Aggregation Quenching of Luminescence in Electroluminescent Conjugated Polymers

Jakubiak, Rachel; Collison, Christopher J.; Wan, Wai Chou; Rothberg, Lewis J.; Hsieh, B.J.

doi:10.1021/jp9839450

Cited by 374 publications

(316 citation statements)

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“…The features at 570 and 610 nm are assigned to ͑0 → 0͒ and ͑0 → 1͒ fluorescence transitions of the polymer, respectively. 12 The nodal point at 520 nm ͑indicated by a star͒ ensures that no apparent shift of the curves is present, but only a different balancing between the two luminescence components. As the polymer chains become separated by the electron transporting small molecules, the emission appears to be dominated by single chain MEH-PPV exciton.…”

Section: Applied Physics Letters 96 033301 ͑2010͒mentioning

confidence: 99%

Interchain and intrachain emission branching in polymer light-emitting diode doped by organic molecules

Krautz

Lunedei

Puigdollers

et al. 2010

Applied Physics Letters

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A blend of the polymer poly͓2-͑2-ethylhexyloxy͒-5-methoxy-1,4-phenylenevinylene͔ ͑MEH-PPV͒ and the electron-transport molecule tris-͑8-hydroxyquinoline͒ aluminum ͑Alq 3 ͒ has been investigated by means of electroluminescence and fluorescence spectroscopy, upon variation of the Alq 3 content in the blend. A decreased interchain emission is observed upon increasing Alq 3 content, due to lower packing of the MEH-PPV chains which leads to a reduction in the interchain interaction, excimer formation, and emission probability. A branching of MEH-PPV interchain and intrachain emissive contributions is clearly time resolved and analyzed as a function of the Alq 3 content. At high doping concentration, direct emission from Alq 3 molecules is observed. © 2010 American Institute of Physics. ͓doi:10.1063/1.3276271͔Conjugated polymers have been extensively investigated due to their interesting physical properties as well as for their large potential for electroluminescent applications. Recently, polymer blends represent an alternative approach to new materials with improved performance for use in semiconductor devices. Numerous reports have demonstrated that utilizing the blending techniques, single-layer polymer light-emitting device ͑PLED͒ with high performance can be achieved. [1][2][3][4][5] Both the carrier injection and transport can be improved by carefully selecting the materials and their proportions in the blend. 1-5 Furthermore, the dopant introduction produces a dilution effect of the polymer solution and reduces polymer interchain interaction, leading to sharper EL spectra with higher color purity than those of the neat polymer film, depending on the dopant concentration. [5][6][7] In conjugated polymers, intrachain singlet excitons can be generated by photons absorption or via carrier-injection followed by electron-hole pair formation on a single chain. These excitations are usually extended over some ͑ϳ6 or 7͒ repeating units. 8 The diffusion of the excitation along the polymer chain as well as between different chains is also possible. Two "molecules" ͑i.e., conjugated lengths͒, one neutral and one in the excited state, belonging to two different sites of the same chain or to different polymer chains can interact resonantly forming one interchain excitation as an excimer. Excimers exhibit by a long radiative lifetime because the transition from the excimer state to the ground state is usually forbidden by symmetry. 9 They exhibit redshifted, broad emission spectra. Nevertheless, since interchain excitations decay pathway is mainly nonradiative, they act as effective luminescence quencher of singlet intrachain states.In this work, we investigate the branching of intrachain and interchain contribution to the emission of the polymer ͑MEH-PPV͒, doped by the electron transporter Alq 3 . Progressively passing from low to high concentrations of Alq 3 in the blend, it is possible to alter the formation of MEH-PPV excimers ͑interchain species͒ due to the segregation of the polymer chains by the Alq 3 molecules and in ...

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Section: Applied Physics Letters 96 033301 ͑2010͒mentioning

confidence: 99%

Interchain and intrachain emission branching in polymer light-emitting diode doped by organic molecules

Krautz

Lunedei

Puigdollers

et al. 2010

Applied Physics Letters

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“…A tightly coiled molecule allows for interactions between its closely stacked segments, thus facilitating efficient three-dimensional exciton diffusion (17). In addition, interchain stacking interactions appear to be responsible for reduction in luminescence yields and red-shifted spectra characteristic of longer conjugation in packed regions (16,19,22,23).…”

Section: ϫ10mentioning

confidence: 99%

“…Because of their size and relative f lexibility, however, polymer molecules are able to aggregate to lower their energy. Conjugated polymer film studies show that aggregation leads to the formation of weakly emissive interchain species in thin films that significantly reduce the quantum yield of thin film devices (16). The formation yield of interchain species remains a subject of study (17), but there is emerging a consensus that the strong processing dependence of luminescence yields results from film morphology (18,19).…”

mentioning

confidence: 99%

Single chain spectroscopy of conformational dependence of conjugated polymer photophysics

Huser

Yan

Rothberg

2000

Proc. Natl. Acad. Sci. U.S.A.

