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Room-temperature phosphorescent (RTP) carbon dots (CDs) have been increasingly used in many applications, including anticounterfeiting and information encryption. However, synthesizing RTP CDs with a specific average lifetime of phosphorescence remains a formidable challenge. A breakthrough is needed in formulating the synthesis process to find a suitable synthesis formulation to produce CDs with an optimal lifetime of phosphorescence. Machine learning (ML) has recently been successfully used for guiding material synthesis and offering insight into the prediction, optimization, and acceleration of the CDs' synthesis process. A regression ML model on microwave-assisted CD synthesis is established to reveal the relationship between various synthesis parameters and enhance the average lifetime of phosphorescence of CDs in the solid-state phase. RTP CDs exhibit a blue emission when irradiating with UV and a green emission afterglow after the UV is turned off. These green emissions can last for 7 s, are easily observed by the naked eye, and show an ultralong phosphorescence lifetime of up to 1.6 s. Moreover, designed and guided by ML, this afterglow feature was explored to achieve multilevel anticounterfeiting and information encryption to encrypt and decrypt secret information in dynamic time-dependent displays. Our results provide a strategy for synthesizing RTP CDs with a specific lifetime and extending their application scope to high-level information security. [ABSTRACT FROM AUTHOR]

A short lifetime, low phosphorescence quantum efficiency (PQE), and unstable room-temperature phosphorescence (RTP) in oxidants and solvents are the core problems in the development of carbon dot (CD)-based RTP materials for anticounterfeiting applications. Herein, a series of CDs/Al2O3 nanocomposites with excitation-dependent RTP properties were fabricated by a sol–gel process followed by high-temperature treatment. The crystalline structure and rigid Al–O network of the Al2O3 matrix could readily benefit the stabilization of the triplet excited state of CDs. The Al–O–C interactions between the CDs and Al2O3 favor the facilitation of intersystem crossing (ISC) to effectively populate triplet excitons, which contributes to the RTP with a low energy gap. As a result, an ultralong lifetime of up to 1.4 s (observed by the naked eye for 22 s) and a high PQE of 12.78% were achieved by CDs/Al2O3-500 and CDs/Al2O3-300, respectively. The results demonstrated that the oxidants, polar solvents, and strong acids and alkalis almost had no effect on the RTP emission of the CDs/Al2O3 nanocomposites. Taking advantage of the ultralong phosphorescence afterglow, excitation-dependent multicolor RTP emission, and excellent stability, graphics of the Eight Trigrams were present for advanced anticounterfeiting via time-resolved luminescence imaging based on different CDs/Al2O3 nanocomposites. [ABSTRACT FROM AUTHOR]

Room-temperature phosphorescence (RTP) carbon dots (CDs) materials have garnered considerable attention from researchers because of their potential applications in anti-counterfeiting. However, the in situ preparation of CDs-based RTP materials with long lifetime and excellent stabilitie remains a considerable challenge. Herein, an in situ manufacturing strategy is proposed to fabricate CDs@Allophane core–shell nanoparticles with double confinement via a simple one-step calcination method. The double confinement arises due to the formation of strong covalent bonds and highly rigid structures via calcination. This double confinement mechanism effectively suppresses the vibration of light-emitting molecules, nonradiative transition of triplet excitons, and environment-induced quenching, affording CDs@Allophane materials with a 1.02 s long lifetime (more than 14 s to the naked eye) and excellent stability. These composites can be preliminarily applied in anti-counterfeiting. This study provides a design approach for the in situ manufacturing of CDs-based RTP materials with a long lifetime and high stability. [ABSTRACT FROM AUTHOR]

Long-lifetime room-temperature phosphorescence (RTP) materials have various applications in many fields due to their long-lived emission and large signal-to-noise ratio. However, it is not easy to attain long-lifetime RTP materials owing to the spin-forbidden nature of triplet exciton transitions. Herein, yellow phosphorescence carbon-dot-based composites embedded in a MgO matrix (MgCDs) have been developed, and the lifetimes were up to 1.81 s (more than 11 s to the naked eye) in a solid state and 254 ms (more than 9 s to the naked eye) in water. X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), and XPS analyses were performed, and the structural characterizations indicate that carbon dots (CDs) embedded in the rigid magnesium oxide matrix restrict the vibration and rotation of CDs chromophores and suppress nonradiative recombination of triplet excitons. Further studies unveiled that the barrier effect of the insoluble MgO matrix on oxygen is likely mainly responsible for the observed long-lived RTP in water. In addition, the codoping of N, P, and Mg elements, as well as the carbonization degree, play an important role in the luminescence properties of MgCDs. Last but not least, applications in bioimaging, screen printing, anticounterfeiting, and information protection are also explored. This work offers fresh ideas for developing ultralong lifetime afterglow materials that can be applied in versatile applications. [ABSTRACT FROM AUTHOR]

