A “turn-on” fluorescence probe towards copper ions based on core-substitued naphthalene diimide

An azathiacrown ether-substituted naphthalene diimide (NDI-4) was synthesized, which was nonlumincescent, but highly emissive once binding with copper ions, exhibiting a typical “turn-on” characteristic. NDI-4 possessed a favorable selectivity towards copper ions over other relevant metal ions, such as Hg2+, Li+, Ba2+, Co2+, Ni2+, Fe2+, Ag+, Zn2+, Mg2+, Na+, Ca2+, K+, Pb2+, Cd2+, Cr3+ and Al3+, and its detection limit was about 4.0 μM, much lower than the maximum acceptable level of Cu2+ in drinking water (∼20 μM). Furthermore, NDI-4 has been successfully applied to the detection of copper ions as “test strips” on silica gel plates.