Circularly polarized luminescence based on cholesterol-tetraphenylethylene-perylene liquid crystal

Advances in chiral luminescent liquid crystals (CLLCs): from molecular design to applications

Research on circularly polarized luminescent (CPL) materials has evolved into a hot research topic because of their potential application prospects in the optoelectronics and chiroptical fields. Achieving a high glum value and high quantum efficiency is essential and challenging in CPL research. To date, various material design strategies, such as chiral organic small molecules, CPL polymers, chiral lanthanide complexes, chiral liquid crystals and supramolecular self-assembly, have been proposed to achieve a CPL emitter with a high glum value. Among them, chiral luminescent liquid crystals (CLLCs) are recognized as a key approach for achieving CPL materials with a high glum factor owing to their exceptional optical properties and flexibility. In this review, we focused on the various synthesis methods employed for developing CLLCs, their properties and their potential applications. The synthesis section discusses various approaches employed to design chiral luminescent liquid crystals, including (i) doping systems for incorporating chiral dopants into achiral liquid crystalline hosts and (ii) nondoping methods for preparing AIE active chiral luminescent liquid crystalline materials. The section on properties highlights how chirality influences the optical, electronic and structural characteristics of CLLCs. Finally, we discuss the diverse applications of CLLCs from photonics and chiral switching to optoelectronic devices and beyond. This review provides new insights into recent research developments and future opportunities in this booming research field. We anticipate that this review could offer a clear picture of the interesting properties of chiral luminescent liquid crystal materials and inspire more researchers to work in this potential area.

Real-Time Observation of Ultrafast Concerted Dynamics between Energy and Chirality Transfer by Femtosecond Time-Resolved Circular Polarization Luminescence Spectroscopy

Elucidating the underlying mechanism of effective chirality and energy transfer processes observed in biological assemblies has cross-disciplinary significance, and it is of special interest in the fields of chemistry and biology due to the pivotal role of chirality in life. Challenges in the field include how to achieve real-time monitoring of the chirality and energy transfer dynamics simultaneously, as well as how to distinguish whether these processes take place in the ground or excited state. Herein, we achieve the first attempt at real-time observation of the concerted ultrafast dynamics between the Förster resonance energy transfer (FRET) and the generation of circularly polarized luminescence (CPL) in the excited state in near-infrared CPL supramolecular nanofibers (SNFs) by using femtosecond time-resolved circularly polarized luminescence (fs-TRCPL) spectroscopy. Our findings reveal a cooperative interplay between FRET and CPL emission, unfolding over time scales from several to hundreds of picoseconds. Notably, we identify that the pivotal mechanism leading to a 0.045 glum value in SNFs is the difference in the FRET rates between left- and right-handed circularly polarized emission channels, which is a reason beyond the well-known relationship of the electronic and magnetic dipoles. Our results not only shed light on the understanding of the chirality transfer mechanism in the excited states but also pave the road for the development of novel CPL materials in the future.

Functionalized Fluorescent Organic Nanoparticles Based AIE Enabling Effectively Targeting Cancer Cell Imaging

We report a fluorescent dye TM by incorporating the tetraphenylethylene (TPE) and cholesterol components into perylene bisimides (PBI) derivative. Fluorescence emission spectrum shows that the dye has stable red emission and aggregation-induced emission (AIE) characteristics. The incorporation of cholesterol components triggers TM to show induced chirality through supramolecular self-assembly. The cRGD-functionalized nanoparticles were prepared by encapsulating fluorescent dyes with amphiphilic polymer matrix. The functionalized fluorescent organic nanoparticles exhibit excellent biocompatibility, large Stokes' shift and good photostability, which make them effective fluorescent probes for targeting cancer cells with high fluorescence contrast.

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.