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Volumn 13, Issue 13, 2007, Pages 3688-3700

Twisting of conjugated oligomers and polymers: Case study of oligo- And polythiophene

Author keywords

Density functional calculations; Oligothiophene; Polymers; Polythiophene

Indexed keywords

BOUNDARY CONDITIONS; CHARGE DISTRIBUTION; DENSITY FUNCTIONAL THEORY; MOLECULAR ORBITALS; MONOMERS; THIOPHENE; WAVELENGTH;

EID: 34250330250     PISSN: 09476539     EISSN: 15213765     Source Type: Journal    
DOI: 10.1002/chem.200600819     Document Type: Article
Times cited : (158)

References (148)
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    • The static polarizability of partially optimized, twisted polythiophene has been calculated by the LCAO-SCF method, see
    • The static polarizability of partially optimized, twisted polythiophene has been calculated by the LCAO-SCF method, see: D.H. Mosley, J. G. Fripiat, B. Champagne, J.-M. André. Int. J. Quantum Chem. 1994, S28, 451-467.
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    • The effect of twisting on intersystem crossing processes has also been theoretically studied for bi, ter- and sexithiophene, see; D. Beljonne, Z. Shuai, G. Pourtois, J. L. Brédas, J. Phys. Chem. A 2001, 105, 3899-3907
    • The effect of twisting on intersystem crossing processes has also been theoretically studied for bi-, ter- and sexithiophene, see; D. Beljonne, Z. Shuai, G. Pourtois, J. L. Brédas, J. Phys. Chem. A 2001, 105, 3899-3907.
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    • It is reported that 1,6-methano[10]- and syn-1.6:8,13- bismethano[14]annulene are aromatic and have twists of up to 34°. whereas anti-bismethano[14]annulene is twisted by 70° and is nonaromatic. a E. Vogel, H. D. Roth. Angew. Chem. 1964, 76, 145;
    • It is reported that 1,6-methano[10]- and syn-1.6:8,13- bismethano[14]annulene are aromatic and have twists of up to 34°. whereas anti-bismethano[14]annulene is twisted by 70° and is nonaromatic. a) E. Vogel, H. D. Roth. Angew. Chem. 1964, 76, 145;
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    • On the basis of the experimental results ref, 17, we believe 36° to be a realistic number
    • On the basis of the experimental results (ref. [17]), we believe 36° to be a realistic number.
  • 103
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    • Although the bonds were constrained where possible, a degree of curvature of the polymer backbone was observed in these optimized structures, and this led to some deviation (by 10° to 20°) from the expected end-to-end interring dihedral angle between the unit cells, probably because it was not possible to constrain the inter-unit angles. To overcome this, we attempted to use a larger unit cell of 12 thiophene units in some PBC calculations to achieve desired interring dihedral angles of 60° and 90°; however, the band gaps and relative energies of these units did not differ significantly from those of the minimally sized unit cell
    • Although the bonds were constrained where possible, a degree of curvature of the polymer backbone was observed in these optimized structures, and this led to some deviation (by 10° to 20°) from the expected end-to-end interring dihedral angle between the unit cells, probably because it was not possible to constrain the inter-unit angles. To overcome this, we attempted to use a larger unit cell of 12 thiophene units in some PBC calculations to achieve desired interring dihedral angles of 60° and 90°; however, the band gaps and relative energies of these units did not differ significantly from those of the minimally sized unit cell.
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    • The twist energy was also calculated for up-down twisting of 6T and polythiophene; however, we prefer to rely on a discussion of spiral twisting because, in the case of the oligomer, up-down twisting leads to compensatory curvature of the chain. This leads to a lower relative energy and a smaller band gap in the case of up-down twist- ing. Nevertheless, we believe that this observation arises not purely as an effect of twisting, but is chiefly attributable to the effect of compensatory curvature. In the case of twisting caused by substituents, chains should not be curved, so we believe spiral twisting represents a better model for the estimation of twisting effects.
