Mono-N-benzyl cyclen: A highly selective, multi-functional “turn-on” fluorescence sensor for Pb2+, Hg2+ and Zn2+

Abstract Metal complexing and fluorescence properties of MB-cyclen (1-phenylmethyl​-1,​4,​7,​10-​tetraazacyclododecan​e) and its complexes with metal ions in 50% CH3OH/H2O are described. The crystallographic structures of the complexes [(Zn(MB-cyclen))2OH](ClO4)3(2.13H2O), [Ag(MB-cyclen)(ClO4)], [Pb(MB-cyclen)(ClO4)2], [Hg(MB-cyclen)(ClO4)2], [Cu(MB-cyclen)(ClO4)2], and [Ni(MB-cyclen)(ClO4)2] are reported. The normal fluorescence peak of the benzyl group was observed at 289 nm and only the ZnII ion showed a strong CHEF (chelation enhanced fluorescence) effect for the 289 nm peak, which is in line with its lower position in the well-known order of ability to form fluorescence quenching π contacts: ZnII