Quantum yield high concentration effects

Most studies of the physical binding of hydrocarbon metabolites and metabolite model compounds have measured the effect of DNA binding on hydrocarbon fluorescence intensities, fluorescence lifetimes and UV absorption spectra Radioactive labelling has also been used, but less frequently. Spectroscopic methods are particularly convenient. These methods, especially fluorescence methods, are also very sensitive. All of the hydrocarbons in Figure 1 except the epoxides have high fluorescence quantum yields, which permit routine detection in the 10 -10 7 M concentration range. 

The effectiveness of various PS proposed for antimicrobial PDT can be judged on several criteria. These PS should be able to kill multiple classes of microbes at relatively low concentrations and low fluences of hght. PS should be reasonably nontoxic in the dark and should demonstrate selectivity for microbial cells over mammalian cells. PS should ideally have large extinction coefficients in the red part of the spectrum and demonstrate high triplet and singlet oxygen quantum yields. 

Carbon disulfide quenches the fluorescence of anthracene quite efficiently,145,149 but seems to have little effect on its triplet lifetime.147 Diphenylanthracene in benzene fluoresces with a quantum yield of 0.8 and shows a high sensitivity to the oxygen concentration in photooxygenation reactions. With about 1 vol% of CS2 present, AC>2 is practically independent of [02] (> 10"5 mole/liter). In jjoth cases, where carbon disulfide was either used as solvent or was added to an otherwise strongly fluorescent solution, the quantum yields of photooxygenation followed... 

The quantum yields of formation of tert-butyl N-(ethoxycyclopropyl)carbamate (13) from irradiation of 12 and of tert-butyl N-(ethoxyethylidene)carbamate (27) and glutarimide (29) from irradiation of 14 are moderately high and are shown in Table 2. The effect of the triplet quencher c/s-piperylene on the quantum yields has been examined. Over the concentration range 0.01—0.1 OM c/s-piperylene, no ap-... 

Irradiation of Ru3(C0)i2 (57. 60), Fe3(C0)j2 (60), or Ru3(C0)9(PPh3)3 (59) under CO cleanly leads to mononuclear complexes. This fact seems to rule out dissociative loss of CO as the dominant reaction from the excited state. If loss of CO were the dominant process, the presence of CO would simply retard the decomposition of the cluster. The lack of an effect from high concentrations of entering group (1-pentene or PPI13) on the quantum yield for photodeclusterification of Fe3(C0)i2 or Ru3(C0)i2 (60) is consistent with this conclusion. 

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