    • The twist energy was also calculated for up-down twisting of 6T and polythiophene; however, we prefer to rely on a discussion of spiral twisting because, in the case of the oligomer, up-down twisting leads to compensatory curvature of the chain. This leads to a lower relative energy and a smaller band gap in the case of up-down twist- ing. Nevertheless, we believe that this observation arises not purely as an effect of twisting, but is chiefly attributable to the effect of compensatory curvature. In the case of twisting caused by substituents, chains should not be curved, so we believe spiral twisting represents a better model for the estimation of twisting effects.
  • 105
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    • -1 per thiophene unit (ring)).
    • -1 per thiophene unit (ring)).
  • 110
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    • These observations are in contrast to those found in the acenes: it was recently found that the energies increase dramatically with increased twisting.[21
    • [21]
  • 111
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    • For a view of the polythiophenes unit cell at a different interring twist angle, see Figure S2-S14 in the Supporting Information.
    • For a view of the polythiophenes unit cell at a different interring twist angle, see Figure S2-S14 in the Supporting Information.
  • 118
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    • In contrast to a lengthening of the C-C interring bond, a shortening in the oligomer length was observed with increasing twist, about 0.1 A for 36°. This is caused by the slight curvature of the backbone of the molecule.
    • In contrast to a lengthening of the C-C interring bond, a shortening in the oligomer length was observed with increasing twist, about 0.1 A for 36°. This is caused by the slight curvature of the backbone of the molecule.
  • 119
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    • We have also carried out PBC calculations on polypyrrole and polyselenophene. Twisting introduces similar changes in their properties (S. S. Zade, M. Bendikov. unpublished results).
    • We have also carried out PBC calculations on polypyrrole and polyselenophene. Twisting introduces similar changes in their properties (S. S. Zade, M. Bendikov. unpublished results).
  • 120
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    • For a detailed explanation of aromatic versus quinoid structures in oligo- and polythiophene, see ref, 41
    • For a detailed explanation of aromatic versus quinoid structures in oligo- and polythiophene, see ref. [41],
  • 121
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    • 1), whereas orbital energies change significantly (≈1 eV), indicates that in the unsubstituted oligothiophene, there is probably significant steric repulsion which forces the molecule out of planarity. The balance between n systems, which prefer a planar conformation, and steric repulsion is very delicate. This results in the molecules being slightly nonplanar in the gas phase and planar in the solid state (owing to crystal packing forces) and enables small substitucnts to disturb the conformation of the molecule.
    • 1), whereas orbital energies change significantly (≈1 eV), indicates that in the unsubstituted oligothiophene, there is probably significant steric repulsion which forces the molecule out of planarity. The balance between n systems, which prefer a planar conformation, and steric repulsion is very delicate. This results in the molecules being slightly nonplanar in the gas phase and planar in the solid state (owing to crystal packing forces) and enables small substitucnts to disturb the conformation of the molecule.
  • 122
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    • Small cyclic oligothiophenes also show large HOMO-LUMO gaps and they are significantly twisted, while large cyclic oligothiophenes are much less twisted and have smaller HOMO-LUMO gaps, sec: S. S. Zade, M. Bendikov, J. Org. Chem. 2006, 71, 2972-2981.
    • Small cyclic oligothiophenes also show large HOMO-LUMO gaps and they are significantly twisted, while large cyclic oligothiophenes are much less twisted and have smaller HOMO-LUMO gaps, sec: S. S. Zade, M. Bendikov, J. Org. Chem. 2006, 71, 2972-2981.
  • 124
    • 34250353250 scopus 로고    scopus 로고
    • The bandwidths for the valence and conduction bands, respectively, are 3.98 and 2.93 eV for 15°; 3.47 and 2.62 eV for 30°; 1.83 and 1.70 eV for 60°; 0.03 and 0.14 eV for a 90° twist.
    • The bandwidths for the valence and conduction bands, respectively, are 3.98 and 2.93 eV for 15°; 3.47 and 2.62 eV for 30°; 1.83 and 1.70 eV for 60°; 0.03 and 0.14 eV for a 90° twist.
  • 130
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    • We note that the minimal stcric hindrance at which deviation from planarity occurs should be strongly dependant on the theoretical method used
