Molecular Engineering for Metal‐Free Amorphous Materials with Room‐Temperature Phosphorescence

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.

Multimode Stimuli-Responsive Room-Temperature Phosphorescence Achieved by Doping Butterfly-like Fluorogens into Crystalline Small-Molecular Hosts

Materials with stimuli-responsive purely organic room-temperature phosphorescence (RTP) exempt from exquisite molecular design and complex preparation are highly desirable but still relatively rare. Moreover, most of them work in a single switching mode. Herein, we employ a versatile host-guest-doped strategy to facilely construct efficient RTP systems with multimode stimuli-responsiveness without ingenious molecular design. By conveniently doping butterfly-like guests, namely, N,N'-diphenyl-dihydrodibenzo[a,c]phenazines (DPACs), featured with vibration-induced emission into the small-molecular hosts via various methods, RTP systems with finely tunable photophysical properties are readily obtained. Through systematic mechanistic studies and with the aid of a series of control experiments, we unveil the critical role of the host crystallinity in achieving efficient RTP. By virtue of the inherent environmental sensitivity of both RTP and fluorescence of the DPACs, our systems exhibit multiple-stimuli-responsiveness with the luminescence not only switching between the fluorescence and phosphorescence but also continuously changing in the fluorescence color. Advanced dynamic anticounterfeiting and multilevel information encryption is thereby realized.

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.

Water-Soluble Luminescent Polymers with Room-Temperature Phosphorescence Based on the α-Amino Acids

Nonconventional luminophores have received increasing attention, owing to their fundamental importance, advantages in outstanding biocompatibility, easy preparation, environmental friendliness, and potential applications in sensing, imaging, and encryption. Purely organic molecules with outstanding fluorescence and room-temperature phosphorescence (RTP) have emerged as a new library of benign afterglow agents. However, the cost, toxicity, high reactivity, and poor stability of materials also limit their practical applications. Therefore, some natural products, synthetic compounds, and biomolecules have entered horizons of people. The as-designed exhibits sky blue and green fluorescence emission and green RTP emission (a lifetime of 343 ms and phosphorescence quantum of 15.3%) under air condition. This study presents an organic fluorescence for biological imaging and RTP for anti-counterfeiting and encryption based on amino acids, maleic anhydride and 4-vinylbenzenesulfonic acid sodium salt hydrate. This study provides a strategy for nonconventional luminophores in designing and synthesizing pure organic RTP materials.

Delayed room temperature phosphorescence enabled by phosphines

Organic ultralong room-temperature phosphorescence (RTP) usually emerges instantly and immediately decays after excitation removal. Here we report a new delayed RTP that is postponed by dozens of milliseconds after excitation removal and decays in two steps including an initial increase in intensity followed by subsequent decrease in intensity. The delayed RTP is achieved through introduction of phosphines into carbazole emitters. In contrast to the rapid energy transfer from single-molecular triplet states (T1) to stabilized triplet states (Tn*) of instant RTP systems, phosphine groups insert their intermediate states (TM) between carbazole-originated T1 and Tn* of carbazole-phosphine hybrids. In addition to markedly increasing emission lifetimes by ten folds, since TM → Tn* transition require >30 milliseconds, RTP is thereby postponed by dozens of milliseconds. The emission character of carbazole-phosphine hybrids can be used to reveal information through combining instant and delayed RTP, realizing multi-level time resolution for advanced information, biological and optoelectronic applications.

Unique Visualization Growth Process of Long-Lived Room Temperature Phosphorescence in Polymer System

Recently, embedding organic phosphors into the polyvinyl alcohol (PVA) matrix has emerged as a convenient strategy to obtain efficient long-lived room temperature phosphorescence (RTP) via forming strong intermolecular hydrogen bonds with organic phosphors to minimize nonradiative relaxations. Regrettably, it is discovered that PVA is unable to trigger RTP emission when a novel functional phosphor THBE containing six extended biphenyl formaldehyde arms is doped into PVA matrix. Surprisingly, the excellent long-lived RTP emission can be easily obtained by doping THBE into PVA analogs, poly(vinyl alcohol-co-ethylene) (PVA-co-PE). The unique visualization growth process (i.e., white streak generation) of long-lived RTP is observed by UV light-driven aggregation of functional molecules THBE in PVA-co-PE matrix. The phosphorescent intensity of the luminescent film is enhanced by 55 times, from 729 to 40,785 a.u., and its phosphorescence lifetime is increased by 38 times, from 37.08 to 1415.41 ms. Due to the dynamically reversible RTP performance, as well as the permeability, flexibility, and wrinkle-free properties of the luminescent film, it can be utilized to create cutting-edge information storage devices.

