Diffuse reflectance laser photolysis studies of energy transfer at interfaces

Wilkinson, Frances; Ferreira, Luis Felipe

doi:10.1016/0022-2313(88)90399-7

Cited by 11 publications

(8 citation statements)

References 4 publications

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“…This provides an interesting extension to classical spin probing. It is hoped that the current work will encourage others to investigate cotton as a host for radical reactions and also aid the interpretation of previous results. − …”

Section: Discussionmentioning

confidence: 83%

“…It is hoped that the current work will encourage others to investigate cotton as a host for radical reactions and also aid the interpretation of previous results. [2][3][4][5][6][7][8][9][10] Note Added in Proof. Prof. Bredereck (Stuttgart) has pointed out to the author that the estimate of the amorphous layer depth is in good agreement with results from exclusion column chromatography (Bredereck, K.; Gruber, M.; Otterbach, A.; Schulz, F. TextilVeredlung 1996, 31, 194).…”

Section: Discussionmentioning

confidence: 99%

“…Surprisingly little information is available on the mobility and local environment of molecules absorbed into the structure or on the surface, although it is clear that only the amorphous zones are readily accessible. Recently this point has been addressed by elegant diffuse reflectance experiments on microcrystalline cellulose, − (which is structurally related to cotton) and cotton itself . These studies used triplet−triplet energy, electron-transfer, and hydrogen-transfer reactions to probe the structure, alongside fluorescence/absorption.…”

Section: Introductionmentioning

confidence: 99%

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Free-Radical and Singlet-Oxygen Mobility in Cotton Probed by EPR Spectroscopy

Batchelor

1999

J. Phys. Chem. B

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Spin probe EPR experiments using TEMPO and TEMPOL are reported on dry cotton. The spectra are in the slow tumbling region with τrot ∼ 1 ns, the line width is found to be affected by Heisenberg spin exchange and aggregation of the radical. To probe the entire amorphous zone of cotton, ethanol and water are used to deposit the radicals; to probe the fiber surface specifically toluene was used. Analysis shows that in both regions the viscosity is 30 cP and that the fiber surface is an amorphous layer with a depth of approximately 2 nm. The radical motion follows normal liquid theory with a diffusion rate constant of 2 × 108 mol-1 L s-1. A small proportion of the radicals deposit to an area of much higher viscosity. The classical spin probe method is extended via a simple electron spin polarization experiment. This involved irradiation of the sample and analysis of the radical−triplet mechanism polarization of TEMPOL/O2, which indicates 1O2 diffuses with a similar rate constant.

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Section: Discussionmentioning

confidence: 83%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Free-Radical and Singlet-Oxygen Mobility in Cotton Probed by EPR Spectroscopy

Batchelor

1999

J. Phys. Chem. B

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“…Investigations on the photochemistry and photophysics of molecules as well as on the behavior of free radicals adsorbed or incorporated onto microcrystalline cellulose reveal interesting possibilities of affecting and controlling the kinetics of a variety of mono-and bimolecular processes. [1][2][3][4][5][6][7] Cellulose can be used as a medium for studies of photoinduced electron3-4 or energy transfer5-6 and also for triplet radical pair (RP) recombination. 7 Since the development of the diffuse reflectance laser flash technique8 there has been a number of direct kinetic observations of adsorbed free radicals and radical ions in opaque samples,9-16 particularly in microcrystalline cellulose.5-7 Short lived radical ion pairs (RIP) with lifetimes varying between 0.1 and 9 µß were observed by applying this technique to zeolites.17 Nonexponential decay kinetics extending over several orders of magnitude in time scale, from microseconds up to seconds, are quite typical not only of surfaces but also of other solids like glasses and rigid polymers, where the matrix controls the chemical process, accounting for a very wide distribution in reactivity (see for example refs 18 and 19 and references therein).…”

Section: Introductionmentioning

confidence: 99%

Recombination kinetics of triplet radical ion pairs adsorbed onto microcrystalline cellulose studied by diffuse-reflectance laser flash photolysis

Levin¹,

Ferreira²,

Costa³

1993

Langmuir

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“…The desire to understand primary photochemical processes occurring in heterogeneous environments has led to considerable recent interest in studies of the photophysics and photochemistry of many organic molecules adsorbed on substrates such as silica, alumina, zeolites and semiconductor surfaces. A most convenient technique for studying such systems is diffuse reflectance laser flash photolysis since it can be used to study transient absorption (and emission) in opaque solids (Wilkinson et al, 1990), or at interfaces of powders or microcxystals (Kessler and Wilkinson, 1981;Turro et ul., 1085;Kamat and Ford, 1987;Wilkinson and Ferreira, 1988;Levin et al, 1990;Kelly et ul., 1990). This enables one to obtain spectroscopic and kinetic information on the excited states of molecules adsorbed at interfaces or within dyed fabrics.…”

Section: Introductionmentioning

confidence: 99%

PHOTOCHEMISTRY ON SURFACES: TRIPLET‐TRIPLET ENERGY TRANSFER ON MICROCRYSTALLINE CELLULOSE STUDIED BY DIFFUSE REFLECTANCE TRANSIENT ABSORPTION and EMISSION SPECTROSCOPY*

Wilkinson

Leicester

Ferreira

et al. 1991

Photochem & Photobiology

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Triplet‐triplet energy transfer has been studied between benzophenone and an oxazine dye (2,7‐bis(diethyl‐amino)‐phenazoxonium chloride) co‐adsorbed on the surface of microcrystalline cellulose. Ground state absorption and fluorescence measurements provide evidence for dimer formation of the oxazine dye when adsorbed on cellulose in contrast to the behaviour in ethanol solution where no dimerization is observed. The equilibrium constant for dimerization, which is found to be (1.0 × 0.1) × 106 mol−1 g (2560 × 250 dm3 mol−1) for oxazine alone on cellulose decreases in the presence of co‐adsorbed benzophenone. Fluorescence is detected from excited monomeric but not from excited dimeric oxazine. The absorption spectrum of the triplet state of oxazine adsorbed on cellulose was obtained and its extinction coefficient evaluated relative to that of triplet benzophenone which was used as a sensitizer. The lifetime of adsorbed triplet oxazine is 4.3 ms which is 300 times longer than that in acetonitrile solution. The efficiency of energy transfer from triplet benzophenone to oxazine on cellulose was studied using both time resolved sensitized absorption and phosphorescence intensity measurements as a function of oxazine concentration. Lifetime measurements show that the energy transfer process involves static quenching since the benzophenone lifetime is independent of oxazine loading at the surface. A mechanism is proposed to explain the results in which one oxazine molecule is suggested as being able to quench phosphorescence from a “pool” consisting of 2 to 3 benzophenone molecules.

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Diffuse reflectance laser photolysis studies of energy transfer at interfaces

Cited by 11 publications

References 4 publications

Free-Radical and Singlet-Oxygen Mobility in Cotton Probed by EPR Spectroscopy

Free-Radical and Singlet-Oxygen Mobility in Cotton Probed by EPR Spectroscopy

Recombination kinetics of triplet radical ion pairs adsorbed onto microcrystalline cellulose studied by diffuse-reflectance laser flash photolysis

PHOTOCHEMISTRY ON SURFACES: TRIPLET‐TRIPLET ENERGY TRANSFER ON MICROCRYSTALLINE CELLULOSE STUDIED BY DIFFUSE REFLECTANCE TRANSIENT ABSORPTION and EMISSION SPECTROSCOPY*

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