Dynamic Ultralong Organic Phosphorescence by Photoactivation

Photoactivated room temperature phosphorescence from lignin

Sustainable photoactivated room temperature phosphorescent materials exhibit great potential but are difficult to obtain. Here, we develop photoactivated room temperature phosphorescent materials by covalently attaching lignin to polylactic acid, where lignin and polylactic acid are the chromophore and matrix, respectively. Initially the phosphorescence of the lignin is quenched by residual O2. However, the phosphorescence is switched on when the residual oxygen is consumed by the triplet excitons of lignin under continuous UV light irradiation. As such, the lifetime increases from 3.0 ms to 221.1 ms after 20 s of UV activation. Interestingly, the phosphorescence is quenched again after being kept under an atmosphere of air for 2 h in the absence of UV irradiation due to the diffusion of oxygen into the materials. Using these properties, as-developed material is successfully used as a smart anti-counterfeiting logo for a medicine bottle and for information recording.

Reversible switching from fluorescence to room temperature phosphorescence amplified by exciton-vibration coupling through pressure-induced tiny packing changes

Investigating the impact of exciton-vibration coupling (EC) of molecular aggregates on regulating the excited-state dynamics and controlling room temperature phosphorescence (RTP) emissions is crucial and challenging. We designed and synthesized ArBFO molecules and cultured two crystals with similar molecular packing and completely different luminescent mechanisms from B-form fluorescence to G-form RTP. The mechanism study combining measurement of photophysical properties, time-resolved fluorescence analysis, X-ray diffraction analysis, and theoretical calculations shows that tiny changes in molecular stacking amplify the EC value from B-form to G-form H-aggregates. The larger EC value accelerates the ISC process and suppresses the radiative singlet decay. Meanwhile, the stronger intermolecular interaction restricts non-radiative transitions. All of these facilitate green RTP emission in G-form aggregates. When treated with pressure-heating cycles, the transformation between B-form and G-form aggregates leads to a reversible blue fluorescence/green RTP switch with good reproducibility and photostability. Moreover, their potential in multi-level information encryption and anti-counterfeiting application has been well demonstrated. The results of this research deepen the understanding of the effect of aggregation on the luminescence mechanism and provide a new design guidance for developing smart materials with good performance.

Recent Progress in Solid-State Room Temperature Afterglow Based on Pure Organic Small Molecules

Organic room temperature afterglow (ORTA) can be categorized into two key mechanisms: continuous thermally activated delayed fluorescence (TADF) and room-temperature phosphorescence (RTP), both of which involve a triplet excited state. However, triplet excited states are easily quenched by non-radiative transitions due to oxygen and molecular vibrations. Solid-phase systems provide a conducive environment for triplet excitons due to constrained molecular motion and limited oxygen permeation within closely packed molecules. The stimulated triplet state tends to release energy through radiative transitions. Despite numerous reports on RTP in solid-phase systems in recent years, the complexity of these systems precludes the formulation of a universal theory to elucidate the underlying principles. Several strategies for achieving ORTA luminescence in the solid phase have been developed, encompassing crystallization, polymer host-guest doping, and small molecule host-guest doping. Many of these systems exhibit luminescent responses to various physical stimuli, including light stimulation, mechanical stimuli, and solvent vapor exposure. The appearance of these intriguing luminescent phenomena in solid-phase systems underscores their significant potential applications in areas such as light sensing, biological imaging, and information security.

Hierarchical Dual-Mode Efficient Tunable Afterglow via J-Aggregates in Single-Phosphor-Doped Polymer

The development of polymer-based persistent luminescence materials with color-tunable organic afterglow and multiple responses is highly desirable for applications in anti-counterfeiting, flexible displays, and data-storage. However, achieving efficient persistent luminescence from a single-phosphor system with multiple responses remains a challenging task. Herein, by doping 9H-pyrido[3,4-b]indole (PI2) into an amorphous polyacrylamide matrix, a hierarchical dual-mode emission system is developed, which exhibits color-tunable afterglow due to excitation-, temperature-, and humidity-dependence. Notably, the coexistence of the isolated state and J-aggregate state of the guest molecule not only provides an excitation-dependent afterglow color, but also leads to a hierarchical temperature-dependent afterglow color resulting from different thermally activated delayed fluorescence (TADF) and ultralong organic phosphorescence (UOP) behaviors of the isolated and aggregated states. The complex responsiveness based on the hierarchical dual-mode emission can serve for security features through inkjet printing and ink-writing. These findings may provide further insight into the regulated persistent luminescence by isolated and aggregated phosphors in doped polymer systems and expand the scope of stimuli-responsive organic afterglow materials for broader applications.

Combining Functional Units to Design Organic Materials with Dynamic Room-Temperature Phosphorescence under Continuous Ultraviolet Irradiation

Developing materials with dynamic room-temperature phosphorescence (RTP) properties is crucial for expanding the applications of organic light-emitting materials. In this study, we designed and synthesized two novel RTP molecules by combining functional units, incorporating the folded unit thianthrene into the classic luminescent cores thioxanthone or anthraquinone to construct TASO and TA2O. In this combination, the TA unit contributes to the enhancement of spin-orbit coupling (SOC), while the luminescent core governs the triplet energy level. After the strategic manipulation of SOC using the thianthrene unit, the target molecules exhibited a remarkable enhancement in RTP performance. This strategy led to the successful development of TASO and TA2O molecules with outstanding dynamic RTP properties when exposed to continuous ultraviolet irradiation, a result that can be ascribed to their efficient RTP, improved absorption ability, and oxygen-sensitive RTP properties. Leveraging the oxygen-mediated ultraviolet-radiation-induced RTP enhancement in TASO-doped polymer films, we developed a novel time-resolved detection technique for identifying phase separation in polymers with varying oxygen permeability. This research offers a promising approach for constructing materials with dynamic RTP properties.

