Fluorescent turn-on sensors based on pyrene-containing Schiff base derivatives for Cu2+ recognition: spectroscopic and DFT computational studies

A new fluorescent chemosensor L1, a pyrene containing a long chain Schiff base derivative at the 1-position has been synthesized. Similarly, the receptors L2 and L3 are also designed in order to compare the binding ability for detection of Cu2+. The receptors exhibit very weak fluorescence (Φ=0.01) due to the photoinduced electron transfer (PET). Upon addition of 10 equiv of Cu2+, the emission intensity of ligands L1 and L2 are increased 65-fold (Φ=0.31) and 25-fold (Φ=0.08) in CH3CN/CH2Cl2 solvents system, respectively. NMR titration experiments, spectroscopic and DFT computational studies confirmed the binding phenomena and sensitivity of Cu2+.