Viologen core dendrimers

Figure 6.12 Structural formula of dendrimer 17 containing a tris-viologen core appended with six [Ru(bpy)3]2+ complexes.57...

Frechet and co-workers [32] studied the ability of the dendrimer shell to provide site isolation of the core porphyrin moiety, using benzene-terminated dendrimers Zn[G-n]4P (i.e. 6). From the cyclic voltammograms in CH2C12, the interfacial electron transfer rate between the porphyrin core and the electrode surface decreased with increasing dendrimer generation. However, small molecules like benzyl viologen could still penetrate the shell of 6 to access the porphyrin core as observed from the quenching of porphyrin fluorescence. Their results also revealed that the dendritic shell did not interfere electrochemically or photochemically with the porphyrin core moiety. 

Bipyridinium-type units (also known as viologens) are well-known electron acceptors64 extensively used in chemical and electrochemical redox processes,65 since they can undergo two reversible one-electron reduction processes. Because of these peculiar properties such units can be profitably used to functionalize the periphery of dendrimers, but examples of dendrimers containing a bipyridinium-type unit as a core are also reported.66... 

Fig. 14 Structural formulas of two families of dendrimers containing a 1,3,5-trisubstituted benzenoide core and 9 (A918+ and B918+) and 21 (A2142+ and B2142+) viologen units in their branches [69-71]...

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