W ater-soluble conjugated polymers have been receiving increasingly greater attention owing to their potential applications in the areas of biosensing, bioimaging, and optoelectronics. For example, they have been successfully utilized in the biosensor applications to detect proteins, nucleic acids, and sugars. 1À6 These polymers can be prepared by attaching ionic side groups to the polymer backbone. However, their synthesis is tedious and their solubility is still limited in the water. Good water solubility or dispersibility of the conjugated polymers can alternatively be achieved by converting them into nanoparticles. 7À13 Such water-dispersible conjugated polymer nanoparticles (CPNs) have been exploited in different applications. For example, Landfester, Sherf, List, and coworkers have demonstrated the use of CPNs in optoelectronic applications including light-emitting diodes and photovoltaics and also as inks in inkjet printing. 14À19 Foulger and co-workers demonstrated the use of hybrid conjugated polymer nanoparticles composed of blue-and green-emitting polymers in the construction of organic light-emitting diodes (OLEDs). 20 The color tuning of the electroluminescence for the devices was achieved through energy transfer. These nanoparticles have also been used in biological applications such as fluorescent images, biosensors, and oxygen sensors. 21À27 Apart from these applications, color tuning is important for the optoelectronic applications, especially for energyefficient indoor and outdoor lighting. 28,29 Water-dispersible conjugated polymer nanoparticles can be prepared mainly by two methods, which are miniemulsion and reprecipitation. In the miniemulsion method, a two-phase system (oil-in-water) is used. 7,8 The polymer is dissolved in an organic solvent, which is not miscible with water, and added into a surfactant containing aqueous solution while sonicating. After the nanoparticle formation, the organic solvent is evaporated off to leave behind the conjugated nanoparticles stabilized by the surfactant. In the reprecipitation method, the polymer is dissolved in an organic * Address correspondence to dtuncel@fen.bilkent.edu.tr, volkan@bilkent.edu.tr.Received for review July 9, 2010 and accepted March 28, 2011. Published online 10.1021/nn103598qABSTRACT We report on the synthesis and characterization of water-dispersible, mechanically stable conjugated polymer nanoparticles (CPNs) in shelled architecture with tunable emission and controllable photometric properties via cross-linking. Using a reprecipitation method, whiteemitting polymer nanoparticles are prepared in different sizes by varying the concentration of polymer; the emission kinetics are tuned by controlling the shell formation. For this purpose, polyfluorene derivatives containing azide groups are selected that can be decomposed under UV light to generate very reactive species, which opportunely facilitate the inter-and intra-cross-linking of polymer chains to form shells. Nanoparticles before and after UV treatment are characterized by v...
Nanocomposites of colloidal quantum dots (QDs) integrated into conjugated polymers (CPs) are key to hybrid optoelectronics, where engineering the excitonic interactions at the nanoscale is crucial. For such excitonic operation, it was believed that exciton diffusion is essential to realize nonradiative energy transfer from CPs to QDs. In this study, contrary to the previous literature, efficient exciton transfer is demonstrated in the nanocomposites of dense QDs, where exciton transfer can be as efficient as 80% without requiring the assistance of exciton diffusion. This is enabled by uniform dispersion of QDs at high density (up to $70 wt%) in the nanocomposite while avoiding phase segregation. Theoretical modeling supports the experimental observation of weakly temperature dependent nonradiative energy transfer dynamics. This new finding provides the ability to design hybrid light-emitting diodes that show an order of magnitude enhanced external quantum efficiencies.
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