Effect of electron-donating/withdrawing substituents on the fluorescence of aniline containing fluorescein Schiff base derivatives

Two Schiff bases fluorescence sensors (FP 1 and FP 2 ) based on fluorescein-monoaldehyde derivatives were designed, synthesized and characterized. The effect of electron-donating and electron-withdrawing substituents on fluorescence of fluorescein was investigated. Through the calculation of the frontier orbital, it is proved that when the probe coexists with Cu 2+ , the complex system is more stable and easier to form. The FP 1 was used as effective fluorescent contrast agent for determining Cu 2+ from 0 to 55 μM with the limit of detection of 0.23 μM in several real water samples, sensing membranes and intracellular imaging.