Naphth[4]arene: Synthesis, Conformations, and Application in Color-Tunable Supramolecular Crystalline Assemblies

A water-soluble cationic [2]biphenyl-extended pillar[6]arene: synthesis, host-guest interaction with hemin and application in chemodynamic/photodynamic cancer therapy

A water-soluble cationic [2]biphenyl-extended pillar[6]arene (CBpExP6) was designed and synthesized successfully. It could form a stable 1 : 1 complex with hemin, thereby enhancing the stability of hemin in water, and can be further applied in cancer CDT and PDT.

Fluorescent Macrocyclic Arenes: Synthesis and Applications

Fluorescent macrocyclic arenes have attracted increasing interest in macrocyclic and supramolecular chemistry due to their exceptional photophysical properties and versatile applications. Classical macrocyclic arenes modified with fluorescent groups at the upper or bottom rims have long provided valuable platforms across various fields. Recently, a large number of novel fluorescent macrocyclic arenes directly composed of polycyclic aromatic or heteroaromatic building blocks including naphthalene, anthracene, tetraphenylethene, pyrene, fluorene, carbazole, acridan, phenothiazine, coumarin, triphenylamine, benzothiadiazole and so on, have been reported, and they have shown specific fluorescent property, and also exhibited broad applications in molecular recognition, sensing, bioimaging and functional materials. In this review, we focus on the recent advances in the synthesis and applications of fluorescent macrocyclic arenes containing polycyclic aromatic or heteroaromatic skeletons emerged in the past decade. By categorizing these fluorescent macrocyclic arenes based on the different building blocks, this review provides a comprehensive summary of their synthesis, properties and applications.

One-step Macrocycle-to-Macrocycle Conversion Towards Two New Macrocyclic Arenes with Different Structures and Properties

Two new macrocyclic arenes H1 and H2 were conveniently synthesized by the one-step reaction of carboxylic acid substituted octopus[3]arene. It was found that H1 was composed of three ethenoanthracene subunits with a rigid hexagonal structure and H2 contained two ethenoanthracene subunits and one anthracene subunit with a rigid house-shaped structure. Among them, H2 exhibited strong blue fluorescence due to the existence of an anthracene subunit. Moreover, both H1 and H2 showed large and electron-rich cavities, which enable them to effectively complex different nitrogen-containing heterocyclic salt guests in solution and the solid state. It was further found that H2 exhibited stronger complexation towards the tested guests than H1 probably due to the stronger charge-transfer interactions between H2 and the guests.

Fluorescent Dye-Based Chiral Crystalline Organic Salt Networks for Circularly Polarized Luminescence

A facile and general strategy is developed herein for the construction of circularly polarized luminescence (CPL) materials with simultaneously high fluorescence quantum efficiency (Φ) and large luminescence dissymmetry factor (glum). The self-assembly of fluorescent dye, disodium 4,4'-bis(2-sulfonatostyryl)biphenyl (CBS), with chiral diamines such as (R,R)/(S,S)-1,2-diaminocyclohexane (R/S-DACH) and R/S-1,2-diaminopropane (R/S-DAP), produces four chiral crystalline organic salt networks (COSNs). These as-synthesized organic salts emit strong blue-color CPL upon excitation, with both high Φ and glum values of up to 79% and 0.022. The well-defined molecular structures and arrangements of CBS are directly observed through single crystal X-ray analysis, offering crucial information regarding the origins of high-efficiency CPL performance. The chirality of amine is effectively transferred to CBS and further amplified to the supramolecular structure by multiple hydrogen bonding and π-π stacking interactions, giving rise to the large glum factors; meanwhile, the fixation and the ordered arrangement of CBS by these multiple interactions empower efficient suppression of molecular motions, facilitating strong fluorescence. This work can inspire the assembly of CPL organic materials with high Φ and glum via charge-assisted hydrogen bonds between fluorescent dyes and chiral inducers. It also offers important insight into the structural origins of supramolecular chirality and CPL performance.