Achieving Bright and Long-Lived Aqueous Room-Temperature Phosphorescence of Carbon Nitrogen Dots Through In Situ Host-Guest Binding

The development of bright and long-lived aqueous room-temperature phosphorescent (RTP) materials holds paramount importance in broadening the application scope of RTP material system. However, the conventional RTP materials usually exhibit low efficiency and short lifetime in aqueous solution. Herein, an in situ host-guest strategy is proposed to achieve cyanuric acid (CA)-derived phosphorescent carbon nitrogen dots (CNDs) composite (CNDs@CA) that demonstrates a significant enhancement of both quantum yield (QY) and lifetime mediated by water. Detailed investigations reveal that the robust hydrogen bonding networks between CNDs@CA and water effectively stabilize triplet excitons and suppress nonradiative decays, as well as facilitate efficient energy transfer from CA to CNDs, thereby prolonging the lifetime and enhancing the efficiency of RTP. The phosphorescent QY and lifetime of CNDs@CA can be increased to 26.89% (3.9-fold increase) and 951.25 ms (5.5-fold increase), respectively, with the incorporation of 50 wt% water under ambient conditions. Even in fully aqueous environments (with up to 400 wt% water added), CNDs@CA exhibits persistent water-boosted RTP properties, demonstrating exceptional stability. The robust water-boosted RTP property of CNDs@CA in aqueous solutions presents significant potential for high signal-to-noise ratio afterglow bioimaging as well as advanced information encryption.

Dual-channel mechano-phosphorescence: a combined locking effect with twisted molecular structures and robust interactions

Organic mechanoluminescence materials, featuring dual emission and ultralong phosphorescence characteristics, exhibit significant potential for applications in real-time stress sensing, pressure-sensitive lighting, advanced security marking techniques, and material breakage monitoring. However, due to immature molecular design strategies and unclear luminescence mechanisms, these materials remain rarely reported. In this study, we propose a valuable molecular design strategy to achieve dual-channel mechano-phosphorescence. By introducing the arylphosphine oxide group into a highly twisted molecular framework, enhanced intra- and intermolecular interactions could be achieved within rigid structures, leading to dual-channel mechanoluminescence with greatly promoted ultralong phosphorescence. Further investigations reveal the substantial boosting effect of intra- and intermolecular interactions on mechanoluminescence and ultralong phosphorescence properties by locking the highly twisted molecular skeleton. This work provides a concise and guiding route to develop novel smart responsive luminescence materials for widespread applications in material science.

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.

Photo-Controllable Ultralong Room-Temperature Phosphorescence: State of the Art

In this concept, we showcase the upsurge in the studies of dynamic ultralong room-temperature phosphorescence (RTP) materials containing inorganic and/or organic components as versatile photo-responsive platforms. The goal is to provide a comprehensive analysis of photo-controllable RTP, and meanwhile delve into the underlying RTP properties of various classes of photochromic materials including metal-organic complexes, organic-inorganic co-crystals, purely organic small molecules and organic polymers. In particular, the design principles governing the integration of the photochromic and RTP moieties within a single material system, and the tuning of dynamic RTP in response to light are emphasized. As such, this concept sheds light on the challenges and opportunities of using these tunable RTP materials for potential applications in optoelectronics, particularly highlighting their use of reversible information encryption, erasable light printing and rewritable smart paper.

A flexible ligand and halogen engineering enable one phosphor-based full-color persistent luminescence in hybrid perovskitoids

Color-tunable room temperature phosphorescent (RTP) materials have raised wide interest due to their potential application in the fields of encryption and anti-counterfeiting. Herein, a series of CdX2-organic hybrid perovskitoids, (H-apim)CdX3 and (apim)CdX2 (denoted as CdX-apim1 and CdX-apim2, apim = 1-(3-aminopropyl)imidazole, X = Cl, Br), were synthesized using apim with both rigid and flexible groups as ligands, which exhibit naked-eye detectable RTP with different durations and colors (from cyan to red) by virtue of different halogen atoms, coordination modes and the coplanar configuration of flexible groups. Interestingly, CdCl-apim1 and CdX-apim2 both exhibit excitation wavelength-dependent RTP properties, which can be attributed to the multiple excitation of imidazole/apim, the diverse interactions with halogen atoms, and aggregated state of imidazoles. Structural analysis and theoretical calculations confirm that the aminopropyl groups in CdCl-apim1 do not participate in luminescence, while those in CdCl-apim2 are involved in luminescence including both metal/halogen to ligand charge transfer and twisted intramolecular charge transfer. Furthermore, we demonstrate that these perovskitoids can be applied in multi-step anti-counterfeiting, information encryption and smart ink fields. This work not only develops a new type of perovskitoid with full-color persistent luminescence, but also provides new insight into the effect of flexible ligands and halogen engineering on the wide-range modulation of RTP properties.

