A new fluorene derived Schiff-base as a dual selective fluorescent probe for Cu and CN.

A new fluorene based fluorogenic chemosensor, 2-[(9H-Fluoren-2-ylmethylene)-amino]-phenol (L), has been designed, synthesized, and characterized by CHN analyses and different spectroscopic methods. This turn-on fluorogenic chemosensor shows high selectivity and sensitivity toward Cu and CN with low detection limits of 1.54 × 10 M and 1.83 × 10 M, respectively. The stoichiometry ratio of L-Cu in solution is 1:1, by the method of Job's plot and ESI-MS. The microcrystalline solid product of the chemosensor reaction with copper is characterized as CuL. The χT value for CuL is temperature independent at a value of 0.403 cm K mol, which is in agreement with a mononuclear copper(II) complex with an isotropic g-value of 2.075. The fluorescence turn-on recognition process for detection of Cu is attributed to the restricted imine isomerization and blocking of intramolecular charge transfer (ICT) quenching process in the analyte-bound sensor. The selectivity of L for Cu is based on the chelation-enhanced fluorescence effect (CHEF) mechanism. Other interfering ions such as Na, K, Ca, Mg, Ag, Fe, Fe, Co, Ni, Zn, Cd, Hg, Mn, Pb and Al, show no change in the fluorescence intensity of L in the presence of Cu. Furthermore, the compound L can be used as a fluorescence and colorimetric sensor for selective detection of CN over a number of other anions based on the nucleophilic addition to the imine CN bond, with consequent hydrogen bond formation and electrostatic interaction of the resulting product with K. The sensing mechanism for CN was theoretically supported by DFT calculations.