Anion-π Interactions in Direct Amination of Core-Unsubstituted Perylene Monoimides

The incorporation of amino substituents at the peri-positions of perylene monoimides (PMIs) produces elusive push-pull systems with absorption and emission properties in the UV-vis and Near-IR regions. We describe a survey of different direct amination methods for the one-step synthesis of a series of 9-alkylamino and 9-arylamino PMIs. The first method tested is direct amination in neat amines and succesfull only for pyrrolidine. The second method uses the PCC/AgNO₃ oxidant system, and high yields are obtained with pyrrolidine. The third method employs KMnO₄/AgNO₃ as a stronger oxidant system. Pyrrolidine and piperidine are favorable amines for this method, and even diamino PMIs can be obtained. The fourth method uses a Cu(II) salt as a catalyst, and cyclic amines afford products in high yields. The final method is the anion-mediated direct amination and provides the most suitable method for a variety of cyclic, alkyl, and aryl amines to give 9-alkylamino and 9-arylamino PMIs in high yields. In this method, TBAF or TBAOH is used as the anion source, and our detailed spectroscopic and synthetic studies reveal that, as a result of single-electron transfer from the anion, PMIs can generate radical anions and participate in a radical mechanism in amination.