Room Temperature Phosphorescence Research Articles

Modulating Room‐Temperature Phosphorescence of Phenothiazine Dioxide via External Heavy Atoms

Developing pure organic materials with ultralong lifetimes and balanced quantum efficiency is attractive but challenging. In this study, we propose a novel strategy to investigate external heavy atoms by linking molecular emitters with halogen through a flexible alkyl chain. X‐ray crystal analysis clearly reveal the halogen C‐X‐π interactions, which can be tuned by halogen donors, as well as the distance and geometry between them. Impressively, DOPTZ‐C3Cl featuring a chloride atom as donor, exhibits a balanced long phosphorescence lifetime of 1351 ms and a phosphorescence quantum yield of 10.1%. We also first demonstrate that Cl can induce more positive effect than heavier halogens (Br and I) on prolonging the lifetime. We envisage that the present study will expedite new molecular design to manipulate the room temperature phosphorescence via external heavy atom effect, and highlight a special C‐Cl··π interaction for the development of ultralong phosphorescent materials.

Modulating Room‐Temperature Phosphorescence of Phenothiazine Dioxide via External Heavy Atoms

Developing pure organic materials with ultralong lifetimes and balanced quantum efficiency is attractive but challenging. In this study, we propose a novel strategy to investigate external heavy atoms by linking molecular emitters with halogen through a flexible alkyl chain. X‐ray crystal analysis clearly reveal the halogen C‐X‐π interactions, which can be tuned by halogen donors, as well as the distance and geometry between them. Impressively, DOPTZ‐C3Cl featuring a chloride atom as donor, exhibits a balanced long phosphorescence lifetime of 1351 ms and a phosphorescence quantum yield of 10.1%. We also first demonstrate that Cl can induce more positive effect than heavier halogens (Br and I) on prolonging the lifetime. We envisage that the present study will expedite new molecular design to manipulate the room temperature phosphorescence via external heavy atom effect, and highlight a special C‐Cl··π interaction for the development of ultralong phosphorescent materials.

Organic Circularly Polarized Room-Temperature Phosphorescence: Strategies, Applications and Challenges.

Organic circularly polarized luminescence (CPL) plays crucial roles in chemistry and biology for the potential in chiral recognition, asymmetric catalysis, 3D displays, and biological probes. The long-lived luminescence, large Stokes shift, and unique chiroptical properties make organic circularly polarized room-temperature phosphorescence (CPP) a new research hotspot in recent years. Nevertheless, achieving high-performance organic CPP is still challenging due to the sensitivity and complexity of integrating triplet excitons and polarization within organic materials. This review summarizes the latest advances in organic CPP, ranging from design strategies and photophysical properties to underlying luminescence mechanisms and potential applications. Specifically, the design strategies for generating CPP are systemically categorized and discussed according to the interactions between chiral units and chromophores. The applications of organic CPP in organic light-emitting diodes, sensing, chiral recognition, afterglow displays, and information encryption are also illustrated. In addition, we present the current challenges and perspectives on developing organic CPP. We expect this review to provide some instructive design principles to fabricate high-performance organic CPP materials, offering an in-depth understanding of the luminescence mechanism and paving the way toward diverse practical applications.

High-Performance Circularly Polarized Phosphorescence by Confining Isolated Chromophores with Chiral Counterions.

Organic room-temperature phosphorescence (RTP) featuring circularly polarized luminescence (CPL) is highly valuable in chiroptoelectronics, but the trade-off issue between luminescence efficiency (Φ) and dissymmetry factor (glum) is still challenging to be solved. Here, chiroptical ionic crystals (R/S-DNP) are constructed through ionization-induced assembly, in which isolated chromophore of carboxylic anion is tightly confined by the surrounding chiral counterions. The long-range ordered and chiral counterions with asymmetric stacking are closely connected with isolated chromophores for molecular assembly via high-density electrostatic interactions, thus enabling the simultaneous realization of excellent single-molecule RTP emission and efficient chirality transfer. The synchronous enhancement of ΦP and glum is further achieved as 43.2% and 0.13, respectively. In view of the excellent CPL performances, the ionic materials hold the promising chiroptical encryption via programmable control in an electric-driven circularly polarized phosphorescent device. This result not only makes deeper insights into the relationship between the structure and chiral RTP property but also provides a guide to developing highly efficient chiroptical materials for potential applications.