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

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

Single-Component Photochemical Afterglow Near-Infrared Luminescent Nano-Photosensitizers: Bioimaging and Photodynamic Therapy

Long afterglow luminescence-guided photodynamic therapy (PDT) performs advantages of noninvasiveness, spatiotemporal controllability, and higher signal to noise ratio. Photochemical afterglow (PCA) system emitting afterglow in an aqueous environment is highly suitable for biomedical applications, but still faces the challenges of poor tissue penetration depth and responsive sensitivity. In this work, two novel compounds, Iso-TPA and ABEI-TPA, are designed and synthesized to integrate the PCA system as a single component by coupling near-infrared (NIR) photosensitizers with singlet oxygen cache units, respectively. Both compounds emit NIR afterglow based on photochemical reaction. ABEI-TPA exhibits higher photoluminescence quantum efficiency with nonconjugated linkage, while Iso-TPA with conjugated linkage possesses better reactive oxygen species generation efficiency to achieve stronger PCA and effective PDT, which is ascribed to stronger intramolecular charge transfer effect of Iso-TPA. Iso-TPA nanoparticles can achieve effective long-lasting NIR afterglow in vivo bioimaging up to 120 s with higher imaging resolution and outstanding PDT efficacy of tumor, exhibiting promising potential on bioimaging and therapy.

Long lifetimes white afterglow in slightly crosslinked polymer systems

Intrinsic polymer room-temperature phosphorescence (IPRTP) materials have attracted considerable attention for application in flexible electronics, information encryption, lighting displays, and other fields due to their excellent processabilities and luminescence properties. However, achieving multicolor long-lived luminescence, particularly white afterglow, in undoped polymers is challenging. Herein, we propose a strategy of covalently coupling different conjugated chromophores with poly(acrylic acid (AA)-AA-N-succinimide ester) (PAA-NHS) by a simple and rapid one-pot reaction to obtain pure polymers with long-lived RTPs of various colors. Among these polymers, the highest phosphorescence quantum yield of PAPHE reaches 14.7%. Furthermore, the afterglow colors of polymers can be modulated from blue to red by introducing three chromophores into them. Importantly, the acquired polymer TPAP-514 exhibits a white afterglow at room temperature with the chromaticity coordinates (0.33, 0.33) when the ratio of chromophores reaches a suitable value owing to the three-primary-color mechanism. Systematic studies prove that the emission comes from the superposition of different triplet excited states of the three components. Moreover, the potential applications of the obtained polymers in light-emitting diodes and dynamic anti-counterfeiting are explored. The proposed strategy provides a new idea for constructing intrinsic polymers with diverse white-light emission RTPs.

Sunlight-Activated Hour-Long Afterglow from Transparent and Flexible Polymers

Afterglow materials featuring long emission durations ranging from milliseconds to hours have garnered increasing interest owing to their potential applications in sensing, bioimaging, and anti-counterfeiting. Unfortunately, polymeric materials rarely exhibit afterglow properties under ambient conditions because of the rapid nonradiative decay rate of triplet excitons. In this study, hour-long afterglow (HLA) polymer films are fabricated using a facile molecular doping strategy. Flexible and transparent polymer films emitted a bright afterglow lasting over 11 h at room temperature in air, which is one of the best performances among the organic afterglow materials reported to date. Intriguingly, HLA polymer films can be activated by sunlight, and their cyan afterglow in air can be readily observed by the naked eye. Moreover, the HLA color of the polymer films could be tuned from cyan to red through the Förster resonance energy transfer mechanism. Their application in flexible displays and information storage has also been demonstrated. With remarkable advantages, including an hour-long and bright afterglow, tunable afterglow colors, superior flexibility and transparency, and ease of fabrication, the HLA polymer paves the way for the practical application of afterglow materials in the engineering sector.

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.

Ultralong afterglow of heavy-atom-free carbon dots with a phosphorescence lifetime of up to 3.7 s for encryption and fingerprinting description

Metal-free room-temperature phosphorescent (RTP) materials with changeable colors have attracted great attention in anti-counterfeiting information encryption. Most ultralong-lifetime RTP (URTP) luminophores are traditionally obtained through heavy atom effects via enhancing the spin-orbit coupling efficiency. Here, we report the self-assembly of URTP carbon dots (CDs) using diphenylaminourea as the precursor through a thermal-evaporation assisted covalent-binding approach in the presence of boric acid (BA). The BA-functionalized diphenylaminourea-derived CDs (denoted as D-CDs1.5/BA composites) show a rigid network structure with B-C linkages connected to the surface of the CDs, which can effectively suppress the free vibration of CDs to promote intersystem crossover, finally resulting in an excellent URTP afterglow performance. They feature a low singlet-triplet energy gap and reduced nonradiative attenuation properties. As a result, the D-CDs1.5/BA composites exhibit a bifunctional fluorescence/phosphorescence performance with a high phosphorescence quantum efficiency (12.67%) and an ultra-long green afterglow phosphorescence lifetime of up to 3.66 s. A high-level information encryption and fingerprinting description based on the URTP D-CDs1.5/BA composites were then investigated. This work contributes to the feasible design and preparation of novel URTP CD materials with both ultra-long afterglow and a high phosphorescence efficiency, making them promising candidates for advanced anti-counterfeiting applications.

