Rational Control of Charge Transfer Excitons Toward High‐Contrast Reversible Mechanoresponsive Luminescent Switching

Commercializable Naphthalene Diimide Anolytes for Neutral Aqueous Organic Redox Flow Batteries

Neutral aqueous organic redox flow batteries (AORFBs) hold the potential to facilitate the transition of renewable energy sources from auxiliary to primary energy, the commercial production of anolyte materials still suffers from insufficient performance of high-concentration and the high cost of the preparation problem. To overcome these challenges, this study provides a hydrothermal synthesis methodology and introduces the charged functional groups into hydrophobic naphthalene diimide cores, and prepares a series of high-performance naphthalene diimide anolytes. Under the synergistic effect of π-π stacking and H-bonding networks, the naphthalene diimide exhibits excellent structural stability and the highest water solubility (1.85 M for dex-NDI) reported to date. By employing the hydrothermal method, low-cost naphthalene diimides are successfully synthesized on a hundred-gram scale of $0.16 g-1 ($2.43 Ah-1), which is also the lowest price reported to date. The constructed full battery achieves a high electron concentration of 2.4 M, a high capacity of 54.4 Ah L-1, and a power density of 318 mW cm-2 with no significant capacity decay observed during long-duration cycling. These findings provide crucial support for the commercialization of AORFBs and pave the way for revolutionary developments in neutral AORFBs.

High Mobility Emissive Excimer Organic Semiconductor Towards Color-Tunable Light-Emitting Transistors

Organic light-emitting transistors (OLETs) are highly integrated and minimized optoelectronic devices with significant potential superiority in smart displays and optical communications. To realize these various applications, it is urgently needed for color-tunable emission in OLETs, but remains a great challenge as a result of the difficulty for designing organic semiconductors simultaneously integrating high carrier mobility, strong solid-state emission, and the ability for potential tunable colors. Herein, a high mobility emissive excimer organic semiconductor, 2,7-di(2-anthryl)-9H-fluorene (2,7-DAF) was reasonably designed by introducing a rotatable carbon-carbon single bond connecting two anthracene groups at the 2,7-sites of fluorene, and the small torsion angles simultaneously guarantee effective conjugation and suppress fluorescence quenching. Indeed, the unique stable dimer arrangement and herringbone packing mode of 2,7-DAF single crystal enables its superior integrated optoelectronic properties with high carrier mobility of 2.16 cm2  ⋅ V-1  ⋅ s-1 , and strong excimer emission with absolute photoluminescence quantum yield (PLQY) of 47.4 %. Furthermore, the voltage-dependent electrically induced color-tunable emission from orange to blue was also demonstrated for an individual 2,7-DAF single crystal based OLETs for the first time. This work opens the door for a new class of high mobility emissive excimer organic semiconductors, and provides a good platform for the study of color-tunable OLETs.

Mechanochromic aromatic hydrocarbons that bear one simple substituent

Structurally simple aromatic hydrocarbons that possess only one isocyano group show luminescent mechanochromism. The structural isomers of these aromatic hydrocarbons exhibit blue- and red-shifted emission bands upon mechanical stress. Their low molecular weight enables their sublimation under mild conditions.

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.

Stimuli-fluorochromic smart organic materials

Smart materials based on stimuli-fluorochromic π-conjugated solids (SFCSs) have aroused significant interest due to their versatile and exciting properties, leading to advanced applications. In this review, we highlight the recent developments in SFCS-based smart materials, expanding beyond organometallic compounds and light-responsive organic luminescent materials, with a discussion on the design strategies, exciting properties and stimuli-fluorochromic mechanisms along with their potential applications in the exciting fields of encryption, sensors, data storage, display, green printing, etc. The review comprehensively covers single-component and multi-component SFCSs as well as their stimuli-fluorochromic behaviors under external stimuli. We also provide insights into current achievements, limitations, and major challenges as well as future opportunities, aiming to inspire further investigation in this field in the near future. We expect this review to inspire more innovative research on SFCSs and their advanced applications so as to promote further development of smart materials and devices.

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.

