Quantum yield singlet

AMI semiempirical molecular orbital calculations have been useful at predicting the nature of the LUMO level, i.e., a or it, and PET bond cleavage propensity [92]. In a series of arylmethyl-p-cyanobenzylsulfonium salts where aryl is phenyl, 1-naphthyl, 9-anthryl and 5-naphthacenyl the LUMO level was calculated to be ct in each case except for the 5-naphthacenyl derivative. The lack of photochemistry in the 5-naphthacenyl derivative as well as fluorescent quantum yields, singlet lifetimes, and reduction potential behavior are consistent with the conclusions from the calculations [92],... 

Ogata and Sawaki [29] examined a large number of a-hydroperoxyketones of the general formula (8) and found, in benzene-methanol, that methyl esters were obtainable in yields up to 100%. Although the compound studied by Richardson gave low yields of ester (about 30%), there is clearly a difference in behaviour. Quantum yields (singlet triplet = 1 300) were low (0cl = 10" ). The conclusion is that dioxetan formation occurs to a small extent, and is responsible for the light emission. Other similar studies [29, 30] show that the route taken depends on several factors, and that hindered bases such as potassium er -butoxide are more likely to result in the cyclic (dioxetan) route with formation of the acid rather than ester. 

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,... 

One characteristic property of dyes is their colour due to absorption from the ground electronic state Sq to the first excited singlet state Sj lying in the visible region. Also typical of a dye is a high absorbing power characterized by a value of the oscillator strength/ (see Equation 2.18) close to 1, and also a value of the fluorescence quantum yield (see Equation 7.135) close to 1. 

A substantial effort has been appHed to iacreaskig i by stmctural modification (114), eg, the phthalaziQe-l,4-diones (33) and (34) which have chemiluminescence quantum yields substantially higher than luminol (115,116). The fluorescence quantum yield of the dicarboxylate product from (34) is 14%, and the yield of singlet excited state is calculated to be 50% (116). Substitution of the 3-amino group of lumiaol reduces the CL efficiency > 10 — fold, whereas the opposite effect occurs with the 4-amino isomer (117). A series of pyridopyridaziae derivatives (35) have been synthesized and shown to be more efficient than luminol (118). 

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). 

In dichloromethane solutions, excitation of the chromophoric groups of the dendrons causes singlet-singlet energy transfer processes that lead to the excitation of the porphyrin core. It was found that the dendrimer 17, which has a spherical morphology, exhibits a much higher energy transfer quantum yield (0.8) than the partially substituted species 13-16 (quantum yield <0.32). Fluo-... 

When D and A are similar molecules emission-reabsorption cannot be very important due to the usually small overlap of the emission and absorption spectra. Also, this mechanism should not be important for triplet-triplet energy transfer because of (a) low phosphorescence quantum yields in fluid solutions and (b) the low oscillator strengths for singlet-triplet absorption. 

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