Transforming Thermally Activated Delayed Fluorescence to Room-Temperature Phosphorescence through Modulation of the Donor in Charge-Transfer Cocrystals

A cocrystallization strategy is used through incorporation of 1,2,4,5-tetracyanobenzene (TCNB) as an acceptor with halogen-substituent thioxanthone (TX) derivatives as donors. The resulting cocrystals TT-R (R = H, F, Cl, Br, or I) transform the thermally activated delayed fluorescence emission in the TT-H, TT-F, and TT-Cl cocrystals to room-temperature phosphorescence in the TT-Br and TT-I cocrystals. Definite crystal packing structures demonstrate a 1:1 alternative donor-acceptor stacking in the TT-H cocrystal, a 2:1 alternative donor-acceptor stacking in the TT-F and TT-Cl cocrystals, and a separate stacking of donor and acceptor in the TT-Br and TT-I cocrystals. A transformation law can be revealed that with an increase in atomic number from H, F, Cl, Br, to I, the cocrystals show the structural transformation of the number of aggregated TX-R molecules from monomers to dimers and finally to multimers. This work will facilitate an understanding of the effect of halogen substituents on the crystal packing structure and luminescence properties in the cocrystals.

Photocured room temperature phosphorescent materials from lignosulfonate

Photocured room temperature phosphorescent (RTP) materials hold great potential for practical applications but are scarcely reported. Here, we develop photocured RTP materials (P-Lig) using a combination of lignosulfonate, acrylamide, and ionic liquid (1-ethyl-3-methylimidazolium bromide). With this design, lignosulfonate simultaneously serves as RTP chromophore and photoinitiator. Specifically, lignosulfonate in the ionic liquid generates radicals to polymerize the acrylamide upon UV irradiation. The resulting lignosulfonate is automatically confined in an as-formed crosslinked matrix to provide RTP. As such RTP with an emission lifetime of ~110 ms is observed from the confined lignosulfonate in P-Lig. Additionally, energy transfer occur between P-Lig and Rhodamine B (RhB), triggering red afterglow emission when P-Lig is in situ loaded with RhB (P-Lig/RhB). As a demonstration of potential applications, the P-Lig and P-Lig/RhB are used as photocured RTP coatings and RTP inks for fabricating 3D materials and for information encryption.

Dynamic Ultra-long Room Temperature Phosphorescence Enabled by Amorphous Molecular "Triplet Exciton Pump" for Encryption with Temporospatial Resolution

Organic ultra-long room-temperature phosphorescence (RTP) materials in the amorphous state have attracted widespread attention due to their simple preparation and flexibility to adopt various forms in sensors, bioimaging, and encryption applications. However, the amorphous molecular host for the host-guest RTP systems is highly demanded but limited. Here, a universal molecular host (DPOBP-Br) has been designed by integration of an amorphous moiety of diphenylphosphine oxide (DPO) and an intersystem crossing (ISC) group of 4-bromo-benzophenone (BP-Br). Various commercial fluorescence dyes were doped into the tight and transparent DPOBP-Br film, respectively, resulting in amorphous host-guest systems with ultra-long RTP colors from green to red. It was found that DPOBP-Br acted as a universal "triplet exciton pump" for promoting the generation of triplet excitons in the guest, through energy transfer processes and external heavy-atom effect based on DPOBP-Br. Interestingly, dynamic RTP was achieved by controlling residual oxygen concentration in the amorphous matrix by UV irradiation. Therefore, multi-dimensional anti-counterfeiting coatings were realized even on curved surfaces, simultaneously exhibiting spatial and 2D-time dependence. This work provides a strategy to design new amorphous molecular hosts for RTP systems and demonstrates the advanced information encryption with tempo-spatial resolution based on the dynamic ultra-long RTP of an amorphous system.

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.