Activating Ultralong Room-Temperature Phosphorescence of Mono-Ring Arylboronic Acid by Hydrogen Bond for Tunable Afterglow Color and Stimulus Response.

Activating the ultralong room-temperature phosphorescence (RTP) of mono-ring arylboronic acid remains a great challenge, because the capacious free spaces shaped by a rubbery polymeric matrix allow the benzene ring skeleton to freely rotate. Herein, the ultralong RTP in mono-ring arylboronic acid derivatives embedded in a polyvinyl alcohol (PVA) matrix is activated, leveraging enhanced intermolecular and intramolecular hydrogen bonding and activating ultralong RTP. By incorporating diverse PBA derivatives into PVA via click chemistry, 3-aminophenylboronic acid (3A-PBA) doped PVA films showcase the most extended RTP lifetimes (2.24 s) and a high quantum yield (11.2%), alongside rapid and sensitive explosive vapor detection capabilities. These findings not only address the activation challenges of RTP in organic systems by highlighting the crucial role of hydrogen bonding and Förster resonance energy transfer in color tunability, but also mark a significant stride toward overcoming the limitations of current luminescent materials. This work heralds a new era in the development of organic phosphorescent materials, offering a promising strategy for broadening their practical applications and enhancing performance, particularly in environmental monitoring and security.

Triplet Energy Gap‐Regulated Room Temperature Phosphorescence in Host–Guest Doped Systems

AbstractThe organic room temperature phosphorescence (RTP) materials via host–guest doped method receive considerable attention in the fields of optoelectronics, bioimaging, and information encryption. Despite many host–guest doped materials with excellent RTP properties have been developed, their luminous mechanism is still limited. Here, a series of host–guest doped materials, using benzophenone as the host and quinone compounds as the guests, were constructed to investigate the effect of the triplet energy gap (ΔET) between the host and guest on triplet states population. The guest's triplet state is proposed to be a “triplet energy reservoir”, gathering the triplet excitons to emit RTP when ΔET is large and returning triplet excitons to the host when ΔET is small. By combining the results of steady‐state and delayed emission spectra, time‐resolved transient absorption spectra, and theoretical calculations, a bidirectional energy transfer process is proved, which are triplet‐triplet energy transfer and reverse triplet‐triplet energy transfer processes. The thermal equilibrium of these two energy transfer processes can be regulated by the ΔET and temperature. The potential applications of these RTP properties are also realized in data encryption and anti‐counterfeiting. This work provides valuable insight into the design of host–guest doped materials based on energy transfer mechanisms.

Triplet Energy Gap-Regulated Room Temperature Phosphorescence in Host-Guest Doped Systems.

The organic room temperature phosphorescence (RTP) materials via host-guest doped method receive considerable attention in the fields of optoelectronics, bioimaging, and information encryption. Despite many host-guest doped materials with excellent RTP properties have been developed, their luminous mechanism is still limited. Here, a series of host-guest doped materials, using benzophenone as the host and quinone compounds as the guests, were constructed to investigate the effect of the triplet energy gap (ΔET) between the host and guest on triplet states population. The guest's triplet state is proposed to be a "triplet energy reservoir", gathering the triplet excitons to emit RTP when ΔET is large and returning triplet excitons to the host when ΔET is small. By combining the results of steady-state and delayed emission spectra, time-resolved transient absorption spectra, and theoretical calculations, a bidirectional energy transfer process is proved, which are triplet-triplet energy transfer and reverse triplet-triplet energy transfer processes. The thermal equilibrium of these two energy transfer processes can be regulated by the ΔET and temperature. The potential applications of these RTP properties are also realized in data encryption and anti-counterfeiting. This work provides valuable insight into the design of host-guest doped materials based on energy transfer mechanisms.

