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.