Room Temperature Phosphorescence Research Articles

Dual-Mechanism Design Strategy for High-Efficiency and Long-Lived Organic Afterglow Materials.

Organic room-temperature phosphorescence (RTP) and afterglow materials hold great potential for various applications, but there remain inherent trade-offs between the afterglow efficiency and the lifetime. Here, we propose a dual-mechanism design strategy, leveraging the RTP or thermally activated delayed fluorescence (TADF) mechanism for a high afterglow efficiency and the organic long-persistent luminescence (OLPL) mechanism for a prolonged afterglow duration. The intramolecular charge transfer (ICT)-type difluoroboron β-diketonate molecules with a large S1 dipole moment are doped as the luminescent component into the organic matrix with a large dipole moment, and a series of TADF-type afterglow materials can be achieved with an afterglow efficiency of up to 88.7% and an afterglow lifetime of 200 ms. To prolong the afterglow duration, an electron donor is introduced as the third component to generate traps and facilitate charge separation. The obtained materials exhibit a dual afterglow mechanism, first exhibiting a TADF/RTP afterglow with an afterglow efficiency of up to 50.9%, followed by an hours-long OLPL afterglow emission with an afterglow efficiency of up to 13.1%. Further investigations reveal that an appropriate heavy-atom effect can facilitate the intersystem crossing process, which can promote the charge separation process and thus improve the OLPL afterglow performance. Additionally, rare-earth upconversion materials are introduced into OLPL materials to enable their near-infrared excitation properties, showcasing their potential applications in bioimaging.

Effect of Alkyl Chain Length on Room-Temperature Phosphorescent Probes for Mitochondria-Targeted Imaging.

Room temperature phosphorescent (RTP) probes have significant advantages in the field of cellular imaging, as their long lifetimes can prevent interference from the spontaneous fluorescence of organisms. Persulfurated arenes are a typical RTP molecular parent nucleus. However, most of the applied research on them is concentrated in anti-counterfeiting, and relatively few are applied in bioimaging. The molecular structure and structure-property relationship of them applied in bioimaging are still in the exploration stage. In this work, we have designed and synthesized a series of RTP probes with long alkyl chains, all of which can be targeted to mitochondria with good water solubility for mitochondria-targeted imaging. Further, we investigated the effect of alkyl chains on the luminescence properties of these probes, and found that the moderate length of alkyl chains can realize the enhancement of phosphorescence intensity. We believe this finding is of guiding significance for the design of molecular structures in the field of RTP probes.

Advanced dual-channel sensing of coumarin with phosphorescent carbon dots: Mechanism insights

Room-temperature phosphorescence carbon dots (CDs) show the highlighted advantages in chemical sensing and bioimaging owing to its long lifetime, however, acquiring the efficient phosphorescence of carbon dots is still encountering difficulty due to the spin prohibition. Here, we synthesized one type of CDs through one-step hydrothermal method. To be specific, the CDs displayed the blue fluorescence in aqueous, and emitted the bright green phosphorescence when being coated on the filter paper. Importantly, introducing coumarin to the CDs resulted in the distinct quenching of both its fluorescence and phosphorescence. Based on this phenomenon, we successfully established a dual-channel detection of coumarin. The fluorescence detection channel exhibited a linear range of 5–350 μM with a detection limit of 0.196 μM, while the phosphorescence detection channel achieved a linear range of 50–1000 μM with a detection limit of 0.268 μM. The further investigation revealed that IFE and SQE were mainly responsible for the fluorescence quenching of CDs, while the phosphorescence quenching was originated from the increased energy gap between the singlet and triplet states (ΔEST) of CDs, thus obstructing the ISC process. Moreover, we employed the CDs as the phosphorescent ink for anti-counterfeiting.

Multifunctional Amino‐Boranes Isomer Room‐Temperature Phosphorescent Material: Multi‐Substrate Multicolor Luminescence, Multi‐Level Anti‐Counterfeiting, Light‐Controlled Data Erasing/Writing, Data Logic Operation, and High Anti‐Laundry Detergent Performance

