130 research outputs found

    Measurement of Exciton Transport in Conjugated Polymer Nanoparticles

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    A novel approach is proposed for determining exciton transport parameters in conjugated polymers. Exciton dynamics of conjugated polymer nanoparticles doped with dyes were investigated by time-resolved fluorescence spectroscopy. Highly efficient energy transfer from the polymer PFBT to the dye perylene red was evident in the fluorescence spectra and excited state kinetics. Exciton transport parameters were obtained by fitting to a model that included the effects of nanoparticle size, exciton diffusion, energy transfer, and quenching by defects. The results indicate substantial quenching by defects, owing primarily to exciton diffusion, which can greatly increase the effective quenching volume of defects. We estimated the amount of quenching by defects, and included quenching by defects in our model, yielding an estimated exciton diffusion length of 12 nm and diffusion constant of 8.0 × 10<sup>–9</sup> m<sup>2</sup> s<sup>–1</sup> for nanoparticles of PFBT. The results indicate that quenching by defects can lead to substantial error in determined exciton transport parameters, unless such quenching is properly accounted for in the model

    Photoactivation and Saturated Emission in Blended Conjugated Polymer Nanoparticles

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    Blended poly­[(9,9-dioctylfluorenyl-2,7-diyl)-<i>co</i>-(1,4-benzo-{2,1′,3}-thiadiazole)] (PFBT)/poly­[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) conjugated polymer nanoparticles were prepared and characterized by conventional and single-particle fluorescence spectroscopy. The particles exhibit red emission and improved quantum efficiency resulting from highly efficient energy transfer from donor PFBT to acceptor MEH-PPV as well as suppression of MEH-PPV aggregation. Photobleaching results indicate better photostability in the blended sample compared to undoped MEH-PPV nanoparticles and photoactivation of donor emission, which could be useful for single-molecule localization-based super-resolution microscopy. Single blended nanoparticles exhibit bright fluorescence as well as saturation behavior at very low excitation intensities. These and other properties of the blended conjugated polymer nanoparticles could provide substantial improvements in resolution when employed in super-resolution microscopy

    Multiple Energy Transfer Dynamics in Blended Conjugated Polymer Nanoparticles

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    Energy transfer dynamics in blended conjugated polymer nanoparticles (CPNs) were investigated in order to further our understanding of photoswitching and anomalous saturation behavior we previously observed, and as a way to probe the complex energy transport processes occurring in similar systems of interest such as nanostructured bulk heterojunction photovoltaic devices. We prepared blended poly­[(9,9-dioctylfluorenyl-2,7-diyl)-<i>co</i>-(1,4-benzo-{2,1′,3}-thiadiazole)] (PFBT)/poly­[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) nanoparticles with varying blending ratios. Efficient energy transfer from PFBT to MEH-PPV was observed, yielding bright, red-shifted emission. The donor exhibited complex decay kinetics consistent with energy transfer in complex, nanoscale, multichromophoric systems. The fluorescence decay kinetics and steady-state quenching efficiencies are compared to a multiple energy transfer model and prior results for dye-doped nanoparticles. The analysis indicates that the high energy transfer efficiency is largely due to multistep energy transfer (i.e., exciton diffusion), while the lifetime heterogeneity appears to be strongly influenced by acceptor polymer polydispersity as well as nanoscale inhomogeneity. The emerging picture could inform efforts to optimize CPNs for advanced imaging applications, and to optimize energy transport in bulk heterojunction photovoltaic devices

    A High-Performance Hierarchical Graphene@Polyaniline@Graphene Sandwich Containing Hollow Structures for Supercapacitor Electrodes

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    An effective design and fabrication of a more steady structure for high-performance electrodes applications still remains a challenge. Herein, we have designed and fabricated a hierarchical heterostructure of a graphene@polyaniline@graphene sandwich consisting of hollow polyaniline spheres as the sandwich layer and graphene both as an internal skeleton shell and a cladding layer. The special sandwich configuration not only enlarged the specific surface area but also improved the electrical conductibility. Most importantly, the graphene double shells could prevent the structural breakdown (swelling or shrinkage) of polyaniline. Therefore, as a supercapacitor electrode, the hybrid exhibited excellent performance with a specific capacitance of 682.75 F g<sup>–1</sup> at 0.5 A g<sup>–1</sup> and a remarkable cycling stability with capacitance retentions of 92.8% after 1000 cycles and even 87.6% after 10,000 cycles, which were better than those of pure polyaniline. In addition, the specific capacitance could reach 217.11 F g<sup>–1</sup> at a high current density of 20 A g<sup>–1</sup>. Thus, it could be considered as a perspective electrode for the next generation of high-performance supercapacitors

    Theoretical Study on the Reaction Mechanism of Ti with CH<sub>3</sub>CN in the Gas Phase

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    To gain a deeper understanding of the reaction mechanisms of Ti with acetonitrile molecules, the triplet and singlet spin-state potential energy surfaces (PESs) has been investigated at B3LYP level of density functional theory (DFT). Crossing points between the different PESs and possible spin inversion processes are discussed by spin–orbit coupling (SOC) calculation. In addition, the bonding properties of the species along the reaction were analyzed by electron localization function (ELF), atoms in molecules (AIM) and natural bond orbital (NBO). The results showed that acetonitrile activation by Ti is a typical spin-forbidden process; larger SOC (by 220.12 cm<sup>–1</sup>) and the possibility of crossing between triplet and singlet imply that intersystem crossing (ISC) would occur near the minimum energy crossing point (MECP) during the transfer of the hydrogen atom

    Left P3 of <i>Arboroharamiya jenkinsi</i> (STM33-9).

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    <p>A–A1, Occlusal view; B–B1, Lingual view. C–C1, Buccal view. A1–C1 are SEM photographs. All images are on the same scale.</p

    Mandibles of <i>Arboroharamiya jenkinsi.</i>

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    <p>A, Buccal view of the right mandible with p4 and the incisor (i). B, Lingual view of the left mandible with p4-m1 and the incisor. C, Close-up view of the angular process area of B, showing no groove or attachment site for the Meckel’s cartilage or the postdentary bones. Scale bar in A is 5 mm. Red arrow points to the possible coronoid bone. A and B are modified from Zheng et al. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0113847#pone.0113847-Zheng1" target="_blank">[26]</a> A new arboreal haramiyid shows the diversity of crown mammals in the Jurassic period. Nature 500: 199–202 (DOI: 10.1038/nature12353). Reproduced by permission of Nature Publishing Group. Abbreviations: <b>ap</b>, angular process; <b>am2</b>, alveolus for m2; <b>amf</b>, anterior extremity of the masseteric fossa; <b>cp</b>, coronoid process; <b>mc</b>, mandibular condyle; <b>mf</b>, mandibular foramen.</p

    Left upper incisor of <i>Arboroharamiya jenkinsi</i> (STM33-9).

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    <p>A–A1, Occlusal view; B–B1, Mesial view. C–C1, Distal view. A1–C1 are SEM photographs. All images are on the same scale.</p
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