Room-temperature Phosphorescence Materials Research Articles

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.

Achieving TADF and RTP with Stimulus‐Responsiveness and Tunability from Phenothiazine‐Based Donor−Acceptor Molecules

AbstractResearch of thermally activated delayed fluorescence (TADF) and room‐temperature phosphorescence (RTP) materials is attractive owing to their extensive applications in various fields. However, achieving organic TADF and RTP materials, particularly those with stimulus‐responsiveness and tunability, is highly desirable but challenging and rarely reported. Herein, two easily synthesized organic molecules are reported with abnormal stimulus‐responsive switchable TADF and RTP effects, in which phenothiazine (PTZ) and benzo[b]phenothiazine (BPTZ) based donor−acceptor molecules PTZ‐DBQ and BPTZ‐DBQ show mechanical‐induced TADF in crystalline phase and photo‐responsive RTP in doping poly(methyl methacrylate) (PMMA) films. This is the first time tetracyclic BPTZ has been used as a donor in achieving TADF and RTP materials, and it is found that BPTZ‐DBQ exhibits remarkably better photophysical properties than PTZ‐DBQ. Systematic studies of experimental results and theoretical calculations indicate that the conformational heterogeneity plays an essential role in achieving mechanical‐induced TADF with mechanochromic luminescence (MCL) property. Embedding the organic phosphors into rigid polymer matrices effectively suppresses the molecular motion, thus turning on the RTP emission channel. The conversion of 3O2 to 1O2 under UV irradiation is mainly responsible for the photo‐induced process. These multifunctional luminescent materials have great potential applications in chemical sensors, information encryption, and anti‐counterfeiting.

Full-color persistent room temperature phosphorescent elastomers with robust optical properties

Persistent room temperature phosphorescent materials with unique mechanical properties and robust optical properties have great potential in flexible electronics and photonics. However, developing such materials remains a formidable challenge. Here, we present highly stretchable, lightweight, and multicolored persistent luminescence elastomers, produced by incorporating ionic room temperature phosphorescent polymers and polyvinyl alcohol into a polydimethylsiloxane matrix. These prepared elastomers exhibit high optical transparency in daylight and emit bright persistent luminescence after the removal of 365 nm excitation. The homogeneous distribution of polymers within the matrix has been confirmed by confocal fluorescence microscopy, scanning electron microscopy, and atomic force microscopy. Mechanical property investigations revealed that the prepared persistent luminescence elastomers possess satisfactory stretchability. Impressively, these elastomers maintain robust optical properties even under extensive and repeated mechanical deformations, a characteristic previously unprecedented. These fantastic features make these persistent luminescence elastomers ideal candidates for potential applications in wearable devices, flexible displays, and anti-counterfeiting.

Design of mechanical-robust phosphorescence materials through covalent click reaction

It remains a great challenge to engineer materials with strong and stable interactions for the simultaneously mechanical-robust and room temperature phosphorescence-efficient materials. In this work, we demonstrate a covalent cross-linking strategy to engineer mechanical-robust room temperature phosphorescence materials through the B–O click reaction between chromophores, polyvinyl alcohol matrix and inorganic layered double hydroxide nanosheets. Through the covalent cross-linkage between the organic polyvinyl alcohol and inorganic layered double hydroxide, a polymeric composite with ultralong lifetime up to 1.45 s is acquired based on the inhibited non-radiative transition of chromophores. Simultaneously, decent mechanical strength of 97.9 MPa can be realized for the composite materials due to the dissipated loading stress through the covalent-bond-accommodated interfacial interaction. These cross-linked composites also exhibit flexibility, processability, scalability and phosphorescence responses towards the mechanical deformation. It is anticipated that the proposed covalent click reaction could provide a platform for the design and modulation of composites with multi-functionality and long-term durability.