Twofold rigidity activates ultralong organic high-temperature phosphorescence

A strategy is pioneered for achieving high-temperature phosphorescence using planar rigid molecules as guests and rigid polymers as host matrix. The planar rigid configuration can resist the thermal vibration of the guest at high temperatures, and the rigidity of the matrix further enhances the high-temperature resistance of the guest. The doped materials exhibit an afterglow of 40 s at 293 K, 20 s at 373 K, 6 s at 413 K, and a 1 s afterglow at 433 K. The experimental results indicate that as the rotational ability of the groups connected to the guests gradually increases, the high-temperature phosphorescence performance of the doped materials gradually decreases. In addition, utilizing the property of doped materials that can emit phosphorescence at high temperatures and in high smoke, the attempt is made to use organic phosphorescence materials to identify rescue workers and trapped personnel in fires.

Construction of Carbon Dots@LiCl-polyacrylamide with Humidity-Induced Ultralong Room-Temperature Phosphorescence to Fluorescence and Rigid-to-Flexible Transition Behavior

The continuous advancement of luminescent materials has placed increasingly stringent requirements on dynamic color-tunable ultralong room-temperature phosphorescence (URTP) materials that can respond to external stimuli. Nevertheless, endowing URTP materials with stimuli-response-induced dynamic color tuning is a challenging task. This study introduces a carbon dots (CDs)@LiCl-polyacrylamide (PAM) polymer system that switches from URTP to fluorescence under humidity stimuli, accompanied by a transition from rigidity to flexibility. The obtained rigid CDs@LiCl-PAM exhibits ultralong green phosphorescence with a lifetime of 560 ms in the initial state. After absorbing moisture, it becomes flexible and its phosphorescence switches off. Moreover, the emission of the CDs@LiCl-PAM film depends on the excitation wavelength. This property can potentially used in multicolored luminescence applications and displays. Moreover, multicolor luminescent patterns can be constructed in situ using the water-absorption ability of the obtained thin film and the Förster resonance energy-transfer strategy. The proposed strategy is expected to promote the interdisciplinary development of intelligent information encryption, anti-counterfeiting, and smart flexible display materials.

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.

Cucurbituril-based supramolecular host-guest complexes: single-crystal structures and dual-state fluorescence enhancement

Two supramolecular complexes were prepared using cucurbiturils [CBs] as mediators and a four-armed p-xylene derivative (M1) as a guest molecule. The single crystals of these two complexes were obtained and successfully analyzed by single-crystal X-ray diffraction (SCXRD). An unexpected and intriguing 1 : 2 self-assembly arrangement between M1 and CB[8] was notably uncovered, marking its first observation. These host-guest complexes exhibit distinctive photophysical properties, especially emission behaviors. Invaluable insights can be derived from these single-crystal structures. The precious single-crystal structures provide both precise structural information regarding the supramolecular complexes and a deeper understanding of the intricate mechanisms governing their photophysical properties.

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.

Photoinduced Carbonyl Radical Luminescence in Host-Guest Systems

Developing a free radical emission system in different states, especially in water, is highly challenging and desired. Herein, a host-guest coassembly strategy was used to protect the in situ photoactivated radical emission of carbonyl compounds in solid and aqueous solutions by doping them into a series of small molecules with hydroxyl groups. The intermolecular interactions between host and guest and the electron-donating ability of the hydroxyl group can significantly promote the formation and stabilization of luminescence by carbonyl radicals. Accordingly, the stimuli-responsive property of the free radical system was investigated in detail, and the self-assembled aggregates showed photoactive and thermoresponsive behaviors. In addition, an advanced ammonia compound identification system can be built based on a radical emission system. Our design strategy sheds light on developing free radical systems that can emit in various states, which will greatly broaden the application range of free radicals.

Microwave-Responsive Flexible Room-Temperature Phosphorescence Materials Based on Poly(vinylidene fluoride) Polymer

The development of flexible, room-temperature phosphorescence (RTP) materials remains challenging owing to the quenching of their unstable triplet excitons via molecular motion. Therefore, a polymer matrix with Tg higher than room temperature is required to prevent polymer segment movement. In this study, a RTP material was developed by incorporating a 4-biphenylboronic acid (BPBA) phosphor into a poly(vinylidene fluoride) (PVDF) matrix (Tg =-27.1 °C), which exhibits a remarkable UV-light-dependent oxygen consumption phosphorescence with a lifetime of 1275.7 ms. The adjustable RTP performance is influenced by the crystallinity and polymorph (α, β, and γ phases) fraction of PVDF, therefore, the low Tg of the PVDF matrix enables the polymeric segmental motion upon microwave irradiation. Consequently, a reduction in the crystallinity and an increase in the α phase fraction in PVDF film induces RTP after 2.45 GHz microwave irradiation. These findings open up new avenues for constructing crystalline and phase-dependent RTP materials while demonstrating a promising approach toward microwave detection.

