Alkoxystilbazoles mesomorphic complexes

Alkoxystilbazoles fall into a sort of in-between scenario as the shorter homologues are non-mesomorphic, while the longer chain homologues show, typically between about 80-90°C, a crystal E and a smectic B phase (the latter over a very narrow range) [36]. However, examples of all chain lengths can be made mesomorphic on complexation to the right metal. 

The behavior is typical of relatively simple dipolar materials where a N phase was found at short chain lengths, giving way to a SmA phase in higher homologs. While the iridium complexes could be cycled in and out of the isotropic phase with few problems of decomposition, the rhodium complexes began to decompose rapidly on melting in air. Lateral fluorination of air-iridium stilbazole complexes strongly destabilized the mesophase the 2-fluorinated 4-alkoxystilbazole systems exhibited only monotropic N and SmA phases, whereas the structural isomeric 3-fluori-nated compounds were not mesomorphic. " ... 

Results were also described from studies which introduced lateral substituents into these complexes and in one paper the effect of introducing lateral alkanoate groups was reported (113). " The use of lateral alkanoates had been described previously by Maitlis and co-workers in palladium complexes of 4-alkoxystilbazoles (Section 7.9.14.3.6(iv)) and had been shown to induce the formation of liquid crystal nematic phases. In the present situation where the complex was polycatenar, it was not clear whether the chains would act to increase the volume of the core of the polycatenar mesogen or simply as extra chains, so rendering the complex more classically discotic. In fact, the answer was neither and at all chain lengths (n and m) and degrees of substitution (R = H or OC H2 +i) where mesomorphism was observed, a nematic phase was seen at or near room temperature. This behavior was somewhat puzzling and is so far without explanation. 

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