A new tetramine bis(2-naphthol)-derivative fluorescent chemosensor for aluminum ion (Al3+)

Abstract A new tetramine bis(2-naphthol)-derivative was synthesized and its structure investigated by 1H- and 13C NMR, UV-Vis absorption and fluorescence spectroscopies, as well as through density functional theory calculations (including time-dependent DFT). The effect of a series of metal ions (Ag +, Al3 +, Ba2 +, Ca2 +, Cd2 +, Co2 +, Cs +, Cu2 +, Fe2 +, Fe3 +, K +, Mg2 +, Mn2 +, Ni2 +, Pb2+ and Zn2+) on the fluorescence spectra of the synthesized compound was then investigated and it was observed that the presence of Al3+ ion causes a strong increase in the fluorescence emission of the ligand, by about 70 times. This exceptional intensification is specific for Al3+ within the whole series of ions investigated, together with the selectivity found for many of the remaining ions (in particular the ions of Groups I and II of the Periodic Table and Mn2+), makes the compound a promising candidate to act as chemosensor for Al3+. Possible structures for the ligand:Al3+ complex are suggested based on DFT results. TD-DFT calculations performed on these structures suggest that the fluorescence enhancement upon binding of Al3+ to the ligand results most probably from metal-to-ligand charge transfer where the acceptor groups of the ligand are the naphthol moieties.