Molecular conformation of 2,2′-bithiophene determined by gas phase electron diffraction and ab initio calculations

Samdal, Svein; Samuelsen, Emil J.; Volden, Hans V.

doi:10.1016/0379-6779(93)91035-z

Cited by 144 publications

(147 citation statements)

References 17 publications

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“…For the parent compound 2T, the inter-ring dihedral angle calculated for the anti form from the HF/6-31G(d) geometry (ω=147°) was found to be in good agreement with those obtained from higher levels of theory 12 and experimental data. 22 Calculations involving substituted HT alkylbithiophenes provided values for w ranging from 119 (propyl, 2T-C3) to 108° (octadecyl, 2T-C18) for anti conformers and from 71 (propyl, 2T-C3) to 60° (octadecyl, 2T-C18) for syn forms (Table 1). For the anti HH molecules, the inter-ring dihedral angle was found to be close to 95° (see Table 2).…”

Section: Resultsmentioning

confidence: 99%

Structure and electronic properties of alkylthiophenes coupled by Head-to-Tail and Head-to-Head regioselectivity

Oliveira¹,

Almeida²,

Santos³

2004

J. Braz. Chem. Soc.

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No presente artigo, métodos teóricos foram utilizados na análise da estrutura e propriedades eletrônicas de oligômeros de alquiltiofenos considerando diferentes regiosseletividades. A lacuna de energia entre as bandas de valência e condução foi calculada nos níveis ab initio Hartree-Fock (HF) e teoria do funcional de densidade (DFT) e semi-empírico ZINDO/S-CI. Os resultados mostraram que o isômero Head-Head-Tail-Tail (HH-TT) apresenta menores valores para a lacuna de energia quando oligômeros com mais de três unidades monoméricas são considerados e que a substituição do anel tiofeno por grupos alquila não afeta significativamente a lacuna de energia. Esse resultado é importante no sentido que mostra que polímeros mais processáveis podem ser obtidos através da alquilação sem perda considerável de suas características condutoras.In the present paper a theoretical analysis of alkylthiophenes with Head-Tail-Head-Tail (HT-HT) and Head-Head-Tail-Tail (HH-TT) regioselectivities up to 6 monomeric units was carried out. Structure and electronic properties for the syn and anti forms were calculated by ab initio HartreeFock (HF) and Density Functional Theory (DFT) approaches. The energy gap between the conduction and valence bands was obtained at HF and DFT levels and also calculated with the semiempirical ZINDO/S-CI method. The results showed that the isomer with HH-TT regioselectivity presents lower energy gap for longer oligomers and the substitution of thiophene by alkyl groups does not change significantly the energy gap. This is important in the sense that more processable polymers can be obtained through alkylation without decrease the energy gap that is a molecular properties related to the electronic conductivity. Regarding to the conformational equilibrium, the syn form was found to be stable only for the HT-HT isomer and in this case the energy gap was found to be lower than those calculated for the anti form.

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Section: Resultsmentioning

confidence: 99%

Structure and electronic properties of alkylthiophenes coupled by Head-to-Tail and Head-to-Head regioselectivity

Oliveira¹,

Almeida²,

Santos³

2004

J. Braz. Chem. Soc.

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“…Nonetheless, it appears that the trans conformer of R2, albeit twisted around the inter-ring bond, is lower in energy. 32, [38][39][40] Note that MOPAC and MNDO93,PM3 incorrectly predict the a Gaussian 92 code was used for all ab initio calculations. For one of them, 6-31G(d), a polarization function (d-orbital) was added for C and S atoms.…”

Section: Resultsmentioning

confidence: 99%

Comprehensive Evaluation of the Absorption, Photophysical, Energy Transfer, Structural, and Theoretical Properties of α-Oligothiophenes with One to Seven Rings

et al. 1996

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A large basis set of R-oligothiophenes with two to seven rings (R2-R7), also including thiophene, R1, have been investigated in five solvents regarding absorption, fluorescence and phosphorescence, quantum yields of fluorescence (φ F ) and triplet formation (φ T ), lifetimes of fluorescence and the triplet state, quantum yields of singlet oxygen production (φ ∆ ), all rate constants k F , k IC , k ISC , and several of the foregoing as a function of temperature. Ten different theoretical calculations across several levels including three levels of ab initio have been carried out regarding which conformer is lowest in energy and the ∆H's among all conformers of R2, R3 and R5, as well as calculations of transitions energies of the R-oligothiophenes. We have shown that the (l) 1 Bu state is the lowest singlet state for all R2-R7 in any solvent, in contradiction to previous predictions for the higher members. Based on absorption and fluorescence data and calculations of atomic charges in S 0 and S 1 , the ground state is twisted while the excited state is planar (quinoidal-like). Significant charge transfer occurs between S 0 and S 1 but not S 0 and T 1 . For all R2-R7, φ IC is small, k 0 F is approximately constant while k ISC decreases significantly from R2 to R7. The decrease is k ISC is believed to arise from a decrease in matrix elements of the type 〈 1 Ψ CT |H′| 3 Ψ 1 〉. The essential lack of phosphorescence is assigned as originating from inter-ring twisting mode coupling between T 1 and S 0 . Triplet energy transfer to 3 O 2 to produce 1 O 2 is highly efficient for R2-R5. Based on all data, the first Rn representative of R-polythiophene is R5.

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“…Electron diffraction experiments have determined that bithiophene is twisted in the gas phase. 20,21 The most recent experiment 21 has shown the existence of two conformations. The planar trans geometry has been only observed in crystals.…”

Section: Computational Detailsmentioning

confidence: 99%

A theoretical study of the electronic spectrum of bithiophene

Rubio

Merchán

Ortı́

et al. 1995

The Journal of Chemical Physics

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The electronic spectrum of bithiophene in the energy range up to 6.0 eV has been studied using multiconfigurational second order perturbation theory ͑CASPT2͒ and a basis set of ANO type, with split valence quality and including polarization functions on all heavy atoms. Calculations were performed at a planar ͑trans͒ and twisted geometry. The calculated ordering of the excited singlet states is 1

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Molecular conformation of 2,2′-bithiophene determined by gas phase electron diffraction and ab initio calculations

Cited by 144 publications

References 17 publications

Structure and electronic properties of alkylthiophenes coupled by Head-to-Tail and Head-to-Head regioselectivity

Structure and electronic properties of alkylthiophenes coupled by Head-to-Tail and Head-to-Head regioselectivity

Comprehensive Evaluation of the Absorption, Photophysical, Energy Transfer, Structural, and Theoretical Properties of α-Oligothiophenes with One to Seven Rings

A theoretical study of the electronic spectrum of bithiophene

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