Pyrene singlet energy transfer

D 1A —- 1D + 1 A (singlet-singlet energy transfer) (e.g. anthracene + per-ylene, or pyrene + perylene). 

This phenomenon is possible in molecules like naphthalene, anthracene and Pyrene, each of which happens to have the lowest singlet energy level about twice hat of the respective triplet. For the generation of these triplets in high concentrations (T — T) type energy transfer from a suitable donor is necessary. Delayed fluorescence in naphthalene has been sensitized by phenanthrene. according to the following scheme ... 

In the mechanism above, two excited naphthalene dimers are included similar to those mentioned earlier in Section V-C. This is because in certain solutions, e.g., pyrene at room temperature and naphthalene at — 105°C., delayed emission is observed from two excited states, the excited monomer and presumably an excited dimer.68 62 These results have been interpreted as being due to a mechanism in which triplet-triplet quenching produces a system of dimers, one of which emits and/or dissociates into an excited and an unexcited singlet state. The term excimer has been proposed to distinguish this type of excited dimer from those produced by direct absorption from a stable ground-state dimer.87 The role of excimers in energy transfer processes is still... 

A racemic, bichromophoric C70-pyrene conjugate showing intramolecular photo-induced energy transfer from the excited singlet state of the PAH to the fullerene has been reported by Daub and co-workers.383 Its chirality is based on the stereogenic center resulting from reduction of a fullerene-fused cyclohexanone, itself obtained by Diels-Alder addition of 2-[(trimethylsilyl)oxy]buta-1,3-diene to the C(l)-C(2) bond of C70 and subsequent hydrolysis of the formed silyl enol ether (cf. Section IV.C.l.d and Scheme 1.18). 

They are well known as compounds which are photoohemically very reactive. The excited singlet and triplet states are the photochemically reactive states,and they also can participate in energy transfer reactions (2,3i10,11). Some of these compoxmds such as anthracene,phenanthrene,pyrene added to polyethylene effect the photodegradation of polymer (118,... 

In the pyrene system, the intermediate X has been identified with an excited dimer or excimer, since characteristic excimer emission is also observed. The process of triplet-triplet annihilation then consists of transfer of energy from one triplet to another to form excited dimeric species (S), which dissociates into an excited and a ground state singlets ... 

Creed, 1978a). It was found that as the charge-transfer character in the transition state increased the rate constant for cycloaddition decreased. The oxidation of crystal violet to its cation radical can be initiated by reaction of the dye with the excited singlet states of many polycyclic aromatic hydrocarbons. This reaction was found to be far less efficient for polymer-bound pyrene than for free pyrene and this was attributed to excimer formation occurring in the polymer system which ultimately led to energy wastage (Tazuke et al., 1979). 

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