Fluorescence and Absorption Studies of the Cation-Binding Behavior of “Crowned” Liquid Crystals in Solution and in the Nematic Phase

4^/-((p^/-Cyanobiphenylyl)ethynyl)benzo crown ethers (3 and 4) not only display a nematic liquid-crystal phase but also show very strong fluorescence, both in solution and in the liquid-crystalline state. The “crowned” liquid crystal compound 4 exhibited a bathochromic shift in fluorescence and a hypsochromic shift in absorption with increasing solvent polarity. The addition of alkali-metal cations produced hypsochromic changes in both the fluorescence and absorption of 4. The cation-induced effects (fluorescence, absorption, and fluorescence quenching with thiocyanate salts) have been used as aids in determining the cation-binding ability of 4 in polar solvents, producing results similar to those obtained from conventional methods. On the basis of solution studies, the binding abilities of 3 and 4 in a eutectic nematic liquid crystal (ZLI-2806) were determined. The results revealed that 3 and 4 also complex alkali-metal cations selectively in the nematic phase, and the cation-binding ability is comparable with that found in methanol solution, but no evidence for 2:1 crown unit:cation complexation of 3 with KSCN was obtained under the present conditions. On the other hand, an energy-transfer quenching study with sodium 3-perylenecarboxylate under the same conditions did not show any specific cation-crown ether interaction.