Twisting of conjugated oligomers and polymers

Case study of oligo- And polythiophene

Sanjio S. Zade, Michael Bendikov

Research output: Contribution to journalArticle

121 Citations (Scopus)

Abstract

Interring twisting (change in the dihedral angle between conjugated rings) of polythiophene was studied theoretically using periodic boundary conditions (PBC) at the B3LYP/6-31G(d) level. We find that the band gap of polymers is strongly dependent on the interring twist angle; yet twisting requires very little energy. A twist of 30° increases the band gap by 0.75 eV in polythiophene. while requiring only 0.41 kcal mol-1 per monomer unit. Such a small energetic value is of the order of crystal packing or van der Waals forces. These results are compared with calculations performed on model oligomers. Sexithiophene, its radical cations, and its dication are optimized at 0-180° end-to-end twist angles (which correspond to 0-36° interring dihedral angles) using the B3LYP/6-31G(d) method. The theoretical results suggest that the HOMOLUMO gap, ionization potential, and charge distribution of oligomers are strongly dependent on twisting, where-as, similar to the case of polythiophene, twisting of neutral oligothiophenes costs very little energy. In the case of the radical cation, the lowest energy transition is shifted to a longer wavelength region on twisting, while the second-lowest energy transition is shifted to a shorter wavelength region. This implies that twisted, doped conducting polymers (modeled here by an oligomer radical cation), in contrast to planar, doped polymers, should be transparent within a certain optical window (in the far-visible region, at ≈ 1.5 eV). This observation is explained on the basis of changes in the shape and overlap of the frontier molecular orbitals.

Original languageEnglish
Pages (from-to)3688-3700
Number of pages13
JournalChemistry - A European Journal
Volume13
Issue number13
DOIs
Publication statusPublished - 2007

Fingerprint

Oligomers
Cations
Polymers
Dihedral angle
Energy gap
Positive ions
Wavelength
Van der Waals forces
Ionization potential
Charge distribution
Conducting polymers
Molecular orbitals
Monomers
Boundary conditions
Crystals
polythiophene
Costs

Keywords

  • Density functional calculations
  • Oligothiophene
  • Polymers
  • Polythiophene

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

Twisting of conjugated oligomers and polymers : Case study of oligo- And polythiophene. / Zade, Sanjio S.; Bendikov, Michael.

In: Chemistry - A European Journal, Vol. 13, No. 13, 2007, p. 3688-3700.

Research output: Contribution to journalArticle

@article{5f1c7fd8426e4924b69eb825fc70f621,
title = "Twisting of conjugated oligomers and polymers: Case study of oligo- And polythiophene",
abstract = "Interring twisting (change in the dihedral angle between conjugated rings) of polythiophene was studied theoretically using periodic boundary conditions (PBC) at the B3LYP/6-31G(d) level. We find that the band gap of polymers is strongly dependent on the interring twist angle; yet twisting requires very little energy. A twist of 30° increases the band gap by 0.75 eV in polythiophene. while requiring only 0.41 kcal mol-1 per monomer unit. Such a small energetic value is of the order of crystal packing or van der Waals forces. These results are compared with calculations performed on model oligomers. Sexithiophene, its radical cations, and its dication are optimized at 0-180° end-to-end twist angles (which correspond to 0-36° interring dihedral angles) using the B3LYP/6-31G(d) method. The theoretical results suggest that the HOMOLUMO gap, ionization potential, and charge distribution of oligomers are strongly dependent on twisting, where-as, similar to the case of polythiophene, twisting of neutral oligothiophenes costs very little energy. In the case of the radical cation, the lowest energy transition is shifted to a longer wavelength region on twisting, while the second-lowest energy transition is shifted to a shorter wavelength region. This implies that twisted, doped conducting polymers (modeled here by an oligomer radical cation), in contrast to planar, doped polymers, should be transparent within a certain optical window (in the far-visible region, at ≈ 1.5 eV). This observation is explained on the basis of changes in the shape and overlap of the frontier molecular orbitals.",
keywords = "Density functional calculations, Oligothiophene, Polymers, Polythiophene",
author = "Zade, {Sanjio S.} and Michael Bendikov",
year = "2007",
doi = "10.1002/chem.200600819",
language = "English",
volume = "13",
pages = "3688--3700",
journal = "Chemistry - A European Journal",
issn = "0947-6539",
publisher = "Wiley-VCH Verlag",
number = "13",

