Pyrrolidino fullerene

Considering the large variety of fullerene adducts, only a few investigations on photochemical processes of fullerene adducts have been reported. These studies deal mainly with reductive processes due to the easy reduction of fullerenes and its adducts. Studies on electron transfer processes of several pyrrolidino fullerenes (Fig. 20) with donors such as dimethylaniline (DMA) or tetrakis(dimethy-lamino)ethylene (TDAE) show that the electron transfer rate constants decrease compared to that of C6o (3.5 X 109 M 1 s 1 for C6o, 0.5 X 109 M 1 s 1 for the derivatives (Table 6, Fig. 21) [179], This can be interpreted in terms of decreasing u-conjugation of the C60 moiety, which causes an increase in LUMO energy level and a decrease in the lowest triplet energy. Therefore, the substituents influ-... 

Changing the solvent from polar to less polar solvents effects not only the electron transfer but also the back-electron transfer. Back-electron transfer rate constants are in less polar solvents larger than those in polar solvents, which can reasonably be interpreted in terms of desolvation process and loose in ion pair formation. The transient absorptions of the pyrrolidino fullerene radical anions are slightly blue-shifted compared to that of Qo (Qo 1076 nm, derivatives radical anions 991-1002 nm) [179],... 

As mentioned previously, photocycloaddition reactions are a useful method for obtaining fullerene derivatives fused directly to heterocycles. Such compounds have attracted much interest because they might have interesting properties, e.g., amino acid fullerene derivatives as biologically active compounds or pyrrolidino-fullerenes as key precursors for a great number of fullerenes donor-acceptor bridged dyads and triads. Fullerenes functionalized with silicon compounds are of great interest in materials science. The synthesis of these compounds will be described in this section. 

Topics which have formed the subjects of reviews this year include excited state chemistry within zeolites, photoredox reactions in organic synthesis, selectivity control in one-electron reduction, the photochemistry of fullerenes, photochemical P-450 oxygenation of cyclohexene with water sensitized by dihydroxy-coordinated (tetraphenylporphyrinato)antimony(V) hexafluorophosphate, bio-mimetic radical polycyclisations of isoprenoid polyalkenes initiated by photo-induced electron transfer, photoinduced electron transfer involving C o/CjoJ comparisons between the photoinduced electron transfer reactions of 50 and aromatic carbonyl compounds, recent advances in the chemistry of pyrrolidino-fullerenes, ° photoinduced electron transfer in donor-linked fullerenes," supra-molecular model systems,and within dendrimer architecture,photoinduced electron transfer reactions of homoquinones, amines, and azo compounds, photoinduced reactions of five-membered monoheterocyclic compounds of the indigo group, photochemical and polymerisation reactions in solid Qo, photo- and redox-active [2]rotaxanes and [2]catenanes, ° reactions of sulfides and sulfenic acid derivatives with 02( Ag), photoprocesses of sulfoxides and related compounds, semiconductor photocatalysts,chemical fixation and photoreduction of carbon dioxide by metal phthalocyanines, and multiporphyrins as photosynthetic models. 

Keywords pyrrolidino[60]fullerene, phase transfer reaction, microwave irradiation, A-alkylpyrrolidino[60]fullerene... 

Figure 3 Comparison of absorption and fluorescence (inset) spectra of different classes of C6oderivatives themethano-C6oderivative l -carboxy-l,2-methano[60]fullerene the pyrrolidino-C6o derivative N-ethyl-trans-2, 5 -dimethylpyrrolidino[3, 4 l,2][60] fullerene 33 (Fig. 24) (- - -),[B14al the C60 derivative 2-hydroxy-tetrahydrofu-ran[4, 5 l,2] [60]fullerene (—), and the amino-C60 derivative 3 (Fig. 4) AW -dimethyl-piperazine [2, 3 l,2][60]fullerene (-). (From Ref. 65.)...

