Pure Organic Room Temperature Phosphorescence from Excited Dimers in Self-Assembled Nanoparticles under Visible and Near-Infrared Irradiation in Water

Achieving Near-Infrared Phosphorescence Supramolecular Hydrogel Based on Amphiphilic Bromonaphthalimide Pyridinium Hierarchical Assembly

Phosphorescent supramolecular hydrogels are currently a prevalent topic for their great promise in various photonic applications. Herein, an efficient near-infrared (NIR) phosphorescence supramolecular hydrogel is reported via the hierarchical assembly strategy in aqueous solution, which is fabricated from amphiphilic bromonaphthalimide pyridinium derivative (G), exfoliated Laponite (LP) nanosheets, and polymeric polyacrylamide (PAAm). Initially, G spontaneously self-aggregates into spherical nanoparticles covered with positively charged pyridinium units and emits single fluorescence at 410 nm. Driven by electrostatic interactions with negatively charged nanosheets, the nanoparticles subsequently function as the cross-linked binders and coassemble with LP into supramolecular hydrogels with an engendered red room-temperature phosphorescence (RTP) up to 620 nm. Benefiting from hydrogen-bonding interactions-mediated physical cross-linkage, the further introduction of PAAm not only significantly elevates the mechanical strength of the hydrogels showing fast self-healing capability, but also increases phosphorescence lifetime from 2.49 to 4.20 ms, especially generating phosphorescence at even higher temperature (τ 363 K = 2.46 ms). Additionally, efficient RTP energy transfer occurs after doping a small amount of organic dye heptamethine cyanine (IR780) as an acceptor into hydrogels, resulting in a long-lived NIR emission at 823 nm with a high donor/acceptor ratio, which is successfully applied for cell labeling in the NIR window.

Tunable multicolor supramolecular assemblies based on phosphorescence cascade energy transfer for photocatalytic organic conversion and anti-counterfeiting

Making full use of the captured energy by phosphorescence light-harvesting systems (PLHSs) and the tunable photoluminescence in energy transfer process to realize the multiple applications is still the challenge of PLHSs research. In this study, we have successfully constructed a highly effective PLHS with tunable multicolor luminescence and efficient conversion of photosensitizer types, which can further be used in photocatalytic organic conversion, information anti-counterfeiting and storage. The supramolecular polymer of BDBP-CB[8], which is generated by cucurbit[8]uril (CB[8]) and 4-(4-bromophenyl)-pyridine derivative (BDBP), realizes a phosphorescence emission and a change in luminescence color. Notably, white light emission was achieved and the logic gate systems were constructed utilizing the application of adjustable luminescence color. More interestingly, PLHS can be constructed by employing BDBP-CB[8] as energy donors, Sulforhodamine 101 (SR101) and Cyanine5 (Cy5) as energy acceptors, which results in a remarkably tunable multicolor photoluminescence to achieve the information storage. Furthermore, we have also found that BDBP-CB[8] can serve as type II photosensitizer for the effective production of singlet oxygen (1O2) during the photooxidation process of styrene in aqueous environments, attaining a remarkable output rate reaching as high as 89 %. Particularly, compared with 1O2 produced by type II photosensitizer BDBP-CB[8], the construction of PLHS can effectively convert type II photosensitizer to type I photosensitizer and efficiently generate superoxide anion radical (O2•-), which can be used for photocatalytic cross-dehydrogenative coupling (CDC) reaction in the aqueous solution with a yield of 90 %. Thus, we have created a PLHS that not only achieves tunable multicolor emission for information anti-counterfeiting and storage, but also realizes the conversion of reactive oxygen species (ROS) for different types photocatalytic oxidation reactions.

Room-temperature phosphorescence from organic materials in aqueous media

In recent years, organic materials with room-temperature phosphorescence (RTP) features have gained significant attention due to their wide applications in the fields of bioimaging, light-harvesting materials, encryption technology, etc. Although several examples of organic RTP materials in the crystalline state and polymer-based systems have been reported in the last decade or so, achieving organic RTP in the solution phase, particularly in the aqueous phase has remained a challenging task. Herein in this review, we summarize the progress in this direction by highlighting design strategies based on supramolecular scaffolding and host-guest complexation and the applications of such aqueous organic RTP materials in bioimaging, sensing, etc.

Employing racemization strategies to simultaneously enhance the quantum yield, lifetime, and water stability of room-temperature phosphorescent materials

Room temperature phosphorescence (RTP) materials are increasingly recognized for their superior luminescent properties, which are pivotal in applications such as anti-counterfeiting, information storage, and optoelectronics. Despite this, the sensitivity of most RTP systems to humidity presents a significant challenge in achieving durable RTP performance in aqueous environments. This study proposes a strategy to enhance organic room-temperature phosphorescence through racemization. By incorporating external racemates of various chiral phosphors-NDBD-Ph, NDBD-Ph-Ph, NDBD-CH3, and NDBD-O-CH3-into a polyacrylonitrile (PAN) matrix, we significantly enhance the RTP properties (quantum yield, lifetime, and afterglow-time) of the resultant films. This enhancement can be attributed to the increased density of racemic molecules in the matrix and the increased spin-orbit coupling (SOC), facilitating the development of a long-lasting polymer RTP system in water. Notably, the racemic rac-NDBD-Ph@PAN film exhibits a persistent bright turquoise afterglow, even after immersion in water for a month. Furthermore, for the first time, we achieved an enhanced green to cyan RTP response to pH variations under both acidic and alkaline conditions (pH = 2-12), with the maximum phosphorescence emission intensity increasing up to threefold. The remarkable water stability, reversible response characteristics, and enhanced phosphorescence properties of this system offer promising potential for dynamic information encryption in aqueous environments.

