Two polymorphs of phenanthro[4,5-abc]phenazine-18-crown-6: Preparation, X-ray diffraction and DFT studies

Phenanthro[4,5-abc]phenazine-18-crown-6 chromophore (1) was synthesized, and its two polymorphic modifications were obtained by recrystallization from dichloromethane/methanol and dichloromethane/hexane solvent mixtures. Both polymorphs 1a and 1b crystallize in the same monoclinic P21/c space group, and represent conformational polymorphs, which differ by the conformation of the macrocyclic cavity. The crystal structures obtained have been compared with molecular structures computed by density functional theory (DFT). As revealed by quantum chemical calculations, both polymorphs reach different minima on potential energy surface that supports our results that different solvents template distinctive conformational isomers found in crystals.

► Two polymorphs of 18-crown-6 chromophore derivative.
► Joint single-crystal and computational study.
► Polymorphs arrive in the different true minima on the potential energy surface.
► Frontier orbitals involved in first 15 excited states are localized mainly in the aromatic core.