A colorimetric and “off–on” fluorescent Pd2+ chemosensor based on a rhodamine-ampyrone conjugate: synthesis, experimental and theoretical studies along with in vitro applications

Abstract

We successfully designed and developed a rhodamine based “turn-on” chemosensor L for the detection of Pd²⁺ ions down to 1.19 × 10⁻⁵ M (11.9 μM). In organo-aqueous solution, probe L displayed highly selective and sensitive colorimetric and fluorescence responses toward Pd²⁺ based on the ring-opening mechanism of the rhodamine spirolactam ring upon complexation with Pd²⁺. In the presence of Pd²⁺ ions, probe L formed an L–Pd²⁺ complex in 1 : 1 stoichiometry which was confirmed by the Job plot and mass spectroscopy. Moreover, we performed DFT (density functional theory) studies to identify the coordination characteristics and binding nature of L and the L–Pd²⁺ complex. In addition, cell imaging experiments revealed that probe L was able to permeate cells, and able to image Pd²⁺ in living cells.