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A new approach to fluorescence “turn-on” chemosensors based on a photoinduced electron transfer (PET) strategy involving conjugated polymers has been developed. Two new conjugated polymers dea-PPETE and tmeda-PPETE were synthesized and characterized. These two polymers use diethylamino and N,N,N‘-trimethylethylenediamino as receptors, respectively, on a poly[p-(phenyleneethylene)-alt-(thienyleneethynylene)] (PPETE) fluorescent conjugated polymer backbone. The polymers were found to be relatively weakly emissive at λ_max  488 nm with quantum yields of 0.11 and 0.09, respectively, at room temperature in THF solution. Initial investigations show that the tmeda-PPETE selectively detects some metal cations by an observed increase in fluoresence. In particular, Hg²⁺ in aqueous solution causes the fluorescence of tmeda-PPETE to increase by a factor of 2.7 at less than micromolar concentrations. The photophysical results are consistent with a PET mechanism for fluorescence quenching, which is removed upon binding of the analyte.