Highly Sensitive and Selective Rhodamine-based "off-on" Reversible Chemosensor for Tin (Sn4+) and Imaging in Living Cells

A structurally characterized new oxo-chromene functionalized rhodamine derivative L1 exhibits high selectivity toward Sn(4+) by forming a 1:1 complex, among other biologically important metal ions, as studied by fluorescence, absorption, and HRMS spectroscopy. Complexing with Sn(4+) triggers the formation of a highly fluorescent ring-open form which is pink in color. The sensor shows extremely high fluorescence enhancement upon complexation with Sn(4+), and it can be used as a "naked-eye" sensor. DFT computational studies carried out in mimicking the formation of a 1:1 complex between L1 and Sn(4+) resulted in a nearly planar pentacoordinate Sn(IV) complex. Studies reveal that the in situ prepared L1-Sn complex is selectively and fully reversible in presence of sulfide anions. Further, confocal microscopic studies confirmed that the receptor shows in vitro detection of Sn(4+) ions in RAW cells.