A new bis(rhodamine)-based fluorescent chemosensor for Fe3+.

A new bis(rhodamine)-based fluorescent probe 4 was synthesized, and it exhibited high selectivity for Fe(3+) over other commonly coexistent metal ions in both 50% ethanol and Tris-HCl buffer. Upon the addition of Fe(3+), the spirocyclic ring of 4 was opened and a significant enhancement of visible color and fluorescence in the range of 500-600 nm was observed.