Potassium ion induced changes of crystal structure and fluorescence of a crown ether

Luminescence properties and the x-ray structures of the fluorescent crown ether, 16-anthracen-ylmethyl-1,4,7,10,13-pentaoxa-16-aza-cyclooctadecane (CEA) and its complex with potassium hexafluorophosphate (CEAK) have been obtained. In the solid state CEAK gives a structured blue emission and CEA gives a broad structureless green emission. The differences in luminescence behavior are explained on the basis of crystal packing. X-ray analysis shows that every two adjacent anthracene moieties in CEA form a sandwich-like anti-parallel dimer; the green-structureless emission then arises from the pi-pi stack of the aromatic rings. In CEAK, disruption of the pi-pi stacking structure forces a large separation between the anthracene rings, which yields an anthracene monomer emission. Luminescence lifetime data support the assignments.