A novel conjugating polyfluorene bearing N,N-diethyl-2-(4-phenoxy)-thioacetamide as side chain was designed for the detection of Hg(II) ions. It was synthesized through postfunctionalization of acetamide-based polyfluorene derivative. Upon the addition of Hg(II) ions, the thioacetamide groups of this polymer side chains were specifically reacted with Hg(II) ions, leading to this chemodosimeter with higher selectivity for Hg(II) over other metal ions tested under the same conditions. In addition, on the basis of the effect of fluorescent signal amplifications originated from electron transmission along the backbone, this designed conjugated polyfluorene with pendent reactive thioacetamide reached ultra high sensitivity for the detection of mercury ions. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012