Auf der Suche nach tieffarbigen organischen Verbindungen

Fabian, Jürgen; Zahradník, R.

doi:10.1002/ange.19891010604

Cited by 75 publications

(37 citation statements)

References 254 publications

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“…The large twist in the central double bond reduces the p overlap, which causes a substantial red shift of the UV-visible absorptions and smaller HOMO-LUMO gaps in the twisted conformations. [80,81] Therefore, the deeply colored thermochromic B form of BAEs may be assigned to a twisted conformation of the molecule, whereas the yellow (or colorless) ambienttemperature form A is confirmed to be the (anti-)folded conformation.…”

Section: Wwwchemeurjorg Discussionmentioning

confidence: 98%

Polymorphism Versus Thermochromism: Interrelation of Color and Conformation in Overcrowded Bistricyclic Aromatic Enes

Biedermann

Stezowski

Agranat

2006

Chemistry A European J

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The nature of the thermochromic form of overcrowded bistricyclic aromatic enes (BAEs) has been controversial for a century. We report the single-crystal X-ray structure analysis of the deep-purple and yellow polymorphs of 9-(2,7-dimethyl-9H-fluoren-9-ylidene)-9H-xanthene (11), which revealed the molecules in a twisted and a folded conformation, respectively. Therefore, the deeply colored thermochromic form B of BAEs is identified as having a twisted conformation and the ambient-temperature form A as having a folded conformation. This relationship between the color and the conformation is further supported by the X-ray structures of the deep-purple crystals of the twisted 9-(9H-fluoren-9-ylidene)-9H-xanthene (10), and of the yellow crystals of the folded 9-(11H-benzo[b]fluoren-11-ylidene)-9H-xanthene (12). Based on this conclusive crystallographic evidence, eleven previously proposed rationales of thermochromism in BAEs are refuted. In the twisted structures, the tricyclic moieties are nearly planar and the central double bond is elongated to 1.40 A and twisted by 42 degrees . In the folded structures, the xanthylidene moieties are folded by 45 degrees and the fluorenylidene moieties by 18-20 degrees . Factors stabilizing the twisted and folded conformations are discussed, including twisting of formal single or double bonds, intramolecular overcrowding, and the significance of a dipolar aromatic "xanthenylium-fluorenide" push-pull structure.

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Section: Wwwchemeurjorg Discussionmentioning

confidence: 98%

Polymorphism Versus Thermochromism: Interrelation of Color and Conformation in Overcrowded Bistricyclic Aromatic Enes

Biedermann

Stezowski

Agranat

2006

Chemistry A European J

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“…[65] There is a small lifting of degeneracy (right side in Figure 5), which is stabilized when a geometrical or electronegative perturbation occurs, but the BRC is retained. [19,66] The VB pictures shown in the Supporting Information ( Figure S4 and Table S2) of these molecules confirm the biradical nature of the molecules. [67,68] Thus, one can consider TDI, BBI and BBT to contain the substructure TMB.…”

Section: Homo Lumo Ip and Eamentioning

confidence: 65%

“…Various factors can influence the band gaps which include aromaticity, p-conjugation length, and quinoid character of the molecule. [19,20] A very common design strategy is to take an electron-rich donor and an electron-deficient acceptor and link them through a p-conjugated spacer. [21,22] Molecules with reasonably high electron affinity (EA) would be suitable as n-type semiconductors (electron transport) and those with low ionization potential (IP) as p-type semiconductors (hole transport).…”

Section: Introductionmentioning

confidence: 99%

Comparative Study of the Semiconducting Properties of Benzothiadiazole and Benzobis(thiadiazole) Derivatives Using Computational Techniques

