Singlet oxygen quantum yields

Like the palladium(II) complexes, the platinum(II) porphyrins show appreciable phosphorescence even in aqueous media at room temperature in one study,169 singlet oxygen quantum yields ranged from 0.1 to 0.9 and were strongly influenced by dimerization/aggregation. Platinum(II) 5,10,15,20-tetrakis(/>-carboxyphenyl)porphyrin and platinum(II)coproporphyrin-I ((36) for Pd read Pt) have been studied as phosphorescent labels of antibodies for use in time-resolved microscopy.189... 

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. 

The cytotoxic and photocytotoxic effects of two water-soluble fullerene derivatives, a dendritic CL mono-adduct and the malonic acid CL tris-adduct were tested on Jurkat cells when irradiated with UVA or UVB light (Rancan et al., 2002). The cell death was mainly caused by membrane damage and it was UV dose-dependent. Tris-malonic acid fullerene was found to be more phototoxic than the dendritic derivative. This result is in contrast to the singlet oxygen quantum yields determined for the two compounds. 

Table 5 Singlet oxygen quantum yields a) of different PS in ethanol obtained by chemical quenching of DPBF and published values...

The DPBF-photooxidative product quantiun yield cPdpbfo2> and singlet oxygen quantum yield of the PS, are related according to the literature as [102] ... 

Singlet lifetimes, fluorescence quantum yields, and singlet oxygen quantum yields are compared for Rose Bengal, Erythrosin, Eosin, and fluorescein in a number of different solvents in Table 11. In virtually every case water differs from the other solvents studied. 

Table 4 presents comprehensive photophysical data of 2T-7T (di-n-butyl), including singlet oxygen quantum yields (4>a) in benzene. Considering the absorption and emission spectra, there is a relatively small effect of solvent on these maxima. In the fluorescence excitation spectra, there is a considerable red shift, 1600 cm-1, in the maxima with an excellent linear correlation between 1/n and the maximum of the first transition, as well as the 0-0 energy particularly for 4T-7T. 

X lO M cm for this Q-type band). The absorption of this species at this wavelength is thus approximately four times greater than that of Photofrin . BPD-MA also displays a good singlet oxygen quantum yield (Table 1) [266-268]. In humans, the pharmacokinetic plasma clearance rate (i.e. pK half-life) of BPD-MA is on the order of 5.5 h (personal communication with David Mitchell, Director of Regulatory Affairs, QLT Phototherapeutics, Inc.)... 

Triplet quantum yields (high rate of intersystem crossing (much faster than for typical aromatic hydrocarbons) and the inefficient fluorescence. These values were determined by photothermal and spectroscopic methods and agree with lower limits determined from singlet oxygen quantum yields [9,10]. (see below). A cyclodextrin complex also produces the triplet state efficiently in water [39]. 

Photodegeadation and Singlet Oxygen Quantum Yields of Photosensiuzees, and Teiplet Quenching Rate Constants in Aeeated Solutions... 

Figure 10.5 Singlet Oxygen Corrected Enhancement Factor on SiFs versus Singlet Oxygen Quantum Yield. (1. Acridine 2. Chloroquine 3. Rose Bengal 4. Indomethacin 5. Riboflavin 6. Naproxen 7. Chloropromazine 8. Quinidine). Error bars are based on the standard deviation of 3 spectral measurements. Adopted from ref [25].

While other photochemical and photophysical processes can compete with this type II process, many porphyrins and similar compounds produce high yields of long-lived excited triplet states and react with oxygen to produce singlet oxygen at near diffusion controlled rates. Thus, triplet quantum yields and singlet oxygen quantum yields are often nearly the same. 

Table 12.6 Singlet Oxygen Quantum Yields, Oa, for Some Drugs, Measured by Time-Resolved...

Optimum sensitizers for PDT have the following qualities high quantum yield of triplet-state formation, high singlet-oxygen quantum yield, and preferential tumor cell selectivity... 

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