Development of highly selective chemosensor for Al3+: Effect of substituent and biological application

A Schiff-base compound, 1-(2-hydroxy-5-methylphenylimino)naphthalen-2-ol (1b), has been synthesized and characterized using elemental analysis and different spectroscopic methods. It behaves as highly selective fluorescent chemosensor for Al(III) in 10 mM HEPES buffer in water:methanol (1:9, v/v) (pH 7.2). Fluorescence intensity at 552 nm (excitation at 450 nm) of 1b increases about 200 fold upon addition of 2 equiv. of Al3+ ion. Quantum yield of 1b increases about 10.8 times upon complex formation with Al3+. 1b forms complex with Al3+ in 1:1 ratio as supported by Job's plot analysis and mass spectroscopic measurement. Chelation enhanced fluorescence of 1b in the presence of aluminum(III) ion is evidenced from large decrease in nonradiative rate constant and high binding constant value. The probe molecule has been applied in living cell imaging study.