Singlet deactivation

There have been several reviews of mechanisms of photosubstitution in rhodium(III) complexes. Bond indexes for ground and excited states have been discussed in relation to D2h species. " The observation of stereospecificity has been discussed in relation to lifetimes for triplet singlet deactivation and geometric rearrangements. Direct evidence has been presented to support the intermediacy of, and role of rearrangement in, five-coordinate intermediates in ligand field irradiation experiments. Rhodium(III) has been discussed in relation to cobalt(III) and iridium(III), and to ruthenium(II) and ruthenium(III) as well. ... 

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... 

Data on duorescence, phosphorescence, excited-state lifetimes, transient absorption spectra, and dye lasers are tabulated in Ref. 16. The main nonduorescent process in cyanine dyes is the radiationless deactivation Sj — Sg. Maximum singlet-triplet interconversion ( 52 ) methanol for carbocyanines is about 3% (maxLgrp > 0.03), and the sum [Lpj + st] I than 0.10. 

The photolysis of dimethyl sulphoxide (at 253.7 nm) in a wide range of solvents has been studied in detail176. Three primary reactions occur, namely (i) fragmentation into methyl radicals and methanesulphinyl radicals, equation (60), (ii) disproportionation into dimethyl sulphone and dimethyl sulphide, equation (61) and (iii) deactivation of the excited state to ground state dimethyl sulphoxide. All chemical processes occur through the singlet state. Further chemical reactions of the initial photochemical products produce species that have been oxidized relative to dimethyl sulphoxide. 

The excited singlet or triplet state returns to the ground state by a radiationless deactivation process (Fig. 15/lV). 

Works [40, 91] surveyed y versus temperature for deactivation of 02( Aj ) on quartz at 350- 900 K. The obtained temperature dependencies were in the Arrhenius form with the activation energy of 18.5kJ/mole. A conclusion was drawn up about the chemisorption mechanism of singlet oxygen deactivation on quartz surface. A similar inference was arrived at by the authors of work [92] relative to 02( A ) deactivation (on a surface of oxygen-annealed gold). 

Deactivation of Singlet Oxygen on a Glass or Quartz Surface... 

If the rate of singlet oxygen deactivation is far less than the rate of desorption, i.e. K2 K.), then... 

The first step of surveying was represented by studying the nature of heterogeneous deactivation of singlet oxygen on a surface of oxidized and partially reduced zinc oxide [102] with the aid of semiconductor sensors. At room temperature and the pressure of O2 10 Torr, the value of y for de-exciting 02( A ) in ZnO is equal or approximately... 

Fig. 5.12. Coefficient of heterogeneous deactivation of singlet oxygen versus the temperature of zinc oxide surface at Pqj = 0.1 Torr [102]...

It should be noted that the value of yon reduced samples of ZnO is far greater than on the oxidized samples. Besides with the singlet oxygen treatment, the coefficient of 02( Ay ) deactivation on the reduced... 

Referring to the figure, additional chemisorption takes place under the action of singlet oxygen, a phenomenon that is accompanied by changes in the electron concentration in the ZnO conduction band. The initial rates of adsorption and changes in the electrical conductivity of ZnO are equal to 1.4 10 ° molecule/s and 1(H electron/s, respectively. From these data one can evaluate the probability of 02( a ) deactivation on... 

M.E. Ryskin, Geterogennaya Dezaktivatsiya Singletnogo Kisloroda na Poverkhnosti Metallov i Dielektrikov (Heterogeneous Deactivation of Singlet Oxygen on Surface of Metals and Dielectrics) Dissertation Cand. Sci.(Phys.-Math.), Moscow, 1983, 113 p. 

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