Fullerene excited triplet state

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... 

Photoinduced [2-1-2] cycloaddition reactions through the excited triplet states of fullerenes are believed to be responsible for the photopolymerization of fullerene molecules in the solid state [136,137] and in solution [81,82], Evidence for the involvement of the excited triplet states is primarily from the oxygen quenching results. 

Sandanayaka, A. S. D. et al. Photoinduced electron-transfer processes between [C60]fullerene and tri-phenylamine moieties tethered by rotaxane structures. Through-space electron transfer via excited triplet states of [60]fullerene. J. Phys. Chem. A 108, 5145-5155, 2004. 

In the case of the oHgothiophene-fullerene dyad molecnles, it has been reported that the CS state of tetrathiophene-Cjo ttyad (Fig. 29c) shows lifetimes as long as 6.3 fis in benzonitrile dne to an eqniUbrium between the CS state and the excited triplet state of C g (Fig. 31a) [120]. The long-lived CS states were also observed for the aromatic amine-Cgo and retinyl-Cgg dyads (Fig. 29d, e) [120-122, 124]. In the latter case the lifetime of the CS state is 20 fjLS. The equilibrinm between the CS state and the triplet state is supported by energetical consideration and some experimental facts, such as o gen sensitivity and solvent polarity dependence of the CS state. The eqnflibrinm is achieved when... 

In several cases, dependent on the donor, the electron transfer triplet energy transfer from the triplet state of the fullerenes to the donor was observed. For example, excitation of C6o/perylene (Pe) mixtures leads to 3Pe and C6o in a fast reaction ((1.4 0.1) X 109 M 1 s-1). The electron transfer from Pe to 3C o occurs with a rate one-third of triplet energy transfer [127]. Ito et al. investigated the photoexcitation of mixed system of C6o and (3-carotene [141], They observed triplet energy transfer from 3C o to (3-carotene in polar as well as in nonpolar solvents besides electron transfer from (3-carotene to 3C o However, the electron transfer rate constant increases with solvent polarity while the energy transfer is only less effected by the change of solvent polarity (Table 5). 

In this chapter we have described the photophysics and photochemistry of C6o/C70 and of fullerene derivatives. On the one hand, C6o and C70 show quite similar photophysical properties. On the other hand, fullerene derivatives show partly different photophysical properties compared to pristine C6o and C70 caused by pertuba-tion of the fullerene s TT-electron system. These properties are influenced by (1) the electronic structure of the functionalizing group, (2) the number of addends, and (3) in case of multiple adducts by the addition pattern. As shown in the last part of this chapter, photochemical reactions of C60/C70 are very useful to obtain fullerene derivatives. In general, the photoinduced functionalization methods of C60/C70 are based on electron transfer activation leading to radical ions or energy transfer processes either by direct excitation of the fullerenes or the reaction partner. In the latter case, both singlet and triplet species are involved whereas most of the reactions of electronically excited fullerenes proceed via the triplet states due to their efficient intersystem crossing. 

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