Triplet state quantum yields

At pressures more than about 20 torr and at wavelengths from 2530 to about 2660 A the triplet state quantum yield for benzene is about 0.72 as recalculated with the factor 1.02 instead of I.37.89,90 Several other methods give about the same result.91 The biacetyl method and the butene method may be said to be in agreement within a rather large experimental error except at this one wavelength. At wavelengths below 2500 A the triplet-state yields decrease but the error also increases. Probably around 2400 A the triplet-state yield has become zero but this statement is made with some reservations. 

Keyw ords DNA, meso-substituted thiacarbocyanine dyes, triplet state quantum yield, stable nitroxyl radical, iodide ion, oxygen. 

Since PDT photosensitisers locate preferentially in tumours they should be in theory of value in the diagnosis of the disease. The procedure of diagnosis would involve measuring the fluorescence of the tumour area before and after treatment with the sensitiser (see Chapter 3, section 3.5.6). For this to work effectively the fluorescence quantum yield should be as high as possible. However, the most effective photosensitisers are those with a high triplet-state quantnm yield and hence a low fluorescence quantum yield. Therefore it is unlikely that the more active photosensitisers can be used for this purpose. 

The singlet excited state of p-xylene may also undergo intersystem crossing to give the triplet with quantum yield... 

Table 4 T-T Absorption Maxima, Triplet Lifetimes, Quantum Yields of Isomerization, and Photostationary State Isomer Ratio...

In photoluminescence, the observed triplet luminescence quantum yield, also depends on the efficiency of formation of the triplet state upon absorption of light, in turn determined by the magnitude of the rate constant of intersystem crossing, kjsc (Eq- 3), where kf and radiative and non-radiative... 

However, the satisfactory explanation of phosphorescence as a radiative transition from the lowest triplet state had to wait till the decisive paper of G.N. Lewis and M. Kasha in 1944. Moreover, considering that the characteristics of the phosphorescence phenomenon, in terms of wavelengths, triplet lifetime, quantum yield, etc., are specific of the emitting molecule, these authors also suggested the potential of phosphorescence for the individual identification of organic compounds in complex mixtures. 

Similar to the fullerene ground state the singlet and triplet excited state properties of the carbon network are best discussed with respect to the tliree-dimensional symmetry. SurjDrisingly, the singlet excited state gives rise to a low emission fluorescence quantum yield of 1.0 x 10 [143]. Despite the highly constrained carbon network,... 

Sodium Acetate-Sodium Chloride Mixtures. Ramasamy and Hurtubise (12) obtained RTF and RTF quantum yields, triplet formation efficiency, and phosphorescence lifetime values for the anion of p-aminobenzoic acid adsorbed on sodium acetate and on several sodium acetate-sodium chloride mixtures. Rate constants were calculated for phosphorescence and for radiationless transition from the triplet state. The results showed that several factors were important for maximum RTF from the anion of p-aminobenzoic acid. One of the most important of these was how efficiently the matrix was packed with sodium acetate molecules. A similar conclusion was found for RTF however, the RTF quantum yield increased more dramatically than the RTF quantum yield. 

A-T ax are the spectral maximum of UV-Vis absorption, emission, and triplet state absorption, respectively, is the molar extinction coefficient, ta and Tt, Oa and r, s and Et, are the lifetime, quantum yield, and energy content of the singlet and triplet excited states of RF, respectively. 

On the other hand. Type II process competes efficiently with the electron-transfer pathway in aerobic environments where the concentration of ground triplet state molecular oxygen is relatively high ( 0.27 mM), and singlet molecular oxygen (1O2) is the most abimdant ROS generated under these conditions, with a quantum yield 0.48 (Valle et al., 2011), eqn. 8. It is also possible an electron-transfer reaction from 3RF to 02 to form anion superoxide, but this reaction occurs with very low efficiency <0.1% (Lu et al., 2000). 

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