Restricted Intramolecular Rotation: A Dual Fluorescence Response to Hg²⁺ Quenching and Ag⁺ Enhancement in Live Rhizoctonia Solani Cells

A novel imidazo[1,2-a]pyridine derivative probe (R) was designed, synthesized, and characterized via various characterization techniques, such as ESI-MS, ¹H NMR, ¹³C NMR, and Dept-135 NMR. The data obtained from single-crystal XRD reveal that probe R has a coplanar configuration and is part of the monoclinic crystal system, designated the P2(1)/n space group. The fluorescence of (R) is further enhanced by silver (I) ions. On the other hand, Hg²⁺ significantly quenches the fluorescence of probe R. The presence of other common metal ions does not influence the fluorescence of probe R in the CH₃CN: H₂O (1:1) mixture, as they neither increase nor quench it. From the fluorescence enhancement data, the low detection limit (LOD) for Ag + ions was determined to be 1.24 × 10^− 8 M, whereas the quenching caused by Hg²⁺ resulted in an LOD of 5.69 × 10^− 9 M. The complex of probe R with Ag⁺/Hg²⁺ exhibited a 1:1 stoichiometry, as confirmed by mass spectrometry and a Job plot. Single-crystal XRD analysis of R and its complex with Hg²⁺ revealed a loss of coplanarity, which confirmed their nonfluorescent behavior. We present a promising application of probe R in visualizing living Rhizoctonia oryzae cells exposed to silver (I) and mercury (II) ions.