Rhodamine hydrazone as OFF–ON–OFF type selective sequential sensor of Al3+ and N3− ions

•A new rhodamine hydrazone (NLAC) is synthesized and characterized using spectroscopic and X-ray diffraction techniques.•Its selective binding with Al3+ ions at nano molar range made it fluorescent.•The fluorescent NLAC − Al3+ ensemble turns out to be non-fluorescent on binding with azide anion and the process is reversible.•Binding process is also demonstrated in a human cervical cancer cell lines (SiHa cells).

A new rhodamine hydrazone obtained by the condensation of rhodamine hydrazide with 5-iodo-3-methoxy salicylaldehyde (NLAC) is synthesized and characterized using spectroscopic (IR, UV–vis, 1H, 13CNMR, ESI-MS) and X-ray diffraction techniques. It binds selectively with Al3+ ions and a strong fluorescence signal is displayed from [NLAC − Al3+] ensemble and has also been supported by DFT calculation. The color change of NLAC in presence of Al3+ ions is further corroborated by UV-visible and fluorescence spectral titrations. The spectral changes are significant in the visible region of the spectrum and enable the detection of Al3+ ions with naked eye. The 1:1 stoichiometry of NLAC:Al3+ is supported by Job’s plot and ESI-MS data. The fluorescence signal displayed from [NLAC − Al3+] is quenched on the addition of N3− ions as an aqueous solution of NaN3 salt which reverts back further on the addition of Al3+ ions. This recognition process is also displayed in a human cervical cancer cell lines (SiHa cells) in an aqueous-acetonitrile medium. The process is repeated several times showing that the system is robust and reversible in the recognition process. A strip tests supports its feasibility for the laboratory demonstration.

Graphical abstractA newly synthesized and characterized non-fluorescent rhodamine hydrazone (NLAC) turned out to be fluorescent on its selective binding with Al3+ ions. The NLAC-Al3+ ensemble further becomes non-fluorescent on selective binding with N3− ions and the process was found reversible as demonstrated by absorption and fluorescence spectral changes. It is also demonstrated in a human cervical cancer SiHa cell lines using confocal microscopic images.Figure optionsDownload full-size imageDownload as PowerPoint slide