Cross conjugation

Phelan, Nelson F.; Orchin, Milton

doi:10.1021/ed045p633

Cited by 168 publications

(158 citation statements)

References 2 publications

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“…On one hand, based on other reports dealing with electronic properties of crossconjugated compounds, which generally also fail to exhibit strong shifts of HOMO ± LUMO transitions, [12,14,18] we are inclined to think that most cross-conjugated systems behave similarly to oligo(p-phenylenevinylidene)s. On the other hand, it should be realized that there are two factors which have an unfavorable effect on the conjugation in oligo(pphenylenevinylidene)s. These are the nonplanar structure [46] and the high resonance energy of the incorporated aromatic moieties. [38] Although, for instance, dendralenes are also not planar, [47] somewhat stronger interactions may be expected for other classes of cross-conjugated systems.…”

Section: Resultsmentioning

confidence: 98%

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Electron Delocalization in Cross‐Conjugated p‐Phenylenevinylidene Oligomers

Klokkenburg

Lutz

Spek

et al. 2003

Chemistry A European J

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The synthesis, structure, and electronic properties of a series of crossconjugated p-phenylenevinylidene oligomers with one to four double bonds are reported. The X-ray crystal structure of the compound with two double bonds reveals a nonplanar conformation with torsion angles about the C(phenylene) ± C(vinylidene) and C(phenyl) ± C(vinylidene) formal single bonds of 39.5(2)8 and 30.5(2)8, respectively. Admixture of quinoid character in the ground state is observed. Infrared and Raman spectroscopy do not provide a clear picture of the degree of electron delocalization in the series, since the CC stretching mode does not adequately reflect the CC bond order and has a local nature. In contrast, electronic spectra and electrochemical data, as well as AM1 and PPP/SCF calculations, reveal that the cross-conjugated compounds basically behave as linearly p-conjugated systems in the sense that molecular orbitals are delocalized over the entire structure and systematically change in energy. The electronic interaction between the repeating units is, however, not very strong, which has the consequence that spatial extension of the molecular orbitals does not lead to a red shift of the highest occupied molecular orbital ± lowest unoccupied molecular orbital (HOMO ± LUMO) electronic transition. This is related to the feature that the modest narrowing of the HOMO ± LUMO gap with the chain length is accompanied by a relatively large reduction of electron repulsion. This finding implies that care should be taken in the use of electronic spectra for the evaluation of conjugation phenomena.

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Section: Resultsmentioning

confidence: 98%

“…[12] Examples of simple cross-conjugated compounds are 3-methylene-1,4-pentadiene, benzophenone, and 1,1-diphenylethene. Recently, interest in this type of conjugation has flourished, as illustrated by the development of dendralene-based [13,14] and enediyne-based [15±17] systems.…”

Section: Introductionmentioning

confidence: 99%

Electron Delocalization in Cross‐Conjugated p‐Phenylenevinylidene Oligomers

Klokkenburg

Lutz

Spek

et al. 2003

Chemistry A European J

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“…A molecule in connection with two leads is termed linearly conjugated if one can draw a path connecting the two leads, which strictly alternate between single and double or triple bonds. A pathway is cross conjugated if it contains two subsequent single bonds and the (sp 2 hybridized) carbon atom linking these single bonds is double bonded to any group or atom in a third direction [16]. A molecule is called cross conjugated if all the pathways are cross conjugated.…”

Section: Introductionmentioning

confidence: 99%

Temperature effects on quantum interference in molecular junctions

Markussen

Thygesen

2014

Phys. Rev. B

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A number of experiments have demonstrated that destructive quantum interference (QI) effects in molecular junctions lead to very low conductances even at room temperature. On the other hand, another recent experiment showed increasing conductance with temperature which was attributed to decoherence effects destroying QI at finite temperatures. Here we study the influence of finite temperatures and electron-phonon interactions on QI in molecular junctions. Two different models leading to two inherently different types of QI effects are considered. Each model is exemplified by specific molecules and studied using first-principles calculations. We find that the molecules exhibiting QI show a much stronger temperature dependence of the conductance compared to molecules without QI. However, the large QI-induced suppression of the conductance remains, showing that QI effects are indeed robust against finite temperatures and inelastic scattering.

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“…These are usually arranged in a linear fashion, but also a branched architecture is possible. [1][2][3][4][5][6][7] In branched π-systems, which are also referred to as cross-conjugated systems, [8,9] several linear π-conjugation paths are present. From a fundamental point of view it is of interest to assess which conjugation path dominates in a given cross-conjugated compound, and by which factors this is controlled.…”

Section: Introductionmentioning

confidence: 99%

On the Structure of Cross‐Conjugated 2,3‐Diphenylbutadiene

Walree¹,

Wiel²,

Jenneskens³

et al. 2007

Eur J Org Chem

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The structure of the cross-conjugated compound 2,3-diphenylbutadiene was investigated by single-crystal X-ray diffraction and computational methods. In the crystal structure the central butadiene fragment adopts an s-gauche geometry [-55.6(2)°torsion angle φ around the essential single bond], whereas the styrene moieties are close to planarity. MP2/6-311G* calculations show that the s-gauche conformation represents the global minimum along the φ coordinate, but also revealed the existence of an s-trans local minimum.

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Cross conjugation

Abstract: Although qualitative conclusions may be obtained by judicious use of simple resonance theory, even in simple systems the electron distribution and extent of conjugation between the nonconjugated centers in cross conjugation is most effectively illustrated by molecular orbital descriptions.

Cited by 168 publications

References 2 publications

Electron Delocalization in Cross‐Conjugated p‐Phenylenevinylidene Oligomers

Electron Delocalization in Cross‐Conjugated p‐Phenylenevinylidene Oligomers

Temperature effects on quantum interference in molecular junctions

On the Structure of Cross‐Conjugated 2,3‐Diphenylbutadiene

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