Substrate-Responsive Pillar[5]arene-Based Organic Room-Temperature Phosphorescence

Through-Space Electron Effect Regulated Selective Expression of Ultralong Organic Room Temperature Phosphorescence and Photochromism

We report a through-space electron effect (TSEE) between two phosphorescent units that significantly modulates the selective expression of ultralong organic room-temperature phosphorescence (UORTP) and photochromism. A series of phosphorescent molecules (DNapTr, DNapBNT, DNapFL, and DNapPy), featuring two phosphorescent units connected by a nonconjugated spacer, were synthesized. Our findings reveal that both TSEE and the energy gap ΔE (defined as EPU2 - EPU1) between the lowest triplet energy levels (T1) of the phosphorescent units play crucial roles in determining UORTP and the photochromic behavior in PMMA films. NMR spectra and molecular simulations confirm the presence of TSEE, with their strength ranked as DNapPy < DNapFL < DNapBNT in the presence of TSEE. The DNap unit is governed by TSEE, where moderate TSEE inhibits radical cation formation, while strong TSEE promotes it. Consequently, DNapTr, DNapBNT, and DNapFL exhibit tunable photochromism, whereas DNapPy remains nonphotochromic. UORTP is jointly influenced by TSEE and ΔE. For DNapTr (ΔE > 0), excitons are trapped by DNap via TSEE, leading to UORTP from DNap. In DNapBNT and DNapFL (ΔE slightly <0), strong TSEE directs UORTP to PU2. In DNapPy (ΔE ≪ 0), moderate TSEE enables UORTP from both DNap and Py. By leveraging TSEE and tuning T1 of PU2, we successfully modulated both photochromism and UORTP. This study provides a strategy for designing intelligent organic phosphorescent materials.

Structure Evolution of Organic Luminescent Molecules Utilizing Through-Space Charge Transfer Mechanism

Organic structures provide an extensive platform for luminescent materials thanks to the easy to design and synthesize, low toxicity and tunable functionalization. Through-space charge transfer (TSCT) in organic molecules, characterized by the transfer of excitons through spatial charge motion, has emerged as a significant research topic in optoelectronics, offering new avenues for the development of high-performance luminescent materials. This review systematically summarizes the fundamental principles of TSCT and highlights the recent advancements in organic small molecules that exhibit this emission mechanism. Key aspects covered include the molecular design strategies that enhance TSCT efficiencies, the role of charge transport spacers, and the correlation between molecular donor-acceptor structures and emission properties. Furthermore, the review addresses the challenges and future directions in the field, emphasizing the importance of understanding TSCT for the development of next-generation light-emitting materials. By providing a comprehensive analysis of current research, this review serves as a crucial resource for researchers and practitioners aiming to innovate in the realm of organic optoelectronic materials, ultimately contributing to a deeper understanding of TSCT processes and their practical applications.

An Aggregation-Induced Room Temperature Phosphorescence Probe for the Efficient and Selective Detection of Heparin and Protamine

Heparin is a vital macromolecule that regulates blood coagulation, while protamine is an essential polypeptide clinically used to counteract heparin overdose. Detecting both heparin and its antidote protamine under physiological conditions is crucial for biological and clinical applications. This report introduces a cucurbituril[8] (CB[8])-based phosphorescent probe for their detection. The method employs a nanoassembly induced phosphorescence switch-on mechanism for heparin sensing and a disassembly induced phosphorescence switch-off approach for protamine detection. An arginine-rich guest forms a supramolecular complex with heparin, enhancing phosphorescence under secondary confinement and enabling its detection. Conversely, protamine sulfate, as a stronger competitor for heparin, disrupts the probe-heparin aggregates, leading to emission quenching and protamine sensing. This sensor demonstrated high selectivity in detecting both analytes in biological samples, such as human blood serum and urine. The detection limits for heparin and protamine were determined to be 61 and 82 ng/mL in 10% HBS, respectively.

