Singlet states energy transfer

As an extension of the fluorescent sensitizer concept, Forrest et al. have applied this approach to phosphorescent OLEDs, in which the sensitizer is a phosphorescent molecule such as Ir(ppy)3 [342]. In their system, CBP was used as the host, the green phosphor Ir(ppy)3 as the sensitizer, and the red fluorescent dye DCM2 as the acceptor. Due to the triplet and the singlet state energy transfer processes, the efficiency of such devices is three times higher than that of fluorescent sensitizer-only doped device. The energy transfer processes are shown in Figure 3.21. 

Deactivation of the excited stabilizer molecule in its excited singlet (screening effect) and triplet state (energy transfer). 

Hirota, N. Use of triplet-state energy transfer in obtaining singlet-triplet absorption in organic crystals. J. Chem. Phys. 44, 2199 (1966). 

It should be noted that the existence of different centers Is also found in covalently-linked dimer 11. Moreover, the analysis of all data obtained for dimers points clearly towards the efficient transfer of the excited singlet state energy from two centers of compound 1 to two acceptor centers of compound 2 in dimers (14,30). Increase In the porphyrin concentration by 300-700 times (say, for compounds 1 and 2) does not cause additional changes In electronic spectra as against diluted solutions. If the results obtained from temperature experiments (Fig. 2b) and measurements of fluorescence lifetimes In different bands are taken Into account, one may conclude that the additional centers observed In... 

OXYGEN, OXIDES 0X0 ANIONS SINGLET STATE JABLONSKI DIAGRAM SINGLET-TRIPLET ENERGY TRANSFER SINGLE-TURNOVER CONDITIONS Site-directed inhibitor,... 

Figure 6.11 The rate of energy transfer et asa function of overlap integral between the emission spectra of the donorand the absorption spectra of the acceptor and the rate constant for energy transfer, In each case donor (dotted line) is benzene and acceptor (solid Vine") are aromatic hydrocarbons of different singlet state energy E . The energy scale is expressed in kcc.l mol-...

Mg(TMOP)-R-H2(TMOP) R = bridge of cofacial porphyrins [Mg(TMOP )]+-R-[H2(TMOP )] Solvent CH2C12 X, = 527 nm = 1 90% of the singlet state energy is stored in the photoproduct fast back electron transfer [195]... 

The proposed mechanism for the chlorinative cleavage involves the initial excitation of the acceptor to its lowest-energy singlet state. Electron transfer to the permethyloli-gogermane produces initially the radical anion of the acceptor and the radical cation of the... 

Singlet-triplet energy transfer Transfer of excitation from an electronically excited donor in a singlet state to produce an electronically excited acceptor in a triplet state. 

Oxygen quenching of phenanthrene phosphorescence involves an exchange mechanism which also operates for triplet state energy transfer involving phenanthrene in biphenyl 2i. Radiationless processes of excited states of 5,6-diazaphenanthrene in hexane and hexafluoroisopropanol have been studied by both triplet and singlet lumi ne s cen ce 2 2 extremely fast radiationless transition in the... 

Stilbene photochemistry continues to provide a mine of riches for the dedicated photochemist, in particular Hochstrasser, Fleming, and their groups. Metcalf et al. have described chiral discrimination in electronic energy transfer processes enantioselective excited state quenching occurs. A study of singlet electronic energy transfer from cyclohexane to benzene appears to require revision of the benzene fluorescence efficiency in cyclohexane to 0.26 0.02 (Johnston and Lipsky). 

The differences in tautomerization in the lowest excited singlet and triplet states of 1 and 2 reflect the pattern observed for the ground state. In contrast to porphyrin, both trans and cis structures are detected in porphycenes, separated by a very small energy gap. The tautomerization barriers are also much lower in 1. Finally, at least in the case of the lowest excited singlet state, synchronous transfer of two hydrogen atoms seems to be preferred over a stepwise mechanism, even when both forms are present (la and lb). 

When the triplet is an excited state, energy transfer occurs to form singlet oxygen. Ground state triplets react with oxygen by a spin-allowed process which, for carbenes in particular, produce carbonyl oxides [64], It seems that triplet nitrenes react with oxygen slowly. This will be discussed more fully later. Here we examine the products formed from reaction of photolysis of phenyl azide in the presence of oxygen. 

The steady state and time-resolved fluorescence measurements unequivocally showed that efficient singlet-singlet excited state energy transfer from the Zn-porphyrin complex to the freebase porphyrin takes place in these assemblies. Indeed, the observed energy transfer rates in both types of assemblies are much faster than those which the Fbrster mechanism would suggest. 

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