AbstractSignificant advances are made in understanding the structure‐property relationship in room‐temperature phosphorescence (RTP) materials. For example, intramolecular charge transfer (ICT) structural molecules based on electron donors(D) and electron acceptors(A) are an efficient method to achieve RTP. However, the ability to precisely regulate the singlet‐triplet energy gap (ΔEST) through molecular design to control RTP emissions remains constrained. Herein, a group of 4BN‐NP and 5BN‐NP isomers is reported with D and A position isomerization, where 4BN‐NP exhibits a photo‐induced orange afterglow phenomenon in PMMA. Calculations show that the spin‐orbit coupling (SOC) value of 4BN‐NP is greater compared to 5BN‐NP and the intersystem crossing (ISC) channel is more efficient, resulting in a smaller ΔEST value for 4BN‐NP. This indicates that the short ICT channel is more conducive to inducing phosphorescence emission. In addition, compound 4BN‐NP co‐doped with red fluorescent dyes (RhB, Rh6G, and RBNN) in PMMA produces phosphorescence resonance energy transfer (PRET), inducing red afterglow emission. Surprisingly, light‐activated yellow RTP can be obtained by attaching 4BN‐NP with polymethyl methacrylate (PMMA) to nylon filaments, and its phosphorescence intensity does not diminish even when it is immersed in water containing detergent solution, thus expanding the prospects of its application in textile encryption.

Regulating the photoluminescence of aluminium complexes from non-luminescence to room-temperature phosphorescence by tuning the metal substituents

Although luminescent aluminum compounds have been utilized for emitting and electron transporting layers in organic light-emitting diodes, most of them often exhibit not phosphorescence but fluorescence with lower photoluminescent quantum yields in the aggregated state than those in the amorphous state due to concentration quenching. Here we show the synthesis and optical properties of β-diketiminate aluminum complexes, such as crystallization-induced emission (CIE) and room-temperature phosphorescence (RTP), and the substituent effects of the central element. The dihaloaluminum complexes were found to exhibit the CIE property, especially RTP from the diiodo complex, while the dialkyl ones showed almost no emission in both solution and solid states. Theoretical calculations suggested that undesired structural relaxation in the singlet excited state of dialkyl complexes should be suppressed by introducing electronegative halogens instead of alkyl groups. Our findings could provide a molecular design not only for obtaining luminescent complexes but also for achieving triplet-harvesting materials.

Ultralong room temperature phosphorescence with multicolor afterglow achieved in a harsh polymeric viscous flow state.

Polymer-based ultralong room temperature phosphorescence (RTP) is more attractive than that of organic small molecules. However, the intrinsic contradictions between the motion of the chain and the stability of phosphors' triplet excitons make achieving ultralong lifetime in polymeric systems a big challenge. Herein, we have achieved ultralong RTP emission in a polymeric viscous flow state with free chain motion through a facile B-O click reaction among boric acid, polyvinyl alcohol, and hydroxyl silicone oil. The yielded RTP putties (RTPPs) exhibited long lifetimes under ambient conditions (up to 2.39 s), surpassing those of all reported elastic RTP polymers and most glassy RTP polymers. Furthermore, multi-color afterglow can be achieved in RTPPs using the triplet-to-singlet Förster resonance energy transfer strategy. Impressively, utilizing viscous liquid features combined with RTP performance, RTPPs can be easily applied in complex models, handiwork, and anti-counterfeiting. Therefore, this progress, achieving a long phosphorescence lifetime in a viscous flow state, greatly expands the application scope of polymeric RTP materials and further compels a conceptual advance of polymeric RTP.

Halogen Engineering Strategy-Induced Color-Tunable Room Temperature Phosphorescence in Metal-Organic Halides.

Color-tunable room temperature phosphorescence (RTP) materials possess potential applications in multicolor imaging, multichannel anticounterfeiting, and information encryption. Herein, we synthesized two zero-dimensional cadmium-organic halides, (H-aepy)2CdX4 (referred to as CdX-aepy; X = Cl-, Br-; aepy = 3-(2-aminoethyl)pyridine), both of which exhibit long-lived excitation wavelength- and time-dependent RTP. Experimental and theoretical results suggest that the multicolor RTP can be ascribed to the coemission of pristine H-aepy ligands and halogen-affected H-aepys, supporting that suitably introducing halogens can be an efficient strategy for constructing multicolor RTP materials. Additionally, we also demonstrate that the two phosphors can be applied in multichannel anticounterfeiting and information encryption. This work reports two hybrids with color-tunable RTP, as well as provides new insight into the effect of halogens on the regulation of RTP.

Harnessing Solar Power for Oxidation of Organic Compounds by Re(I)Dipyrrinato Complexes.