Recent developments in pillar[5]arene-based nanomaterials for cancer therapy

Nanomaterials possess unique size characteristics, enabling them to cross tissue gaps, penetrate the blood-brain barrier and endothelial cells, and release drugs at the cellular level. Additionally, the surface of nanomaterials is readily functionalized, endowing them with good biocompatibility, low biotoxicity, and specific targeting. All these advantages render nanomaterials broad application prospects in tumor therapy. Pillar[5]arenes are a new category of macrocyclic host compounds featuring rich host-guest properties and diverse environmental responses. In recent years, by combining the advantages of pillar[5]arenes and nanomaterials, the application of pillar[5]arene-based nanomaterials in tumor therapy has drawn extensive attention from scientists. In this review, we summarize five distinct types of pillar[5]arene-based nanomaterials: (1) pillar[5]arene-modified inorganic nanomaterials; (2) pillar[5]arene-modified organic porous materials; (3) pillar[5]arene-modified organic/inorganic hybrid materials; (4) nanomaterials self-assembled from pillar[5]arene-based host-guest complexes; (5) nanomaterials self-assembled from amphiphilic pillar[5]arenes. Moreover, the different tumor treatment modes of these nanomaterials, including chemotherapy, photodynamic therapy, photothermal therapy, gene therapy, and multimodal synergistic therapy, are also elaborated in detail.

Synthesis and Structure of Pillar[m]arene[1]phthalimide and Pillar[m]arene[1]naphthalimide

A series of monofunctionalized pillar[n]arenes skeleton macrocycles pillar[m]arene[1]phthalimide and pillar[m]arene[1]naphthalimide (m = 4-6) were synthesized successfully through fragment coupling cyclization in a one-pot reaction. The introduction of pyromellitic diimide and naphthalene diimide units into the pillar[n]arenes skeleton not only disturbs the symmetry of the pillar[n]arenes but also changes their self-assembly behavior in the solid state. This functionalization approach greatly expands the structural diversity of the pillar[n]arenes.

Promoting WLED-Excited High Temperature Long Afterglow by Orthogonally Anchoring Chromophores into 0D Metal-Organic Cages

Afterglow materials have garnered significant interest due to distinct photophysical characteristics. However, it is still difficult to achieve long afterglow phosphorescence from organic molecules due to aggregation-caused quenching (ACQ) and energy dissipation. In addition, most materials reported so far have long afterglow emission only at room or even low temperatures, and mainly use UV light as an excitation source. In this work, we report a strategy to achieve high temperature long afterglow emission through the assembly of isolated 0D metal-organic cages (MOCs). In which, both ACQ and phosphorescence quenching effects are effectively mitigated by altering the stacking mode of organic chromophores through orthogonally anchoring into the edges of cubic MOCs. Furthermore, improvement in molecular rigidity, promotion of spin-orbit coupling and broadening of the absorption range are achieved through the MOC-engineering strategy. As a result, we successfully synthesized MOCs that can produce afterglow emission even after excitation by WLEDs at high temperatures (380 K). Moreover, the MOCs are capable of generating afterglow emissions when excited by mobile phone flashlight at room temperature. Given these features, the potential applications of MOCs in the visual identification of explosives, information encryption and multicolor display are explored.

Tunable Nano-Supramolecules Based on Cucurbiturils for Near-Infrared Phosphorescence Imaging

