A conjugated polymer was synthesized by the polymerization of 4,7-dibromobenzo[2,1,3]thiadiazole (M-1) with tri{1,4-diethynyl-2,5-bis(2-(2-methoxyethoxy)-ethoxy)}-benzene (M-2) via Pd-catalyzed Sonogashira reaction. The polymer shows strong orange fluorescence. The responsive optical properties of the polymer on various metal ions were investigated through photoluminescence and UVvis absorption measurements. The polymer displays highly sensitive and selective on-off Hg2+ fluorescence quenching property in tetrahydrofuran solution in comparison with the other cations including Mg2+, Zn2+, Co2+, Ni2+, Cu2+, Ag+, Cd2+, and Pb2+. More importantly, the fluorescent color of the polymer sensor disappears after addition of Hg2+, which could be easily detected by naked eyes. The results indicate that this kind of polymer sensor incorporating benzo[2,1,3]thiadiazole moiety as a ligand can be used as a novel colorimetric and fluorometric sensor for Hg2+ detection. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 50: 517-522, 2012