Highly Selective Schiff-Base Fluorescent Probe for Rare Earth Ion Lu3+

A novel Schiff base fluorescent probe for rare earth ion Lu3+ is reported. Emission intensity of the probe is intrinsically non-fluorescent, which is due to isomerization of the C=N bond in the excited-state proton transfer (ESPT) of phenolic protons of the salicylic amide moiety. In the presence of Lu3+, fluorescence intensifies significantly due to inhibition of the C=N isomerization and ESPT. The Schiff base is characterized by high sensitivity and selectivity towards Lu3+. The fluorescence turn-on mechanism of Lu[L]2 system is proposed.