Room-temperature phosphorescence (RTP) holds tremendous potential in various fields such as optoelectronic devices, bioimaging, and information security applications. However, achieving efficient RTP in aqueous environments has been a challenge due to nonradiative deactivation caused by dissolved oxygen and solvent-induced relaxation. In this study, we propose a design strategy to enhance the phosphorescence emission of carbon dots (CDs) in aqueous solutions by constructing hydrogen-bonded networks between CDs and ammeline (AM). The formation of robust hydrogen-bonded networks, combined with the synergistic effect of bound water, significantly enhances the phosphorescence emission by stabilizing the triplet excited states of CDs. Furthermore, the prepared AM-CD suspension exhibits an exceptionally long phosphorescence lifetime of up to 697.58 ms, showcasing its potential applications in two-photon information encryption and decryption. [ABSTRACT FROM AUTHOR]

Room-temperature phosphorescence (RTP) plays an important role in the field of information encryption due to its ability to effectively eliminate interference caused by background fluorescence (FL). Herein, a series of RTP carbon dots (CDs) containing different nitrogen contents were prepared via a molten salt method. In the reaction system, magnesium chloride and potassium nitrate were used as doping salts to form salt shells, and potassium nitrate was used as salt medium to promote the reaction. By adjusting the amount of melamine, the synthesized CDs-3 exhibit cyan FL and yellow phosphorescence, with a long phosphorescence lifetime of 673.29 ms. It is worth noting that the yellow RTP can be maintained either in dry or wet state, which facilitates for the information encryption. It is suggested that the salt shell composed of magnesium salt with high charge density has a rigid structure, which inhibits the nonradiative transition process of the triplet-state exciton and enhances the phosphorescence intensity. Unfortunately, when the amount of melamine increases to a certain extent, due to the incomplete encapsulation of the salt shell, the phosphorescence of the prepared CDs quenches accordingly. In addition, CDs-3 can also be mixed with epoxy resin to obtain the desired fluorescent/phosphorescent composites. These excellent optical properties indicate that the synthesized CD materials have great development prospects in fields such as anti-counterfeiting and luminescent materials. [ABSTRACT FROM AUTHOR]

Stimuli-responsive organic afterglow materials, which feature long-lived excited states compared to their fluorescence counterparts, have been shown to exhibit distinct advantages to work normally even in the presence of a strong fluorescence background. However, most stimuli-responsive afterglow materials only function in the solid state, with those in the aqueous environment being rarely explored. Besides, most responsive afterglow systems can only respond to single stimulus. Here, we report the fabrication of thermally activated delayed fluorescence (TADF)-type organic afterglow nanoparticles with temperature and oxygen dual-responsive property in an aqueous environment. Experimental and computational studies reveal that the key to realize the dual responsiveness is the TADF mechanism. The kRISC/kP ratio determines the TADF/phosphorescence intensity ratio and consequently afterglow color, where kRISC and kP represent the reverse intersystem crossing rate and phosphorescence rate, respectively. The dark triplets of TADF-type afterglow nanoparticles are sensitive to oxygen, whose intensity and lifetime would increase in the hypoxia condition. Since the afterglow color and TADF intensity (or lifetime) can be monitored at different channels for potential multiplexed sensing, the temperature and oxygen dual-responsive afterglow nanoparticles would display promising application in the biomedical area. [ABSTRACT FROM AUTHOR]

Multicolor tuning is one of the most remarkable features of carbon dots (CDs), used as a color convertor in making white-light-emitting diodes (WLEDs). Herein, a solvent-controlled method has been employed to prepare the multicolor-emissive CDs from 1,2,4-triaminobenzene and melamine, where the green-, orange-, and red-color-emissive carbon dots (G-, O-, and R-CDs) have been synthesized in acetone, water, and dimethylformamide (DMF), respectively. It has noted that the reaction solvent has impacted the growth of the particle size, elemental concentration, surface functionalization, and ultimately fluorescence emission. To avoid aggregation quenching emission (AQE), fluorescent polymeric films have been shaped by mixing poly-(methyl methacrylate) (PMMA) with R- and G-CDs, while O-CDs was made with poly-(vinyl alcohol) (PVA). Interestingly, PVA exhibited red-shifted emission of O-CDs from 585 to 597 nm in O-CDs/PVA, while PMMA accompanied a blue-shifting emission. The enriched nitrogen and oxygen elemental contents, especially the graphitic N of O-CDs/PVA, and hydrogen-bonding affinity of PVA cause the red-shifted emission of O-CDs/PVA. Fluorescent solid films have been used to develop monochromatic and white-color-emissive light-emitting diodes. Further, all of the synthesized CDs served as carbon precursors to develop room-temperature phosphorescence (RTP) by a molten salt method, where only R- and O-CDs achieved their RTP emissions with different intensities. The mechanism behind the RTP formation with particular CDs and their emission intensity dependency has been studied by the CO moieties. [ABSTRACT FROM AUTHOR]

Room-temperature phosphorescent (RTP) carbon dots (CDs) demonstrate significant potential applications in the field of information anticounterfeiting due to their excellent optical properties. However, RTP emission of CDs remains significantly limited due to the spin-forbidden properties of triplet exciton transitions. In this work, an in situ nitrogen doping strategy was employed to design and construct strong spin-orbit coupling nitrogen-doped CDs with mesoporous silica with alumina (N-CDs@MS@Al 2 O 3 ) RTP composites. Both experimental results and theoretical calculations confirmed that the formation of 1 (n, π*) following the introduction of nitrogen breaks the spin-forbidden restriction from 1 (π, π*) to 3 (π, π*), thereby enhancing spin-orbit coupling, which further promotes intersystem crossing and leads to the effective population of triplet excitons. The designed N-CDs@MS@Al 2 O 3 benefiting from an impressive long lifetime of 3.18 s demonstrates potential application prospects in the field of multilevel information encryption. This work provides a new concept to boost the RTP lifetime of CDs.