Light‐Induced Electron Transfer Toward On/Off Room Temperature Phosphorescence in Two Photochromic Coordination Polymers

AbstractPhotoswitchable room temperature phosphorescence (RTP) materials are of great interest due to their potential applications in optical devices and switches. Herein, two Zn‐based coordination polymers (CPs) (H3‐TPB)·[Zn6(H‐HEDP)(HEDP)3(H2O)2]·5H2O (complex 1; HEDP = hydroxyethylidene diphosphonate; TPB = 1,3,5‐tris(4‐pyridyl)benzene) and (H‐TPB)·[Zn3(H‐HEDP)(HEDP)(H2O)]·2H2O (complex 2) with distinguishable photochromism and tunable RTP are synthesized involving photoactive TPB molecules with different packing modes. Complex 1 exhibits bidirectionally on/off RTP regulation via on‐switch with excitation of 250−330 nm light and off‐switch with 350−380 nm, and the “turn‐on” behavior can be attributed to the advance of Förster resonance energy transfer‐assisted intersystem crossing (ISC) process while “turn‐off” process due to the transformation from H3‐TPB cations to H3‐TPB· radicals. Complex 2 exhibits photoswitchable RTP accompanied with reversible photochromism by leveraging the self‐absorption and RTP emission. Two demos based on the above compounds are further applied to demonstrate the application in information recording and encryption fields. This work supplies a strategy toward the design of switchable RTP systems using electron transfer photochromism, shedding light on broadening the frontiers of photoresponsive materials.

Construction and Application of Large Stokes-Shift Organic Room Temperature Phosphorescence Materials by Intermolecular Charge Transfer.

Notably, the intermolecular charge transfer between pyrene (Py) and benzophonenes (BPs) can significantly enhance the quantum yield of the triplet state of Py, which will convert Py from a fluorescence molecule to a phosphorescence molecule. The intermolecular charge transfer is confirmed by steady-state and time-resolved spectroscopy and theoretical study. Based on these foundations, Py is doped into BPs systems and a large Stokes-shift organic room temperature phosphorescence (ORTP) is observed. By using different benzophenone derivatives, a series of host-guest ORTP materials with different luminescent properties adjusted by intermolecular charge transfer features are developed. Fortunately, these host-guest ORTP systems from benzophenone derivatives and pyrene are readily fabricated, and the red gradient color lasting as long as 3 s is observed after removing UV excitation. This host-guest charge transfer strategy plays an important role in the mechanism of the luminous type shift. Our strategy paves the way to design ORTP materials conveniently and apply these materials in encryption and temperature alarm device.

Multi-Responsive Afterglows from Aqueous Processable Amorphous Polysaccharide Films.

Polymer-based room-temperature phosphorescence (RTP) materials, especially polysaccharide-based RTP materials, earn sustained attention in the fields of anti-counterfeiting, data encryption, and optoelectronics owing to their green regeneration, flexibility, and transparency. However, those with both ultralong phosphorescence lifetime and excitation wavelength-dependent afterglow are rarely reported. Herein, a kind of amorphous RTP material with ultralong lifetime of up to 2.52 s is fabricated by covalently bonding sodium alginate (SA) with arylboronic acid in the aqueous phase. The resulting polymer film exhibits distinguished RTP performance with excitation-dependent emissions from cyan to green. Specifically, by co-doping with other fluorescent dyes, further regulation of the afterglow color from cyan to yellowish-green and near-white can be achieved through triplet-to-singlet Förster resonance energy transfer. In addition, the water-sensitive properties of hydrogen bonds endow the RTP property of SA-based materials with water/heat-responsive characteristics. On account of the color-tunable and stimuli-responsive afterglows, these smart materials are successfully applied in data encryption and anti-counterfeiting.

1,10-Phenanthroline-5-amine derived N-doped carbon dots for long-lived visible-light-activated room temperature phosphorescence in the matrix and information encryption application

Room temperature phosphorescence (RTP) materials have received a lot of attention. However, it is still a challenge to realize the practical application of RTP excited under visible light. Herein, five different carbon dots (CDs) were prepared using 1,10-phenanthroline-5-amine (Aphen) as the co-carbon source and nitrogen source, and several polymer-based RTP films were prepared by simple doping. It was found that the phosphorescence emission behavior of polymer films was changed by the surface state structure of different CDs. Non-radiative transition of the triplet excitons of Aphen structure on the CDs surface was effectively inhibited by the hydrogen bonding interaction and the fixed domain-limiting effect of the polymer matrix. Meanwhile, the Aphen structure was bound to the CDs through covalent interaction, which further suppressed the molecular vibration, realizing the efficient organic RTP. The phosphorescence lifetime of the prepared ACCDs-PVA films reached 352.88 ms with a photoluminescence quantum yield of 36.7%. In addition, the dye RhB was co-doped in the ACCDs-PVA system to modulate the afterglow color of the materials via the triplet to single-state energy resonance transfer (TS-FRET) process. Finally, we also developed stable ACCDs-EPO RTP material by exploiting the dense three-dimensional network structure and hydrophobic property of the cured epoxy resin (EPO) matrix. The as-constructed long-lived RTP materials can be employed in information encryption.

