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 Cd2+ over many other metal ions (K+, Na+, Ca2+, Mg2+, Mn2+, Fe2+, Ni2+, Co2+, Cu2+, Ag+, Hg2+, Zn2+, and Cr3+) based on the intramolecular charge-transfer mechanism, which makes HPDQ a potential fluorescence sensor or probe for Cd2+. An obvious color change between HPDQ and HPDQ + Cd2+ 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.