Site-selective fluorescence studies of poly(p-phenylene vinylene) and its derivatives (original) (raw)
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The efficiency and time-dependence of luminescence from poly (p-phenylene vinylene) and derivatives
Chemical Physics Letters, 1993
We report measurements of the quantum efficiency and time decay of photoluminescence in the conjugated polymers poly(g phenylenevinylene) (PPV) and poly(Z-methoxy, 5-(2'ethyl-hexyloxy)-p-phenylenevinylene) (MEH-PPV). MEH-PPV is soluble and we measure values for the quantum yield for luminescence of order 35% for dilute solutions in toluene and chloroform. By comparison of luminescence decay rates in solution and in solid films we estimate luminescence efticiencies in solid films, which can be as high as 50% in partially conjugated PPV. Decay time distribution analysis of the luminescence reveals a broad distribution of decay rates, and this is consistent with the distribution of conjugation lengths known to be present in these materials. Exciton migration in better conjugated material results in narrower distributions of emitting chromophores.
Electronic excitations in luminescent conjugated polymers
Solid State Communications, 1997
We report progress in the processing and application of poly(phenylene vinylene), PPV, as the emissive layer in electroluminescent diodes, LEDs. Photoluminescence efficiencies above 60% for solid films of PPV are now achieved and single-layer EL diodes achieve luminous efficiencies above 2 Lumen W−1 and peak brightnesses up to 90 000 cd m−2. We discuss measurements of photoconductivity, photovoltaic response, photoluminescence excitation spectra and stimulated emission in films of PPV. We consider that the photoexcited state in these films of PPV is the intrachain singlet exciton. We demonstrate that PPV of this type can show stimulated emission in sub-picosecond pump-probe experiments and can be used as the active lasing medium when incorporated in suitable microcavity structures.
Interchain luminescence in poly (acetoxy-p-phenylene vinylene)
2002
The synthesis of a new substituted poly(phenylene vinylene) (PPV) derivative poly(acetoxy-p-phenylene vinylene) is reported. A new pathway, combining chemical and electrochemical steps was employed, resulting in a highly regular, polar, monosubstituted PPV. The participation of excimers and/of aggregates as emitting units in PPV and some of its derivatives has been demonstrated previously in various papers. This contribution provides evidence from fluorescence studies of the participation of those associated forms in the emission of this novel structure. A pattern of progressive fluorescent aggregate formation was observed, a result not reported to date. r
Interchain photoluminescence in poly(phenylene vinylene) derivatives
Physical review, 1996
We calculate that in cyano-substituted poly͑phenylene vinylene͒, CN-PPV, and poly͓2-methoxy, 5-͑2Ј-ethyl-hexyloxy͒phenylene vinylene͔, MEH-PPV, the lowest-energy arrangement has the chains parallel, with the perpendicular distance between chains 3.4 Å in the former case, 4.1 Å in the latter. Although there is evidence that most of the excitations created by above-band-gap light are polaron pairs or excimers in both cases, only those in CN-PPV luminesce because the smaller interchain distance results in a much larger matrix element for emission. ͓S0163-1829͑96͒50528-X͔ PHYSICAL REVIEW B
Time resolved emission spectroscopy of poly(2,5-dicyano-p-phenylene-vinylene) films
Journal of The Brazilian Chemical Society, 2008
Films of poly (2,5-dicyano-p-phenylene vinylene), DCNPPV, were obtained by electrochemical synthesis over gold thin layer (20 nm) transparent electrode deposited on a glass plate. The DCNPPV films of 4 µm thickness were produced by electropolymerization process of α,α,α',α'-tetrabromo-2-5-dicyano-p-xilene at different applied potentials (-0.15, -0.25, -0.40, -0.60, -0.80, and -1.0 V) using 0.1 mol L-1 of tetraethylammonium bromide in acetonitrile as the supporting electrolyte. The emission decays have three exponential components: a fast component in the picosecond range (200-400 ps), and two other of about one and five nanoseconds at 293 K. The fluorescence quenching process seems to occur by exciton trapping in a low-energy site and quenching by residual bromine monomer attached at the end of the polymer chain. However, the electrochemical synthesis generates entrapped bromide or ion pairs during the growth step of the film which also contributes to the deactivation. The change of the electrolyte from bromide to perchlorate reduces significantly this additional quenching effect by allowing ion exchange of formed bromide with the nonquenching perchloride anion.
Sensitized intrinsic phosphorescence from a poly(phenylene-vinylene) derivative
Chemical Physics Letters, 2003
Intrinsic phosphorescence in a phenyl-substituted poly(phenylene-vinylene) (PhPPV) film sensitized by a phosphorescent dye dopant has been directly observed for the first time for PPV class conjugated polymers. Efficient triplet energy transfer from the platinum porphyrin dye molecules to the PhPPV polymer was found to occur as the triplet level of the dopant (1.91 eV) is above the triplet level of PhPPV, which was determined to be at 1.63 eV. Intrinsic phosphorescence emission has been observed at room temperature as well. A significant decrease in emission intensity of phosphorescence has been found, if the sample was measured in air indicating quenching of triplets by oxygen.
Synthetic Metals, 1996
Processible conjugated polymers can be used to fabricate a range of thin-film diodes which can be designed to show good characteristics both as electroluminescent diodes and as photoconductive diodes. We highlight the improvement to the electroluminescence efficiency that can be produced by the use of two polymer layers selected so that the heterojunction between the two layers is able to confine charge and, thus, bring about electron-hole capture to generate excitons at this interface. We present results on the photophysical properties of the cyanosubstituted poly(phenylenevinylene)s which provide electron transport layers if these heterostructure devices; we find evidence for strong interchain interactions (excimer formation) for the neutral excited states in these polymers, with strong red shifts of the luminescence, though preserving high photoluminescence efficiencies.
Nature of the primary photoexcitations in poly(arylene-vinylenes)
Synthetic Metals, 1994
We present an overview of the optical properties and related experimental results obtained from poly(para-phenylene vinylene), PPV, and its soluble derivatives, and we critically examine the interpretation of these data in the context of both the band model and the exciton model of the electronic structure of these semiconducting and luminescent polymers. Results obtained from highly oriented and structurally ordered PPVs demonstrate that the observed disparities between the physical properties of PPV and the polydiacetylenes (PDAs) are not due to disorder; these differences are intrinsic and arise from the fundamental difference in the nature of the low energy photoexcited states: excitons in the PDAs and free carriers in the PPVs.