Engineering Tunable Ratiometric Dual Emission in Single Emitter-based Amorphous Systems

Molecular emitters with multi-emissive properties are in high demand in numerous fields, while these properties basically depend on specific molecular conformation and packing. For amorphous systems, special molecular arrangement is unnecessary, but it remains challenging to achieve such luminescent behaviors. Herein, we present a general strategy that takes advantage of molecular rigidity and S1 -T1 energy gap balance for emitter design, which enables fluorescence-phosphorescence dual-emission properties in various solid forms, whether crystalline or amorphous. Subsequently, the amorphism of the emitters based polymethyl methacrylate films endowed an in situ regulation of the dual-emissive characteristics. With the ratiometric regulation of phosphorescence by external stimuli and stable fluorescence as internal reference, highly controllable luminescent color tuning (yellow to blue including white emission) was achieved. There properties together with a persistent luminous behavior is of benefit for an irreplaceable set of optical information combination, featuring an ultrahigh-security anti-counterfeiting ability. Our research introduces a concept of eliminating the crystal-form and molecular-conformational dependence of complex luminescent properties through emitter molecular design. This has profound implications for the development of functional materials.

Intermolecular donor-acceptor stacking to suppress triplet exciton diffusion for long-persistent organic room-temperature phosphorescence

Controlling triplet states is crucial to improve the efficiency and lifetime of organic room temperature phosphorescence (ORTP). Although the intrinsic factors from intramolecular radiative and non-radiative decay have been intensively investigated, the extrinsic factors that affect triplet exciton quenching are rarely reported. Diffusion to the defect sites inside the crystal or at the crystal surface may bring about quenching of triplet exciton. Here, the phosphorescence lifetime is found to have a negative correlation with the triplet exciton diffusion coefficient based on the density functional theory (DFT)/time-dependent density functional theory (TD-DFT) calculations on a series of ORTP materials. For systems with a weak charge transfer (CT) characteristic, close π-π stacking will lead to strong triplet coupling and fast triplet exciton diffusion in most cases, which is detrimental to the phosphorescence lifetime. Notably, for intramolcular donor-acceptor (D-A) type systems with a CT characteristic, intermolecular D-A stacking results in ultra-small triplet coupling, thus contributing to slow triplet diffusion and long phosphorescence lifetime. These findings shed some light on molecular design toward high-efficiency long persistent ORTP.

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.

Large-Scale Syntheses of Multicolor Stimulus Responsive Room-Temperature Phosphorescent Polymer-Carbonyl-Modified Carbon Nitrogen Quantum Dots

Carbonyl-modified solid-state carbon nitrogen quantum dots (m-O═CNQDs) have emerged as promising room-temperature phosphorescent (RTP) materials close to commercialization. However, high-crystallinity m-O═CNQDs are insensitive to external stimuli such as water and heat due to strong stacking interactions between layers, restricting their applications in stimulus responsive fields. Here, a polymer template space-confined growth strategy is established for the large-scale synthesis of water stimulus responsive polyvinylpyrrolidone-functionalized m-O═CNQDs with ultralong room-temperature phosphorescence (181 ms) using urea and PVP as precursors. Theoretical and experimental results indicate that the PVP template linked at the rim of m-O═CNQDs formed by in situ self-polymerization of urea inhibits interactions between layers and increases their affinity for water, which is the key to increasing their sensitivity with water. This strategy offers a new path for developing commercial stimulus responsive RTP materials.

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.

Organic Excitonic State Management by Surface Metallic Coupling of Inorganic Lanthanide Nanocrystals

The ability to harness charges and spins for control of organic excitonic states is critical in developing high-performance organic luminophores and optoelectronic devices. Here we report a facile strategy to efficiently manipulate the electronic energy states of various organic phosphors by coupling them with inorganic lanthanide nanocrystals. We show that the metallic atoms exposed on the nanocrystal surface can introduce strong coupling effects to 9-(4-ethoxy-6-phenyl-1,3,5-triazin-2-yl)-9H-carbazole (OCzT) and some organic chromophores with carbazole functional groups when the organics are approaching the nanocrystals. This unconventional organic-inorganic hybridization enables a nearly 100 % conversion of the singlet excitation to fast charge transfer luminescence that does not exist in pristine organics, which broadens the utility of organic phosphors in hybrid systems.

A Photoactivatable Luminescent Motif through Ring-Flipping Isomerization for Multiple Photopatterning

Photoactivatable luminescent materials have garnered enormous attention in the field of intelligent responsive materials, yet their design and applications remain challenging due to the limited variety of photoactivatable motifs. In the work described herein, we discovered a new photoactivatable luminescent motif that underwent ring-flipping isomerization under UV irradiation. The emission of this motif exhibited a rapid transformation from dark yellow to bright green, accompanied by a significant enhancement of quantum yield from 1.9% to 34.2%. Experimental and theoretical studies revealed that the effective intramolecular motion (EIM) was crucial to the distinct luminescence performance between two isomers. In addition, polymers containing this motif were achieved through a one-pot alkyne polymerization, exhibiting both photofluorochromic and photo-cross-linking properties. Furthermore, multiple types of photopatterning, including luminescent encryption, fluorescent grayscale imaging, and high-resolution photolithographic patterns, were realized. This work developed a new photoactivatable luminescent motif and demonstrated its potential applications in both small molecules and macromolecules, which will help in the future design of photoactivatable luminescent materials.

