Rhodamine 6G-based efficient chemosensor for trivalent metal ions (Al3+, Cr3+ and Fe3+) upon single excitation with applications in combinational logic circuits and memory devices

Abstract

A new rhodamine 6G-based chemosensor (L³) was synthesized and characterized by ¹H, ¹³C, IR and mass spectroscopy studies. It exhibited an excellent selective and sensitive CHEF-based recognition of trivalent metal ions M³⁺ (M = Fe, Al and Cr) over mono and di-valent and other trivalent metal ions with prominent enhancement in the absorption and fluorescence intensity for Fe³⁺ (669-fold), Al³⁺ (653-fold) and Cr³⁺ (667-fold) upon the addition of 2.6 equivalent of these metal ions in the probe in H₂O/CH₃CN (7 : 3, v/v, pH 7.2). The corresponding K_d values were evaluated to be 1.94 × 10⁻⁵ (Fe³⁺), 3.15 × 10⁻⁵ (Al³⁺) and 2.26 × 10⁻⁵ M (Cr³⁺). The quantum yields of L³, [L³–Fe³⁺], [L³–Al³⁺] and [L³–Cr³⁺] complexes in H₂O/CH₃CN (7 : 3, v/v, pH 7.2) were found to be 0.0005, 0.335, 0.327 and 0.333, respectively, using rhodamine-6G as the standard. The LODs for Fe³⁺, Al³⁺ and Cr³⁺ were determined by 3σ methods and found to be 2.57, 0.78 and 0.47 μM, respectively. The cyanide ion snatched Fe³⁺ from the [Fe³⁺–L³] complex and quenched its fluorescence via its ring-closed spirolactam form. Advanced level molecular logic devices using different inputs (2 and 4 input) and a memory device were constructed.