An Organophosphorescence Probe with Ultralong Lifetime and Intrinsic Tissue Selectivity for Specific Tumor Imaging and Guided Tumor Surgery

Organic phosphorescent materials are excellent candidates for use in tumor imaging. However, a systematic comparison of the effects of the intensity, lifetime, and wavelength of phosphorescent emissions on bioimaging performance has not yet been undertaken. In addition, there have been few reports on organic phosphorescent materials that specifically distinguish tumors from normal tissues. This study addresses these gaps and reveals that longer lifetimes effectively increase the signal intensity, whereas longer wavelengths enhance the penetration depth. Conversely, a strong emission intensity with a short lifetime does not necessarily yield robust imaging signals. Building upon these findings, an organo-phosphorescent material with a lifetime of 0.94 s was designed for tumor imaging. Remarkably, the phosphorescent signals of various organic nanoparticles are nearly extinguished in blood-rich organs because of the quenching effect of iron ions. Moreover, for the first time, we demonstrated that iron ions universally quench the phosphorescence of organic room-temperature phosphorescent materials, which is an inherent property of such substances. Leveraging this property, both the normal liver and hepatitis tissues exhibit negligible phosphorescent signals, whereas liver tumors display intense phosphorescence. Therefore, phosphorescent materials, unlike chemiluminescent or fluorescent materials, can exploit this unique inherent property to selectively distinguish liver tumor tissues from normal tissues without additional modifications or treatments.

Narrowband Organic/Inorganic Hybrid Afterglow Materials

Narrowband afterglow materials display interesting functions in high-quality anti-counterfeiting and multiplexed bioimaging. However, there is still a limited exploration of these afterglow materials, especially for those with a full width at half maxima (FWHM) around 30 nm. Here, we report the fabrication of narrowband organic/inorganic hybrid afterglow materials via energy transfer technology. Coronene (Cor) with a long phosphorescence feature and broad phosphorescence band is selected as the donor for energy transfer, and inorganic quantum dots (QDs) of CdSe/ZnS with a narrowband emission are used as acceptors. Upon doping into the organic matrix, the resultant three-component materials exhibit a narrowband afterglow with an afterglow lifetime of approximately 3.4 s and an FWHM of 31 nm. The afterglow wavelength of the afterglow materials can be controlled by the QDs. This work based on organic/inorganic hybrids provides a facile approach for developing multicolor and narrowband afterglow materials, as well as opens a new way for expanding the features of organic afterglow for multifunctional applications. It is expected to rely on narrowband afterglow emitters to solve the "spectrum congestion" problem of high-density information storage in optical anti-counterfeiting and information encryption.

Cucurbit[8]uril-based supramolecular theranostics

Different from most of the conventional platforms with dissatisfactory theranostic capabilities, supramolecular nanotheranostic systems have unparalleled advantages via the artful combination of supramolecular chemistry and nanotechnology. Benefiting from the tunable stimuli-responsiveness and compatible hierarchical organization, host-guest interactions have developed into the most popular mainstay for constructing supramolecular nanoplatforms. Characterized by the strong and diverse complexation property, cucurbit[8]uril (CB[8]) shows great potential as important building blocks for supramolecular theranostic systems. In this review, we summarize the recent progress of CB[8]-based supramolecular theranostics regarding the design, manufacture and theranostic mechanism. Meanwhile, the current limitations and corresponding reasonable solutions as well as the potential future development are also discussed.

Visible-light-excited robust room-temperature phosphorescence of dimeric single-component luminophores in the amorphous state

Organic room temperature phosphorescence (RTP) has significant potential in various applications of information storage, anti-counterfeiting, and bio-imaging. However, achieving robust organic RTP emission of the single-component system is challenging to overcome the restriction of the crystalline state or other rigid environments with cautious treatment. Herein, we report a single-component system with robust persistent RTP emission in various aggregated forms, such as crystal, fine powder, and even amorphous states. Our experimental data reveal that the vigorous RTP emissions rely on their tight dimers based on strong and large-overlap π-π interactions between polycyclic aromatic hydrocarbon (PAH) groups. The dimer structure can offer not only excitons in low energy levels for visible-light excited red long-lived RTP but also suppression of the nonradiative decays even in an amorphous state for good resistance of RTP to heat (up to 70 °C) or water. Furthermore, we demonstrate the water-dispersible nanoparticle with persistent RTP over 600 nm and a lifetime of 0.22 s for visible-light excited cellular and in-vivo imaging, prepared through the common microemulsion approach without overcaution for nanocrystal formation.

Phosphorescent acyclic cucurbituril solid supramolecular multicolour delayed fluorescence behaviour

Organic photoluminescent macrocyclic hosts have been widely advanced in many fields. Phosphorescent hosts with the ability to bind organic guests have rarely been reported. Herein, acyclic cucurbituril modified with four carboxylic acids (ACB-COOH) is mined to present uncommon purely organic room-temperature phosphorescence (RTP) at 510 nm with a lifetime of 1.86 μs. Its RTP properties are significantly promoted with an extended lifetime up to 2.12 s and considerable quantum yield of 6.29% after assembly with a polyvinyl alcohol (PVA) matrix. By virtue of the intrinsic self-crimping configuration of ACB-COOH, organic guests, including fluorescence dyes (Rhodamine B (RhB) and Pyronin Y (PyY)) and a drug molecule (morphine (Mor)), could be fully encapsulated by ACB-COOH to attain energy transfer involving phosphorescent acyclic cucurbituril. Ultimately, as-prepared systems are successfully exploited to establish multicolor afterglow materials and visible sensing of morphine. As an expansion of phosphorescent acyclic cucurbituril, the host afterglow color can be readily regulated by attaching different aromatic sidewalls. This study develops the fabrication strategies and application scope of a supramolecular phosphorescent host and opens up a new direction for the manufacture of intelligent long-lived luminescent materials.

Dynamic Transition between Monomer and Excimer Phosphorescence in Organic Near-Infrared Phosphorescent Crystals

Achieving efficient near-infrared room-temperature phosphorescence of purely organic phosphors remains scarce and challenging due to strong nonradiative decay. Additionally, the investigation of triplet excimer phosphorescence is rarely reported, despite the fact that excimer, a special emitter commonly formed in crystals with strong π-π interactions, can efficiently change the fluorescent properties of compounds. Herein, a series of dithienopyrrole derivatives with low triplet energy levels and stable triplet states, exhibiting persistent near-infrared room-temperature phosphorescence, is developed. Via the modification of halogen atoms, the crystals display tunable emissions of monomers from 645 to 702 nm, with a maximum lifetime of 3.68 ms under ambient conditions. Notably, excimer phosphorescence can be switched on at low temperatures, enabled by noncovalent interactions rigidifying the matrix and stabilizing triplet excimer. Unprecedentedly, the dynamic transition process is captured between the monomer and excimer phosphorescence with temperature variations, revealing that the unstable triplet excimers in crystals with a tendency to dissociate can result in the effective quench of room-temperature phosphorescence. Excited state transitions across varying environments are elucidated, interpreting the structural dynamics of the triplet excimer and demonstrating strategies for devising novel near-infrared phosphors.

