Ion-Induced Chromo(fluoro)genic Rearrangements of Rhodamine Derivatives

Abstract— A series of rhodamine B derivatives containing hydroxyimine receptor fragments was synthesized. The reaction of a 1-hydroxynaphthalene-2-carbaldehyde derivative in acetonitrile proceeds selectively with copper(II) cations and is accompanied by chromogenic naked-eye effect, a change in color from pale yellow to crimson red (λ_abs 548 nm) due to the cation-induced opening of the spirolactam ring, and the appearance of fluorescence in the region of 578 nm. The subsequent addition of CN^– ions to the in situ formed complex leads to its selective anion-induced reverse isomerization into the spiro form, and the original spectral parameters are restored. In ethanol, o-hydroxy(dihydroxy)naphthalenecarbaldehyde derivatives selectively detect Al³⁺ cations that induce the rhodamine spirolactam ring opening with the attendant chromogenic naked eye effect, a change in the color of the solution from pale yellow to crimson violet, and a burst of strong fluorescence (λ_fl 584 nm).