Detection of a diradical intermediate in the cis–trans isomerization of 5,5′-bis(4,5-diphenyl-2H-imidazol-2-ylidene)-5,5′-dihydro-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"><mml:mrow><mml:msup><mml:mrow><mml:mi mathvariant="normal">Δ</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn><mml:mtext>,</mml:mtext><mml:msup><mml:mrow><mml:mn>2</mml:mn></mml:mrow><mml:mrow><mml:mo>′</mml:mo></mml:mrow></mml:msup></mml:mrow></mml:msup></mml:mrow></mml:math>-bithiophene

Kozaki, Masatoshi; Isoyama, Asuka; Okada, Keiji

doi:10.1016/j.tetlet.2006.05.084

Cited by 18 publications

(10 citation statements)

References 28 publications

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“…Organic radicals have been extensively studied since the early 20th century because of fundamental interest in the structure and property of chemical species with unpaired electrons inside. − In addition to fundamental interests, organic radicals have opened up several potential applications such as to radical polymerization initiators, radical batteries, − and two-photon absorption materials. − Meanwhile, various stable organic radicals have been synthesized by delocalizing their unpaired electrons over the molecule and by protecting them with bulky substituents. Almost all studies related to the delocalized biradicals, however, focused on the static aspects of the biradicals constructed from rigid molecular frameworks of π-conjugation systems. ,,,, On the other hand, only a few studies − have been reported for the properties of π-delocalized biradicals in flexible structures where the geometrical arrangement is associated with the change of the electronic structure.…”

Section: Introductionmentioning

confidence: 99%

Direct Observation of the Ultrafast Evolution of Open-Shell Biradical in Photochromic Radical Dimer

et al. 2017

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Delocalized biradicals have been extensively studied because of fundamental interests to singlet biradicals and several potential applications such as to two-photon absorption materials. However, many of the biradical studies only focus on the static properties of the rigid molecular structures. It is expected that the biradical properties of the delocalized biradicals are sensitive to the subtle changes of the molecular structures and their local environments. Therefore, the studies of the dynamic properties of the system will give further insight into stable radical chemistry. In this study, we directly probe the ultrafast dynamics of the delocalized biradical of a photochromic radical dimer, pentaarylbiimidazole (PABI), by time-resolved visible and infrared spectroscopies and quantum chemical calculations with the extended multistate complete active space second-order perturbation theory (XMS-CASPT2). While the photogenerated transient species was considered to be a single species of the biradical, the present ultrafast spectroscopic study revealed the existence of two transient isomers differing in the contributions of biradical character. The origin of the two metastable isomers is most probably due to the substantial van der Waals interaction between the phenyl rings substituted at the imidazole rings. Unraveling the temporal evolution of the biradical contribution will stimulate to explore novel delocalized biradicals and to develop biradical-based photofunctional materials utilizing the dynamic properties.

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Section: Introductionmentioning

confidence: 99%

Direct Observation of the Ultrafast Evolution of Open-Shell Biradical in Photochromic Radical Dimer

et al. 2017

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“…Each line further split into 9 lines due to the coupling with four terminal nitrogen atoms. It must be noticed that the observed hyperfine coupling constants of β -protons are more than 10 times larger than the reported values for non-fused QT2CN2 • - (R = H, g = 2.0026, a H = 0.3, a N = 0.6 G) 7c. The higher spin density in the uncovered β -protons should facilitate intermolecular electron exchange, thus an increase in mobility is expected.…”

mentioning

confidence: 61%

“…Although the spin and charge delocalization are important for understanding unique device properties and the conduction mechanism, there have been only a small number of papers concerning anionic species of QT n CN2-type compounds . Takahashi and co-workers have recently reported that a carbonyl-bridged bithienoquinoid 1 exhibits high conductivity in the radical anion form .…”

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confidence: 99%

Preparation, Properties, and Reduction of a Novel TCNQ-Type Thienoquinoid

et al. 2006

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[Structure: see text] TCNQ-type bithienoquinoid condensed with a alpha-dicarbonyl group was synthesized. The compound revealed a reversible reduction wave at +0.32 V vs SCE. The radical anion species was cleanly generated by a reduction with Na-Hg and characterized: lambdamax=1027 nm in vis-NIR and a large spin density of the beta-carbon atoms on the fused ring by EPR spectroscopy. The radical anion salts were isolated by a reduction with iodide and showed moderate conductivity.

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“…Thiele's 4 and Chichibabin's 5 hydrocarbons are the first examples of systems characterized by a biradicaloid ground state, as proven by both spectroscopic analysis and theoretical modeling. 6 Several further series of Chichibabin-type compounds with dicyanomethylene, 7 oxocyclohexadienylidene 8,9 or imidazolylidene 10 end groups have then been synthesized. It has been observed that molecules with a rather short sequence of conjugated units exhibit a quinoidal structure, whereas a diradical contribution occurs when increasing the conjugation length.…”

Section: Introductionmentioning

confidence: 99%

Outside rules inside: the role of electron-active substituents in thiophene-based heterophenoquinones

Colella

Nardone

Parisini

et al. 2015

Phys. Chem. Chem. Phys.

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The biradicaloid vs. quinoidal character of the ground state of thiophene-based heterophenoquinones bearing donor or acceptor groups is investigated. Keeping the conjugation length fixed, namely, the 5,5'-bis(3,5-di-tert-butyl-4-oxo-2,5-cyclohexadiene-1-ylidene)-2,2'-dihydroxy bithiophene backbone, an opposite effect occurs depending on the donating or withdrawing nature of the substituents. The character of the ground state depends not only on the electronic nature of the substituents but also on their position on the molecular skeleton: donor groups on the 3,3'-positions of the bithiophene central core stabilize a quinoidal ground state, whereas a biradicaloid electronic structure results from the introduction of the same donor groups onto the lateral phenones. Withdrawing groups behave similar to donors, but in the opposite direction.

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Detection of a diradical intermediate in the cis–trans isomerization of 5,5′-bis(4,5-diphenyl-2H-imidazol-2-ylidene)-5,5′-dihydro-Δ2,2′-bithiophene

Cited by 18 publications

References 28 publications

Direct Observation of the Ultrafast Evolution of Open-Shell Biradical in Photochromic Radical Dimer

Direct Observation of the Ultrafast Evolution of Open-Shell Biradical in Photochromic Radical Dimer

Preparation, Properties, and Reduction of a Novel TCNQ-Type Thienoquinoid

Outside rules inside: the role of electron-active substituents in thiophene-based heterophenoquinones

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