Regulating the Excited State Chirality to Fabricate High-Performance-Solid-State Circularly Polarized Luminescence Materials

Tunable circularly polarized luminescence behaviors caused by the structural symmetry of achiral pyrene-based emitters in chiral co-assembled systems

The regulation of circularly polarized luminescence (CPL) behavior is of great significance for practical applications. Herein, we deliberately designed three achiral pyrene derivatives (Py-1, Py-2, and Py-3) with different butoxy-phenyl substituents and the chiral binaphthyl-based inducer (R/S-B) with anchored dihedral angle to construct chiral co-assemblies, and explored their induced CPL behaviors. Interestingly, the resulting co-assemblies demonstrate tunable CPL emission behaviors caused by the structural symmetry effect of achiral pyrene-based emitters during the chiral co-assembly process. And in spin-coated films, the dissymmetry factor (gem) values were 9.1 × 10-3 for (R/S-B)1-(Py-1)10, 5.6 × 10-2 for (R/S-B)1-(Py-2)7, and 8.6 × 10-4 for (R/S-B)1-(Py-3)1, respectively. The strongest CPL emission (|gem| = 5.6 × 10-2, λem = 423 nm, QY = 34.8 %) was detected on (R/S-B)1-(Py-2)7 due to the formation of regular and ordered helical nanofibers through the strong π-π stacking interaction between the R/S-B and the achiral Py-2 emitter. The strategy presented here provides a creative approach for progressively regulating CPL emission behaviors in the chiral co-assembly process.

Dual-Stimuli-Responsive Turn-On Luminescence of Chiral Bisimidazolyl BINOL Dimethyl Ether Crystals

Stimuli-responsive organic luminescent crystals have attracted significant attention in recent years for their potential in sensor and memory applications. While turn-on luminescence is superior in detection sensitivity compared with turn-off luminescence, the development of organic crystals that exhibit turn-on luminescence in response to multiple stimuli remains a significant challenge. Herein, the crystals of chiral bisimidazolyl 1,1'-bi-2-naphthol (BINOL) dimethyl ether have exhibited a dual-stimuli-responsive turn-on luminescence based on two distinct mechanisms. In the crystalline state, luminescence was substantially quenched by the intermolecular hydrogen bonds between the imidazole rings. Mechanical stimulation induced a transition to a blue-violet-emissive amorphous state. In contrast, thermal stimulation produced an orange luminescence, attributed to excited-state intramolecular proton transfer (ESIPT) luminescence from thermally demethylated products. Furthermore, the thermally induced state exhibited circularly polarized luminescence (CPL), marking a rare instance of stimuli-responsive turn-on CPL in a solid-state system. This study provides new insights into environmental and structural factors for solid-state luminescent properties and advances the design guidelines for multifunctional luminescent sensors.

Aggregation-induced generation of circularly polarized luminescence in naphthaleneimide-based nanostructures with high dissymmetry factor

Extensive efforts have been dedicated towards designing new organic materials that display solid-state fluorescence and possess optical activity, thereby leading to the fabrication of materials emitting circularly polarized light. Existing organic materials usually suffer from two limitations, a low dissymmetry factor (glum) and weak or no fluorescence in the solid state. Herein, we have demonstrated a naphthalene imide-based dyad system that remains fluorescent even in powder form and displays circularly polarized luminescence in its aggregated and solid state with significantly high glum values.

From individuals to families: design and application of self-similar chiral nanomaterials

Establishing an intimate relationship between similar individuals is the beginning of self-extension. Various self-similar chiral nanomaterials can be designed using an individual-to-family approach, accomplishing self-extension. This self-similarity facilitates chiral communication, transmission, and amplification of synthons. We focus on describing the marriage of discrete cages to develop self-similar extended frameworks. The advantages of utilizing cage-based frameworks for chiral recognition, enantioseparation, chiral catalysis and sensing are highlighted. To further promote self-extension, fractal chiral nanomaterials with self-similar and iterated architectures have attracted tremendous attention. The beauty of a fractal family tree lies in its ability to capture the complexity and interconnectedness of a family's lineage. As a type of fractal material, nanoflowers possess an overarching importance in chiral amplification due to their large surface-to-volume ratio. This review summarizes the design and application of state-of-the-art self-similar chiral nanomaterials including cage-based extended frameworks, fractal nanomaterials, and nanoflowers. We hope this formation process from individuals to families will inherit and broaden this great chirality.