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) 2 ZnCl 2 , (2HP) 2 ZnBr 2 , (2TP) 2 ZnCl 2 , and (2TP) 2 ZnBr 2 (2HP = 2-hydroxypyridine, 2TP = pyridine-2-thiol). By changing the ligands and halides, a remarkable increase in the photoluminescence quantum yield of (2HP) 2 ZnCl 2 (44.7%) compared to (2TP) 2 ZnBr 2 (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.

Purely organic room temperature phosphorescence (RTP) materials are a new kind of triplet emitter, which can harvest both singlet and triplet excitons in theory, thus showing great application potential for organic light-emitting diodes (OLEDs). However, nondoped OLEDs based on RTP emitters have been rarely explored owing to challenges in realizing efficient phosphorescence in single-component systems. Herein, three donor-acceptor-type luminogens were designed and synthesized in which phenothiazine, with different oxidation degrees, acted as the electron donor and acetophenone as the acceptor. The adjustable oxidation states of phenothiazine enabled the modulation of excited states, facilitating the transition from dual RTP and thermally activated delayed fluorescence emissions to pure RTP. A nondoped OLED device was then fabricated based on the pure RTP emitter, achieving a high exciton utilization efficiency of 86%, clearly demonstrating the enhancement of electroluminescence performance through RTP properties.

Aggregation-induced phosphorescence (AIP) has attracted much attention for its unique luminescent characteristics. Nevertheless, this fascinating phenomenon is rarely reported in the field of carbon dots (CDs). Herein, a simple method to prepare CDs simultaneously with dispersion-state fluorescence, aggregation-state fluorescence, and phosphorescence is presented by a one-step solvothermal process. The resultant AIP CDs (A-CDs) display a long afterglow lifetime of 0.51 s in the aggregation state, lasting about 5 s to the naked eye. The phosphorescence emission of A-CDs resulted from the rigid, protective structure due to the aggregation state. In addition, inorganic silica has been employed as a doping matrix to effectively improve phosphorescent properties (1.11 s). Benefitting from the unique luminescence feature and excellent water dispersibility, the A-CDs can be dispersed directly in water, and the phosphorescent emission could be controlled by regulating the concentration, thus enabling information encryption. [ABSTRACT FROM AUTHOR]

Room-temperature phosphorescent carbon dots (RTP-CDs) have received increasing attention due to their excellent optical properties and potential applications. Nevertheless, the realization of RTP-CDs in aqueous solutions remains a considerable challenge due to the water-molecule- and oxygen-induced deactivation of the triplet excitons, which leads to phosphorescence quenching. In this study, ultralong phosphorescence in water was achieved by in situ self-assembly of CDs encapsulated in a rigid hydrogen-bonded organic framework (HOF). The phosphorescence lifetime reaches an impressive 956.96 ms and exhibits long-lasting optical and structural stability in water for more than 90 days. The composite material not only has ultralong luminescence life and excellent luminescence stability but also has two-color phosphorescence emission, as well as excellent antiphotobleaching and phosphorescence stability in aqueous solution, which can solve the current problem that RTP is easily burst out by water and moisture. In addition, this study introduced a fluorescent dye based on the triplet-singlet Förster resonance energy transfer system (TS-FRET) to fine-tune the afterglow properties. This work will inspire the design of RTP systems with dual phosphor light sources and provide new strategies for the development of smart RTP materials in water.

Sulfur dots are a new class of recently developed nonmetallic luminescent nanomaterials with various potential applications. Herein, we synthesized sulfur dots using a mild chemical etching method and then modified the structural features of the as-synthesized sulfur dots using a slow and defined solvent-assisted aggregation process. This increases the particle size and overall crystallinity along with the modifications of the surface functional groups, which eventually show a new emission band at longer wavelengths. Detailed photophysical and temperature-dependent luminescence studies confirmed that the new emissive state evolves due to interparticle interactions in the excited state. Furthermore, the occurrence of a new emissive state in a longer-wavelength region helped reduce the energy gap between the lowest excited singlet state and the lowest excited triplet state in modified sulfur dots, resulting in an aqueous stable room-temperature phosphorescence/afterglow emission through efficient intersystem crossing. This typical efficacious afterglow emission directly shows the potential applicability of structurally modified sulfur dots in encryption devices and can also be potentially effective in light emitting diodes (LED) and sensing devices.

It is of practical significance to develop polymer-based room-temperature phosphorescence (RTP) materials with ultralong lifetime and multicolor afterglow. Herein, the benzocarbazole derivatives were selected and combined with a poly(vinyl alcohol) (PVA) matrix by a coassembly strategy. Owing to the hydrogen-bonding interactions between benzocarbazole derivatives and the PVA matrix, the nonradiative transition and the quenching of triplet excitons are effectively inhibited. Therefore, the maximum phosphorescence emission lifetime of 2202.17 ms from ABfCz-PVA and the maximum phosphorescence quantum efficiency of 34.97% from ABtCz-PVA were obtained, respectively. In addition, commercially available dye molecules were selected to construct phosphorescent resonance energy transfer (PRET) systems for energy acceptors, enabling full-color afterglow emission in blue, green, yellow, red, and even white. Based on the characteristics of prepared RTP materials, multifunctional applications to flexibility, information encryption, and erasable drawing were deeply explored.

