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Efficient Energy Transfer (efficient + energy_transfer)
Selected AbstractsEnhancement of Aggregation-Induced Emission in Dye-Encapsulating Polymeric Micelles for BioimagingADVANCED FUNCTIONAL MATERIALS, Issue 9 2010Wen-Chung Wu Abstract Three amphiphilic block copolymers are employed to form polymeric micelles and function as nanocarriers to disperse hydrophobic aggregation-induced emission (AIE) dyes, 1,1,2,3,4,5-hexaphenylsilole (HPS) and/or bis(4-(N -(1-naphthyl) phenylamino)-phenyl)fumaronitrile (NPAFN), into aqueous solution for biological studies. Compared to their virtually non-emissive properties in organic solutions, the fluorescence intensity of these AIE dyes has increased significantly due to the spatial confinement that restricts intramolecular rotation of these dyes and their better compatibility in the hydrophobic core of polymeric micelles. The effect of the chemical structure of micelle cores on the photophysical properties of AIE dyes are investigated, and the fluorescence resonance energy transfer (FRET) from the green-emitting donor (HPS) to the red-emitting acceptor (NPAFN) is explored by co-encapsulating this FRET pair in the same micelle core. The highest fluorescence quantum yield (,62%) could be achieved by encapsulating HPS aggregates in the micelles. Efficient energy transfer (>99%) and high amplification of emission (as high as 8 times) from the NPAFN acceptor could also be achieved by spatially confining the HPS/NPAFN FRET pair in the hydrophobic core of polymeric micelles. These micelles could be successfully internalized into the RAW 264.7 cells to demonstrate high-quality fluorescent images and cell viability due to improved quantum yield and reduced cytotoxicity. [source] A Wide-Bandgap Semiconducting Polymer for Ultraviolet and Blue Light Emitting Diodes,MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 18 2003Ping Lu Abstract A novel wide-bandgap conjugated polymer (PDHFSCHD) consisting of alternating dihexylfluorene and rigidly twisted biphenyl units has been synthesized. The new fluorene-based copolymer composed of rigid twisting segments in the main-chain exhibits an optical bandgap of as high as 3.26 eV, and a highly efficient ultraviolet emission with peaks at 368 nm and 386 nm. An electroluminescence device from PDHFSCHD neat film as an active layer shows UV emission which peaks at 395 nm with a turn on voltage below 8 V. By optimizing the device conditions, a peak EL quantum efficiency of 0.054% and brightness of 10 cd,·,m,2 was obtained. Furthermore, blending a poly(dihexylfluorene) in the PDHFSCHD host gave pure blue emission peaking at 417 nm and 440 nm without long wavelength emission from aggregated species. Efficient energy transfer from PDHFSCHD to PDHF was demonstrated in these blended systems. Depressed chain-aggregation of PDHF in the PDHFSCHD host can correspond to pure blue emission behaviors. The structure of the copolymer PDHFSCHD. [source] Effect of Electric Field on Coulomb-Stabilized Excitons in Host/Guest Systems for Deep-Blue ElectrophosphorescenceADVANCED FUNCTIONAL MATERIALS, Issue 15 2009Stephan Haneder Abstract Here, a study of the electric field induced quenching on the phosphorescence intensity of a deep-blue triplet emitter dispersed in different host materials is presented. The hosts are characterized by a higher triplet excitonic level with respect to the emitter, ensuring efficient energy transfer and exciton confinement, whereas they differ in the highest occupied molecular orbital (HOMO) alignment, forming type I and type II host/guest heterostructures. While the type I structure shows negligible electric field induced quenching, a quenching up to 25% for the type II at a field of 2,MV/cm is reported. A similar quenching behaviour is also reported for thin films of the pure emitter, revealing an important luminescence loss mechanism for aggregated emitter molecules. These results are interpreted by considering Coulomb stabilized excitons in the type II heterostructure and in the pure emitter, that become very sensitive to dissociation upon application of the field. These results clarify the role of external electric field quenching on the phosphorescence of triplet emitters and provide useful insights for the design of deep-blue electrophosphorescent devices with a reduced efficiency roll-off. [source] Energy-Modulated Heterostructures Made with Conjugated