Temperature-Dependent Circularly Polarized Luminescence Measurement Using KBr Pellet Method

Contrasting Mechanochromic Luminescence of Enantiopure and Racemic Pyrenylprolinamides: Elucidating Solid-State Excimer Orientation by Circularly Polarized Luminescence

Circularly polarized luminescence (CPL) and mechanochromic luminescence (MCL) have independently made substantial progress in recent years. However, the exploration of MCL in solid-state CPL materials, which holds practical significance, is still in its infancy. Herein, we report the MCL properties of readily accessible chiral pyrenylprolinamides bearing tert-butoxycarbonyl (Boc) or 2,2,2-trichloroethoxycarbonyl (Troc) groups. Enantiopure crystals of the Boc derivative display a greater MCL wavelength shift than racemic crystals, while the Troc derivative exhibit the opposite trend. Most notably, the enantiopure crystals show mechanochromic CPL. Unlike in previous examples, where CPL is quenched upon amorphization, robust CPL spectra were observed even in the amorphous states. By applying the excimer chirality rule, we have, for the first time, acquired insights into the excited-state structures within mechanically generated amorphous states. These findings offer a novel design strategy for developing mechanochromic CPL materials, paving the way for the future advancements in this emerging field.

From synthesis to chiroptical activities: advancements in circularly polarized luminescent inorganic quantum dots

Circularly polarized luminescence (CPL) in inorganic quantum dots (QDs) represents a burgeoning and dynamic research domain, offering immense potential across a spectrum of applications, including three-dimensional displays, optical data storage, asymmetric catalysis, and chiral sensing. However, the persistent trade-off between fluorescence brightness and the emission dissymmetry factor highlights the nascent stage of current research. This review delves into the synthesis methodologies of CPL QDs, providing an exhaustive analysis of existing approaches and the resulting material properties. It elucidates the critical factors influencing CPL characteristics, such as ligand types, interaction modes, and QD architectures. Furthermore, it synthesizes the theoretical frameworks underlying chirality and CPL generation, ranging from time-dependent density functional theory (TDDFT) to ab initio molecular dynamics (AIMD), thereby deepening the understanding of CPL mechanisms within QDs. The review culminates with a comprehensive exploration of potential applications, alongside a forward-looking perspective on the future trajectory of CPL QD research.

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.

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.

Fundamentals, Advances, and Artifacts in Circularly Polarized Luminescence (CPL) Spectroscopy

Objects are chiral when they cannot be superimposed with their mirror image. Materials can emit chiral light with an excess of right- or left-handed circular polarization. This circularly polarized luminescence (CPL) is key to promising future applications, such as highly efficient displays, holography, sensing, enantiospecific discrimination, synthesis of drugs, quantum computing, and cryptography. Here, a practical guide to CPL spectroscopy is provided. First, the fundamentals of the technique are laid out and a detailed account of recent experimental advances to achieve highly sensitive and accurate measurements is given, including all corrections required to obtain reliable results. Then the most common artifacts and pitfalls are discussed, especially for the study of thin films, for example, based on molecules, polymers, or halide perovskites, as opposed to dilute solutions of emitters. To facilitate the adoption by others, custom operating software is made publicly available, equipping the reader with the tools needed for successful and accurate CPL determination.

Circularly Polarized Photoluminescence of Chiral 2D Halide Perovskites at Room Temperature

Chiral halide perovskites have attracted considerable attention because of their chiroptical, second-harmonic generation, and ferroelectricity properties and their potential application in chiroptoelectronics and chiral spintronics. However, the fundamental research of these properties is insufficient. In this work, chiral perovskites were synthesized using precursor solutions with various stoichiometric ratios ⟨n⟩. The chiral perovskite film prepared from the solution with ⟨n⟩ = 1 is composed of (R-/S-/rac-MBA)₂PbBr₄, whereas the films prepared from the solutions with ⟨n⟩ larger than 1 are a mixture of (R-/S-/rac-MBA)₂(CsMA)_n-1Pb_nBr_3n+1 with n = 1 and large n values. A photoluminescence quantum yield of approximately 90 was obtained. Symmetric circular dichroism (CD) spectra were observed without an external magnetic field. Under various magnetic fields, magnetic field-induced CD features are superimposed with the intrinsic chirality-induced CD features. For the ⟨n⟩ = 1 chiral perovskite film, the energy level splitting induced by chiral molecules are a few 10 μeV, whereas the energy level splitting induced by magnetic fields are at the range of ∼-250 to ∼250 μeV. Circularly polarized photoluminescence spectra were observed at room temperature and associated with the spin-preserved energy funneling from highly energetic phases to the lower energetic phases.

Gelation behavior and supramolecular chirality of a BTA derivative in a deep eutectic solvent

As novel solvents, deep eutectic solvents (DESs) are non-toxic, easily producible and biocompatible, which is attractive for eutectogel fabrication. In this work, a benzene 1,3,5-tricarboxamide (BTA) derivative (substituted by three hexanoic acid) was selected to prepare a supramolecular gel in a suitable DES composed of choline chloride and phenylacetic acid molecules. The obtained eutectogel exhibited higher stability than that produced in conventional solvents. The gel microstructure was composed of spiral fiber networks as confirmed from atomic force microscopy and scanning electron microscopy observations. Macroscopic chirality was therefore recognized by the circular dichromatic spectrum, though such a supramolecular chiral signal was random. To explore the gelation mechanism, the effect of BTA derivative molecular structure change was systematically investigated. With the help of Fourier transform infrared spectroscopy and powder X-ray diffraction, the gel formation was attributed to the π-π stacking of adjacent BTA molecules and the three-fold hydrogen bond between amide groups or the hydrogen bond between carboxylic groups. Furthermore, the directional hydrogen bonds between BTA and solvent molecules induced their aggregate to form one-dimensional fibers, which were either left- or right-handed. The obtained results not only extend the gel systems in DESs, but also help design the supramolecular chirality from non-chiral molecules.

Tunable Circularly Polarized Luminescence from Single Crystal and Powder of the Simplest Tetraphenylethylene Helicate

Tetraphenylethylene and its derivatives are a class of aggregation-induced emission (AIE) compounds that are most extensively and successfully studied. It has been found that the simplest TPE is easy to crystallize into homochiral M crystals or P crystals. However, no research on circularly polarized luminescence (CPL) of TPE solid is documented. In this paper, we report that TPE can grow into big and nonefflorescent single crystals in single helical conformation and has large birefringence that is comparative with commercially available products. The TPE single crystals can emit strong CPL with a very high g_lum value up to 0.53. Moreover, the sense and magnitude of CPL signals can be willfully tuned by simple rotation of the single crystal due to anisotropy of the crystals. This simple and promising CPL photonic material integrates emission, chirality, and birefringence together in one single crystal without needing an additional chiral dopant or conjugate polymer that can produce linearly polarized light. After being ground into fine powder and pressed as KBr pellets, the obtained nanocrystals of TPE also emit strong CPL light. Exceptionally, by mixing other achiral luminescent dyes together with TPE powder in KBr pellets, induced CPL signals were obtained, which could give full-color CPL emission. Although there were no interactions between TPE and the dyes in the pellets, induced CPL signals were realized through radiative energy transfer, providing a very simple method for the tuning of CPL emission.