Color-Tunable, Excitation-Dependent, and Time-Dependent Afterglows from Pure Organic Amorphous Polymers

Functional Roles of Polymers in Room-Temperature Phosphorescent Materials: Modulation of Intersystem Crossing, Air Sensitivity and Biological Activity

Organic room-temperature phosphorescent (RTP) materials routinely incorporate polymeric components, which usually act as non-functional or "inert" media to protect excited-state phosphors from thermal and collisional quenching, but are lesser explored for other influences. Here, we report some exemplary "active roles" of polymer matrices played in organic RTP materials, including: 1) color modulation of total delayed emissions via balancing the population ratio between thermally-activated delayed fluorescence (TADF) and RTP due to dielectric-dependent intersystem crossing; 2) altered air sensitivity of RTP materials by generating various surface morphologies such as nano-sized granules; 3) enhanced bacterial elimination for enhanced electrostatic interactions with negatively charged bio-membranes. These active roles demonstrated that the vast library of polymeric structures and functionalities can be married to organic phosphors to broaden new application horizons for RTP materials.

Conformation-dependent dynamic organic phosphorescence through thermal energy driven molecular rotations

Organic room-temperature phosphorescent (RTP) materials exhibiting reversible changes in optical properties upon exposure to external stimuli have shown great potential in diverse optoelectronic fields. Particularly, dynamic manipulation of response behaviors for such materials is of fundamental significance, but it remains a formidable challenge. Herein, a series of RTP polymers were prepared by incorporating phosphorescent rotors into polymer backbone, and these materials show color-tunable persistent luminescence upon excitation at different wavelengths. Experimental results and theoretical calculations revealed that the various molecular conformations of monomers are responsible for the excitation wavelength-dependent (Ex-De) RTP behavior. Impressively, after gaining insights into the underlying mechanism, dynamic control of Ex-De RTP behavior was achieved through thermal energy driven molecular rotations of monomers. Eventually, we demonstrate the practical applications of these amorphous polymers in anti-counterfeiting areas. These findings open new opportunities for the control of response behaviors of smart-responsive RTP materials through external stimuli rather than conventional covalent modification method.

Switchable and Highly Robust Ultralong Room-Temperature Phosphorescence from Polymer-Based Transparent Films with Three-Dimensional Covalent Networks for Erasable Light Printing

In this work, an efficient polymer-based organic afterglow system, which shows reversible photochromism, switchable ultralong organic phosphorescence (UOP), and prominent water and chemical resistance simultaneously, has been developed for the first time. By doping phenoxazine (PXZ) and 10-ethyl-10H-phenoxazine (PXZEt) into epoxy polymers, the resulting PXZ@EP-0.25 % and PXZEt@EP-0.25 % films show unique photoactivated UOP properties, with phosphorescence quantum yields and lifetimes up to 10.8 % and 845 ms, respectively. It is found that the steady-state luminescence and UOP of PXZ@EP-0.25 % are switchable by light irradiation and thermal annealing. Moreover, the doped films can still produce conspicuous UOP after soaking in water, strong acid and base, and organic solvents for more than two weeks, exhibiting outstanding water and chemical resistance. Inspired by these exciting results, the PXZ@EP-0.25 % has been successfully exploited as an erasable transparent film for light printing.

Color-Tunable Dual-Mode Organic Afterglow from Classical Aggregation-Caused Quenching Compounds for White-Light-Manipulated Anti-Counterfeiting

Color-tunable dual-mode organic afterglow excited by ultraviolet (UV) and white light was achieved from classical aggregation-caused quenching compounds for the first time. Specifically, two luminescent systems, which could produce significant organic afterglow composed of persistent thermally activated delayed fluorescence and ultralong organic phosphorescence under ambient conditions, were constructed by doping fluorescein sodium and calcein sodium into aluminum sulfate. Their lifetimes surpassed 600 ms, and the dopant concentrations were as low as 5×10^-6  wt %. Moreover, the persistent luminescence colors of the materials could be tuned from blue to green and then to yellow by simply varying the concentrations of guest compounds or the temperature in the range of 260-340 K. Inspired by these exciting results, the afterglow materials were used for UV- and white-light-manipulated anti-counterfeiting and preparation of elastomers with different colors of persistent luminescence.

