Persistent Room-temperature Phosphorescence Research Articles

Excellent Persistent Near-Infrared Room Temperature Phosphorescence from Highly Efficient Host-Guest Systems.

Organic near-infrared (NIR) room temperature phosphorescence (RTP) materials become a hot topic in bioimaging and biosensing for the large penetration depth and high signal-to-background ratio (SBR). However, it is challenging to achieve persistent NIR phosphorescence for severe nonradiative transitions by energy-gap law. Herein, a universal system with persistent NIR RTP is built by visible (host) and NIR phosphorescence (guest) materials, which can efficiently suppress the nonradiative transitions by rigid environment of crystalline host materials with good matching, and further promote phosphorescence emission by the additional phosphorescence resonance energy transfer (≈100%) between them. The persistent NIR phosphorescence with ten-folds enhancement of RTP lifetimes, compared to those of guest luminogens, can be achieved by modulation of aggregated structures of host-guest systems. This work provides a convenient way to largely prolong the phosphorescence lifetimes of various NIR luminogens, promoting their application in afterglow imaging with deeper penetration and higher SBRs.

Visible-light-excited robust room-temperature phosphorescence of dimeric single-component luminophores in the amorphous state

Organic room temperature phosphorescence (RTP) has significant potential in various applications of information storage, anti-counterfeiting, and bio-imaging. However, achieving robust organic RTP emission of the single-component system is challenging to overcome the restriction of the crystalline state or other rigid environments with cautious treatment. Herein, we report a single-component system with robust persistent RTP emission in various aggregated forms, such as crystal, fine powder, and even amorphous states. Our experimental data reveal that the vigorous RTP emissions rely on their tight dimers based on strong and large-overlap π-π interactions between polycyclic aromatic hydrocarbon (PAH) groups. The dimer structure can offer not only excitons in low energy levels for visible-light excited red long-lived RTP but also suppression of the nonradiative decays even in an amorphous state for good resistance of RTP to heat (up to 70 °C) or water. Furthermore, we demonstrate the water-dispersible nanoparticle with persistent RTP over 600 nm and a lifetime of 0.22 s for visible-light excited cellular and in-vivo imaging, prepared through the common microemulsion approach without overcaution for nanocrystal formation.

Controllable Blue Shift and Enhancement Emission during the Gradually Increasing Molecular Weight of Polyacrylamide.

Nonconventional luminescent polymers have become research hotspots due to their advantages such as persistent room temperature phosphorescence (p-RTP) emission and strong film-forming properties. It is proven that the molecular weight (MW) of such luminescent polymers has a significant impact on their emission over a large range, generally with a red shift as the MW increases. Herein, four controllable MW polyacrylamides are prepared via reversible addition-fragmentation chain transfer polymerization (RAFT), and their photoluminescence quantum yield and p-RTP lifetimes gradually increase with the increasing MW. The emission of p-RTP gradually shifts blue with increasing MW, which is likely due to the gradually changing interactions between the electron-rich portion in RAFT reagent and the increasing acrylamide (AM) units in the molecular chain. These can be reasonably explained through small angle X-ray scattering, the clustering-triggered emission (CTE) mechanism, and supported by theoretical calculations. Powder with controllable p-RTP capability has the potential for strategic anti-counterfeiting encryption. The above results not only promote the development of the CTE mechanism toward more precise explanations but also provide new ideas for the preparation of nonconventional luminescent polymers with controllable p-RTP emission performance.

