Manipulation of fluorescent and colorimetric changes of fluorescein derivatives and applications for sensing silver ions

Three structurally similar compounds, 1-3, bearing a fluorescence chromophore to which are appended morpholine, thiomorpholine and methylpiperazine substituents, display opposite fluorescence responses to pH changes, in contrast to that observed for fluorescein; 1 and 2 have extremely high binding selectivity towards Ag⁺ ions and show completely different fluorescent and colorimetric changes upon addition of Ag⁺, and the differences are proposed to be associated with different binding modes of 1 and 2 to this metal ion.