Structure-activity strategies for mechanically responsive fluorescent materials: a molecular perspective

Mechanical response luminescence (MRL) describes the photophysical properties triggered by mechanical stimulation. Usually, MRL can be regulated by intermolecular interactions, molecular conformation or molecular packing, to achieve the desirable optical properties. Herein, at the molecular level, this review covers the factors that influence mechanically responsive fluorescent materials, involving the single- or multifactorial modulation of aliphatic chains, donor-receptor switch, substituent adjustment, and position isomerism. According to these factors, the structure-activity strategies can be summarized as: (i) the self-recovery of optical properties, from the final to initial state, can be regulated by introducing long alkyl chains to a fluorophore. (ii) The sensitivity of MRL materials can be controlled by modifying the donor-acceptor structure via the changed ICT (intramolecular charge transfer) and intramolecular interaction. (iii) The electronic and steric effects of substituents can affect ICT and intermolecular interactions, thereby resulting in high quantum yield and high-contrast MRL materials via changing the molecular stacking of crystalline states. (iv) Intermolecular interaction is modulated by the position isomerism of the substituents, which results in switched molecular packing for the extended response toward a wide range of stimuli. It is anticipated that the molecular mechanisms of these structure-activity relationships will serve as a significant reference for developing novel, high contrast, recyclable mechanical response luminous materials.

Spatially Resolved Organic Whispering-Gallery-Mode Hetero-Microrings for High-Security Photonic Barcodes

Whispering-gallery-mode (WGM) microcavities featuring distinguishable sharp peaks in a broadband exhibit enormous advantages in the field of miniaturized photonic barcodes. However, such kind of barcodes developed hitherto are primarily based on microcavities wherein multiple gain medias were blended into a single matrix, thus resulting in the limited and indistinguishable coding elements. Here, a surface tension assisted heterogeneous assembly strategy is proposed to construct the spatially resolved WGM hetero-microrings with multiple spatial colors along its circular direction. Through precisely regulating the charge-transfer (CT) strength, full-color microrings covering the entire visible range were effectively acquired, which exhibit a series of sharp and recognizable peaks and allow for the effective construction of high-quality photonic barcodes. Notably, the spatially resolved WGM hetero-microrings with multiple coding elements were finally acquired through heterogeneous nucleation and growth controlled by the directional diffusion between the hetero-emulsion droplets, thus remarkably promoting the security strength and coding capacity of the barcodes. The results would be useful to fabricate new types of organic hierarchical hybrid WGM heterostructures for optical information recording and security labels.

Functional Molecular Crystals from the Arylation of a Halogenoplatinum Complex: Stimuli Responsiveness, Comproportionation, and π-Bridged Dimerization

A chloroplatinum complex was arylated to obtain stimuli-responsive molecular crystals. The resulting arylplatinum complex showed polymorph-dependent emission, mechano- and thermochromic luminescence as well as comproportionation and π-bridged dimerization. Simple mixing of structurally similar arylplatinum complexes at room temperature resulted in the transfer of their aryl groups (comproportionation), which allowed their mechanochromic profiles to be tuned. We also found that recrystallization of the complex afforded a dimerized product in which two platinum ions are bridged by aryl groups resulting in a very short (3.0466(10) Å) Pt-Pt distance.

Hypso- or bathochromic phosphorescent mechanochromic mononuclear Cu(I) complexes with a bis(2-diphenylphosphinophenyl)ether auxiliary ligand

Six phosphorescence-emitting metal-organic mononuclear Cu(I) complexes, namely four quinoline-containing three-coordinate Cu(I) complexes and two N-heterocyclic carbene-containing four-coordinate Cu(I) complexes, have been successfully developed and fully characterized. All these Cu(I) complexes include the same bis(2-diphenylphosphinophenyl)ether bidentate auxiliary ligand. Significantly, four-coordinate Cu(I) complexes 1 and 2 display typical aggregation-induced emission phenomena. Their solid samples of luminogenic complexes 1-6 emit a variety of different phosphorescence. Furthermore, solid-state phosphorescence of these Cu(I) complexes can be effectively manipulated by external mechanical force. Remarkably, luminophores 1, 2 and 5 exhibit blue-shifted mechanoluminochromism responses, while luminophores 3, 4 and 6 present red-shifted mechanoluminochromism characteristics. All of the observed mechano-responsive phosphorescence changes of solids 1-6 are reversible by the method of solvent fuming. Powder X-ray diffraction results confirm that the reversible mechanically induced phosphorescence changes of complexes 1-6 are due to the mutual transformation of ordered crystalline and metastable amorphous states.