The Impact of Molecular Packing on Organic Room Temperature Phosphorescence and Corresponding Stimulus Response Effect

AbstractOrganic luminescent materials exhibiting persistent room temperature phosphorescence (RTP) have garnered considerable interest due to their versatile applications. However, the mechanism is still unclear, especially for the molecular structure‐molecular arrangement‐property relationship. Herein, six derivatives of phenothiazine 5,5‐dioxide are synthesized, revealing their distinct RTP properties and the associated underlying mechanisms. Careful analyses of their single crystal structures, combined with initial theoretical calculations, indicate that the persistent RTP effect is facilitated by effective intermolecular π–π interactions in the solid state led by folded conformation. Specifically, PTZO‐CF3‐3F exhibits distinctive photo‐activated phosphorescence both in crystal and grinding state in response to the changes of molecular arrangement. Besides, a porous structure is found to be present in PTZO‐CF3‐2F crystal, offering it great sensitivity to oxygen for both RTP intensity and lifetime. Accordingly, the visual oxygen warning device is fabricated successfully. Furthermore, PTZO‐CF3‐3F with photo‐activated RTP effect in a grinding state is successfully utilized in the applications of anti‐counterfeiting and optical logic gates, expanding the scope of stimulus‐responsive phosphorescence materials for broader applications.

Multicolour room temperature phosphorescence of carbon nitride nanoparticles in sodium borohydride and borax matrix

Carbon nitride based materials find applications in photocatalysis, sensing, and bioimaging. The fluorescence properties of carbon nitride based nanomaterials is widely studied. However, its phosphorescence phenomenon is relatively less explored. Herein, we report a simple and economic one step thermal synthesis of highly fluorescent pure carbon nitride nanoparticles (CNNPs) from organic solvent formamide at 220 °C, just above its boiling point without any further passivation or purification.The fluorescent CNNPs is dispersed in sodium borohydride and borax which act as suitable host matrix resulting in activation of persistent room temperature phosphorescence of CNNPs with high phosphorescence lifetimes of 1.144 s and 0.737 s respectively. Moreover, the CNNPs-Sodium borohydride composite display tricolour, blue, green and yellow-orange phosphorescence under 254 nm, 365 nm and 400 nm light respectively while CNNPs-Borax composite show dual blue and green phosphorescence under 254 nm and 365 nm UV light respectively. Hence, these CNNPs-Composite may be used as multicolour anti-counterfeiting materials in future.

Improvement in persistent room temperature phosphorescence of polymeric systems via a melt‐pressing method

AbstractPolymer‐based afterglow materials with persistent room temperature phosphorescence (pRTP) have attracted ever‐increasing attention due to their excellent mechanical property, suitability for large‐area production, and diverse processing methods. However, most pRTP polymers were solution‐processed into the films via casting. Herein, a simple processing method of melt‐pressing was proposed, which can improve the phosphorescence of various emitters when doped into polyamide‐12 (PA12) or its copolymer PA4 matrix. Notably, for Be@PA4 and Ch@PA4 (benzo[c]phenanthrene, Be and chrysene, Ch), their casted films did not show any afterglow, while the melt‐pressed ones exhibited bright afterglow of over 4.0 s, even if there were no hydrogen or ionic interaction between the emitters and the matrix. Detailed investigations demonstrate the melt‐pressing procedure can increase the non‐covalent interaction among the matrix as well as offer a rigid and dense environment. The melt‐pressed RTP improvement strategy was also applied to other polar polymers. Additionally, the melt‐pressing method would be of great potential in high‐level anti‐counterfeiting like preparing colorful camouflage patterns. Therefore, we offered a feasible method of melt‐pressing to improve the phosphorescence of polymeric materials without a change in chemical composition or feeding ratio. This work also gained a deeper understanding of the luminescence of polymer‐based systems.

