Linear and nonlinear optical properties of the conjugated polymers PPV and MEH-PPV

Martin, Simon J.; Bradley, Donal D. C.; Lane, Paul A.; Mellor, H.; Burn, Paul L.

doi:10.1103/physrevb.59.15133

Cited by 100 publications

(90 citation statements)

References 30 publications

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“…An even parity state at 2.73-3.15 eV above the ground state in MEH-PPV has been observed using two-photon absorption and electroabsorption. 32 Linear absorption to this state is parity forbidden in conjugated polymers, but it may acquire some oscillator strength in MEH-PPV, where charge conjugation symmetry is partially broken by side substitution. However, it is negligible as compared to absorption by the lowest optical transition, which shows a vibronic progression up to ϳ3.2 eV 13,14,32 and is strongly polarized along the polymer chain.…”

Section: Discussionmentioning

confidence: 99%

“…32 Linear absorption to this state is parity forbidden in conjugated polymers, but it may acquire some oscillator strength in MEH-PPV, where charge conjugation symmetry is partially broken by side substitution. However, it is negligible as compared to absorption by the lowest optical transition, which shows a vibronic progression up to ϳ3.2 eV 13,14,32 and is strongly polarized along the polymer chain. 33 Thus, the primarily excited and emitting electronic states have the same orientation of the transition dipole moment and hence a pure electronic relaxation is not a plausible explanation of rapid depolarization.…”

Section: Discussionmentioning

confidence: 99%

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Ultrafast depolarization of the fluorescence in a conjugated polymer

et al. 2005

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The effect of the extent of electron conjugation on the primary photophysics in semiconducting polymers is reported. A rapid depolarization of photoluminescence and transient absorption, which indicates a reorientation of the transition dipole moment by ϳ30°on a sub-100 fs time scale, is observed in the fully conjugated polymer poly͓2-͑2'-ethylhexyloxy͒-5-methoxy-1,4-phenylenevinylene͔ ͑MEH-PPV͒. In contrast, partially conjugated polymers exhibit a much slower depolarization. The results reveal rapid changes of exciton delocalization in the fully conjugated MEH-PPV driven by structural relaxation.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Ultrafast depolarization of the fluorescence in a conjugated polymer

et al. 2005

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“…The change in shape of the CD must accordingly be attributed to the formation of an interchain aggregate in accordance with what was observed by Langeveld-Voss et al 31 and Oda et al 32 In this scenario we assume that the 2B u state has been split into the two states given by the linear combination with energy eigenvalues E ± = E 2B u ± V ab / 2. As for the symmetry of the system, we note that the PPV systems can in principle be described by C 2h symmetry, 36,53 although this assumes an ideal conformation of the polymer chain. The reality is, however, different; experimental data suggest that structural disorder breaks up the symmetry.…”

Section: Circular Dichroismmentioning

confidence: 99%

“…1 The PPV system has very intriguing properties, for instance, an unusually high nonlinear response, and the system has accordingly been studied extensively within a range of experimental optical techniques, among them are site-selection luminescence and electroabsorption, etc. [35][36][37][38][39][40] However, there are still unresolved questions regarding the nature of the interactions, particularly the interchain type, and the strength of the interactions. With this in mind two related PPV LEPs were investigated using CD spectroscopy in combination with polarized linear spectroscopy: linear dichroism ͑LD͒ and polarized luminescence ͑PL͒.…”

Section: Introductionmentioning

confidence: 99%

Polarized optical spectroscopy applied to investigate two poly(phenylene-vinylene) polymers with different side chain structures

Pålsson

Vaughan

Monkman

2006

The Journal of Chemical Physics

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Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Two related poly͑phenylene-vinylene͒ ͑PPV͒ light-emitting polymers have been investigated by means of polarized optical spectroscopy. The purpose of the investigation was to investigate the nature of the interactions in thin films and to examine what impact the difference in side chain structure and molecular weight in poly͑2Ј-methoxy-5-2-ethyl-hexoxy͒-1,4-phenylene vinylene ͑MEH-PPV͒ and poly͑2-͑3Ј ,7Ј-dimethyloctyloxy͒-5-methoxy-1,4-phenylene-vinylene͒ ͑OC 1 C 10 -PPV͒ has on the electronic and optical properties of the two polymers. Aligning the polymers by dispersing them in anisotropic solvents and stretched films shows that the side chains have an impact on the relative orientations of the transition dipole moments. In anisotropic solvents the linear dichroism is larger for MEH-PPV than for the related polymer OC 1 C 10 -PPV, while in stretched films the opposite situation prevails. A lower polarization of the luminescence from OC 1 C 10 -PPV, relative to MEH-PPV, was also obtained independent of alignment medium used. The data therefore suggest that while mechanical stretching may align the OC 1 C 10 -PPV to a greater degree, the emitting species is distinct from the absorbing species. The circular dichroism ͑CD͒ spectra of both polymers undergo dramatic changes when the liquid phase and the solid state ͑film͒ are compared. The solution CD spectra shows no evidence of interchain interactions; instead the spectra of both systems indicate a helical conformation of the polymers. The CD spectra of films are dramatically different with the strong Cotton effect being observed. This points to the formation of an aggregate in the film, with an associated ground state interaction, an interchain species such as a physical dimer, or a more complex higher aggregate.

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“…28 The absorption coefficient of PF-TAA varies strongly in the range from 400 to 450 nm. We studied all three devices using laser diodes with emission wavelengths of 408 and 440 nm.…”

Section: Experimental Methodsmentioning

confidence: 99%

Relation between the built-in voltage in organic light-emitting diodes and the zero-field voltage as measured by electroabsorption

et al. 2010

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For developing understanding of the current density onset voltage and injection barriers in organic lightemitting diodes ͑OLEDs͒, a precise determination of the built-in voltage, V bi , is of crucial importance. Commonly, V bi is assumed to be equal to the voltage V 0,EA at which in an electroabsorption ͑EA͒ experiment the reflection of light at the OLED is found to become insensitive to a small voltage modulation. However, this assumption is shown to lead to significant errors for devices with well-injecting contacts. From an analysis of EA experiments for hole-only devices containing a polyfluorene-based copolymer, it is shown that V 0,EA may be interpreted as an effective current density onset voltage, agreeing with the commonly accepted picture, but that for these devices V bi is ϳ0.5 V larger than V 0,EA . This is found to be consistent with predictions of V 0,EA from model calculations of the electric field and light-absorption profiles in the semiconducting layer.

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Linear and nonlinear optical properties of the conjugated polymers PPV and MEH-PPV

Cited by 100 publications

References 30 publications

Ultrafast depolarization of the fluorescence in a conjugated polymer

Ultrafast depolarization of the fluorescence in a conjugated polymer

Polarized optical spectroscopy applied to investigate two poly(phenylene-vinylene) polymers with different side chain structures

Relation between the built-in voltage in organic light-emitting diodes and the zero-field voltage as measured by electroabsorption

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