Fluorometric Turn Off Detection of Cu and Pd Ions Using 1-(Imidazo[5,1-a]isoquinolin-3-yl)naphthalen-2-ol.

The fused heterocycle 1-(imidazo[5,1-a]isoquinolin-3-yl)naphthalen-2-ol (LH) has been synthesized and characterized by spectroscopic methods. Probe LH upon irradiation with λ = 336 nm exhibited strong fluorescence with λ = 437 nm in MeOH/HEPES buffer (5 mM, pH = 7.4, 2:8, v/v). Upon adding several metal ions, the fluorescence intensity was quenched only by Cu and Pd ions. This fluorescence turn-off response by Cu and Pd ions was observed even in the coexistence of other metal ions and anions. From the Job's plot and mass spectra analysis, a 2:1 ratio of LH:M was obtained, and the composition [Cu(L)HO] and [Pd(L)] has been assigned. The detection limit for Cu and Pd ions was determined to be 0.24 and 0.35 μM, respectively, and workable pH window to be 4-10. The binding of LH to Cu and Pd resulted in red-shift in the UV-visible spectrum, which was supported by DFT/TDDFT calculations.