Optical spectra and excitations in phenylene vinylene oligomers

Woo, Hyung-Suk; Lhost, Olivier; Graham, Stephen C.; Bradley, Donal D. C.; Friend, Richard H.; Quattrocchi, C.; Brédas, J. L.; Schenk, Rainer; Müllen, Kläus

doi:10.1016/0379-6779(93)91153-s

Cited by 166 publications

(97 citation statements)

References 37 publications

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“…As mentioned previously, the spin-coating procedure induces in-plane chain orientation in the skin layer of the film, 4,8,27,28 whereas the polymer chains adopt random conformations in the spongy layer (Figure 1). Consequently, the skin layer is characterized by polymer chains with longer average conjugation length and by the red-shifted absorption, 30 as compared to the spongy one. In >200 nm thick films, the absorption spectrum is dominated by the spongy layer, whereas in thinner films, the skin layer becomes more valuable, leading to the red shift ( Figure 5).…”

Section: Resultsmentioning

confidence: 99%

Exciton Quenching Close to Polymer−Vacuum Interface of Spin-Coated Films of Poly(p-phenylenevinylene) Derivative

et al. 2009

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Polymer-fullerene bilayer heterostructures are suited to study excitonic processes in conjugated polymers. Excitons are efficiently quenched at the polymer-fullerene interface, whereas the polymer-vacuum interface is often considered as an exciton-reflecting interface. Here, we report about efficient exciton quenching close to the polymer-vacuum interface of spin-coated MDMO-PPV (poly[2-methoxy-5-(2′-ethyl-hexyloxy)-pphenylenevinylene]) films. The quenching efficiency is estimated to be as high as that of the polymer-fullerene interface. This efficient quenching is consistent with enhanced intermolecular interactions close to the polymer-vacuum interface due to the formation of a "skin layer" during the spin-coating procedure. In the skin layer, the polymer density is higher; that is, the intermolecular distances are shorter than in the rest of the film. The effect of exciton quenching at the polymer-vacuum interface should be taken into account when the thickness of the polymer film is on the order of the exciton diffusion length; in particular, in the determination of the exciton diffusion length.

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Section: Resultsmentioning

confidence: 99%

Exciton Quenching Close to Polymer−Vacuum Interface of Spin-Coated Films of Poly(p-phenylenevinylene) Derivative

et al. 2009

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“…Such welldefined behavior is well-established and is the basis for our understanding of linear conjugated systems. 2,[19][20][21][22] It is clear, however, that both the short chain limit and the rate of decrease with increasing chain limit differ significantly with monomeric structure and the degree of coupling between the monomeric units. The differences in the long chain limit of the phenyl versus the acenes series mirrors the differences in band gaps of cis versus trans polyacetylene 7 and zigzag versus armchair singlewalled carbon nanotubes.…”

Section: Resultsmentioning

confidence: 99%

Structure−Property Relationships for Electron−Vibrational Coupling in Conjugated Organic Oligomeric Systems

O’Neill¹,

Byrne²

2005

J. Phys. Chem. B

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A series of π-conjugated oligomers containing one to six monomer units were studied by absorption and photoluminescence spectroscopy. As is common for these systems, a linear relationship between the positioning of the lowest-energy absorption and the highest-energy photoluminescence maxima plotted versus inverse conjugation length is observed, in good agreement with a simple nearly free electron model, one of the earliest descriptions of the properties of one-dimensional organic molecules. It was observed that the Stokes shift and therefore Huang-Rhys factor also exhibit a well-defined relationship with increasing conjugation length, implying a correlation between the electron-vibrational coupling and chain length. This correlation is further examined using Raman spectroscopy, whereby the integrated relative Raman scattering is seen to behave superlinearly with chain length. The Stokes shift and the Raman activity are also well-correlated in these systems. There is a clear indication that the vibrational activity and thus nonradiative decay processes are controllable through molecular structure.

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“…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%

“…8,10 Exciton delocalization in solutions and unoriented spin-coated films of MEH-PPV as well as those of unsubstituted poly͑phenylenevinylene͒ ͑PPV͒ prepared from a precursor was estimated to be between 6 and 17 repeat units from fits to absorption spectra. 14,15 This estimate depends on whether the blueshift and broadening of absorption originates from conjugation-disrupting defects, such as kinks and twists in the backbone 16 or from the "wormlike" conformational disorder, which gradually weakens the conjugation in the absence of abrupt conjugation breaks. 15,17 Quantum-chemical calculations indicate that topological defects, such as twists and kinks, do not result in a complete exciton localization on individual segments, they just shift electronic transitions towards higher energies.…”

Section: Introductionmentioning

confidence: 99%

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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Optical spectra and excitations in phenylene vinylene oligomers

Cited by 166 publications

References 37 publications

Exciton Quenching Close to Polymer−Vacuum Interface of Spin-Coated Films of Poly(p-phenylenevinylene) Derivative

Exciton Quenching Close to Polymer−Vacuum Interface of Spin-Coated Films of Poly(p-phenylenevinylene) Derivative

Structure−Property Relationships for Electron−Vibrational Coupling in Conjugated Organic Oligomeric Systems

Ultrafast depolarization of the fluorescence in a conjugated polymer

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