Nano-supramolecules based on artificial macrocycles can not only regulate assembly morphology but also boost phosphorescence resonance energy transfer (PRET). Herein, a water-soluble phosphorescence supramolecule was constructed from the hyaluronic acid-modified bromophenylpyridinium (HAPY), cucurbit[n]uril (CB[n], n = 7/8), and energy acceptor phenyl-bridged phenothiazine derivatives, displaying efficient PRET and achieving near-infrared (NIR) phosphorescence by macrocyclic CB[n] and the assembly confinements. As compared with weak phosphorescent nanofibers of HAPY/CB[7], the spherical nanoparticles of HAPY/CB[8] not only gave strong green phosphorescence with extended lifetime to 1.27 ms but also could act as the energy donor and confine cationic phenothiazine in the secondary assemblies, leading to highly efficient PRET efficiency (87.27%) from the phosphors to triplet acceptors, realizing phosphorescence emission at 750 nm and an ultralarge Stokes shift of 440 nm. Ultimately, the nanoassembly achieved by the multiscale confinements boosting PRET was successfully applied in targeted cancer cell imaging, providing new insight for fabricating NIR phosphorescence materials.

"Bis-Clamp-Cavity Synergy", an Efficient Approach to Improve Guest Binding Properties of Macrocyclic Host and Its Application on Detection of Al3+ and Arg in Living Cells

Improving the selective and sensitive binding properties of macrocyclic hosts to target guests is always an interesting challenge. Herein, we introduce a novel "bis-clamp-cavity synergy" strategy to enhance the selectivity and binding sensitivity of pillararenes toward target guests. To achieve this goal, we designed and synthesized A,A'-bis-hydroxynaphthoylhydrazone-functionalized conjugated pillar[5]arene (HGP5), in which bis-hydroxynaphthoylhydrazone plays the role of clamps, while the pillar[5]arene provides the macrocyclic cavity. The bis-clamps and macrocyclic cavity could supply synergistic binding for target guests through multicoordination interactions, multihydrogen bonds, C-H···π and cation···π interactions, and so on. Furthermore, the introduction of the conjugated pillar[5]arene can enhance the signal transmission ability, thereby improving the sensitivity for guest recognition. Benefiting from the bis-clamp-cavity synergy, HGP5 exhibits efficient selective recognition for Arg and Al3+. It achieves colorimetric and fluorescent dual-channel recognition for Arg (with the LOD of 2.99 × 10-8 M) and ultrasensitive recognition of Al3+ (with the LOD of 7.94 × 10-9 M). This strategy can be effectively applied to detect Arg and Al3+ in aqueous solution and live cells.

Designing High-Sensitivity Mechanochromic Luminescent Materials Through Friction-Induced Crystallization Strategy

Despite recent significant breakthroughs in novel mechanochromic luminescent (ML) materials, developing a high-sensitivity ML material is still challengeable. Herein, a "friction-induced crystallization" strategy is proposed to realize highly sensitive transformations of luminescent signal, through an integration of polymeric chains and an aggregation-sensitive luminescent core, which act as mechanical sensors and fluochromic actuators, respectively. The coupling of these two components enables the material to crystallize in response to shear friction, thereby exhibiting blue-shift fluorescence due to a more restricted relaxation pathway. This study underscores a high-sensitivity ML material based on the precise regulation of molecular-scale motions, and also expands the scope and potential of ML materials toward user-friendly, interactive wearable devices.

Supramolecular control over the variability of color and fluorescence in low-molecular-weight glass

Colorful and fluorescent transparent materials have been extensively used in industrial and scientific activities, with inorganic and polymeric glasses being the most typical representatives. Recently, artificial glass originating from low-molecular-weight monomers has attracted considerable attention. Compared with the deep understanding of the building blocks and driving forces of supramolecular glass, related studies on its optical properties are insufficient in terms of systematicness and pertinence. In this study, a supramolecular strategy was applied to introduce versatile colors and fluorescence emissions into a low-molecular-weight glass. Pillar[5]arene and cucurbit[8]uril were selected to recognize the functional components and yield the desired optical performances. Macrocycle-based host-guest chemistry endows artificial glass with controllable and programmable colors and fluorescence emissions.

