Porous Interdigitation Molecular Cage from Tetraphenylethylene Trimeric Macrocycles That Showed Highly Selective Adsorption of CO2 and TNT Vapor in Air

The Designs and Applications of Tetraphenylethylene Macrocycles and Cages

Macrocycles and cages are very attractive for the development of functional materials due to their unique inner cavities. Building blocks with interesting functions and synthetic conveniences are especially attractive. Tetraphenylethylene (TPE) is such an entity with C2 symmetry and tetrakis-functional groups easily modifiable. As a typical aggregation-induced emission (AIE) active compound, TPE perfectly unites the functions of fluorescence and structural building blocks together. The unique marriage of the two roles into one component makes TPE an ideal platform for the development of functional molecular systems including macrocycles and cages. The TPE macrocycles and cages are not merely a simple combination of those two but also generate added values unseen in either component alone. The fluorescence properties of TPE in macrocycles/cages are greatly improved or modulated, which makes them more suitable for various applications compared to their linear counterparts. In this review, the chemistry and design principles of TPE macrocycles/cages are surveyed first. The unique properties of those compounds are also discussed to provide general guidance for their functionalization. A brief discussion of their applications focusing on the utilization of their unique fluorescence is also presented. In the last, outlooks and future perspectives of TPE macrocycles/cages are provided for further developments.

Shape-Persistent Tetraphenylethylene Macrocycle: Highly Efficient Synthesis and Circularly Polarized Luminescence

Circularly polarized luminescence (CPL) is an emerging field with significant applications in molecular electronics, optical materials, and chiroptical sensing. Achieving efficient CPL emission in organic systems remains a major challenge, particularly in the development of materials with high fluorescence quantum yields (ΦF) and large luminescence dissymmetry factors (glum). Herein, we report the efficient synthesis of shape-persistent tetraphenylethylene macrocycles and investigate its potential as a CPL material. Chiral side chains were introduced to induce chiroptical properties. The macrocycles and their properties were characterized using NMR, MALDI-TOF MS, FT-IR, TGA, DSC, UV-Vis spectroscopy, SEM, fluorescence spectroscopy, ECD, and CPL. A significant fluorescence enhancement was observed upon aggregation, demonstrating a typical aggregation-induced emission (AIE) behavior. Moreover, one of the macrocycles in the solid state displayed distinct CPL emission with a high glum of 2 × 10-2 and a ΦF value reaching 60%, and exhibited aggregation-induced circularly polarized luminescence (AICPL). These findings highlight the advantage of using a macrocycle with a noncollapsible backbone for the design of organic systems with CPL property, offering promising applications in chiroptical materials.

Preparation of Langmuir-Blodgett Films from Quinoxalines Exhibiting Aggregation-Induced Emission and Their Acidochromism

The development of aggregation-induced emission (AIE)-exhibiting compounds heavily relies on our evolving comprehension of their behavior at interfaces, an understanding that still remains notably limited. In this study, we explored the preparation of two-dimensional (2D) sensing films from 2,3-diphenylquinoxaline-based diazapolyoxa- and polyazamacrocycles displaying AIE via the Langmuir-Blodgett (LB) technique. This systematic investigation highlights the key role of the heteroatom-containing tether of 2,3-diphenylquinoxalines in the successful fabrication of Langmuir layers at the air-water interface and the transfer of AIE-emitting supramolecular aggregates onto solid supports. Using both diazapolyoxa- and polyazamacrocycles, we prepared AIE-exhibiting monolayer films containing emissive supramolecular aggregates on silica, mica, and quartz glass and characterized them using ultraviolet-visible (UV-vis) and photoluminescence (PL) spectroscopies, atomic force microscopy (AFM) imaging, and fluorescence microscopy. We also obtained multilayer AIE-emitting films through the LB technique, albeit with increased complexity. Remarkably, by employing the smallest macrocycle N2C3Q, we successfully prepared LB films suitable for the visual detection of acidic vapors. This sensing material, which contains a much lesser amount of organic dye compared with traditional drop-cast films, can be regenerated and utilized for real-life sample analysis, such as monitoring the presence of ammonia in the air and the freshness of meat.

