A differentially selective probe for trivalent chemosensor upon single excitation with cell imaging application:...

A new rhodamine 6G-benzylamine-based sensor (L¹), having only hydrocarbon skeletons in the extended part, was synthesized and characterized by single-crystal X-ray crystallographic study. It exhibited excellent selective and sensitive recognition of trivalent metal ions M³⁺ (M = Fe, Al and Cr) over mono- and di-valent and other trivalent metal ions. A large enhancement of the fluorescence intensity for Fe³⁺ (41-fold), Al³⁺ (31-fold) and Cr³⁺ (26-fold) was observed upon the addition of 3.0 equivalent of these metal ions into the probe in H₂O/CH₃CN (4 : 1, v/v, pH 7.2) with naked eye detection. The corresponding K_f values were evaluated to be 9.4 × 10³ M^-1 (Fe³⁺), 1.34 × 10⁴ M^-1 (Al³⁺) and 8.7 × 10³ M^-1 (Cr³⁺). Quantum yields of the L¹, [L¹-Fe³⁺], [L¹-Al³⁺] and [L¹-Cr³⁺] complexes in H₂O/CH₃CN (4 : 1, v/v, pH 7.2) were found to be 0.012, 0.489, 0.376 and 0.310, respectively, using rhodamine-6G as standard. LODs for Fe³⁺, Al³⁺ and Cr³⁺ were determined by 3σ methods and found to be 1.28, 1.34 and 2.28 μM, respectively. Cyanide ion scavenged Fe³⁺ from the [Fe³⁺-L¹] complex and quenched its fluorescence via its ring-closed spirolactam form. Advanced level molecular logic devices using different inputs (2 and 4 inputs) as advanced level logic gates and memory devices were constructed. The large enhancement in fluorescence emission of L¹ upon complexation with M³⁺ metal ions makes the probe suitable for the bio-imaging of M³⁺ (M = Fe, Al and Cr) in living cells.