Regulating Isolated-Molecular and Aggregated-State Phosphorescence for Multicolor Afterglow by Photoactivation

Ultralong organic phosphorescence (UOP) materials have attracted considerable attention in recent years. Herein, a new type of flexible films is fabricated by doping amphipathic pyrene tetrasulfonic acid sodium salts into amorphous poly(vinyl alcohol) matrix, which enables the realization of color-tunable UOP spanning from orange-red to green after excitation light is switched off. Interestingly, precise control of the proportion of isolated-molecular and aggregated-state phosphorescence is demonstrated for colorful afterglow using photo-activation. An increase in the dynamic phosphorescence lifetime of isolated molecules is observed from 894.75 to 1735.71 ms following an 8 min irradiation under ambient conditions. The photo-activation, however, showed little influence on aggreated-state phosphorescence. This flexible and processable film exhibits versatile applications in multicolor afterglow displays, ultraviolet detection, multilevel information encryption, etc. This study not only provides a strategy for the rational regulation of UOP colors but also expands the application potential of color-tunable UOP materials.

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

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

Photo-Controlled Self-Assembly of Nanoparticles: A Promising Strategy for Development of Novel Structures

Photo-controlled self-assembly of nanoparticles (NPs) is an advanced and promising approach to address a series of material issues from the molecular level to the nano/micro scale, owing to the fact that light stimulus is typically precise and rapid, and can provide contactless spatial and temporal control. The traditional photo-controlled assembly of NPs is based on photochemical processes through NPs modified by photo-responsive molecules, which are realized through the change in chemical structure under irradiation. Moreover, photoexcitation-induced assembly of NPs is another promising physical strategy, and such a strategy aims to employ molecular conformational change in the excited state (rather than the chemical structure) to drive molecular motion and assembly. The exploration and control of NP assembly through such a photo-controlled strategy can open a new paradigm for scientists to deal with "bottom-up" behaviors and develop unprecedented optoelectronic functional materials.

Synthesis of Naphthalimide Derivatives and Their Luminescence upon Complexation with Cucurbit[n]uril Hosts

A series of naphthalimide derivatives are synthesized and their binding behavior upon complexation with cucurbit[n]urils (CB[n]s) has been investigated. With a heavy atom (bromine) on the naphthalimide core, 4-bromo-1,8-naphthalimide derivatives 1-4 show short room-temperature phosphorescence (RTP) lifetimes with low quantum yields. Their RTP properties are significantly enhanced in the presence of CB[8] or CB[10] both in aqueous solution and solid state owing to the efficient suppression of nonradiative decay and isolation of quenching factors by the rigid cavity of CB[n]. Without the bromine atom, 1,8-naphthalimide derivatives 5 and 6 show strong excimer emission upon complexation with CB[10] accompanied by fluorescence transition from blue to cyan. The fluorescence colors of 4-(dimethylamino)-1,8-naphthalimide derivatives 7 and 8 change from blue to white to yellow with the addition of CB[n]. This host-guest complexation strategy to modulate the luminescence of the luminophore would further broaden the application of luminescent materials.

How Matrixes Influence Room Temperature Ultralong Organic Phosphorescence: 4-Dimethylaminopyridine vs Carbazole Derivative

How matrixes influence room temperature ultralong organic phosphorescence (RTUOP) in the doping systems is a fundamental question. In this study, we construct guest-matrix doping phosphorescence systems by using the derivatives (ISO2N-2, ISO2BCz-1, and ISO2BCz-2) of three phosphorescence units (N-2, BCz-1, and BCz-2) and two matrixes (ISO2Cz and DMAP) and systematically investigate their RTUOP properties. Firstly, the intrinsic phosphorescence properties of three guest molecules were studied in solution, in the pure powder state, and in PMMA film. Then, the guest molecules were doped into the two matrixes with increasing weight ratio. To our surprise, all of the doping systems in DMAP feature a longer lifetime but weaker phosphorescence intensity, while all of the doping systems in ISO2Cz exhibit a shorter lifetime but higher phosphorescence intensity. According to the single-crystal analysis of the two matrixes, resemblant chemical structures of the guests and ISO2Cz enable them to approach each other and interact with each other via a variety of interactions, thus facilitating the occurrence of charge separation (CS) and charge recombination (CR). The HOMO-LUMO energy levels of the guests match well with the ones of ISO2Cz, which also significantly promotes the efficiency of the CS and CR process. To our best knowledge, this work is a systematic study on how matrixes influence the RTUOP of guest-matrix doping systems and may give deep insight into the development of organic phosphorescence.

Photoinduced crystal melting with luminescence evolution based on conformational isomerisation

The phenomenon of crystal melting by light irradiation, known as photo-induced crystal-to-liquid transition (PCLT), can dramatically change material properties with high spatiotemporal resolution. However, the diversity of compounds exhibiting PCLT is severely limited, which hampers further functionalisation of PCLT-active materials and the fundamental understandings of PCLT. Here, we report on heteroaromatic 1,2-diketones as the new class of PCLT-active compounds, whose PCLT is based on conformational isomerisation. In particular, one of the diketones demonstrates luminescence evolution prior to crystal melting. Thus, the diketone crystal exhibits dynamic multistep changes in the luminescence colour and intensity during continuous ultraviolet irradiation. This luminescence evolution can be ascribed to the sequential PCLT processes of crystal loosening and conformational isomerisation before macroscopic melting. Single-crystal X-ray structural analysis, thermal analysis, and theoretical calculations of two PCLT-active and one inactive diketones revealed weaker intermolecular interactions for the PCLT-active crystals. In particular, we observed a characteristic packing motif for the PCLT-active crystals, consisting of an ordered layer of diketone core and a disordered layer of triisopropylsilyl moieties. Our results demonstrate the integration of photofunction with PCLT, provide fundamental insights into the melting process of molecular crystals, and will diversify the molecular design of PCLT-active materials beyond classical photochromic scaffolds such as azobenzenes.

