Microwave-assisted synthesis for a highly selective rhodamine 6G-derived fluorescent sensor and bioimaging

A new rhodamine 6G derivative R1 has been synthesized by condensation of rhodamine hydrazide and 6-hydroxymethyl-pyridine using microwave-assisted reaction. Naked-eye colorimetric and photo physical studies show the synthesized compound is selectively sensing Cu²⁺ in CH₃CN/H₂O (9:1, v/v) solution. Upon coordination with Cu²⁺ ion, the spirolactam of R1 is opened, which results in a formation of highly fluorescent complex and change in color of the solution. The Job's plot indicates 1:2 binding stoichiometry between Cu²⁺ ion and R1. Limit of detection for Cu²⁺ was determined to be 1.23 μM. The sensor was successfully applied to fluorescent imaging of Cu²⁺ ion in living cells.