Water-borne, durable and multicolor silicon nanoparticles/sodium alginate inks for anticounterfeiting applications

Recently, water-borne fluorescent inks have attracted extensive attention in anti-counterfeiting applications due to their convenient implementation and eco-friendliness. However, due to poor service durability, the latent authorization information from the inks is easily damaged, and even disappears when encountering water. Moreover, most of the existing fluorescent inks are monochromic, toxic, and allergic to skin, thus are unsuitable for their sustainability during real-life applications. Herein, this work presents environment-friendly, durable, and multicolor fluorescent anti-counterfeiting silicon nanoparticles (SiNPs)/sodium alginate (SA) inks. The multicolor SiNPs are synthesized by a one-pot method with defined morphologies and optical properties. Subsequently, SA is employed as the binder to prepare the fluorescent inks with optimized rheological properties. Practicability results show that the SiNPs/SA inks not only exhibit excellent printability, but also impart authentic information with superior covert performance. More notably, spraying solution of calcium dichloride can further improve fluorescent fastnesses of the SiNPs/SA inks by ionic crosslinking.

A processable, scalable, and stable full-color ultralong afterglow system based on heteroatom-free hydrocarbon doped polymers

Although room-temperature phosphorescence (RTP) organic materials are a widely-studied topic especially popular in recent decades, long-lived RTP able to fulfil broad time-resolved application requirements reliably, are still rare. Polymeric materials doped with phosphorescent chromophores generally feature high productivity and diverse applications, compared with their crystalline counterparts. This study proves that pure polycyclic aromatic hydrocarbons (PAHs) may even outperform chromophores containing hetero- or heavy-atoms. Full-color (blue, green, orange and red) polymer-PAHs with lifetimes >5000 ms under ambient conditions are constructed, which provide impressive values compared to the widely reported polymer-based RTP materials in the respective color regions. The polymer-PAHs could be fabricated on a large-scale using various methods (solution, melt and in situ polymerization), be processed into diverse forms (writing ink, fibers, films, and complex 3D architectures), and be used in a range of applications (anti-counterfeiting, information storage, and oxygen sensors). Plus their environmental (aqueous) stability makes the polymer-PAHs a promising option to expand the portfolio of organic RTPs.

High-contrast reversible multiple color-tunable solid luminescent ionic polymers for dynamic multilevel anti-counterfeiting

Dynamic color-tunable luminescent materials, which possess huge potential applications in advanced multilevel luminescence anti-counterfeiting, are of considerable interest. However, it remains challenging to develop simple high-contrast reversible multiple (triple or more than triple) color-tunable high-efficiency solid luminescent materials with low cost, facile synthesis, and good processability. Herein, by simply grafting charged multi-color AIEgen-based chromophores into polymers, a series of high-efficiency multiple color-tunable luminescent single ionic polymers are constructed through tuning feed ratios, counter anions and reaction solvents. Remarkably, some ionic polymers can not only achieve rare high-contrast reversible multiple color-tunable emission in solid states in response to different solvent stimuli, but also could realize excitation-dependent color-tunable emission. To the best of our knowledge, such charming multiple (triple or more than triple) color-tunable solid polymers responding to multiple external stimuli are still rare. Based on comparative studies of emission spectra, excitation spectra and fluorescence lifetimes before and after swelling, it could be inferred that solvent stimuli could induce microstructure changes of these ionic polymers and then change the aggregated-states of their corresponding AIE-active emission centers. Moreover, the different solvent stimuli could induce to produce different degrees of microstructure changes, resulting in their unique multiple color-tunable emission. More significantly, these smart color-tunable ionic polymers show great promise for applications in dynamic multilevel (three-level or even more than three-level) anti-counterfeiting.

