Competition between Arene-Perfluoroarene and Charge-Transfer Interactions in Organic Light-Harvesting Systems

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.

Organic Cocrystal Alloys: From Three Primary Colors to Continuously Tunable Emission and Applications on Optical Waveguides and Displays

Multicolor luminescence of organic fluorescent materials is an essential part of lighting and optical communication. However, the conventional construction of a multicolor luminescence system based on integrating multiple organic fluorescent materials of a single emission band remains complicated and to be improved. Herein, organic alloys (OAs) capable of full-color emission are synthesized based on charge transfer (CT) cocrystals. By adjusting the molar ratio of electron donors, the emission color of the OAs can be conveniently and continuously regulated in a wide visible range from blue (CIE: 0.187, 0.277), to green (CIE: 0.301, 0.550), and to red (CIE: 0.561, 0.435). The OAs show analogous 1D morphology with smooth surface, allowing for full-color waveguides with low optical-loss coefficient. Impressively, full-color optical displays are easily achieved through the OAs system with continuous emission, which shows promising applications in the field of optical display and promotes the development of organic photonics.

Precise Synthesis of Organic Cocrystal Alloys with Full-Spectrum Emission Characteristics for the Stepless Color Changing Display

Organic luminescent materials are indispensable in optoelectronic displays and solid-state luminescence applications. Compared with single-component, multi-component crystalline materials can improve optoelectronic characteristics. This work forms a series of full-spectrum tunable luminescent charge-transfer (CT) cocrystals ranging from 400 to 800 nm through intermolecular collaborative self-assembly. What is even more interesting is that o-TCP-Cor(x)-Pe(1-x), p-TCP-Cor(x)-Pe(1-x), and o-TCP-AN(x)-TP(1-x) alloys are prepared based on cocrystals by doping strategies, which correspondingly achieve the stepless color change from blue (CIE [0.22, 0.44]) to green (CIE [0.16, 0.14]), from green (CIE [0.27, 0.56]) to orange (CIE [0.58, 0.42]), from yellow (CIE [0.40, 0.57]) to red (CIE [0.65, 0.35]). The work provides an efficient method for precisely synthesizing new luminescent organic semiconductor materials and lays a solid foundation for developing advanced organic solid-state displays.

White-Light Emission from a Host-Guest Composite between Carboxylatopillar[5]arene-Modified N-Doped Carbon Dots and Rhodamine 6G for Rutin Detection

The construction of tunable white-light-emitting materials has garnered increasing attention in the scientific community. In this study, N-doped carbon dots (N-CDs) were surface-modified with carboxylatopillar[5]arene (CP[5]) using an EDC-NHS coupling reaction to create CCDs. CCDs were then conjugated with rhodamine 6G (R6G) through host-guest interactions to fabricate the CCDs-R6G composites. These composites produced two-color fluorescence emission peaks at 447 and 557 nm when excited by a wavelength of 340 nm. Excitingly, white-light emission (0.28, 0.30) can be readily achieved by varying the R6G concentration. To further explore potential applications, a new detection method for rutin (RT) based on the inner filter effect (IFE) was developed. Experimental results verify the practicality and reliability of the fluorescence sensor based on CCDs-R6G composites for RT detection in real samples.

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.

Control of Relative Positions of Electron-Donor and Electron-Acceptor Molecules in Charge-Transfer Complexes for Luminescent Property Modulation

Charge-transfer complexes can exhibit various physical properties that depend on the relative positions of electron-donor and electron-acceptor molecules. Several studies have investigated the relationship between the relative positions of electron-donor and electron-acceptor molecules and their luminescence properties. However, elucidating the correlation between the relative positions and detailed luminescence processes without changing the molecular structures has not been explored. Herein, we report control of the relative position based on charge-assisted hydrogen bonds between sulfo and amino groups and on alkylamines' steric factors, and report concomitant modulation of the luminescent properties. Six charge-transfer complexes were prepared from anthracene-2,6-disulfonic acid and 1,2,4,5-tetracyanobenzene as electron-donor and electron-acceptor molecules, and various alkylamines. Different alkylamines' steric factors drastically and precisely changed the relative positions of the electron-donor and electron-acceptor molecules without changing their molecular structures. Consequently, the six crystals exhibited maximum emission wavelengths from 543 to 624 nm and different luminescence processes.

