A highly selective rhodamine based turn-on optical sensor for Fe3+

A reversible turn-on sensor (Rh–OH–Rh) which can selectively detect Fe3+ in solution has been developed. The sensor combines two rhodamine moieties with a 3-oxygen Fe3+ receptor to provide excellent selectivity for Fe3+ over a range of biologically relevant metal ions. It binds Fe3+ in a 1:1 stoichiometry with an apparent binding constant 5.2 × 106 M− 1 (log K = 5.28) in ACN/DMF (9/1 v/v) solution. The sensor displays distinct “on–off” changes in color and fluorescence upon the alteration of free Fe3+ levels in solution with a reversible response and little interference with other biological relevant metal ions.