Quinoxaline-based azamacrocycles: synthesis, AIE behavior and acidochromism

The development of luminescent molecular materials has advanced rapidly in recent decades, primarily driven by the synthesis of novel emissive compounds and a deeper understanding of excited-state mechanisms. Herein, we report a streamlined synthetic approach to light-emitting diazapolyoxa- and polyazamacrocycles N2CnOxQ and NyCnQ (n = 3-10; x = 2, 3; y = 2-5), incorporating a 2,3-diphenylquinoxaline residue (DPQ). This synthetic strategy based on macrocyclization through Pd-catalyzed amination reaction yields the target macrocycles in good or high yields (46-92%), enabling precise control over their structural parameters. A key role of the PhPF-tBu ligand belonging to the JosiPhos series in this macrocyclization was elucidated through DFT computation. This macrocyclization reaction eliminates the need for complex protecting-deprotecting procedures of secondary amine groups, offering a convenient and scalable method for the preparation of target compounds. Moreover, it boasts a potentially broad substrate scope, making it promising for structure-properties studies within photophysics, sensor development, and material synthesis. Photophysical properties of representative macrocycles were investigated, employing spectroscopic techniques and DFT computation. It was demonstrated that DPQ-containing macrocycles display aggregation-induced emission in a DCM-hexane solvent mixture despite the presence of flexible tethers within their structures. Single-crystal X-ray diffraction analysis of a representative compound N2C8O3Q allowed us to gain deeper insight into its molecular structure and AIE behaviour. The emissive aggregates of the N2C10O3Q macrocycle were immobilized on filter paper yielding AIE-exhibiting test strips for measuring acidity in vapors and in aqueous media.

A Highly Efficient Fluorescent Sensor Based on AIEgen for Detection of Nitrophenolic Explosives

The detection of nitrophenolic explosives is important in counterterrorism and environmental protection, but it is still a challenge to identify the nitroaromatic compounds among those with a similar structure. Herein, a simple tetraphenylethene (TPE) derivative with aggregation-induced emission (AIE) characteristics was synthesized and used as a fluorescent sensor for the detection of nitrophenolic explosives (2, 4, 6-trinitrophenol, TNP and 2, 4-dinitrophenol, DNP) in water solution and in a solid state with a high selectivity. Meanwhile, it was found that only hydroxyl containing nitrophenolic explosives caused obvious fluorescence quenching. The sensing mechanism was investigated by using fluorescence titration and ¹H NMR spectra. This simple AIE-active probe can potentially be applied to the construction of portable detection devices for explosives.

Recent Advances in the Synthesis and Applications of Nitrogen-Containing Macrocycles

Macrocyclic nitrogen-containing compounds are versatile molecules. Supramolecular, noncovalent interactions of these macrocycles with guest molecules enables them to act as catalysts, fluorescent sensors, chiral or nonchiral selectors, or receptors of small molecules. In the solid state, they often display a propensity to form inclusion compounds. All of these properties are usually closely connected with the presence of nitrogen atoms in the macrocyclic ring. As most of the reviews published so far on macrocycles were written from the viewpoint of functional groups, synthetic methods, or the structure, search methods for literature reports in terms of the physicochemical properties of these compounds may be unobvious. In this minireview, the emphasis was put on the synthesis and applications of nitrogen-containing macrocyclic compounds, as they differ from their acyclic analogs, and at the same time are the driving force for further research.

Reticular Chemistry in the Construction of Porous Organic Cages

Reticular chemistry offers the possibility of systematic design of porous materials with different pores by varying the building blocks, while the emerging porous organic cage (POC) system remains generally unexplored. A series of new POCs with dimeric cages with odd-even behaviors, unprecedented trimeric triangular prisms, and the largest recorded hexameric octahedra have been prepared. These POCs are all constructed from the same tetratopic tetraformylresorcin[4]arene cavitand by simply varying the diamine ligands through Schiff-base reactions and are fully characterized by X-ray crystallography, gas sorption measurements, NMR spectroscopy, and mass spectrometry. The odd-even effects in the POC conformation changes of the [2 + 4] dimeric cages have been confirmed by density functional theory calculations, which are the first examples of odd-even effects reported in the cavitand-based cage system. Moreover, the "V" shape phenylenediamine linkers are responsible for the novel [3 + 6] triangular prisms. The window size and environment can be easily functionalized by different groups, providing a promising platform for the construction of multivariate POCs. Use of linear phenylenediamines led to record-breakingly large [6 + 12] truncated octahedral cages, the maximum inner cavity diameters and volumes of which could be readily modulated by increasing the spacer length of the phenylenediamine linkers. This work can lead to an understanding of the self-assembly behaviors of POCs and also sheds light on the rational design of POC materials for practical applications.

Macrocycles and cages based on tetraphenylethylene with aggregation-induced emission effect

Syntheses, photophysical properties and applications of macrocycles and cages based on tetraphenylethylene with aggregation-induced emission (AIE) effect.