Recent advances in novel chiral macrocyclic arenes

Chiral macrocyclic arenes possess confined three-dimensional asymmetric cavities, electron-rich structures, chiral luminescence properties and excellent enantioselective recognition properties and have become a frontier and hotspot of macrocyclic chemistry and supramolecular chemistry. In recent years, there has been growing interest in the development of novel chiral macrocyclic arenes, which have found applications in various research areas. In this review, the construction, properties and functional applications of novel chiral macrocyclic arenes in enantioselective recognition, chiral sorting and construction of chiral luminescent materials according to their chiral types, including central, axial, planar, and inherent chiralities, are summarized. It is expected that this review will be helpful for research on supramolecular chemistry and for promoting the development of synthetic chemistry, materials chemistry and biochemistry.

Supramolecular-macrocycle-based functional organic cocrystals

Supramolecular macrocycles, renowned for their remarkable capabilities in molecular recognition and complexation, have emerged as pivotal elements driving advancements across various innovative research fields. Cocrystal materials, an important branch within the realm of crystalline organic materials, have garnered considerable attention owing to their simple preparation methods and diverse potential applications, particularly in optics, electronics, chemical sensing and photothermal conversion. In recent years, macrocyclic entitles have been successfully brought into this field, providing an essential and complementary channel to create novel functional materials, especially those with multiple functionalities and smart stimuli-responsiveness. In this Review, we present an overview of the research efforts on functional cocrystals constructed with macrocycles, covering their design principles, preparation strategies, assembly modes, and diverse functions and applications. Finally, the remaining challenges and perspectives are outlined. We anticipate that this review will serve as a valuable and timely reference for researchers interested in supramolecular crystalline materials and beyond, catalyzing the emergence of more original and innovative studies in related fields.

Simple cyclic chalcone dye with multiple optical functions: Piezochromism and lysosomes staining

Both artificially synthesized and naturally occurring cyclic chalcones have been widely studied for their excellent biological activities. However, research on its photophysical properties is still limited. In the present study, we designed and synthesized a small molecule fluorescent dye based on the ICT effect, using dimethylamino as the electron-donating group and carbonyl as the electron withdrawing group, and investigated its photophysical properties in depth. Although YB is a simple small molecule, it exhibits significant piezochromic properties. The fluorescence of YB can change from green to yellow through grinding. After solvent fumigation, the fluorescence reverts to green. Furthermore, YB was used successfully in the lysosomal targeting. This study expands the research on the photophysical properties of cyclic chalcone and give richness to application of cyclic chalcone compounds.

Octopus[5]arene from Pagoda[5]arene by Macrocycle-to-Macrocycle Conversion

Macrocycle-to-macrocycle conversion is an effective strategy to construct new macrocyclic arenes with specific structures. Herein, a new class of chiral macrocyclic arene, namely, octopus[5]arenes (Oc5s), cannot be synthesized by the direct approach from the corresponding chiral monomers but can be successfully achieved by a macrocycle-to-macrocycle conversion strategy utilizing racemic pagoda[5]arenes as the starting materials. It was found that enantiomeric Oc5s showed fixed conformations and stable chiral structures and exhibited significant chiral recognition toward chiral diamines.

Macrocycle-Based Charge Transfer Cocrystals with Dynamically Reversible Chiral Self-Sorting Display Chain Length-Selective Vapochromism to Alkyl Ketones

Chirality-driven self-sorting plays an essential role in controlling the biofunction of biosystems, such as the chiral double-helix structure of DNA from self-recognition by hydrogen bonding. However, achieving precise control over the chiral self-sorted structures and their functional properties for the bioinspired supramolecular systems still remains a challenge, not to mention realizing dynamically reversible regulation. Herein, we report an unprecedented saucer[4]arene-based charge transfer (CT) cocrystal system with dynamically reversible chiral self-sorting synergistically induced by chiral triangular macrocycle and organic vapors. It displays efficient chain length-selective vapochromism toward alkyl ketones due to precise modulation of optical properties by vapor-induced diverse structural transformations. Experimental and theoretical studies reveal that the unique vapochromic behavior is mainly attributed to the formation of homo- or heterochiral self-sorted assemblies with different alkyl ketone guests, which differ dramatically in solid-state superstructures and CT interactions, thus influencing their optical properties. This work highlights the essential role of chiral self-sorting in controlling the functional properties of synthetic supramolecular systems, and the rarely seen controllable chiral self-sorting at the solid-vapor interface deepens the understanding of efficient vapochromic sensors.