Dopant-Matrix Afterglow Systems: Manipulation of Room-Temperature Phosphorescence/Thermally Activated Delayed Fluorescence Afterglow Mechanism via Mismatch/Match of Intermolecular Charge Transfer between Dopants and Matrices

Dopant-matrix organic afterglow materials exhibit ease of fabrication and intriguing functions in diverse fields. However, a deep and comprehensive understanding of their photophysical behaviors remains elusive. Here we report manipulation of a room-temperature phosphorescence/thermally activated delayed fluorescence (RTP/TADF) afterglow mechanism via the mismatch/match of intermolecular charge transfer between dopants and matrices. When dispersed in inert crystalline matrices, the luminescent dopants show RTP lifetimes up to 2 s. Interestingly, when suitable organic matrices are selected, the resultant dopant-matrix materials display a TADF-type afterglow under ambient conditions due to the formation of dopant-matrix intermolecular charge transfer complexes. Detailed studies reveal that reverse intersystem crossing from dopants' T1 states to charge transfer complexes' S1 states, which features a moderate kRISC of 101-102 s-1, is responsible for the emergence of a TADF-type organic afterglow in rigid crystalline matrices. Such less reported delicate photophysics reveals a new aspect of the excited state property in dopant-matrix afterglow systems.

Phosphorescence resonance energy transfer from purely organic supramolecular assembly

Phosphorescence energy transfer systems have been applied in encryption, biomedical imaging and chemical sensing. These systems exhibit ultra-large Stokes shifts, high quantum yields and are colour-tuneable with long-wavelength afterglow fluorescence (particularly in the near-infrared) under ambient conditions. This review discusses triplet-to-singlet PRET or triplet-to-singlet-to-singlet cascaded PRET systems based on macrocyclic or assembly-confined purely organic phosphorescence introducing the critical toles of supramolecular noncovalent interactions in the process. These interactions promote intersystem crossing, restricting the motion of phosphors, minimizing non-radiative decay and organizing donor-acceptor pairs in close proximity. We discuss the applications of these systems and focus on the challenges ahead in facilitating their further development.

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.

Large-Scale Preparation for Multicolor Stimulus-Responsive Room-Temperature Phosphorescence Paper via Cellulose Heterogeneous Reaction

The large-scale preparation of sustainable room-temperature phosphorescence (RTP) materials, particularly those with stimulus-response properties, is attractive but remains challenging. This study develops a facile heterogeneous B─O covalent bonding strategy to anchor arylboronic acid chromophores to cellulose chains using pure water as a solvent, resulting in multicolor RTP cellulose. The rigid environment provided by the B─O covalent bonds and hydrogen bonds promotes the triplet population and suppresses quenching, leading to an excellent lifetime of 1.42 s for the target RTP cellulose. By increasing the degree of chromophore conjugation, the afterglow colors can be tuned from blue to green and then to red. Motivated by this finding, a papermaking production line is built to convert paper pulp reacted with an arylboronic acid additive into multicolor RTP paper on a large scale. Furthermore, the RTP paper is sensitive to water because of the destruction of hydrogen bonds, and the stimuli-response can be repeated in response to water/heat stimuli. The RTP paper can be folded into 3D afterglow origami handicrafts and anti-counterfeiting packing boxes or used for stimulus-responsive information encryption. This success paves the way for the development of large-scale, eco-friendly, and practical stimuli-responsive RTP materials.

UV-Curing-Enhanced Organic Long-Persistent Luminescence Materials

Amorphous organic long-persistent luminescence materials (OLPLMs) can realize simpler solution processing and large-area uniform luminescence, where the luminescent properties are significantly influenced by the rigid environment. However, research on utilizing the rigidity to promote long-persistent luminescence (LPL) properties of amorphous OLPLMs is still relatively rare due to the lack of an unambiguous and effective strategy to construct the rigid environment. Here, a universal strategy is proposed to enhance the LPL performance of organic host-guest doping systems by UV curing, which utilizes the rigid environment constructed by UV curing to promote the interaction between host and guest, thus inducing a generation of materials with highly efficient LPL performance. This solution-processable, large-area, and "easy-to-realize" material fabrication strategy can make amorphous OLPLMs show broader application prospects in some fields, such as anti-counterfeiting, nondestructive detection, and pattern marking or indication.

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.

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.

