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Investigation of Triphenylamine–Thiophene–Azomethine Derivatives: Toward Understanding Their Electrochromic Behavior

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journal contribution
posted on 25.04.2016, 13:05 by Marie-Hélène Tremblay, Thomas Skalski, Yohan Gautier, Grégory Pianezzola, W. G. Skene
A series of thiophenoazomethines connected to a central triphenylamine were prepared. The effect of the type of aminothiophene used to prepare the conjugated azomethines and the number of azomethine bonds, ranging from one to three, flanking the triphenylamine on the spectral, electrochemical, and spectroelectrochemical properties were investigated. Both the absorption and fluorescence of the azomethines (68) derived from 2,5-diaminothiophene (1) were found to be contingent on the number of the azomethines. The spectral properties were red-shifted with increasing the number of azomethine bonds. In contrast, the azomethines (911) derived from 2-aminothiophene (2) were not perturbed by the number of azomethines. However, their spectral properties were red-shifted relative to their triphenylamine counterparts derived from 1. The oxidation potentials of the azomethines were also contingent on structure. They were shifted to more positive potentials with increasing number of azomethines. The oxidation potentials of 68 were less positive than 911, owing to the electron-donating effect of the terminal amine. Reversible oxidation was observed with the triphenylamine having methyl groups in the 4′-positions. All the compounds examined underwent color changes upon both electrochemical and chemical oxidation. The oxidized state was shifted upward of 165 nm for the series 68 relative to the neutral state, whereas it was shifted at most by 85 nm for 911. The most pronounced color changes between the neutral and oxidized states occurred with the triphenylamine–thiophene–triphenylamine bisazomethine derivative (12).