Recognition between V- and dumbbell-shaped molecules

A series of 2,6-bis(imino)pyridyl-based V-shaped compounds bearing various para-substituents on the terminal aromatic rings [C sub(5)H sub(3)N(CH&z.db d; N-C sub(6)H sub(4)R) sub(2); R = OMe, super()ir, Me, H, Cl, F, and CF sub(3)] have been prepared and investigated for their reversible binding with the dumbbell-shaped cations NH sub(2) super(+)-{CH sub(2)-C sub(6)H sub(3 )(OMe-3,5) sub(2)} sub(2) and 9-anthryl-CH sub(2)-NH sub(2) super(+)-CH sub(2)-C sub(6)H sub(3)(OMe-3 ,5) sub(2). Three crystalline V-shaped compounds and a dumbbell hexafluorophosphate were characterised in the solid state by X-ray structural analysis. The binding mode of the 1 : 1 V-shaped molecule.dumbbell complexes was evaluated by super(1)H NMR spectroscopy. The binding constants (90-400 M super(-1) in dichloromethane) and stoichiometries of the complexes were determined using the Method of Continuous Variations and the Rose-Drago Method based on super(1)H NMR spectroscopic data. In a series of V-shaped compounds, the binding strength with both dumbbell cations diminishes with the decreasing electron-donating ability of the R substituents. Specifically, one of the diimine V-shaped compounds shows a stronger binding with the symmetrical dumbbell than with the unsymmetrical anthracene-containing dumbbell. Fluorescence measurements of equimolar mixtures of the V-shaped compounds and the unsymmetrical dumbbell have revealed a reduced anthracene emission which is approximately 50% that of the original intensity. Rapid and complete dissociation (