Metal dipyrrinato complexes of 4d and 5d metals have distinctive features such as high absorption coefficients in the visible section and room temperature phosphorescence in the red region. This work demonstrates the light-assisted oxidation of organic compounds employing rhenium(I)dipyrrinato complexes as catalysts. The heavy atom effect in rhenium(I)dipyrrinato complexes leads to the formation of long-lived triplet excited states, and these complexes can generate singlet oxygen in excellent yields (up to 84 %). A method was developed for photocatalytic aerobic oxidation of sulfides and amines using only 0.05 mol % and 0.025 mol % of the rhenium(I)dipyrrinato complexes, respectively. The method is efficient, and within 2 h, a variety of substrates were oxidized to produce sulfoxides and imines in high yields (up to 97 %). Rhenium(I)dipyrrinato complexes work very well both in visible light and sunlight, making them promising candidates for photocatalytic applications.

Stable Persistent Room-Temperature Phosphorescent Hydrogels Based on Ionically Crosslinked Nonaromatic Carboxylate Polymers.

Developing pure organic room-temperature phosphorescent (RTP) hydrogels is important for expanding the practical applications of phosphorescent materials. However, most of the reported RTP hydrogels containing aromatic phosphors suffer from short phosphorescent lifetimes, unstable underwater RTP emissions, and complex preparation processes. Herein, novel nonaromatic RTP hydrogels are prepared by using two types of non-traditional luminescent polymers, sodium alginate and a polymeric carboxylate, which are not RTP emissive or very weakly emissive in aqueous environments. The prepared hydrogels exhibit the following features: I) color-tunable RTP emissions with ultra-long lifetimes up to 451.1ms, II) excellent anti-swelling properties and stable persistent RTP emission even after being immersed in deionized water for months, III) efficient and large-scale preparation of hydrogel fibers by wet spinning technique. Experiment results and theoretical calculations show that the stable and long-lifetime RTP emissions of the hydrogels originate from the introduction of more nonconventional chromophores which are strongly crosslinked with ionic bonding between carboxylate groups and calcium ions and enhanced through-space interactions between them. This work provides a reliable strategy for designing nonaromatic hydrogels with stable and persistent RTP.

A 1H-imidazo[4,5-f][1,10]phenanthroline based ligand and its binuclear Cu(I) complexes: Syntheses, structures and luminescence sensing for Cr2O72− and MnO4−

Dichromate (Cr2O72−) and permanganate (MnO4−) ions have been important targets for sensing and detection in the field of luminescent complexes and their corresponding ligands due to their significant impact on the ecological environment and human health. However, many Cu(I) complexes with good room-temperature phosphorescence are rarely used as luminescent sensors for ions in water due to the insolubility and the disproportionation of the Cu(I) ion. Herein, 2,6-di-1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl-4-tertbutylphenol (diptpH3) and its two luminescent binuclear Cu(I) complexes, [Cu(diptpH3)(POP)]ClO4 (1) and [Cu(diptpH3)(xantphos)]ClO4 (2), were designed and synthesized (POP = bis[(2-diphenylphosphino)phenyl] ether, and xantphos = 9,9-dimethyl-4,5-bis(diphenylphosphino)-9H-xanthene). All compounds in DMSO/H2O (1: 9, v: v) show high stability to water, which was confirmed by the results of electrospray ionization mass spectrometry (ESI-MS). Cr2O72− and MnO4− ions showed high luminescence quenching coefficients (Cr2O72−: 3.042 × 104 − 2.946 × 105 M−1; MnO4−: 1.476 × 104 − 2.254 × 105 M−1) for all the three compounds. DiptpH3, complexes 1 and 2 exhibited good luminescent sensing properties toward Cr2O72− and MnO4− ions with short response times, good selectivity and low detection limits (Cr2O72−: 1.845 × 10−7 − 2.359 × 10−6 mol⋅L−1; MnO4−: 1.850 × 10−7 − 6.221 × 10−6 mol⋅L−1) in DMSO/H2O. The plausible sensing mechanisms were fully discussed.

Thermal Annealing Effects on Long-Lived Fluorenol Room Temperature Phosphorescence for Styrene Detection.

