Singlet-oxygen formation quantum yields

In a spectrofluorimeter, the sensitised phosphorescence emission spectra of singlet oxygen from optically matched solutions of the samples and that of the reference compound should be obtained in identical experimental conditions (see Fig. 15.3). The singlet oxygen formation quantum yield is then determined by comparing the integrated area under the emission spectra of the samples solutions (J I(Ay dA) and that of the reference solution (f /(Ay dA) and applying Eq. 15.10,... 

If singlet oxygen is formed by an energy transfer reaction from excited diphenylanthracene to oxygen, the quantum yield of which is the quantum yields of endoperoxide formation are given by... 

TABLE 10 Quantum Yield of Fluorescence, Triplet Formation, and Singlet Oxygen Formation for Simple Xanthenes°... 

Polymer Rose Bengal was synthesized using Merrifield chemistry [296] from chloromethylated polystyrene beads [297] and has quantum yields of singlet oxygen formation about the same as does Rose Bengal in similar solvents. It does not bleach, does not undergo self-quenching, and therefore seems not susceptible to electron transfer between dye molecules, a phenomenon induced by dye site isolation on the backbone of the polymer. 

Table I. Visible Absorption Spectra and Quantum Yields of Singlet Oxygen Formation of Rose Bengal Derivatives...

Since all photooxidation reactions were carried out under similar experimental conditions in solution both for oxidations sensitized by RB and reactions sensitized by P -RB, the ratio of the rate of photooxidation with RB and the rate of photooxidation with P-RB is equal to the ratio of the quantum yield for singlet oxygen formation with RB to that of the quantum yield for singlet oxygen formation with P-RB (7). 

It is clear that as the amount of rose bengal attached to the polymeric support increased in the regime where the polymer can be called "lightly functionalized", the quantum yield of singlet oxygen formation increases also, reaching a maximum value for the... 

Figure 5. Quantum Yield of Singlet Oxygen Formation as a Function of the Amount of RB Attached to a Polymer...

Both curves have similar shapes and it is clear that the photooxidation process is controlled by the diffusion of oxygen into the rose bengal sites in the polymer solution. These results suggest that when a snail amount of rose bengal is attached to the polymeric backbone (P-RB-51, 102 152 305) the quantum yield of of singlet oxygen formation is essentially the same (about 0.38). 

Quantum Yield Measurements of Singlet Oxygen Formation... 

Note. A. — wavelength related to TPA cross section measured, 6 = TP absorption cross section, = quantum yield of singlet oxygen formation. 

No emission at 1269 nm was detected, which was taken to mean that no 02 was formed or that its formation quantum yield, fl>A, was lower than the sensitivity limit of the detector (5 x 10-3). In two-laser, two-color experiments, after excitation at 355 nm the merocyanine formed was excited (2-ns delay) with a green layer (532 nm), and again no 02 was detected, a clear indication that the (photo)merocyanine did not participate in the sensitized formation of singlet oxygen, the species that could induce oxidative degradation of the photochromes. The only noticeable exception was found for 11 for which fl>Awas measured to be 0.15. 

Table 12.2 Quantum Yields for Singlet Oxygen Formation, A, of Antimalarial Drugs in D20/Phosphate at pD = 7a...

Chignell (1987) developed a near-infrared detective system, based on the phosphorescence emission of the excited singlet oxygen, under steady state conditions. Using this technique, Motten et al. (1999) have determined the quantum yields of singlet oxygen formation for a series of antimalarial drugs in D20 as shown in Table 12.2. 

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