Enhanced Room-Temperature Phosphorescence through Intermolecular Halogen/Hydrogen Bonding.

Purely organic room temperature phosphorescence (RTP) materials have shown broad application prospects in organic light‐emitting diodes (OLEDs) due to their theoretical 100% exciton utilization, cost‐effectiveness, and flexibility. In recent years, with the deepening of research, various luminescent mechanisms have been proposed, and RTP materials have made significant progress, which have been effectively applied to OLEDs. This article comprehensively reviews the research progress of RTP materials in OLEDs and introduces the development of a series of high‐efficiency RTP materials from the perspective of molecular design strategies and photophysical properties. These conclusions draw a roadmap to address the inherent challenges in utilizing organic RTP materials to specifically advance the investigation of OLEDs.

Polymeric room-temperature phosphorescence (RTP) materials have attracted much attention due to their advantages of easy processing and excellent luminescent properties. However, it is still a challenge to obtain industrial production grade material through simple and green processing strategies. Herein, through the codoping strategy, different phosphors were embedded into nylon, a kind of polymer matrix, to obtain a series of highly efficient RTP materials without any organic solvents, for which the phosphorescence lifetime and brightness could reach 628.8 ms and 14 cd/m2, respectively. Besides, we found that the photophysical properties of these RTP materials varied greatly among different types of nylon matrix, owing to the divergence in the number of hydrogen bonding "sites". The superiority of the injection molding processing strategy enables the preparation of RTP materials to achieve desolvation, which could also be processed into any complex and desiring shape. Significantly, nylon can affect molecular chain changes due to aging and other problems, so that these RTP materials are considered as potential nondestructive testing for nylon product aging levels. This strategy also paves the way for the development of large-scale, eco-friendly, and practical application RTP materials and provides new ideas to industrialized preparation of long-lived RTP materials in the future.

Pure organic room temperature phosphorescence (RTP) materials are considered as potential candidates for replacing precious metal-based complexes to fabricate highly efficient organic light emitting devices (OLEDs). However, for reported RTP materials, low photoluminescence quantum yields (PLQYs) in thin film state seriously impede their applications in OLEDs. On the other hand, how using normal organic fluorescence materials to fabricate OLEDs with an internal quantum efficiency (IQE) over 25% remains a great unaddressed issue beyond the thermally activated delayed fluorescence (TADF) sensitization approach. Here, we establish a strategy to construct highly efficient OLEDs based on pure organic RTP material sensitized fluorescence emitter. The key point for our strategy is that benzimidazole-triazine molecules (PIM-TRZ), 2,6-di(phenothiazinyl)naphthalene (β-DPTZN) and 5,6,11,12-tetraphenylnaphthacene (rubrene) were screened as host, phosphor sensitizer and fluorescent emitter, respectively. Detail photophysical characterizations demonstrate that the host material PIMTRZ with unique RTP nature is critical for achieving phosphor sensitizing process. As an organic RTP compound, the singlet and triplet state energy levels of β-DPTZN perfectly match with those of PIMTRZ, resulting in the formation and lasting existence of phosphor’s excitons in emitting layer. The large overlap between the absorption spectrum of rubrene and PL spectrum of PIM-TRZ:10% β-DPTZN film can facilitate the Förster energy transfer from the triplet β-DPTZN to the singlet rubrene and the finally displayed fluorescence is derived from singlet excited states of rubrene. The perfect collocation of host, phosphorescent sensitizer and fluorescent emitter in the emitting layer promise the predominant performance of the devices with external quantum efficiency (EQE) of 15.7%. The PLQY of emitting layer is 60.3%, and therefore about 90% carrier injection induced excitons are harvested for light emission. We present a new strategy to fabricate efficient fluorescent devices by employing ingenious combination of host, phosphorescent sensitizer and fluorescent emitter, which is significant to the development of OLEDs.

Long-lived room temperature phosphorescence (RTP) materials are promising for applications in various fields including security information, medical diagnostics, and molecular imaging because of their unique optical properties. Previous RTP materials are mainly excited by ultraviolet light, while synthesizing long-lived RTP materials with visible-light-excitation remains a challenge. In particular, long-lived RTP materials that can be excited by green light are rare. Herein, a feasible and concise chemical strategy for constructing hydrogen-bonded frameworks in an aqueous environment is developed to fabricate large-size, green-light-excited, and excitation-dependent long-lived RTP carbon dot crystals (m,p/CDs-ME). The RTP performance of the crystals exhibits strong excitation wavelength dependence, leading to a full range of visible-light tuning from blue to red. Importantly, the maximum excitation wavelength of the RTP crystals is around 500 nm, thus successfully realizing green light excitation. m,p/CDs-ME presents long-lived phosphorescence (130 ms) under 500 nm excitation in aqueous solution, making it highly suitable for dopamine detection. This work not only provides a general guideline for the development of large size long-lived RTP crystals but also extends the operation scope of long-lived RTP materials in the detection of biomarkers by visible light excitation.