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 Charge-Transfer Chiral π-Materials: Stimuli-Responsive Circularly Polarized Luminescence and Chiroptical Photothermic Effects

Despite significant achievements in the field of chiroptical organic materials, the full utilization of both the excited state and ground state chiroptical properties in a single supramolecular system is still rarely disclosed. Here, we report that the rational combination of the charge-transfer (CT) interaction with the spacer effect and controlled protonation of π-histidine leads to chiroptical organic π-materials with both circularly polarized luminescence (CPL) and the supramolecular chirality-directed chiroptical photothermic effect. Three pyrene-conjugated histidine derivatives with varied acyl linkers (PyHis, PyC1His, and PyC3His) were designed to coassemble with electron-deficient 1,2,4,5-tetracyanobenzene (TCNB), leading to the formation of supramolecular CT complexes with intense orange to red CPL depending on the linker length. The linker length also affected the protonation-induced CPL responsiveness of the corresponding CT assemblies. Upon protonation of the histidine moiety, PyC3His/TCNB CT assemblies exhibited an inverted CPL signal, while PyHis/TCNB pairs gave quenched CPL due to the disassembly. The protonation-controlled PyC3His/TCNB CT assemblies at varied pH values showed different chiroptical photothermic effects (CPEs) for the same incident chiral light despite the molecular chirality of PyC3His remaining unchanged, supporting an interesting supramolecular chirality-directed photothermic effect.

Full-Color Emissive D-D-A Carbazole Luminophores: Red-to-NIR Mechano-fluorochromism, Aggregation-Induced Near-Infrared Emission, and Application in Photodynamic Therapy

The preparation of multifunctionalized luminophores with full-color emission based on an identical core skeleton is a significative but challenging research topic. In this work, eight donor-donor-acceptor (D-D-A)-type luminogens based on a central carbazole core bearing a C₆ hydrocarbon chain were designed by using different kinds of donor and acceptor units on the left and right, and synthesized in good yields. These D-D-A carbazole derivatives display deep-blue, sky-blue, cyan, green, yellow-green, yellow, orange and red fluorescence in the solid state, achieving full-color emission covering the whole visible light range under UV light illumination. Notably, the dicyano-functionalized triphenylamine-containing carbazole derivative exhibits rare aggregation-induced near-infrared emission and red-to-near-infrared mechano-fluorochromism with high contrast beyond 100 nm. Furthermore, the red-emissive luminogen can serve as a potential candidate for cell imaging and photodynamic therapy (PDT). This work not only provides reference for the construction of full-color emissive systems but also opens a new avenue to the preparation of multifunctionalized luminophores capable of simultaneous application in near-Infrared mechanical-force sensors and PDT fields.

Energy Level, Crystal Morphology and Fluorescence Emission Tuning in Cocrystals via Molecular-Level Engineering

Organic donor-acceptor complexes as new organic semiconductor class have attracted wide attention, due to their potential applications in functional optoelectronics. Herein, we present two new charge transfer cocrystals of di-cyanodiazafluorene -perylene (DCPE) and di-cyanodiazaflfluorene-pyrene (DCPY) through a rational cocrystal-engineering strategy. Although they are both 1 : 1 mixed stacking cocrystals with similar chemical structures, the DCPE cocrystal possesses a non-centrosymmetric space group and narrower band gap compared to DCPY cocrystal, because of the non-covalent bonding variation. The electrostatic potential accumulated in the lateral facets leads to highly twisted DCPE nanobelts, and the small band gap causes near infrared fluorescence. Meanwhile, the DCPY crystals with centrosymmetric space groups and weaker intermolecular interactions exhibited an untwisted morphology and red emission. This study will be helpful for the design and understanding of functional cocrystal materials that can be used in flexible micro/nano-mechanics, mechanical energy, and optical devices.

Synthesis, Photoswitching Behavior and Nonlinear Optical Properties of Substituted Tribenzo[a,d,g]coronene

A family of tribenzocoronene derivatives bearing various substituents (3) were constructed through the Diels-Alder reaction, followed by the Scholl oxidation, where the molecular structure of 3b was determined via single crystal X-ray diffraction analysis. The effect of substitution on the optical and electrochemical property was systematically investigated, with the assistance of theoretical calculations. Moreover, the thin films of the resulting molecules 3b and 3e complexed with fullerene produced strong photocurrent response upon irradiation of white light. In addition, 3b and 3e exhibit a positive nonlinear optical response resulting from the two-photon absorption and excited state absorption processes.

