Disubstituted Liquid Crystalline Polyacetylene Derivatives That Exhibit Linearly Polarized Blue and Green Emissions

We synthesized disubstituted liquid crystalline polyacetylene (di-LCPA) derivatives by polymerizing acetylene derivatives consisting of LC moieties either directly or indirectly attached to the main chain through flexible alkyl spacers. The di-LCPA derivatives show either enantiotropically thermotropic LC or lyotropic LC behavior. The origin of emission of substituted PAs, with respect to their substituents and structure, was elucidated. Depending on the substituents of the side chains, the polymers exhibit blue (470–485 nm) and green (500–540 nm) photoluminescence (PL) in chloroform and in cast film. The di-LCPA derivatives were macroscopically aligned using rubbing technique, and the aligned structures of the polymers are characterized in terms of main chain and side chain type alignments through XRD measurements. The emission color and alignment direction toward an external force in the di-LCPA derivatives are crucially determined by both the linkage forms (direct or indirect attachment) between the main chain and side chains and the molecular moieties (alkyl or aromatic moiety) of the side chains. The macroscopically aligned films of the polymers exhibit linearly polarized photoluminescence (LPL) with notable dichroic ratios. We fabricate multilayer electroluminescence (EL) devices using the polymers as the emissive polymer layer that emit 480 nm light with promising EL properties. We emphasize that although substituted PA derivatives are usually nonluminescent, the di-LCPA derivatives emit intense fluorescence with notable linear dichroism, and they could be promising for optically anisotropic luminescent materials.