Advances in white light-emitting organic crystals

In past decades, organic crystals have presented considerable potential in the field of optoelectronics due to their rich tunable physical and chemical properties and excellent optoelectronic characteristics. White-light emission, as a special application, has received widespread attention and has been applied in various fields, generating significant interest in the scientific community. By preparing white light-emitting organic crystals, a series of applications for future white-light sources can be realized. This article reviews the research progress on the molecular design and synthesis, preparation, and application of white light-emitting organic crystals in recent years. We hope that this review will help to understand and facilitate the development of white light-emitting organic crystals.

Helical Cage Rotors Switched on by Brake Molecule with Variable Fluorescence and Circularly Polarized Luminescence

While chiral molecular rotors have unique frames and cavities to possibly generate switchable chiroptical functions, it still remains a formidable challenge to precisely restrict their rotations to activate certain functions such as fluorescence as well as circularly polarized luminescence (CPL), which are strongly related to the local molecular rotations. Herein, we design a pair of enantiopure helical cage rotors, which emit light neither at the molecular state nor in the crystal or aggregation states, although they contain luminophore groups. However, upon mounting with fluoroaromatic borane (TFPB) as a molecular brake, the phenyl rotation of the helical cage can be effectively hindered and fluorescence and CPL activities of the molecular cage are switched on. Crystal structure analysis reveals that the rotation is restricted through synergistic B-O-H-N bonding and a fluoroaromatic-aromatic (ArF-Ar) dipole interaction. Moreover, the helical cages are switched on stepwise with color-variable fluorescence and CPL by the inner brake in the molecular state and the outer brake in the supramolecular assemblies, respectively. This work not only provides the design idea of chiroptical molecular rotors but also unveils how fluorescence and CPL could be generated in cage rotor systems.

The Key Role of Molecular Packing in Luminescence Property: From Adjacent Molecules to Molecular Aggregates

The luminescence materials act as the key components in many functional devices, as well as the detection and imaging systems, which can be permeated in each aspect of modern life, and attract more and more attention for the creative technology and applications. In addition to the diverse properties of organic luminogens, the multiple molecular packing at aggregated states frequently offers new and/or exciting performance. However, there still lacks comprehensive analysis of molecular packing in these organic materials, resulting in an increased gap between molecular design and practical applications. In this review, from the basic knowledge of organic compounds as single molecules, to the discernable property of excimer, charge transfer (CT) complex or self-assembly systems by adjacent molecules, and finally to the opto-electronic performance of molecular aggregates, the relevant factors to molecular packing and practical applications are discussed.

The host-guest inclusion driven by host-stabilized charge transfer for construction of sequentially red-shifted mechanochromic system

Developing more extensive methods to understand the underlying structure-property relationship of mechanochromic luminescent molecules is demanding but remains challenging. Herein, the effect of host-guest interaction on the mechanochromic properties of organic molecules is illustrated. A series of pyridinium-functionalized triphenylamine derivatives show bathochromic-shifted emission upon mechanical stimulation. These derivatives bind to cucurbit[8]uril to form homoternary host-guest inclusion complexes through host-stabilized intermolecular charge transfer interactions. Remarkably, the homoternary complexes exhibit longer emission than that of free guests in the solid state (even longer than ground guests), and a further bathochromic-shifted emission is observed upon grinding. Additionally, a heteroternary complex constructed through the encapsulation of pyrene (donor) and pyridinium (acceptor) guest pair in cucurbit[8]uril also displays the mechanochromic luminescent property. This work not only discloses the effect of host-guest inclusion on the mechanochromic property of organic molecules, but also provides a principle and a facile way to design the sequentially red-shifted mechanochromic materials.

Self-assembled supramolecular artificial light-harvesting nanosystems: construction, modulation, and applications

Artificial light-harvesting systems, an elegant way to capture, transfer and utilize solar energy, have attracted great attention in recent years. As the primary step of natural photosynthesis, the principle of light-harvesting systems has been intensively investigated, which is further employed for artificial construction of such systems. Supramolecular self-assembly is one of the feasible methods for building artificial light-harvesting systems, which also offers an advantageous pathway for improving light-harvesting efficiency. Many artificial light-harvesting systems based on supramolecular self-assembly have been successfully constructed at the nanoscale with extremely high donor/acceptor ratios, energy transfer efficiency and the antenna effect, which manifests that self-assembled supramolecular nanosystems are indeed a viable way for constructing efficient light-harvesting systems. Non-covalent interactions of supramolecular self-assembly provide diverse approaches to improve the efficiency of artificial light-harvesting systems. In this review, we summarize the recent advances in artificial light-harvesting systems based on self-assembled supramolecular nanosystems. The construction, modulation, and applications of self-assembled supramolecular light-harvesting systems are presented, and the corresponding mechanisms, research prospects and challenges are also briefly highlighted and discussed.

