Polymorphism and resulting luminescence properties of 1-acetylpyrene

Structures of three polymorphs of 1-acetylpyrene were determined using single-crystal X-ray diffraction and their solid state luminescence was investigated. While the formerly known 1AP-alpha polymorph, with its herringbone packing motif, is proved to be non-luminescent, the newly discovered polymorphs beta and gamma, with crystal structures based on pi MIDLINE HORIZONTAL ELLIPSIS pi-dimers, luminesce intensely in blue and green accordingly. This discovery contradicts a possibility of systematic control over the packing of pyrene units in crystals by progressive addition of acetyl groups, formerly claimed for n-acetyl-pyrenes.