A new fluorene-based Schiff-base as fluorescent chemosensor for selective detection of Cr3+ and Al3.

2-((9H-fluoren-2-ylimino) methyl)phenol (F3) was synthesized by condensation reaction of 9H-fluoren-2-amine and 2-hydroxybenzaldehyde in EtOH and characterized by its melting point, 1H-,13C NMR and molecular mass. F3 exhibits a high selectivity for detection of Cr3+ and Al3+ ions as a fluorescent chemosensor and showed a single emission band at 536nm upon excitation at 333nm according to fluorescence emission studies. The addition of Cr3+ and Al3+ make a significant increase in fluorescent intensity at 536nm in CH3CN, while other metal ions have almost no influence on the fluorescence. The fluorescence enhancement was attributed to the inhibited CN isomerization and the obstructed excited state intra-molecular proton transfer (ESIPT) of compound F3. Job's plot and DFT calculations data showed that the binding stoichiometries of F3 with Cr3+ and Al3+ are 2:1. The association constants (Ka) for Cr3+ and Al3+ were calculated and found to be 8.33×104M-1 and 5.44×104M-1, respectively. The detection limits were also calculated for Cr3+ and Al3+ and found to be 2.5×10-7mol/L and 3.1×10-7mol/L, respectively.