A Fluorescent Sensor for Cu2+ Ion with High Selectivity and Sensitivity Based on ICT and PET.

A novel fluorescent sensor (L) based on 1,8-naphthalic anhydride has been developed which can selectively detect Cu2+ in CH3CN medium over other metal ions at 408 nm in the fluorescence spectra. When Cu2+ was added into L, L showed fluorescent turn-off by coordinating with Cu2+. A fresh absorption band was found at the position of 290 nm as was a red-shifted absorption band from 356 nm to 376 nm in UV-vis spectra which might be attributed to the intramolecular charge transfer (ICT). Meanwhile, L-Cu2+ showed fluorescence quenching via photoinduced electron transfer (PET). The complexation ratio was proposed to be 1:1 which was determined by Job's plot, fluorescence titration and 1H NMR titration. The detection limit was 9.1 × 10-8 mol·L-1, a satisfying level to detect Cu2+ in the micromolar scale. Corresponding molecular geometries, orbital energies and electron contributions of sensor L were calculated by the DMol3 program package using the density functional theory.