Construction of room temperature phosphorescent materials with ultralong lifetime by in-situ derivation strategy

Although room temperature phosphorescence (RTP) materials have been widely investigated, it is still a great challenge to improve the performance of RTP materials by promoting triplet exciton generation and stabilization. In this study, an in-situ derivation strategy was proposed to construct efficient RTP materials by in-situ deriving guest molecules and forming a rigid matrix during co-pyrolysis of guest molecules and urea. Characterizations and theoretical calculations revealed that the generated derivatives were beneficial for promoting intersystem crossing (ISC) to produce more triplet excitons, while rigid matrix could effectively suppress the non-radiative transition of triplet excitons. Thus, the in-situ derivation strategy was concluded to simultaneously promote the generation and stabilization of triplet excitons. With this method, the ultralong lifetime of RTP materials could reach up to 5.33 s and polychromatic RTP materials were easily achieved. Moreover, the potential applications of the RTP materials in reprocessing or editable anti-counterfeiting were successfully demonstrated.

Polymer-Based Long-Lived Phosphorescence Materials over a Broad Temperature Based on Coumarin Derivatives as Information Anti-Counterfeiting

The development of new polymer-based room-temperature phosphorescence materials is of great significance. By a special molecule design and a set of feasible property-enhancing strategies, coumarin derivatives (CMDs, M_a-M_f) were doped into polyvinyl alcohol (PVA), polyacrylamide (PAM), corn starch, and polyacrylonitrile (PAN) as information anti-counterfeiting. CMDs-doped PVA and CMDs-doped corn starch films showed long-lived phosphorescence emissions up to 1246 ms (M_a-PVA) and 697 ms (M_a-corn starch), reaching over 10 s afterglow under naked eye observation under ambient conditions. Significantly, CMDs-doped PAM films can display long-lived phosphorescence emissions in a wide temperature range (100-430 K). For example, the M_e-PAM film has a phosphorescence lifetime of 16 ms at 430 K. The use of PAM with the strong polarity and rigidity has expanded the temperature range of long-life polymer-based phosphorescent materials. The present long-lived phosphorescent systems provide the possibility for developing new polymer-based organic afterglow materials with robust phosphorescence.

Radioluminescent Cu-Au Metal Nanoclusters: Synthesis and Self-Assembly for Efficient X-ray Scintillation and Imaging

Zero-dimensional (0D) scintillation materials have drawn tremendous attention due to their inherent advantages in the fabrication of flexible high-energy radiation scintillation screens by solution processes. Although considerable progress has been made in the development of 0D scintillators, such as the current leading lead-halide perovskite nanocrystals and quantum dots, challenges still persist, including potential issues with self-absorption, air stability, and eco-friendliness. Here, we present a strategy to overcome those limitations by synthesis and self-assembly of a new class of scintillators based on metal nanoclusters. We demonstrate the gram-scale synthesis of an atomically precise nanocluster with a Cu-Au alloy core exhibiting high phosphorescence quantum yield, aggregation-induced emission enhancement (AIEE) behavior, and intense radioluminescence. By controlling solvent interactions, the AIEE-active nanoclusters were self-assembled into submicron spherical superparticles in solution, which we exploited as a novel building block for flexible particle-deposited scintillation films with high-resolution X-ray imaging performance. This work reveals metal nanoclusters and their self-assembled superstructures as a promising class of scintillators for practical applications in high-energy radiation detection and imaging.

High-definition and robust visualization of latent fingerprints utilizing ultrabright aggregation-induced emission of iridium developer

Creation of AIEgens with high brightness is compactly related to acquiring optimum AIE capabilities and still faces challenges. This study proposes an ingenious structurally regulative approach for preparing ultrabright AIEgens, taking iridium complexes as the model. The incremental rotational activity of substituents obtained by fine adjustment of the stereoscopic configuration efficaciously activates the AIE of iridium complexes and synchronously imparts high-brightness luminescence. Subsequently, benefitting from the ultrabright AIE, high-resolution visualization of latent fingerprints (LFPs) is achieved on diverse substrates by transient immersion in a solution of the AIE-active iridium complex (Ir3) for 60 s. The LFPs stained by Ir3 are integral and distinct enough to possess level 1-3 detail features, which allow precisely realizing personal identification. The LFP photograph emerges inconspicuous attenuation of contrast when aged under ambient light for 10 days and then being continuously irradiated with high-power ultraviolet light for 1 h, reflecting extraordinary aging resistance. Notably, the ultrabright AIE of Ir3 with room-temperature phosphorescence feature successfully achieves enhanced visualization of local fingerprint details with ultrahigh contrast. This LFP visualization protocol based on the ultrabright AIEgens is practical and provides a reliable solution for forensic investigations in actual scenarios.

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.