Thomas

Bhanuprakash

2012

ChemPhysChem

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Recent literature reports indicate that derivatives of benzothiadiazole (BT) and benzobis(thiadiazole) (BBT), which differs from BT by an extra thiadiazole ring, exhibit good semiconducting properties, such as high electron mobility and low-lying lowest unoccupied molecular-orbital (LUMO) levels. In this study herein, computational techniques like density functional theory (DFT), spin-flip DFT and valence-bond methods are used to analyze the semiconducting properties of these molecules. Calculations at the B3LYP/cc-pVTZ level reveal that all the BBT molecules, including the bare BBT ring, have lower lying LUMO energies (3.70-4.11 eV) compared to the BT derivatives (2.56-3.41 eV) with similar substitution. The reorganization energies (λ(+)/λ(-)) obtained at this level of theory of the BT derivatives are around (225-333)/(246-315) meV, while BBT derivatives have much smaller reorganization energies and these are in the range of (129-259)/(150-230) meV. We observe that the different behavior of BBT is due to the inherited biradicaloid character from the parent molecule tetramethylenebenzene (TMB), a disjoint non-Kekule biradical having non-bonding molecular orbitals (NBMOs) as the highest occupied molecular orbital (HOMO) and LUMO. Additionally, the perturbation of the orbitals of the biradical TMB to obtain BBT is the major cause for the BBT derivatives to have a larger electron affinity (EA) and a smaller HOMO-LUMO gap (HLG) compared to BT derivatives.

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“…and on the other hand, a lengthening compared to 7c bonds in other similar compounds. Thus, in 4 the Rh-Rh distance is 2.827(1) A (average value), whilst for [(PCy,),ReH-(p-PCy,),Rh(l ,5-cod)][BF4] (cod = cyclooctadiene) with diphosphido-bridged metal centers, a Re-Rh distance of 2.9361 (8) for a 0 bond is observed. In the hydridosulfido- Because the rhodium(1) atom in 3-5 has one or two free coordination sites for two-electron donors, we were also interested in the homogeneous catalytic properties of these compounds.…”

Section: The First Clusters With a Y-shapedmentioning

confidence: 98%

The First Clusters with a Y‐Shaped Arrangement of Ligands at Three‐Coordinate Rh^I Atoms in the Solid State: [M¹M²{μ‐P(C₆H₁₁)₂}(CO)₈Rh(PPh₃)] (M¹, M² = Mn, Re)

Beckers

Flörke

Haupt

1995

Angew. Chem. Int. Ed. Engl.

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Auf der Suche nach tieffarbigen organischen Verbindungen

Cited by 75 publications

References 254 publications

Polymorphism Versus Thermochromism: Interrelation of Color and Conformation in Overcrowded Bistricyclic Aromatic Enes

Polymorphism Versus Thermochromism: Interrelation of Color and Conformation in Overcrowded Bistricyclic Aromatic Enes

Comparative Study of the Semiconducting Properties of Benzothiadiazole and Benzobis(thiadiazole) Derivatives Using Computational Techniques

The First Clusters with a Y‐Shaped Arrangement of Ligands at Three‐Coordinate Rh^I Atoms in the Solid State: [M¹M²{μ‐P(C₆H₁₁)₂}(CO)₈Rh(PPh₃)] (M¹, M² = Mn, Re)

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Auf der Suche nach tieffarbigen organischen Verbindungen

Cited by 75 publications

References 254 publications

Polymorphism Versus Thermochromism: Interrelation of Color and Conformation in Overcrowded Bistricyclic Aromatic Enes

Polymorphism Versus Thermochromism: Interrelation of Color and Conformation in Overcrowded Bistricyclic Aromatic Enes

Comparative Study of the Semiconducting Properties of Benzothiadiazole and Benzobis(thiadiazole) Derivatives Using Computational Techniques

The First Clusters with a Y‐Shaped Arrangement of Ligands at Three‐Coordinate RhI Atoms in the Solid State: [M1M2{μ‐P(C6H11)2}(CO)8Rh(PPh3)] (M1, M2 = Mn, Re)

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The First Clusters with a Y‐Shaped Arrangement of Ligands at Three‐Coordinate Rh^I Atoms in the Solid State: [M¹M²{μ‐P(C₆H₁₁)₂}(CO)₈Rh(PPh₃)] (M¹, M² = Mn, Re)