Printable Block Molecular Assemblies with Controlled Exciton Dynamics

Creating hierarchical molecular block heterostructures, with the control over size, shape, optical, and electronic properties of each nanostructured building block can help develop functional applications, such as information storage, nanowire spectrometry, and photonic computing. However, achieving precise control over the position of molecular assemblies, and the dynamics of excitons in each block, remains a challenge. In the present work, the first fabrication of molecular heterostructures with the control of exciton dynamics in each block, is demonstrated. Additionally, these heterostructures are printable and can be precisely positioned using Direct Ink Writing-based (DIW) 3D printing technique, resulting in programable patterns. Singlet excitons with emission lifetimes on nanosecond or microsecond timescales and triplet excitons with emission lifetimes on millisecond timescales appear simultaneously in different building blocks, with an efficient energy transfer process in the heterojunction. These organic materials also exhibit stimuli-responsive emission by changing the power or wavelength of the excitation laser. Potential applications of these organic heterostructures in integrated photonics, where the versatility of fluorescence, phosphorescence, efficient energy transfer, printability, and stimulus sensitivity co-exist in a single nanowire, are foreseen.

Dopants Induce Persistent Room Temperature Phosphorescence in Triarylamine Boronate Esters

Purely organic materials exhibiting room temperature phosphorescence (RTP) are promising candidates for oxygen sensors and information encryption owing to their cost-effective and environmentally friendly nature. Herein, we report a bimolecular RTP system where DTBU acts as the guest and TBBU serves as the host. In contrast to previously reported results, we find that both pure DTBU and TBBU do not exhibit RTP in the solid state even under N2 atmosphere. A DTBU/TBBU system with a low doping ratio (0.1 mol %) exhibits persistent yellowish-green afterglow with a lifetime of 340 ms and is highly sensitive to oxygen. A DTBU/TBBU system with a higher doping ratio (10 mol %) maintains a phosphorescence lifetime of 179 ms under air. Applications of DTBU/TBBU at varied doping ratios in both oxygen sensing and information encryption are demonstrated. We propose that the T1 state of TBBU acts as an energy transfer intermediate between Tn and T1 of DTBU, ultimately leading to the generation of persistent RTP. Overall, this work demonstrates the critical importance of material purity in the design of RTP systems, and how an understanding of host-guest doping enables their photophysical properties to be precisely tuned.

Stable and ultralong room-temperature phosphorescent copolymers with excellent adhesion, resistance, and toughness

Developing stable room-temperature phosphorescence (RTP) emission without being affected by moisture and mechanical force remains a great challenge for purely organic systems, due to their triplet states sensitive to the infinitesimal motion of phosphors and the oxygen quencher. We report a kind of highly robust phosphorescent systems, by doping a rigid phosphor into a copolymer (polyvinyl butyral resin) matrix with a balance of mutually exclusive features, including a rigidly hydrophilic hydrogen bond network and elastically hydrophobic constituent. Impressively, these RTP polymeric films have superior adhesive ability on various surfaces and showed reversible photoactivated RTP with lifetimes up to 5.82 seconds, which can be used as in situ modulated anticounterfeit labels. They can maintain a bright afterglow for over 25.0 seconds under various practical conditions, such as storage in refrigerators, soaking in natural water for a month, or even being subjected to strong collisions and impacts. These findings provide deep insights for developing stable ultralong RTP materials with desirable comprehensive performance.

Covalently hybridized carbon dots@mesoporous silica nanobeads as a robust and versatile phosphorescent probe for time-resolved biosensing and bioimaging

Phosphorescence analyses have attracted broad attention due to their remarkable merits of the elimination of auto-fluorescence and scattering light. However, it remains a great challenge to develop novel materials with uniform size and morphology, stability, long lifetime, and aqueous-phase room temperature phosphorescence (RTP) characteristics. Herein, monodisperse and uniform RTP nanobeads were fabricated by an in situ covalent hybridization of carbon dots (CDs) and dendritic mesoporous silicon nanoparticles (DMSNs) via silane hydrolysis. The formation of Si-O-C and Si-C/N covalent bonds is beneficial for the fixation of vibrations and rotations of the luminescent centers. Specially, the nanopores of DMSNs provide a confined area that can isolate the triplet state of CDs from water and oxygen and thus ensure the occurrence of aqueous-phase RTP with an ultra-long lifetime of 1.195 s (seen by the naked eye up to 9 seconds). Through surface modifying folic acid (FA), CDs@DMSNs can serve as a probe to distinguish different cell lines that feature varying FA receptor expression levels. In addition, taking MCF-7 as the model, highly sensitive and quantitative detection (linear range: 103-106 cells per mL) has been achieved via an RTP probe. Furthermore, their potential applications in cellular and in vivo time-gated phosphorescence imaging have been proposed and demonstrated, respectively. This work would provide a new route to design CD-based RTP composites and promote their further applications in the medical and biological fields.

Achieving Ultralong Room-Temperature Phosphorescence in Covalent Organic Framework System

The combination of room-temperature phosphorescence (RTP) and covalent organic frameworks (COFs) would give rise to a new class of functional materials with sensing and responsive properties. However, such organic materials have been rarely reported, especially for those with long phosphorescence lifetimes. Here we report the incorporation of RTP emitters into COFs either via chemical decoration or noncovalent doping to achieve ultralong RTP in a COF system. The RTP emitters are designed with small phosphorescence rates and consequently exhibit ultralong phosphorescence lifetimes when nonradiative decay and oxygen quenching are suppressed in COF system. The RTP-COF materials have been found to possess oxygen sensing properties with large response of phosphorescence lifetimes.