General Graph Neural Network-Based Model To Accurately Predict Cocrystal Density and Insight from Data Quality and Feature Representation

Cocrystal engineering as an effective way to modify solid-state properties has inspired great interest from diverse material fields while cocrystal density is an important property closely correlated with the material function. In order to accurately predict the cocrystal density, we develop a graph neural network (GNN)-based deep learning framework by considering three key factors of machine learning (data quality, feature presentation, and model architecture). The result shows that different stoichiometric ratios of molecules in cocrystals can significantly influence the prediction performances, highlighting the importance of data quality. In addition, the feature complementary is not suitable for augmenting the molecular graph representation in the cocrystal density prediction, suggesting that the complementary strategy needs to consider whether extra features can sufficiently supplement the lacked information in the original representation. Based on these results, 4144 cocrystals with 1:1 stoichiometry ratio are selected as the dataset, supplemented by the data augmentation of exchanging a pair of coformers. The molecular graph is determined to learn feature representation to train the GNN-based model. Global attention is introduced to further optimize the feature space and identify important atoms to realize the interpretability of the model. Benefited from the advantages, our model significantly outperforms three competitive models and exhibits high prediction accuracy for unseen cocrystals, showcasing its robustness and generality. Overall, our work not only provides a general cocrystal density prediction tool for experimental investigations but also provides useful guidelines for the machine learning application. All source codes are freely available at https://github.com/Xiao-Gua00/CCPGraph.

Doping of charge-transfer molecules in cocrystals for the design of materials with novel piezo-activated luminescence

A novel piezo-activated luminescent material with wide range modulation of the luminescence wavelength and a giant intensity enhancement upon compression was prepared using a strategy of molecular doping. The doping of THT molecules into TCNB-perylene cocrystals results in the formation of a weak but pressure-enhanced emission center in the material at ambient pressure. Upon compression, the emissive band from the undoped component TCNB-perylene undergoes a normal red shift and emission quenching, while the weak emission center shows an anomalous blue shift from 615 nm to 574 nm and a giant luminescence enhancement up to 16 GPa. Further theoretical calculations show that doping by THT could modify intermolecular interactions, promote molecular deformation, and importantly, inject electrons into the host TCNB-perylene upon compression, which contributes to the novel piezochromic luminescence behavior. Based on this finding, we further propose a universal approach to design and regulate the piezo-activated luminescence of materials by using other similar dopants.

Organic binary charge-transfer compounds of 2,2' : 6',2'' : 6'',6-trioxotriphenylamine and a pyrene-annulated azaacene as donors

Three binary charge-transfer (CT) compounds resulting from the donor 2,2' : 6',2'' : 6'',6-trioxotriphenylamine (TOTA) and the acceptors F4TCNQ and F4BQ and of a pyrene-annulated azaacene (PAA) with the acceptor F4TCNQ are reported. The identity of these CT compounds are confirmed by single-crystal X-ray diffraction as well as by IR, UV-vis-NIR and EPR spectroscopy. X-ray diffraction analysis reveals a 1 : 1 stoichiometry for TOTA·F4TCNQ, a 2 : 1 donor : acceptor ratio in (TOTA)2·F4BQ, and a rare 4 : 1 stoichiometry in (PAA)4·F4TCNQ, respectively. Metrical parameters of the donor (D) and acceptor (A) constituents as well as IR spectra indicate full CT in TOTA·F4TCNQ, partial CT in (TOTA)2·F4BQ and only a very modest one in (PAA)4·F4TCNQ. Intricate packing motifs are present in the crystal lattice with encaged, π-stacked (F4TCNQ-)2 dimers in TOTA·F4TCNQ or mixed D/A stacks in the other two compounds. Their solid-state UV-vis-NIR spectra feature CT transitions. The CT compounds with F4TCNQ are electrical insulators, while (TOTA)2·F4BQ is weakly conducting.