Polymers for Directional Energy Transfer and Carrier Confinement,ADVANCED FUNCTIONAL MATERIALS, Issue 15 2007R. Favarim Abstract In this paper we demonstrate that multilayer structures with modulated bandgaps can be used for efficient energy transfer and carrier confinement inside a nanostructured film of a light-emitting polymer. The films were produced with the layer-by-layer technique (LbL) with a poly(p -phenylene vinylene) (PPV) precursor and a long chain dodecylbenzenesulfonate ion (DBS). DBS is incorporated selectively into the precursor chain, and with a rapid, low temperature conversion process (100,°C) superstructures with variable HOMO,LUMO gap could be formed along the deposition direction by changing the DBS concentration. Structures with different stair-type energy modulations were produced, which are thermally stable and reproducible, as demonstrated by UV-VIS. absorption measurements. Energy differences of up to 0.5,eV between the lowest and highest conjugated layers inside the stair structure could be achieved, which was sufficient to guide the excitation over long distances to the lower bandgap layer. [source] A New Sol,Gel Material Doped with an Erbium Complex and Its Potential Optical-Amplification Application,ADVANCED FUNCTIONAL MATERIALS, Issue 6 2005L.-N. Sun Abstract The crystal structure of a ternary Er(DBM)3phen complex (DBM,=,dibenzoylmethane; phen,=,1,10-phenanthroline) and its in-situ synthesis via a sol,gel process are reported. The infrared (IR), diffuse reflectance (DR), and fluorescence spectra of the pure complex and the Er3+/DBM/phen co-doped luminescent hybrid gel, formed via an in-situ method (ErDP gel), have been investigated. The results reveal that the erbium complex is successfully synthesized in situ in the ErDP gel. Excitation at the maximum absorption wavelength of the ligands resulted in the typical near-IR luminescence (centered at around 1.54,,m) resulting from the 4I13/2,,,4I15/2 transition of the Er3+ ion, which contributes to the efficient energy transfer from the ligands to the Er3+ ion in both the Er(DBM)3phen complex and the ErDP gel (an antenna effect). The full width at half maximum (FWHM) centered at 1541,nm in the emission spectrum of the ErDP gel is 72,nm, which has potential for optical-amplification applications. Further theoretical analysis on the Er3+ ion in the ErDP gel shows that it appears to be a promising candidate for tunable lasers and planar optical amplifiers. [source] Water Stability and Luminescence of Lanthanide Complexes of Tripodal Ligands Derived from 1,4,7-Triazacyclononane: Pyridinecarboxamide versus Pyridinecarboxylate DonorsHELVETICA CHIMICA ACTA, Issue 11 2009Grégory Nocton Abstract A series of europium(III) and terbium(III) complexes of three 1,4,7-triazacyclononane-based pyridine containing ligands were synthesized. The three ligands differ from each other in the substitution of the pyridine pendant arm, namely they have a carboxylic acid, an ethylamide, or an ethyl ester substituent, i.e., these ligands are 6,6,,6,-[1,4,7-triazacyclononane-1,4,7-triyltris(methylene)]tris[pyridine-2-carboxylic acid] (H3tpatcn), -tris[pyridine-2-carboxamide] (tpatcnam), and -tris[pyridine-2-carboxylic acid] triethyl ester (tpatcnes) respectively. The quantum yields of both the europium(III) and terbium(III) emission, upon ligand excitation, were highly dependent upon ligand substitution, with a ca. 50-fold decrease for the carboxamide derivative in comparison to the picolinic acid (=pyridine-2-carboxylic acid) based ligand. Detailed analysis of the radiative rate constants and the energy of the triplet states for the three ligand systems revealed a less efficient energy transfer for the carboxamide-based systems. The stability of the three ligand systems in H2O was investigated. Although hydrolysis of the ethyl ester occurred in H2O for the [Ln(tpatcnes)](OTf)3 complexes, the tripositive [Ln(tpatcnam)](OTf)3 complexes and the neutral [Ln(tpatcn)] complexes showed high stability in H2O which makes them suitable for application in biological media. The [Tb(tpatcn)] complex formed easily in H2O and was thermodynamically stable at physiological pH (pTb 14.9), whereas the [Ln(tpatcnam)](OTf)3 complexes showed a very high kinetic stability in H2O, and once prepared in organic solvents, remained undissociated in H2O. [source] Emission Colour Tuning in Semiconducting Polymer Nanotubes by Energy Transfer to Organo- Lanthanide