A chiral supramolecular liquid crystal based on pillararene and its application in information encryption

A chiral supramolecular liquid crystal based on a pillararene mesogen was constructed. The regulation of liquid crystal behavior was achieved through the host-guest interactions between the pillararene-based mesogen and a tetraphenylethylene-containing guest. In addition, this supramolecular liquid crystal system, showing pH-responsive fluorescence emission character, was applied as an information encryption material capable of storing multiple levels of distinct information, thereby enriching the application of liquid crystal materials in the field of information security.

An anthracene-containing crown ether: synthesis, host-guest properties and modulation of solid state luminescence

Organic solid state vapochromic materials are of great significance for the development of supramolecular chemistry and materials science. Herein, we synthesize a crown ether derivative (An34C10) containing two anthracene units and construct new crown ether-based vapochromic host-guest co-crystals. Due to the presence of anthracene, An34C10 not only shows good fluorescence properties but also displays mechanochromism. Single crystal structural analysis, powder X-ray diffraction and differential scanning calorimetry experiments demonstrate that the transformation between different stacking modes of An34C10 is responsible for mechanochromism. In addition, An34C10 can complex with 1,2,4,5-tetracyanobenzene (TCNB) to form host-guest complex (An34C10@TCNB) co-crystals. Because organic solvent fuming alters charge-transfer interactions in An34C10@TCNB, the fluorescence of the co-crystals can be turned on and off by 4-methylpyridine and chloroform vapors, respectively, realizing selective detection with opposite emission outputs. Meanwhile, the stimuli-responsive properties of An34C10 and An34C10@TCNB possess good cycling performance. This work provides a new strategy for the construction of organic solid state luminescent materials.

Host-Guest Interactions Induced Enhancement in Oxidase-Like Activity of a Benzothiadiazole Dye Inside an Aqueous Pd8L4 Barrel

The effect of host-guest interactions on the chemistry of encapsulated molecules is a fascinating field of research that has gained momentum in recent years. Much of the work in this field has been focused on the effect of such interactions on catalysis and photoluminescence of encapsulated dyes. However, the effect of such interactions on related photoinduced processes, such as photoregulated oxidase-mimicking activity, has not been explored much. Herein, we report a unique example of enhancement of oxidase-like activity of a benzothiadiazole dye (G1) in water through encapsulation within a M8L4 molecular barrel (1). Favorable host-guest interactions helped the encapsulated guest G1 to have better photoinduced electron transfer to molecular oxygen leading to increased production of superoxide radical anions and oxidase-like activity. Furthermore, encapsulation inside 1 also caused a change in the redox potentials of the guest (G1) which after photoinduced electron transfer produced a better oxidizing agent than free G1. These phenomena combined to enhance the oxidase-like activity of dye G1 upon encapsulation inside cage 1. The present report demonstrates a unique effect of host-guest chemistry on photoregulated processes.

Tandem Four-Component Reaction to Access Fused Polycycles Exhibiting Aggregation-Enhanced Through-Space Charge Transfer Emission

Rapid construction of new fluorescence emitters is essential in advancing synthetic luminescent materials. This study illustrated a piperidine-promoted reaction of chiral dialdehyde with benzoylacetonitrile and malonitrile, leading to the formation of the 6/6/7 fused cyclic product in good yield. The proposed reaction mechanism involves a dual condensation/cyclization process, achieving the formation of up to six bonds for fused polycycles. The single crystal structure analysis revealed that the fused cyclic skeleton contains face-to-face naphthyl and cyanoalkenyl motifs, which act as the electronic donor and acceptor, respectively, potentially resulting in through-space charge transfer (TSCT) emission. While the TSCT emissions were weak in solution, a notable increase in luminescence intensity was observed upon aggregation, indicating bright fluorescent light. A series of theoretical analyses further supported the possibility of spatial electronic communication based on frontier molecular orbitals, the distance of charge transfer, and reduced density gradient analysis. This work not only provides guidance for the one-step synthesis of complex polycycles, but also offers valuable insights into the design of aggregation-enhanced TSCT emission materials.