A new strategy: realization of organic heteroepitaxy and organic alloys based on the similarity of CC and NN

The similarity of NN and CC in trans-4,4′-azobis(pyridine) and trans-1,2-bis(pyridin-4-yl)ethene offers an innovative approach for creating controllable and versatile organic heterostructure and organic alloy.

Harnessing Polymer-Matrix-Mediated Manipulation of Intermolecular Charge-Transfer for Near-Infrared Security Applications

Precise recognition of near-infrared (NIR) signals holds great prospects in optical communication, remote sensing, information security, and anti-counterfeiting. For these applications, filters with good NIR transparency are typically essential components. Currently, such NIR transparent filters are dominated by inorganic materials such as chalcogenide glasses. There are, so far, only a handful of organic molecules with suitable optical properties due to the rarity of organic materials with good NIR transparency and relatively flat absorption over the UV-visible region. Here, it is found that the library of NIR-transparent organic materials can be expanded by forming a charge-transfer complex (CTC) between a donor (D) and an acceptor (A) molecule that are commercially available. Via regulating the DA interaction, the CTC filter shows tunable absorption from the visible to NIR region with a relatively high penetration of NIR radiation (≈80%). The CTC filter can successfully highlight NIR information hidden in a complex environment and allow reading of NIR security images for advanced anti-counterfeiting. Moreover, the CTC filter can be used for viewing protected NIR information with good resolution, and thus provide a convenient tool for different security applications using NIR-encoded information.

Controlled tuning of radiative-nonradiative transition via solvent perturbation: Franck-Condon emission vs. aggregation caused quenching

Organic molecules with tunable fluorescence quantum yield are attractive for opto-electronic applications. A fluorophore with tunable fluorescence quantum yield should be a better choice for a variety of applications that demand fluorophores with different quantum yields. Here organic emitters with a continuous bell-shaped fluorescence yield profile would be promising in view of sustainability and reusability; however, fluorophores with these properties are rarely reported. A bis-indole derivative, 3,3'-bisindolyl(phenyl)methane (BIPM), was synthesised and found to undergo a unique 'rise-and-fall' profile in fluorescence yield with a compositional change of the 1,4-dioxane (DiOx)-H₂O solvent system. A predominant interplay of two contrasting factors, (a) polarity and proticity induced emission enhancement and (b) aggregation caused fluorescence quenching, on either side of a crossover solvent composition (∼50% f_W), resulted in a continuous bell-patterned fluorescence yield profile. Interestingly, these two factors could be observed individually or simultaneously by adjusting the H₂O fraction. Detailed spectroscopic, electron microscopic and computational studies have been performed to substantiate the photophysics behind the solvent regulated modulation of fluorescence quantum yield.

Hierarchical supramolecular co-assembly formation employing multi-component light-harvesting charge transfer interactions giving rise to long-wavelength emitting luminescent microspheres

Charge transfer (CT) interaction induced formation of a hierarchical supramolecular assembly has attracted attention due to its wide diversity of structural and functional characteristics. In the present work, we report the generation of green luminescent microspheres from the charge transfer interaction induced co-assembly of a bis-naphthyl dipicolinic amide (DPA) derivative with tetracyanobenzene (TCNB) for the first time. The properties of these self-assemblies were studied both in solution and the solid-state using spectroscopic and a variety of microscopy techniques. The X-ray crystal structure analysis showed a mixed stack arrangement of DPA and TCNB. The molecular orbital and energy level calculations confirm the charge transfer complex formation between DPA and TCNB. Furthermore, energy transfer was observed from the green luminescent CT complex to a red-emitting dye, pyronin Y, in the microsphere matrix, leading to the formation of a light-harvesting tri-component self-assembly.

Single-Component White Light Emission from a Metal-Coordinated Cyclotriveratrylene-Based Coordination Polymer

A coordination polymer, namely, [Cd₃L(H₂O)₃]·DMA·4H₂O (1) (DMA = N,N-dimethylacetamide), was prepared by the solvothermal reaction of cyclotriveratrylene-based ligand 5,6,12,13,19,20-hexacarboxy-methoxy-cyclotriveratrylene (H₆L) and Cd(NO₃)₂·4H₂O. In 1, a two-dimensional structure was constructed by the connection of hexanuclear Cd-O clusters and L^6- anions. Photoluminescence measurements indicated that 1 displayed tunable photoluminescence through the variation of the excitation wavelength. Significantly, the white light emission of 1 can be observed with a broad excitation wavelength range from 320 to 385 nm. When 1 is excited by 385 nm light, its chromatic coordinate is (0.29, 0.34), which is located very close to the pure white light region (0.33, 0.33). Meanwhile, the color temperature (CCT) is 7994 K, which corresponds well to "cold" white light.

