Spacers dimers/oligomers

The phase behavior of several polybibenzoates with oxyalkylene spacers has been reported [11,14,15,20-27]. These spacers include the dimer of trimethylene glycol and different ethylene oxide oligomers. The most noticeable characteristic of these polybibenzoates with ether groups in the spacer is the considerable decrease of the rate of the mesophase-crystal transformation. Thus, Fig. 8 shows the DSC curves corresponding to a sample of poly[oxybis(trimethylene)p,p -bibenzoate], PDTMB, with a structure similar to that of P7MB but with the... 

The modulation of the electronic properties of PTA oligomers by re-electron-deficient and -rich aromatic and heteroaromatic spacer units was first tested in DEE dimers 38a-j and 39a,b (Figure 16) [43]. The insertion of such spacers was found to have a profound influence on the molecular properties, such as the fluorescence behavior. Thus, whereas the quantum yields of compounds 39a,b and hybrid trimer 38j were below 5 % in chloroform (2exc = 356 nm), hybrid derivatives 38a, 38e, 38g, and 38i exhibited quantum yields between 20 and... 

Figure 23 Synthesis of twin discotic dimer and branched oligomers from CTTV-7 mesogens connected with a hexadecane spacer. (From Ref. 76.)...

This influence of the rigidity of the spacer was also observed in a supramolecular polymer comprised of CD dimers and homoditopic guests (resembling an AA-BB polycondensation). When a rigid linker was employed in the homoditopic guest, supramolecular polymers were obtained, whereas the use of a flexible linker led to the formation of cyclic oligomers [52]. 

Two main sections will be devoted to well-defined porphyrin oligomers. The first deals with porphyrin dimers, trimers, and higher oligomers connected by various types of spacers. The second section will focus on similar compounds associated with nonporphyrinic species. It should be noted that assemblies of porphyrins connected to surfaces will be treated separately at the end of the chapter. 

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