Synergetic Conformational Regulations in Ground and Excited States for Realizing Stimulus-Responsive and Wide-Tuning Room-Temperature Phosphorescence.

Understanding the changes of molecular conformations is crucial for realizing multiple emissive triplet states in room-temperature phosphorescence (RTP) materials. In this work, we report two molecules, 4,4'-dimethylbenzil (DMBZ) and 4,4'-di-tert-butylbenzil (DBBZ) with conformation-dependent luminescence, and demonstrate that stimulus-responsive and wide-tuning RTP emissions can be realized via synergetic conformational regulations in ground and excited states. Due to conformational changes, DMBZ and DBBZ show abundant RTP variations upon external stimuli, including light, force, heat, and fumigation. Notably, DBBZ exhibits multiple conformational changes in both ground and excited states, which endow DBBZ with multiple emissive states and unique stimulus-responsive behaviors. DBBZ presents multiple phase transitions between the supercooled liquid state and different solid states accompanied by different phosphorescence transitions, in which the excited-state conformations are effectively regulated. Moreover, wide-range RTP regulations (between cyan, green, and yellow) are realized in both single component and host-guest systems of DBBZ, showing potential applications in temperature sensing, multicolor dynamic displays, and information encryption. These results may provide new visions for understanding the complicated conformational changes in the aggregated state, as well as unique insights into the relationship between molecular conformations, RTP emissions, and stimulus responsiveness.

Time-Dependent Colorful Circularly Polarized Organic Ultralong Room Temperature Phosphorescence from a Single-Component Chiral Molecule.

Colorful circularly polarized organic ultralong room temperature phosphorescence (CP-OURTP) materials have attracted much attention due to their superior optoelectronic properties for various applications. However, the development of colorful CP-OURTP materials in a single-component molecular system is currently facing great challenges. Herein, a feasible strategy is proposed to develop colorful CP-OURTP material from a single-component chiral molecule by introducing a chiral unit into the phosphorescence chromophore. A dual CP-OURTP band originated from inherent triplet excitons emission showing a lifetime of 946.44ms and triplet-triplet annihilation induced delayed emission with a short lifetime of 209.91ms as well as maximum asymmetry factors of ≈10-3 are realized. Owing to the changed OURTP intensity ratios between inherent CP-OURTP and delayed emission at different delayed times, time-dependent colorful CP-OURTP turned from yellow to green is obtained. This study provides a potential platform to prepare circularly polarized material systems showing colorful luminescent properties.

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.

Aggregation-regulated room-temperature phosphorescence materials with multi-mode emission, adjustable excitation-dependence and visible-light excitation

Constructing room-temperature phosphorescent materials with multiple emission and special excitation modes is fascinating and challenging for practical applications. Herein, we demonstrate a facile and general strategy to obtain ecofriendly ultralong phosphorescent materials with multi-mode emission, adjustable excitation-dependence, and visible-light excitation using a single organic component, cellulose trimellitate. Based on the regulation of the aggregation state of anionic cellulose trimellitates, such as CBtCOONa, three types of phosphorescent materials with different emission modes are fabricated, including blue, green and color-tunable phosphorescent materials with a strong excitation-dependence. The separated molecularly-dispersed CBtCOONa exhibits blue phosphorescence while the aggregated CBtCOONa emits green phosphorescence; and the CBtCOONa with a coexistence state of single molecular chains and aggregates exhibits color-tunable phosphorescence depending on the excitation wavelength. Moreover, aggregated cellulose trimellitates demonstrate unique visible-light excitation phosphorescence, which emits green or yellow phosphorescence after turning off the visible light. The aggregation-regulated phenomenon provides a simple principle for designing the proof-of-concept and on-demand phosphorescent materials by using a single organic component. Owing to their excellent processability and environmental friendliness, the aforementioned cellulose-based phosphorescent materials are demonstrated as advanced phosphorescence inks to prepare various disposable complex anticounterfeiting patterns and information codes.

A Heavy-atom-free Molecular Motif Based on Centrosymmetric Bird-like Structured Tetraphenylenes with Room-Temperature Phosphorescence (RTP) Afterglow over 8s.