Investigation of Electronic Structures of Triplet States Using Step-Scan Time-Resolved Fourier-Transform Near-Infrared Spectroscopy

Triplet transitions of light-emitting materials, including rose bengal, tris(2-phenylpyridine)iridium(III) [Ir(ppy)3], tris(1-phenylisoquinoline)iridium(III) [Ir(piq)3], and bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium(III) (FIrpic), were studied using step-scan time-resolved Fourier-transform near-infrared spectroscopy. The samples were excited to their singlet excited states by a 355 nm laser and then underwent efficient conversions/crossings to their triplet manifolds. For rose bengal, a transient absorption band appeared at 9400 cm-1, attributed to the T3 ← T1 transition based on the corresponding time evolution and the theoretical calculations. For Ir(ppy)3, Ir(piq)3, and FIrpic, the most intense bands were observed at 7700, 7500, and 7500 cm-1 and assigned to T7 ← T1, T6 ← T1, and T6 ← T1 transitions, respectively. For Ir(ppy)3, the most intense band involved transitions between different triplet metal-to-ligand charge transfer (3MLCT) states, while for Ir(piq)3 and FIrpic, they involved a metal center to 3MLCT transition. These T1 states were assigned to 3MLCT.

Modulation of Deep-Red to Near-Infrared Room-Temperature Charge-Transfer Phosphorescence of Crystalline "Pyrene Box" Cages by Coupled Ion/Guest Structural Self-Assembly

Organic cocrystals obtained from multicomponent self-assembly have garnered considerable attention due to their distinct phosphorescence properties and broad applications. Yet, there have been limited reports on cocrystal systems that showcase efficient deep-red to near-infrared (NIR) charge-transfer (CT) phosphorescence. Furthermore, effective strategies to modulate the emission pathways of both fluorescence and phosphorescence remain underexplored. In this work, we dedicated our work to four distinct self-assembled cocrystals called "pyrene box" cages using 1,3,6,8-pyrenetetrasulfonate anions (PTS4-), 4-iodoaniline (1), guanidinium (G+), diaminoguanidinium (A2G+), and hydrated K+ countercations. The binding of such cations to PTS4- platforms adaptively modulates their supramolecular stacking self-assembly with guest molecules 1, allowing to steer the fluorescence and phosphorescence pathways. Notably, the confinement of guest molecule 1 within "pyrene box" PTSK{1} and PTSG{1} cages leads to an efficient deep-red to NIR CT phosphorescence emission. The addition of fuming gases like triethylamine and HCl allows reversible pH modulations of guest binding, which in turn induce a reversible transition of the "pyrene box" cage between fluorescence and phosphorescence states. This capability was further illustrated through a proof-of-concept demonstration in shrimp freshness detection. Our findings not only lay a foundation for future supramolecular designs leveraging weak intermolecular host-guest interactions to engineer excited states in interacting chromophores but also broaden the prospective applications of room-temperature phosphorescence materials in food safety detection.

Fused-Ring Pyrrole-Based Near-Infrared Emissive Organic RTP Material for Persistent Afterglow Bioimaging

Organic near-infrared room temperature phosphorescence (RTP) materials offer remarkable advantages in bioimaging due to their characteristic time scales and background noise elimination. However, developing near-infrared RTP materials for deep tissue imaging still faces challenges since the small band gap may increase the non-radiative decay, resulting in weak emission and short phosphorescence lifetime. In this study, fused-ring pyrrole-based structures were employed as the guest molecules for the construction of long wavelength emissive RTP materials. Compared to the decrease of the singlet energy level, the triplet energy level showed a more effectively decrease with the increase of the conjugation of the substituent groups. Moreover, the sufficient conjugation of fused ring structures in the guest molecule suppresses the non-radiative decay of triplet excitons. Therefore, a near-infrared RTP material (764 nm) was achieved for deep penetration bioimaging. Tumor cell membrane is used to coat RTP nanoparticles (NPs) to avoid decreasing the RTP performance compared to traditional coating by amphiphilic surfactants. RTP NPs with tumor-targeting properties show favorable phosphorescent properties, superior stability, and excellent biocompatibility. These NPs are applied for time-resolved luminescence imaging to eliminate background interference with excellent tissue penetration. This study provides a practical solution to prepare long-wavelength and long-lifetime organic RTP materials and their applications in bioimaging.

Cucurbit[8]uril Confinement-Based Secondary Coassembly for High-Efficiency Phosphorescence Energy Transfer Behavior

Aqueous supramolecular long-lived near-infrared (NIR) material is highly attractive but still remains great challenge. Herein, we report cucurbit[8]uril confinement-based secondary coassembly for achieving NIR phosphorescence energy transfer in water, which is fabricated from dicationic dodecyl-chain-bridged 4-(4-bromophenyl)-pyridine derivative (G), cucurbit[8]uril (CB[8]), and polyelectrolyte poly(4-styrene-sulfonic sodium) (PSS) via the hierarchical confinement strategy. As compared to the dumbbell-shaped G, the formation of unprecedented linear polypseudorotaxane G⊂CB[8] with nanofiber morphology engenders an emerging phosphorescent emission at 510 nm due to the macrocyclic confinement effect. Moreover, benefiting from the following secondary assembly confinement, such tight polypseudorotaxane G⊂CB[8] can further assemble with anionic polyelectrolyte PSS to yield uniform spherical nanoparticle, thereby significantly strengthening phosphorescence performance with an extended lifetime (i.e., 2.39 ms, c.f., 45.0 μs). Subsequently, the organic dye Rhodamine 800 serving as energy acceptor can be slightly doped into the polyelectrolyte assembly, which enables the occurrence of efficient phosphorescence energy transfer process with efficiency up to 80.1% at a high donor/acceptor ratio, and concurrently endows the final system with red-shifted and long-lived NIR emission (710 nm). Ultimately, the as-prepared assembly is successfully exploited as versatile imaging agent for NIR window labeling and detecting in living cells.

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.

Molecularly Engineered Room-Temperature Phosphorescence for Biomedical Application: From the Visible toward Second Near-Infrared Window

Phosphorescence, characterized by luminescent lifetimes significantly longer than that of biological autofluorescence under ambient environment, is of great value for biomedical applications. Academic evidence of fluorescence imaging indicates that virtually all imaging metrics (sensitivity, resolution, and penetration depths) are improved when progressing into longer wavelength regions, especially the recently reported second near-infrared (NIR-II, 1000-1700 nm) window. Although the emission wavelength of probes does matter, it is not clear whether the guideline of "the longer the wavelength, the better the imaging effect" is still suitable for developing phosphorescent probes. For tissue-specific bioimaging, long-lived probes, even if they emit visible phosphorescence, enable accurate visualization of large deep tissues. For studies dealing with bioimaging of tiny biological architectures or dynamic physiopathological activities, the prerequisite is rigorous planning of long-wavelength phosphorescence, being aware of the cooperative contribution of long wavelengths and long lifetimes for improving the spatiotemporal resolution, penetration depth, and sensitivity of bioimaging. In this Review, emerging molecular engineering methods of room-temperature phosphorescence are discussed through the lens of photophysical mechanisms. We highlight the roles of phosphorescence with emission from visible to NIR-II windows toward bioapplications. To appreciate such advances, challenges and prospects in rapidly growing studies of room-temperature phosphorescence are described.

