Ultrafast Carbonylcarbene Formation and Spin-Equilibration

Hess, Gina C.; Kohler, Bern; Likhotvorik, I. R.; Peón, Jörge; Platz, Matthew S.

doi:10.1021/ja0011358

Cited by 19 publications

(38 citation statements)

References 21 publications

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“…For excited state dynamics for one‐ (400 nm) and two‐photon (800 nm) excitation, we used both femtosecond fluorescence up‐conversion and transient absorption spectroscopy. Both instruments are described in detail elsewhere . Briefly, the setups are based on a regenerative amplified Ti : Sapphire laser centered at 800 nm, with a repetition frequency of 1 kHz, temporal width of 180 fs and 0.8 mJ per pulse.…”

Section: Methodsmentioning

confidence: 99%

Synthesis and Photodynamics of Stilbenyl‐Azopyrroles: Two‐Photon Controllable Photoswitching Systems

et al. 2019

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Three new stilbenyl‐azopyrroles 3 a–c were synthesized through a Mizoroki‐Heck C−C‐type coupling reaction between the 2‐(4′‐iodophenyl‐azo)‐N‐methyl pyrrole (1), and three different para‐substituted styrene derivatives. Inclusion of additional NO2 and NMe2 groups at the para‐position of the stilbenyl section resulted in significant changes of their linear and non‐linear optical properties. The photoisomerization behavior was studied through ultrafast laser techniques for single‐ and two‐photon excitation. The time‐resolved studies indicate that, despite the drastic changes in conjugation, the typical path for photoisomerization is maintained in these systems for both single and biphotonic excitation. In particular, the NO2 substituted molecule showed improved two‐photon absorption capacities, together with a significant trans−cis isomerization channel, implying that the photoswitching process can be controlled with high spatial precision through non‐linear optical excitation.

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Section: Methodsmentioning

confidence: 99%

Synthesis and Photodynamics of Stilbenyl‐Azopyrroles: Two‐Photon Controllable Photoswitching Systems

et al. 2019

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“…From femtosecond pump-probe spectroscopy, a lower limit for the rate of 1 162 Ǟ 3 162 crossing of 10 11 sec Ϫ1 was obtained. [179] In the absence of quenchers, the rate of ketene growth equals the rate of carbene decay. The ketene 160 arises almost exclusively from the carbene 162.…”

Section: Laser Flash Photolysis (Lfp)mentioning

confidence: 99%

100 Years of the Wolff Rearrangement

2002

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The conversion of α‐diazo ketones into ketenes, and products derived therefrom, was discovered by Wolff in 1902. Major applications of the Wolff rearrangement, such as the Arndt−Eistert reaction (homologation of carboxylic acids) and the ring contraction of cyclic ketones, have been with us for some while. Nevertheless, substantial progress has been made recently. The reaction mechanism has been explored by means of matrix isolation, time‐resolved spectroscopy, and computation. Full retention of configuration of the migrating group has been established by using enantioselective chromatography. The Arndt−Eistert reaction has witnessed a renaissance in the field of natural products, in particular β‐amino acids and β‐peptides. Ring‐contracting Wolff rearrangements and ketene cycloadditions have been applied in syntheses of increasingly complex, biologically active target molecules. These accomplishments, as well as unsolved problems, are addressed in the present review. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

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“…Only a few ultrafast studies of diaryl carbenes have been reported and they deal exclusively with diphenylcarbene, , fluorenylidene, and naphthylcarbomethoxycarbene . These carbenes were subject to initial study because of their historical importance to the development of mechanistic theory, − the ease of synthesis and handling of their precursor diazo compounds, and their favorable spectroscopic properties.…”

Section: Introductionmentioning

confidence: 99%

Ultrafast Study of p-Biphenylyldiazomethane and p-Biphenylylcarbene

2006

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p-Biphenylyldiazomethane was excited by femtosecond pulses of UV light in acetonitrile, in cyclohexane, and in methanol. Ultrafast photolysis produces a singlet excited state of p-biphenylyldiazomethane with lambdamax = 490 nm, and lifetimes of less than 300 fs in acetonitrile, in cyclohexane, and in methanol. The decay of the excited state is accompanied by the growth of transient absorption with lambdamax = 360 nm. The carrier of this transient absorption is attributed to singlet p-biphenylylcarbene, a result that is consistent with the predictions of TD-DFT calculations. The singlet carbene lifetimes are 200 and 77 ps in acetonitrile and cyclohexane, respectively, and are controlled by intersystem crossing to the lower energy triplet state. The transient absorption does not decay to baseline in acetonitrile, because of the formation of nitrile ylide. The equilibrium mixture of singlet and triplet p-biphenylylcarbene reacts with acetonitrile to form a nitrile ylide (lambdamax = 370 nm), and with cyclohexane by C-H insertion 1-20 ns after the laser pulse. The singlet carbene lifetime is only 7.9 ps in methanol, owing to a rapid reaction with the solvent. Reaction with the solvent gives rise, in part, to a p-biphenylylbenzyl cation (lambdamax = 450 nm, tau = 6.3 ps) in methanol.

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Ultrafast Carbonylcarbene Formation and Spin-Equilibration

Cited by 19 publications

References 21 publications

Synthesis and Photodynamics of Stilbenyl‐Azopyrroles: Two‐Photon Controllable Photoswitching Systems

Synthesis and Photodynamics of Stilbenyl‐Azopyrroles: Two‐Photon Controllable Photoswitching Systems

100 Years of the Wolff Rearrangement

Ultrafast Study of p-Biphenylyldiazomethane and p-Biphenylylcarbene

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