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

Organic room-temperature phosphorescence (RTP) materials with large Stokes shifts and prolonged afterglows are gaining increasing attention in a variety of applications, including displays, anti-counterfeiting, sensing, and bioimaging. However, achieving high-performance organic RTP remains challenging due to weak spin-orbit coupling, rapid non-radiative decay, and unstable triplet excitons. Early studies focused on crystal engineering, as ordered lattices restrict molecular motion and stabilize triplet excitons. Analyzing crystal structures and packing provides valuable insights into intermolecular interactions, while theoretical calculations have clarified electronic structures, laying the foundation for rational RTP material design. However, recent findings suggest RTP in many single-component systems may arise from trace impurities, significantly influencing RTP properties. This discovery has greatly advanced the understanding of impurity-induced phosphorescence. This review systematically examines the role of impurities in RTP, detailing their origins from starting materials, solvents, and side reactions. It also explores how these identified impurities can serve as essential building blocks for designing new RTP materials. Finally, essential methods for evaluating compound purity, emphasizing the critical importance of rigorous analysis and validation are presented. Material purity plays a pivotal role in RTP research, as impurities can distort experimental data, potentially leading to misinterpretations that can impede advancements in understanding the underlying mechanisms.

Ultralong sodium alginate-based room temperature phosphorescence materials with advantages of color tunability, flexibility and facile large-area fabrication

Designing ultralong‐lived aqueous room temperature phosphorescence (RTP) materials has become an actively pursued but challenging research area. Herein, a coordination‐induced structural rigidity (CISR) strategy is proposed to achieve ultralong RTP lifetime in magnesium/pyromellitic acid phosphorescent materials (Mg/PMA‐PMs) with abundant Mg2+ ions sites and hydrophilic groups in aqueous solution. Compared to their dry state (448.77 ms), the lifetime of Mg/PMA‐PMs significantly increases to 1026.17 ms with the addition of a small amount of water (50 wt%). Even in a fully non‐deoxygenated aqueous environment (above 200 wt% water), where Mg/PMA‐PMs disintegrate to form a nanosuspension, they still exhibit an ultralong aqueous RTP lifetime of ≈800 ms. The water‐enhanced RTP properties are attributed to water molecules coordinating with Mg2+ ions and acting as bridging agents to bind with hydrophilic groups through hydrogen bonding. This interaction rigidifies functional groups and inhibits their motions, leading to a substantial reduction in nonradiative decay. Furthermore, the CISR mechanism effectively explains the RTP enhancement effect of water on inorganic salt phosphorescent systems. This work not only provides a new approach for constructing efficient aqueous RTP materials, but also develops a powerful tool for visual anion recognition.

Achieving highly efficient phosphorescence in purely organic luminophors at room temperature remains a major challenge due to slow intersystem crossing (ISC) rates in combination with effective non‐radiative processes in those systems. Most room temperature phosphorescent (RTP) organic materials have O‐ or N‐lone pairs leading to low lying (n, π*) and (π, π*) excited states which accelerate k isc through El‐Sayed's rule. Herein, we report the first persistent RTP with lifetimes up to 0.5 s from simple triarylboranes which have no lone pairs. RTP is only observed in the crystalline state and in highly doped PMMA films which are indicative of aggregation induced emission (AIE). Detailed crystal structure analysis suggested that intermolecular interactions are important for efficient RTP. Furthermore, photophysical studies of the isolated molecules in a frozen glass, in combination with DFT/MRCI calculations, show that (σ, B p)→(π, B p) transitions accelerate the ISC process. This work provides a new approach for the design of RTP materials without (n, π*) transitions.

Developing full-color circularly polarized organic ultralong room-temperature phosphorescence (CP-OURTP) materials with high dissymmetry factor (glum) holds significant promise for diverse optoelectronic applications. Controlling glum values is crucial for enhancing the performance and functionality of these materials, as it directly influences their chiroptical properties and potential utilities in advanced technologies. However, achieving reversible and dynamic manipulation of glum in CP-OURTP materials remains a formidable challenge. Herein, an effective strategy is presented to fabricate the chiral superstructure elastomers (CSEs) that display selective reflection colors, dynamically tunable CP-OURTP with robust glum values, full-color afterglow emissions, and superior processability within a single system. By integrating room temperature phosphorescence (RTP) polymers into the CSEs, CSEs are produced demonstrating tunable CP-OURTP with glum values switching between 0.8 and 0.15 by mechanical deformation. More importantly, these mechanochromic, programmable, and full-color CP-OURTP films enable the development of flexible and dynamic information encryption and decryption. The work provides new insights into the development of novel RTP materials and advances in their potential applications.

