New chiral ferrocenyl-pyridinium salts for non-linear optics

Three enantiomerically pure chiral analogues of 4-[(E)-2-ferrocenyl-ethenyl]pyridinium iodide have been synthesized. Their bulk efficiencies in second harmonic generation (SHG) have been measured (from 0 to 0.25 times that of urea). Furthermore, the crystal structures for two of them and for the parent 4-[(E)-2-ferrocenyl-ethenyl]pyridinium iodide have been determined by X-ray diffraction studies. Crystal packing could explain the very different SHG bulk efficiencies in this family of materials.