Strategies for Constructing Macrocyclic Arene-Based Color-Tunable Supramolecular Luminescent Materials

Over the past decades, supramolecular luminescent materials (SLMs) have attracted considerable attention due to their dynamic noncovalent interactions, versatile functions, and intriguing applications in many research fields. From construction to application, great efforts and progress have been made in color-tunable SLMs in recent years. In order to realize multicolor luminescence, various design strategies have been proposed. Macrocyclic chemistry, one of the brightest jewels in the field of supramolecular chemistry, has played a crucial role in the construction of stimuli-responsive and emission-tunable SLMs. Moreover, the flexible and tunable conformation and multiple noncovalent complexation sites of the macrocyclic arenes (MAs) afford a new opportunity to create such dynamic smart luminescent materials. Inspired by our reported work on the color-tunable supramolecular crystalline assemblies modulated by the conformation of naphth[4]arene, this Concept provides a summary of the latest developments in the construction of color-tunable MA-based SLMs, accompanied by the various construction strategies. The aim is to provide researchers with a new perspective to construct color-tunable SLMs with fascinating functions.

Prism[2]dihydrophenazines: Synthesis, Configurational Analysis, and Supramolecular Tessellation through Exo-Wall Interactions

Macrocyclic arenes have gained considerable attention for their structural diversity and widespread applications. In this research, a new kind of macrocyclic arenes, namely prism[2]dihydrophenazines (anti-P2P20, syn-P2P20, and P2P22), composed of two dihydrophenazine derivatives subunits bridged by methylene groups, were conveniently synthesized by AlCl3-catalyzed one-pot condensation in 1,2-dichloroethane. Both anti-P2P20 and its isomer syn-P2P20 exhibited flexible and convertible conformation with narrow cavity, while P2P22 possessed rigid and rhombic-like skeleton due to the more steric hindrance on subunits. In addition, the selection of electron-deficient guest was found to influence the outside binding behavior of syn-P2P20. Fantastic regular supramolecular tessellation was fabricated by tiling of syn-P2P20 with tetrafluoro-1,4-benzoquinone (TFB) through the exo-wall interactions. Using 1,5-difluoro-2,4-dinitrobenzene (DFN) as a linker, only the regular 2D network superstructure with periodic units in a plane was obtained through cocrystallization. This work not only reports the construction of supramolecular tessellations by using prism[2]dihydrophenazines as building blocks, but also provides a new perspective for the design of macrocyclic arenes and fabrication of 2D supramolecular materials.

Solid-State Emissive Pillar[6]arene Derivative Having Alternate Methylene and Nitrogen Bridges

Macrocyclic arenes show conformational adaptability, which allows host-guest complexations with the size-matched guest molecules. However, their emission properties are often poor in the solid states due to the self-absorption. Herein, we newly synthesized pillar[6]arene derivatives having alternate methylene and nitrogen bridging structures. Solvatochromic study reveals that the nitrogen-embedding into the cyclic structures can strengthen the intramolecular charge transfer (CT) nature compared to that of the linear nitrogen-bridged precursor. Owing to the large Stokes shift in the solid state, one of the nitrogen-embedded pillar[6]arenes shows high absolute photoluminescence quantum yield (ΦPL=0.36). Furthermore, it displays a turn-off sensing ability toward nitrobenzene (NB) vapor; a fluorescence quenching is observed when exposed to the NB vapor. From the structural analysis before and after the exposure of NB vapor, the amorphous nitrogen-embedded pillar[6]arene efficiently co-crystallize with NB and formed non-emissive intermolecular CT complexes with NB.

Hydrophilic Cocrystals with Water Switched Luminescence

Utilizing water molecules to regulate the luminescence properties of solid materials is highly challenging. Herein, we develop a strategy to produce water-triggered luminescence-switching cocrystals by coassembling hydrophilic donors with electron-deficient acceptors, where 1,2,4,5-Tetracyanobenzene (TCNB) was used as the electron acceptor and pyridyl benzimidazole derivatives were used as the electron donors enabling multiple hydrogen-bonds. Two cocrystals, namely 2PYTC and 4PYTC were obtained and showed heat-activated emission, and such emission could be quenched or weakened by adding water molecules. The cocrystal structure exhibited the donor molecule that can form multiple hydro bonds with water and acceptor molecules due to the many nitrogen atoms of them. The analyses of the photophysical data, powder X-ray diffraction, and other data confirmed the reversible fluorescence "on-off" effects were caused by eliminating and adding water molecules in the crystal lattice. The density functional theory calculations indicate that the vibration of the O-H bond of water molecules in the cocrystal can absorb the excitation energy and suppress fluorescence. Furthermore, the obtained cocrystals also showed temperature, humidity, and H+ /NH4 + responsive emission behavior, which allows their applications as thermal and humidity sensors, and multiple information encryptions. This research paves the way for preparing intelligent hydrophilic organic cocrystal luminescent materials.

