Selective recognition of Cu2+ by di-O-picolyl derivative of 1,1′-methylene-bis(2-naphthol)

Di-derivatives of 1,1′-methylene-bis(2-naphthol) (L1) possessing ester (L2), carboxylic acid (L3) or picolyl (L4) as end groups of the pendants have been synthesized and characterized. Titration of these derivatives for their recognition towards M2+ (where M = Mg, Ca, Mn, Fe, Co, Ni, Cu, Zn) were performed by following the fluorescence emission intensities in methanol solution. The picolyl derivative (L4) has been found to be well suited for Cu2+ recognition (≤630 ppb) via the formation of 1:1 complex that was further proven based on absorption as well as ESI MS studies. On the other hand, L1 and L2 were mainly insensitive towards M2+, where as the carboxylic derivative (L3) shows fluorescence changes with almost all the metal ions and hence none of the L1, L2 and L3 are suited for any M2+ recognition. The studies clearly suggested that the chemical nature of the functional groups and the coordination preferences of the metal ion seem to play important role in the selective recognition of the metal ion.