A quick and selective rhodamine based “smart probe” for “signal-on” optical detection of Cu²⁺ and Al³⁺ in water, cell imaging, computational studies and solid state analysis

A novel rhodamine hydrazone 1 has been synthesized by the condensation of rhodamine B hydrazide with allylsalicylaldehyde and has been fully characterized using various physicochemical techniques including single crystal XRD. Probe 1 can detect Cu²⁺ and Al³⁺ ions in aqueous media and displays a turn-on response in absorbance with a high degree of selectivity amongst other common interfering analytes. Al³⁺ ions lead to fluorescence enhancementby the opening of the spirolactum ring resulting in chelation enhanced fluorescence. DFT and TDDFT calculations support the experimental results. The 1-Al³⁺ ensemble acts as secondary sensor for pyrophosphate anion due to metal ion induced decomplexation resulting in a low detection limit. Probe 1 can be utilized for bio imaging and displays morphological transformations from crystalline to amorphous state with associated color changes due to mechanical switching. In the solid state, probe 1 displays distinct color changes with emission at different wavelengths in particular Al³⁺ and Hg²⁺result in a red shift of the CIE-diagram. While the band gap of probe 1can be tuned from 2.08 eV to 1.60 eV.Probe 1 meets many real-world-challenges in that it is prepared using simple synthetic methods, produces fast and distinct response towards multiple-ions, observed by the “naked eye” in solution and on a TLC plate, and can be exploited for binary data storage.