Yutao Sang obtained his B.Sc. and M.Sc. degrees in chemistry from Qingdao University, China. In 2016, he enrolled on a Ph.D. course at the Institute of Chemistry, Chinese Academy of Sciences (ICCAS), under the supervision of Prof. Minghua Liu, where he is currently in his third year. His ongoing research includes supramolecular chirality, chiroptical materials, and symmetry breaking of achiral molecules in gels and related systems. Pengfei Duan received his Ph.D. degree from the Institute of Chemistry, Chinese Academy of Sciences (CAS) in 2011 with Prof. Minghua Liu on chiral selfassembly in colloid and interface chemistry. He was a postdoctoral research fellow with Prof. Nobuo Kimizuka at Kyushu University, working on photon upconversion in self-assembled systems. In 2015, he became a professor at the National Center for Nanoscience and Technology (NCNST). His current research interests focus on photochemistry and photophysics in chiral supramolecular systems.

Amplification of circularly polarized luminescence (CPL) is demonstrated in a triplet-triplet annihilation-based photon upconversion (TTA-UC) system. When chiral binaphthyldiamine acceptors are sensitized with an achiral Pt(II) octaethylporphine (PtOEP) in solution, upconverted circularly polarized luminescence (UC-CPL) were observed for the first time, in which the positive or negative circularly polarized emission could be obtained respectively, following the molecular chirality of the acceptors (R/S). More interestingly, one order of magnitude amplification of the dissymmetry factor g in UC-CPL was obtained in comparison with the normal promoted CPL. The multistep photophysical process of TTA-UC including triplet-triplet energy transfer (TTET) and triplet-triplet annihilation (TTA) have been suggested to enhance the UC-CPL, which provided a new strategy to design CPL materials with a higher dissymmetry factor.

Circularly polarized luminescent (CPL) materials are currently attracting great interest. While a chiral building is usually necessary in order to obtain CPL materials, here, this study proposes a general approach for fabricating 1D circularly polarized luminescent nanoassemblies from achiral aromatic molecules or aggregation-induced emissive compounds (AIEgens). It is found that a C symmetric chiral gelator can individually form hexagonal nanotube structures and encapsulate the guest molecules. When achiral AIEgens are encapsulated into the confined nanotubes via organogelation, the AIEgens will emit circularly polarized luminescence. Further, the direction of the CPL could be controlled by the supramolecular chirality of the nanotube. Remarkably, the approach is universal and various kinds of the AIEgens can be doped to show such property, providing a full-color-tunable circularly polarized luminescence.

Conspectus Chiral functional materials with circularly polarized luminescence (CPL) have risen rapidly in recent years because of their fascinating characteristics and potential applications in various research fields. CPL refers to the differential spontaneous emission of left (L)- and right (R)-handed circularly polarized light upon photon or electron excitation. Generally, an outstanding CPL-active material needs to possess a high luminescence dissymmetry factor (g lum) (defined as 2­(I L – I R)/(I L + I R) where I is the emission intensity), which is between −2 and +2. Although the exciting development in CPL-active materials was achieved, the modulation of CPL signs is still a challenge. For small organic systems, a relatively small g lum value, one of the key parameters of CPL, limits their practical applications. Searching for efficient approaches for amplifying g lum is important. Therefore, over the past decades, besides optimizing the structure of small molecules, many other strategies to obtain efficient CPL-active materials have been developed. For instance, self-assembly has been well demonstrated as an effective approach to amplify the supramolecular chirality as well as the g lum values. On the other hand, chiral liquid crystals (CLCs), which are capable of selective reflection of left- and right-handed circularly polarized light, also to serve as a host matrix for endowing guest emitters with CPL activity and high g lum values. However, self-assembly focuses on modulating the conformation and spatial arrangement of chiral emitters. And the CPL of a luminophore-doped CLC matrix depends on the helix pitch and band gap positions. Lately, novel photophysical approaches to modulate CPL signs have gradually emerged. In this Account, we discuss the recent progress of excited-state-regulation involved CPL-active materials. The emergence, amplification, and inversion of CPL can be adjusted through regulation of the excited state of chiral emitters. For example, Förster resonance energy transfer (FRET) can amplify the g lum values of chiral energy acceptors in chiral supramolecular assemblies. By combining the concepts of photon upconversion and CPL, high-energy upconverted circularly polarized emission was achieved under excitation of low-energy light, accompanied by an amplified g lum. In addition, the organic systems with unpaired electrons, i.e., charge transfer (CT) system and open-shell π-radical, show favorable CPL properties, which can be flexibly tuned with an applied magnetic field. It should be noted that these photophysical process are associated with the excited state of chiral emitters. So far, while the main focus is on the regulation of the molecular and supramolecular nanostructures, direct regulation of the excited state of the chiral system will serve as a new platform to understand and regulate the CPL activity and will be helpful to develop smart chiroptical materials.

Achieving al arge dissymmetry factor (g lum )i s ac hallenge in the field of circularly polarized luminescence (CPL). Ac hiral charge-transfer (CT) system consisting of chiral electron donor and achiral electron acceptor shows bright circularly polarized emission with large g lum value.T he chiral emissive CT complexes could be fabricated through various approaches,s uch as grinding,c rystallization, spin coating,a nd gelatinization, by simply blending chiral donor and achiral acceptor.T he structural synergy originating from p-p stacking and strong CT interactions resulted in the longrange ordered self-assembly,enabling the formation of supramolecular gels.B enefiting from the large magnetic dipole transition moment in the CT state,t he CPL activity of CT complexes exhibited large circular polarization. Our design strategy of the chiral emissive CT complexes is expected to help the development of new molecular engineering strategies for designing highly efficient CPL-active materials.

By blending a chiral acceptor and a sensitizer into a nematic liquid crystal, a chiral nematic liquid crystal showing amplified upconverted circularly polarized luminescence could be obtained.

Photosensitive cinnamic acid conjugated glutamides were designed to demonstrate photocontrolled hierarchical chirality transfer and switching in self‐assembled systems. In methanol, the cinnamic acid derivatives self‐assembled into superhelices, which could be switched into nanokebabs upon UV irradiation. These two nanostructures showed opposite helicity. The chiral nanostructures could further convey their chirality to achiral fluorescent molecules and result in the emission of circularly polarized luminescence (CPL). Remarkably, the CPL followed the helicity of the chiral nanostructure rather than the inherent molecular chirality. Photodriven dimerization of the cinnamic moiety lead to a significant change in molecular packing and subsequent switching of the helicity of the formed nanostructures.

Chiral optical materials based on circularly polarized luminescence (CPL) have emerged rapidly due to their feasible applications in diverse fields of research. However, limited to the small luminescence dissymmetry factor (glum), real application examples have rarely been reported. Here, we present a complex system, which show intense circularly polarized ultraviolet luminescence (CPUVL) with large glum value, enabling a chiral UV light triggered enantioselective polymerization. By integrating sensitized triplet-triplet annihilation upconversion and CPL, both visible-to-UV upconversion emission and upconverted circularly polarized ultraviolet luminescence (UC-CPUVL) were obtained in the systems, built of chiral annihilator R(S)-4,12-biphenyl[2,2]paracyclophane (R-/S-TP), and a thermally activated delayed fluorescence (TADF) sensitizer. After dispersing this upconversion system into room-temperature nematic liquid crystal, induced chiral nematic liquid crystal could significantly amplify the glum value (0.19) of UC-CPUVL. Further, the UC-CPUVL emission has been used to trigger the enantioselective photopolymerization of diacetylene. This work paves the way for the further development of functional application of CPL active materials.