Benzo[g]chrysene Discotic Liquid Crystals: Synthesis, Columnar Mesophase and Photophysical Properties

Discotic liquid crystal consisting of polycyclic aromatic hydrocarbon (PAH) core and peripheral alkyl chains is a kind of soft organic materials showing semiconductivity and fluorescence, and it can be fabricated into opto-electronic devices by solution process or printing technique, with low-cost advantage. We report benzo[g]chrysene unsymmetrical functional discotic liquid crystals, which were synthesized by Suzuki-Miyaura cross-coupling reaction and Scholl oxidative annulation. Five new p-extended compounds containing ester, anhydride, imide and benzoimidazole unit were synthesized and characterized. Their liquid crystalline property was fully characterized by differential scanning calorimetry (DSC), polarized optical microscopy (POM) and small-angle X-ray scattering (SAXS), these compounds showed ordered columnar hexagonal (Colhex) mesophase with broad mesophase range as wide as 206 degrees C. The functional groups have essential impact on the phase transition temperatures. The ultraviolet-visible (UV-Vis) absorption and photoluminescent property were studied, they displayed fluorescent quantum yield as high as 34% in solution, and the emission spectra can be tuned from blue, green to red by functional group and p-conjugation extension. Density functional theory (DFT) computation results explained these physical properties. We anticipate that more p-extended functional molecules can be developed from naphthalic anhydride by our method.

Automated summary

The study synthesized new benzo[g]chrysene unsymmetrical functional discotic liquid crystals, which showed a broad mesophase range and high fluorescent quantum yield. The emission spectra can be tuned from blue, green to red by functional group and p-conjugation extension, with potential for developing more functional molecules from naphthalic anhydride.