A Single Carbon-Dot System Enabling Multiple Stimuli Activated Room-Temperature Phosphorescence

Room-temperature phosphorescent carbon dots (RTPCDs) have attracted considerable interests due to their unique nanoluminescent characteristic with time resolution. However, it is still a formidable challenge to construct multiple stimuli-activated RTP behaviors on CDs. Since the address of this issue facilitates complex and high-regulatable phosphorescent applications, we here develop a novel strategy to achieve a multiple stimuli responsive phosphorescent activation on a single carbon-dot system (S-CDs), using persulfurated aromatic carboxylic acid as the precursor. The introduction of aromatic carbonyl groups and multiple S atoms can promote the intersystem crossing process to generate RTP characteristic of the produced CDs. Meanwhile, by introducing these functional surface groups into S-CDs, the RTP property can be activated by light, acid, and thermal stimuli in solution or in film state. In this way, multistimuli responsive and tunable RTP characteristics are realized in the single carbon-dot system. Based on this set of RTP properties, S-CDs is applied to photocontrolled imaging in living cells, anticounterfeit label, and multilevel information encryption. Our work will benefit the development of multifunctional nanomaterials together with extending their application scope.

Room temperature phosphorescence from natural wood activated by external chloride anion treatment

Producing afterglow room temperature phosphorescence (RTP) from natural sources is an attractive approach to sustainable RTP materials. However, converting natural resources to RTP materials often requires toxic reagents or complex processing. Here we report that natural wood may be converted into a viable RTP material by treating with magnesium chloride. Specifically, immersing natural wood into an aqueous MgCl₂ solution at room temperature produces so-called C-wood containing chloride anions that act to promote spin orbit coupling (SOC) and increase the RTP lifetime. Produced in this manner, C-wood exhibits an intense RTP emission with a lifetime of ~ 297 ms (vs. the ca. 17.5 ms seen for natural wood). As a demonstration of potential utility, an afterglow wood sculpture is prepared in situ by simply spraying the original sculpture with a MgCl₂ solution. C-wood was also mixed with polypropylene (PP) to generate printable afterglow fibers suitable for the fabrication of luminescent plastics via 3D printing. We anticipate that the present study will facilitate the development of sustainable RTP materials.

Modulating Emission of Boric Acid into Highly Efficient and Color-Tunable Afterglow via Dehydration-Induced Through-Space Conjugation

Inorganic boric acid (BA) is generally not considered an efficient afterglow material, and several groups have reported its extremely weak room-temperature phosphorescence (RTP) in the blue spectral region. It is discovered that heat treatment of BA results in increased afterglow intensity (27-fold increase) and prolonged emission lifetime (from 0.83 to 1.59 s), attributed to enhanced through-space conjugation (TSC) of BA. The afterglow intensity of BA can be increased further (≈415 folds) by introducing p-hydroxybenzoic acid (PHA), which contains a conjugated molecular motif, to further promote the TSC of the BA system. This combination results in the production of afterglow materials with a photoluminescence quantum yield of 83.8% and an emission lifetime of 2.01 s. In addition, a tunable multicolor afterglow in the 420-490 nm range is achieved owing to the enhancement of the RTP and thermally activated delayed fluorescence of PHA, where BA exerts a confinement effect on the guest molecules. Thus, this study demonstrates promising afterglow materials produced from extremely abundant and simple precursor materials for various applications.

Photoactivated organic phosphorescence by stereo-hindrance engineering for mimicking synaptic plasticity

Purely organic phosphorescent materials with dynamically tunable optical properties and persistent luminescent characteristics enable more novel applications in intelligent optoelectronics. Herein, we reported a concise and universal strategy to achieve photoactivated ultralong phosphorescence at room temperature through stereo-hindrance engineering. Such dynamically photoactivated phosphorescence behavior was ascribed to the suppression of non-radiative transitions and improvement of spin-orbit coupling (SOC) as the variation of the distorted molecular conformation by the synergistic effect of electrostatic repulsion and steric hindrance. This "trainable" phosphorescent behavior was first proposed to mimic biological synaptic plasticity, especially for unique experience-dependent plasticity, by the manipulation of pulse intensity and numbers. This study not only outlines a principle to design newly dynamic phosphorescent materials, but also broadens their utility in intelligent sensors and robotics.

D-O-A based organic phosphors for both aggregation-induced electrophosphorescence and host-free sensitization

Pure organic phosphors capable of room-temperature phosphorescence show a great potential in organic light-emitting diodes, while it is limited by the big challenge to realize efficient electroluminescence under electric excitation. Herein, we develop a class of organic phosphors based on acridine as the electron donor, triazine as the electron acceptor and oxygen as the bridge between them. Benefitting from the characteristic donor-oxygen-acceptor geometry, these compounds are found to behave an exciting aggregation-induced organic room-temperature electrophosphorescence, and achieve a record-high external quantum efficiency of 15.8% for non-doped devices. Furthermore, they can sensitize multi-resonant emitters in the absence of any additional wide bandgap host, leading to an effective narrowband emission with a peak external quantum efficiency of 26.4% and a small full-width at half maximum of 26 nm. The results clearly indicate that donor-oxygen-acceptor geometry is a promising strategy to design organic phosphors suitable for organic light-emitting diodes.