Carbon dots (CDs) are new carbon nanomaterials, among which those prepared from biomass are popular due to their excellent optical properties and environmental friendliness. As representative natural phenolic compounds, tea polyphenols are ideal precursors with fluorescent aromatic rings and phenolic hydroxyl structures. Usually, polyphenolic precursors can only be used to produce blue or green fluorescent CDs, and fluorescence in long wavelength domains, such as orange or red, cannot be achieved. Herein, the high reactivity of the phenolic hydroxyl groups in tea polyphenols with o -phthalaldehyde was exploited to modulate the pH during the carbonation process, which led to redshifts of the fluorescence wavelengths. Different pH values during the reaction caused the precursors to take different reaction paths and form fluorescent groups exhibiting different conjugated structures, resulting in carbon dots providing different fluorescent colors. Finally, by utilizing the in situ hydrolysis of ethyl orthosilicate, the tea polyphenol-based carbon dots were embedded into a silica matrix, inducing phosphorescence of the carbon dots. This study provides a new approach for green preparation and application of natural polyphenolic CDs.

Water/light regulated room-temperature phosphorescence (RTP) of polypseudorotaxane supramolecular gel is constructed by threading the poly(ethylene glycol)- block -poly(propylene glycol)- block -poly(ethylene glycol) (PEG-PPG-PEG) chain with the bromoaromatic aldehyde into mono-(6-ethylenediamine-6-deoxygenated)-β-cyclodextrin (ECD) cavities and further assembling with negatively charged Laponite XLG (CNS) and diarylethene derivative (DAE) through electrostatic interaction. This hydrogel exhibits significant blue fluorescence emission; instead, after lyophilization to xerogel, the system exhibits both blue fluorescence and yellow RTP based on the rigid network structure of the xerogel, which restricts the vibration of the phosphor and suppresses the nonradiative relaxation process. Interestingly, the addition of excess ECDs to the gel system can enhance the RTP emission. Furthermore, the reversible luminescence behavior can be adjusted by the photoresponsive isomerism of DAE and humidity. This polypseudorotaxane supramolecular gel system provides a novel strategy for constructing tunable RTP materials.

Developing polymer-based organic afterglow materials with switchable ultralong organic phosphorescence (UOP) that are insensitive to moisture remains challenging. Herein, two organic luminogens, BBCC and BBCS, were synthesized by attaching 7 H -benzo[ c ]carbazole (BBC) to benzophenone and diphenyl sulfone. These two emitters were employed as guest molecules and doped into epoxy polymers (EPs), which were constructed by in situ polymerization to achieve polymer materials BBCC-EP and BBCS-EP. It was found that BBCC-EP and BBCS-EP films exhibited significant photoactivated UOP properties. After light irradiation, they could produce a conspicuous organic afterglow with phosphorescence quantum yields and lifetimes up to 5.35% and 1.91 s, respectively. Meanwhile, BBCS-EP also presented photochromic characteristics. Upon thermal annealing, the UOP could be turned off, and the polymer films recovered to their pristine state, showing switchable organic afterglow. In addition, BBCC-EP and BBCS-EP displayed excellent water resistance and still produced obvious UOP after soaking in water for 4 weeks. Inspired by the unique photoactivated UOP and photochromic properties, BBCC and BBCS in the mixtures of diglycidyl ether of bisphenol A (DGEBA) and 1,3-propanediamine were employed as security inks for light-controlled multilevel anticounterfeiting. This work may provide helpful guidance for developing photostimuli-responsive polymer-based organic afterglow materials, especially those with stable UOP under ambient conditions.

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.

Organic solid-state materials with long-lived room-temperature phosphorescence (RTP) emission have been widely developed and applied in many fields, while works in developing solution-phase phosphorescence materials were rarely reported owing to the ultrafast nonradiative relaxation and quenchers from the liquid medium. Herein, we report an ultralong RTP system in water through assembly based on a β-cyclodextrin host and p -biphenylboronic acid guest with a lifetime of 1.03 s under ambient conditions. It is worth noting that the long-lived phosphorescence depends on the host-guest inclusion as well as intermolecular hydrogen bonding interactions, which suppress nonradiative relaxation and avoid quenchers effectively. Furthermore, the addition of fluorescent dyes to the assembly system achieved the tuning of the afterglow color through radiative energy transfer of reabsorption.

Room-temperature phosphorescent carbon dots (RTPCDs) have attracted considerable interests due to their unique nanoluminescent characteristic with time resolution. However, it is still a formidable challenge to construct multiple stimuli-activated RTP behaviors on CDs. Since the address of this issue facilitates complex and high-regulatable phosphorescent applications, we here develop a novel strategy to achieve a multiple stimuli responsive phosphorescent activation on a single carbon-dot system (S-CDs), using persulfurated aromatic carboxylic acid as the precursor. The introduction of aromatic carbonyl groups and multiple S atoms can promote the intersystem crossing process to generate RTP characteristic of the produced CDs. Meanwhile, by introducing these functional surface groups into S-CDs, the RTP property can be activated by light, acid, and thermal stimuli in solution or in film state. In this way, multistimuli responsive and tunable RTP characteristics are realized in the single carbon-dot system. Based on this set of RTP properties, S-CDs is applied to photocontrolled imaging in living cells, anticounterfeit label, and multilevel information encryption. Our work will benefit the development of multifunctional nanomaterials together with extending their application scope.

