1、Energy Transfer Mediated Fluorescence from Blended Conjugated Polymer NanoparticlesChangfeng Wu, Hongshang Peng, Yunfei Jiang, and Jason McNeill*2Abstract Nanoparticles consisting of a derivative of the blue-emitting conjugated polymer polyfluorene doped with green-, yellow-, and red-emitting conjug
2、ated 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. 3Abstract Fluorescence quenching analysis of the host polymer as a function of the dopan
3、t 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 numbe
4、r of highly efficient energy acceptors per nanoparticle. 4Abstract 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 brightn
5、ess and tunable fluorescence of these blended nanoparticles is promising for ultrasensitive fluorescence-based assays.5Contents1. Introduction2. Experimental Section3. Results and Discussion4. Conclusions6 1.Introduction Highly fluorescent nanoparticles have attracted much attention due to a variety
6、 of fluorescence-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 o
7、f conjugated polymer nanoparticles in fluorescence labeling is still a largely unexplored area.7 1.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 fluore
8、scence from conjugated polymer nanoparticles consisting of polyfluorene (PF) doped with three different conjugated polymer acceptors. 82.Experimental Section2.1 Materials2.2 Nanoparticle Preparation2.3 Characterization Methods92.1. MaterialsHostPF：poly(9,9-dihexylfluorenyl-2,7-diyl) ( MW 55 000, pol
9、ydispersity 2.7) 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-ethylhe
10、xyloxy)-1,4-phenylenevinylene ( MW 200 000, polydispersity7.0) THF：Tetrahydrofuran (anhydrous, 99.9%),102.2. Nanoparticle PreparationTHF+ polymerinert atmospherestirring overnightfilteredc=40 ppmhomogeneous solutions+ dopant(0 to 10 wt %)dilutedstirredPreparation of the aqueous dispersion of blended
11、 conjugated polymer nanoparticles112.2. Nanoparticle Preparation8 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 aggrega
12、tion.122.3. Characterization MethodsMorphology 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 spec
13、tra were collected with a commercial fluorometer (Quantamaster, PTI, Inc.), using a 1 cm quartz cuvette.133.Results and DiscussionDiagram3.1. Nanoparticle Size and Morphology3.2. Optical Properties3.3. Nanoparticle Energy Transfer Model143.1. Nanoparticle Size and Morphology(a) Chemical structures o
14、f the conjugated polymers153.1. Nanoparticle Size and Morphology(b) a representative AFM image of blend nanoparticles dispersed on silicon substrate(c) histogram of particle height data taken from AFM image163.2. Optical Properties(d) photograph of fluorescence emission from aqueous suspensions of t
15、he blend nanoparticles taken under a UV lamp (365 nm).173.2. Optical PropertiesFigure 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
16、spectra (solid) of pure PF and polymer blend nanoparticles.415550535500430183.2. Optical PropertiesFigure 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
17、of dopant concentration in blend nanoparticles. 193.3. Nanoparticle Energy Transfer ModelThe 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 abse
18、nce of quencherF - fluorescence intensities in the presence of quencherKSV - Stern-Volmerquenching constantQ - the concentration of the quencherF0/F=1=KsvQ20 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
19、 present in the nanoparticle (F/F0)-relative fluorescence intensity q-quenching efficiency per quencher molecule n - the average number of donor molecules per nanoparticle. 3.3. Nanoparticle Energy Transfer Model21Figure 4. Fluorescence quenching of PF donor versus molar fraction of quenchers in pol
20、ymer blend nanoparticles. The scattered squares are experimental 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. Nanoparticle Energy Transfer M
21、odel22 4.Conclusions PF nanoparticles doped with PFPV, PFBT, and 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 dependenc
22、e of nanoparticle fluorescence on composition was found to deviate substantially from the Stern-Volmer relation.23 4.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.24 THANK YOU !
