X-ray scattering from poly(thiophene): crystallinity and crystallographic structure

Mo, Zhishen; Lee, K. B.; Moon, Yong-Tae; Kobayashi, Masakazu; Heeger, A.J.; Wudl, Fred

doi:10.1021/ma00152a028

“…13,14 We use the Car-Parrinello scheme 23 to obtain the DFT-LDA geometries of the single polymer chains and take the experimental crystal structures. 24,25 For PT this leads to an orthorhombic unit cell with aϭ14.80 ͑chain direction͒, bϭ14.75, and c ϭ10.45 a.u. and a setting angle of 32°between the two chains in the cell.…”

Section: Theory: the Quasiparticle And Bethe-salpeter Equationsmentioning

confidence: 99%

“…In an experimental study of supposedly crystalline, unsubstituted PT, a density of ϭ1.21 g/cm 3 was found. 45 For the crystal structure we have used for PT, ϭ1.54 g/cm 3 . If we assume the disorder in the size of the unit cell in the chain direction to be small ͑which is plausible since in that direction we have covalent bonds only͒, this means that the average interchain distances in the sample are Ϸ12% larger than for the crystal structure we have used.…”

Section: Static Disordermentioning

confidence: 99%

Electronic and optical excitations in crystalline conjugated polymers

Horst

¹

,

Bobbert

²

,

Michels

³

2002

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We calculate the electronic and optical excitations of crystalline polythiophene and polyphenylenevinylene, using the GW approximation for the electronic self-energy and including excitonic effects by solving the electron-hole Bethe-Salpeter equation. We compare with our earlier calculations on an isolated polythiophene chain and polymer chains embedded in a dielectric medium. Surprisingly, we find for the crystalline calculations optical gaps and exciton binding energies that are significantly smaller than present experimental values. We attribute the disagreement to the fact that the quantum-mechanical coherence between polymer chains, present in the calculations, is absent in most experimental situations. We discuss possible reasons for this absence. Our general conclusion is that the picture of a polymer chain in a dielectric medium is most appropriate in describing the present experimental data on electronic and optical excitations in conjugated polymers.

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“…13,14 We use the Car-Parrinello scheme 23 to obtain the DFT-LDA geometries of the single polymer chains and take the experimental crystal structures. 24,25 For PT this leads to an orthorhombic unit cell with aϭ14.80 ͑chain direction͒, bϭ14.75, and c ϭ10.45 a.u. and a setting angle of 32°between the two chains in the cell.…”

Section: Theory: the Quasiparticle And Bethe-salpeter Equationsmentioning

confidence: 99%

“…In an experimental study of supposedly crystalline, unsubstituted PT, a density of ϭ1.21 g/cm 3 was found. 45 For the crystal structure we have used for PT, ϭ1.54 g/cm 3 . If we assume the disorder in the size of the unit cell in the chain direction to be small ͑which is plausible since in that direction we have covalent bonds only͒, this means that the average interchain distances in the sample are Ϸ12% larger than for the crystal structure we have used.…”

Section: Static Disordermentioning

confidence: 99%

“…Moreover, even in the ordered regions of the sample, the average displacement of the atoms from the perfect lattice sites is Ϸ0.3 Å. 45 Since the amount of wave-function overlap between two chains depends exponentially on the interchain distance, effective hybridization is practically impossible, even in more ordered samples. This means that most experimental studies effectively look at isolated polymer chains in a dielectric medium, which is exactly what we studied for PT in situation II, the situation in which we have good agreement with present experimental data for the exciton binding energies, for various level splittings, and for the QP gap.…”

Section: Static Disordermentioning

confidence: 99%

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Electronic and optical excitations in crystalline conjugated polymers

Horst¹,

Bobbert²,

Michels³

2003

View full text Add to dashboard Cite

We calculate the electronic and optical excitations of crystalline polythiophene and polyphenylenevinylene, using the GW approximation for the electronic self-energy and including excitonic effects by solving the electron-hole Bethe-Salpeter equation. We compare with our earlier calculations on an isolated polythiophene chain and polymer chains embedded in a dielectric medium. Surprisingly, we find for the crystalline calculations optical gaps and exciton binding energies that are significantly smaller than present experimental values. We attribute the disagreement to the fact that the quantum-mechanical coherence between polymer chains, present in the calculations, is absent in most experimental situations. We discuss possible reasons for this absence. Our general conclusion is that the picture of a polymer chain in a dielectric medium is most appropriate in describing the present experimental data on electronic and optical excitations in conjugated polymers.

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