Synthesis, mesomorphism and dual-state emission behavior of hexacatenar liquid crystals based on cyanostilbene architecture

Abstract

To advance the development of dual-state emissive liquid crystals, a series of hexacatenar molecules featuring two cyanostilbene units directly linked within the aromatic core and three terminal alkyl chains on each end was rationally designed and synthesized via Suzuki and Knoevenagel reactions. All compounds self-organized into a rectangular columnar mesophase, with the number of molecules per columnar slice systematically tunable by varying the alkyl chain length. Photophysical studies in different states revealed that these derivatives exhibited dual-state emission and slight positive solvatochromism attributable to an extended π-conjugated aromatic core with distorted conformation and moderate intramolecular charge transfer, respectively. Notably, these hexacatenars exhibited an anomalous temperature-dependent fluorescence behavior wherein the emission intensity initially increased upon heating but progressively diminished at higher temperatures, a trend ascribed to thermally induced conformational variations and molecular motions that modulated the non-radiative decay pathways. This work establishes a molecular design strategy that integrates building blocks into a single liquid crystalline molecule with tunable mesophase and emission behaviors, positioning them as promising candidates for stimulus-responsive materials.