    • We note that the minimal stcric hindrance at which deviation from planarity occurs should be strongly dependant on the theoretical method used.
  • 131
    • 34250350147 scopus 로고    scopus 로고
    • In a head-to-head polymer constrained to be planar, the calculated band gap is similar to a planar head-to-tail polymer 1.97 eV
    • In a head-to-head polymer constrained to be planar, the calculated band gap is similar to a planar head-to-tail polymer (1.97 eV).
  • 132
    • 0345482413 scopus 로고    scopus 로고
    • This is in contrast to HF/STO-3G calculations (R. D. McCullough, R. D. Lowe, M. Jayaraman, D. L. Anderson, J. Org. Chem. 1993, 55, 904-912 and ref, 51, performed on alkylthiophene trimers that predicted high (>5 kcal mol-1) planarization energies
    • -1) planarization energies.
  • 133
    • 34250357992 scopus 로고    scopus 로고
    • We note that the calculations for substituted thiophenes should be compared to up-down twisting of polythiophene because the unit cell of substituted thiophenes consists of two thiophene units
    • We note that the calculations for substituted thiophenes should be compared to up-down twisting of polythiophene because the unit cell of substituted thiophenes consists of two thiophene units.
  • 137
    • 34250362864 scopus 로고    scopus 로고
    • The large difference in the planarity and band gap between polymer 2 a and isomeric poly(3-methyl)thiophene results from the conformation of methyl groups in 2 a. The in-plane hydrogen atom of the methyl group of 2a is located anti to the thiophene ring to minimize steric repulsion of the two methyl groups in the 3,4-positions of thiophene ring. This in-plane hydrogen is affected by steric repulsion from sulfur atom of the adjacent ring thus leading to a deviation from planarity in 2 a.
    • The large difference in the planarity and band gap between polymer 2 a and isomeric poly(3-methyl)thiophene results from the conformation of methyl groups in 2 a. The in-plane hydrogen atom of the methyl group of 2a is located anti to the thiophene ring to minimize steric repulsion of the two methyl groups in the 3,4-positions of thiophene ring. This in-plane hydrogen is affected by steric repulsion from sulfur atom of the adjacent ring thus leading to a deviation from planarity in 2 a.
  • 138
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    • A large difference between the band gap of poly(3,4- ethylenedithiathiophene) (PEDTT) and poly(3.4-ethylenedioxythiophcne) (PEDOT) has been observed and has been explained based on the importance of conformational effects on the band gap of polythiophenes. a) A. Cravino, H. Neugebauer, A. Petr, P. J. Skabara, H. J. Spencer, J. J. W. McDouall, L. Dunsch, N. S. Sariciftci, J. Phys. Chem. B 2006, 110, 2662-2667;
    • A large difference between the band gap of poly(3,4- ethylenedithiathiophene) (PEDTT) and poly(3.4-ethylenedioxythiophcne) (PEDOT) has been observed and has been explained based on the importance of conformational effects on the band gap of polythiophenes. a) A. Cravino, H. Neugebauer, A. Petr, P. J. Skabara, H. J. Spencer, J. J. W. McDouall, L. Dunsch, N. S. Sariciftci, J. Phys. Chem. B 2006, 110, 2662-2667;
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    • d) S. Y. Hong, Synth. Met. 2003, 135-136, 439-441;
    • (2003) Synth. Met , vol.135-136 , pp. 439-441
    • Hong, S.Y.1
  • 143
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    • Except for 6TCR at 30° where one additional band is observed [HOMO-4(β)→SOMO(β), f= 0.514].
    • Except for 6TCR at 30° where one additional band is observed [HOMO-4(β)→SOMO(β), f= 0.514].
  • 144
    • 0037448728 scopus 로고    scopus 로고
    • Recently, a conducting polymer that has a large transparent region in the UV-Vis range has been synthesized: H. Meng, D. Tucker, Chaffins, Y. Chen, R. Helgeson, B. Dünn, F. Wudl. Adv. Mater. 2003, 15, 146-149.
    • Recently, a conducting polymer that has a large transparent region in the UV-Vis range has been synthesized: H. Meng, D. Tucker, Chaffins, Y. Chen, R. Helgeson, B. Dünn, F. Wudl. Adv. Mater. 2003, 15, 146-149.
  • 145
    • 34250338299 scopus 로고    scopus 로고
    • Recently, new candidates for the transparent conductive polymer have been proposed theoretically. See ret. [25b]
    • Recently, new candidates for the transparent conductive polymer have been proposed theoretically. See ret. [25b]
  • 146
    • 34250355717 scopus 로고    scopus 로고
    • Note that the conjugation length in the 1ST radical cation is already sufficient to enable absorption in the entire Vis-NIR region.
    • Note that the conjugation length in the 1ST radical cation is already sufficient to enable absorption in the entire Vis-NIR region.


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