Dopants,ADVANCED MATERIALS, Issue 18 2007S. Moynihan Tuning of emission chromaticity in poly(N -vinylcarbazole) nanotubes by efficient energy transfer to luminescent Eu(dbm)3(Phen) organo-lanthanide chelate dopants is demonstrated. Nanotubes are synthesized by solution assisted template wetting. Under optical excitation, undoped tubes luminesce in the blue while doped tubes exhibit red europium ion emission with good color purity at the single nanotube level. [source] Host copolymers containing pendant carbazole and oxadiazole groups: Synthesis, characterization and optoelectronic applications for efficient green phosphorescent OLEDsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 15 2008Kun-Ming Yeh Abstract Vinyl copolymers (PCOn), containing pendant carbazole and aromatic 1,3,4-oxadiazole attached with dodecyloxy group, were prepared from their corresponding precursor poly(9-vinyl carbazole- co -4-vinylbenzyl chloride) (PCBn) by the Williamson condensation (n: mole% of 4-vinylbenzyl chloride). These copolymers were used as host materials for green phosphorescent light-emitting diodes after blending 4 wt % of Ir(ppy)3. PL spectra of the PCOn films showed the formation of excimer or exciplex. The phosphorescent EL devices were fabricated with a configuration of ITO/PEDOT:PSS/host copolymers:Ir(ppy)3/BCP/Ca/Al. The PL and EL spectra of the blends [PCOn:Ir(ppy)3] revealed dominant green emission at 517 nm attributed to Ir(ppy)3 due to efficient energy transfer from the host to Ir(ppy)3. Efficient green phosphorescent OLEDs was obtained when employing copolymer PCO16 as the host and Ir(ppy)3 as the guest. The maximal luminance efficiency and the maximal luminance of this device were 17.9 cd/A and 19,903 cd/m2, respectively. After doped with Ir(ppy)3, the morphology of the films, both controlled PCO20 and PCO20 with attached dodecyloxy groups, were investigated by tapping-mode AFM and FE-SEM. The film of PCO20 exhibited uniform, featureless image and showed much better device performance than PCO20, which have been attributed to good compatibility of PCO20 with Ir(ppy)3. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5180,5193, 2008 [source] Synthesis and optical and electroluminescent properties of novel conjugated polyelectrolytes and their neutral precursors derived from fluorene and benzoselenadiazoleJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 8 2006Fei Huang Abstract Novel copolymers derived from amino-functionalized fluorene- and selenium-containing heterocycles [2,1,3-benzoselenadiazole (BSeD)] were synthesized by the palladium-catalyzed Suzuki coupling method. Their quaternized salt polyelectrolytes of corresponding compositions were obtained by a postpolymerization treatment. The resulting copolymers were soluble in polar solvents. An efficient energy transfer due to exciton trapping on the BSeD sites was observed. Devices from such copolymers emitted orange-red light peaked at 560,610 nm. All the polymers showed good device performance with high-work-function metal Al as a cathode without the use of an additional electron-injection layer and are promising candidates for polymer light-emitting diode applications. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2521,2532, 2006 [source] Novel saturated red-emitting poly(p -phenylenevinylene) copolymers with narrow-band-gap units of 2,1,3-benzothiadiazole synthesized by a palladium-catalyzed Stille coupling reactionJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 11 2005Xianzhen Li Abstract Novel poly(p -phenylenevinylene) (PPV) copolymers derived from 1-methoxy-4-octyloxyphenylene (MOP), 2,1,3-benzothiadiazole (BT), and trans -1,2-bis(tributylstannyl)ethylene were first prepared by a palladium-catalyzed Stille coupling reaction. The feed ratios of MOP to BT were 99.5:0.5, 99:1, 95:5, 85:15, 70:30, and 50:50. An efficient energy transfer from the 2-methoxy-5-octyloxy- p -phenylenevinylene segment to the narrow-band-gap units was observed. The poly(2-methoxy-5-octyloxy- p -phenylenevinylene-2,1,3-benzothiadiazolevinylene) copolymers emitted deep red light. The maximum electroluminescence emission of these PPV copolymers occurred at 659,724 nm and was accompanied by gradual redshifting with an increasing BT concentration. The photophysical properties were examined in comparison with those of copolymers based on BT and fluorene or N -alkylcarbazole doped with the same BT concentration in the copolymer main chain. