Quantitative time-resolved EPR CIDEP study of the photodecomposition oftrans-azocumene in solution

Savitsky, Anton; Paul, H.

doi:10.1007/bf03164126

Cited by 21 publications

(18 citation statements)

References 34 publications

(45 reference statements)

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“…Under the conditions of the experiment, the species cannot stem from a direct photolysis of AC. First, the direct photolysis of azoalkanes occurs from their excited singlet state and, therefore, leads to TREPR spectra, which initially exhibit a spin polarization with enhanced absorption on the low ®eld site and emission on the high ®eld site [15]. Second, at 355 nm the absorption coecients of 1-NN and AC are 3200 M ¡1 cm ¡1 and 40 M ¡1 cm ¡1 , respectively.…”

Section: Methodsmentioning

confidence: 99%

Magnetic field dependence of the deactivation rates of triplet azocumene in solution

et al. 2002

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The triplet sensitized photo-decomposition of azocumene into nitrogen and cumyl radicals is investigated by time resolved EPR and optical absorption spectroscopy. It is found that the cumyl radicals carry an initial spin polarization and are formed with a yield that depends on both the solution viscosity and the strength of an external magnetic ®eld. The phenomenon is interpreted in terms of a depopulation-type triplet mechanism, i.e. a competition between decay into radicals and fast, triplet sublevel selective intersystem crossing (ISC) back to the azocumene ground state. Analysis of the data yields relative rate constants for the ISC processes and the cleavage reaction of triplet azocumene. The energetically lower zero ®eld triplet substate is depopulated by ISC about seven times faster than the upper one and about two orders of magnitude faster than depopulation by cleavage occurs. Cleavage probably takes place on the nanosecond time scale, while the ISC must proceed on the picosecond scale, as at elevated viscosity it becomes faster than the rotational Brownian motion of the molecule.

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Section: Methodsmentioning

confidence: 99%

Magnetic field dependence of the deactivation rates of triplet azocumene in solution

et al. 2002

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“…Under the conditions of the experiment, the species can not stem from a direct photolysis of AC. Firstly, the direct photolysis of azoalkanes occurs from their excited singlet state and, therefore, leads to TREPR spectra, which initially exhibit a spin polarization with enhanced absorption on the low-field and emission on the high-field site [57]. Secondly, at 355 nm the absorption coefficients of 1-NN and AC are 3200 M -1 cm -1 and 40 M -1 cm -1 , respectively.…”

Section: Trepr Spectrum Of Cumyl Radicals After Triplet-sensitized Phmentioning

confidence: 99%

The Excited Triplet State of Azoalkanes: Electron Spin Polarization and Magnetic Field Effects During Triplet-Sensitized Photolysis of trans-Azocumene in Solution

Milikisiyants

Steiner

Paul³

2011

Appl Magn Reson

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The triplet-sensitized photodecomposition of azocumene into nitrogen and cumyl radicals is investigated by time-resolved electron paramagnetic resonance and absorption spectroscopy. The radicals are found to be created spin polarized with a yield depending on the strength of the applied magnetic field. The phenomenon arises because in triplet azocumene, the decay into radicals competes with a fast triplet-sublevel selective intersystem crossing back to the azocumene ground state. The size of the initial spin polarization of the radicals and the magnetic field effect on their yield are determined in solvents of different viscosities. Data analysis yields rate constants for the intersystem crossing and the cleavage reaction of triplet azocumene as well as its zero-field splitting D ZFS. At room temperature in nonpolar solvents, the most probable values are: k x = k y = 1.2 × 1011 s−1 and k z = 1.9 × 1010 s−1 for the intersystem crossing from the energetically lower and upper triplet substates, respectively, k p = 1.6 × 109 s−1 for the cleavage reaction and for the zero-field splitting D ZFS = −3.4 × 1010 s−1 (0.18 cm−1).

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“…At the moment, we do not need a detailed discussion of this problem; it will be quite enough to show how the resonance line appears in the TREPR experiment at t obs /T 2 ≤ 1. A similar analysis has been performed already using a set of modified Bloch equations [42,43].…”

Section: Features Of Trepr Spectroscopy: Spin-polarized "Free" Radicalsmentioning

confidence: 99%

“…However, this is mostly information about the radical pair itself. Extraction of information about molecular motion from these experiments, that is, using the polarization patterns of free radicals observed in TREPR experiments, and their time evolution, is accompanied by many theoretical and computational difficulties, see for instance [42,43,45,46]. This has motivated us to obtain further insight into the analysis of the CIDEP patterns of radical pairs experiencing restricted translation diffusion.…”

Section: Features Of Trepr Spectroscopy: Spin-polarized "Free" Radicalsmentioning

confidence: 99%

Investigation of Liquid‐Phase Inhomogeneity on the Nanometer Scale Using Spin‐Polarized Paramagnetic Probes

Tarasov¹,

Forbes²

2017

Properties and Uses of Microemulsions

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The concept, basic physics, and experimental details of time-resolved electron paramagnetic resonance (TREPR) spectroscopy for the study of spin-correlated radical pairs (SCRPs) in heterogeneous media are presented and discussed. The delicate interplay between electron spin wave function evolution (governed by magnetic interactions such as the isotropic electron spin-spin exchange interaction and the electron-nuclear hyperfine interaction) and diffusion (governed by the size and microviscosity of the medium) provides a mechanism for assessing molecular mobility in confined spaces on the nanoscale (e.g., micelles, vesicles, and microemulsions). Experimental examples from micellar SCRPs are used to highlight the dominant features of the TREPR under different degrees of confinement and microviscosity, and spectral simulation methods are described to show how molecular mobility can be quantified.

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Quantitative time-resolved EPR CIDEP study of the photodecomposition oftrans-azocumene in solution

Cited by 21 publications

References 34 publications

Magnetic field dependence of the deactivation rates of triplet azocumene in solution

Magnetic field dependence of the deactivation rates of triplet azocumene in solution

The Excited Triplet State of Azoalkanes: Electron Spin Polarization and Magnetic Field Effects During Triplet-Sensitized Photolysis of trans-Azocumene in Solution

Investigation of Liquid‐Phase Inhomogeneity on the Nanometer Scale Using Spin‐Polarized Paramagnetic Probes

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