 s), highest contrast (67.7%), best coloration efficiency (98.4 cm2/C) and cycle stability, which were confirmed by the cyclic voltammetry, atomic force microscope and electrochemical impedance analysis. These results imply that changing the terminal groups properly can tune the electrochromic performance of aniline oligomers to a certain extent.