A unique 'ON-OFF-ON' switch with two perturbations at two different concentrations of Ag+

The sterically crowded 1,2-dipod 3 and 1,2,4,5-tetrapod 4 undergo fluorescence quenching (λmax 395 nm) with <1.0 equiv of Ag+ and fluorescence enhancement (λmax 500 nm) with >3 equiv of Ag+ and can be used for estimation of two different concentration ranges of Ag+.