Discovery of a highly selective turn-on fluorescent probe for Ag ⁺

An ideal fluorescent probe should show the strongest affinity with the relevant target (binding-selectivity) by means of a selective fluorescence change (signal-selectivity). [15]aneNO₂S₂ (1,4-dioxa-7,13-dithia-10-azacyclopentadecane) based probes usually show high binding selectivity for Ag⁺ but signal selectivity for Hg ²⁺, because Ag⁺ can quench or silence the fluorescence. To amplify the Ag⁺ binding to the greatest extent, a carbonyl group was positioned between 1,8-naphthalimide and [15]aneNO₂S₂ which played a key role of displaying selective fluorescence enhancements with Ag⁺ through increasing the oxidation potential of the fluorophore, blocking Ag⁺ from sterically interacting with the naphthalimide fluorophore, and by acting as a sacrificial donor. Probe 2 can detect Ag ⁺ with a selective fluorescence enhancement (∼14 fold) and high affinity (K_a = 1.64 × 10⁵ M^-1).