Dopants Induce Persistent Room Temperature Phosphorescence in Triarylamine Boronate Esters

AbstractPurely organic materials exhibiting room temperature phosphorescence (RTP) are promising candidates for oxygen sensors and information encryption owing to their cost‐effective and environmentally friendly nature. Herein, we report a bimolecular RTP system where DTBU acts as the guest and TBBU serves as the host. In contrast to previously reported results, we find that both pure DTBU and TBBU do not exhibit RTP in the solid state even under N2 atmosphere. A DTBU/TBBU system with a low doping ratio (0.1 mol %) exhibits persistent yellowish‐green afterglow with a lifetime of 340 ms and is highly sensitive to oxygen. A DTBU/TBBU system with a higher doping ratio (10 mol %) maintains a phosphorescence lifetime of 179 ms under air. Applications of DTBU/TBBU at varied doping ratios in both oxygen sensing and information encryption are demonstrated. We propose that the T1 state of TBBU acts as an energy transfer intermediate between Tn and T1 of DTBU, ultimately leading to the generation of persistent RTP. Overall, this work demonstrates the critical importance of material purity in the design of RTP systems, and how an understanding of host–guest doping enables their photophysical properties to be precisely tuned.

Dopants Induce Persistent Room Temperature Phosphorescence in Triarylamine Boronate Esters.

Purely organic materials exhibiting room temperature phosphorescence (RTP) are promising candidates for oxygen sensors and information encryption owing to their cost-effective and environmentally friendly nature. Herein, we report a bimolecular RTP system where DTBU acts as the guest and TBBU serves as the host. In contrast to previously reported results, we find that both pure DTBU and TBBU do not exhibit RTP in the solid state even under N2 atmosphere. A DTBU/TBBU system with a low doping ratio (0.1 mol %) exhibits persistent yellowish-green afterglow with a lifetime of 340 ms and is highly sensitive to oxygen. A DTBU/TBBU system with a higher doping ratio (10 mol %) maintains a phosphorescence lifetime of 179 ms under air. Applications of DTBU/TBBU at varied doping ratios in both oxygen sensing and information encryption are demonstrated. We propose that the T1 state of TBBU acts as an energy transfer intermediate between Tn and T1 of DTBU, ultimately leading to the generation of persistent RTP. Overall, this work demonstrates the critical importance of material purity in the design of RTP systems, and how an understanding of host-guest doping enables their photophysical properties to be precisely tuned.

Symmetry-Breaking Triplet Excited State Enhances Red Afterglow Enabling Ubiquitous Afterglow Readout.

Molecular vibrations are often factors that deactivate luminescence. However, if there are molecular motion elements that enhance luminescence, it may be possible to utilize molecular movement as a design guideline to enhance luminescence. Here, the authors report a large contribution of symmetry-breaking molecular motion that enhances red persistent room-temperature phosphorescence (RTP) in donor-π-donor conjugated chromophores. The deuterated form of the donor-π-donor chromophore exhibits efficient red persistent RTP with a yield of 21% and a lifetime of 1.6s. A dynamic calculation of the phosphorescence rate constant (kp) indicates that the symmetry-breaking movement has a crucial role in selectively facilitating kp without increasing nonradiative transition from the lowest triplet excited state. Molecules exhibiting efficient red persistent RTP enable long-wavelength excitation, indicating the suitability of observing afterglow readout in a bright indoor environment with a white-light-emitting diode flashlight, greatly expanding the range of anti-counterfeiting applications that use afterglow.

A Universal Strategy for Tuning Afterglow Color In Situ Via Radiative Energy Transfer

AbstractColorful afterglow materials have promising applications in optoelectronic displays. To effectively fine‐tune the afterglow color, an assembly structure that includes UV lamp, persistent room temperature phosphorescence (pRTP) layer, and fluorescent layer (from the bottom to the top) with superimposition of pRTP and fluorescence, is designed. The fluorescence component is emitted from a PMMA film doped with asymmetric 4‐(7‐methoxy‐5,6‐dinitrobenzo[c][1,2,5,]thiadiazol‐4‐yl)‐N,N‐diphenylaniline (TPA‐TD), which has a broad absorption that covers the entire visible region, facilitating effective radiative energy transfer between various pRTP materials and TPA‐TD. Due to its aggregation‐induced‐emission nature, the fluorescence intensity of TPA‐TD enhances with increased doping concentration in PMMA films. Meanwhile, the transmission of TPA‐TD film reduces as the doping concentration increases, which results in a reduction of pRTP intensity through the TPA‐TD film. Therefore, the afterglow color can be fine‐tuned in situ by regulating the ratio of pRTP and fluorescence.