Color-Tunable Upconversion-Emission Switch Based on Cocrystal-to-Cocrystal Transformation

Cocrystal engineering, involving the assembly of two or more components into a highly ordered solid-state superstructure, has emerged as a popular strategy for tuning the photophysical properties of crystalline materials. The reversible co-assembly and disassembly of multicomponent cocrystals and their reciprocal transformation in the solid state remain challenging objectives. Herein, we report a color-tunable upconversion-emission switch based on the interconversion between two cocrystals. One red- and one yellow-emissive cocrystal, composed of an electron-deficient naphthalenediimide-based triangular macrocycle and different electron donors, have been obtained. The red- and yellow-emissive cocrystals undergo reversible transformations on exchanging the electron donors. Benefiting from intermolecular charge transfer interactions, the two cocrystals display superior two-photon excited upconversion emission. Accompanying the interconversion of the two cocrystals, their luminescent color changes between red and yellow, forming a dual-color upconversion-emission switch. This research provides a rare yet critical example involving precise control of cocrystal-to-cocrystal transformation and affords a reference for fabricating color-tunable nonlinear optical materials in the solid state.

Universal Concept for Bright, Organic, Solid-State Emitters─Doping of Small-Molecule Ionic Isolation Lattices with FRET Acceptors

Brightly fluorescent solid-state materials are highly desirable for bioimaging, optoelectronic applications, and energy harvesting. However, the close contact between π-systems most often leads to quenching. Recently, we developed small-molecule ionic isolation lattices (SMILES) that efficiently isolate fluorophores while ensuring very high densities of the dyes. Nevertheless, efficient Förster resonance energy transfer (FRET) energy migration in such dense systems is inevitable. While attractive for energy harvesting applications, FRET also significantly compromises quantum yields of fluorescent solids by funneling the excitation energy to dark trap states. Here, we investigate the underlying property of FRET and exploit it to our favor by intentionally introducing fluorescent dopants into SMILES materials, acting as FRET acceptors with favorable photophysical properties. This doping is shown to outcompete energy migration to dark trap states while also ruling out reabsorption effects in dense SMILES materials, resulting in universal fluorescent solid-state materials (thin films, powders, and crystals) with superior properties. These include emission quantum yields reaching as high as 50-65%, programmable fluorescence lifetimes with mono-exponential decay, and independent selection of absorption and emission maxima. The volume normalized brightness of these FRET-based SMILES now reach values up to 32,200 M^-1 cm^-1 nm^-3 and can deliver freely tunable spectroscopic properties for the fabrication of super-bright advanced optical materials. It is found that SMILES prohibit PET quenching between donor and acceptor dyes that is observed for non-SMILES mixtures of the same dyes. This allows a very broad selection of donor and acceptor dyes for use in FRET SMILES.

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.

Mechanofluorochromism of 2-Biarylyl Cinchoninic Acids with High Sensitivity and Large Mechanochromic Shift

In recent years, organic mechanofluorochromism (MFC) materials have attracted wide attention in many fields. However, the exploration of MFC materials with high-contrast, high-sensitivity and high-responsiveness remains a challenge. Herein, a series of MFC materials with 2-biarylyl cinchoninic acid skeleton were successfully established, which are based on interconversion of classical/ frustrated Brönsted pairs. These compounds have the mechanochromic shift of up to 115 nm, as well as the property of stunning sensitivity and multiple responses to external mechanical force stimuli. The luminescence properties can be easily tuned by changing the substituents.

Extension of the mechanoresponsive luminescence shift via formation of a doped organic crystal

Herein, we propose a new strategy to tune the magnitude of the mechanoresponsive shift of the maximum emission wavelength (Δλ_em). The Δλ_em of thienylbenzothiadiazole crystals has been extended to 69 nm by doping with a trace amount of dithienylbenzothiadiazole, whereas the pure crystal of thienylbenzothiadiazole exhibited a Δλ_em of 10 nm. This doping strategy should accelerate the development of advanced mechanosensing materials composed of organic crystals.

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.

Development of a New Multiple Stimuli-Responsive Fluorescent Material Using the Minus Strategy Based on the Structure of Tetraphenyl-1,3-butadiene

In this study, we designed and synthesized a new class of aggregation-induced emission luminogens, which was inspired and developed from the structure of tetraphenyl-1,3-butadienes derivative (TPB-1) through the minus strategy by removing one of the phenyl groups. Among them, L1 and L4 exhibited an aggregation-induced emission effect and multistimuli-responsive chromic behavior. Moreover, two types of single crystals of L1 were obtained, and their different emission behaviors were elucidated clearly by analyzing the single-crystal data.