Color-Tunable Supramolecular Luminescent Materials

Constructing multicolor photoluminescent materials with tunable properties is an attractive research objective on account of their abundant applications in materials science and biomedical engineering. By comparison with covalent synthesis, supramolecular chemistry has provided a more competitive and promising strategy for the production of organic materials and the regulation of their photophysical properties. By taking advantage of dynamic and reversible noncovalent bonding interactions, supramolecular strategies can, not only simplify the design and fabrication of organic materials, but can also endow them with dynamic reversibility and stimuli responsiveness, making it much easier to adjust the superstructures and properties of the materials. Occasionally, it is possible to introduce emergent properties into these materials, which are absent in their precursor compounds, broadening their potential applications. In an attempt to highlight the state-of-the-art noncovalent strategies available for the construction of smart luminescent materials, an overview of color-tunable materials is presented in this Review, with the emphasis being placed on the examples drawn from host-guest complexes, supramolecular assemblies and crystalline materials. The noncovalent synthesis of room-temperature phosphorescent materials and the modulation of their luminescent properties are also described. Finally, future directions and scientific challenges in the emergent field of color-tunable supramolecular emissive materials are discussed.

Rubrene-Directed Structural Transformation of Fullerene (C60) Microsheets to Nanorod Arrays with Enhanced Photoelectrochemical Properties

One-dimensional (1D) nanostructures possess huge potential in electronics and optoelectronics, but the axial alignment of such 1D structures is still a challenging task. Herein, we report a simple method that enables two-dimensional (2D) C₆₀ microsheets to evolve into highly ordered nanorod arrays using rubrene as a structure-directing agent. The structural transformation is accomplished by adding droplets of rubrene-m-xylene solution onto C₆₀ microsheets and allowing the m-xylene solvent to evaporate naturally. In sharp contrast, when rubrene is absent from m-xylene, randomly oriented C₆₀ nanorods are produced. Spectroscopic and microscopic characterizations collectively indicate a rather plausible transformation mechanism that the close lattice match allows the epitaxial growth of rubrene on C₆₀ microsheets, followed by the reassembly of dissolved C₆₀ along the aligned rubrene due to the intermolecular charge-transfer (CT) interactions, leading to the formation of ordered nanorod arrays. Due to the aligned structures and the CT interactions between rubrene and C₆₀, the photocurrent density of the nanorod arrays is improved by 31.2% in the UV region relative to the randomly oriented counterpart. This work presents a facile and effective strategy for the construction of ordered fullerene nanorod arrays, providing new ideas for the alignment of fullerene and other relevant organic microstructures.

Mechanical stimuli-induced multiple photophysical responsive AIEgens with high contrast properties

A new cyano-distyrylbenzene derivative with a mechano-force induced high contrast transition in color and emission was demonstrated here. Under mechanical stimuli, the emission peak can undergo a large wavelength shift from 440 nm to 650 nm, while the appearance color can switch from white to pink.

Growth direction dependent separate-channel charge transport in the organic weak charge-transfer co-crystal of anthracene-DTTCNQ

Co-crystallization is an efficient way of molecular crystal engineering to tune the electronic properties of organic semiconductors. In this work, we synthesized anthracene-4,8-bis(dicyanomethylene)4,8-dihydrobenzo[1,2-b:4,5-b']-dithiophene (DTTCNQ) single crystals as a template to study the crystal growth direction dependent charge transport properties and attempted to elucidate the mechanism by proposing a separate-channel charge transport model. Single-crystal anthracene-DTTCNQ field-effect transistors showed that ambipolar transport properties could be observed in all crystal growth directions. Furthermore, upon changing the measured crystal directions, the electronic properties experienced a weak change from n-type dominated ambipolar, balanced ambipolar, to p-type dominated ambipolar properties. The theoretical calculations at density functional theory (DFT) and higher theory levels suggested that the anthracene-DTTCNQ co-crystal motif was a weak charge-transfer complex, in line with the experiment. Furthermore, the detailed theoretical analysis also indicated that electron or hole transport properties originated from separated channels formed by DTTCNQ or anthracene molecules. We thus proposed a novel separate-channel transport mechanism to support additional theoretical analysis and calculations. The joint experimental and theoretical efforts in this work suggest that the engineering of co-crystallization of weak charge-transfer complexes can be a practical approach for achieving tuneable ambipolar charge transport properties by the rational choice of co-crystal formers.