Translating efficient fluorescence into persistent room-temperature phosphorescence by doping bipolar fluorophores into polar polymer matrix

In the doped phosphorescent films, highly polar PAA afforded the best phosphorescence performance mainly due to the strong host–guest polar–polar interaction.

Simultaneously enhancing organic phosphorescence quantum yields and lifetimes for triphenylphosphine salt doped polymer films.

Simultaneously enhancing the quantum yields and luminescence lifetimes of organic persistent room temperature phosphorescence (RTP) molecules is a priority in the organic photonic area, but it remains a formidable challenge. Here, an effective strategy was proposed to improve both quantum efficiencies and emission decay times for phosphorescent triphenylphosphine salts. This approach involves integrating an electron donor unit into a triphenylphosphine salt via an alkyl chain. This structure facilitates an intermediate through-space charge transfer excited state, which enhances the intersystem crossing process to boost RTP performance. Moreover, the electron donor moiety contributes additional triplet excitons to the triphenylphosphine salts through triplet-to-triplet energy transfer, substantially increasing the population of triplet excitons. Specifically, compared to butyl(naphthalen-1-yl) diphenylphosphonium bromide (Φphos. = 4.9% and τ = 255.79 ms), (2-(9H-carbazol-9-yl)ethyl)(naphthalen-1-yl)diphenylphosphonium bromide demonstrates a higher phosphorescence quantum yield of 19.6% and an extended emission lifetime of 800.59 ms. This advancement lays the groundwork for developing high-performance organic RTP materials, unlocking new possibilities for advanced photonic applications.

Hour-Level Persistent Multicolor Phosphorescence Enabled by Carbon Dot-Based Nanocomposites Through a Multi-Confinement-Based Approach.

Hour-level persistent room temperature phosphorescence (RTP) phenomena based on multi-confinement carbon dots (CDs) are reported. The CDs-based system reported here (named Si-CDs@B2 O3 ) can be efficiently synthesized by a simple pyrolysis method compared to the established persistent RTP systems. The binding modes of CDs, silica (SiO2 ), and boron oxide (B2 O3 ) are deduced from a series of characterizations including XRD, FT-IR, and TEM characterization. Further studies show that the formation of covalent bonds between B2 O3 , SiO2 , and CDs play a key role in activating the persistent RTP and preventing its quenching. This is a rare example of a persistent RTP system that exhibits hourly persistent RTP under environmental conditions. Finally, the applications of Si-CDs@B2 O3 are demonstrated for anti-counterfeiting, long-duration phosphorescence imaging, and fingerprinting. This synthetic strategy is expected to provide strong technical support for the preparation of persistent RTP CDs and pave the way for the synthesis of persistent RTP CDs in the future.

Promoting intersystem crossing by charge transfer state of dimers for persistent room temperature phosphorescence

Efficient intersystem crossing (ISC) is essential for phosphorescence emission. The charge transfer (CT) state is traditionally constructed by highly twisted donor-acceptor type structures to facilitate the ISC process. However, the highly twisted structural properties limit the diversity of room-temperature phosphorescence (RTP) molecules. By establishing the CT state in the intermolecular dimers structure, the dependence on the distorted donor-acceptor in the single-molecule design can be well eliminated. Based on this strategy, three novel pure organic luminescent molecules with long afterglow and mechanochromic luminescence (MCL) property were designed and synthesized. All of those exhibited triple emission, including prompt fluorescence (PF), delayed fluorescence (DF) and persistent RTP (pRTP) emission. In particular, CzC4-PhCN showed great potential for application in the field of anti-counterfeiting with its ultralong phosphorescent lifetime of 862 ms. Single crystal analysis and theoretical calculation revealed that the formation of CT states of intermolecular dimers effectively reduced ΔEST and promoted ISC process. This study would be highly instructive for realizing efficient ISC process and high-efficiency pRTP emission in pure organic systems.