Fluorene derivatives have been widely developed in OLEDs because of its efficient fluorescence quantum efficiency, but for which unique rigid biphenyl planar structure and large conjugated system, we hypothesize that they have a great potential for room temperature phosphorescence (RTP) applications, and confirmed this conjecture by subjecting polyvinyl alcohol (PVA) and phosphors to thermal annealing. The cross-linked structure formed during thermal annealing judiciously modulates the phosphorescence emission characteristics of the fluorenol with the synergistic interaction between PVA and fluorenol. Specifically, the lifetime exhibited a substantial increase from 1352.2 ms to 2874.1 ms, accompanied by a quantum yield augmentation from 4.8 % to 11.3 %, which substantiate that cross-linked induced by thermal annealing effectively amplifies the phosphorescent intensity and stability of the phosphors, facilitating ultralong phosphorescent emission at ambient conditions. Furthermore, an effective probe based on this film is developed for its highly sensitive, quantitative and immediate detection of volatile organic compounds. This investigation not only proffers a novel paradigm for the development of advanced RTP materials but also imparts insightful considerations for optimizing the performance of polymers in conjunction with functional materials, encompassing bioimaging, sensing, and optoelectronic devices.

Simple Organic Host/Guest Room Temperature Phosphorescence Materials and Their Application in Security Printing

Simple Organic Host/Guest Room Temperature Phosphorescence Materials and Their Application in Security Printing

Heavy-Atom-Free Covalent Organic Frameworks for Organic Room-Temperature Phosphorescence via Förster and Dexter Energy Transfer Mechanism.

Covalent organic frameworks (COFs), with their accessible nanoscale porosity, selectable building blocks, and precisely engineered topology, offer unique benefits in the design of room-temperature phosphorescent (RTP) materials. However, their potential has been limited by phosphorescence quenching caused by interlayer π-π stacking interactions. This paper presents a novel strategy to enhance RTP in heavy-atom-free COFs by employing a donor-acceptor (D-A) system that leverages the Förster resonance energy transfer (FRET) and Dexter energy transfer (DET) mechanisms. Among the materials investigated, the best-performing COF exhibits a phosphorescence lifetime of 4.35ms at room temperature. Spectral analysis, structural analysis, and theoretical calculations indicate the presence of intralayer FRET processes as well as interlayer DET processes within the D-A COF system. Potential anti-counterfeiting applications are explored by exploiting the unique phosphorescent properties of these materials. Additionally, the inherent permanent porosity of COFs presents new opportunities for future development and application. This strategy offers many promising prospects for advancing the RTP technology in COF materials and broadens their potential applications in various fields.

Coordination‐Induced Structural Rigidity for Achieving Ultralong‐Lived Aqueous Room Temperature Phosphorescence

Coordination‐Induced Structural Rigidity for Achieving Ultralong‐Lived Aqueous Room Temperature Phosphorescence

Oxygen-doped Carbon Nitrides with Visible Room-temperature Phosphorescence and Invisible Thermal-Stimuli-Responsive Ultraviolet Delayed Fluorescence for Security Applications.

Multi-mode emissive materials with stimuli-responsive producing invisible signals are very attractive for advanced security applications, but development of such materials remains highly challenging. In this work, oxygen-doped carbon nitrides (O-CNs) are prepared via microwave-assisted heating of urea, which exhibit ultraviolet (UV) solid-state fluorescence (SSFL), visible room temperature phosphorescence (RTP) and thermal-stimuli production of invisible UV delayed fluorescence (DF) properties. Further studies confirmed that the SSFL and RTP could be attributed to the introduction of oxygen functional group (e.g., C=O) in the skeleton of O-CNs, thus minimizing the aggregation caused quenching effect, facilitating intersystem crossing, and stabilizing the excited triplet states. The specific thermal-stimuli production of UV DF is deemed to be the relatively large energy gap between ground and excited singlet states as well as an effective triplet-triplet annihilation. Notably, the emission maximum of UV DF locates at ~310 nm with an ultra-narrow full width at half maximum (FWHM) down to 19 nm, so it is completely invisible to the naked eyes, but detectable by a UV camera. To employ the unique characteristics of O-CNs, security protection strategies with superior concealment by virtue of the thermal-stimuli quenching visible RTP and meanwhile producing invisible UV DF are demonstrated.

