Counterion Effects on the Columnar Mesophases of Triphenylene‐Substituted [18]Crown‐6 Ethers: Is Flatter Better?

The twisted lateral tetraalkyloxy ortho ‐terphenyl units in dibenzo[18]crown‐6 ethers 1 a – f were readily converted into the flat tetraalkyloxytriphenylene systems 2 a – f by oxidative cyclization with FeCl 3 in nitromethane. Reactions of the latter with potassium salts gave complexes KX ⋅2 , which displayed mesomorphic properties. The aromatization increased both the clearing and melting points; the mesophase stabilities, however, were mainly influenced by the respective anions upon complexation with various potassium salts. In contrast, the alkyl chain lengths played only a secondary role. Among the potassium complexes of triphenylene‐substituted crown ethers KX ⋅2 , only those with the soft anions I − and SCN − displayed mesophases with expanded phase temperature ranges of 93 °C and 132 °C (for KX ⋅2 e ), respectively, as compared to the corresponding o ‐terphenyl‐substituted crown ether complexes KI ⋅1 e (ΔT=51 °C) and KSCN ⋅1 e (plastic crystal phase). Anions such as Br − , Cl − , and F − decreased the mesophase stability, and PF 6 − led to complete loss of the mesomorphic properties of KPF 6 ⋅2 although not for KPF 6 ⋅1 . For crown ether complexes KX ⋅2 (X=F, Cl, Br, I, BF 4 , and SCN), columnar rectangular mesophases of different symmetries ( c 2  mm , p 2  mg , and p 2  gg ) were detected. In contrast to findings for the twisted o ‐terphenyl crown ether complexes KX ⋅1 , the complexation of the flat triphenylene crown ethers 2 with KX resulted in the formation of organogels. Characterization of the organogel of KI ⋅2 e in CH 2 Cl 2 revealed a network of fibers.