Multifunctional Wearable Silver Nanowire Decorated Leather Nanocomposites for Joule Heating, Electromagnetic Interference Shielding and Piezoresistive Sensing

Multifunctional wearable electronic devices based on natural materials are highly desirable for versatile applications of energy conversion, electronic skin and artificial intelligence. Herein, multifunctional wearable silver nanowire decorated leather (AgNW/leather) nanocomposites with hierarchical structures for integrated visual Joule heating, electromagnetic interference (EMI) shielding and piezoresistive sensing are fabricated via the facile vacuum-assisted filtration process. The AgNWs penetrate the micro-nanoporous structures in the corium side of leather constructing highly-efficient conductive networks. The resultant flexible and mechanically strong AgNW/leather nanocomposites exhibit extremely low sheet resistance of 0.8 Ω/sq, superior visual Joule heating temperatures up to 108 °C at low supplied voltage of 2.0 V due to efficient energy conversion, excellent EMI shielding effectiveness (EMI SE) of ≈55 dB and outstanding piezoresistive sensing ability in human motion detection. This work demonstrates the fabrication of multifunctional AgNW/leather nanocomposites for next-generation wearable electronic devices in energy conversion, electronic skin and artificial intelligence, etc.

Polymer Electrolyte Dielectrics Enable Efficient Exciton-Polaron Quenching in Organic Semiconductors for Photostable Organic Transistors

The photoelectric response of organic field-effect transistors (OFETs) will cause severe photoelectric interference, which hinders the applications of OFETs in the light environment. It is highly challenging to relieve this problem because of the high photosensitivity of most organic semiconductors. Here, we propose an efficient "exciton-polaron quenching" strategy to suppress the photoelectric response and thus construct highly photostable OFETs by utilizing a polymer electrolyte dielectric─poly(acrylic acid) (PAA). This dielectric produces high-density polarons in organic semiconductors under a gate electric field that quench the photogenerated excitons with high efficiency (∼70%). As a result, the OFETs with PAA dielectric exhibit unprecedented photostability against strong light irradiation up to 214 mW/cm², which far surpasses the reported values and solar irradiance value (∼138 mW/cm²). The strategy shows high universality in OFETs with different OSCs and electrolytes. As a demonstration, the photostable OFET can stably drive an organic light-emitting diode (OLED) under light irradiation. This work presents an efficient exciton modulation strategy in OSC and proves a high potential in practical applications.

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.

Efficient Photoinduced Electron Transfer from Pyrene-o-Carborane Heterojunction to Selenoviologen for Enhanced Photocatalytic Hydrogen Evolution and Reduction of Alkynes

A series of pyrene or pyrene-o-carborane-appendant selenoviologens (Py-SeV²⁺ , Py-Cb-SeV²⁺ ) for enhanced photocatalytic hydrogen evolution reaction (HER) and reduction of alkynes is reported. The efficient photoinduced electron transfer (PET) from electron-rich pyrene-o-carborane heterojunction (Py-Cb) with intramolecular charge transfer (ICT) characteristic to electron-deficient selenoviologen (SeV²⁺ ) (k_ET = 1.2 × 10¹⁰ s^-1 ) endows the accelerating the generation of selenoviologen radical cation (SeV^+• ) compared with Py-SeV²⁺ and other derivatives. The electrochromic/electrofluorochromic devices' (ECD and EFCD) measurements and supramolecular assembly/disassembly processes of SeV²⁺ and cucurbit[8]uril (CB[8]) results show that the PET process can be finely tuned by electrochemical and host-guest chemistry methods. By combination with Pt-NPs catalyst, the Py-Cb-SeV²⁺ -based system shows high-efficiency visible-light-driven HER and highly selective phenylacetylene reduction due to the efficient PET process.

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...

Luminescent polymorphic crystals: mechanoresponsive and multicolor-emissive properties

Polymorphic organic crystals that can switch their photophysical properties in response to mechanical stimuli are highlighted.

Tunable multiple light emissions of core-shell structures based on rare earth ions doped on the surfaces of organic cocrystals

The charge transfer (CT) interactions play a vital role in tuning the luminescence of organic crystals. Enhanced energy transfer (ET) effect in rare-earth (RE) ions is a significant method to...