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.

Functionalized heteroatom-doped carbon dots for biomedical applications: A review

Carbon nanoparticles (CDs) have recently drawn a great attention in (bio)chemical analysis, sensing and bioimaging owing to their photostability, water stability, minimal toxicity, biocompatibility and ease of surface functionalization. While the vast majority of CDs applications rely on exploiting their fluorescent properties, doping such nanomaterials with various elements has recently received increasing attention as an effective approach to modify their optoelectronic characteristics, introducing novel improved optical features such as phosphorescence, upconversion luminescence or multimodal imaging capabilities. This review article focuses in the recent advances on the synthesis of heteroatom-doped CDs, exhibiting distinctive features of high value for sensing and imaging, as well as various functionalization schemes developed for guided analyte labeling. Relevant applications in chemical sensing, bioimaging and disease therapy are here presented. A final section intends to provide an overview towards future developments of such emerging light-emitting nanomaterials in the design of future devices and strategies for (bio)analytical chemistry.

Recent Advances in Organic Molecular-to-Supramolecular Self-Assembled Room-Temperature Phosphorescent Materials for Biomedical Applications

This minireview focuses on recent advancements in organic molecular-to-supramolecular self-assembled room-temperature phosphorescent (RTP) materials and their prospective biomedical applications. RTP materials, having their unique capacity to emit long-lasting phosphorescence at ambient temperature, have piqued researchers' interest in various biological applications, including biosensing, bioimaging, drug delivery, and photodynamic therapy (PDT). These materials have several benefits, including high sensitivity, remarkable photostability, and low cytotoxicity. RTP materials' self-assembly into supramolecular structures improves their performance and broadens their uses. Researchers have built organic RTP systems with long-lasting phosphorescence by leveraging weak noncovalent interactions in aquatic conditions. These materials have demonstrated incredible promise as biosensors that enable sensitive analyte detection and as photosensitizers in PDT that target and sensitize specific cell types. The review also outlines future directions and challenges in developing and utilizing pure organic RTP materials for biological imaging purposes, providing valuable guidelines for their future design and application.

Recent advances in the design of afterglow materials: mechanisms, structural regulation strategies and applications

Afterglow materials are attracting widespread attention owing to their distinctive and long-lived optical emission properties which create exciting opportunities in various fields. Recent research has led to the discovery of many new afterglow materials featuring high photoluminescence quantum yields (PLQY) and lifetimes of up to several hours under ambient conditions. Afterglow materials are typically categorized according to their luminescence mechanism, such as long-persistent luminescence (LPL), room temperature phosphorescence (RTP), or thermally activated delayed fluorescence (TADF). Through rational design and novel synthetic strategies to modulate spin-orbit coupling (SOC) and populate triplet exciton states (T1), luminophores with long lifetimes and bright afterglow characteristics can be realized. Initial research towards afterglow materials focused mainly on pure inorganic materials, many of which possessed inherent disadvantages such as metal toxicity or low energy emissions. In recent years, organic-inorganic hybrid afterglow materials (OIHAMs) have been developed with high PLQY and long lifetimes. These hybrid materials exploit the tunable structure and easy processing of organic molecules, as well as enhanced SOC and intersystem crossing (ISC) processes involving heavy atom dopants, to achieve excellent afterglow performance. In this review, we begin by briefly discussing the structure and composition of inorganic and organic-inorganic hybrid afterglow materials, including strategies for regulating their lifetime, PLQY and luminescence wavelength. The specific advantages of organic-inorganic hybrid afterglow materials, including low manufacturing costs, diverse molecular/electronic structures, tunable structures and optical properties, and compatibility with a variety of substrates, are emphasized. Subsequently, we discuss in detail the fundamental mechanisms used by afterglow materials, their classification, design principles, and end applications (including sensing, anticounterfeiting, and photoelectric devices, among others). Finally, existing challenges and promising future directions are discussed, laying a platform for the design of afterglow materials for specific applications.

Tunable Aggregation-induced Emission and Emission Colors of Imidazolium and Pyridinium Based Hydrazones

Aggregation-induced emission (AIE) materials have drawn great attention for their wide applications as optical materials. The applications of AIE materials, however, are restricted by the complicated syntheses, hydrophobic properties and short emission wavelengths. Herein, an imidazolium based hydrazone (E)-1-(4-methoxyphenyl)-2-((1-methyl-1H-imidazol-2-yl)methylene)hydrazine hydrochloride (1) and a pyridinium based hydrazone (E)-1-(4-methoxyphenyl)-2-(pyridin-4-ylmethylene)hydrazine hydrochloride (2) have been synthesized. Notably, 1 and 2 in crystals show distinct green and near-infrared (NIR) fluorescence, with emission peaks at 530 and 688 nm, and Stokes shifts of 176 and 308 nm, respectively. After grinding the crystals to powder, the absolute fluorescence quantum yield (ΦF) of 1 is increased from 4.2% to 10.6%, and the ΦF of 2 is increased from 0.2% to 0.7%. X-ray crystallography studies together with theoretical calculations indicate that the enhanced emission of 1 arises from hydrogen bonding induced rigid network, and the fluorescence in the NIR region and large Stokes shift of 2 are attributed to its twisted molecular structure and strong push-pull effect.

A narrow-band deep-blue MRTADF-type organic afterglow emitter

We report a multi-resonant thermally activated delayed fluorescent (MRTADF) afterglow emitter with unprecedented long emission lifetime > 100 ms, full-width at half-maximum < 40 nm, and deep-blue emission color of CIEy at 0.048. Such emitters remain rarely achieved and would show potential applications in multiplexed bioimaging and high-density information encryption.

