Turn-on fluorescent Fe3+ sensor based on tris(rhodamine) ligand

This chapter describes the prominent Fe³⁺ selective and sensitive fluorescence signaling behavior of tris(rhodamine)-based fluorescent chemosensor 2 in 75% CH3CN, 25% 0.01 M Tris-HCl buffer system. The fluorescence signaling of tris(rhodamine)-based fluorescent chemosensors 2 is remarkably selective fluorescence enhancement toward Fe³⁺ ions over other metal ions at 580 nm, under the optimized conditions. The fluorescence titrations of chemosensor 2 with various metal ions were conducted to examine the selectivity. Though Cu2+ gave a small color change and a very small fluorescence enhancement, the spectroscopy and interaction of chemosensor 2 with Cu²⁺ is completely different form of 2 with Fe³⁺ as reported by others. In chemosensor 2, several _{carbonyl oxygens as well as several amide oxygens can provide a stable binding pocket for Fe³⁺ ions. Mechanistically, tris(rhodamine) derivative has a good assosiation constant with Fe³⁺ as its complex with three carbonyl oxygens and three amide oxygens, thereby assisting the ring-opening of spirolactam, which increase the fluorescence instensity.}