Soft and Sustainable Synthesis of Perylene Diimides through Soluble Surrogates of Perylenetetracarboxylic Acid Dianhydride

An unprecedented strategy for the efficient and direct synthesis of perylene-3,4,9,10-tetracarboxylic diimides (PDIs) through a well-defined and controlled reaction mechanism has been developed. The procedure is based on the opening of the anhydride groups of perylene-3,4,9,10-tetracarboxylic dianhydride (PDA) as nonplanar diester-type perylene-3,4,9,10-tetracarboxylic acid (MESAC), which act as highly soluble surrogates of PDA that enable the preparation of PDIs under soft conditions compatible with thermolabile groups. A ready interconversion, in amine methanolic solution, between the cyclic anhydride groups of PDA and the groupings resulting from their methanolysis (methyl esters+ammonium carboxylate) and aminolysis (amide+ammonium carboxylate) was studied, and the presence of postulated (nonisolated) intermediates was detected by UV–vis and HPLC/HRMS. The intermediates originated by double aminolysis with primary amines of both anhydride groups of PDA render diamide-type perylene-3,4,9,10-tetracarboxylic acid (s-AMAC) intermediates whose selective cyclization to yield PDIs required basic media, while acidic media produce reversion to the anhydride (PDA). The procedure emerging from these studies provides a robust methodology with a wide scope for the synthesis of PDIs under soft and environmentally friendly conditions.