Tunable Blue-Light-Emitting Organic-Inorganic Zinc Halides with Thermally Activated Delayed Fluorescence and Room-Temperature Phosphorescence.

Hybrid metal halides have received great interests in the field of solid-state lighting technologies due to their diverse structures and excellent emission properties. In this work, we report the synthesis and characterization of four blue-emitting zero-dimensional hybrid metal halides, namely, (2HP)2ZnCl2, (2HP)2ZnBr2, (2TP)2ZnCl2, and (2TP)2ZnBr2 (2HP = 2-hydroxypyridine, 2TP = pyridine-2-thiol). By changing the ligands and halides, a remarkable increase in the photoluminescence quantum yield of (2HP)2ZnCl2 (44.7%) compared to (2TP)2ZnBr2 (1.8%) is realized. The 2HP series features excitation-dependent emission characteristics, whereas the 2TP series does not due to the effect of a different organic ligand. Utilizing time-resolved and temperature-dependent photoluminescence spectroscopies, all four compounds exhibit both thermally activated delayed fluorescence and room-temperature phosphorescence properties. These materials have excellent ambient and thermal stabilities and are solution-processable. Our work shows the importance of carefully incorporating organic ligands with the appropriate inorganic metal center to achieve tunable emission properties.

Organic Room Temperature Phosphorescence from BN‐Substituted Xanthene Derivatives

AbstractEmissive organic materials are predominantly fluorescent and there is significant interest in realizing and understanding examples that defy this paradigm and exhibit phosphorescence under ambient conditions. Organic room temperature phosphorescence (ORTP) offers the long‐lived excited states and bathochromically‐shifted emission maxima of phosphorescence without the use of potentially toxic and expensive transition metals. Most ORTP materials rely on well‐studied structural motifs that include aryl carbonyls, sulfones, and heavy main group elements. We report the unexpected ORTP of a series of heavy atom‐free BN‐substituted xanthene derivatives. The creation of heteroatom‐rich scaffolds, combined with stabilizing C−H⋅⋅⋅F interactions in the solid‐state, resulted in oxygen‐tolerant heavy atom‐free organic phosphorescence without relying on the use of cryogenic temperatures, polymer matrices, or host–guest interactions. The observation of ORTP in these simple systems sets a blueprint for the further development of heavy atom‐free organic phosphors.

Halogen Impact on the Supramolecular Organization of Chiral Phthalimide Emitters Displaying Room Temperature Phosphorescence.

Room temperature phosphorescence from organic materials has attracted an increasing attention in the recent years due to their potential application in various advancing technologies, notably in bioimaging and displays. In this context, heavy atoms such as halogen ones revealed useful tools to enhance the spin-orbit coupling (SOC) of molecular organic phosphors. However, the effect of halogen at the supramolecular level remains less understood, especially in the field of molecular crystals where additional factors can impact the phosphorescence emission. Here, we investigate external effect of halogens on the phosphorescence of chiral phthalimides molecular crystals. The results show that changing the nature of the halogen atom onto the phthalimide core leads to an evolution of the photophysical properties of the materials which does not necessarily follow the classical trend imposed by the expected internal heavy atom effect. Beyond this aspect, we showed that the halogen atom has a profound impact on the packing between the chromophores at the supramolecular level which is of paramount importance towards the optical properties (PLQY and lifetimes) of the different phosphors examined.

Organic Materials with Ultrabright Phosphorescence at Room Temperature under Physiological Conditions for Bioimaging

AbstractIn contrast to the high efficiency of room temperature phosphorescence in crystal states, the generally utilized nanoparticles of organic materials in bioimaging demonstrated sharply decreased performance by orders of magnitude under physiological conditions, badly limiting the realization of their unique advantages. This case, especially for organic red/near‐infrared (NIR) phosphorescence materials, is not only the challenge present in reality but more importantly, for the theoretical problem of deeply understanding and avoiding the quenching effect by oxygen and water toward excited triplet states. Herein, thanks to the intelligent molecular design by the introduction of abundant hydrophobic chains and highly‐branched structures, bright and persistent red/NIR phosphorescence under physiological conditions has been realized, which demonstrated the shielding effect towards oxygen, and the strengthened intermolecular interactions to suppress the non‐radiative transitions. Accordingly, the record phosphorescence intensity of nanoparticles in bioimage, up to 8.21±0.36×108 p s−1 cm−2 sr−1, was achieved, to realize the clear phosphorescence imaging of liver and tumors in living mice, even lymph nodes in rabbit models with high SBRs. This work afforded an efficient way to achieve the bright red/NIR phosphorescence nanoparticles, guiding their further applications in biology and medicine.