The modulation effect of an electron-rich guest on the luminescence of naphthalene diimide-based metal–organic frameworks

A series of host–guest MOF materials were successfully fabricated by virtue of donor–acceptor interactions, which exhibit color-tunable emissions in a wide wavelength range by rational selection of guest molecules.

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.

Mechanochromic Luminescence (MCL) of Purely Organic Two-Component Dyes: Wide-Range MCL over 300 nm and Two-Step MCL by Charge-Transfer Complexation

Despite recent extensive studies on mechanochromic luminescence (MCL), rational control over the magnitude of the emission-wavelength shift in response to mechanical stimuli remains challenging. In the present study, a two-component donor-acceptor approach has been applied to create a variety of organic MCL composites that exhibit remarkable emission-wavelength switching. Dibenzofuran-based bis(1-pyrenylmethyl)diamine and typical organic fluorophores have been employed as donor and acceptor dyes, respectively. Outstanding wide-range MCL with an emission-wavelength shift of over 300 nm has been achieved by mixing the diamine with 3,4,9,10-perylenetetracarboxylic diimide. Unprecedented two-step MCL in response to mechanical stimuli of different intensity has also been realized for a two-component mixture with 9,10-anthraquinone. Fluorescence microscopy observations at the single-particle level revealed that the segregation and mixing of the two-component dyes contribute to the stimuli-responsive emission-color switching of the MCL composites.

Red to Near-Infrared Mechanochromism from Metal-free Polycrystals: Noncovalent Conformational Locks Facilitating Wide-Range Redshift

Piezochromic organic materials that present a large difference in fluorescence wavelength in the near-infrared region have important potential applications; however, few such metal-free luminophores have been reported. In this study, we design and prepare π-conjugated electron acceptors whose planar conformation can be locked by the noncovalent interactions. The planar fused-ring geometry can narrow the optical band gap, enhance the molecular stability and rigidity, as well as increase the radiative rate. As expected, the polymorphs Re-phase and Ni-phase emit the high-brightness fluorescence with wavelength maxima (λ_em,max ) at 615 and 727 nm, respectively. Upon full grinding, the λ_em,max of Re-phase is bathochromically shifted to 775 nm. The ground powder of Re-phase becomes metastable as a consequence of noncovalent conformational locking and that the red to near-infrared (large colour difference) mechanochromism arises from the high degree of conformational coplanarity. This strategy is both conceptually and synthetically simple and offers a promising approach to the development of organic piezochromic materials with wide-range redshift and excellent penetrability.

Understanding Mechanochromic Luminescence on Account of Molecular Level Based on Phosphorescent Iridium(III) Complex Isomers

Mechanochromic luminescent (MCL) materials are promising in pressure sensors, security papers, photoelectric devices and optical data recording. Although some kinds of MCL-active iridium(III) complexes with various soft substituent functional ligands (e.g., dendritic carbazole, flexible chains, and Schiff base ligands) were reported, the MCL mechanism is still not clear and mainly ascribes to the physical phase transformations from crystalline state to amorphous state in response to force stimulus at present stage, and deserves further study in order to obtain more intelligent MCL materials. Herein, two new iridium(III) complex isomers are tactfully constructed and show distinctly opposite MCL properties in spite of the same physical phase transformations happening on them. The absolutely out of the ordinary MCL mechanism has been presented on account of molecular level for the first time via the comparative study of photophysical properties based on isomers 1 and 2 with the help of crystal structure analysis, room/low temperature emission spectra, NMR, PXRD, and TD-DFT calculations. All of these results suggest that the emitting state dominated by the triplet charge transfer excited state (³CT) plays a key role in achieving mechanochromic luminescence in iridium(III) complex systems.

Rich-colour mechanochromism of a cyanostilbene derivative with chiral self-assembly

The tricolored fluorescence switching was realized in a novel chiral fluorophore. The fabrication of a helical assembly was proposed as a candidate strategy for attaining an additional metastable state, which contributed to enriched PL colors via pairwise excimer emission.

Supramolecular complex strategy for pure organic multi-color luminescent materials and stimuli-responsive luminescence switching

Pure organic multi-color luminescent materials were finely tuned from blue through green to red using a supramolecular complex strategy, exhibiting force- and solvent-sensitive luminescence switching in the stimuli-responsive field.

A two-component molecular hybrid with enhanced emission characteristics and mechanoresponsive luminescence properties

A new binary charge transfer cocrystal system was successfully fabricated by virtue of donor–acceptor interaction and exhibited enhanced emission and sensitive mechanoresponsive luminescence properties.

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.