Host-Guest Mesomorphism: Cooperative Stabilization of a Bowlic Columnar Phase.

The azo-substituted calix[4]arene I (R = N:N-C6H3-(O(CH2)10H)2-3,4) in pure form does not display a stable thermotropic mesophase. A novel method is reported for stabilization of mesomorphic behavior by making use of the calix[4]arene’s receptor properties. In particular host-guest interactions between I and 1,4-(diformamide)butane (II) stabilize a bowlic hexagonal columnar phase (Bh) with very low clearing enthalpies and high fluidity. X-ray diffraction studies indicate that the Bh phase is the only mesophase present at I:II ratios of 2:1, but at ratios of 4:1 and 1:1 this phase coexists with small amts. of other unidentified phases. This system also displays the unusual properties that the range of mesomorphism is independent of the host/guest ratio and that only a fractional amt. of guest is required to stabilize the mesophase. The latter feature is indicative of a cooperative transition to the mesomorphic state. [on SciFinder(R)]