Triphenylamines consisting of bulky 3,5-di‑tert‑butyl‑4-anisyl group: Synthesis, redox properties and their radical cation species

Triphenylamine (TPA) derivatives have been widely used as useful building blocks for diverse functional materials because of their excellent redox activity. Most of the molecular structures of TPA-based organic functional materials contain 4-anisyl groups, which on one hand could reduce their oxidation potential and on the other hand significantly delocalize the spin density of the resultant TPA radical cation species and enhance their stability. However, molecular-level investigation of the redox behavior of triphenylamines consisting of 4-anisyl group and the electronic structures of their radical cation species has not been reported in the literature. Herein, we design a series of triphenylamines consisting of one, two, or three 3,5-di-tert-butyl-4-anisyl groups and investigate their redox behaviors and corresponding radical cation species. We disclose that the resonance hybrid and steric protection could both contribute to the stability of triphenylamine radical cations. Moreover, further oxidation leads to an unexpected oxidative demethylation. The findings in this work may reveal new insights for the understanding of the unique redox properties of 4-anisyl substituted triphenylamines.