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Periasamy, N.; Danieli, R.; Ruani, G.; Zamboni, R.; Taliani, C.

doi:10.1103/physrevlett.68.919

Cited by 115 publications

(41 citation statements)

References 28 publications

(31 reference statements)

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“…Earlier work has shown that the lowest optically forbidden excited state 2A g lies below the optically allowed excited state 1B u in polyene molecules [2] ( thus preventing any significant luminescence in such compounds ), while an independent electron model gives the opposite picture; similar results have been found by Periasamy et al in the case of polycrystalline sexithienyl [3] or Lawrence et al in single crystal polydiacetylene [4]. These examples serve as evident manifestation of electron correlation in conjugated molecules.…”

supporting

confidence: 72%

Quantum-confinement effects on the ordering of the lowest-lying excited states in conjugated chains

et al. 1997

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The symmetrized density matrix renormalization group approach is applied within the extended Hubbard-Peierls model (with parameters U/t, V /t, and bond alternation δ) to study the ordering of the lowest one-photon (1 1 B − u ) and two-photon (2 1 A + g ) states in one-dimensional conjugated systems with chain lengths, N , up to N = 80 sites. Three different types of crossovers are studied, as a function of U/t, δ, and N . The U -crossover emphasizes the larger ionic character of the 2A g state compared to the lowest triplet excitation. The δ crossover shows strong dependence on both N and U/t. The N -crossover illustrates the more localized nature of the 2A g excitation relative to the 1B u excitation at intermediate correlation strengths. It is well established that correlated electron systems behave differently from independent electron systems, especially in the case of excitations. Earlier work has shown that the lowest optically forbidden excited state 2A g lies below the optically allowed excited state 1B u in polyene molecules [2] ( thus preventing any significant luminescence in such compounds ), while an independent electron model gives the opposite picture; similar results have been found by Periasamy et al. in the case of polycrystalline sexithienyl [3] or Lawrence et al. in single crystal polydiacetylene [4]. These examples serve as evident 1

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supporting

confidence: 72%

Quantum-confinement effects on the ordering of the lowest-lying excited states in conjugated chains

et al. 1997

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“…It is experimentally known that for the longer all-trans polyenes, starting with hexatriene, 11 the lowest singlet 0-0 transition corresponds to an electronic state of the same symmetry as the ground state ͑for example, in dodecahexaene the 2 1 B transition in bithiophene. 2 The fact that the energy difference between these two 0-0 bands is much smaller in hexathiophene ͑0.11 eV͒, although the same ordering is found, suggests that the reversed order prevails for longer chains ͑Ͼ6 monomer units͒, that is, 2 1 A is below 1 1 B. Periasamy et al 12,13 have, however, suggested that the electronic energetics of ''real'' polythiophene follows the same excited states ordering as in hexathiophene based on the similarity observed between the photoluminescence of the polymer and the oligomer.…”

Section: Introductionmentioning

confidence: 86%

“…Although the vertical excitation energies place the 2 claim that the two lowest excited states of thiophene oligomers and polyenes are similar, and therefore the lowest excited state is predicted to have the same symmetry as the ground state, which is contrary to the experimental evidence. 1,2,12,13 In order to explain the experimental information, they suggest that the 1 A g experimentally observed is the 3 1 A g state. Here, one could note that a comparison of the two lowest excited states of 1,3 cis-butadiene and thiophene shows important differences.…”

Section: Introductionmentioning

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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“…Among organic molecules, ␣-hexathiophene (T6) is a well-characterized prototypical compound for polyconjugated systems. [5][6][7][8][9][10][11][12] Furthermore, T6 possesses interesting properties of hole injection into highly fluorescent polymers. 13 It is then of utmost importance, in order to engineer new materials with suitable optoelectronic properties, to understand the essential processes in which T6 molecules form solid structures and to what extent their order can be driven by the substrate structure.…”

mentioning

confidence: 99%

Ordering of a prototypical conjugated molecular system during monolayer growth on the (1×2)-Au(110) surface

et al. 1996

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The UHV deposition of ␣-hexathiophene (T6) oligomers on the 1ϫ2 reconstructed Au͑110͒ surface has been studied in situ. The evolution of the surface morphology during the deposition is followed by the He atom scattering method. A proliferation of Au monoatomic steps is observed during deposition, indicating a strong interaction between Au substrate and T6 molecules. The build-up of a well-ordered single monolayer is obtained with a rectangular unit cell. Its dimensions indicate that T6 molecules lie on the surface, aligned along the rows of close-packed Au atoms.Organic molecules with -conjugated electrons have been shown to have unique electronic properties 1 that offer exciting opportunities for applications in both photonics 2 and optoelectronics.3 In particular, the interaction with and the ordering processes of these molecules at metal surfaces are of basic interest for organic light-emitting diode 4 technologies. Among organic molecules, ␣-hexathiophene (T6) is a well-characterized prototypical compound for polyconjugated systems.5-12 Furthermore, T6 possesses interesting properties of hole injection into highly fluorescent polymers.13 It is then of utmost importance, in order to engineer new materials with suitable optoelectronic properties, to understand the essential processes in which T6 molecules form solid structures and to what extent their order can be driven by the substrate structure. In the context of growth mechanisms of organic monolayers, 12,14 -20 it is worth mentioning that organic structures grown quasiepitaxially under ultrahigh vacuum ͑UHV͒ have been claimed to show interesting optical properties. 21,22 In the present work we present a study of the formation of a single molecular layer of T6 by UHV deposition on the (1ϫ2)-Au͑110͒ surface. He atom scattering has been used to study the surface morphology during deposition. This method has been shown to be particularly suited for studying organic overlayers, 23,24 being a nonpenetrating and nondestructive technique with a very high surface sensitivity.The first stages of T6 deposition show substantial modification of the substrate with proliferation of up-down correlated monoatomic steps, but the step density substantially reduces when a highly ordered T6 monolayer with a rectangular unit cell is reached. In this layer, the T6 molecules lie flat on the surface and are aligned along the rows of close packed Au atoms with a periodicity of 27.4Ϯ0.5 Å and 16.3Ϯ0.2 Å, respectively, along the Au rows ͑⌫X direction͒ and perpendicular to them ͑⌫Y direction͒. The former distance is consistent with the length of a single molecule while the latter is twice that of the (1ϫ2)-Au͑110͒ missing row structure.The He beam apparatus, described in detail elsewhere, 25 has a fixed scattering geometry with angle of incidence i ϭ55°Ϫ␣ and exit angle out ϭ55°ϩ␣. The sample is mounted on a high-precision manipulator with six degrees of freedom and with an angular reproducibility better than 0.01°. The diffraction intensities are collected by scanning the angle ␣, ...

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Location of the low-energy1Ag

Cited by 115 publications

References 28 publications

Quantum-confinement effects on the ordering of the lowest-lying excited states in conjugated chains

Quantum-confinement effects on the ordering of the lowest-lying excited states in conjugated chains

A theoretical study of the electronic spectrum of bithiophene

Ordering of a prototypical conjugated molecular system during monolayer growth on the (1×2)-Au(110) surface

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