Highly Elastic Full Hydrocarbon Ultralong RTP Polymers with Visible Light Excitable S0→T1 Population

AbstractHighly elastic ultralong organic room temperature phosphorescence (RTP) polymers are highly desired in wearable optoelectronic fields, but they are hardly realized in rubbers since chain segment motions deactivate triplet excitons. In the current work, it is revealed that polystyrene (PS) can inhibit triplet thermal deactivation of coronene (Cor), and it is the serious oxygen diffusion and quenching that disables RTP emission of Cor/polymers. In view of oxygen barrier function of rubbers, PS−polyisoprene−PS tri‐block elastomers (SIS) are used as Cor's doping matrices. The results show that Cor/SIS sheets show bright and ultralong afterglow with RTP lifetime up to 3.64 s in air after brief 365 nm light excitation. More impressively, Cor/SIS and its red fluorescent dye doped sheets all exhibit ultralong room temperature afterglow under large dynamic elastic deformation. Further, all these sheets exhibit long‐wave blue light excited afterglow despite Cor/SIS having no visible light absorption band, and the unique photoexcitation and emission mechanism is verified. This work not only provides the development strategy of the latest elastic RTP materials, but also will evoke a fresh understanding on organic doped RTP polymers.

Impurities in Arylboronic Esters Induce Persistent Afterglow.

Several recent reports suggest that arylboronic esters can exhibit room temperature phosphorescence (RTP), an optical property that is desirable for applications in security printing, oxygen sensing, and bioimaging. These findings challenged the fundamental notion that heavy elements or changes in orbital symmetry were required for intersystem crossing to occur in organic compounds. As we had not observed long afterglow in the many arylboronic esters we had synthesized over many years, we suspected that the RTP observed in these systems had a simpler explanation: the materials reported were impure. Herein, we synthesized 12 arylboronic esters that were previously reported to show RTP, and carefully purified them by column chromatography, recrystallization, and sublimation. We re-examined their photophysical properties alongside single-crystal X-ray diffraction analysis and detailed theoretical studies. While 4 of the 12 compounds showed long afterglows as crude products, none of them showed persistent RTP after careful purification. We also successfully isolated the impurity 4-amino-3,5-bis(pinacolatoboryl)benzonitrile (2), identifying it as the impurity responsible for inducing delayed fluorescence in 3,5-bis(pinacolatoboryl)benzonitrile (1). Doping 1 with 1.0 mol % 2 led to a persistent afterglow with a lifetime of 67 ms, which is mediated by a dimer charge transfer state. Our findings call for a re-examination of previous studies reporting RTP from arylboronic esters, highlight the importance of careful purification in photophysical research, and provide a practical strategy for designing organic materials with a long afterglow.

Photoactivated Multicolor Organic Phosphorescence in Intrinsically Stretchable, Self‐Healable and Recyclable Polymers

AbstractSmart persistent organic room‐temperature phosphorescence (RTP) materials, capable of responding to microenvironmental changes, are critically important in various optoelectronic applications. However, conventional persistent RTP materials usually have not stretchability and flexibility, limiting some practical applications. This study reports a facile and one‐pot photo‐initiated copolymerization method to prepare photoactivated persistent RTP polymers with multicolored afterglow, excellent stretchability, self‐healable and recyclable properties. Impressively, the polymers can be stretched up to 500% without significant loss in RTP intensity and lifetime, and they possess a self‐healing ability with a healing efficiency of 69.6%. Utilizing these photoactivated and stretchable persistent RTP polymers, dual encryption can be achieved under UV irradiation and stretching conditions, thereby enhancing the security levels of the stored confidential information. Overall, this study represents the first example of self‐healable and recyclable stimuli‐responsive RTP materials, demonstrating their bright future for the flexible and wearable optoelectronics.

