An exceptionally simple method of preparing matrix-isolated biradicals, biradicaloids, and carbenes

Haider, Karl W.; Platz, Matthew S.; Despres, A.; Lejeune, V.; Migirdicyan, E.; Bally, Thomas; Haselbach, Edwin

doi:10.1021/ja00215a062

Cited by 36 publications

(15 citation statements)

References 1 publication

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“…However, 41 and similar molecules are in fact relaxed molecules in an excited state; this can be recognized by the existence of an anomalous fluorescence or a rapid radiationless deactivation. [9ob1 The light absorption of interest here can be detected only by rapid spectroscopic methods; such have confirmed the twisted structure 41, since characteristic absorptions of the fragment molecules could be detected.…”

Section: We0 41mentioning

confidence: 99%

The Search for Highly Colored Organic Compounds

Fabian

Zahradník

1989

Angew. Chem. Int. Ed. Engl.

147

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Until now the study of organic compounds in which the n-electron system is excited by absorbed light has been mainly concentrated on the ultraviolet and visible regions of the electromagnetic spectrum. Various new applications, such as the use of conjugated organic compounds as dye lasers or as materials for storing information with the help of diode lasers, led to the synthesis of new compounds which absorb light in the near infrared (NIR). It is possible to use structure-color relationships to predict the properties of such new compounds when they belong to dyestuff classes which have already been studied in detail; in this case the approach involves decreasing the energy difference between the ground state and the first excited state. A less conventional starting point is provided by molecular structures in which from the outset there is only a very small energy difference between the lowest-energy electronic states; such diradicaloid molecules occupy a special position among the various types of organic compounds. It is possible by means of suitable structural modification to stabilize such molecules in a singlet form which absorbs light at very long wavelengths (i.e. at small wave numbers).

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Section: We0 41mentioning

confidence: 99%

The Search for Highly Colored Organic Compounds

Fabian

Zahradník

1989

Angew. Chem. Int. Ed. Engl.

147

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“…The ground states of these diradicals can often be rationalized by considering the spin polarization of the π‐system . In contrast, typical ππ and πππ di‐ and triradicals, such as the non‐Kekule hydrocarbon m ‐xylylene (1,3‐quinodimethane) 1 or 1,3,5‐trimethylenebenzene 2 , show a strong preference for ferromagnetic coupling with robust 3 B 2 and 4 A 2 ground states, respectively, according to their strongly nondisjoint NBMOs (Scheme ) . The singlet–triplet energy splitting of 1 was determined by photoelectron spectroscopy to 9.6 ± 0.2 kcal/mol, in reasonable agreement with vertical and adiabatic excitation energies for the ã 1 A 1 ← X ̃ 3 B 2 transition of 13.8 and 11.3 kcal/mol, respectively, computed at the equation‐of‐motion spin‐flip coupled‐cluster level (EOM‐SF‐CCSD) .…”

Section: Introductionmentioning

confidence: 99%

“…[35] In contrast, typical pp and ppp di-and triradicals, such as the non-Kekule hydrocarbon m-xylylene (1,3-quinodimethane) 1 or 1,3,5-trimethylenebenzene 2, show a strong preference for ferromagnetic coupling with robust 3 B 2 and 4 A 2 ground states, respectively, according to their strongly nondisjoint NBMOs (Scheme 1). [40][41][42][43][44][45][46][47][48][49] The singlet-triplet energy splitting of 1 was determined by photoelectron spectroscopy to 9.6AE0.2kcal/mol, [42] in reasonable agreement with vertical and adiabatic excitation energies for the ã 1 A 1 X 3 B 2 transition of 13.8 and 11.3kcal/mol, respectively, computed at the equation-of-motion spin-flip coupled-cluster level (EOM-SF-CCSD). [43] A detailed matrix-isolation study of 1, including infrared (IR) and electron paramagnetic resonance (EPR) spectroscopy, as well as investigations of various photoisomerization processes, became possible only recently, employing 1,3-bis-(iodomethyl)benzene as a thermal precursor.…”

Section: Introductionmentioning

confidence: 99%

EPR spectroscopic and computational characterization of the 2‐dehydro‐m‐xylylene and 4‐dehydro‐m‐xylylene triradicals

Neuhaus

Winkler

Sander

2011

J of Physical Organic Chem

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The isomeric 2‐dehydro‐ and 4‐dehydro‐1,3‐benzoquinodimethanes, 18 and 19, were generated by irradiation of the corresponding triiodo compounds in cryogenic argon matrices and characterized by electron paramagnetic resonance spectroscopy. In agreement with multireference computations, both systems possess quartet ground states, whereas in the isomeric 5‐dehydro‐m‐xylylene 20 the 2B2 doublet state lies energetically below the 4B2 state, so that no characteristic quartet signals could be observed for this triradical under similar experimental conditions. The best estimates for the adiabatic doublet–quartet energy splittings (CAS(7,7)‐AQCC/cc‐pVTZ//CAS(9,9)‐RS2c/cc‐pVTZ) of 18–20 are 10.4, 7.7, and −1.3 kcal/mol, respectively. The measured zero‐field splitting parameters of 18 and 19 are discussed in terms of the contributions of carbenoid resonance structures (spin polarization of the π‐system) to the resonance hybrid of the title triradicals. Copyright © 2011 John Wiley & Sons, Ltd.

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“…Scheme 1 We now report that in analogy to the rn-xylylene system, photolysis of the geminal dihalide dichlorodiphenylmethane (5) at 77 K leads to the formation of diphenylcarbene (7) via a twostep photodissociation mechanism involving initial formation of the diphenylchloromethyl radical (6) (Scheme 2). This represents a new entry for matrix isolation studies of carbenes which may be of use when diazo compounds or diazirine precursors are inconvenient.…”

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The double photodissociation of a geminal dichloride: Evidence for the stepwise formation of a diaryl carbene

Haider

Platz

1989

J of Physical Organic Chem

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Photolysis of dichlorodiphenylmethane in glassy 2‐methyltetrahydrofuran at 77 K results in the formation of diphenylcarbene and the diphenylchloromethyl radical, which were detected by their fluorescence emission and excitation spectra. The relative yields of the carbene and biradical are shown to vary dramatically as a function of photolysis time. The photolability of the diphenylchloromethyl radical is also demonstrated. These results were interpreted in terms of a two‐step mechanism, in which the diphenylchloromethyl radical is an intermediate in the formation of diphenylcarbene.

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An exceptionally simple method of preparing matrix-isolated biradicals, biradicaloids, and carbenes

Cited by 36 publications

References 1 publication

The Search for Highly Colored Organic Compounds

The Search for Highly Colored Organic Compounds

EPR spectroscopic and computational characterization of the 2‐dehydro‐m‐xylylene and 4‐dehydro‐m‐xylylene triradicals

The double photodissociation of a geminal dichloride: Evidence for the stepwise formation of a diaryl carbene

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