Boosting Circularly Polarized Luminescence from Alkyl-Locked Axial Chirality Scaffold by Restriction of Molecular Motions

Boosting the circularly polarized luminescence of small organic molecules has been a stubborn challenge because of weak structure rigidity and dynamic molecular motions. To investigate and eliminate these factors, here, we carried out the structure-property relationship studies on a newly-developed axial chiral scaffold of bidibenzo[b,d]furan. The molecular rigidity was finely tuned by gradually reducing the alkyl-chain length. The environmental factors were considered in solution, crystal, and polymer matrix at different temperatures. As a result, a significant amplification of the dissymmetry factor glum from 10-4 to 10-1 was achieved, corresponding to the situation from (R)-4C in solution to (R)-1C in polymer film at room temperature. A synergistic strategy of increasing the intramolecular rigidity and enhancing the intermolecular interaction to restrict the molecular motions was thus proposed to improve circularly polarized luminescence. The though-out demonstrated relationship will be of great importance for the development of high-performance small organic chiroptical systems in the future.

Structurally Diverse Pyrene-decorated Planar Chiral [2,2]Paracyclophanes with Tunable Circularly Polarized Luminescence between Monomer and Excimer

We reported the synthesis of a series of structurally diverse CPL-active molecules, in which pyrene units were installed to chiral pm/po-[2,2]PCP scaffolds either with or without a triple bond spacer for pm/po-PCP-P1 and pm/po-PCP-P2, respectively. The X-ray crystallographic analyses revealed that these pyrene-based [2,2]PCP derivatives exhibited diverse structures and crystal packings in the solid phases. The pyrene-based [2,2]PCP derivatives exhibit various (chir)optical properties in organic solutions, depending on their respective structures. In a mixture of dioxane and water, pm/po-PCP-P1 emit green excimer fluorescence, whereas pm/po-PCP-P2 emit blue one. The chiroptical investigation demonstrated that Rp-pm-PCP-P1 and Rp-pm-PCP-P2 exhibited completely opposite CD and CPL signals even they possess the same chiral Rp-[2,2]PCP core. The same argument also holds for other chiral pyrene-based [2,2]PCP derivatives. The theoretical calculation revealed that these unusual phenomena were attributed to different orientation between transition electric dipole moments and the magnetic dipole moments originating from the presence or absence of a triple bond spacer. These pyrene-based [2,2]PCP derivatives display various colours and fluorescence emissions in the solid state and PMMA films, possibly due to the different packings as observed in the crystal structure. Moreover, these compounds also can interact with perylene diimide through π-π interactions, leading to near-white fluorescence.

Dynamically stable and amplified circularly polarized excimer emission regulated by solvation of chiral co-assembly process

Chiral supramolecular assembly has been assigned to be one of the most favorable strategies for the development of excellent circularly polarized luminescent (CPL)-active materials. Herein, we report our study of an achiral boron-containing pyrene (Py)-based chromophore (PyBO) as a circularly polarized excimer emission (CPEE) dye induced by chiral co-assemblies containing chiral binaphthyl-based enantiomers (R/S-M). Chiral co-assembly R/S-M-(PyBO)₄ fresh film spin-coated from toluene solution can exhibit orderly nanofibers and strong green CPEE (λ_em = 512 nm, g_em = ±0.45, Φ_FL = 51.2 %) resulting from an achiral PyBO excimer. In contrast, only a very weak blue CPL was observed (λ_em = 461 nm, g_em = ±  0.0125, Φ_FL = 19.0 %) after 187 h due to PyBO monomer emission as spherulite growth. Interestingly, this kind of chiral co-assembly R-M-(PyBO)₄-T film from tetrahydrofuran (THF) solution retains uniform morphology and affords the most stable and strongest CPEE performance (λ_em = 512 nm, g_em = + 0.62, Φ_FL = 53.3 %) after 10 days.

Chiral supramolecular assembly is an important strategy for the development of excellent circularly polarized luminescent (CPL)-active materials, but often they suffer from low quantum yield and luminescence dissymmetry factor. Herein, the authors we report a chiral coassembly process of achiral pyrene-based dyes leading to chiral excimers emitting with a high dissymmetry factor.