N-Heteroacenes

The synthesis and the property evaluation of several large N‐heteroacenes are discussed. Issues of stability and aromaticity are compared and investigated and a historical perspective of the field is given. Some of the larger heterocyclic materials that are evaluated in this concept article have been around for more than one hundred years, yet their chemistry and properties are not well known/understood. Aromatic or not? An account of the coexistence of formally antiaromatic 4n π heterocycles and their 4n+2 π perimeters is presented. In a significant number of cases both the formally antiaromatic and the aromatic species are known and have been isolated and investigated. In the diazatetracene case both species are stable, isolable, and interconvertible (see scheme).