Surface photochemistry: radical pair combination on a silica gel surface and in micelles

Surface photochemistry: generation of benzyl radical pairs on dry silica gel

“…Extensive geminate recombinstarting material. An increased amount of adsorbate might be ation has been recorded for benzyl radical pairs generated in expected either to interfere with, or to increase, radical movemicellar environments from 6 (24) and from 5 (24) and from ment. The latter could, presumably, occur because the probaseveral other dibenzyl ketones (9,27).…”

Surface photochemistry: 13C enrichment by photolysis on silica gel

“…The authors suggested that the synthetic monolayer surface was analogous to a micelle in providing an artificial "reflecting boundary" which led to an enhanced magnetic isotope effect. However, it appeared more likely that the above results were a reflection of the silica gel surface properties rather than the micelle-like properties of the synthetic monolayer surface, since a number of studies have indicated that radical mobility is restricted on Can silica surfaces (12)(13)(14)(15)(16). For example, limited translational motion has been shown to precede recombination of a singlet radical pair generated on silica gel by the photo-Fries rearrangement (12).…”

“…Our previous experimental results on the photolysis of an unsymmetrically substituted dibenzyl ketone in micelles showed that there is a strong dependence of geminate formation of dibenzyl on the average number of molecules per micelle fl (13). The probability of geminate combination decreases from 92% to 51% when N is changed from 0.35 to 0.85.…”

“…For example, limited translational motion has been shown to precede recombination of a singlet radical pair generated on silica gel by the photo-Fries rearrangement (12). A greater amount of movement has been reported for both benzyl (13) and cyanopropyl (14) radical pairs on silica gel. Similarly, some surface mobility has been observed for radical pairs generated by photolysis of azocumene ( 15a) and diacyl peroxides (15 b ) on silica gel.…”

Reviews of Environmental Contamination and Toxicology

“…In contrast, Calumpang et al (1984) found a good correlation between maximum molar absorptivity in solution and photolysis rate for eight organophosphate insecticides on silica gel. Avnir et al (1981) also examined the reaction profiles of radicals by using benzyl phenylacetate and dibenzyl ketone. Johnston et al (1984) studied photodegradation of azobis(isobutyronitrile) on dry silica gel by using UV light and demonstrated that some portion of radicals could escape from their original partners by a translational motion.…”