A novel rhodamine-3,4-dihydro-2H-1,3-benzoxazine conjugate as a highly sensitive and selective chemosensor for Fe 3+ ions with cytoplasmic cell imaging possibilities

A novel, highly sensitive and selective fluorescent chemosensor ‘rhodamine-3,4-dihydro-2 H -1,3-benzoxazine’ [RH-BZN ( 1 )] has been synthesized and characterized by single crystal X-ray diffraction and other physicochemical techniques. In 3 : 7 water : MeCN (v/v) at pH 7.2 (10 mM HEPES buffer, μ = 0.05 M LiCl) it selectively recognizes Fe 3+ through 1 : 1 complex formation resulting in a 240-fold fluorescence enhancement and a binding constant ( K f ) of 1.50 × 10 4 M −1 . The otherwise non-fluorescent spirolactam form of the probe results in dual changes in absorbance and fluorescence arising out of opening of the spirolactam ring through coordination to Fe 3+ ions. This probe could suitably be employed for cytoplasmic intracellular imaging of Fe 3+ without notable cytotoxicity. The reversible binding of RH-BZN to Fe 3+ was confirmed by reacting with tetra- n -butylammonium fluoride both in extra- and intra-cellular conditions.