Photoinduced Radical Persistent Luminescence in Semialiphatic Polyimide System with Temperature and Humidity Resistance

Organic persistent luminescence (pL) systems with photoresponsive dynamic features have valuable applications in the fields of data encryption, anticounterfeiting, and bioimaging. Photoinduced radical luminescent materials have a unique luminous mechanism with the potential to achieve dynamic pL. It is extremely challenging to obtain radical pL under ambient conditions; on account of it, it is unstable in air. Herein, a new semialiphatic polyimide-based polymer (A0) is developed, which can achieve dynamic pL through reversible conversion of radical under photoexcitation. A "joint-donor-spacer-acceptor" molecular design strategy is applied to effectively modulate the intramolecular charge-transfer and charge-transfer complex interactions, resulting in effective protection of the radical generated under photoirradiation. Meanwhile, polyimide-based polymers of A1-A4 are obtained by doping different amine-containing fluorescent dyes to modulate the dynamic afterglow color from green to red via the triplet to singlet Förster resonance energy-transfer pathway. Notably, benefiting from the structural characteristics of the polyimide-based polymer, A0-A4 have excellent processability, thermal stability, and mechanical properties and can be applied directly in extreme environments such as high temperatures and humidity.

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.

Photoexcitation-Induced Assembly: A Bottom-Up Physical Strategy for Driving Molecular Motion and Phase Evolution

ConspectusIn the field of molecular assembly, photodriven self-assembly is a smart and crucial strategy to regulate the molecular orderliness, multiscale structure, and optoelectronic properties. Traditionally, photodriven self-assembly is based on photochemical processes, through molecular structural change induced by photoreactions. Despite great progress in the photochemical self-assembly, there still exists disadvantages (e.g., the photoconversion rate never reaches 100% with the possible side reactions). Therefore, the photoinduced nanostructure and morphology are often difficult to predict due to insufficient phase transition or defects. In contrast, the physical processes based on photoexcitation are straightforward and can fully utilize photons to avoid the drawbacks of photochemistry. The photoexcitation strategy excludes the change of molecular structure, only utilizing the molecular conformational change from the ground state to excited state. Then, the excited state conformation is employed to drive molecular movement and aggregation, further promoting the synergistic assembly or phase transition of the entire material system. The regulation and exploration of molecular assembly upon photoexcitation can open up a new paradigm to deal with the "bottom-up" behavior and develop unprecedented optoelectronic functional materials.This Account starts with a brief introduction to the problems faced by photocontrolled self-assembly and presents the photoexcitation-induced assembly (PEIA) strategy. Then, we focus on exploring PEIA strategy based on persulfurated arenes as the prototype. The molecular conformational transition of persulfurated arenes from the ground state to the excited state is conducive to the formation of intermolecular interactions, successively driving molecular motion, aggregation, and assembly. Next, we describe our progress in exploring PEIA of persulfurated arenes at the molecular level and then demonstrate that the PEIA of persulfurated arenes can synergistically drive molecular motion and phase transition in various block copolymer systems. Moreover, we provide the potential applications of PEIA in dynamic visual imaging, information encryption, and surface property regulation. Finally, an outlook on further development of PEIA is prospected.

Conformation-dependent dynamic organic phosphorescence through thermal energy driven molecular rotations

Organic room-temperature phosphorescent (RTP) materials exhibiting reversible changes in optical properties upon exposure to external stimuli have shown great potential in diverse optoelectronic fields. Particularly, dynamic manipulation of response behaviors for such materials is of fundamental significance, but it remains a formidable challenge. Herein, a series of RTP polymers were prepared by incorporating phosphorescent rotors into polymer backbone, and these materials show color-tunable persistent luminescence upon excitation at different wavelengths. Experimental results and theoretical calculations revealed that the various molecular conformations of monomers are responsible for the excitation wavelength-dependent (Ex-De) RTP behavior. Impressively, after gaining insights into the underlying mechanism, dynamic control of Ex-De RTP behavior was achieved through thermal energy driven molecular rotations of monomers. Eventually, we demonstrate the practical applications of these amorphous polymers in anti-counterfeiting areas. These findings open new opportunities for the control of response behaviors of smart-responsive RTP materials through external stimuli rather than conventional covalent modification method.