Deep-red ultralong room temperature phosphorescence of chitosan-based nanofibrous membrane activated by carboxylic acids

Organic non-conjugated materials with room temperature phosphorescence (RTP) have attracted increasing attention due to their fundamental importance and advantages like environmental friendliness, good biocompatibility, and various processing methods. However, most non-conjugated systems often suffered from the problem with very short RTP lifetimes in ambient conditions. Here, we proposed an efficient strategy to improve the RTP performance of chitosan (CTS) by constructing a strong ionic bond network based on carboxylic acids. The CA/CTS film prepared using citric acid (CA) as a solvent was found to emit a bright afterglow of about 5 s with a phosphorescence lifetime of up to 515 ms at 530 nm. Our experimental results indicated that forming synergistic networks of ionic and hydrogen bonding was a highly efficient method for achieving persistent RTP of CTS itself. Furthermore, due to the strong ionic interaction between 1-pyrenecarboxylic acid (PCA) and CTS, the PCA@CTS nanofibrous membrane with bright deep-red afterglow was first achieved through an electrostatic spinning technique using polyethylene glycol (PEG) or polyvinyl alcohol (PVA) as a co-spinning agent. This work not only offered a new kind of persistent RTP nanofibrous membrane but also gained a deeper insight into improving the phosphorescence properties of non-conjugated materials, especially natural polysaccharide.

Photoirradiation‐Gated Excitation‐Dependent Room‐Temperature Phosphorescence in Through‐Space Charge Transfer Molecules

AbstractOrganic materials showing reversible changes in persistent room‐temperature phosphorescence (RTP) upon exposure to external stimuli have attracted considerable attention in recent years. One potentially groundbreaking development in this area is the introduction of the gating concept for organic persistent RTP materials. This refers to a material where a desired responsive ability only occurs when it is triggered by a specific stimulus, but it remains a formidable challenge. In this study, photoirradiation‐gated excitation‐dependent (Ex‐De) persistent RTP is achieved. A series of molecules, triphenylphosphine and carbazole derivatives connected through flexible carbon chains, are designed and prepared. Upon removal of ultraviolet (UV) irradiation, all these compounds doped polyvinyl alcohol (PVA) films exhibit obvious blue or green afterglow RTP. Among them, (2‐(9H‐[3,9′‐bicarbazol]−9‐yl)ethyl)triphenylphosphonium bromide (TPP‐2C‐Cz) doped PVA film initially exhibits blue persistent RTP after removal of 300 nm excitation but no RTP upon ceasing 365 nm irradiation. Interestingly, upon UV irradiation with a power density of 0.05 W cm−2 (UVA) for 50 min, the Ex‐De RTP behavior of TPP‐2C‐Cz doped PVA film is activated. Eventually, photoirradiation‐gated Ex‐De afterglow emission will be used for a wide range of applications, including the quantitative determination of UV irradiation dose and the permanent record of UV irradiation history, and read on‐demand.

Single Molecular Persistent Room-Temperature Phosphorescence and Circularly Polarized Luminescence from Binaphthol-Decorated Optically Innocent Cyclotriphosphazenes.

