Theoretical study of protonation effects in polyaniline oligomers

Dávila, Liliana Yolanda Ancalla; Caldas, M. J.

doi:10.1016/s0379-6779(00)00916-4

Cited by 8 publications

(3 citation statements)

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“…Indeed, our study with AM1 for longer polyaniline oligomers (up to 10 rings 31 ) indicates that when oxidation occurs in an internal section of the oligomer, the angles around the oxidized unit may decrease. This does not happen, however, when oxidation occurs near a chain end.…”

Section: Leucoemeraldine and Pernigraniline Trimersmentioning

confidence: 82%

Applicability of MNDO techniques AM1 and PM3 to ring‐structured polymers

Dávila¹,

Caldas²

2002

J Comput Chem

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Semiempirical Hartree-Fock techniques are widely used to study properties of long ring-structured chains, although these types of systems were not included in the original parametrization ensembles. These techniques are very useful for an ample class of studies, and their predictive power should be tested. We present here a study of the applicability of some techniques from the NDDO family (MNDO, AM1, and PM3) to the calculation of the ground state geometries of a specific set of molecules with the ring-structure characteristic. For this we have chosen to compare results against ab initio Restricted Hartree-Fock 6-31G(d,p) calculations, extended to Møller-Plesset 2 perturbation theory for special cases. The systems investigated comprise the orthobenzoquinone (O(2)C(6)H(4)) molecule and dimers (O(2)C(6)H(4))(2), as well as trimers of polyaniline, which present characteristics that extend to several systems of interest in the field of conducting polymers, such as ring structure and heterosubstitution. We focus on the torsion between rings, because this angle is known to affect strongly the electronic and optical properties of conjugated polymers. We find that AM1 is always in qualitative agreement with the ab initio results, and is thus indicated for further studies of longer, more complicated chains.

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Section: Leucoemeraldine and Pernigraniline Trimersmentioning

confidence: 82%

Applicability of MNDO techniques AM1 and PM3 to ring‐structured polymers

Dávila¹,

Caldas²

2002

J Comput Chem

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“…There have been various theoretical approaches to determine the electronic and structural properties of polyaniline such as extended Hückel theory (EHT) [10], the valence effective Hamiltonian (VEH) technique [11][12][13][14][15], ab initio calculations based on density functional theory (DFT) [16][17][18][19], or Car-Parrinello molecular dynamics [20,21]. In addition, there has been research to explain the effect of protonation [22][23][24] and the conduction mechanism [25][26][27][28] of polyaniline.…”

Section: Introductionmentioning

confidence: 99%

Theory of electron transport through single molecules of polyaniline

Lee¹,

Speyer²,

Sankey³

2007

J. Phys.: Condens. Matter

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We present theoretical results for the electron transport properties of the organic molecule polyaniline, especially leucoemeraldine (LEB), the fully reduced form. The electron tunnelling characteristics of these chain-like molecules are described by their complex band-structure. We explore how the bandgap and tunnelling decay parameter β depend on the oxidation state of the molecule and on the torsion angle between rings. It is found that the metal Fermi level lies near the HOMO for gold contacts with a single leucoemeraldine molecule, which results in non-linear I -V characteristics. The conductance of a hepta-aniline (LEB) oligomer is obtained from a first-principles I -V curve and compared with the recent experimental results. We examine the effect of stretching of the molecule on its conductance to explain the discrepancy between the theoretical simulations and single-molecule conductance measurement experiment.

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“…14 Our values for the C-S bond of T rings are smaller, by 0.02-0.04 Å, than experimental data 12 as expected for AM1. 15 The use of AM1 is justified by its superior qualities when treating ring-torsion angles, 16 known to be important for modulating -electron interactions across monomers, 17 and strongly influencing the optical properties. 18 The ionization potentials I P for the studied systems are shown in Table I.…”

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confidence: 99%

Tailoring of light emission properties of functionalized oligothiophenes

Caldas

Pettenati

Goldoni

et al. 2001

Applied Physics Letters

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We investigate theoretically the light emission properties of short oligothiophenes containing a thienyl-S,S-dioxide moiety, which have recently been shown to exhibit strong photoluminescence efficiency and tunability. We find that the dioxide substitution tends to increase the torsion angle between rings and strongly affects the states at the optical band edges, in a way depending on the position of the substituted ring. We have identified a low-energy transition which is optically active only when the dioxide unit is inserted between two thiophene rings, as a result of increased inter-ring torsional angle also in the excited state. With the dioxide unit in a terminal position, planarity is favored in the excited state, and the transition is optically inactive. For short oligomers, this can lead to nonradiative decay quenching the luminescence.

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Theoretical study of protonation effects in polyaniline oligomers

Cited by 8 publications

References 0 publications

Applicability of MNDO techniques AM1 and PM3 to ring‐structured polymers

Applicability of MNDO techniques AM1 and PM3 to ring‐structured polymers

Theory of electron transport through single molecules of polyaniline

Tailoring of light emission properties of functionalized oligothiophenes

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