A supramolecular photosensitizer based on triphenylamine and pyrazine with aggregation-induced emission properties for high-efficiency photooxidation reactions

Recently, there has been a great interest in the study of photocatalysts (PCs) and photosensitizers (PSs) in the field of organic photocatalysis. In the present study, a pure organic thermally activated delayed fluorescence (TADF) molecule 4,4'-(12-(pyridin-4-yl)dibenzo[f,h]pyrido[2,3-b]quinoxaline-3,6-diyl)bis(N,N-diphenylaniline) (DPQ-TPA) was designed and synthesized, which not only have excellent TADF property and small energy splitting (ΔEST), but also can self-assembly in water to form cross-linked nanoparticles with exceptional aggregation-induced emission (AIE) characteristics. DPQ-TPA exhibits excellent remarkable selectivity and notably enhances the production capacity of reactive oxygen species (ROS), particularly 1O2, which was employed as a highly effective photocatalyst in the photooxidation reaction of phosphine and hydroazobenzenes under blue light irradiation with high yields up to 94% and 91%, respectively. This work expands the potential application of (donor-acceptor) D-A type AIE-TADF molecules in photocatalytic organic transformations through supramolecular self-assembly.

Förster Resonance Energy Transfer: Stimulus-Responsive Purely Organic Room Temperature Phosphorescence through Dynamic B-N bond

Recently, stimulus-responsive organic materials with room-temperature phosphorescence (RTP) properties have attracted significant attention owing to their potential applications in chemical sensing, anticounterfeiting, and displays. However, molecular design currently lacks systematicity and effectiveness. Herein, we report a capture-release strategy for the construction of reversible RTP via B/N Lewis pairs. Specifically, the RTP of the Lewis acid of 7-bromo-5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracene (BrBA) can be deactivated through capturing by the Lewis base, N,N-diphenyl-4-(pyridin-4-yl)aniline (TPAPy), and reactivated by dissociation of B-N bonds to release BrBA. Reversible RTP is attributed to the exceptional self-assembly capability of BrBA, whereas the tunable RTP colors are derived from distinct Förster resonance energy transfer (FRET) processes. The potential applications of RTP materials in information storage and anti-counterfeiting were also experimentally validated. The capture-release approach proposed in this study offers an effective strategy for designing stimulus-responsive 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.

Polymorphism-Dependent Organic Room Temperature Phosphorescent Scintillation for X-Ray Imaging

Organic phosphorescent scintillating materials have shown great potential for applications in radiography and radiation detection due to their efficient utilization of excitons. However, revealing the relationship between molecule stacking and the phosphorescent radioluminescence of scintillators is still challenging. This study reports on two phenothiazine derivatives with polymorphism-dependent phosphorescence radioluminescence. The experiments reveal that molecule stacking significantly affects the non-radiation decay of the triplet excitons of scintillators, which further determines the phosphorescence scintillation performance under X-ray irradiation. These phosphorescent scintillators exhibit high radio stability and have a low detection limit of 278 nGys-1. Additionally, the potential application of these scintillators in X-ray radiography, based on their X-ray excited radioluminescence properties, is demonstrated. These findings provide a guideline for obtaining high-performance phosphorescent scintillating materials by shedding light on the effect of crystal packing on the radioluminescence of organic molecules.

Enhancing Purely Organic Room Temperature Phosphorescence via Supramolecular Self-Assembly

Long-lived and highly efficient room temperature phosphorescence (RTP) materials are in high demand for practical applications in lighting and display, security signboards, and anti-counterfeiting. Achieving RTP in aqueous solutions, near-infrared (NIR) phosphorescence emission, and NIR-excited RTP are crucial for applications in bio-imaging, but these goals pose significant challenges. Supramolecular self-assembly provides an effective strategy to address the above problems. This review focuses on the recent advances in the enhancement of RTP via supramolecular self-assembly, covering four key aspects: small molecular self-assembly, cocrystals, the self-assembly of macrocyclic hosts and guests, and multi-stage supramolecular self-assembly. This review not only highlights progress in these areas but also underscores the prominent challenges associated with developing supramolecular RTP materials. The resulting strategies for the development of high-performance supramolecular RTP materials are discussed, aiming to satisfy the practical applications of RTP materials in biomedical science.