Photo-controllable Luminescence from Radicals Leading to Ratiometric Emission Switching via Dynamic Intermolecular Coupling

The development of photoinduced luminescent radicals with dynamic emission color is still challenging. Herein we report a novel molecular radical system (TBIQ) that shows photo-controllable luminescence, leading to a wide range of ratiometric color changes via light excitation. The conjugated skeleton of TBIQ is decorated with steric-demanding tertiary butyl groups that enable appropriate intermolecular interaction to make dynamic intermolecular coupling possible for controllable behaviors. We reveal that the helicenic pseudo-planar conformation of TBIQ experiences a planarization process after light excitation, leading to more compactly stacked supermolecules and thus generating radicals via intermolecular charge transfer. The photo-controllable luminescent radical system is employed for a high-level information encryption application. This study may offer unique insight into molecular dynamic motion for optical manufacturing and broaden the scope of smart-responsive materials for advanced applications.

Making multi-twisted luminophores produce persistent room-temperature phosphorescence

Multi-twisted molecules, especially those with more than four branched rotation axes, have served as superior prototypes in diverse fields like molecular machines, optical materials, sensors, and so forth. However, due to excessive non-radiative relaxation of these molecules, it remains challenging to address their persistent room-temperature phosphorescence (pRTP), which limits their further development. Herein, we develop a host-guest energy-transfer relay strategy to improve the phosphorescence lifetime of multi-twisted luminophores by over thousand-fold to realize pRTP, which can be witnessed by the naked eye after removing the excitation light source. Moreover, we employ photoexcitation-induced molecular rearrangement to further prolong the phosphorescence lifetime, which, to the best of our knowledge, is the first example of photoactivation in ordered host-guest systems. Our systems show superior humidity and oxygen resistance, enabling long-term (at least over 9-12 months) stability of the pRTP properties. By achieving pRTP of multi-twisted luminophores, this work can advance the understanding of molecular photophysical mechanisms and guide the study of more molecular systems that are difficult to achieve pRTP.

A processable, scalable, and stable full-color ultralong afterglow system based on heteroatom-free hydrocarbon doped polymers

Although room-temperature phosphorescence (RTP) organic materials are a widely-studied topic especially popular in recent decades, long-lived RTP able to fulfil broad time-resolved application requirements reliably, are still rare. Polymeric materials doped with phosphorescent chromophores generally feature high productivity and diverse applications, compared with their crystalline counterparts. This study proves that pure polycyclic aromatic hydrocarbons (PAHs) may even outperform chromophores containing hetero- or heavy-atoms. Full-color (blue, green, orange and red) polymer-PAHs with lifetimes >5000 ms under ambient conditions are constructed, which provide impressive values compared to the widely reported polymer-based RTP materials in the respective color regions. The polymer-PAHs could be fabricated on a large-scale using various methods (solution, melt and in situ polymerization), be processed into diverse forms (writing ink, fibers, films, and complex 3D architectures), and be used in a range of applications (anti-counterfeiting, information storage, and oxygen sensors). Plus their environmental (aqueous) stability makes the polymer-PAHs a promising option to expand the portfolio of organic RTPs.

Versatile Electroluminescence Color-Tuning Strategy of an Efficient Light-Emitting Electrochemical Cell (LEC) by an Ionic Additive

The color-tuning strategies of solid-state light-emitting devices (ss-LEDs) are mainly focused on engineering molecular structures. In this paper, for the first time, we developed a facile strategy for tuning the electroluminescence (EL) color from orange to green through the addition of the ionic additive TBAP (tetrabutylammonium perchlorate). To achieve the active ionic emissive compound for use in a light-emitting electrochemical cell (LEC), the neutral biscyclometalated bromo tetrazole iridium(III) [Ir(ppy)₂(BrTz)] was exchanged to its cationic complex, [Ir(ppy)₂(BrTz-Me)]ClO₄ (ppy = 2-phenyl pyridine, BrTz = 4-bromo-2-pyridine tetrazole, BrTz-Me = 4-bromo-2-pyridine methyl tetrazole) with a new synthetic strategy. This method allows employing neutral Ir-cyclometalated complexes, which are ruled out for use in LECs because of their non-ionic behaviors. In the following, an LEC based on the new cationic [Ir(ppy)₂(BrTz-Me)]ClO₄ as the emissive layer was fabricated between the FTO (fluorine-doped tin oxide) anode and Ga:In alloy cathode without using any additive or polymers, which makes this configuration the simplest ss-LED so far. By adding the ionic additives, the electroluminescence characteristics of [Ir(ppy)₂(BrTz-Me)]ClO₄ were dramatically increased, including luminance (L) from 162.8 cd/m² for the device with an additive to 212.9 and 355.9 cd/m² for devices containing LiTFSI (bis(trifluoromethane)sulfonamide lithium salt) and TBAP, respectively. In particular, when TBAP was added to the [Ir(ppy)₂(BrTz-Me)]ClO₄ complex, the irradiance was significantly increased from 166.4 to 220.8 μW/cm² with an efficacy of 1.78 cd/A and external quantum efficiency (EQE) value of 2.14%. The obtained EL results clearly showed that adding TBAP and LiTFSI significantly improved the electroluminescence characteristics and tuned the electroluminescence color.

Polymerization-Enhanced Photophysical Performances of AIEgens for Chemo/Bio-Sensing and Therapy

AIE polymers have been extensively researched in the fields of OLEDs, sensing, and cancer treatment since its first report in 2003, which have achieved numerous breakthroughs during the years. In comparison with small molecules, it can simultaneously combine the unique advantages of AIE materials and the polymer itself, to further enhance their corresponding photophysical performances. In this review, we enumerate and discuss the common construction strategies of AIE-active polymers and summarize the progress of research on polymerization enhancing luminescence, photosensitization, and room-temperature phosphorescence (RTP) with their related applications in chemo/bio-sensing and therapy. To conclude, we also discuss current challenges and prospects of the field for future development.