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2325-2336, 2005 [source] Energy Transfer Process for the Blue Up-Conversion in Calcium Aluminate Glasses Doped with Tm3+ and Nd3+JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2001Woon Jin Chung Excitation of Tm3+ to 3H4 using the 791 nm pump source showed the frequency up-converted blue emission (,480 nm) due to the Tm3+:1G4,3H6 transition in Tm3+/Nd3+ codoped CaO·Al2O3 glasses. Intensity and lifetime changes with rare-earth concentrations suggested the efficient energy transfer of Tm3+:3H4, Nd3+:4F5/2 and Nd3+:4F3/2, Tm3+:1G4. The latter transfer enabled Tm3+ to reach its 1G4 level, and the blue emission became possible through the 1G4,3H6 transition. Quantitative analysis with rate equations proved that these two transitions were the most efficient among all the possible energy transfer routes between Tm3+ and Nd3+. Calculated up-conversion efficiency of the Tm3+/Nd3+ combination in CaO·Al2O3 glass was 6.6 × 10,3, and it was ,4 orders of magnitude larger than those reported for other oxide glasses. [source] Design and Synthesis of Phosphorescent Iridium Containing Dendrimers for Potential Applications in Organic Light-Emitting Diodes,MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 18 2008Qin-De Liu Abstract Three phosphorescent dendrimers (IrC1, IrC3, and IrF2) with an iridium complex core and oligocarbazole or oligofluorene substituted ligands were synthesized and characterized. The structures of the oligocarbazole were designed to maintain high triplet energy of the ligands so that phosphorescence quenching in the resulting dendrimers can be prevented, while the oligofluorene in IrF2 resulted in undesired phosphorescence quenching. Best performance was obtained from an IrC3 based electrophosphorescent light-emitting device with a maximum luminance of 13,060 cd,·,m,2 at a driving voltage of 11.5 V and a peak current-efficiency of 4.3 cd,·,A,1 at a luminance of 3,400 cd,·,m,2, owing to its high PL efficiency, and efficient energy transfer between the iridium complex core and the ligands. [source] Flood disturbance, algal productivity, and interannual variation in food chain lengthOIKOS, Issue 1 2000Jane C. Marks The length of a river food chain changed from year to year, shifting with the hydrologic regime. During drought years, grazers suppressed algae across a nutrient gradient, while predators were functionally unimportant. Following flood disturbance, predators suppressed grazers, releasing algae. These results suggest that hydrologic regime, rather than productivity, determines the functional length of this river food chain. Within years, algae and grazer biomass responded to an experimental productivity gradient in patterns predicted by simple trophic models that assume efficient energy transfer. Understanding differences among species within trophic levels, however, was crucial in delineating the controlling interactions. [source] Microwave and conventional curing of thick-section thermoset composite laminates: Experiment and simulationPOLYMER COMPOSITES, Issue 2 2001Erik T. Thostenson In conventional processing, thermal gradients cause differential curing of thick laminates and undesirable outside-in solidification. To reduce thermal gradients, thick laminates are processed at lower cure temperatures and heated with slow heating rates, resulting in excessive cure times. Microwaves can transmit energy volumetrically and instantaneously through direct interaction of materials with applied electromagnetic fields. The more efficient energy transfer of microwaves can alleviate the problems associated with differential curing, and the preferred inside-out solidification can be obtained. In this work, both microwave curing and thermal curing of 24.5 mm (1 inch) thick-section glass/epoxy laminates are investigated through the development of a numerical process simulation and conducting experiments in processing thick laminates in a conventional autoclave and a microwave furnace. Outside-in curing of the autoclave-processed laminate resulted in visible matrix cracks, while cracks were not visible in the microwave-processed laminate. Both numerical and experimental results show that volumetric heating due to microwaves promotes an inside-out cure and can dramatically reduce the overall processing time. [source] Synthesis of Symmetrical Multichromophoric Bodipy Dyes and Their Facile Transformation into Energy Transfer