Design, synthesis and photophysics of fluorescence 'turn-on' conjugated polymer chemosensors | Posted on:2007-09-02 | Degree:Ph.D | Type:Thesis | University:State University of New York at Binghamton | Candidate:Fan, Li-juan | Full Text:PDF | GTID:2451390005980143 | Subject:Chemistry | Abstract/Summary: | | This dissertation explores the synthesis, characterization, and application of conjugated polymers as fluorescence "turn-on" chemosensors. A series of conjugated polymers using the poly[p-(phenyleneethynelene)-alt-(thienylene-ethylene)](PPETE) polymer backbone were prepared using N,N-diethylamino (dea) and N,N,N'-trimethylethylenediamino (tmeda) groups as receptors. The conjugated polymers were designed as fluorescence "turn-on" chemosensors based on a photoinduced electron transfer (PET) mechanism in which the polymer fluorescence is quenched in the absence of coordinating analytes. A chelation-enhanced fluorescence (CHEF) phenomenon results upon coordination of a cation to the redox active receptor as a result of termination of the fluorophore quenching process. The polymers were fully characterizated by NMR, FTIR, Gel Permeation Chromatography (GPC) and elemental analysis.; Detailed photophysical studies of dea-PPETE and tmeda-PPETE demonstrated relatively weak emission at lambdamax = 488 nm with quantum yields of 0.11 and 0.09. Room temperature emission studies show that tmeda-PPETE exhibited a fluorescence "turn-on" response in the presence of many cations at less than 500 nM concentrations. For example, Hg2+ in aqueous solution causes the fluorescence of tmeda-PPETE to increase by a factor of 2.7 at less than millimolar concentrations. This represents the first example of a conjugated polymer applied as a fluorescence "turn-on" chemosensor based on the PET mechanism.; The competitive role of PET and energy migration is critical to sensor function. This was investigated by synthesizing a series of PPETE's with different amino receptor loadings. Theoretical and experimental studies revealed that the limited sensitivity achieved in this system may be attributed to relatively slow energy migration (<109s-1) along the polymer backbone relative to the emissive lifetime (∼10-10s).; A highly selective and sensitive sensory system towards iron cations in solution was achieved by preparing a transition metal derivatized conjugated polymer based on Cu2+ quenching. By preloading Cu2+ onto the receptor of tmeda-PPETE, fluorescence enhancements of 150 fold were achieved in the presence of 10 micromolar of iron cations. The combination of the conjugated polymer and metal cation created a selective sensor and offers a new paradigm for further sensor design. | Keywords/Search Tags: | Conjugated polymer, Fluorescence, Sensor, Turn-on | | Related items |
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