Circularly polarized luminescence (CPL) features of BINOL-decorated cyclotriphosphazenes (CPs) are reported for the first time. The luminescence dissymmetry factor (glum ) of these compounds in chloroform solutions and polymethyl methacrylate (PMMA) thin films with wt 1 % doping concentrations are found to be 1.0×10-3 , and 2.9×10-3 , respectively. However, no CPL signal is observed for the pristine solids. The enantiomers (CP-(R)/CP-(S)) show ultraviolet photoluminescence (~350-360 nm) in solution and the solid state. These compounds show ~10 times larger absolute photoluminescence quantum yield (PLQY) than the simple BINOLs in the solutions state. In the solid state, CP-(R) shows larger PLQY than binaphthol-(R); in contrast, the S enantiomer shows lower PLQY than binaphthol-(S); this indicates that the isomer-dependent solid-state packing of these compounds plays a crucial role in controlling the PL. Thin films with more than 1 % doping concentration and pristine solids of these compounds do not show persistent room-temperature phosphorescence (pRTP) due to concentration-caused quenching. However, thin films with wt 1 % of these chiral emitters exhibit pRTP characteristics with a ~159-343 ms lifetime under vacuum. Theoretical calculations reveal that the cyclophosphazene acts as an optically innocent dendritic core, and the optical features of these compounds are dictated by the pendent BINOL chromophore.

Activating Molecular Room-Temperature Phosphorescence by Manipulating Excited-State Energy Levels in Poly(vinyl alcohol) Matrix.

Poly(vinyl alcohol) (PVA) has been found as a wonderful matrix for chromophores to boost their room-temperature phosphorescence (RTP) character by forming abundant hydrogen bonding. Despite the well-utilized protective effect, the constructive role in accelerating the intersystem crossing is less investigated. Here, we focus on its role in manipulating the excited-state energy level to facilitate multiple intersystem crossing channels. Six benzoyl carbazole derivatives do not emit RTP in their solutions, powders, or crystals but exhibit significantly persistent RTP signals when embedded into the PVA matrix. Charge-transfer excited states were trapped by cofacial stacking in crystal, which blocks the intersystem crossing channels. In the PVA matrix, the allowed broad distribution of charge-transfer states covers the locally excited states, offering multiple intersystem crossing pathways via spin-vibronic orbit coupling. Consequently, efficient and persistent heavy-atom-free phosphors have been developed with the highest quantum yields of 7.7% and the longest lifetime of 2.3 s.

Co-crystallization and Clustering Afforded Simultaneously Boosted Efficiency, Lifetime, and Color Tunability of Organic Afterglows.

Pure organic persistent room-temperature phosphorescence (p-RTP) is in urgent demand for advanced optoelectronic and bioelectronic applications. However, it remains an enormous challenge to modulate the emission colors while simultaneously boosting the phosphorescence lifetimes and efficiencies. Herein, we report the co-crystallization between melamine and cyclic imide-based non-conventional luminophores, which affords co-crystals owning multiple hydrogen bonds and effective clustering of electron-rich units, thus resulting in diverse emissive species with highly rigidified conformations and promoted spin-orbit coupling. Consequently, p-RTP co-crystals with simultaneously enhanced efficiencies and lifetimes of up to 12.0% and 898 ms, alongside remarkably improved color tunability, are obtained. These results may spur the future rational design of high-performance p-RTP materials and advance the mechanism of understanding of the origin of color-tunable phosphorescence.

Achieving persistent room-temperature phosphorescence of 1, 8-naphthalimide and persistent luminescence of Rhodamine B by polymer doping

1, 8-Naphthylimide (NI) was doped in polyvinyl alcohol (PVA) or polyacrylic acid (PAA) matrices (0.2%, mass ratio) to achieve persistent room-temperature phosphorescence (pRTP). The resulting pRTP can be attributed to the formation of a rigid environment constructed by abundant hydrogen bonds. Moreover, due to the overlap between NI's phosphorescent emission and Rhodamine B's absorption, the color-tunable persistent luminescence of RB@NI@PVA and RB@NI@PAA doped films were successfully achieved through phosphorescent resonance energy transfer strategy. This work provided an effective way to achieve the pRTP of NI by polymer doping, as well as persistent luminescence of Rhodamine B by phosphorescence resonance energy transfer from NI in the developed phosphorescent film system.