Synthesis-and Characterization Of Double-fan-shaped Mesogens

Based on its high–branched and perfect topological structural properties,dendrimers have become one type of most important building blocks for constructing liquid crystals.Wedge-shaped molecules,such as dendrons,are among the most important building blocks for directed supramolecular self-assembly.It is indicated that fan–shaped molecules incline to self–organize in a columnar lattice,while conical–shaped molecules are likely to self–organize in a cubic lattice.In previous work,molecular structures are often modified by increasing the generation of dendrons or changing the structure of branched groups.Here we present a new approach aimed at widening the range and complexity of potential mesophase types by introducing a series of novel AB₃–AB₃ and AB₃–AB₇ double–fan–shaped minidendrons based on benzoate salts.The main contents are as follows:In the first part,two types of AB₃–AB₃ double–fan–shaped compounds 1M and 2M（M=Li,Na,Cs）are presented,both alkali metal salts of 3,4,5-tris-alkoxybenzoic acid with a second tapered tris-alkoxyaryl group attached at the end of the alkoxy chain in the 4-position.After being analysed by DSC,SAXS and POM,it is shown that all compounds 1M and 2M display an unusual hexagonal columnar phase consisting of two different types of columns,one ionic and the other non-ionic,in the ratio 1:3.The cation size has a pronounced effect on number of molecules in a unit cell.Unlike most columnar phases,the current phases show high dimensional stability on heating.The columns show signs of remarkably high stiffness in spite consisting of80-85%flexible alkyl chains.The structure can be fine-tuned by varying the cation and the nature of the peripheral aryl group.The described results can potentially be used in designing co-assembly of multifunctional materials,e.g.parallel p-and n-semiconducting nanowires or parallel ionic and electronic conductors.In the second part,compared with the AB₃–AB₃ double–fan–shaped minidendrons in the first part,the volume of the aliphatic chains was increased in order to change their disorder conformation,which may form the conical–shaped molecular structures so that the cubic phase can be produced.Based on sodium tris（alkoxy）benzoates,the molecule was designed via pentaerythritol derivative with more alkyl chain branches.Finally,AB₃–AB₇ double–fan–shaped minidendron 3Na was successfully synthesized through ten–step chemical reactions.The structure of new compound 3Na was confirmed by ¹H NMR,¹³C NMR and elemental analysis experiments.It provides opportunities for the continuing investigation of their liquid crystalline properties and its relationship with molecular structures.