Derivatives of N-benzyl-2-phenylpyridinium bromide, minimalist models for face-to-face, center-to-edge π-stacking in water

The substitution pattern of the benzyl ring was varied in preparations of derivatives of N-benzyl-2-phenylpyridinium bromide (1-8). The salts showed monomeric behavior at NMR concentrations in D₂O. The title compounds are discussed in the context of their propensity to intramolecularly stack aromatic substituents in water solvent and in the solid state. The series of derivatives, 1-8, populated similar stacked conformational space in solution. Neither perturbation in the quadrupole moment nor perturbation in donor/acceptor properties of the interacting aromatic rings had observable effects on the solution conformation of 1-8. The propensity of arene and perfluoroarenes to stack in a fact-to-face manner may have been the reason for the minor changes in conformation observed in the solid state. Derivatives 1-8 served as a unique tether for arene stacking, consisting of two trigonal and one tetrahedral center.