Enhanced luminescence of single-benzene fluorescent molecules through halogen bond cocrystals

Organic single fluorescent molecules often suffer from aggregation-induced quenching effect under solid-state conditions, especially for red-emissive molecules, due to the flat rigid molecular framework and strong π-π interaction. Cocrystal engineering...

Arene-Perfluoroarene Interactions Confer Enhanced Mechanical Properties to Synthetic Nanotubes

Supramolecular nanotubes prepared through macrocycle assembly offer unique properties that stem from their long-range order, structural predictability, and tunable microenvironments. However, assemblies that rely on weak non-covalent interactions often have limited aspect ratios and poor mechanical integrity, which diminish their utility. Here pentagonal imine-linked macrocycles are prepared by condensing a pyridine-containing diamine and either terephthalaldehyde or 2,3,5,6-tetrafluoroterephthalaldehyde. Atomic force microscopy and synchrotron in solvo X-ray diffraction demonstrate that protonation of the pyridine groups drives assembly into high-aspect ratio nanotube assemblies. A 1 : 1 mixture of each macrocycle yielded nanotubes with enhanced crystallinity upon protonation. UV-Vis and fluorescence spectroscopy indicate that nanotubes containing both arene and perfluoroarene subunits display spectroscopic signatures of arene–perfluoroarene interactions. Touch-spun polymeric fibers containing assembled nanotubes prepared from the perhydro- or perfluorinated macrocycles exhibited Young's moduli of 1.09 and 0.49 GPa, respectively. Fibers containing nanotube assemblies reinforced by arene–perfluoroarene interactions yielded a 93% increase in the Young's modulus over the perhydro derivative, up to 2.1 GPa. These findings demonstrate that tuning the chemical composition of the monomeric macrocycles can have profound effects on the mechanical strength of the resulting assemblies. More broadly, these results will inspire future studies into tuning orthogonal non-covalent interactions between macrocycles to yield nanotubes with emergent functions and technological potential.

Arene–perfluoroarene interactions resulted in enhanced crystallinity between analogous perhydro- and perfluoro macrocycles in a supramolecular nanotube assembly.

The competitive role of C–H⋯X (X = F, O) and π–π interactions in contributing to the degree of charge transfer in organic cocrystals: a case study of heteroatom-free donors with p-fluoranil (FA)

Four binary organic charge transfer cocrystals were grown by the slow cooling method. The competitive role of C–H⋯X (X = F, O) and π–π interactions in contributing to the degree of charge transfer in the cocrystals was investigated.

Unravelling Supramolecular Features and Opto-electronic Properties of Binary Charge Transfer Cocrystal of Blue Fluorescent Di-carbazole and TFT

Co-assembled crystalline organic systems demonstrate advanced opto-electronic properties by maintaining high molecular order in the crystal packing through non-covalent interactions. In this contribution, a 1:2 donor acceptor charge transfer cocrystal...

Hyperbranched Microwire Networks of Organic Cocrystals with Optical Waveguiding and Light-Harvesting Abilities

We report the synthesis of hyperbranched organic microwire (MW) networks comprising 1,4-bis(pentafluorostyryl)benzene (10Ft) and 9,10-bis(phenylethynyl)anthracene (BA) using a simple solution co-assembly route. Pure 10Ft or BA assemblies cannot produce such complex MW networks; in contrast with a binary cocrystal of 10Ft and BA with a 2:1 molar ratio ((2:1)10Ft:BA), which is formed via intermolecular arene-perfluoroarene (AP) interactions. A new generation of multiple MWs grow epitaxially on the previous generation of MWs to form MW arrays in which BA may also act as an intermediate product to facilitate the regeneration of (2:1)10Ft:BA. Highly aligned and well-connected MW networks enable superior optical waveguiding ability. Moreover, a red-emitting dopant, 5,12-bis(phenylethynyl)naphthacene (BN) was incorporated into (2:1)10Ft:BA host MWs, giving light-harvesting hierarchical MW networks via an energy-transfer (ET) process. The realization of the hyperbranched MWs provides us with deep insight into the rational creation of complex branched arrays from functional organic cocrystals.