A Supramolecular Naphthalene Diimide Radical Anion with Efficient NIR-II Photothermal Conversion for E. coli-Responsive Photothermal Therapy

We report a supramolecular naphthalene diimide (NDI) radical anion with efficient NIR-II photothermal conversion for E. coli-responsive photothermal therapy. The supramolecular radical anion (NDI-2CB[7])⋅- , which is obtained from the E. coli-induced in situ reduction of NDI-2CB[7] neutral complex, formed by the host-guest interaction between an NDI derivative and cucurbit[7]uril (CB[7]), exhibits unexpectedly strong NIR-II absorption and remarkable photothermal conversion capacity in aqueous solution. The NIR-II absorption is caused by the self-assembly of NDI radical anions to form supramolecular dimer radicals in aqueous solution, which is supported by theoretically predicted spectra. The (NDI-2CB[7])⋅- demonstrates excellent NIR-II photothermal antimicrobial activity (>99 %). This work provides a new approach for constructing NIR-II photothermal agents and non-contact treatments for bacterial infections.

A functional unit combination strategy for enhancing red room-temperature phosphorescence

Red room-temperature phosphorescence (RTP) materials based on non-metallic organic compounds are less reported compared to the commonly found green RTP materials. Here, we propose a novel approach to obtain red RTP materials by integrating and combining two functional units, resembling a jigsaw puzzle. In this approach, benzo[c][2,1,3]thiadiazole (BZT) serves as the red RTP unit, while a folding unit containing sulphur/oxygen is responsible for enhancing spin-orbit coupling (SOC) to accelerate the intersystem crossing (ISC) process. Three new molecules (SS-BZT, SO-BZT, and OO-BZT) were designed and synthesized, among which SS-BZT and SO-BZT with folded geometries demonstrate enhanced red RTP in their monodisperse films compared to the parent BZT. Meanwhile, the SS-BZT film shows a dual emission consisting of blue fluorescence and red RTP, with a significant spectral separation of approximately 150 nm, which makes the SS-BZT film highly suitable for applications in optical oxygen sensing and ratiometric detection. Within the oxygen concentration range of 0-1.31%, the SS-BZT film demonstrates a quenching constant of 2.66 kPa-1 and a quenching efficiency of 94.24%, indicating that this probe has the potential to accurately detect oxygen in a hypoxic environment.

Visible-light-excitable aqueous afterglow exhibiting long emission wavelength and ultralong afterglow lifetime of 7.64 s

We utilize the dopant-matrix strategy and emulsion polymerization to obtain aqueous afterglow dispersions from a liquid precursor, which avoids the processing of solid materials, protects organic triplets and achieves long phosphorescence lifetime of 7.64 s. The aqueous afterglow dispersions display great potential for biomedical applications due to their ultralong-lived excited states.

Conformationally confined three-armed supramolecular folding for boosting near-infrared biological imaging

Herein, a triphenylamine derivative (TP-3PY) possessing 4-(4-bromophenyl)pyridine (PY) as an electron-accepting group and tris[p-(4-pyridylvinyl)phenyl]amine (TPA) with large two-photon absorption cross-sections as an electron-donating group was obtained, and showed intense absorption in the visible light region (λmax = 509 nm) and weak near-infrared (NIR) fluorescence emission at 750 nm. After complexation with cucurbit[8]uril (CB[8]), TP-3PY showed bright NIR fluorescence emission at 727 nm and phosphorescence emission at 800 nm. When the supramolecular assembly (TP-3PY⊂CB[8]) further interacted with dodecyl-modified sulfonatocalix[4]arene (SC4AD), the fluorescence and phosphorescence emissions were further enhanced at 710 and 734 nm, respectively. However, only the fluorescence emission of TP-3PY was enhanced in the presence of cucurbit[7]uril (CB[7]) and SC4AD. More interestingly, the photoluminescence of TP-3PY⊂CB[8]@SC4AD and TP-3PY⊂CB[7]@SC4AD assemblies could be excited by both visible (510 nm) and NIR light (930 nm). Finally, these ternary supramolecular assemblies with bright NIR light emission were applied to lysosome imaging of tumor cells and real-time biological imaging of mice.

Mechanism landscape in pyrylium induced organic afterglow systems

Manipulation of excited states and their dynamics represents a central topic in luminescence systems. We report an unexpected emergence of a high-performance organic afterglow in pyrylium induced photopolymerization systems, as well as the establishment of the mechanism landscape of the afterglow systems as a function of monomer types. In the case of methyl methacrylate, after pyrylium-catalyzed photopolymerization, the obtained materials exhibit a TADF-type organic afterglow with an afterglow efficiency of 70.4%. By using heavy-atom-containing methacrylate, the external heavy atom effect speeds up phosphorescence decay and switches on room-temperature phosphorescence in pyrylium-polymer systems. When 9-vinylcarbazole is used, the resultant materials display organic long persistent luminescence with hour-long durations and emission maxima around 650 nm. The intriguing mechanism landscape reflects the delicate balance of multiple photophysical processes in the pyrylium induced organic afterglow systems, which has been rarely explored in the reported studies.

Switching Singlet Exciton to Triplet for Efficient Pure Organic Room-Temperature Phosphorescence by Rational Molecular Design

The design and regulation of phosphors are attractive but challenging because of the spin-forbidden intersystem crossing (ISC) process. Here, a new perspective on the enhancement of the ISC is proposed and demonstrated. Different from current strategies, the ISC yield (Φ_ISC) is enhanced by decreasing the fluorescence radiative transition rate constant (k_F) via rational molecular designing rather than boosting the spin-orbit coupling by decorating the molecular skeleton with a heavy atom, heteroatom, or carbonyl. The k_F of the designed molecule in this case is associated with the substituent position of the methoxy group, which alters the distribution of the front orbitals. The S₀ → S₁ transition of these compounds evolves from a bright state to a dark state gradually with the variation of the substituent position, accompanied by the decrease of k_F and increase of Φ_ISC. The fluorescence emission is switched to phosphorescence emission successfully by regulating the k_F. This work provides an alternative strategy to design efficient room-temperature phosphorescence material.

