Study on a highly selective fluorescent chemosensor for Cu2+ and its direct sensing for proton based on 1,3,4-oxadiazole

Abstract A photoinduced electron transfer cation sensor, oxadiazole-bridge-bis(N,N-bis(2-pyridylmethyl)amine), was designed and prepared. This sensor displayed an “off–on–off” fluorescent switch for proton and an “on–off” fluorescent switch for Cu 2+ . The fluorescence emission of the sensor was quenched upon addition of Cu 2+ and proton in CH 3 CN/H 2 O solution (v/v, 4:1) due to electron transfer between the N,N-bis(2-pyridylmethyl)amine and the oxadiazole. The sensor presented high selectivity for Cu 2+ over other metal ions and determined Cu 2+ concentration in a linear fashion from 5×10 −7  M to 8×10 −5  M. Stern–Volmer analysis showed the binding stoichiometry to be 1:2 (host-guest) with a binding constant of 1.8×10 10  M −2 , calculated using the Benesi–Hilderbrand equation. The response of the sensor to Cu 2+ was instantaneous and reversible, and the usual anions did not influence the selectivity for Cu 2+ .