Spin‐Statistical Factors in Diffusion‐Controlled Reactions

Saltiel, Jack; Atwater, Beauford W.

doi:10.1002/9780470133446.ch1

Cited by 137 publications

(87 citation statements)

References 232 publications

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“…The efficiency of the oxygen activation, in this type of catalysis, is determined by the photophysical properties of the photosensitizer utilized. Thus, the ability to control parameters, such as quantum yield, energy and lifetime of the photosensitizer's triplet state, is fundamental in optimizing the catalysis toward its application [2][3][4][5]. In this context, relatively little attention has been paid to corrole-based photosensitizers, although their photophysical parameters may readily be tuned by varying the core metal, axial ligands, and peripheral substituents [6][7][8][9][10].…”

Section: Introductionmentioning

confidence: 99%

Structure-function relationship in antimony corrole photosensitizers: Time-resolved electron paramagnetic resonance and optical study

Wagnert

Berg

Stavitski

et al. 2007

J. Porphyrins Phthalocyanines

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Three photosensitizers based on tris-(pentafluorophenyl)antimony corroles that differ in oxidation state and axial ligands, namely, (pyridine)Sb(III)-, (oxo)Sb(V)-and (difluoro)Sb(V) complexes, were studied by time-resolved electron paramagnetic resonance spectroscopy and laser flash photolysis. The magnetic and orientational parameters of the corroles oriented in a nematic liquid crystal as well as their triplet lifetimes in liquid toluene were determined and interpreted in terms of their structure and geometry. The negative zero-field splitting parameter D assigned to all studied corroles is explained by the asymmetric π-electron withdrawal effect caused by perfluorinated peripheral aryl groups, which force the triplet electron spins to align in head-to-tail configuration. The effect of the axial ligands on the photoexcited triplet state properties of the corroles is correlated with their different efficiency to perform photoassisted aerobic oxygenation of some organic molecules. This is explained by the dependence of the main parameters of the photoexcited complexes on the interaction between the central ion and corrole π-system. This interaction is strongly influenced by axial ligands coordination, affecting the macrocycle symmetry, planarity, and rigidity.

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Section: Introductionmentioning

confidence: 99%

Structure-function relationship in antimony corrole photosensitizers: Time-resolved electron paramagnetic resonance and optical study

Wagnert

Berg

Stavitski

et al. 2007

J. Porphyrins Phthalocyanines

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“…On the other hand, the migration of phosphorescent photons also occurs much faster than phosphorescence emission; and the distribution of the phosphorescence photon density U p (r) in each moment of time should also satisfy the steady-state approximation (9) where q p (r s ) is a static phosphorescent source inside the medium. The evolution of a phosphorescent source in time is typically given by a single-exponential operator with the time constant τ(r s ), which is related to the local oxygen concentration through the Stern-Volmer relationship [Eq.…”

Section: A Forward Problemmentioning

confidence: 99%

Tomographic imaging of oxygen by phosphorescence lifetime

2006

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Imaging of oxygen in tissue in three dimensions can be accomplished by using the phosphorescence quenching method in combination with diffuse optical tomography. We experimentally demonstrate the feasibility of tomographic imaging of oxygen by phosphorescence lifetime. Hypoxic phantoms were immersed in a cylinder with scattering solution equilibrated with air. The phantoms and the medium inside the cylinder contained near-infrared phosphorescent probe(s). Phosphorescence at multiple boundary sites was registered in the time domain at different delays (t d ) following the excitation pulse. The duration of the excitation pulse (t p ) was regulated to optimize the contrast in the images. The reconstructed integral intensity images, corresponding to delays t d , were fitted exponentially to give the phosphorescence lifetime image, which was converted into the threedimensional image of oxygen concentrations in the volume. The time-independent diffusion equation and the finite element method were used to model the light transport in the medium. The inverse problem was solved by the recursive maximum entropy method. We provide what we believe to be the first example of oxygen imaging in three dimensions using long-lived phosphorescent probes and establish the potential of these probes for diffuse optical tomography.

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“…It is known, that triplet-triplet annihilation (TTA) generates excited singlet state population with an increased fluorescence lifetime. But TTA is diffusion controlled and therefore, at the concentrations studied in this work, too slow to explain the <5 ns fluorescence risetime observed in our experiments [38]. Furthermore, the triplet ground state of DPH is very low in energy, so that the energy available by triplet-triplet annihilation is insufficient to populate the lowest excited singlet state [24,39].…”

Section: Resultsmentioning

confidence: 70%

Intense Long-Lived Fluorescence of 1,6-Diphenyl-1,3,5-Hexatriene: Emission from the S<sub>1</sub>-State Competes with Formation of O<sub>2</sub> Contact Charge Transfer Complex

Hunger¹,

Kleinermanns²

2013

OJPC

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The fluorescence kinetics of 1,6-diphenyl-1,3,5-hexatriene (DPH) dissolved in cyclohexane was investigated as a function of temperature, concentration and 355 nm excitation pulse energy. At concentrations above 2.5 μM and excitation energies above 1 mJ a long-lived, very intense emission, which appears within less than 5 ns and lasts up to 70 ns, is observed. During the first 50 ns the decay does not follow an exponential but rather a linear behaviour. In oxygen saturated solutions the long-lived emission is suppressed and solely short-lived fluorescence with τ < 5 ns can be detected. A kinetic simulation was performed, based on a model whereupon the long-lived emission originates from the S 1 -state and competes with the formation of DPH-O 2 contact charge-transfer complexes and intersystem crossing which both quench the fluorescence. Our investigations show that even the small amount of oxygen dissolved in nitrogen saturated solutions has a distinct influence on the fluorescence kinetics of DPH.

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Spin‐Statistical Factors in Diffusion‐Controlled Reactions

Cited by 137 publications

References 232 publications

Structure-function relationship in antimony corrole photosensitizers: Time-resolved electron paramagnetic resonance and optical study

Structure-function relationship in antimony corrole photosensitizers: Time-resolved electron paramagnetic resonance and optical study

Tomographic imaging of oxygen by phosphorescence lifetime

Intense Long-Lived Fluorescence of 1,6-Diphenyl-1,3,5-Hexatriene: Emission from the S<sub>1</sub>-State Competes with Formation of O<sub>2</sub> Contact Charge Transfer Complex

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Spin‐Statistical Factors in Diffusion‐Controlled Reactions

Cited by 137 publications

References 232 publications

Structure-function relationship in antimony corrole photosensitizers: Time-resolved electron paramagnetic resonance and optical study

Structure-function relationship in antimony corrole photosensitizers: Time-resolved electron paramagnetic resonance and optical study

Tomographic imaging of oxygen by phosphorescence lifetime

Intense Long-Lived Fluorescence of 1,6-Diphenyl-1,3,5-Hexatriene: Emission from the S&lt;sub&gt;1&lt;/sub&gt;-State Competes with Formation of O&lt;sub&gt;2&lt;/sub&gt; Contact Charge Transfer Complex

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Intense Long-Lived Fluorescence of 1,6-Diphenyl-1,3,5-Hexatriene: Emission from the S<sub>1</sub>-State Competes with Formation of O<sub>2</sub> Contact Charge Transfer Complex