NOEsy and fluorescence spectroscopy reveal that conversion of conformationally flexible (phenylalkyl)pyridines into their corresponding N-methyl-pyridinium iodides results in intramolecular pi-stacking.

The crystal structures of phenylpropylpyridine-N-oxide and N-methyl-phenylpropylpyridinium iodide are compared, revealing that hydrogen bonding with the solvent molecule plays an important role in the N-oxide compound, whilst electrostatic interactions are predominant in controlling the solid-state orientation of the N-methylated compound. Fluorescence spectroscopy and NOESY indicate that in contrast to the previously reported pyridinium iodide, the N-oxide is not subject to intramolecular pi-stacking, as judged by excimer emission and a lack of corresponding cross peaks, respectively.