nBenzimidazole-chalcone 3 functions as an optical probe on the basis of intramolecular charge-transfer (ICT) interaction involving bi-dentate chelation. Dramatic changes were observed both in the UV-vis and fluorescence behaviors of 3 in the presence of Zn2+, while other metal ions e.g. Li+, Na+, K+, Ca2+, and Mg2+ produced relatively insignificant optical changes.