}

TY - JOUR

T1 - Twisting of conjugated oligomers and polymers

T2 - Case study of oligo- And polythiophene

AU - Zade, Sanjio S.

AU - Bendikov, Michael

PY - 2007

Y1 - 2007

N2 - Interring twisting (change in the dihedral angle between conjugated rings) of polythiophene was studied theoretically using periodic boundary conditions (PBC) at the B3LYP/6-31G(d) level. We find that the band gap of polymers is strongly dependent on the interring twist angle; yet twisting requires very little energy. A twist of 30° increases the band gap by 0.75 eV in polythiophene. while requiring only 0.41 kcal mol-1 per monomer unit. Such a small energetic value is of the order of crystal packing or van der Waals forces. These results are compared with calculations performed on model oligomers. Sexithiophene, its radical cations, and its dication are optimized at 0-180° end-to-end twist angles (which correspond to 0-36° interring dihedral angles) using the B3LYP/6-31G(d) method. The theoretical results suggest that the HOMOLUMO gap, ionization potential, and charge distribution of oligomers are strongly dependent on twisting, where-as, similar to the case of polythiophene, twisting of neutral oligothiophenes costs very little energy. In the case of the radical cation, the lowest energy transition is shifted to a longer wavelength region on twisting, while the second-lowest energy transition is shifted to a shorter wavelength region. This implies that twisted, doped conducting polymers (modeled here by an oligomer radical cation), in contrast to planar, doped polymers, should be transparent within a certain optical window (in the far-visible region, at ≈ 1.5 eV). This observation is explained on the basis of changes in the shape and overlap of the frontier molecular orbitals.

AB - Interring twisting (change in the dihedral angle between conjugated rings) of polythiophene was studied theoretically using periodic boundary conditions (PBC) at the B3LYP/6-31G(d) level. We find that the band gap of polymers is strongly dependent on the interring twist angle; yet twisting requires very little energy. A twist of 30° increases the band gap by 0.75 eV in polythiophene. while requiring only 0.41 kcal mol-1 per monomer unit. Such a small energetic value is of the order of crystal packing or van der Waals forces. These results are compared with calculations performed on model oligomers. Sexithiophene, its radical cations, and its dication are optimized at 0-180° end-to-end twist angles (which correspond to 0-36° interring dihedral angles) using the B3LYP/6-31G(d) method. The theoretical results suggest that the HOMOLUMO gap, ionization potential, and charge distribution of oligomers are strongly dependent on twisting, where-as, similar to the case of polythiophene, twisting of neutral oligothiophenes costs very little energy. In the case of the radical cation, the lowest energy transition is shifted to a longer wavelength region on twisting, while the second-lowest energy transition is shifted to a shorter wavelength region. This implies that twisted, doped conducting polymers (modeled here by an oligomer radical cation), in contrast to planar, doped polymers, should be transparent within a certain optical window (in the far-visible region, at ≈ 1.5 eV). This observation is explained on the basis of changes in the shape and overlap of the frontier molecular orbitals.

KW - Density functional calculations

KW - Oligothiophene

KW - Polymers

KW - Polythiophene

UR - http://www.scopus.com/inward/record.url?scp=34250330250&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=34250330250&partnerID=8YFLogxK

U2 - 10.1002/chem.200600819

DO - 10.1002/chem.200600819

M3 - Article

VL - 13

SP - 3688

EP - 3700

JO - Chemistry - A European Journal

JF - Chemistry - A European Journal

SN - 0947-6539

IS - 13

ER -