Conformational Polymorphism of Octadehydrodibenzo[12]annulene with Dimethyl Phthalate Moieties

In this study, we found that an octadehydrodibenzo[12]annulene derivative with two dimethyl phthalate moieties yielded three polymorphic crystals I, II, and III, in which the annulene core arranges in herringbone, parallel-pi-stacked, and zigzag-pi-stacked fashion, respectively. This is the first example for dehydroannulenes to show polymorphic crystal structures. These polymorphs are brought from varied conformations of the dimethyl phthalate moieties because the direction of the carbonyl oxygen atoms in the phthalate affects the manner of CH/O interaction abundantly observed in the present systems. It is also revealed that the decomposition temperature of the polymorphic crystals varied over a wide range of values (112-163 degrees C), even though the crystals are composed of an identical molecule. This indicates that the molecular arrangement might have significant influence on the thermal stability and/or intermolecular reactivity of the annulene.