An in-depth understanding of structure-property relationships and the construction of multifunctional stimuli-responsive materials are still difficult challenges. Herein, we discovered a 4,4'-bipyridinium derivative with both photochromism and dynamic afterglow at 77 K for the first time. A one-dimensional (1D) Cd(II) coordination polymer ( 1 ) assembled by only a 4,4'-bipyridinium derivative and cadmium chloride showed photochromism, room-temperature phosphorescence (RTP), and electrochromism. Interestingly, we found that 1 underwent single-crystal-to-single-crystal transformation during the anion exchange process, and the color of the crystal changed from colorless to yellow ( 1-SCN - ) within 10 min. Complex 1 exhibited photochromism, whereas 1-SCN - did not. The difference in the photochromic behavior between the two complexes was ascribed to the electron transfer pathway between the carboxylate groups and viologen. The DFT calculation based on the crystal structure of 1-SCN - indicated that the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) were mainly located on bipyridine and cadmium atoms, eliminating the possibility of electron transfer, whereas for complex 1 , electron transfer was probable from O and Cl atoms to pyridinium N atoms in viologen as demonstrated by density of states (DOS) calculations. In addition, complex 1 was successfully made into test paper for the rapid detection of I - and SCN - and displayed potential applications in inkless printing, multiple encryption, and anticounterfeiting.

Molecular persistent luminescence, such as room-temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF), have attracted broad attention in the fields of biological imaging, information security, and optoelectronic devices. However, the development of molecular micro/nanostructures combining both RTP and TADF properties is still in an early stage. Herein, a new type of organic metal hybrid perovskitoid (OMHP) two-dimensional (2D) microcrystal has been fabricated through a facile solution method. The long-lived TADF-RTP dual emission can be highly tuned by changing the excitation wavelength, temperature, and decayed time. Moreover, the 2D OMHP microsheet exhibits an asymmetric and anisotropic optical waveguide with low optical loss coefficient, together with extremely high linearly polarized fluorescence-phosphorescence emission (anisotropy = 0.96), which is promising for the development of polarization-sensitive luminescent materials. Therefore, this work not only demonstrates new OMHP showing colorful persistent luminescence under different modes (such as excitation wavelength, temperature, polarization, lifetime, and dimension) but also takes advantage of the 2D micro/nanostructure to provide potential applications as optical logic gates and for delicate multiple information encryption.

Carbon dots (CDs) have aroused widespread interest in the construction of room-temperature phosphorescent (RTP) materials. However, it is a great challenge to obtain simultaneous multicolor long-wavelength RTP emission and excellent stability in CD-based RTP materials. Herein, a novel and universal "CDs-in-YOHF" strategy is proposed to generate multicolor and long-wavelength RTP by confining various CDs in the Y(OH) x F 3- x (YOHF) matrix. The mechanism of the triplet emission of CDs is related to the space confinement, the formation of hydrogen bonds and C-F bonds, and the electron-withdrawing fluorine atoms. Remarkably, the RTP lifetime of orange-emissive CDs-o@YOHF is the longest among the reported single-CD-matrix composites for emission above 570 nm. Furthermore, CDs-o@YOHF exhibited higher RTP performance at long wavelength in comparison to CDs-o@matrix (matrix = PVA, PU, urea, silica). The resulting CDs@YOHF shows excellent photostability, thermostability, chemical stability, and temporal stability, which is rather favorable for information security, especially in a complex environment.

Molecule-based afterglow materials with ultralong-lived excited states have attracted great attention owing to their unique applications in light-emitting devices, information storage, and anticounterfeiting. Herein, a series of new types of two-component ionic crystalline materials were fabricated by the self-assembly of cytosine and different anions under ambient conditions. The multiple intermolecular interactions of cytosine with phosphate and halogens anions can lead to abundant energy levels and different crystal stacking modes to control molecular aggregation and excited-state intermolecular proton transfer (ESIPT) process. Interestingly, H-aggregation-induced green to yellow room-temperature phosphorescence (RTP) and ESIPT-dominated cyan RTP to deep blue thermally activated delayed fluorescence (TADF) emission can be generated by tuning excitation wavelength, time evolution, and temperature. Furthermore, the combination of two-component ionic crystals can be used as multicolored candidates for quadruple information encryption. Therefore, this work not only develops an anion-modulated strategy to achieve color-tunable afterglow from both static and dynamic fashions but also provides a guideline for designing forward/reverse excitation-dependent luminescent materials.

