Two new pyridine-type rhodamine B chemosensors (RBPO and RBPF) used to detect Fe ³⁺ have been designed and synthesized, and the sensing behavior towards various metal ions was evaluated via UV–vis and fluorescence spectroscopic techniques.

A new fluorescent chemosensor based on a Rhodamine B and a benzyl 3-aminopropanoate conjugate (RBAP) was designed, synthesized, and structurally characterized. Its single crystal structure was obtained and analyzed by X-ray analysis. In a MeOH/H₂O (2:3, v/v, pH 5.95) solution RBAP exhibits a high selectivity and excellent sensitivity for Sn²⁺ ions in the presence of many other metal cations. The binding analysis using the Job’s plot suggested the RBAP formed a 1:1 complex with Sn²⁺.

A novel Rhodamine B-derivatized host [2]rotaxane, containing a dibenzyl-24-crown-8 (DB24C8) ring as the wheel and a pyrene as another fluorophore blocking group, was designed, synthesized and structurally characterized. A comparison of the ¹H NMR spectra of RhBPy [2]rotaxane with those of 2 and DB24C8, nuclear Overhauser effect spectroscopy (NOESY), mass spectrometry and fluorescence spectroscopy confirmed the interlocked nature of RhBPy [2]rotaxane. The temperature dependence of the rotaxane studied by ¹H NMR spectroscopy further demonstrated that RhBPy [2]rotaxane can be applied as a molecular switch. RhBPy [2]rotaxane has also been demonstrated to be an efficient transport agent for delivering the cancer drug doxorubicin (DOX) into tumor cells. Indeed, DOX delivered by RhBPy [2]rotaxane could effectively inhibit tumor cell growth.