One- vs Two-Photon Processes in the Photochemistry of 1,<i>n</i>-Dihaloalkanes

Miranda, Miguel A.; Pérez‐Prieto, Julia; Font‐Sanchis, Enrique; Scaiano, J. C.

doi:10.1021/ar000107r

Cited by 44 publications

(52 citation statements)

References 54 publications

(104 reference statements)

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“…It is distinguished from singlet methylene by its enhanced selectivity and by the lack of CϪH insertion. After considerable speculation about the potential role of the iodomethyl radical (81), the iodomethyl cation (82), and the iodonium ylide 83, [126] the nature of the intermediate was recently explored by means of spectroscopic and computational methods.…”

Section: Interactions Of Carbenes With Halogensmentioning

confidence: 99%

Carbene Complexes of Nonmetals

Kirmse

2005

Eur J Org Chem

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Electrophilic carbenes accept a variety of n‐ and π‐donors. The products range from persistent ylides to matrix‐isolated xenon complexes. Ylides can be viewed as carbene complexes if they regenerate carbenes thermally or undergo concerted methylene transfer reactions. According to these definitions, the present review focuses on oxonium and iodonium ylides. Transient π‐complexes appear to be involved in addition reactions of carbenes with arenes (but not with alkenes). Nucleophilic carbenes form adducts with Lewis acids which are, for the most part, stable and have been well characterized structurally. Only recently attention has been directed to reversible systems. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

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Section: Interactions Of Carbenes With Halogensmentioning

confidence: 99%

Carbene Complexes of Nonmetals

Kirmse

2005

Eur J Org Chem

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“…Carbocations are key intermediates in many organic reactions. [1][2][3][4][5] They can be generated by photoinduced heterolysis of organic halides such as RÀCl [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] or other precursors. [6-8, 21, 23-26] The photolysis of these precursors can also lead to the generation of carbon-centered radicals.…”

Section: Introductionmentioning

confidence: 99%

“…[6-8, 21, 23-26] The photolysis of these precursors can also lead to the generation of carbon-centered radicals. [9][10][11]26] Photoinduced heterolysis and homolysis are ideal processes for the time-resolved investigation of bond cleavage and subsequent reactions involving the photogenerated ionic and radical intermediates through ultrafast pump-probe spectroscopy. Systems can be chosen for which no spectroscopically relevant frag-ment population is produced thermally.…”

Section: Introductionmentioning

confidence: 99%

“…The photoinduced processes were previously investigated by the nanosecond pump-probe experiments of McClelland [6] as well as Miranda, Scaiano, and co-workers, [10] and by the product studies of Hilborn et al [27] Their data have led researchers to propose that in addition to the direct generation of carbocations and carboncentered radicals by photoinduced bond cleavage, there is a pathway by which initially generated radical pairs decay into ion pairs through electron transfer. [6,10,27] It was suggested that this pathway is the main source of carbocations. [27,28] However, the factors contributing to the electron transfer responsible for the interconversion of radicals to cations are not yet clear.…”

Section: Introductionmentioning

confidence: 99%

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A Comprehensive Microscopic Picture of the Benzhydryl Radical and Cation Photogeneration and Interconversion through Electron Transfer

et al. 2013

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Bond cleavage and bond formation are central to organic chemistry. Carbocations play a key role in our understanding of nucleophilic substitution reactions that involve both processes. The precise understanding of the mechanism and dynamics of the photogeneration of carbocations and carbon radicals is therefore an important quest. In particular, the role of electron transfer for the generation of carbocations from the radical pair is still unclear. A quantitative femtosecond absorption study is presented, with ultrabroad probing on selected donor and acceptor substituted benzhydryl chlorides irradiated with 270 nm (35 fs) pulses. The ultrafast bond cleavage within 300 fs is almost exclusively homolytic, thus leading to a radical pair. The carbocations observable in the nanosecond regime are generated from these radicals by electron transfer from the benzhydryl to the chlorine radical within the first tens of picoseconds. Their concentration is reduced by geminate recombination within hundreds of picoseconds. In moderately polar solvents this depletion almost extinguishes the cation population; in highly polar solvents free ions are still observable on the nanosecond timescale. The explanation of the experimental findings requires the microscopic realm of the intermediates to be accounted for, including their spatial and environmental distributions. The distance dependent electron transfer described by Marcus theory is combined with Smoluchowski diffusion. The depletion of the radical pair distribution at small distances causes a temporal increase of the mean distance and the observed stretched exponential electron transfer. A close accord with experiment can only be reached for a broad distribution of the nascent radical pairs. The increase in the inter-radical and inter-ion pair distance is measured directly as a shift of the UV/Vis absorption of the products. The results demonstrate that, at least for aprotic solvents, traditional descriptions of reaction mechanisms based on the concept of contact and solvent-separated pairs have to be reassessed.

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“…Their approach was to attempt to ablate the adsorbate by using large exposures, but there is an alternative approach, based upon the photochemical modification of the adsorbate, and recent work in the author's laboratory has exploited this to create nanostructured materials by SNP [98]. When benzyl chloride 2 is exposed to UV light at a wavelength of approximately 250 nm in the bulk phase, it undergoes an elimination of chlorine, and in the presence of oxygen, the resulting radical reacts to form benzaldehyde 3 [99]. On further exposure, the aldehyde may be converted to benzoic acid 4.…”

Section: Chloromethylphenylsilane Monolayers On Silicon Dioxidementioning

confidence: 99%

Bionanofabrication by Near-Field Optical Methods

Leggett

2007

Nanobiotechnol

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Near-field optical methods offer unique potential in nanofabrication, because they provide the capacity to initiate highly selective chemical transformations with nanometer scale precision. The basic principles behind scanning near-field photolithography (SNP), in which a scanning near-field optical microscope coupled to a UV laser is used to initiate surface chemical reactions, are described. The fundamental principles underlying the patterning of self-assembled monolayers by SNP are described, and the resolution limits and the basic principles that enable routine achievement of sub-50 nm resolution are discussed. Illustrations are provided of the application of SNP to the patterning of protein molecules on gold surfaces. The patterning of molecular adsorbates on oxide surfaces, including the fabrication of highly miniaturized arrays of DNA on silicon dioxide, is also described. It is argued that SNP holds great promise for the organization of biomolecules on nanometer length scales.

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One- vs Two-Photon Processes in the Photochemistry of 1,n-Dihaloalkanes

Cited by 44 publications

References 54 publications

Carbene Complexes of Nonmetals

Carbene Complexes of Nonmetals

A Comprehensive Microscopic Picture of the Benzhydryl Radical and Cation Photogeneration and Interconversion through Electron Transfer

Bionanofabrication by Near-Field Optical Methods

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