Ether electron transfer bridge

Single stranded oligomers exhibit a completely different behavior than double strands. As shown in Fig. 6, the increase of the number n of thymine bases in the bridge between the electron donor guanine and the enol ether radical cation as electron acceptor influence the rate of the electron transfer only slightly. This can be explained by the flexibility of the single strand, which levels out the distance between donor and acceptor [13]. 

Intramolecular electron transfer initiated cyclization reaction of 7V-allyliminium salt systems may also generate 3-pyrrolidinyl ethers or alcohols in monocyclic and bridged or fused bicyclic systems (e.g. equations 63 - 65)122,123. 

Cycloadditions only proceeding after electron transfer activation via the radical cation of one partner are illustrated by the final examples. According to K. Mizono various bis-enolethers tethered by long chains (polyether or alkyl) can be cyclisized to bicyclic cyclobutanes using electron transfer sensitizer like dicyanonaphthalene or dicyano-anthracene. Note that this type of dimerization starting from enol ethers are not possible under triplet sensitization or by direct irradiation. Only the intramolecular cyclization ci the silane-bridged 2>. s-styrene can be carried out under direct photolysis. E. Steckhan made use of this procedure to perform an intermolecular [4+2] cycloaddition of indole to a chiral 1,3-cyclohexadiene. He has used successfully the sensitizer triphenylpyrylium salt in many examples. Here, the reaction follows a general course which has been developed Bauld and which may be called "hole catalyzed Diels-Alder reaction". 

In some cases where bridged dianhydrides were used, four signals were observed in NMP, evidently because of the ability to transfer K-electron density through such bonds as ether, sulfone, or ketone as discussed above. As an example of such behavior, the diamic acid isomeric solution based on l,l -bis(3,4-carboxyphenyl)sulfone dianhydride (SDA) displayed the spectrum illustrated in... 

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. 

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