A selective ‘turn-on’ fluorescent chemosensor for detection of Al3+ in aqueous medium: Experimental and theoretical studies.

A Schiff-base compound, 2-((E)-1-(2-(dimethylamino)ethylimino)ethyl)phenol (HL), has been synthesized and characterized by different spectroscopic methods The chemosensor shows selective “turn–on” cyan colour fluorescence response to Al 3+ ion over a wide variety of other competing metal ions such as Zn 2+ , Cu 2+ , Co 2+ , Ni 2+ , Cd 2+ , Fe 2+ , Mg 2+ , Hg 2+ , Mn 2+ , Ca 2+ , Pb 2+ , Fe 3+ , Cr 3+ , Na + and K + . The fluorescence emission intensity at 462 nm displayed by the chemosensor, increases progressively during the addition of Al 3+ ion until saturation point, with over 20 fold intensity enhancement. Additionally, the linear range for the chemosensor has been found to be 0.5 × 10 −6 to 10 × 10 −6  mol/L, the detection limit of the chemosensor is 4.32 × 10 −6  M and the stability constant is 2.1 × 10 4  M −1 . Similar fluorescence behaviour is also observed in a variety of solvents and solvent mixtures in the presence of Al 3+ . The fluorescent emission has also been detected when a sample solution of HL containing Al 3+ is irradiated by UV light. UV–vis titration experiment has established that the chemosensor HL, binds to Al 3+ in 2:1 ratio. The Density Functional Theory (DFT) and Time Dependent-Density Functional Theory (TD–DFT) calculations were performed on HL, L − and its aluminium complex which give insight into the geometric, electronic, thermodynamic and optical properties of chemosensor-Al 3+ interactions. [ABSTRACT FROM AUTHOR]