Observation of Chiral-selective room-temperature phosphorescence enhancement via chirality-dependent energy transfer

Pure organic room-temperature phosphorescence (RTP), particularly from guest-host doped systems, has seen exponential growth in the last several years due to their high modulation flexibility, and yet challenges remain with respect to mechanistic elucidations and advantageous applications. Here we show that by constructing guest-host doped RTP systems from chiral components, namely, chiral amino compound-modified phthalimide hosts and naphthalimide guests, a chiral-selective RTP enhancement phenomenon can be observed. For example, R-enantiomeric guests in R-enantiomeric hosts produce strong red RTP afterglow while no appreciable RTP could be observed in the S-R guest-host counterpart. An unprecedented RTP intensity difference > 10² folds with the ability to distinguish an enantiomeric excess of 98% could be achieved. Temperature-dependent measurements suggest that a chirality-dependent energy transfer process may be involved in the observed phenomenon, which can be harnessed to extend the RTP application to the chiral recognition of amino compounds, such as amino alcohols.

Room-Temperature Phosphorescence and Cellular Phototoxicity Activated by Triplet Dynamics in Aggregates of Push-Pull Phenothiazine-Based Isomers

In this study, we report a comprehensive time-resolved spectroscopic investigation of the excited-state deactivation mechanism in three push-pull isomers characterized by a phenothiazine electron donor, a benzothiazole electron acceptor, and a phenyl π-bridge where the connection is realized at the relative ortho, meta, and para positions. Spin-orbit charge-transfer-induced intersystem crossing takes place with high yield in these all-organic donor-acceptor compounds, leading also to efficient production of singlet oxygen. Our spectroscopic results give clear evidence of room-temperature phosphorescence not only in solid-state host-guest matrices but also in highly biocompatible aggregates of these isomers produced in water dispersions, as rarely reported in the literature. Moreover, aggregates of the isomers could be internalized by lung cancer and melanoma cells and display bright luminescence without any dark cytotoxic effect. On the other hand, the isomers showed significant cellular phototoxicity against the tumor cells due to light-induced reactive oxygen species generation. Our findings strongly suggest that nanoaggregates of the investigated isomers are promising candidates for imaging-guided photodynamic therapy.

A Highly Stable Organic Luminescent Diradical

It is very challenging to obtain stable room-temperature luminescent open-shell singlet diradicals. Herein we report the first stable Müller's hydrocarbon TTM-PhTTM with luminescent properties. Variable-temperature electron paramagnetic resonance spectroscopy measurements and theoretical calculations show that TTM-PhTTM has an open-shell singlet ground state with a diradical character of 90 %. Because of a small singlet-triplet energy gap, the open-shell singlet ground state can be thermally excited to a triplet state. TTM-PhTTM shows room-temperature deep-red emission in various solutions. Unusually high stability of TTM-PhTTM was also observed owing to effective steric hindrance and spin delocalization. Our results are beneficial to the rational design and discovery of more stable luminescent diradical materials.

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.

Poly-L-aspartic acid based nonconventional luminescent biomacromolecules with efficient emission in dilute solutions for Al3+ detection

Nonconventional luminescent macromolecules exhibiting bright fluorescence or phosphorescence emission at high concentrations and solid-state have attracted significant attention due to their promising application in different fields. However, most reported nonconventional luminescent macromolecules show weak or no emission in dilute solutions, limiting their large-scale applications. Herein, nonconventional luminescent biomacromolecules with hydrophobic rigid chains, hydrophilic flexibility and inter- or intra-molecular hydrogen bonding interactions were proposed to achieve effective luminescence in dilute solutions. Poly-L-aspartic acid (PASA) with a fluorescence quantum yield of 4.6 % in a dilute solution (0.8 mg/mL) was synthesized to validate this design strategy. The fluorescence intensity of PASA solution increased with the increase of the concentration, demonstrating a clustering-triggered emission (CTE) effect. Furthermore, the fluorescence intensity significantly enhanced when adding Al³⁺ into PASA aqueous solution via the Al³⁺ recognition effect. The detection limits for Al³⁺ (1.71 × 10^-6 mol/L) meet the World Health Organization (WHO) requirements for food detection. At last, PASA solid-state samples exhibit room temperature phosphorescence emission.