Nematic phase nuclear magnetic resonance investigations of rotational isomerism. III. Conformational preferences and interconversion barrier of 2,2'-bithienyl

Bucci, P.; Longeri, M.; Veracini, C. A.; Lunazzi, Lodovico

doi:10.1021/ja00812a007

Cited by 102 publications

(64 citation statements)

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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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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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“…It should be pointed out that this approximation only holds for small angular differences. A more realistic torsional potential [18] that covers the whole angular domain will be considered in a forthcoming publication. We therefore restrict ourselves here to soft conformational defects.…”

Section: Model and Formalismmentioning

confidence: 99%

Dynamic interaction between polarons and torsional vibrations in conjugated polymers

Brito¹,

Silva²

2005

Int J of Quantum Chemistry

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ABSTRACT:We propose a model for the electronic interaction associated with torsional and bond length vibrations in quasi-one-dimensional chains of conjugated polymers. The model admits conformational bond length objects like polarons and bipolarons and torsional modes of vibration. It is shown that the dynamics of these objects can be studied by numerically integrating the corresponding time-dependent equations of motion for the bond length; ring torsion angle, and -electrons. An extension of the PPP and SSH models is numerically solved using the time-dependent Hartree-Fock approximation. A wide range of conducting polymers is simulated by varying the moment of inertia of the monomers [ranging from polypyrrole to poly(3-hexyl)thiophene]. The stereometric interactions between chains are parametrically considered with different torsional potentials. The results show that polarons and bipolarons are trapped between the antinodes of torsional vibration modes with wavelengths larger than their widths. This effect damps down their mobility. We also found that torsional vibration modes with very long wavelengths or wavelengths shorter than the width of polarons and bipolarons produce almost no effect on their propagation.

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“…Examples include studies of the bipyridyls and bithiophenes [90][91][92][93][94] and substituted biphenyls [95][96][97][98][99].…”

Section: Substituted Biphenyls In Liquid Crystalsmentioning

confidence: 99%

NMR studies of oriented molecules

Sinton¹

1981

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The properties of liquid crystalline mesophases have been of continuing interest in physics and chemistry since the discovery of these novel compounds. Recently, nuclear magnetic resonance (NMR) spectroscopy has been extensively used to probe the microscopic nature of liquid crystal samples. The NMR spectra contain information which is sensitive to internal molecular parameters and reflect the anisotropic potential in which the molecules reorient. Fast diffusion and rotational motion remove the effects of couplings between molecules.

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Nematic phase nuclear magnetic resonance investigations of rotational isomerism. III. Conformational preferences and interconversion barrier of 2,2'-bithienyl

Cited by 102 publications

References 0 publications

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

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

Dynamic interaction between polarons and torsional vibrations in conjugated polymers

NMR studies of oriented molecules

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