Isostructural Crystallization Behavior of Dihydroanthracene and Dihydroacridine

The crystal packing motifs of acenes are usually built up by heringbone C–H···π interactions; on the contrary, N-heteroacenes form C–H···N contacts. In the case of dihydroazaacenes the molecular structure of a rigid aromatic system is interrupted by a flexible part. The influence of heterocyclic CH2/NH substitution on the crystallization behavior and crystal packing of 9,10-dihydroacridine (DHAC) and 9,10-dihydroanthracene (DHAN) as well as a 1:1 mixture of both compounds was investigated by differential scanning calorimetry (DSC) measurements, hot stage microscopy methods, and crystal structure determination.