Supermolecular Confined Silicon Phosphorescence Nanoprobes for Time-Resolved Hypoxic Imaging Analysis

Room temperature phosphorescence (RTP) nanoprobes play crucial roles in hypoxia imaging due to their high signal-to-background ratio (SBR) in the time domain. However, synthesizing RTP probes in aqueous media with a small size and high quantum yield remains challenging for intracellular hypoxic imaging up to present. Herein, aqueous RTP nanoprobes consisting of naphthalene anhydride derivatives, cucurbit[7]uril (CB[7]), and organosilicon are reported via supermolecular confined methods. Benefiting from the noncovalent confinement of CB[7] and hydrolysis reactions of organosilicon, such small-sized RTP nanoprobes (5-10 nm) exhibit inherent tunable phosphorescence (from 400 to 680 nm) with microsecond second lifetimes (up to ∼158.7 μs) and high quantum yield (up to ∼30%). The as-prepared RTP nanoprobes illustrate excellent intracellular hypoxia responsibility in a broad range from ∼0.1 to 21% oxygen concentrations. Compared to traditional fluorescence mode, the SBR value (∼108.69) of microsecond-range time-resolved in vitro imaging is up to 2.26 times greater in severe hypoxia (<0.1% O2), offering opportunities for precision imaging analysis in a hypoxic environment.

Hydroxyl-functionalized pillar[5]arene with high separation performance for gas chromatography

Here we report the first example of employing hydroxyl-functionalized pillar[5]arene (P5A-C10-OH) as stationary phase for capillary gas chromatographic (GC) separations. The statically coated P5A-C10-OH capillary column possessed moderate polarity and column efficiency of 3233 plates per m determined by n-dodecane. As a result, the P5A-C10-OH column exhibited high-resolution capability for the mixture of 17 analytes from apolar to polar nature. Importantly, it exhibited advantageous performance for high resolution of the challenging isomers of bromonitrobenzene, chloroaniline, bromoaniline, iodoaniline and dimethylaniline with good peak shapes over the P5A-C10 and commercial HP-35 columns. In addition, eight cis-/trans-isomers with diverse types were baseline separated on the P5A-C10-OH column. And the application of detecting isomeric impurities in real samples gave strong evidence of its potential and feasibility for the viable GC analysis.

Chaperone Mimetic Strategy for Achieving Organic Room-Temperature Phosphorescence based on Confined Supramolecular Assembly

The development of organic materials that deliver room-temperature phosphorescence (RTP) is highly interesting for potential applications such as anticounterfeiting, optoelectronic devices, and bioimaging. Herein, a molecular chaperone strategy for controlling isolated chromophores to achieve high-performance RTP is demonstrated. Systematic experiments coupled with theoretical evidence reveal that the host plays a similar role as a molecular chaperone that anchors the chromophores for limited nonradiative decay and directs the proper conformation of guests for enhanced intersystem crossing through noncovalent interactions. For deduction of structure-property relationships, various structure-related descriptors that correlate with the RTP performance are identified, thus offering the possibility to quantitatively design and predict the phosphorescent behaviors of these systems. Furthermore, application in thermal printing is well realized for these RTP materials. The present work discloses an effective strategy for efficient construction of organic RTP materials, delivering a modular model which is expected to help expand the diversity of desirable RTP systems.