Luminous Fish‐Inspired Hydrogels with Underwater Long‐Lived Room Temperature Phosphorescence

AbstractSome marine animals form long‐lived luminescence for predation, communication, camouflage, and anti‐predation. These marine animals demonstrate soft nature, sustainable glowing, and underwater emission, which are difficult to achieve in synthetic room temperature phosphorescence (RTP) materials. Inspired by these marine animals, here the study reports RTP hydrogels that show long‐lived phosphorescence (lifetime >500 ms and afterglow >10 s) in water. Exceptional underwater mechanical properties are simultaneously achieved, including tensile strength of 5.1 MPa, tensile strain of 452%, and toughness of 19.3 MJ m−3. The key to this achievement lies in the in situ phase separation microarchitecture formed between polyacrylamide (PAM) and its partial hydrolysates, which confines the motions of polymer chains and protects vulnerable triplet excitons from quenching of water. Such a strategy shows the merits of facile fabrication without laborious synthesis. In addition, these RTP hydrogels offer repeatable photoprinting and highly stability in water, providing a versatile platform for underwater applications of RTP materials, including information encryption and camouflage of marine animals.

Photoinduced On and Off Polymeric Room Temperature Phosphorescence Based On Polycyclic Aromatic Hydrocarbon Isomers.

As family members of polycyclic aromatic hydrocarbons, compound anthracene (Ant) and phenanthrene (Phe) as isomers are widely used in organic optical materials and electronic materials. But their photochemical and physical properties are very different. In this work, the room temperature phosphorescence (RTP) properties of PVA-B-Ant and PVA-B-Phe are discussed carefully which are prepared by B-O click reaction through polyvinyl alcohol (PVA) with 9-anthraceneboronic acid (B-Ant) and 9-phenanthrenylboronic acid (B-Phe), respectively. PVA-B-Phe 1 % film exhibits excellent fluorescence (FL) emission at 374 nm and RTP emission at 523 nm with green afterglow and around 1.9 s phosphorescence lifetime. However, PVA-B-Ant 1 % film only shows strong blue FL emission at 414 nm, and the emission intensity decreases seriously with the extension of irradiation time. Experimental and theoretical calculations results suggest that the photodimer of Ant which is formed in PVA matrix under the UV light irradiation would be competitive with the process of RTP emission. This work demonstrates that the RTP properties of organic molecules might be probably affected by the photostability of the organic phosphor under UV irradiation.

Visualizing Triplet Energy Transfer in Organic Near‐Infrared Phosphorescent Host‐Guest Materials

AbstractLimited by the energy gap law, purely organic materials with efficient near‐infrared room temperature phosphorescence are rare and difficult to achieve. Additionally, the exciton transition process among different emitting species in host–guest phosphorescent materials remains elusive, presenting a significant academic challenge. Herein, using a modular nonbonding orbital‐π bridge‐nonbonding orbital (n‐π‐n) molecular design strategy, we develop a series of heavy atom‐free phosphors. Systematic modification of the π‐conjugated cores enables the construction of a library with tunable near‐infrared phosphorescence from 655 to 710 nm. These phosphors exhibit excellent performance under ambient conditions when dispersed into a 4‐bromobenzophenone host matrix, achieving an extended lifetime of 11.25 ms and a maximum phosphorescence efficiency of 4.2 %. Notably, by eliminating the interference from host phosphorescence, the exciton transition process in hybrid materials can be visualized under various excitation conditions. Spectroscopic analysis reveals that the improved phosphorescent performance of the guest originates from the triplet‐triplet energy transfer of abundant triplet excitons generated independently by the host, rather than from enhanced intersystem crossing efficiency between the guest singlet state and the host triplet state. The findings provide in‐depth insights into constructing novel near‐infrared phosphors and exploring emission mechanisms of host–guest materials.

Visualizing Triplet Energy Transfer in Organic Near-Infrared Phosphorescent Host-Guest Materials.