Supramolecular materials exhibiting unique functions unavailable from their individual components are attracting great attention. Here, we report a novel supramolecule emission strategy, where the emission originated from a two-dimensional (2D) ionic hydrogen bond (H-bond) supramolecular network. High-quality crystals were obtained by rapid self-assembly of liquid aliphatic amine and ketone. The 2D ionic H-bonding network was characterized by single-crystal X-ray diffraction (XRD) that shows a planar electron system similar to aromatic species. First-principles calculations demonstrated that the charge-separated transition process and high spin-orbital coupling constants of the rigid supramolecular structure contribute to the enhanced singlet-triplet intersystem crossing process. The emission could be well regulated via the substituents of either the enol or amine part, and a maximum quantum efficiency of 26% was realized. The emission system demonstrated stable room-temperature phosphorescence (RTP), which is even hard to obtain for aromatic species, and the lifetime reached 0.45 s with an 8% luminescence quantum yield. For application, with liquid amine and enol as ink, high-quality RTP patterns can be fabricated by computer-controlled precision printing. Our findings will surely bring completely fresh thinking for photoluminescence and other functions purely originated by the supramolecular structure.

Amorphous nonconjugated room-temperature phosphorescent (RTP) polymers have aroused ever-increasing attention. However, the variety of such polymers is still rare due to limited preparation strategies. Herein, we report a facile strategy to achieve ultralong RTP emission in biobased nonconjugated polymers through a hydrolyzation process. The investigated polymers are synthesized by free radical solution copolymerization using biomass methyl isoeugenol and maleic anhydride as monomers. Noticeably, the obtained polymers carry no conventional fluorescent units but can exhibit blue fluorescence. More interestingly, after hydrolysis in sodium hydroxide aqueous solution, the resulting hydrolyzed polymers emit both enhanced blue emission and persistent RTP (up to 400 ms) under air conditions, with reversible emission performance switched via the uptake and removal of water. Also worthy to be highlighted is that the emission can be remarkably regulated by the cations in carboxylate or the substituents on the benzene ring. The as-obtained polymers demonstrate potential applications in anticounterfeiting and information encryption.

Films with the capacity for photoluminescence and haze, which can convert UV to visible light and enhance light management, are of great importance for optoelectronic devices. Here, taking advantage of the inherent fluorescence and self-assembly properties of lignin, we have developed a sustainable lignin-derived multifunctional dopant (L-MS-NPs) for fabricating optical films with haze, fluorescence, and room-temperature phosphorescence (RTP) together with poly(vinyl alcohol) (PVA). The optical films are used to improve the light-harvesting efficiency of solar cells. Specifically, attributed to the robust morphology in the film matrix, L-MS-NPs cause a rough morphology in the surface of an L-MS-NPs/PVA composite film, which eventually triggers the great optical haze. Additionally, L-MS-NPs inherit fluorescence properties from lignin and show fluorescence emission when embed in the film matrix. Moreover, the PVA film matrix can stabilize the excited triplet state, which finally induces RTP of L-MS-NPs. The combined haze, fluorescence, and RTP properties of the L-MS-NPs/PVA composite film enhances the power conversion efficiency (PCE) of dye-sensitized solar cells from ∼3.9 to ∼4.1%.

Developing room-temperature phosphorescence (RTP) materials with color-tunability performance in an aqueous environment is crucial for application in optoelectronic areas to a higher stage, such as multicolor display, visual detection of external stimulus, and high-level information anticounterfeiting, but still faces a formidable challenge. Herein, we propose an efficient design strategy to develop excitation wavelength-responsive RTP supramolecular co-assembly systems of a simple benzoic acid derivative and Laponite ( Lap ) clay nanoplates in aqueous solution, displaying an ultralong lifetime (0.632 s) and a high phosphorescence quantum efficiency (18.04%) simultaneously. Experimental and theoretical research studies suggest that this distinctive feature is due to the generation of more and efficient intersystem crossing pathways benefiting from the coexistence of isolated and J-aggregation states via controlling the doping of the benzoic acid derivative and the inhibition of phosphorescence quenching by water because of the synergistic effects of robust hydrogen-bonding interactions between Lap and the benzoic acid derivative, J-aggregations of the benzoic acid derivative, and good oxygen tolerance of the Lap clay. By virtue of their excellent RTP performances in aqueous solution, the visual colorimetric detection of Ag + in a water environment was achieved for the first time, and visible and high-level information encryption was accomplished as well.

Circular polarized luminescence (CPL) is essential to chiral sciences and photonic technologies, but the achievement of circular polarized room-temperature phosphorescence (CPRTP) remains a great challenge due to the instability of triplet state excitons. Herein, we found that dual CPL and CPRTP were demonstrated by hybrid chiral photonic films designed by the coassembly of cellulose nanocrystals (CNCs), poly(vinyl alcohol) (PVA), and carbon dots (CDs). Tunable photonic band gaps were achieved by regulating the ratio of CNC/PVA in the hybrid films, leading to tunable CPL with invertible handedness, tunable wavelengths, and considerable dissymmetric factors ( g lum ) up to -0.27. In particularly, triplet excitons produced by CDs were stable in the chiral photonic crystal environment, resulting in tunable right-handed CPRTP with long lifetimes up to 103 ms and large RTP dissymmetric factors ( g RTP ) up to -0.47. Moreover, patterned films with multiple polarized features were demonstrated by a mold technique.