Efficient Visible-Light-Activated Ultra-Long Room-Temperature Phosphorescence Triggered by Multi-Esterification

The development of ultra-long room-temperature phosphorescence (UL-RTP) in processable amorphous organic materials is highly desirable for applications in flexible displays, anti-counterfeiting, and bio-imaging. However, achieving efficient UL-RTP from amorphous materials remains a challenging task, especially with activation by visible light and a bright afterglow. Here we report a general and rational molecular-design strategy to enable efficient visible-light-excited UL-RTP by multi-esterification of a rigid large-plane phosphorescence core. Notably, multi-esterification minimizes the aggregation-induced quenching and accomplishes a 'four birds with one stone' possibility in the generation and radiation process of UL-RTP: i) shifting the excitation from ultraviolet light to blue-light through enhancing the transition dipole moment of low-lying singlet-states, ii) facilitating the intersystem crossing process through the incorporation of lone-pair electrons, iii) boosting the decay process of long-lived triplet excitons resulting from a significantly increased transition dipole moment, and iv) reducing the intrinsic triplet nonradiative decay by substitution of high-frequency vibrating hydrogen atoms. All these factors synergistically contribute to the most efficient and stable visible-light-stimulated UL-RTP (lifetime up to 2.01 s and efficiency up to 35.4 % upon excitation at 450 nm) in flexible films using multi-esterified coronene, which allows high-tech applications in single-component time-delayed white light-emitting diodes and information technology based on flashlight-activated afterglow encryption.

Cavity-Shape-Dependent Divergent Chemical Reaction inside Aqueous Pd6L4 Cages

Chemical reactions inside the confined pockets of enzyme-mimicking hosts, such as cages and macrocycles, have been an emerging field of interest over the past decade. Although many such reactions are known, the use of such cages toward the divergent synthesis of nonisomeric products has not been well explored. Divergent synthesis is a technique of forming two or more distinct products from the same reagents by changing the catalyst or reaction conditions. Changing the shape of the cage can also change the nature and magnitude of the host-guest interactions. Thus, is it possible for such changes to cause differences in the reaction pathways leading to formation of nonisomeric products? Herein, we report a divergent chemical transformation of anthrone [anthracen-9(10H)-one] inside different water-soluble M6L4 cages. When anthrone was encapsulated inside a newly synthesized M6L4 octahedral cage 1, it dimerized to form dianthrone [9,9'-bianthracen-10,10'(9H,9'H)-dione]. In contrast, when the same chemical reaction was performed inside a M6L4 double-square shaped cage 2, it was oxidized to form anthraquinone [anthracene-9,10-dione]. Similar results were obtained with a different set of isomeric aqueous Pd6 cages 3a (octahedral cage) and 3b (double-square cage), indicating the dependence of the shape of cavity on the divergent synthesis. The present report demonstrates a unique example of different outcomes/results of a reaction depending on the shape of the molecular container, which was driven by the host-guest interactions and the preorganization of the substrates.

Disorder-Enhanced Charge-Transfer-Mediated Room-Temperature Phosphorescence in Polymer Media

Room-temperature phosphorescence (RTP) polymers have important applications for biological imaging, oxygen sensing, data encryption, and photodynamic therapy. Despite the many advantages polymeric materials offer such as great control over gas permeability and processing flexibility, disorder is traditionally considered as an intrinsic negative impact on the efficiency for embedded RTP luminophores, as various allowed thermal motions could quench the emitting states. However, we propose that such disorder-enabled freedoms of microscopic motions can be beneficial for charge-transfer-mediated RTP, which is facilitated by molecular conformational changes among different electronic transition states. Using the "classic" pyrene-aniline exciplex as an example, we demonstrate the mutual enhancement of red/near-infrared and green RTP emissions from the pyrene and aniline moieties, respectively, upon doping the aniline polymer with trace pyrene derivatives. In comparison, a pyrene-doped crystal formed with the same aniline structure exhibits only charge-transfer fluorescence with no red or green RTP observed, suggesting that order suppresses the RTP channels. The proposed polymerization strategy may be used as a unified method to generate multi-emissive polymeric RTP materials from a vast pool of known and unknown exciplexes and charge-transfer complexes.