Bipyridinium units

Figure 6.18 Structural formulas of two families of dendrimers containing a 1,3,5-trisubsti-tuted benzenoide core and 9 (A918 + and B918 + ) and 21 (B2142+ and A2142 + ) 4,4 -bipyridinium units in their branches.68 The -type dendrimers are terminated with tetraaryl-methane bulky moieties while the -type dendrimers contain in their periphery less bulky aryloxy groups. For comparison purposes the structural formulas of dendrons A24 + and B24 + and model compound DoV2 + are also reported.

Further examples of hybrid pseudorotaxanes containing a linear component incorporating two dialkylammonium centres and a 4,4 -bipyridinium unit associated with an assortment of macrocyclic polyethers have been reported. Both multi-component rotaxanes and polyrotaxanes based on the above tetracationic thread were observed to form. The reversible acid-base-controlled dethreading/rethread-ing of such [n]-rotaxanes has been demonstrated using a combination of NMR, absorption and fluorescence spectroscopies. ... 

The macrocyclic polyether, tris(l,5-naphtho)-57-crown-15 (Figure 5.12) contains a sufficiently large ring size to permit the simultaneous accommodation of two threaded 4,4 -bipyridinium units, which are then appropriately orientated for further template formation of tetracationic cyclophanes. However, the efficacy of template formation for [3]-catenane formation proved to be less than anticipated. The... 

Among the systems proposed as models for the photosynthetic reaction center, supramolecular assemblies in which Ru(II)-polypyridine complexes and 4,4 -bipyridinium units are held together noncovalently in threaded and interlocked structures have been extensively studied [43, 82-88]. In such assemblies, connections between the molecular components rely on charge transfer interactions between the electron acceptor bipyridinium units and aromatic electron donor groups (Fig. 3). For instance, in the various pseudorotaxanes formed in acetonitrile solution at 298 K by the threading of cyclophane 4 + by the dioxybenzene-containing tethers of 192+ (Fig. 17) [84], an efficient photoinduced electron... 

Domenech, A., Alvaro, M., Ferrer, B., and Garcia, H. 2003b. Electrochemistry of mesoporous organosilica of MCM-41 type containing 4,4 -bipyridinium units Voltammetric response and electrocatalytic effect on 1,4-dihydrobenzoquinone oxidation. Journal of Physical Chemistry B 107, 12781-12788. 

Recently, a third process has been identified which constitutes an example of strict self-assembly.The so-called slippage approach to rotaxane synthesis Figure 5) is based upon size complementarity between the macrocyclic polyether, BPP34C10, containing two 7i-electron rich recognition sites and the stoppers comprised of suitable tetra-arylmethane groups at the ends of dumbbell-shaped molecules incorporating at least one 4,4 -bipyridinium unit. ... 

The investigated dendrimers contain three types of chromophoric groups, namely a 4,4 -bipyridinium unit at the core, 1,3-dimethyleneoxybenzene units in the branches, and benzene units at the periphery. Dendrimers exhibit a strong absorption band in the UV region that does not coincide with the summation of the spectra of the component units, particularly because of the presence of a broad and weak... 

---