A unique ‘ON–OFF–ON’ switch with two perturbations at two different concentrations of Ag+

The dipod 1,2-bis(8-quinolinoxymethyl)benzene 3 and tetrapod 1,2,4,5-tetrakis(8-quinolinoxymethyl)benzene 4 show two perturbations in fluorescence with Ag+, (i) fluorescence quenching with <1.0 equiv of AgNO3 at λmax 395 nm and (ii) fluorescence enhancement at λmax 500 nm with >3 equiv of AgNO3. This ‘ON–OFF–ON’ switching of 3 and 4 in comparison with simultaneous fluorescence quenching and enhancement in the case of 8-methoxyquinoline 1 and the tripod 1,3,5-trimethyl-2,4,6-tris(8-quinolinoxymethyl)benzene 2 point to the unique role of molecular architectures arising due to the number and spatial positions of quinoline units in the fluorescence behaviour of an 8-alkoxyquinoline moiety towards Ag+.