A general supramolecular strategy for fabricating full-color-tunable thermally activated delayed fluorescence materials

Developing a facile and feasible strategy to fabricate thermally activated delayed fluorescence materials exhibiting full-color tunability remains an appealing yet challenging task. In this work, a general supramolecular strategy for fabricating thermally activated delayed fluorescence materials is proposed. Consequently, a series of host-guest cocrystals are prepared by electron-donating calix[3]acridan and various electron-withdrawing guests. Owing to the through-space charge transfer mediated by multiple noncovalent interactions, these cocrystals all display efficient thermally activated delayed fluorescence. Especially, by delicately modulating the electron-withdrawing ability of the guest molecules, the emission colors of these cocrystals can be continuously tuned from blue (440 nm) to red (610 nm). Meanwhile, high photoluminescence quantum yields of up to 87% is achieved. This research not only provides an alternative and general strategy for the fabrication of thermally activated delayed fluorescence materials, but also establishes a reliable supramolecular protocol toward the design of advanced luminescent materials.

Crystallography, Charge Transfer, and Two-Photon Absorption Relations in Molecular Cocrystals for Two-Photon Excited Fluorescence Imaging

Two-photon excited fluorescence imaging requires high-performance two-photon absorption (TPA) active materials, which are commonly intramolecular charge transfer systems prepared by traditional chemical synthesis. However, this typically needs harsh conditions and new methods are becoming crucial. In this work, based on a collaborative intermolecular charge transfer (inter-CT) strategy, three centimeter-sized organic TPA cocrystals are successfully obtained. All three cocrystals exhibit a mixed stacking arrangement, which can effectively generate inter-CT between the donor and acceptor. The ground and excited state characterizations compare their inter-CT ability: 1,2-BTC > 2D-BTC > 1D-BTC. Transient absorption spectroscopy detects TCNB•- , indicating that the TPA mechanism arises from molecular polarization caused by inter-CT. Meanwhile, 1,2-BTC exhibits the highest excited-state absorption and the longest excited-state lifetime, suggesting a stronger TPA response. First-principles calculations also confirm the presence of inter-CT interactions, and the significant parameter Δµ which can assess the TPA capability indicates that inter-CT enhances the TPA response. Besides, cocrystals also demonstrate excellent water solubility and two-photon excited fluorescence imaging capabilities. This research not only provides an effective method for synthesizing TPA crystal materials and elucidates the connection between inter-CT ability and TPA property but also successfully applies them in the fields of multi-photon fluorescence bioimaging.

Aromatic Bridged Bis(triphenylamine) Cascade Assembly Achieved Tunable Nanosupramolecular Morphology and NIR Targeted Cell Imaging

Possessing four cationic pyridium groups, phenyl-bridged bis(triphenylamine) derivatives (G1, G2) were encapsulated by cucurbit[8]uril (CB[8]) at a 1:2 stoichiometry to form the network-like organic two-dimensional nanosheet, which could efficiently enhance the near-infrared (NIR) luminescence and companies with a red-shift from 750 to 810 nm for G1. Benefiting from the supramolecular multivalent interaction, α-cyclodextrin modified hyaluronic acid (HACD) and G1/CB[8] formed nanoparticles to further enhance NIR luminescence behaviors. Compared with the short rigid aromatic bridged bis(triphenylamine) derivative (G2), the supramolecular assembly derived from G1 with long flexible cationic arms gives a larger Stokes shift, which further coassembles with the phosphorescent bromophenylpyridinium derivative/CB[8] pseudorotaxane, leading to efficient phosphorescent resonance energy transfer (PRET). Especially, the nanoparticle showed delayed NIR fluorescence under 308 nm light excitation with an ultralarge Stokes shift up to 502 nm, which was successfully applied in targeted NIR cell imaging.