Fluorescent Columnar Liquid‐Crystalline Polymers: Synthesis, Mesomorphic Behaviors and Tunable Emission Wavelengths †

Thermo-Induced Bathochromic Emission in Columnar Discotic Liquid Crystals Realized by Intramolecular Planarization

Most organic thermochromic fluorescent materials exhibit thermo-induced hypsochromic emission due to the formation of excimers in ordered molecular solids; however, it is still a challenge to endow them with bathochromic emission despite its significance in making up the field of thermochromism. Here, a thermo-induced bathochromic emission in columnar discotic liquid crystals is reported realized by intramolecular planarization of the mesogenic fluorophores. A three-armed discotic molecule of dialkylamino-tricyanotristyrylbenzene was synthesized, which preferred to twist out of the core plane to accommodate ordered molecular stacking in hexagonal columnar mesophases, giving rise to bright green monomer emission. However, intramolecular planarization of the mesogenic fluorophores occurred in isotropic liquid increasing the conjugation length, and as a result led to thermo-induced bathochromic emission from green to yellow light. This work reports a new concept in the thermochromic field and provides a novel strategy to achieve fluorescence tuning from intramolecular actions.

Supramolecular Structure and Photo-Thermo-Electric Property of Hydrogen-Bonded Liquid Crystalline Polymer Containing Poly(4-vinylpridine) and Cyanostilbene Side Chains

A series of side-chain liquid crystalline polymers P4VP(CN-DBE)_x , where x is the molar ratio of cyanostilbene (CN-DBE) to poly(4-vinylpyridine) (P4VP) repeating unit, was synthesized based on the intermolecular hydrogen bonding between P4VP and CN-DBE. Their luminescent property, liquid crystalline structure and photo-thermo-electric property were elucidated using photoluminescence spectra, X-ray diffraction, thermal imaging and thermoelectric experiments. With the increase of x, the supramolecular system can be changed from lamellar structure to hexagonal columnar structure. Moreover, the P4VP(CN-DBE)_x polymer with columnar structure exhibits more efficient photothermal effect. The temperature of P4VP(CN-DBE)_0.6 can rise to 130 °C within 10 s under the irradiation of ultraviolet lamp. In addition, the supramolecular system possesses unique photo-thermo-electric conversion ability, and 25 mA current can be detected in the circuit coupled with the thermoelectric module. This work broadens the potential applications of hydrogen-bonded polymer, and provides a simple and facile strategy to prepare liquid crystalline polymers with photo-thermo-electric property.

Perylene Bisimide-Based Luminescent Liquid Crystals with Tunable Solid-State Light Emission

Perylene bisimides are among the most studied building blocks for supramolecular assemblies in the fabrication of optoelectronic devices for their exceptional optical and electronic properties; however, developing perylene bisimide-based luminescent liquid crystals remains a challenge for the strong π-stacking tendency of the large planar aromatic core to quench the emission. We here reported a novel strategy to achieve luminescent liquid crystals based on perylene bisimides by introducing a conformation-adjustable core to control the molecular stacking arrangement of planar perylene bisimides in the solid state. The emission wavelength is in the deep-red region with a luminescence efficiency of up to 10%. Fluorescence properties of the liquid crystals can be further regulated by photoisomerization-induced structural evolution from columnar to lamellar mesophases. These luminescent liquid crystals are also able to not only exhibit strong emission at high temperatures but also show attractive thermochromic luminescence tuning behaviors. This work provides a new strategy for the design and development of novel solid-state luminescent materials with potential for various optoelectronic applications.