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1、Energy Transfer Mediated Fluorescence from Blended Conjugated Polymer NanoparticlesChangfeng Wu, Hongshang Peng, Yunfei Jiang, and Jason McNeill*Abstract Nanoparticles consisting of a derivative of the blue-emitting conjugated polymer polyfluorene doped with green-, yellow-, and red-emitting conjuga
2、ted polymers were prepared by a reprecipitation method. The nanoparticles can be described as a system of densely packed chromophores that exhibit efficient energy transfer from the host to the dopant polymers. 2Abstract Fluorescence quenching analysis of the host polymer as a function of the dopant
3、 concentration indicates that one energy acceptor molecule can effectively quench 90% of the fluorescence of a nanoparticle consisting of 100-200 host conjugated polymer molecules. A nanoparticle energy transfer model was developed that successfully describes the quenching behavior of a small number
4、 of highly efficient energy acceptors per nanoparticle. 3Abstract The fluorescence brightness of the blended polymer nanoparticles was determined to be much higher than that of inorganic quantum dots and dye-loaded silica particles of similar dimensions. The combination of high fluorescence brightne
5、ss and tunable fluorescence of these blended nanoparticles is promising for ultrasensitive fluorescence-based assays.4Contents1.Introduction2.ExperimentalSection3.ResultsandDiscussion4.Conclusions51.Introduction Highly fluorescent nanoparticles have attracted much attention due to a variety of fluor
6、escence-based applications such as biosensing, imaging, and high-through put assays. Conjugated polymers are known to possess high absorption coefficients and high fluorescence efficiency, which have led to a wide range of applications in optoelectronic thin film devices. However, the use of conjuga
7、ted polymer nanoparticles in fluorescence labeling is still a largely unexplored area.61.Introduction Energy transfer in nanoscale systems has recently been demonstrated as the basis of molecular beacons for efficient biomolecule detection. Here we report on energy transfer mediated fluorescence fro
8、m conjugated polymer nanoparticles consisting of polyfluorene (PF) doped with three different conjugated polymer acceptors. 72.ExperimentalSection2.1Materials2.2NanoparticlePreparation2.3CharacterizationMethods82.1.MaterialsHostPF：poly(9,9-dihexylfluorenyl-2,7-diyl) ( MW 55 000, polydispersity 2.7)
9、DopantsPFPV： poly9,9-dioctyl-2,7-divinylenefluorenylene-alt-co-2-methoxy-5-(2- ethylhexyloxy)-1,4-phenylene ( MW 270 000, polydispersity 2.7), PFBT：poly(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-2,1,3-thiadiazole) ( MW 10 000, polydispersity 1.7)MEH-PPV：poly2-methoxy-5-(2-ethylhexyloxy)-1,4-pheny
10、lenevinylene ( MW 200 000, polydispersity7.0) THF：Tetrahydrofuran (anhydrous, 99.9%),92.2.NanoparticlePreparationTHF+ polymerinert atmospherestirring overnightfilteredc=40 ppmhomogeneous solutions+ dopant(0 to 10 wt %)dilutedstirredPreparation of the aqueous dispersion of blended conjugated polymer
11、nanoparticles102.2.NanoparticlePreparation8 mL of deionizedwater nanoparticle dispersionssuspension 2 mL of solution mixture added quicklysonicatingfiltered partial vacuum evaporationThe resulting nanoparticle dispersions are clear and stable for months with no signs of aggregation.112.3.Characteriz
12、ationMethodsMorphology and size distribution of the polymer blend nanoparticles were characterized by atomic force microscopy (AFM). The UV-vis absorption spectra were recorded with a Shimadzu UV-2101PC scanning spectrophotometer, using 1 cm quartz cuvettes. Fluorescence spectra were collected with
13、a commercial fluorometer (Quantamaster, PTI, Inc.), using a 1 cm quartz cuvette.123.ResultsandDiscussionDiagram3.1.NanoparticleSizeandMorphology3.2.OpticalProperties3.3.NanoparticleEnergyTransferModel133.1.NanoparticleSizeandMorphology(a) Chemical structures of the conjugated polymers143.1.Nanoparti
14、cleSizeandMorphology(b) a representative AFM image of blend nanoparticles dispersed on silicon substrate(c) histogram of particle height data taken from AFM image153.2.OpticalProperties(d) photograph of fluorescence emission from aqueous suspensions of the blend nanoparticles taken under a UV lamp (
15、365 nm).163.2.OpticalPropertiesFigure 2. (Left) Normalized absorption and fluorescence emission spectra of conjugated polymers PF, PFPV, PFBT, and MEH-PPV in THF solution. (Right) Normalized absorption (dashed) and fluorescence excitation and emission spectra (solid) of pure PF and polymer blend nan
16、oparticles.415550535500430173.2.OpticalPropertiesFigure 3. (Left) Concentration-dependent fluorescence spectra of polymer blend nanoparticles under 375 nm excitation. (Right) Fluorescence intensity change of PF host and dopant polymers as a function of dopant concentration in blend nanoparticles. 18
17、3.3.NanoparticleEnergyTransferModelThe dependence of host polymer fluorescence intensity on the concentration of dopant (quencher) was modeled by using the Stern-Volmer relation, which can be expressed as：F0 - fluorescence intensities in the absence of quencherF - fluorescence intensities in the pre
18、sence of quencherKSV - Stern-Volmerquenching constantQ - the concentration of the quencherF0/F=1=KsvQ19 kr -radiative rates of the host knr - nonradiative rates of the host ket - energy transfer rate of a single quencher n-the number of quenchers present in the nanoparticle (F/F0)-relative fluoresce
19、nce intensity q-quenching efficiency per quencher molecule n - the average number of donor molecules per nanoparticle. 3.3.NanoparticleEnergyTransferModel20Figure 4. Fluorescence quenching of PF donor versus molar fraction of quenchers in polymer blend nanoparticles. The scattered squares are experi
20、mental data, while the black dashed curves are model results given by eq 5. The solid lines represent linear Stern-Volmer plots of PF fluorescence quenched by three quenchers in the low concentration range. 3.3.NanoparticleEnergyTransferModel214.Conclusions PF nanoparticles doped with PFPV, PFBT, an
21、d MEH-PPV, respectively, were prepared by a reprecipitation method. Salient features of the nanoparticles include their high fluorescence brightness and suitability for fluorescence multiplexing applications. In some cases, the dependence of nanoparticle fluorescence on composition was found to devi
22、ate substantially from the Stern-Volmer relation.224.Conclusions Analyses by both Stern-Volmer relation and the nanoparticle energy transfer model reveal highly efficient energy transfer between the host and the guest molecules. Both models indicate that approximately 100 or more host molecules are quenched by a single dopant molecule.23THANKYOU!24
