A highly selective on/off fluorescence sensor for cadmium(II).

A polypyridyl ligand, 2,3,6,7,10,11-hexakis(2-pyridyl)dipyrazino[2,3-f:2',3'-h]quinoxaline (HPDQ), was found to have excellent fluorescent selectivity for Cd(2+) over many other metal ions (K(+), Na(+), Ca(2+), Mg(2+), Mn(2+), Fe(2+), Ni(2+), Co(2+), Cu(2+), Ag(+), Hg(2+), Zn(2+), and Cr(3+)) based on the intramolecular charge-transfer mechanism, which makes HPDQ a potential fluorescence sensor or probe for Cd(2+). An obvious color change between HPDQ and HPDQ + Cd(2+) can be visually observed by the naked eye. The structure of the complex HPDQ-Cd has been characterized by X-ray crystallography. Density functional theory calculation results on the HPDQ and HPDQ-Cd complexes could explain the experimental results.