Organic Cocrystals: Recent Advances and Perspectives for Electronic and Magnetic Applications

Cocrystal engineering is an advanced supramolecular strategy that has attracted a lot of research interest. Many studies on cocrystals in various application fields have been reported, with a particular focus on the optoelectronics field. However, few articles have combined and summarized the electronic and magnetic properties of cocrystals. In this review, we first introduce the growth methods that serve as the basis for realizing the different properties of cocrystals. Thereafter, we present an overview of cocrystal applications in electronic and magnetic fields. Some functional devices based on cocrystals are also introduced. We hope that this review will provide researchers with a more comprehensive understanding of the latest progress and prospects of cocrystals in electronic and magnetic fields.

Creating Organic Functional Materials beyond Chemical Bond Synthesis by Organic Cocrystal Engineering

Organic cocrystal engineering refers to two or more organic molecules stoichiometrically combined and held together by noncovalent intermolecular interactions, which differs from standard chemical synthesis involving covalent bond breakage and formation. Organic cocrystals have unique properties and offer a new strategy for creating enhanced organics. First, however, some key questions need to be addressed: How do diverse monomers affect the intermolecular interaction kinetics during cocrystallization? How do the intermolecular forces in cocrystals affect cocrystal functions? In this Perspective, the definition and advantages of organic cocrystal engineering, specifically in the construction of a reliable intermolecular interaction-stacking structure-performance relationship, are outlined. Additionally, recent developments in the field and the questions above are discussed. Finally, a brief conclusion and some hints on likely future developments are provided.

Synthesis of luminescent cocrystals based on fluoranthene and the analysis of weak interactions and photophysical properties

A series of luminescent cocrystals with fluoranthene (C₁₆H₁₀) as the fluorophore and benzene-1,2,4,5-tetracarbonitrile (TCNB, C₁₀H₂N₄), 2,3,5,6-tetrafluorobenzene-1,4-dicarbonitrile (TFP, C₈F₄N₂) and 1,2,3,4,5,6,7,8-octafluoronaphthalene (OFN, C₁₀F₈) as the coformers was designed and synthesized. Structure analysis revealed that these layered structures were due to charge transfer, π-π interactions and hydrogen bonding. Density functional theory (DFT) calculations show that fluoranthene-TCNB and fluoranthene-TFP have charge-transfer properties, while fluoranthene-OFN does not, indicating that fluoranthene-OFN has arene-perfluoroarene (AP) interactions, which was also demonstrated by spectroscopic analysis, which shows that the photophysical properties of luminescent materials can be tuned by forming cocrystals. These results all prove that utilizing supramolecular cocrystals to develop new fluorescent materials is an effective strategy, which has much potential in optoelectronic applications.

Visualization and Manipulation of Solid-State Molecular Motions in Cocrystallization Processes

Solid-state molecular motions (SSMM) play a critical role in adjusting behaviors and properties of materials. However, research on SSMM, especially for multicomponent systems, suffers from various problems and is rarely explored. Herein, through collaboration with cocrystal engineering, visualization and manipulation of SSMM in two-component systems, namely, FSBO ((E)-2-(4-fluorostyryl)benzo[d]oxazole)/TCB (1,2,4,5-tetracyanobenzene) and PVBO ((E)-2-(2-(pyridin-4-yl)vinyl)benzo[d]oxazole)/TCB, were realized. The obtained yellow-emissive F/T (FSBO/TCB) cocrystal displayed turn-on fluorescence, and the green-emissive P/T (PVBO/TCB) cocrystal presented redder emission, both of which exhibited an aggregation-induced emission property. At varied pressure and temperature, the grinding mixtures of FSBO/TCB and PVBO/TCB displayed different molecular motions that were readily observed through the fluorescence signal. Notably, even without grinding, FSBO and TCB molecules could move over for 4 mm in a 1D tube. The unique emission changes induced by SSMM were applied in information storage and dynamic anticounterfeiting. This work not only visualized and manipulated SSMM but offered more insights for multicomponent study in aggregate science.