Limited by the energy gap law, purely organic materials with efficient near-infrared room temperature phosphorescence are rare and difficult to achieve. Additionally, the exciton transition process among different emitting species in host-guest phosphorescent materials remains elusive, presenting a significant academic challenge. Herein, using a modular nonbonding orbital-π bridge-nonbonding orbital (n-π-n) molecular design strategy, we develop a series of heavy atom-free phosphors. Systematic modification of the π-conjugated cores enables the construction of a library with tunable near-infrared phosphorescence from 655 to 710 nm. These phosphors exhibit excellent performance under ambient conditions when dispersed into a 4-bromobenzophenone host matrix, achieving an extended lifetime of 11.25 ms and a maximum phosphorescence efficiency of 4.2 %. Notably, by eliminating the interference from host phosphorescence, the exciton transition process in hybrid materials can be visualized under various excitation conditions. Spectroscopic analysis reveals that the improved phosphorescent performance of the guest originates from the triplet-triplet energy transfer of abundant triplet excitons generated independently by the host, rather than from enhanced intersystem crossing efficiency between the guest singlet state and the host triplet state. The findings provide in-depth insights into constructing novel near-infrared phosphors and exploring emission mechanisms of host-guest materials.

Polymer microparticles with ultralong room-temperature phosphorescence for visual and quantitative detection of oxygen through phosphorescence image and lifetime analysis

Room-temperature phosphorescence (RTP) materials exhibiting long emission lifetimes have gained increasing attention owing to their potential applications in encryption, anti-counterfeiting, and sensing. However, most polymers exhibit a short RTP lifetime (<1 s) because of their unstable triplet excitons. Herein, a new strategy of polymer chain stabilized phosphorescence (PCSP), which yields a new kind of RTP polymers with an ultralong lifetime and a sensitive oxygen response, has been reported. The rigid polymer chains of poly(methyl mathacrylate) (PMMA) immobilize the emitter molecules through multiple interactions between them, giving rise to efficient RTP. Meanwhile, the loosely-packed amorphous polymer chains allow oxygen to diffuse inside, endowing the doped polymers with oxygen sensitivity. Flexible and transparent polymer films exhibited an impressive ultralong RTP lifetime of 2.57 s at room temperature in vacuum, which was among the best performance of PMMA. Intriguingly, their RTP was rapidly quenched in the presence of oxygen. Furthermore, RTP microparticles with a diameter of 1.63 μm were synthesized using in situ dispersion polymerization technique. Finally, oxygen sensors for quick, visual, and quantitative oxygen detection were developed based on the RTP microparticles through phosphorescence lifetime and image analysis. With distinctive advantages such as an ultralong lifetime, oxygen sensitivity, ease of fabrication, and cost-effectiveness, PCSP opens a new avenue to sensitive materials for oxygen detection.

Triplet Harvesting in Trifluoromethyl Quinoxaline Derivatives via TADF and RTP Mechanisms

In this study, we explore the impact of donor strength on the photophysical properties of novel trifluoromethyl quinoxaline derivatives, which incorporate various electron-donating moieties exhibiting distinct conformational characteristics. The triplet harvesting mechanisms within these quinoxaline systems are facilitated through thermally activated delayed fluorescence (TADF) and room-temperature phosphorescence (RTP), both of which can be modulated by subtle structural alterations in the donor unit. The derivatives demonstrate varying photophysical properties, including pure RTP activity, dual activity (exhibiting both TADF and RTP), and pure TADF, contingent upon the nature of the electron-donating moieties employed. Notably, the intersystem crossing (ISC) rates are significantly higher than the rates of radiative decay, leading to diminished fluorescence quantum yields (ΦDF) of the compounds in toluene solutions. However, embedding the TADF compounds within a rigid polystyrene (PS) matrix results in a remarkable enhancement of ΦDF due to significant reduction of nonradiative pathways related to intramolecular twisting. A considerable conformational disorder of the polymer doped films was observed resulting in non-exponential fluorescence decay and significant shifts of prompt and delayed fluorescence in time-resolved spectra.