Dynamic B/N Lewis Pairs: Insights into the Structural Variations and Photochromism via Light-Induced Fluorescence to Phosphorescence Switching

Ultralong afterglow emissions due to room-temperature phosphorescence (RTP) are of paramount importance in the advancement of smart sensors, bioimaging and light-emitting devices. We herein present an efficient approach to achieve rarely accessible phosphorescence of heavy atom-free organoboranes via photochemical switching of sterically tunable fluorescent Lewis pairs (LPs). LPs are widely applied in and well-known for their outstanding performance in catalysis and supramolecular soft materials but have not thus far been exploited to develop photo-responsive RTP materials. The intramolecular LP M1BNM not only shows a dynamic response to thermal treatment due to reversible N→B coordination but crystals of M1BNM also undergo rapid photochromic switching. As a result, unusual emission switching from short-lived fluorescence to long-lived phosphorescence (rad-M1BNM, τ_RTP =232 ms) is observed. The reported discoveries in the field of Lewis pairs chemistry offer important insights into their structural dynamics, while also pointing to new opportunities for photoactive materials with implications for fast responsive detectors.

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.

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.

Phosphorus and Nitrogen Codoped Carbonized Polymer Dots with Multicolor Room Temperature Phosphorescence for Anticounterfeiting Painting

Visible spectral afterglow materials offer unprecedented potential for a myriad of applications due to their long luminescence characteristics, but it is still insufficient to prepare matrix-free materials with multicolor afterglow including the blue color. In this study, we successfully developed phosphorus and nitrogen codoped carbonized polymer dots (CPDs) with multicolor room temperature phosphorescence (RTP) including the blue color by microwave-assisted chemical reactions under different reaction time. After ceasing UV light, all four prepared CPDs were able to emit vivid RTP with a maximum absolute phosphorescence quantum yield (QY) of 59.41% and a maximum lifetime of about 1 s (yellow CPDs). With the increase of microwave reaction time, the RTP color of CPDs showed a gradual blue shift from yellow to blue. The reason why the RTP color of CPDs showed a gradual blue shift was the decrease of C═O units as the extension of the microwave reaction time. In view of their fascinating multicolor RTP properties, potential applications of the four CPDs in the field of anticounterfeiting painting were presented and demonstrated. This work would inspire other researchers to enrich multicolor afterglow materials.

Excitation-Wavelength-Dependent Organic Long-Persistent Luminescence Originating from Excited-State Long-Range Proton Transfer

Stimuli-responsive functional luminescent materials with tunable color and long-persistent emission have emerged as a powerful tool in information encryption, anticounterfeiting, and bioelectronics. Herein, we prove a novel strategy for manipulating the proton transfer pathways in the salicylaldehyde derivative EQCN solutions/powder to produce excitation wavelength-dependent (Ex-De) performances with switchable emissions (blue-sky, green, and orange). The experiments and theoretical results demonstrated that the different luminous colors are originated from enol (E) form (blue-sky), Keto-1 (K1) form (orange) through the excited-state intramolecular proton transfer (ESIPT) process, and Keto-2 (K2) form (green) through the excited-state long-range proton transfer (ESLRPT) process. We leverage synergistic effects between the dopant and matrix (dimethyl terephthalate, DTT) to manipulate the excited-state proton transfer pathway in EQCN@DTT mixture powders to generate Ex-De long-persistent luminescence (Ex-De-LPL), which can be well applied in multilevel information encryption. This strategy not only paves an intriguing way for the construction and preparation of pure organic Ex-De materials but also offers a guideline for developing LPL materials based on ESLRPT processes.

Dynamic Anticounterfeiting Through Novel Photochromic Spiropyran-Based Switch@Ln-MOF Composites

Fluorescent materials presenting unique color changes in response to external stimuli have wide applications in information storage and anticounterfeiting. However, developing intelligent fluorescent materials with high security levels and dynamically displaying encrypted information is still a challenge. Herein, we report a new method for constructing excellent fluorescent materials by loading the photochromic molecule spiropyran into a lanthanide metal-organic framework. Controlling the isomerization of the spiropyran unit regulates the fluorescence resonance energy transfer (FRET) mechanism between the spiropyran acceptor and the lanthanide donor, leading to an exceptional reversible absorption/luminescence modulation ability. As the irradiation time is extended, the fluorescent color changes continuously from yellow-greenish to orange and then to red through the FRET process within 60 s. This composite system has great potential in anticounterfeiting because of the following advantages: (1) the materials have different fluorescence emissions and optical colors regulated by ultraviolet radiation, which is convenient for designing complex anticounterfeiting patterns; (2) the system can be repeatedly verified quickly and exhibit dynamic fluorescence color within 60 s, having great potential in advanced anticounterfeiting, where time is key in encryption/decryption. These unique advantages will greatly enhance the reliability of anticounterfeiting measures and increase the difficulty of anticounterfeiting.

