Investigating the photophysics of fluorescent conjugated polymer chemosensors in the solid state.

摘要

A functionalized fluorescent conjugated polymer, poly[2,5-(3-[1,2,( E)-ethenyl-1,4-phenylene-4-{2,6-di(pyridin-2-yl)}pyridinyl]thiophenediyl)-1,2-ethynediyl-1,4-(2,5-didodecoxyphenylenediyl)-1,2-ethyndiyl] (ttp-PPETE) was designed, and synthesized by Sonogoshira type coupling, to detect trace amounts of toxic transition metal pollutants in ground water. Photophysical studies in tetrahydrofuran (THF) successfully demonstrated this polymer was a selective and sensitive chemosensor for Ni2+ and Co2+ in aqueous solution. Solid state composites of these chemosensors have now been prepared which can be modified to provide inexpensive and portable field based chemical detection tools. Solid composite of ttp-PPETE, blended with poly (methyl methacrylate) shows UV-Vis absorption and fluorescence emission spectra which are red- shifted when compared to solution phase spectra, suggesting an increase in conjugation in the solid state. An additional absorption peak, not present in solution, is also observed in the solid state. The presence of this new peak provides evidence of aggregation and pi-interactions of the fluorescent conjugated polymer chains in the solid state. Concentration dependent experiments were done on the solid composites which show red-shifted emission peaks accompanied by a significant reduction in the fluorescent quantum yield, these observations are consistent with aggregation. Minimal fluorescence quenching is observed when surface receptors are exposed to the Ni 2+ analyte in solution. However, increased quenching is seen when below-surface receptors are exposed to the analyte. Downward curvature of Stern-Volmer plots reveal that some fluorophores are accessible to the analyte while others are not. Intermolecular interactions of this type can be manipulated in the design of sensitive and selective solid state fluorescent conjugated polymer sensors.;A new polymeric chemosensor with bulky pentacene framework was designed and synthesized that has the potential of reducing intermolecular interaction of polymer strands in the solid state. Preliminary solution phase studies of this new polymer shows fluorescence quenching in the presence of several cation such an Fe3+, Fe2+, Ni2+and Co2+. Fluorescence lifetime data were best fitted to a single exponential function, which shows a slightly higher lifetime in solution relative to the solid state. The data obtained from fluorescence quenching and lifetime experiment was treated quantitatively by Stern-Volmer analysis. The fluorescence quenching plot shows an upward curvature which is indicative of two quenching mechanisms, one of which is confirmed by the relatively constant fluorescence lifetime of the sensors when titrated with similar concentrations of Ni 2+ ions. The invariance in fluorescence lifetime is indicative of a static quenching mechanism.