Flying-seed-like liquid crystals 3: new guideline for the induction of mesomorphism by using bulky groups instead of long alkyl chains

Abstract

In our previous work, we synthesized a series of phthalocyanine-based flying-seed-like compounds, (nnnnPh-PhO)₄444PcCu (n = 3, 2, 1 and 0 in nnnnnnnnnnnnnnnnnnnPh-PhO: a–d), and revealed that each of them shows a columnar liquid crystalline phase (Col_ho or Col_rho) from rt to an extremely high temperature near 500 °C. Thus, we could obtain columnar liquid crystalline phases for discotic compounds by using bulky substituents (a–d) instead of long alkyl chains. In order to further study the utility of these bulky substituents (a–d) on the induction of mesomorphism for other shaped molecules, we have synthesized novel flying-seed-like calamitic phenoxybenzoic acid derivatives, nnnnnPh-PhOBA (3a–d), and their Mitsubishi-Mark-shaped terbium complexes, (nnnPh-PhOBA)₃33Tb·mmmMeOH (4a–d), in this work. Very interestingly, the mesomorphism of the phenoxybenzoic aids derivatives nnnnnPh-PhOBA (n = 0–3) was induced to show a mesophase (M_x) only by the bulky substituent d (n = 0), whereas the mesomorphism of their corresponding terbium complexes (nnnnnnnnnnnnnnnnnnPh-PhOBA)₃33333333333333333Tb(III) (n = 0–3) was induced to show rectangular columnar (Col_r) mesophases by the bulky substituents c and d (n = 1, 0). On the other hand, the mesomorphism of the PcCu complexes (nnPh-PhOBA)₄4PcCu (n = 0–3) in our previous work was induced by all the bulky substituents a, b, c and d (n = 0–3). Thus, it becomes apparent that both calamitic and columnar mesomorphism can be induced by the substitution of bulky groups instead of long alkyl chains, and that the balance of the core size and the bulkiness of the substituents is very important to obtain mesomorphism in flying-seed-like compounds. We believe that this is a new guideline for the induction of mesomorphism by using bulky groups instead of long alkyl chains.