In recent years, pure organic room-temperature phosphorescence (RTP) with highly efficient and long-persistent afterglow has drawn substantial awareness. Commonly, spin-orbit coupling can be improved by introducing heavy atoms into pure-organic molecules. However, this strategy will simultaneously increase the radiative and non-radiative transition rate, further resulting in dramatic decreases in the excited state lifetime and afterglow duration. Here in this work, a highly centrosymmetric bird-like structure tetraphenylene (TeP), and its three symmetrical halogenated derivatives (TeP-F, TeP-Cl and TeP-Br) are synthesized, while their RTP properties and mechanisms are systematically investigated by both theoretical and experimental approaches. As the results, the rigid, highly twisted conformation of TeP restricts the non-radiative processes of RTP and gives rise to the enhancement of electron-exchange, which can contribute to the RTP radiation process. Despite the faint RTP of the bromine and chlorine-substituted ones (TeP-Br, TeP-Cl), the fluoro-substituted TeP-F exhibited a long phosphorescent lifetime of up to 890 ms, corresponding to an extremely long RTP afterglow over 8 s, which could be incorporated into the best series of non-heavy-atom RTP materials reported in previous literature.

A Heavy‐atom‐free Molecular Motif Based on Symmetric Bird‐like Structured Tetraphenylenes with Room‐Temperature Phosphorescence (RTP) Afterglow over 8 s

AbstractIn recent years, pure organic room‐temperature phosphorescence (RTP) with highly efficient and long‐persistent afterglow has drawn substantial awareness. Commonly, spin‐orbit coupling can be improved by introducing heavy atoms into pure‐organic molecules. However, this strategy will simultaneously increase the radiative and non‐radiative transition rate, further resulting in dramatic decreases in the excited state lifetime and afterglow duration. Here in this work, a highly symmetric bird‐like structure tetraphenylene (TeP), and its three symmetrical halogenated derivatives (TeP−F, TeP−Cl and TeP−Br) are synthesized, while their RTP properties and mechanisms are systematically investigated by both theoretical and experimental approaches. As the results, the rigid, highly twisted conformation of TeP restricts the non‐radiative processes of RTP and gives rise to the enhancement of electron‐exchange, which can contribute to the RTP radiation process. Despite the faint RTP of the bromine and chlorine‐substituted ones (TeP−Br, TeP−Cl), the fluoro‐substituted TeP−F exhibited a long phosphorescent lifetime up to 890 ms, corresponding to an extremely long RTP afterglow over 8 s, which could be incorporated into the best series of non‐heavy‐atom RTP materials reported in previous literature.

Wide-range tunable phosphorescence emission in cellulose-based materials enabled by complementary-color phosphors

Developing color-tunable pure organic room-temperature phosphorescent (RTP) materials based on biopolymers is of great significance for efficient utilization of natural resources, yet still challenging. Herein, tunable multicolor phosphorescence emission, including white-light, is achieved in cellulose-based RTP materials by co-organizing complementary cyan and red organic phosphors into the strong hydrogen-bonding networks of cellulose. The non-radiative transition of phosphors can be effectively suppressed by the high density of hydrogen bonding among the cellulose chains as well as the covalent interaction. The difference in optical properties between the two phosphors enables the adjustment of the phosphorescence emission color of the material from green to cyan, white and then red. It is demonstrated that the designed material can be used as versatile inks for pattern drawing and information encryption, with favorable multicolor emission and excellent aqueous processability. Therefore, considering the biodegradability and sustainability of cellulose materials, cellulose-based RTP has enormous potential in advanced anti-counterfeiting and information encryption as eco-friendly phosphorescent inks and coatings.

Isomer and substituent engineering of TADF emitters toward tunable room-temperature phosphorescence

Metal-free organic phosphorescent materials are crucial for the advancement of optoelectronics and bioelectronics. Nonetheless, achieving rational control over the performance of room-temperature phosphorescence (RTP) presents a significant challenge. In this study, two sets of isomeric thermally activated delayed fluorescence (TADF) emitters with a donor–acceptor (D-A) configuration are designed and synthesized. Their RTP efficiency and lifetime are regulated by tuning their energy levels and molecular packing modes through isomer and substituent engineering. All of these materials exhibited afterglow emission, with the exception of 4-CzAIPh. A comprehensive investigation was conducted on the packing modes in the crystalline state, which revealed that the three RTP materials possess strong π-π interactions and numerous intermolecular forces, providing stability to the long-lived triplet excitons of RTP. Especially, 4-CzAIAd demonstrated the fastest intersystem crossing rate, the smallest fractional free volume and relatively larger spin–orbit coupling between its singlet and triplet states, as well as between its triplet state and ground state, which explains its longest phosphorescence lifetime of 301 ms.