A Class of Organic Units Featuring Matrix-Controlled Color-Tunable Ultralong Organic Room Temperature Phosphorescence

A novel class of organic units (N-1 and N-2) and their derivatives (PNNA-1 and PNNA-2) with excellent property of ultralong organic room temperature phosphorescence (UORTP) is reported. In this work, N-1, N-2, and their derivatives function as the guests, while organic powders (PNCz, BBP, DBT) and polymethyl methacrylate (PMMA) serve as the host matrixes. Amazingly, the color of phosphorescence can be tuned in different states or by varying the host matrixes. At 77 K, all molecules show green afterglow in the monomer state but yellow afterglow in the aggregated state because strong intermolecular interactions exist in the self-aggregate and induce a redshift of the afterglow. In particular, PNNA-1 and PNNA-2 demonstrate distinctive photoactivated green UORTP in the PMMA film owing to the generation of their cation radicals. Whereas the PNNA-1@PNCz and PNNA-2@PNCz doping powders give out yellow UORTP, showing matrix-controlled color-tunable UORTP. In PNCz, the cation radicals of PNNA-1 and PNNA-2 can stay stably and form strong intermolecular interactions with PNCz, leading to a redshift of ultralong phosphorescence.

Highly Efficient and Ultralong Afterglow Emission with Anti-Thermal Quenching from CsCdCl3 : Mn Perovskite Single Crystals

Triplet exciton-based long-lived phosphorescence is severely limited by the thermal quenching at high temperature. Herein, we propose a novel strategy based on the energy transfer from triplet self-trapped excitons to Mn²⁺ dopants in solution-processed perovskite CsCdCl₃ . It is found the Mn²⁺ doped hexagonal phase CsCdCl₃ could simultaneously exhibit high emission efficiency (81.5 %) and long afterglow duration time (150 s). Besides, the afterglow emission exhibits anti-thermal quenching from 300 to 400 K. In-depth charge-carrier dynamics studies and density functional theory (DFT) calculation provide unambiguous evidence that carrier detrapping from trap states (mainly induced by Cl vacancy) to localized emission centers ([MnCl₆ ]^4- ) is responsible for the afterglow emission with anti-thermal quenching. Enlightened by the present results, we demonstrate the application of the developed materials for optical storage and logic operation applications.

Multicolor-tunable room-temperature afterglow and circularly polarized luminescence in chirality-induced coordination assemblies

Dynamic long-lived multicolor room temperature afterglow and circularly polarized luminescence (CPL) are promising for optoelectronic applications, but integration of these functions into a single-phase chiroptical material is still a difficult and meaningful challenge. Here, a nitrogen-doped benzimidazole molecule 1H-1,2,3-triazolopyridine (Trzpy) showing pure organic room-temperature phosphorescence (RTP) acted as a linker, and then, we propose a chirality-induced coordination assembly strategy to prepare homochiral crystal materials. Two homochiral coordination polymers DCF-10 and LCF-10 not only exhibit multicolor-tunable RTP, the color changed from green to orange under various excitation wavelengths, but also show remarkable excitation-dependent circularly polarized luminescence (CPL), and the dissymmetry factors of CPL in DCF-10 and LCF-10 are 1.8 × 10^-3 and 2.4 × 10^-3, respectively. Experimental and theoretical studies demonstrated that molecular atmospheres with different aggregation degrees give rise to multiple emission centers for the generation of multicolor-tunable emission. The multicolor-tunable photophysical properties endowed LCF-10 with a huge advantage for multi-level anti-counterfeiting. This work opens up new perspectives for the development and application of color-tunable RTP and CPL.

