Synthesis and Stability of N,N′‐Dialkyl‐1,13‐dimethoxyquinacridinium (DMQA⁺): A [4]Helicene with Multiple Redox States

N , N ′‐Dialkyl‐1,13‐dimethoxyquinacridinium (DMQA + ) is a configurationally locked [4]helicene, a stable carbenium ion and a potent near‐infrared emitter. The versatile synthesis and resolution into M and P enantiomers has made DMQA + and its congener helicenium derivatives attractive chiral dyes and building blocks. In the present study, electrochemical and spectroscopic studies showed that several redox states of DMQA + are accessible and stable. The cation stability towards nucleophiles is determined and it is shown that the addition of OH − proceeds with a surprisingly low rate of reaction. The synthetic methodologies leading to DMQA + are described, and the chemistry occurring from the different redox states of DMQA is identified. This [4]helicene is shown to be a unique molecular framework that is stable as a neutral radical and very stable as a carbenium ion.