Improving the Overall Properties of Circularly Polarized Luminescent Materials Through Arene-Perfluoroarene Interactions

A major trade-off in the field of circularly polarized luminescence (CPL) of pure organic materials is that the large luminescence dissymmetry factor (g_lum ) usually gives rise to the suppression of luminescence efficiency (Φ_PL ). Here, a supramolecular self-assembled system, driven by arene-perfluoroarene (AP) interactions of chiral polycyclic aromatic hydrocarbons (PAHs) and octafluoronaphthalene (OFN), is reported to provide a solution to this problem. Two kinds of chiral PAHs based on pyrene and anthracene could co-assemble with OFN in hybrid solvents to form long-range-ordered AP assemblies. The detailed process of AP interaction driving self-assembly was verified by morphological measurements and fluorescence spectra. The AP assemblies exhibited chirality amplification not only in the excited state but also in the ground state. In addition, the AP assemblies showed an enhanced luminescence efficiency compared with the individual chiral PAHs due to the energy-barrier effect of OFN. The present strategy based on AP interactions could be applied to boost the development of highly efficient CPL-active materials.

Molecular Crystal Microcapsules: Formation of Sealed Hollow Chambers via Surfactant-Mediated Growth

Hollow organic molecular cocrystals comprised of 9-methylanthracene-1,2,4,5-tetracyanobenzene (9MA-TCNB) and naphthalene-1,2,4,5-tetracyanobenzene (NAPH-TCNB) were fabricated using a surfactant-mediated co-reprecipitation method. The crystals exhibit a narrow size distribution that can be easily tuned by varying the concentration of surfactant and incubation temperature. The rectangular crystals possess symmetrical twinned cavities with an estimated storage volume on the order of 10^-10  L. An aqueous dye solution can be incorporated into the cavities during crystal growth and stored inside for up to several hours, confirming the sealed nature of the hollow chambers. Our results demonstrate that it is possible to harness non-classical crystal growth to fabricate organic molecular crystals with novel topologies.

Green Grinding-Coassembly Engineering toward Intrinsically Luminescent Tetracene in Cocrystals

Developing an effective and green method toward organic functional cocrystals based on the solubility-mismatched coformers is highly desirable and very important. Herein, we applied a green two-step liquid-assisted-grinding coassembly (LAGC) in fabricating tetracene-octafluoronaphthalene (TC-OFN) cocrystals from solubility-mismatched pairs of tetracene (TC, poorly soluble, 0.2 mg mL^-1) and octafluoronaphthalene (OFN, highly soluble, 0.2 × 10⁴ mg mL^-1). Such cocrystals are extremely difficult to prepare through the common solution-processing strategies. More importantly, this two-step LAGC process could allow us to efficiently prepare TC-OFN cocrystals in gram scale. The as-prepared cocrystals displayed the intrinsic green emission of TC with much higher photoluminescence quantum yield (13.75%) comparing with the pure solid TC with the almost-quenched emission (0.41%, aggregation-caused quenching (ACQ)). The ultrafast spectra study on these cocrystals verifies the successful barrier function of OFN molecules in interrupting the well-known singlet fission (SF) in TC solids. Furthermore, this method can allow us to easily fabricate fluorescent TC-OFN water inks, which can be employed to prepare luminescent paintings or highly emissive ultratransparent/flexible films.

Multifunctional Features of Organic Charge-Transfer Complexes: Advances and Perspectives

The recent progress of charge-transfer complexes (CTCs) for application in many fields, such as charge transport, light emission, nonlinear optics, photoelectric conversion, and external stimuli response, makes them promising candidates for practical utility in pharmaceuticals, electronics, photonics, luminescence, sensors, molecular electronics and so on. Multicomponent CTCs have been gradually designed and prepared as novel organic active semiconductors with ideal performance and stability compared to single components. In this review, we mainly focus on the recently reported development of various charge-transfer complexes and their performance in field-effect transistors, light-emitting devices, lasers, sensors, and stimuli-responsive behaviors.

The Stoichiometry of TCNQ-Based Organic Charge-Transfer Cocrystals

Organic charge-transfer cocrystals (CTCs) have attracted significant research attention due to their wide range of potential applications in organic optoelectronic devices, organic magnetic devices, organic energy devices, pharmaceutical industry, etc. The physical properties of organic charge transfer cocrystals can be tuned not only by changing the donor and acceptor molecules, but also by varying the stoichiometry between the donor and the acceptor. However, the importance of the stoichiometry on tuning the properties of CTCs has still been underestimated. In this review, single-crystal growth methods of organic CTCs with different stoichiometries are first introduced, and their physical properties, including the degree of charge transfer, electrical conductivity, and field-effect mobility, are then discussed. Finally, a perspective of this research direction is provided to give the readers a general understanding of the concept.