Achieving White-Light Emission Using Organic Persistent Room Temperature Phosphorescence

Artificial lighting currently consumes approximately one-fifth of global electricity production. Organic emitters with white persistent RTP have potential for applications in energy-efficient lighting technologies, due to their ability to harvest both singlet and triplet excitons. Compared to heavy metal phosphorescent materials, they have significant advantages in cost, processability, and reduced toxicity. Phosphorescence efficiency can be improved by introducing heteroatoms, heavy atoms, or by incorporating luminophores within a rigid matrix. White-light emission can be achieved by tuning the ratio of fluorescence to phosphorescence intensity or by pure phosphorescence with a broad emission spectrum. This review summarizes recent advances in the design of purely organic RTP materials with white-light emission, describing single-component and host-guest systems. White phosphorescent carbon dots and representative applications of white-light RTP materials are also introduced.

Ultra-long Near-infrared Repeatable Photochemical Afterglow Mediated by Reversible Storage of Singlet Oxygen for Information Encryption

Photochemical afterglow systems have drawn considerable attention in recent years due to their regulable photophysical properties and charming application potential. However, conventional photochemical afterglow suffered from its unrepeatability due to the consumption of energy cache units as afterglow photons are emitted. Here we report a novel strategy to realize repeatable photochemical afterglow (RPA) through the reversible storage of ¹ O₂ by 2-pyridones. Near-infrared afterglow with a lifetime over 10 s is achieved, and its initial intensity shows no significant reduction over 50 excitation cycles. A detailed mechanism study was conducted and confirmed the RPA is realized through the singlet oxygen-sensitized fluorescence emission. Furthermore, the generality of this strategy is demonstrated and tunable afterglow lifetimes and colors are achieved by rational design. The developed RPA is further applied for attacker-misleading information encryption, presenting a repeatable-readout.

Chemometrics-assisted mechanism study of the room-temperature phosphorescence on nanoscopic boronate assemblies

Boronate assemblies, derived from benzene-1,4-diboronic acid, showed room-temperature phosphorescence (RTP) in both the solid-state and dispersions, being quite sensitive to the preparation conditions. Our chemometrics-assisted quantitative structure-property relationship (QSPR) analysis between the nanostructure and RTP behavior of boronate assemblies led us not only to understand their RTP mechanism but also to predict the RTP properties of unknown assemblies from the PXRD patterns.

Theoretical study on the origin of the dual phosphorescence emission from organic aggregates at room temperature

Purely organic materials with dual room temperature phosphorescence (RTP) phenomenon were reported recently, but the underlying mechanism was still ambiguous. Herein, we revealed the source of dual RTP emission, taking CzDPS crystal as prototype, by using hybrid quantum mechanics and molecular mechanics (QM/MM) coupled with the thermal vibration correlation function rate theory. Theoretical calculations verified that the emission lifetimes are prolonged from 70 ms in the higher triplet state T₂ to 216 ms in the lowest triplet state T₁, which is well consistent with the increase of RTP lifetimes from 74 ms for the peak at 465 nm to 627 ms for the band at 565 nm. This is because the radiative and nonradiative decay rates are larger for T₂ → S₀ than that of T₁ → S₀, which was mainly contributed by the synergistic effect of the increase of spin-orbit coupling and excitation energy, as well as the decrease of reorganization energy. Moreover, the simulated RTP spectra agree well with the experimental ones, including the emission position and profiles. Therefore, the upper-lying triplet excited states are responsible for the dual RTP in CzDPS crystal. This work could contribute to further understanding on the multiple luminescence of organic aggregates.

Benzophenone-containing phosphors with an unprecedented long lifetime of 1.8 s under ambient conditions

It is well-known that benzophenone has a short phosphorescence lifetime of around 1 ms even at 77 K. Here we report a benzophenone-containing emitter with an unprecedented long phosphorescence lifetime of 1.8 s under ambient conditions, which can be attributed to its T₁ state of localized excitation nature as revealed by detailed studies.

Long-Lived Dynamic Room Temperature Phosphorescence from Carbon Dots Based Materials

As a type of room temperature phosphorescence (RTP) material, carbon dots (CDs) always show short lifetime and low phosphorescence efficiency. To counter these disadvantages, several strategies, such as embedding in rigid matrix, introducing of heteroatom, crosslink-enhanced emission, etc., are well developed. Consequently, lots of CDs-based RTP materials are obtained. Doping of CDs into various matrix is the dominant method for preparation of long-lived CDs-based RTP materials so far. The desired CDs@matrix composites always display outstanding RTP performances. Meanwhile, matrix-free CDs and carbonized polymer dots-based RTP materials are also widely developed. Amounts of CDs possessing ultra-long lived, multiple colored, and dynamic RTP emission are successfully obtained. Herein, the recent progress achieved in CDs-based RTP materials as well as the corresponding efficient strategies and emission mechanisms are summarized and reviewed in detail. Due to CDs-based RTP materials possess excellent chemical stability, photostability and low biological toxicity, they exhibit great application potential in the fields of anti-counterfeiting, data encryption, and biological monitoring. The application of the CDs-based RTP materials is also introduced in this review. As a promising functional material, development of long wavelength RTP emitting CDs with long lifetime is still challengeable, especially for the red and near-infrared emitting RTP materials.

Ultralong Organic Phosphorescence: From Material Design to Applications

Organic phosphorescence is defined as a radiative transition between the different spin multiplicities of an organic molecule after excitation; here, we refer to the photoexcitation. Unlike fluorescence, it shows a long emission lifetime (∼μs), large Stokes shift, and rich excited state properties, attracting considerable attention in organic electronics during the past years. Ultralong organic phosphorescence (UOP), a type of persistent luminescence in organic phosphors, shows an emission lifetime of over 100 ms normally according to the resolution limit of the naked eye. According to the Jablonski energy diagram, two prerequisites are necessary for UOP generation and enhancement. One is to promote intersystem crossing (ISC) of the excitons from the excited singlet to triplet states by enhancing the spin-orbit coupling (SOC); the other is to suppress the nonradiative transitions of the excitons from the excited triplet states.In this Account, we will give a summary of our research on ultralong organic phosphorescence, including the design of materials, manipulation of properties, fabrication of nano/microstructures, and function applications. First, we give a brief introduction to the UOP development. Then, we discuss the constructed methods of UOP materials from the inter/intramolecular interaction types, including π-π interactions, intermolecular hydrogen bonds, halogen bonds, ionic bonds, covalent bonds, and so on. These effective interactions can build a rigid environment to restrain the nonradiative transitions from the molecular motions or external quenching by oxygen, moisture, or heat, and thus enhance the UOP performance. Next, the manipulation of UOP properties, containing excitation wavelength, emission colors, lifetimes, and quantum efficiency (QE), through molecular or crystal engineering will be summarized. Recently, the excitation wavelengths of the materials for UOP can be regulated in different regions, such as UV, visible light, and X-ray; the emission colors of UOP can cover the whole visible-light region, from deep blue to red; the phosphorescence lifetime of UOP materials can reach 2.5 s, and the quantum efficiency can be achieved up to 96.5%. Moreover, we will present the fabrication of micro/nanoscale UOP materials, including the preparation of micro/nanostructure, optical performance, and device fabrication. Afterward, we will review the potential applications of UOP materials in organic/bio-optoelectronics, such as information encryption, bioimaging, sensing, afterglow display, etc. Finally, an outlook on the development of UOP materials and applications will be proposed.

