Metal-centred versus ligand-centred luminescence quenching of a macrocyclic copper(II) complex

The new macrocyclic ligand trans-6-(9-anthracenylmethylamino)-6,13-dimethyl -1,4,8,11-tetraazacyclotetradecan-13-amine has been synthesized and charact erised as its copper(II) complex and the crystal structure of this complex has been determined. Fluorescence of the anthracenyl group of the macrocycl e is quenched in its free base form and when complexed with Cu-II. Fluoresc ence returns when Lewis acids such as H+ and Zn-II are added to solutions o f the ligand, indicating that photoinduced electron transfer from the amine lone pairs is responsible for fluorescence quenching in the free base form . By contrast, fluorescence of the complex is quenched by intramolecular el ectronic energy transfer.