The effect of the number of cyanostilbene building blocks on the self-assembly and photophysical property of pyrene-based liquid crystals

The synthesis, self-assembly and physical properties of two series of di/tetra-substituted pyrene-based liquid crystals were reported. These compounds were synthesized by using Suzuki coupling and Knoevenagel reactions as key steps. The effects of the number of cyanostilbene arms connecting to central pyrene on the mesomorphic and emission behaviors with structurally related compounds were investigated. The lower pyrene-based homologue containing two cyanostilbene arms could self-assemble into rectangular columnar phase in which two molecules aggregated into a disc, whereas the higher pyrene-based homologues could self-assemble into hexagonal columnar phase in which four molecules aggregated into a disc. The pyrene-based liquid crystals containing four cyanostilbene arms could also self-assemble into hexagonal columnar phase in which two molecules aggregated into a disc. The self-assembly process and the models for arrangements within these columnar phases were proposed and discussed in detail. These compounds also exhibited distinct slovatochromism and strong fluorescence in both solution and aggregated states. Therefore, controlling molecular structures of functional liquid crystal materials was an efficient way to tune the self-assemblies and emission properties.