Oxygen‐doped Carbon Nitrides with Visible Room‐temperature Phosphorescence and Invisible Thermal‐Stimuli‐Responsive Ultraviolet Delayed Fluorescence for Security Applications

Multi‐mode emissive materials with stimuli‐responsive producing invisible signals are very attractive for advanced security applications, but development of such materials remains highly challenging. In this work, oxygen‐doped carbon nitrides (O‐CNs) are prepared via microwave‐assisted heating of urea, which exhibit ultraviolet (UV) solid‐state fluorescence (SSFL), visible room temperature phosphorescence (RTP) and thermal‐stimuli production of invisible UV delayed fluorescence (DF) properties. Further studies confirmed that the SSFL and RTP could be attributed to the introduction of oxygen functional group (e.g., C=O) in the skeleton of O‐CNs, thus minimizing the aggregation caused quenching effect, facilitating intersystem crossing, and stabilizing the excited triplet states. The specific thermal‐stimuli production of UV DF is deemed to be the relatively large energy gap between ground and excited singlet states as well as an effective triplet‐triplet annihilation. Notably, the emission maximum of UV DF locates at ~310 nm with an ultra‐narrow full width at half maximum (FWHM) down to 19 nm, so it is completely invisible to the naked eyes, but detectable by a UV camera. To employ the unique characteristics of O‐CNs, security protection strategies with superior concealment by virtue of the thermal‐stimuli quenching visible RTP and meanwhile producing invisible UV DF are demonstrated.

Time-Dependent Color-Changing Room-Temperature Phosphorescence Materials with Mutual Achievement between Guest and Host Molecules.

Host-guest doping strategy has gradually become the mainstream in constructing organic room-temperature phosphorescence (RTP) materials. The two-component doped system typically emits monochromatic phosphorescence dominated by the guest molecule, which also means that the intrinsic phosphorescence emission of the host molecule is not well utilized. In this work, a time-dependent color-changing RTP material is constructed based on host-guest doped system, in which the initial yellow phosphorescence stems from the isoquinoline-pyrazole guest and the final cyan phosphorescence originates from the intrinsic emission of the polymer host. The phenomenon of the strong interaction between host and guest molecules leading to their respective intrinsic phosphorescence provides new design inspiration for designing and developing two-component doped materials with RTP properties of color variation over time.

Achieving Near-Infrared Phosphorescence Supramolecular Hydrogel Based on Amphiphilic Bromonaphthalimide Pyridinium Hierarchical Assembly.

Phosphorescent supramolecular hydrogels are currently a prevalent topic for their great promise in various photonic applications. Herein, an efficient near-infrared (NIR) phosphorescence supramolecular hydrogel is reported via the hierarchical assembly strategy in aqueous solution, which is fabricated from amphiphilic bromonaphthalimide pyridinium derivative (G), exfoliated Laponite (LP) nanosheets, and polymeric polyacrylamide (PAAm). Initially, G spontaneously self-aggregates into spherical nanoparticles covered with positively charged pyridinium units and emits single fluorescence at 410nm. Driven by electrostatic interactions with negatively charged nanosheets, the nanoparticles subsequently function as the cross-linked binders and coassemble with LP into supramolecular hydrogels with an engendered red room-temperature phosphorescence (RTP) up to 620nm. Benefiting from hydrogen-bonding interactions-mediated physical cross-linkage, the further introduction of PAAm not only significantly elevates the mechanical strength of the hydrogels showing fast self-healing capability, but also increases phosphorescence lifetime from 2.49to 4.20ms, especially generating phosphorescence at even higher temperature (τ 363 K = 2.46ms). Additionally, efficient RTP energy transfer occurs after doping a small amount of organic dye heptamethine cyanine (IR780) as an acceptor into hydrogels, resulting in a long-lived NIR emission at 823nm with a high donor/acceptor ratio, which is successfully applied for cell labeling in the NIR window.

Rational Design of Multi‐color Phosphorescent Carbon Dots Based on Binaphthyldiamine with Chiral Signals

Comprehensive SummaryChiral phosphorescent materials have received extensive research owing to the unique properties of optical activity in recent years. Many phosphorescent carbon dots (CDs) materials have been reported, but the research on chiral phosphorescence is still in the exploratory stage. This work designs multi‐color room temperature phosphorescent (RTP) CDs with chiral signals, which are fully mixed with aromatic aldehyde precursors and chiral amino compounds precursors in a boric acid (BA) matrix and can be easily prepared by solvent‐free thermal method. The prepared (R)‐GCDs, (R)‐YCDs and (R)‐RCDs achieved phosphorescence emission at 545 nm, 582 nm, and 654 nm, respectively, and exhibited corresponding circular dichroism (CD) signals at 341 nm, 394 nm, 384 nm, and 380 nm, 448 nm, and 435 nm, respectively. The longest phosphorescence lifetime is up to 946 ms. Specifically, YCDs exhibit time‐dependent phosphorescence under UV excitation, and the afterglow time under white light excitation can reach 40 s. This article provides a new approach to the study of chiral phosphorescence.

Photoactivated room temperature phosphorescence from lignin

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