Caged compounds quantum yield

The dimethyl ester of this acid in solution shows a quantum efficiency photochemical products. On the other hand, when the same acid is copolymerized with a glycol to form a polymeric compound with molecular weight 10,000 the quantum yield drops by about two orders of magnitude, 0.012. The reason for this behavior appears to be that when the chromophore is in the backbone of a long polymer chain the mobility of the two fragments formed in the photochemical process is severely restricted and as a result the photochemical reactions are much reduced. If radicals are formed the chances are very good that they will recombine within the solvent cage before they can escape and form further products. Presumably the Norrish type II process also is restricted by a mechanism which will be discussed below. 

Fluorescence quantum yields of the C o derivatives were quantitatively determined. For the mono-functionalized Cgo derivatives, the compound with a (5-6)-open fulleroid addition pattern on the fullerene cage appeared to be considerably less fluorescent than those with a [6,6]-closed cage addition pattern. Despite the disturbance of the electronic structure via multiple additions to the fullerene cage, the multiple-functionalized Cgo derivatives exhibited no dramatic changes in fluorescence quantum yields in... 

The principles of design and interpretation of kinetic investigations with photolabile precursors can be best illustrated by some of the many uses of npe-ATP. The important parameters to be determined with each compound are the absorption spectrum, quantum yield, rate of appearance of active substrate, the possible binding (competitive inhibition) of the caged compound and the effects of any photoproducts. Additional to these compound specific parameters, instrumentation parameters have to be considered. These are concerned with the light source for photolysis and with the detection equipment. The latter can either monitor the photolytic reaction of the caged compound or the physiological process stimulated by... 

In the gas phase, the quantum 3deld of dissociation of a molecule to radicals (atoms) is equal to unity. In the liquid phase it is much lower than unity because the radicals that formed partially recombine in the cage. For example, for iodine dissociation in CCI4 at 298 K the quantum yield 4> = 0.14, and for bromine under the same conditions cj) = 0.22. For the photodissociation of azo compounds in a solution = 0.25-K).10. 

The caged coumaryl compounds were synthesized in 11 to 34% yield, clearly a limitation with this photoremovable protecting group. The addition of the carboxymethoxy groups in 55b and 55c dramatically enhanced the water solubihty of these analogs as compared with the ester 55a, and their photorelease occurred with good quantum efficiencies as seen in Table 69.15. On the other hand, the less water-soluble 55a had the best quantum efficiency, and its absorption maximum was the most red shifted in the series. 

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