Recently, the room-temperature phosphorescence (RTP) properties of carbon dots (CDs) have attracted significant interest. However, the regulation of RTP emission faces great challenges because of untunable emissive lifetime and wavelength. Here, ultrahigh-yield acrylamide-based N-doped carbonized polymer dots (AN-CPDs) with ultralong RTP lifetime are synthesized by a one-step hydrothermal addition polymerization and carbonization strategy. The RTP lifetime and wavelength of the proposed AN-CPDs can be regulated by changing the carbonization degree. Thus, the AN-CPDs' RTP lifetimes are in the range of 61.4-466.5 ms, while the RTP emission wavelengths vary from 485 to 558 nm. Further experiment and theoretical calculation proved that RTP can be attributed to the polymer/carbon hybrid structure and nitrous functional groups as the molecular state related emission centers. Supramolecular cross-linking in the aggregated state is vital for the RTP emission of the AN-CPDs by restricting the nonradiative transition of the triplet excitons. AN-CPDs of different RTP lifetimes can be applied to time-resolved multistage information encryption and multistage anticounterfeiting. This work facilitates the optical regulation and application potential of CDs and provides profound insights into the effect of the polymer/carbon hybrid structure on the properties of CDs.

Formaldehyde (FA) is a widespread indoor air pollutant, and its efficient detection is a major industrial challenge. The development of a building material with real-time and visual self-detection of FA gas is highly desirable for meeting both construction and human health demands. Herein, a luminescent transparent wood (LTW) as the building material was developed for dual-channel, real-time, and visual detection of FA gas. It was fabricated by encapsulating multicolor lignin-derived carbon dots (CDs) and poly(vinyl alcohol) (PVA) into a delignified wood framework. It exhibited 85% optical transmittance, tunable room-temperature phosphorescence (RTP), and ratiometric fluorescence (FL) emission. The tunable luminescence was attributed to different CD graphitization and surface functionalization. The color-responsive ratiometric FL and delayed RTP detections of FA were displayed over the range of 20-1500 μM ( R 2 = 0.966, LOD = 1.08 nM) and 20-2000 μM ( R 2 = 0.977, LOD = 45.8 nM), respectively. The LTW was also used as an encapsulation film on a UV-emitting InGaN chip to form white light-emitting diodes, indicating the feasibility as an FA-responsive planar light source. The operational notion of functional LTW can expand its applications to new fields such as a stimuli-responsive light-transmitting window or planar light sources while monitoring indoor air pollutants, temperature, and humidity.

Metal-free organic phosphorescent materials are promising alternatives to the organometallic counterparts predominantly adopted in organic light-emitting diodes due to their low cost, chemical stability, and large molecular design window. However, only a few reports on OLED devices incorporating metal-free organic phosphors have been presented due to the lack of understanding on material properties, device physics, and device fabrication processes. Here, we report a tailor-designed novel fluorene-based organic phosphor with efficient spin-orbit coupling activated by bromine, aromatic carbonyl, and spiro-annulated phenyl moieties. Photoluminescence quantum yield of 24.0% was achieved when doped in optically inert amorphous polymer hosts. Effects of OLED host materials on the phosphor were investigated in terms of color purity, suppression of exciplex emission, and restraint of molecular motion. Bright green phosphorescence emission (1430 cd/m 2 at 100 mA/cm 2 ) was realized with 2.5% maximum external quantum efficiency at 1 mA/cm 2 .

The relationship between the thickness of surface molecularly imprinted polymers (MIPs) and specific recognition performance of transferrin (Trf) as well as the quantitative relation between the grafting amount of Mn-ZnS room-temperature phosphorescence (RTP) quantum dots (QDs) (short for PQDs) and RTP signals for recognition of Trf was analyzed in this study. Based on analysis results, RTP protein mesoporous imprinting microspheres (SiO 2 -PQDs-MIPs) with high specificity and strong interference resistance were developed using a mesoporous SiO 2 nanomaterial that can create more three-dimensional precise recognition sites as the matrix and using PQDs with strong resistance to background fluorescence interference as the luminescent materials. A discriminatory analysis of Trf was realized by the phosphorescence quenching principle based on light quenching caused by the photoinduced electron transfer. The concentration range, limit of detection, relative standard deviation, and imprinting factor of Trf detection under pH 7.4 are 0.05-1.0 μM, 0.014 μM, 3.23%, and 3.09, respectively. Although the sensing signals of SiO 2 -PQDs-MIPs for proteins are based on the phosphorescence of PQDs, they are particularly suitable for specific recognition and accurate quantitative detection of proteins in biological fluids. Research conclusions are expected to realize high-efficiency recognition of target proteins in actual biological samples.

Luminescent metal-organic frameworks (MOFs) have received much attention due to their applications in color displays, sensors, and smart materials. However, how to balance the energy distribution between singlet and triplet excited states for a new generation of persistent luminescent MOFs is still a challenging goal. In this work, we report that the construction of cluster-based MOFs can supply an effective way to modulate the fluorescence and room-temperature phosphorescence (RTP) emission based on adjustable π-π stacking, halogen-bonding interaction, and metal-cluster units. Compared to the pristine ligand (5-bromoisophthalic acid) with obvious spin-orbit coupling, Zn 5 and Zn 3 cluster-based MOFs exhibit tunable photoluminescence (such as fluorescence and RTP wavelength, lifetime, and quantum yield). The ultralong-lived RTP visualization and temperature-dependent luminescence also provide the Zn 5 cluster-based MOF as a new type of anticounterfeiting and temperature-responsive phosphorescent switch material. Therefore, this work highlights the first example of cluster-based MOFs as ultralong-lived persistent luminescent materials for tuning singlet and triplet excited states, which may be extended to other similar systems for developing ultralong RTP and delayed fluorescence materials.