Cassettes,CHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2010Altan Bozdemir Dr. Abstract Multichromophoric boron-dipyrromethene (Bodipy) dyes synthesized on phenylene-ethynylene platforms have been be converted to energy transfer cassettes in a one-step chemical transformation. Excitation energy transfer processes in these highly symmetrical derivatives were studied in detail, including time-resolved fluorescence spectroscopy techniques. Excitation spectra and the emission lifetimes suggest efficient energy transfer between the donor and acceptor chromophore. These novel energy transfer cassettes, while highlighting a short-cut approach to similar energy transfer systems, could be useful as large pseudo-Stokes shift multichromophoric dyes with potential applications in diverse applications. Fenilenetilen platformu üzerinde sentezlenen multikromoforik Bodipy boyarmaddeleri, tek basamakl, bir kimyasal transformasyonla enerji transferi kasetlerine dönü,türülmü,tür. Zaman ayr,ml, floresans spektroskopisi tekniklerinin de içinde bulundu,u yöntemlerle, yüksek simetri ö,eleri bulunduran bu türevlerdeki eksitasyon enerjisi transferi süreçleri ayr,nt,l, olarak çal,,,lm,,t,r. Eksitasyon spektrumlar, ve emisyon ömürlerindeki de,i,im, donör ve akseptör kromoforlar, aras,nda etkin bir enerji transferi oldu,unu dü,ündürmektedir. Bu yeni enerji transfer kasetleri, benzer enerji transfer sistemlerine kolay bir geçi, yolu göstermekle birlikte, pek çok farkl, alanda potansiyel uygulamalar, olabilecek, büyük pseudo-Stokes kaymas, de,erlerine sahip multikromoforik boyarmaddeler olarak da yararl, olabilirler. [source] A Mechanically Interlocked [3]Rotaxane as a Light-Harvesting Antenna: Synthesis, Characterization, and Intramolecular Energy TransferCHEMISTRY - A EUROPEAN JOURNAL, Issue 14 2009Jie-Yu Wang Abstract Mimicking photosynthesis: The concept of light-harvesting by using a mechanically interlocked [3]rotaxane is developed through synthesis and characterization. Our results provide a new candidate for light-harvesting systems and also open up the possibility of creating intelligent or controllable energy-collecting machines (see figure). A mechanically interlocked light-harvesting system [3]rotaxane A has been synthesized in high yield through Cu(I)-catalyzed azide,alkyne cycloaddition; the hexyl-substituted truxene units are introduced into the wheels as donors and an oligo(para -phenylenevinylene) (OPV) unit into the axis as the acceptor. The structure and the purity of [3]rotaxane A were confirmed by 1H and 13C,NMR spectroscopy and ESI HRMS. The azide,alkyne cycloaddition is demonstrated to be an efficient stoppering method in the synthesis of the rotaxane containing dibenzo[24]crown-8 and dibenzyl ammonium units. Detailed steady-state UV/Vis absorption, photoluminescent, and time-resolved fluorescence spectroscopy were performed to investigate the photophysical properties of [3]rotaxane A and its reference compounds in solution and as thin films. Even in dilute solution, efficient energy transfer from the truxene-functionalized wheels to the OPV-based axis, through the dibenzo[24]crown-8 and dibenzyl ammonium interaction, is observed in [3]rotaxane A. The unique topology of [3]rotaxane A not only efficiently promotes the intramolecular energy-transfer process, but also prevents intermolecular aggregation in the solid state. The new antenna system opens up the possibility of controllable light-harvesting molecular machines or other optoelectronic devices on the nanometer scale. [source] Multi-Colour Electroluminescence of Dendronic Antennae Containing Pyrenes as Light HarvestersCHEMPHYSCHEM, Issue 3 2010Umberto Giovanella Dr. Abstract Dendronic antennae systems containing pyrene units as energy donors and a styrylpyridinium derivative as energy acceptor show efficient energy transfer from the green-emitting pyrene excimer to the red-emitting acceptor. For the third dendron generation the effective screening of the pyrene units on the acceptor provides thin films showing bright red emission. Single-layer light-emitting diodes prepared by properly balancing the dendrons and donor units concentration in polyvinylcarbazole show electroluminescence from the blue, green and red components of the monomeric donor, the donor excimer and the acceptor when excitons are generated in the polymer and subsequently transferred to the molecules by resonant energy transfer. [source] | ||||||||||||||||||||||