Development of a new chemosensor for Al3+ ion: Tuning of properties

We have synthesized and characterized three Schiff-base molecules, namely, 1-(((2-hydroxybenzylidene)hydrazono)methyl)naphthalen-2-ol (H2L), (1-(((2-hydroxy-5-nitrobenzylidene)hydrazono)methyl)naphthalen-2-ol (H2L-NO2) and 1-(((2-hydroxy-5-methylbenzylidene)hydrazono)methyl)naphthalen-2-ol) (H2L-Me). Out of these three compounds, H2L-NO2 has been found to be a selective fluorescent chemosensor for Al3+ Fluorescence intensity of H2L-NO2 at 517 nm (lambda(ex) = 390 nm) is increased significantly in the presence of Al3+ Other relevant metal ions cannot induce considerable enhancement in its emission intensity. The enhancement has been explained using PET and CHEF mechanism. Quantum yield and life -time of H2L-NO2 have increased in the presence of one equivalent of Al3+. H2L-NO2 forms 1:1 complex with the metal ion which is confirmed from Job's plot and ESI mass spectral analysis. Its sensitivity has been determined by 3 sigma method and found to be moderate. Emission intensity of H2L and H2L-Me does not increase appreciably in the presence of Al3+. Presence of electron withdrawing group in H2L-NO2 may be responsible for its aluminum sensing properties.