Developing materials that simultaneously exhibit high stability, high brightness, and a large dissymmetry factor (glum) for circularly polarized luminescence (CPL) is crucial for advancing the field of chiral optics, however, it remains a significant challenge.
Circularly polarized luminescence (CPL), a manifestation of molecular chirality in the excited state, holds great potential for next-generation photonic technologies such as high-efficiency 3D displays and secure information encryption. The pursuit of materials with a high luminescence dissymmetry factor (glum) is therefore a central goal in recent years. Over past few years, numerous CPL materials with high glum value have been developed. Embedding emitters in cholesteric liquid crystal (CLC) hosts is an effective strategy to achieve near-theoretical glum values.
Recently, we have developed a series of CLC materials. For example, we designed and constructed a long-lived room-temperature phosphorescent (RTP) polymer-doped chiral helical superstructure system, exhibiting a distinct green afterglow with a glum value of 1.49 (Advanced Functional Materials 2023, 2306834). Moreover, a bilayered film comprising a RTP layer and a molecular motor-doped soft helical superstructure layer were fabricated (Angewandte Chemie International Edition 2024, 63, e202319536). By regulating the photoisomerization of the molecular motor through UV irradiation and temperature, the photonic bandgap of the soft helical superstructure was remotely and precisely regulated, ultimately achieving dynamic and reversible modulation of glum between 0.6 and 1.38. Next, we have further developed a bilayer assembly integrating a photoactivated afterglow film with the selective reflection of CLC, achieving a multicolor afterglow with glum value up to 1.6 (Advanced Functional Materials 2025, 35, 2424404).
Nevertheless, this approach is fundamentally hampered by phase instability and a requisite ≥50% photon loss via polarization filtering, precluding the simultaneous realization of high stability, brightness, and dissymmetry. To date, less attention has been paid on the study of robust emissive CLC system. A standard strategy to impart this necessary stability is through in-situ polymerization, locking the ordered structure into a durable polymer network. However, the act of polymerization intended to create a robust material often generates network stress that catastrophically disrupts the delicate helical order. There is therefore an urgent demand to elucidate the underlying mechanism of network stress and fabricate structurally robust CLC polymer networks.
Herein, we directly confront this challenge by establishing principles through a synergistic strategy that combines rational molecular engineering with network design. Through a systematic investigation of three tailored emissive liquid crystal monomers, we have demonstrated that the preservation of high glum value during the critical transition from a fluidic assembly to a crosslinked polymer network is not a matter of chance, but a direct consequence of rational molecular and topological co-design (Fig. 1).
The key advances in this work are reported as the following:
- A series of fluorene-based liquid crystal monomers were designed to systematically study the effects of core planarity and linker flexibility. The key findings reveal that an optimal synergy between intrinsic molecular planarity and segmental linker flexibility (as embodied in monomer FC6) is crucial for forming a nearly ideal pre-polymerized helical superstructure with an exceptional glum of 0.60.
- The effect of the crosslinker and network stress on the ordered structure of CLC in the crosslinking process was examined. A multi-functional crosslinker induces catastrophic stress, shattering the chiral architecture, causing the glum to drop sharply to 0.03. Notably, a flexible, linear crosslinker that is topologically compatible with the LC template can gently solidify the network, preserving its exquisite LC chiral order. Moreover, the resulting robust CLC network film maintains a high glum value of 0.54 while simultaneously achieving excellent solvent resistance, thermal stability and electric-field stability.
Look into the future, our rational strategy not only provides a powerful paradigm for the rational design of next-generation CPL-active materials but also deepens our fundamental understanding of how to control and permanently capture supramolecular chirality in functional polymeric systems for advanced photonic applications.
More details can be found in our paper " Achieving robust cholesteric liquid crystal polymer networks with high luminescence dissymmetry factor" published in Nature Communications.