Crown ethers fullerene derivatives

The most commonly used method is to graft cyclodextrins and their derivatives (aza-crown ethers, fullerenes, linear carbohydrate biopolymers and inorganic/organic hybrid networks) onto the textile materials. Cyclodextrins are potential high-performance carrier materials that have the ability to alter physical, chemical and biological properties of drug molecules. This... 

Moreover, supra-molecular systems involving crown ethers, fullerene and k-extended systems have been achieved that can mimic the photosynthetic process [9-14]. The fullerene Qo has been used successfully as an electron acceptor in the construction of model photosynthetic systems [9], the r-extended systems, such as porphyrins [12], phthalocyanines [13], r-extended tetrathiafulvalene (w -exTTF) derivatives [9,10], which are utilized as electron donors, while the crown ethers act as a bridge between the electron donor and acceptor. In the absorption spectrum of the complexes, the absorption maxima are associated experimentally and theoretically with the formation of charge-transfer states [14-16]. Consequently, these supramolecular systems have potential for applications in photonic, photocatalytic, and molecular optoelectronic gates and devices [9-14]. As a result, the study of the conformations and the complexation behavior of crown ethers and their derivatives are motivated both by scientific curiosity regarding the specificity of their binding and by potential technological applications. 

A methanofullerene derivative possessing an ammonium subunit has been prepared and subsequently shown to form a supramolecular complex with a porphyrin-crown ether conjugate <06T1979>. The synthesis and study of these fullerene-containing supramolecular photoactive devices have also been reported <06CRC1022>. 

Supramolecnlar derivatives containing crown ether [228], calixarenes [264, 265] or dendrimers [267, 279] have been synthesized with the precursors shown in Table 4.10. Fullerene-flavonoid [268] or the fuUerene glycoconjugate [258] derived from 237 and 235, respectively, are expected to show biological activity. 

A similar supramolecular approach, in which both n-n stacking stacking of pyrene on the SWNT surface and alkyl ammonium-crown ether interactions were used in the self-assembly process of a fullerene derivative with SWNTs, was recently reported (Scheme 9.22).72 The nanohybrid integrity was probed with various spectroscopic techniques, , and electrochemical measurements. Nanosecond transient absorption studies confirmed electron transfer as the quenching mechanism of the singlet excited state of C60 in the nanohybrid resulting in the formation of SWNT"1"/ Pyr-NH3 + /crown- charge-separated state. 

The scope of the tether-directed remote functionalization has been expanded from Cgo to the higher fullerene C70, and the described reactions are completely regioselective, featuring, in the case of C70, the kinetically disfavored addition pattern. The crown ether is a real template, since it can be readily removed by transesterification, giving a much-improved access to certain bis-adducts that are not accessible by the direct route. Cation-binding studies by CV reveal that cyclophane-type crown ethers derived from C60 and C70 form stable complexes with metal cations, and a perturbation of the fullerene reduction potentials occurs because the cation is tightly held close to the fullerene surface. This conclusion is of great importance for future developments of fullerene-based electrochemical ion sensors. 

The [4 -I- 2] cycloadditions have been used to synthesize fullerene multiadducts in the past. A sixfold Diels-Alder product has been reported not only by the reaction of an excess of 2,3-dimethyl-1,3-butadiene with Cgo, but also by different bisadducts connected crown ethers to the fullerene spheroid. The properties of these derivatives have been studied for several potential applications, such as molecular sensors and complexation chemistry. 

Different isomers of the complexes of Ph2NH2 —1 and Ph2NH2 —2 with 18 and 18A or 18B were determined and optimized. The full optimization of these structures led to two and eight low-lying energy minima of the complexes of cations with the crown ether 18 and the fullerene crown ether 18A or 18B in the gas phase, respectively, see Figs. 31.2 and 31.3. A derivative of the Ph2NHj—1 isomer was... 

The complex of fullerene crown ethers with a r-exTTF derivative of Ph2NH2 presents charge transfer transitions in its absorption spectrum and may have potential for applications in organic photovoltaics and molecular electronic devices. 

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