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Single molecule confocal fluorescence microscopy was used to perform photoluminescence spectroscopy on single, isolated molecules of the conjugated polymer poly[2-methoxy,5-(2-ethylhexyloxy)-p-phenylene-vinylene] (MEH-PPV). We show that the fluorescence from single chains of this electroluminescent polymer depends strongly on chain conformation. The time evolution of the spectra, emission intensity, and polarization all provide direct evidence that memory of the chain conformation in solution is retained after solvent evaporation. Chains cast from toluene solution are highly folded and show memory of the excitation polarization. Exciton funneling to highly aggregated low energy regions causes the chain to mimic the photophysical behavior of a single chromophore. Chains cast from chloroform, however, behave as multichromophore systems, and no sudden discrete spectral or intensity jumps are observed. These also exhibit different spectroscopy from the folded chromophores. R ecent advances in instrumentation have allowed the detection and manipulation of single molecules at room temperature (for recent reviews see, e.g., ref. 1). These techniques have led to the observation of physical effects and properties of individual molecules that could not be probed by previous ensemble-averaging studies. For example, measurements of inter-and intramolecular binding forces and elastic moduli of biological macromolecules by magnetic beads (2, 3), atomic force microscopy (4), hydrodynamic flow (5), or optical tweezers (6) have provided significant insight to the mechanical properties of DNA and proteins. Single molecule fluorescence detection has seen particular interest, because the fluorescence labeling of DNA, RNA, enzymes, and proteins allows for dynamic studies of macromolecular interactions and function, such as complexation (7). The optical visualization of these molecules, however, requires specific labeling with fluorescent dyes or the use of intercalating dyes.Single molecule studies of intrinsically fluorescent macromolecules, such as photosynthetic light harvesting complexes (8) or the green fluorescent protein (9), have exhibited interesting quantum effects. Protein molecules with several chromophores, for example, were shown to behave as a single quantum system (10). The close packing of chromophores in such proteins leads to strong interchromophore interaction that gives rise to cooperative effects such as intermittent fluorescence (11, 12) and photon-antibunching (10). Single molecule fluorescence studies of green fluorescent protein revealed similar intermittent fluorescence (9).Most remarkably, intermittent fluorescence together with the observation of discrete emission levels was also reported for single molecules of conjugated polymers estimated to consist of over 1000 chromophores (13). Another surprising result is the recent observation of efficient photoluminescence quenching of polymer chains by extremely low amounts of cationic electron acceptors (14), which provides a unique bio-probe scheme with high ...

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“…These morphology studies investigated as a stand alone were used to explain the device characteristics that related charge transport and morphology. [9][10][11][12] We have extended these studies to working device configurations such as diodes and transistors made from MEH-PPV.…”

Section: Introductionmentioning

confidence: 99%

Review of Morphology Dependent Charge Carrier Mobility in MEH‐PPV

Inigo

Huang

White

et al. 2010

J Chinese Chemical Soc

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Charge carrier mobility in poly(2-methoxy,5(2¢-ethyl-hexyloxy)-p-phenylene vinylene) (MEH-PPV) films were measured as a function of temperature and electric field parallel and perpendicular to the substrate for devices prepared from different solvents and under different processing conditions. Bulk structural morphology was characterized by various X-ray diffraction measurements such as wide angle, small angle and X-ray reflection. Surface morphology was characterized using various scanning probe microscopic techniques. Mobilities were found to follow Gaussian disorder model (GDM) and to be highly anisotropic not only depending on the solvents used but also on the film preparation method such as spin-coating or drop-casting. While no direct correlation was found between charge carrier mobility and photoluminescence, charge transport parameters were correlated with structural morphology.

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Aggregation Quenching of Luminescence in Electroluminescent Conjugated Polymers

Cited by 374 publications

References 40 publications

Interchain and intrachain emission branching in polymer light-emitting diode doped by organic molecules

Interchain and intrachain emission branching in polymer light-emitting diode doped by organic molecules

Single chain spectroscopy of conformational dependence of conjugated polymer photophysics

Review of Morphology Dependent Charge Carrier Mobility in MEH‐PPV

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