Synthesis of a conjugated polymer for sensing ferric/ferrous cations based on dual responses

Abstract

AbstractA conjugated polymer (PPETE‐RB) with poly[p‐(phenylene ethynylene)‐alt‐(thienylene‐ethynylene)] (PPETE) as the backbone with pendant rhodamine B (RB) groups in the close‐ring spirolactam form was synthesized. With long spacer between backbone and pedant groups as well as long solubilizing side chains, the polymer possesses good solubility in most organic solvents and relatively large molecular weight. The fluorescence of the conjugated polymer in THF exhibited selective dual responses upon adding Fe3+/Fe2+ but negligible response upon other cations. The emission around 481 nm (excited at 360 nm) decreased and that around 571 nm (excited at 520 nm) emerged and increased when increasing the concentration of iron ions. The responses to Fe3+ and Fe2+ are very similar. The limits of detection were found to fall in between 6 μM and 8 μM. The mechanism study showed that the quenching around 481 nm was due to the inner filter effect (IFE) between the Fe3+/Fe2+ and PPETE‐RB; while that enhancement around 571 nm could be attributed to the formation of fluorescent ring‐open structure from nonfluorescent spirolactam of pedant RB group upon Fe3+/Fe2+. Such dual and opposite responses provided more reliable information than single response for sensing applications.