Singlet efficiency

The photolytic decomposition of 1,2-dioxetanes has been studied much less extensively in comparison to their thermal decompositions. Bartlett and Schaap34 observed that prolonged irradiation times in the preparation of 1,2-dioxetanes In by photooxygenation decreased the yields substantially. Presumably the dioxetane was photosensitive. This was confirmed by Wilson and Schaap" in their classical paper on the mechanism of chemiluminescence of dioxetane In, showing that the photoenergized 9,10-diphenyl- and 9,10-dibromoanthracene singlets efficiently induced the decomposition of In. 

Introductory descriptions of Hartree-Fock calculations [often using Rootaan s self-consistent field (SCF) method] focus on singlet systems for which all electron spins are paired. By assuming that the calculation is restricted to two electrons per occupied orbital, the computation can be done more efficiently. This is often referred to as a spin-restricted Hartree-Fock calculation or RHF. 

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). 

Fluorescence from the ExcitedSj State. In Figure 1, after absorption (A) and vibrational deactivation (VD) occur, the lowest or nearly lowest level of the singlet excited state is reached. If the molecule is fluorescent with a high quantum efficiency, fluorescent emission of a quantum of... 

PM spectra and their decays in DOO-PPV films and dilute solutions, we conclude that the primary excitations in DOO-PPV films are also singlet excitons [26]. The long excitonic lifetime and a corresponding high PL quantum efficiency [27] indicates that DOO-PPV is a high quality polymer material, which is very suitable for electrooptics and laser action applications [28],... 

The efficient formation of singlet excitons from the positive and negative charge carriers, which are injected via the metallic contacts and transported as positive and negative polarons (P+ and P ) in the layer, and the efficient radiative recombination of these singlet excitons formed are crucial processes for the function of efficient electroluminescence devices. 

A critical parameter in determining the operating efficiency of polymer LEDs is the luminescence quantum efficiency of singlet excilons in the polymer i.e. the probability that a singlet exciton will decay radiatively. The luminescence quantum elft-... 

The dimerization of ketones to 1,2-diols can also be accomplished photochemi-cally indeed, this is one of the most common photochemical reactions. The substrate, which is usually a diaryl or aryl alkyl ketone (though a few aromatic aldehydes and dialkyl ketones have been dimerized), is irradiated with UV light in the presence of a hydrogen donor such as isopropyl alcohol, toluene, or an amine. In the case of benzophenone, irradiated in the presence of 2-propanol, the ketone molecule initially undergoes n — k excitation, and the singlet species thus formed crosses to the T, state with a very high efficiency. 

Figure 7. Absence of a linear correlation of either oxidation potential or singlet energy to chemiluininescence efficiency for the peroxyoxalate reaction.

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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