Unlike the reversed shift of the emission band compared to the dihydrogen addend type, the singlet lifetime in the bis- and tris(bis-(ethoxycarbonyl)-methylene) derivatives is increased comparable to the former multiple adducts. The values range from 1.7 to 3.1 ns (tris-adduct), depending on the distorted T7-electron system of the fullerene core [67,108], In comparison to C6o, the fluorescence quantum yield for the malonic ester hexaadduct is increased by the factor 10 (30 X 10 4) [67,111], In the case of both pyrrolidino hexa-adducts (Th 14 and D3 15, Fig. 13), the effect is remarkably higher. The fluorescence quantum yields are increased about 100-fold (-0.02) compared to C6o. On the other hand, the singlet lifetime is only partly increased with -3.5 ns [111,112],... 

For methanofullerenes, the triplet-triplet absorption appears arround 720 nm, for cyclohexylfused derivatives, pyrrolidino- and dihydro-fullerene, the absorption appears arround 700 nm [62,71,72]. 

Chen, N., Zhang, E.Y., Tan, K. et al. (2007) Size effect of encaged clusters on the exohedral chemistry of endohedral fullerenes a case study on the pyrrolidino reaction of ScjGd3 xN Cgo (x = 0-3). Organic Letters, 9, 2011-2013. 

Figure Cl.2.5. Illustration of the p7r orbital energy levels in [60]fullerene. [TOJfullerene and monofunctionalized pyrrolidino[M]fullerene [26],...

Figure 20 The absorption (a) and the uncorrected fluorescence (b) spectra of A -ethyl-tranj-2, 5 -dimethyl-pyrrolidino[3, 4 l,2][60]fullerene. (From Ref. 71.)...

Azomethine ylides A general method for functionalization of Ceo (1) involves 1,3-dipolar cycloaddition of azomethine ylides. This process was first described by Prato and leads to the formation of pyrrolidino[60] fullerenes this method has been widely used [32]. 

Zeng and coworkers [39] described the synthesis, under microwave irradiation, of several donor-acceptor systems based on amino-pyrrolidino[60]fullerene in which the Cgo (electron acceptor) and amino group (electron donor) were covalently bonded with a short linker (Scheme 21.13). 

As indicated above, the yields of fullerene[60]-ethylcarbazole and the fullerene[60]-triphenylamines were not particularly high, but were reasonable in fullerene chemistry because of the need to avoid bis and/or tris addition. Photophysical studies on these compounds (32a-c) showed that efficient photoinduced electron transfer occurs in these amino-pyrrolidino[60]fullerene derivatives. 

The synthesis of Nl-f-pyrrolidino[60]fullerenes under the action of microwave irradiation has been described in Section 21.1.2.2. These compounds provide access to... 

Dipolar cycloaddition reactions of azomethine ylides are probably the most widely used reactions for functionalization of [60]fullerene. This reaction has also been used to obtain SWNT derivatives and, occasionally, microwave irradiation has been used [89]. Pyrrolidino-SWNT 76 was synthesized by reaction of pristine... 

Scheme 34.6 Retro-cycloaddition reaction of pyrrolidino[3,4 l,2][60]fullerenes (16a-e).

Also, chiral fullerene derivatives have found use in biological applications [50] and in polymer science as helicity inducers [51]. Recently, fullerene chirality has demonstrated to be critical in generating a supramolecular architecture of donor-acceptor dyads (based in a chiral pyrrolidino[60]fullerene) giving rise to photoconductive nanofibers displaying very high ambipolar charge-carrier mobility ( 10 cm /(V s)), which was higher than that obtained from racemic dyads in spherical assembly [52]. 

A major breakthrough in this respect has been the introduction of asymmetric metal catalysis for the preparation pyrrolidino[3,4 l,2][60]fullerenes with a complete control on the absolute configuration [53],... 

Figure 34.3 Absolute configuration assigned for both cw-2-carboximethyl-5-(p-methoxyphenyl)pyrrolidino[3,4 l,2][60]fullerene enantiomers using the sector rule. See insert for color representation of the figure.)...

Similarly, when Cu(II)/(/ )-DTBM segphos complexes are used, the trans pyrrolidino[60]fullerene features a 2R,5S) configuration. Moreover, chiral complexes affording the trans adduct present a higher intensity at the 430 nm peak, as both substituents lay above the sectors with the same sign, thereby resulting in an additive effect (Fig. 34.4). 

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