Synthesis of a fluorescent polymer bearing covalently linked thienylene moieties and rhodamine for efficient sensing

A novel conjugated polymer (RB-PPETE) of poly[p-(phenylene ethynylene)-alt-(thienylene ethynylene)] (PPETE) bearing covalently linked thienylene rings and Rhodamine B units has been synthesized and successfully used to detect metal ions. The Rhodamine B exists as a lactone, which is colorless and non-fluorescent. Hg(2+) ions can induce the Rhodamine group to form a ring-opened state. The fluorescence resonance energy transfer (FRET) was demonstrated in the polymer, and in the presence of Hg(2+) ions the excitation energy along the backbone of the conjugated polymer is transferred to the energy acceptor (Rhodamine B), which leads to a visual color change of the solution from slight yellow to orange. Meanwhile, this new system shows outstanding Hg(2+) -selective FRET off-on type fluoroionophoric properties among the representative metal ions in tetrahydrofuran.