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, Ma-Mf) 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 (Ma-PVA) and 697 ms (Ma-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 Me-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.

Inorganic salt recrystallization strategy for achieving ultralong room temperature phosphorescence through structural confinement and aluminized reconstruction

Achieving highly efficient and stable room temperature phosphorescence (RTP) with ultralong lifetime is critical for the multi-purpose applications of phosphorescent materials. In this work, we propose an inorganic salt heating recrystallization strategy to simultaneously improve the lifetime, quantum efficiency, and stability of phosphorescent scandium/leucine microspheres (Sc/Leu-MSs). Inorganic salt-treated Sc/Leu-MSs are obtained by simply heating and drying inorganic salt solution containing Sc/Leu-MSs, which can achieve a maximum lifetime increase of 4.42-times from 208.37 ms (Sc/Leu-MSs) to 920.08 ms (Al2(SO4)3-treated Sc/Leu-MSs), accompanied by a RTP intensity increase up to 24.08-times. The enhancement mechanism of RTP efficiency is attributed to the stabilization of triplet excitons caused by inorganic salt coating that suppresses molecular motion and isolates oxygen on the one hand, and the efficient intersystem crossing promoted by aluminized reconstruction-caused duplex heavy atom effects on the other hand. This study provides new design principle and a facile strategy to construct RTP materials with ultralong lifetime, high phosphorescent quantum efficiency, and high stability for promising applications such as anti-counterfeiting and light emitting diodes.

Smart phosphorescence from solid to water through progressive assembly strategy based on dual phosphorescent sources

AbstractDeveloping smart room‐temperature phosphorescence (RTP) materials with facile and efficient strategies have attracted increasing attention. Herein, tunable RTP materials with two phosphorescent sources and stepwise enhanced phosphorescence in water are obtained through an in‐situ self‐assembly strategy based on the sensitization of phosphors by trimesic acid (TMA) through simple doping and the rigidification of phosphors by hydrogen‐bonded organic frameworks (HOFs). As expected, doped TMA+phosphors simultaneously promote the RTP emission of phosphors and maintain TMA phosphorescence. In‐situ assembled HOF(MA‐TMA)@phosphors facilitate smart RTP emission in water due to the coexistence of phosphorescent HOF(MA‐TMA) host and phosphors guest. Additionally, such RTP materials with good processability demonstrate the application potential in information security, benefitting from their varied afterglow lifetimes and easy luminous recognition in the darkness. This work will inspire the design of dual phosphorescent source RTP systems and provide new strategies for the development of smart RTP materials in water.

Supramolecular Surface Engineering of Carbon Dots Enables Matrix‐Free Room Temperature Phosphorescence†

Comprehensive SummaryCarbon dots (CDs) are an emerging class of nanomaterials with intriguing photophysical properties. Recently, achieving room temperature phosphorescence (RTP) for CDs has attracted considerable attention for biomedical and information applications. However, the CDs based RTP materials generally require the use of polymeric and inorganic matrix to provide the rigid environments, which remains a great challenge to obtain matrix‐free CDs with RTP. Herein, a novel supramolecular strategy based on strong interparticle interactions has been developed to attain this objective, by covalent decoration of ureido‐pyrimidinone (UPy, a multiple hydrogen bonding unit) on the surface of CDs. Structural characterizations validated the core‐shell structure of the as‐prepared CDs (EDTA‐CDs) and demonstrated the successful attachment of UPy via post‐modification (UPy‐CDs). The presence of UPy recognition units render the strong hydrogen bonding between UPy‐CDs, which stabilizes the triplet state via rigidifying effect. As a result, UPy‐CDs exhibit matrix‐free efficient RTP (λem = 534 nm) with high brightness and long lifetime (33.6 ms) in the solid state. Owing to the dual‐emission character, we further explored the application potential of UPy‐CDs in information encryption and anti‐counterfeiting. Overall, this work provides a new and facile strategy for achieving matrix‐free phosphorescent CDs with elegant incorporation of supramolecular chemistry.