Mesogenic compounds molecular self-assembly

The molecular self-organization of an amphiphilic compound with imidazole induces smectic layer structures [28]. Mesogenic compounds 26 and 27 contain dihydroxy and monohydroxy moieties at the extremity of their alkyl terminal groups, respectively. These compounds show only nematic phases. However, a mixture of compound 26 and imidazole forms a self-organized smectic A structure over a wide range around room temperature. A molecular self-assembly of type A-II-b (Fig. 1) is induced for the mixture. No induction of a smectic phase is seen for 27 and imidazole 28. 

Recent work focuses on non-classical mesogenes which are built up by self-assembly. One example is a family of polymers containing disk-like groups which form no liquid crystalline phase, but ean act as an electron acceptor or donor. Charge transfer complexation with a complementary low molecular mass compound induces nematic or columnar discotic liquid crystalline order [153,154]. Figure 13 demonstrates this with the example of a polyester, bearing electron-rich tetra(alkoxy)tri-phenylene-units in the main chain, mixed with the electron deficient aromatic 2,4,7-trinitro-9-fluorenone (TNF). While the pure polymer shows a non-ordered isotropic melt, a columnar phase appears on addition of TNF. 

The most obvious family of compounds able to induce columnar phases is that constituted by the macrocyclic compounds which often possess a discoid molecular shape. The ability of macrocyclic systems to stack and to self-assemble into columnar mesophases confers on these systems the properties required for potential utilization in molecular devices based on photonics, electronics, or low-dimensional ionic transport. The search for new discotic mesogens is thus still of current interest, in order to improve their chemical, thermal, and photophysical stabihty, and new families of discogenic materials appear regularly. 

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