A Highly Selective and Sensitive Fluorescent Turn-Off Probe for Cu2+ Based on a Guanidine Derivative.

A new highly selective and sensitive fluorescent probe for Cu2+, N-n-butyl-4-(1'-cyclooctene-1',3',6'-triazole)-1,8-naphthalimide (L), was synthesized and evaluated. The structure of compound L was characterized via IR, ¹H-NMR, 13C-NMR and HRMS. The fluorescent probe was quenched by Cu2+ with a 1:1 binding ratio and behaved as a "turn-off" sensor. An efficient and sensitive spectrofluorometric method was developed for detecting and estimating trace levels of Cu2+ in EtOH/H₂O. The ligand exhibited excitation and emission maxima at 447 and 518 nm, respectively. The equilibrium binding constant of the ligand with Cu2+ was 1.57 × 10⁴ M-1, as calculated using the Stern.