More than Carbazole Derivatives Activate Room Temperature Ultralong Organic Phosphorescence of Benzoindole Derivatives

The mechanism of carbazole (Cz)-based phosphors is still unclear since its isomer (1H-benzo[f]indole, Bd) is discovered in 2020. Herein, the successful synthesis of four Cz/Bd derivatives is reported, named as 2CzBr, CzBdBr, 2BdBr, and 3Bd, and the general mechanism for their ultralong organic phosphorescence (UOP) is provided. Bd and its derivatives give double groups of phosphorescence, including the short-wavelength phosphorescence with a short lifetime and the ultralong phosphorescence at long wavelengths, assigned to their neutral molecules and radical cations, respectively. Interestingly, the doped poly(methyl methacrylate) (PMMA) films of CzBdBr and 2BdBr show photo-activated ultralong phosphorescence at room temperature. The activation of Bd derivatives 'UOP involves three factors: 1) well dispersion in the matrix with limited amount, 2) generation of their radical cations and 3) the matrix-mediated stabilization of radical cations. The function of Cz derivatives to activate the Bd derivatives' UOP could be replaced by photo-activation or using other matrixes. Significantly, the application of the doped PMMA films is practiced and gives an exciting result that the high-resolution QR code could be reversibly printed and erased on the film. This research has expanded the understanding in the field of organic phosphorescence and it may pave a new way for its development.

Resonance-Induced Stimuli-Responsive Capacity Modulation of Organic Ultralong Room Temperature Phosphorescence

Organic ultralong room temperature phosphorescence (OURTP) materials having stimuli-responsive attributes have attracted great attention due to their great potential in a wide variety of advanced applications. It is of fundamental importance but challengeable to develop stimuli-responsive OURTP materials, especially such materials with modulated optoelectronic properties in a controlled manner probably due to the lack of an authentic construction approach. Here, we propose an effective strategy for OURTP materials with controllably regulated stimuli-responsive properties by engineering the resonance linkage between flexible chain and phosphor units. A quantitative parameter to demonstrate the stimuli-responsive capacity is also established by the responsivity rate constant. The designed OURTP materials demonstrate efficient photoactivated OURTP with lifetimes up to 724 ms and tunable responsivity rate constants ranging from 0.132 to 0.308 min^-1 upon continuous UV irradiation. Moreover, the applications of stimuli-responsive resonance OURTP materials have been illustrated by the rewritable paper for snapshot and Morse code for multiple information encryption. Our works, which enable the accomplishment of OURTP materials capable of on-demand manipulated optical properties, demonstrate a viable design to explore smart OURTP materials, giving deep insights into the dynamically stimuli-responsive process.

Halide-containing organic persistent luminescent materials for environmental sensing applications

Great progress has been made in the development of various organic persistent luminescent (OPL) materials in the past few years, and increasing attention has been paid to their interesting applications in environmental sensing due to their long emission lifetimes and high sensitivity. Especially, the introduction of different halogen elements facilitates highly efficient OPL emission with distinct lifetimes and colours. In this review, we summarize the current status of the halide-containing OPL materials for environmental sensing applications. To begin with, the photophysical processes and luminescence mechanisms of OPL materials are expounded in detail to better understand the relationship among molecular structures, OPL properties, and sensing applications. Then, representative halide-containing material systems, such as small molecules, polymers, and doping systems, are summarized with their interesting applications in sensing temperature, oxygen, H₂O, UV light and organic solvents. In addition, several challenges and future research opportunities in this field are discussed. This review aims to provide some reasonable guidance on the material design of OPL sensors and their practical applications, and tries to provide a new perspective on the application direction of organic optoelectronics.

This review presents a summary of the molecular design of halide-containing organic persistent luminescent materials, and their environmental sensing applications.

Efficient Room-Temperature Phosphorescence from Discrete Molecules Based on Thianthrene Derivatives for Oxygen Sensing and Detection

In this work, two thianthrene (TA) derivatives, 1-phenylthianthrene (TA1P) and 2-phenylthianthrene (TA2P), were synthesized with single-phenyl modification for pure organic discrete-molecule room-temperature phosphorescence (RTP). They both show the dual emission of fluorescence and RTP in amorphous polymer matrix after deoxygenation, as a result of a new mechanism of folding-induced spin-orbit coupling (SOC) enhancement. Compared with TA1P, TA2P exhibits a higher RTP efficiency and a larger spectral separation between fluorescence and RTP, which is ascribed to the substituent effect of TA at the 2-position. With decreasing oxygen concentration from 1.61% to 0%, the discrete-molecule TA2P shows an about 18-fold increase in RTP intensity and an almost constant fluorescence intensity, which can make TA2P as a self-reference ratiometric optical oxygen sensing probe at low oxygen concentrations. The oxygen quenching constant (K_SV) of TA2P is estimated as high as 10.22 KPa⁻¹ for polymethyl methacrylate (PMMA)-doped film, and even reach up to 111.86 KPa⁻¹ for Zeonex^®-doped film, which demonstrates a very high sensitivity in oxygen sensing and detection. This work provides a new idea to design pure organic discrete-molecule RTP materials with high efficiency, and TA derivatives show a potential to be applied in quantitative detection of oxygen as a new-generation optical oxygen-sensing material.

Cucurbit[n]uril-based host-guest interaction enhancing organic room-temperature phosphorescence of phthalic anhydride derivatives in aqueous solution

A cyan RTP in aqueous solution was enhanced by supramolecular host–guest complexation of water-soluble halogen-substituted phthalic anhydride (PA) derivatives with cucurbit[n]urils (CB[n]s).