The optical properties of meta-alkoxy-substituted difluoroboron dibenzoylmethane dyes were investigated in solution and in the solid state. Meta-alkoxy substitution induced strong intramolecular charge transfer (ICT) from the oxygen-donating substituent to the halide and boron acceptors in the excited state, as compared to the π-π* transition that is observed with para-alkoxy substitution. The optical properties of para- and meta-substituted alkoxy boron dyes were evaluated by calculations, in dilute solution, and in solid-state films. When embedded in amorphous matrixes (e.g., PLA, PMMA, PS, cholesterol), all dyes showed fluorescence (F) and phosphorescence (P) emission. In this report, we show that meta-substitution resulted in enhanced solvatochromism and an increased phosphorescence-to-fluorescence ratio in solid-state films compared to analogous para-substituted samples. With enhanced phosphorescence intensity via the heavy-atom effect, iodo-substituted dyes were further studied in PLA-PEG nanoparticles. Oxygen calibrations revealed stronger phosphorescence and a greater oxygen-sensing range for the meta- versus para-alkoxy-substituted dyes, features that are important for oxygen-sensing materials design.

Difluoroboron β-diketonate poly(lactic acid) materials exhibit both fluorescence (F) and oxygen sensitive room-temperature phosphorescence (RTP). Introduction of halide heavy atoms (Br and I) is an effective strategy to control the oxygen sensitivity in these materials. A series of naphthyl-phenyl (nbm) dye derivatives with hydrogen, bromide and iodide substituents were prepared for comparison. As nanoparticles, the hydrogen derivative was hypersensitive to oxygen (0-0.3%), while the bromide analogue was suited for hypoxia detection (0-3% O 2 ). The iodo derivative, BF 2 nbm(I)PLA, showed excellent F to RTP peak separation and an 0-100% oxygen sensitivity range unprecedented for metal-free RTP emitting materials. Due to the dual emission and unconventionally long RTP lifetimes of these O 2 sensing materials, a portable, cost-effective camera was used to quantify oxygen levels via lifetime and red/green/blue (RGB) ratiometry. The hypersensitive H dye was well matched to lifetime detection, simultaneous lifetime and ratiometric imaging was possible for the bromide analogue, whereas the iodide material, with intense RTP emission and a shorter lifetime, was suited for RGB ratiometry. To demonstrate the prospects of this camera/material design combination for bioimaging, iodide boron dye-PLA nanoparticles were applied to a murine wound model to detect oxygen levels. Surprisingly, wound oxygen imaging was achieved without covering (i.e. without isolating from ambient conditions, air). Additionally, would healing was monitored via wound size reduction and associated oxygen recovery, from hypoxic to normoxic. These single-component materials provide a simple tunable platform for biological oxygen sensing that can be deployed to spatially resolve oxygen in a variety of environments.

The dual-emissive properties of solid-state difluoroboron β-diketonate-poly(lactic acid) (BF2bdkPLA) materials have been utilized for biological oxygen sensing. In this work, BF2dbm(X)PLA materials were synthesized, where X = H, F, Cl, Br, and I. The effects of changing the halide substituent and PLA polymer chain length on the optical properties in dilute CH2Cl2 solutions and solid-state polymer films were studied. These luminescent materials show fluorescence, phosphorescence, and lifetime tunability on the basis of molecular weight, as well as lifetime modulation via the halide substituent. Short BF2dbm(Br)PLA (6.0 kDa) and both short and long BF2dbm(I)PLA polymers (6.0 or 20.3 kDa) have fluorescence and intense phosphorescence ideal for ratiometric oxygen sensing. The lighter halide-dye polymers with hydrogen, fluorine, and chlorine substitution have longer phosphorescence lifetimes and can be utilized as ultrasensitive oxygen sensors. Photostability was also analyzed for the polymer films.

Single-component materials with both fluorescence and room-temperature phosphorescence (RTP) are useful for ratiometric sensing and imaging applications. On the basis of a general design principle, an amino-substituted benzophenone is covalently incorporated into waterborne polyurethanes (WPU) and results in fluorescence and RTP single-component dual-emissive materials (SDMs). At different aminobenzophenone concentrations, the statistical, thermal, and optical properties of these SDMs are characterized. Despite their similar thermal behaviors, the luminescence properties as a function of the chromophore concentration are quite different: increasing concentrations led to progressively narrowed singlet-triplet energy gaps. The tunability of fluorescence and RTP via chromophore concentration is explained by a previously proposed model, polymerization-enhanced intersystem crossing (PEX). The proposal of PEX is based on Kasha's molecular exciton theory with a specific application in polymeric systems, where the polymerization of luminophores results in excitonic coupling and enhanced forward and reverse intersystem crossing. The mechanism of PEX is also examined by theoretical calculations for the WPU system. It is found that the presence of K1 aggregates indeed enhances the crossover from singlet excited states to triplet ones.