Multiarm Aniline Oligomers: Molecular Architecture, Self-Assembly, and Electrochromic Performance

Solution-processable aniline oligomers with a benzene ring as the core and para, meta, and triple substituted amino/carboxyl-capped tetraaniline (NH2-(Ani)4-COOH) as arms, named as Bi(p)-(Ani)4-COOH, Bi(m)-(Ani)4-COOH, and Tri-(Ani)4-COOH, were synthesized and characterized. It was found that aniline oligomers with increased arms presented a more regular porous breathing structure revealed by atomic force microscopy. An electrochemical quartz crystal microbalance was used to study their long-term stability by recording the mass change of electrochromic films during redox and analyze the mechanism of ion conduction in the electrochromic process. The results suggested that the porous breathing structure was conducive to H+ conduction, which contributed to their improved performance in switching time, coloration efficiency, and cycling stability. Tri-(Ani)4-COOH had the shortest switching time (tb = 1.45 s, tc = 1.82 s), highest coloration efficiency (190.7 cm2/C), and best cycling stability. Especially on the conductive glass, in 0.5 mol/L sulfuric acid electrolyte, it reached the charge retention of 96.8% after 3000 cycles, implying that the multiarm star-shaped aniline oligomer will be a promising material in electrochromic area with good processability, short switching time, and high cycling stability.