Polymer carbon dots (PCDs) are proposed as a new class of room-temperature phosphorescence (RTP) materials. The abundant energy levels in PCDs increase the probability of intersystem crossing (ISC) and their covalently crosslinked framework structures greatly suppress the nonradiative transitions. The efficient methods allow the manufacture of PCDs with unique RTP properties in air without additional metal complexation or complicated matrix composition. They thus provide a route towards the rational design of metal-free RTP materials that may be synthesized easily. Furthermore, we find that RTP is associated with a crosslink-enhanced emission (CEE) effect, which provides further routes to design improved PCDs with diverse RTP performance. Our results show the potential of PCDs as a universal route to achieve effective metal-free RTP.

While room-temperature phosphorescence (RTP) materials have been predominantly realized in solid films, the development of liquid and hydrogel systems that retain ultralong afterglow remains highly desirable. Here, we report a high-solid-content (∼30%) afterglow emulsion system based on an electron-deficient naphthalimide (NI) derivative as the luminescent dopant and a copolymer matrix of methyl methacrylate (MMA) with methyl acrylate (MA), denoted as P(MMA/MA). Although the NI-doped P(MMA/MA) exhibits a much lower glass transition temperature than the PMMA homopolymer, it surprisingly delivers a longer afterglow duration (tag), revealing that matrix rigidity is not the sole determinant of ultralong RTP. Under ambient conditions, the NI-doped P(MMA/MA) emulsion achieves a lifetime of up to 1.95 s (tag ≈ 29 s), while the corresponding solid film exhibits a lifetime of 2.18 s (tag ≈ 34 s), placing both among the top-performing systems in their respective states. Beyond UV excitation, both the emulsion and the film can also be activated using safer 405 nm visible light, yielding tag values of up to 14 s and 16 s, respectively. When blended with poly(vinyl alcohol), the emulsion forms stretchable hydrogels with a tag of ∼20 s, significantly surpassing most reported hydrogel-based RTP materials. Furthermore, through phosphorescence resonance energy transfer, we extend the emission into the red region, producing emulsions with tag exceeding 10 s and demonstrating the spectral tunability of this approach across the green-to-red range. This work provides a versatile strategy for designing multistate RTP materials with long afterglow and good processability, showing promise for applications in bioimaging, sensing, and information encryption.

Developing metal-free and long lifetime room-temperature phosphorescence (RTP) materials has received tremendous interest due to their numerous potential applications, of which stable triplet-excited state is the core challenge. Here, boron carbon oxynitride (BCNO) dots, emitting stable blue fluorescence and green RTP, are reported for the first time. The obtained BCNO dots exhibit an unexpected ultralong RTP lifetime of 1.57 s, lasting over 8 s to naked eyes. The effective doping of carbon and oxygen elements in boron nitride (BN) actually provides a small energy gap between singlet and triplet states, facilitating the intersystem crossing (ISC) and populating of triplet excitons. The formation of compact cores via crystallization and effective inter-/intra-dot hydrogen bonds further stabilizes the excited triplet states and reduces quenching of RTP by oxygen at room temperature. Based on the water-soluble feature of BCNO dots, a novel advanced security ink is developed toward anti-counterfeiting tag and confidential information encryption. This study extends BCNO dots to rarely exploited phosphorescence fields and also provides a facile strategy to prepare ultralong lifetime metal-free RTP materials.

Triphenylphosphine (TPP) salt derivatives, with their rich chemistry of core-substitution, have emerged as promising candidates for ultralong room temperature phosphorescence (RTP) materials owing to their distinct molecular structures, high quantum efficiency and exceptional phosphorescence properties. This feature article highlights the vast potential of TPP salt derivatives in tunable RTP properties by exploring some factors such as the alkyl chains, halogen anions, through-space charge transfer states, etc., and recent advancements in multi-level information encryption, high-level anticounterfeiting tags and X-ray imaging applications. We anticipate that this article will assist in directing future analyses based on the mechanisms underlying the RTP behavior of TPP derivatives and offer guidance for the rational design of high-performance RTP materials.

Organic materials with room-temperature phosphorescence (RTP) are in high demand for optoelectronics and bioelectronics. Developing RTP materials highly relies on expert experience and costly excited-state calculations. It is a challenge to find a tool for effectively screening RTP materials. Herein we first establish ground-state orbital descriptors (πFMOs ) derived from the π-electron component of the frontier molecular orbitals to characterize the RTP lifetime (τp ), achieving a balance in screening efficiency and accuracy. Using the πFMOs , a data-driven machine learning model gains a high accuracy in classifying long τp , filtering out 836 candidates with long-lived RTP from a virtual library of 19,295 molecules. With the aid of the excited-state calculations, 287 compounds are predicted with high RTP efficiency. Impressively, experiments further confirm the reliability of this workflow, opening a novel avenue for designing high-performance RTP materials for potential applications.