Reaction of Zn(II) with a BINOL-amino-acid Schiff base: An unusual off-on-off fluorescence response

Abstract An amino-acid based Schiff base ( S )- 2 is prepared from the condensation of ( S )-3,3′-diformyl BINOL (BINOL = 1,1′-bi-2-naphthol) with l -valine in the presence of tetrabutylammonium hydroxide in methanol. This compound is found to exhibit off-on-off fluorescence response toward Zn 2+ . The spectroscopic studies reveal that ( S )- 2 reacts with 1 equiv Zn 2+ to form a dimeric [2+2] complex with greatly enhanced fluorescence. Excess amount of Zn 2+ might cause dissociation of this dimeric complex to give significantly reduced fluorescence.