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

Abstract

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 (6–8) 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 (9–11) 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 6–8 were less positive than 9–11, 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 6–8 relative to the neutral state, whereas it was shifted at most by 85 nm for 9–11. The most pronounced color changes between the neutral and oxidized states occurred with the triphenylamine–thiophene–triphenylamine bisazomethine derivative (12).

Design rules for the preparation of low-cost hole transporting materials for perovskite solar cells with moisture barrier properties

“…For TPA-OMeTPA we observed that the HOMO is more localized on the terminal triphenylamines, which we ascribe to the disruption of the conjugation of the central triphenylamine. [46,47] The disturbance of the conjugation in the triphenylamine-based azomethines was experimentally observed by Skene and co-workers in a previous study. [47] HOMO energy levels obtained from computational chemistry for single molecules in vacuum generally strongly differ from the experimentally results.…”

“…[46,47] The disturbance of the conjugation in the triphenylamine-based azomethines was experimentally observed by Skene and co-workers in a previous study. [47] HOMO energy levels obtained from computational chemistry for single molecules in vacuum generally strongly differ from the experimentally results. Chi et al showed that it is possible to get a good estimate of the experimental HOMO energy levels from the HOMO energy levels obtained from DFT calculations (B3LYP/6-31G(d,p) in dichloromethane) [45] using the following formula:…”

Effect of Protonation on Optical and Electrochemical Properties of Thiophene–Phenylene-Based Schiff Bases with Alkoxy Side Groups

“… 9 , 10 These types of materials were extensively studied due to their interesting thermal, 11 electrical, 12 and optical 13 − 15 properties and also due to the possible activity in some optoelectronic systems, such as bulk heterojunction photovoltaic cells, 16 − 19 perovskite solar cells, 20 − 22 organic light-emitting devices, 23 , 24 or electrochemical systems. 25 , 26 …”

N-Substituted Phenothiazines as Environmentally Friendly Hole-Transporting Materials for Low-Cost and Highly Stable Halide Perovskite Solar Cells

“…The electron density in the case of HOMO energy levels of both the compounds is located on the electron-donating triarylamine units, while the LUMO energy levels are spread over the electron-withdrawing azomethine linkage and the aryl spacer unit between phenothiazine and azomethine(s). 41 , 42 Simulations of the vertical excitations of AZO-III and AZO-IV indicate that the first transition refers to the HOMO–LUMO transitions ( Tables S2 and S3 ) through intramolecular charge transfer.…”