Reversible ‘turn off’ fluorescence response of Cu2+ ions towards 2-pyridyl quinoline based chemosensor with visible colour change

Abstract

A novel chemosensor, 4(1H-benzo[d]imidazol-2-yl)-2-(pyridin-2-yl)quinoline is described which could selectively detect Cu2+ ions. Addition of Cu2+ ions changes solution of chemosensor from colourless to yellow which is clearly visible to the naked eyes. Fluorescence of chemosensor was quenched by 18 folds in presence of Cu2+ ions. Cu2+ ions sensing property of chemosensor was remained unaffected in presence of other metal ions (Na+, Mg2+, K+, Mn2+, Ca2+, Fe2+, Co2+, Zn2+, Cd2+, Ba2+, Hg2+ and Pb2+). Moreover, the sensing of Cu2+ was found to be reversible, since the Cu2+ induced quenching of emission spectra was reversed upon addition of EDTA. The stoichiometry of binding of chemosensor and Cu2+ was determined by Job‘s plot which was found to be 1:1 and further it was confirmed by ESI-MS analysis. Binding of Cu2+ ions to chemosensor was studied over the wide pH range and the result demonstrated maximum fluorescence quenching in the pH range of 3.0–10. The binding association constant (Ka) value determined from Benesi–Hildebrand equation was 3.38×105M−1.