Controlling the Nature of Photoluminescence of Emissive Metal Nanoclusters

Photoluminescence (PL) serves as one of the most attractive chemical-physical properties of metal nanoclusters. However, the control over the PL nature of metal nanoclusters as fluorescence or phosphorescence remains challenging. Basically, the PL nature control concerns the transition regulation of excited electrons in nanoclusters from their excited state to the ground state. Up to the present, some cases have been reported on adjusting the PL nature of emissive nanoclusters via different means, including the composition regulation, the isomerization, the aggregation, and the temperature variation. At the same time, theoretical calculations have been performed to thoroughly understand the PL nature transformation of these emissive nanoclusters in terms of their electronic structures and transition pathways. This Concept highlights and reviews the recent progress in controlling the PL nature of emissive nanoclusters as fluorescence or phosphorescence, which hopefully paves the way for fabricating novel nanoclusters or cluster-based nanomaterials with customized PL properties.

A dish-like molecular architecture for dynamic ultralong room-temperature phosphorescence through reversible guest accommodation

Developing dynamic organic ultralong room-temperature phosphorescent (URTP) materials is of practical importance in various applications but remains a challenge due to the difficulty in manipulating aggregate structures. Herein, we report a dish-like molecular architecture via a bottom-up way, featuring guest-responsive dynamic URTP. Through controlling local fragment motions in the molecular architecture, fascinating dynamic URTP performances can be achieved in response to reversible accommodation of various guests, including solvents, alkyl bromides and even carbon dioxide. Large-scale regulations of phosphorescence lifetime (100-fold) and intensity (10-fold) can be realized, presenting a maximum phosphorescence efficiency and lifetime of 78.8% and 483.1 ms, respectively. Moreover, such a dish-like molecular architecture is employed for temperature-dependent multiple information encryption and visual identification of linear alkyl bromides. This work can not only deepen our understanding to construct multifunctional organic aggregates, but also facilitate the design of high-performance dynamic URTP materials and enrich their practical applications.

Thiazole Boron Difluoride Dyes with Large Stokes Shift, Solid State Emission and Room-Temperature Phosphorescence

The small Stokes shift and weak emission in the solid state are two main shortcomings associated with the boron-dipyrromethene (BODIPY) family of dyes. This study presents the design, synthesis and luminescent properties of boron difluoro complexes of 2-aryl-5-alkylamino-4-alkylaminocarbonylthiazoles. These dyes display Stokes shifts (Δλ, 77-101 nm) with quantum yields (ϕ_FL ) up to 64.9 and 34.7 % in toluene solution and in solid state, respectively. Some of these compounds exhibit dual fluorescence and room-temperature phosphorescence (RTP) emission properties with modulable phosphorescence quantum yields (ϕ_PL ) and lifetime (τ_p up to 251 μs). The presence of intramolecular H-bonds and negligible π-π stacking revealed by X-ray crystal structure might account for the observed large Stokes shift and significant solid-state emission of these fluorophores, while the enhanced spin-orbit coupling (SOC) of iodine and the self-assembly driven by halogen bonding, π-π and C-H^… π interactions could be responsible for the observed RTP of iodine containing phosphors.

Organic Phosphorescence Lasing Based on a Thermally Activated Delayed Fluorescence Emitter

Organic phosphorescence materials provide an opportunity to use triplets for lasing. However, population inversion based on phosphorescence is hard to establish, owing to low luminescent quantum efficiency and intensive optical loss. By comparison, thermally activated delayed fluorescence emitters exhibit excellent optical gain with the aid of the reverse intersystem crossing (RISC) process. In this work, we designed a multifunctional gain material, not only serving as a thermally activated delayed fluorescence (TADF) emitter with excellent optical gain but also working as a phosphorescence source with high utilization of triplets. The lone pair of electrons in oxygen substitutions promotes a fast spin-flip and high delayed fluorescence quantum yield (Φ_DF = 55%), enabling TADF amplified spontaneous emissions (ASE) of CH₂Cl₂ solution. Single-crystalline nanowires of H-aggregates effectively lower triplet energy levels with high phosphorescence quantum yield (Φ_P = 27%), demonstrating Fabry-Perot mode phosphorescence lasing at 630 nm.

Highly efficient discrimination of cancer cells based on in situ-activated phosphorescence energy transfer for targeted cell imaging

Highly efficient discrimination between cancer cells and normal cells is full of challenges for precise diagnosis. Herein, we report an effective in situ-activated phosphorescence energy transfer supramolecular assembly constructed by a bromophenyl pyridine derivative (BPPY), cucurbit[8]uril (CB[8]), and rhodamine B-grafted hyaluronic acid (HAR) through noncovalent interaction. As compared with BPPY, CB[8] encapsulated two BPPY molecules, resulting in a biaxial pseudorotaxane supramolecular assembly showing purely organic room-temperature phosphorescence induced by macrocyclic confinement, which when further co-assembled with HAR, formed a multivalent supramolecular assembly with phosphorescence energy transfer. Benefitting from the targeting of hyaluronic acid and the cyclolactam ring ON-OFF reaction of HAR, such supramolecular assembly with an open ring presents red delayed fluorescence through phosphorescence energy transfer in cancer cells, while the assembly showed only green phosphorescence in normal cells, realizing highly efficient discrimination between cancer and normal cells. This supramolecular assembly is responsive to the physiological environment and provides a supramolecular platform for precise diagnosis.