Effects of solvent polarity and structure on intersystem crossing in diphenylcarbenes. A picosecond laser study on dimesitylcarbene

Sitzmann, E. V.; Langan, J.G.; Griller, D.; Eisenthal, Kenneth B.

doi:10.1016/0009-2614(89)85098-5

Cited by 29 publications

(44 citation statements)

References 51 publications

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“…90 This is of particular interest because the solvent effect on the relative spin populations may determine the solvent effect on relative product yields. [91][92][93] Eisenthal et al [87][88][89] found that the gap for diphenylcarbene decreases from A positive value implies the triplet is lower in energy than the singlet. b BPW91/ aug-cc-pVDZ//BPW91/cc-pVDZ level for 1 -, BPW91/cc-pVDZ level for 2 and 3 + .…”

Section: Resultsmentioning

confidence: 99%

Singlet−Triplet Splittings and 1,2-Hydrogen Shift Barriers for Methylphenylborenide, Methylphenylcarbene, and Methylphenylnitrenium in the Gas Phase and Solution. What a Difference a Charge Makes

1997

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In the isoelectronic series methylphenylborenide, methylphenylcarbene, and methylphenylnitrenium, fundamental differences are predicted for singlet state geometries, singlet-triplet state splittings, barriers to singlet 1,2-hydrogen migration, and sensitivity of 1,2-hydrogen migration to solvent effects in n-heptane and acetonitrile. We conclude that isoelectronic analogies are dangerous for systems having different formal charges, and that the interaction of the divalent center with a conjugating substituent is very sensitive to the electron donating or withdrawing nature (and power) of the hypovalent atom. Solvent effects on the singlet-triplet splitting result from static polarity differences whereas the solvent effects on 1,2-hydrogen migration result primarily from polarizability differences. For the experimentally characterized carbene case, extensive comparison of calculated and measured results is provided.

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Section: Resultsmentioning

confidence: 99%

Singlet−Triplet Splittings and 1,2-Hydrogen Shift Barriers for Methylphenylborenide, Methylphenylcarbene, and Methylphenylnitrenium in the Gas Phase and Solution. What a Difference a Charge Makes

1997

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“…Carbene chemistry is a multifaceted research area by virtue of the highly spin-dependent reactivity of carbenes 1 . Various spectroscopic investigations ranging from laser flash-photolysis 2 3 4 5 6 7 8 9 10 11 12 , matrix-isolation studies 13 to ultrafast measurements in different environments 14 15 16 17 18 19 20 21 22 have unveiled the role of carbenes as intermediates in (photo)chemical reactions. In particular, the reactivity of diphenylcarbene (diphenylmethylene, Ph 2 C) intrigues researchers owing to the simplicity of the system accompanied by the variety of possible reaction pathways depending on whether the spin-configuration is either a singlet or a triplet state 23 24 25 .…”

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confidence: 99%

Competitive solvent-molecule interactions govern primary processes of diphenylcarbene in solvent mixtures

et al. 2016

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Photochemical reactions in solution often proceed via competing reaction pathways comprising intermediates that capture a solvent molecule. A disclosure of the underlying reaction mechanisms is challenging due to the rapid nature of these processes and the intricate identification of how many solvent molecules are involved. Here combining broadband femtosecond transient absorption and quantum mechanics/molecular mechanics simulations, we show for one of the most reactive species, diphenylcarbene, that the decision-maker is not the nearest solvent molecule but its neighbour. The hydrogen bonding dynamics determine which reaction channels are accessible in binary solvent mixtures at room temperature. In-depth analysis of the amount of nascent intermediates corroborates the importance of a hydrogen-bonded complex with a protic solvent molecule, in striking analogy to complexes found at cryogenic temperatures. Our results show that adjacent solvent molecules take the role of key abettors rather than bystanders for the fate of the reactive intermediate.

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“…Previous studies reveal that polar solvents reduce the S-T gap of carbenes by increasing the dipole moment of the singlet state. [11][12][13][14][15][16] The reduction of the S-T gap for carbenes in polar solvents has been computationally verified. 12 The plot of experimentally determined S-T gaps as a function of solvent polarity was found to be linear, 11 which led to the conclusion that specific carbene-solvent interaction does not play a significant role.…”

Section: Resultsmentioning

confidence: 93%

“…This is in agreement with previous theoretical studies on the preferential stabilization of the singlet state in a polar solvent due to an increase in dipole moment. [11][12][13][14][15][16] For personal use only. Figure 2 shows the optimized geometries of the carbene… solvent complexes at the B3LYP/6-311++G(d, p) level of theory.…”

Section: Resultsmentioning

confidence: 99%

“…11 Apart from the effect of substituents, solvents are found to stabilize the singlet state more than the triplet state. [12][13][14][15][16] Products of carbene reactions are solely determined by the carbene's spin state. For example, the singlet carbene inserts in to the O-H bonds of alcohol, 17 whereas the triplet carbene undergoes insertion into C-H bonds 18 (Figure 1).…”

Section: Introductionmentioning

confidence: 99%

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Switching of carbene spin states: effect of hydrogen bond donors

Guha¹,

Boruah²,

Hazarika³

et al. 2015

RTC

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Quantum chemical calculations predict that the spin states of simple carbenes can be switched over from triplet to singlet via hydrogen bonding, and thus the spin specificity of their reactions can be tuned. The stability of the singlet state of simple carbenes like: CH 2 increases due to hydrogen bond formation with a single molecule of water or methanol, although the triplet state is found to be the ground state. However, the most dramatic effect of spin switch is found for diphenylcarbene (Ph 2 C), which becomes a ground state singlet due to formation of a hydrogen bond with the hydrogen atom of water or methanol. The present calculations reveal that the effect of hydrogen bonds on switching the spin state of carbenes is only applicable to Ph 2 C, as it has a very small singlet-triplet gap in its free form, ie, when it is not hydrogen bonded with water or methanol. Further, the presence of such hydrogen-bonding interaction has been verified within the realm of atoms-in-molecules analysis of the electron density.

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Effects of solvent polarity and structure on intersystem crossing in diphenylcarbenes. A picosecond laser study on dimesitylcarbene

Cited by 29 publications

References 51 publications

Singlet−Triplet Splittings and 1,2-Hydrogen Shift Barriers for Methylphenylborenide, Methylphenylcarbene, and Methylphenylnitrenium in the Gas Phase and Solution. What a Difference a Charge Makes

Singlet−Triplet Splittings and 1,2-Hydrogen Shift Barriers for Methylphenylborenide, Methylphenylcarbene, and Methylphenylnitrenium in the Gas Phase and Solution. What a Difference a Charge Makes

Competitive solvent-molecule interactions govern primary processes of diphenylcarbene in solvent mixtures

Switching of carbene spin states: effect of hydrogen bond donors

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