Triplet state energy transfer

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). 

Intermolecular triplet-state energy transfer is well known in photochemistry. McDowell et al. (334) first demonstrated by ESR the triplet energy transfer from benzophenone to naphthalene in a rigid glass. The excitation transfer is found to be independent of orientation (335a), while the probability of excitation transfer per lifetime is dependent on concentration (335b). 

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... 

There are other cases in which triplet-mediated energy transfer might compete with LMCT-mediated energy transfer, particularly where the metal ion is either europium or samarium. In these cases, the redox potentials of the metal ions are such that LMCT is feasible, although the LMCT state will be lower in energy than the emissive state of the metal, precluding luminescence.65... 

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. 

Helene110 says that thymidine fluorescence from aqueous solutions at 77°K of a thymidine-adenosine mixture (as well as the identical fluorescence from rigid solutions of G + T, AcC + T or C + T) is owing to a triplet energy transfer to the thymidine moiety. The order of triplet-state energies among the purines and pyrimidines is given as... 

An increase in the ion annihilation exergonicity AG to values comparable to the excited triplet-state energies (AG I LT < 0) opens an additional electron transfer channel (T-route). In the simplest case, only one excited triplet 3 A or 3 D becomes accessible. Triplet emission can be directly observed from the ECL systems involving rare earth and transition metal complexes with allowed (due to extensive spin-orbit coupling) triplet-singlet electronic transition. 

The most investigated system for energy transfer from the excited triplet states of fullerenes to an acceptor is the formation of singlet oxygen. Both the fullerenes, C6o and C70, in their triplet states efficiently transfer energy to 302 to... 

TDDFT calculations results were consistent with the band shapes of the optical spectra of the parent complexes and are shown in Fig. 14. The calculated optical transitions are shown as bars under the experimental spectra and consist of MLLCT, ligand-to-ligand charge transfer transitions (LLCT), intraligand n - tt transitions (IL), and metal-complex delocalized-charge transfer transitions (MCDCT). Triplet state energies were also calculated based on a3 MLLCT state and correlated with experimental emission spectral results [53]. 

Sandros, K., and H. L, J. Bdckstrom Transfer of triplet state energy in fluid solutions. II. Further studies of the quenching of biacetyl phos-phorscence in solution. Acta chem. scand. 16, 958 (1962). 

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