Hydrogen-bond organized 2D metal-organic microsheets: direct ultralong phosphorescence and color-tunable optical waveguides

Ultralong phosphorescent materials have numerous applications across biological imaging, light-emitting devices, X-ray detection and anti-counterfeiting. Triplet-state molecular phosphorescence typically accompanies the singlet-state fluorescence during photoluminescence, and it is still difficult to achieve direct triplet photoemission as ultralong room temperature phosphorescence (RTP). Here, we have designed Zn-IMDC (IMDC, 4,5-imidazoledicarboxylic acid) and Cd-IMDC, two-dimensional (2D) hydrogen-bond organized metal-organic crystalline microsheets that exhibit rarely direct ultralong RTP upon UV excitation, benefiting from the appropriate heavy-atom effect and multiple triplet energy levels. The excitation-dependent and thermally stimulated ultralong phosphorescence endow the metal-organic systems great opportunities for information safety application and temperature-gated afterglow emission. The well-defined 2D microsheets present color-tunable and anisotropic optical waveguides under different excitation and temperature conditions, providing an effective way to obtain intelligent RTP-based photonic systems at the micro- and nano-scales.

Metal-Halide Coordination Polymers with Excitation Wavelength- and Time-Dependent Ultralong Room-Temperature Phosphorescence

Metal-organic hybrids with ultralong room-temperature phosphorescence (RTP) have potential applications in many fields, including optical communications, anticounterfeiting, encryption, bioimaging, and so on. Herein, we report two isostructural one-dimensional zinc-organic halides as coordination polymers ZnX₂(bpp) (X = Cl, 1; Br, 2; bpp = 1,3-di(4-pyridyl)propane) with excitation wavelength- and time-dependent ultralong RTP properties. The dynamic multicolor afterglow can be assigned to the emission of the pristine ligand bpp and its interactions with halogen atoms. Experiments and theoretical calculations both suggest that ZnX₂ is crucial for ultralong RTP: (a) the metal coordination and X...π bonds in coordination polymers fix the bpp molecules and suppress the nonradiative transitions; (b) the spin-orbital coupling of coordination polymers is largely enhanced relative to the bpp because of the heavy atom effect; and (c) the charge transfer exists between halogens and bpp ligand. Therefore, this work not only presents metal-halide coordination polymers with excitation wavelength- and time-dependent RTP properties, but also provides a facile method for the new types of dynamic multicolor afterglow materials.

Germanium silicon oxide achieves multi-coloured ultra-long phosphorescence and delayed fluorescence at high temperature

Colour-tuned phosphors are promising for advanced security applications such as multi-modal anti-counterfeiting and data encryption. The practical adoption of colour-tuned phosphors requires these materials to be responsive to multiple stimuli (e.g., excitation wavelength, excitation waveform, and temperature) and exhibit excellent materials stability simultaneously. Here we report germanium silicon oxide (GSO) – a heavy-metal-free inorganic phosphor – that exhibits colour-tuned ultra-long phosphorescence and delayed fluorescence across a broad temperature range (300 – 500 K) in air. We developed a sol-gel processing strategy to prepare amorphous oxides containing homogeneously dispersed Si and Ge atoms. The co-existence of Ge and Si luminescent centres (LC) leads to an excitation-dependent luminescence change across the UV-to-visible region. GSO exhibits Si LC-related ultra-long phosphorescence at room-temperature and thermally activated delayed fluorescence at temperatures as high as 573 K. This long-lived PL is sensitized via the energy transfer from Ge defects to Si LCs, which provides PL lifetime tunability for GSO phosphors. The oxide scaffold of GSO offers 500-day materials stability in air; and 1-week stability in strong acidic and basic solutions. Using GSO/polymer hybrids, we demonstrated colour-tuned security tags whose emission wavelength and lifetime can be controlled via the excitation wavelength, and temperature, indicating promise in security applications.

Advanced security applications require materials responsive to different stimuli with remarkable stability. Here, Sargent et al. introduce Ge homogenously into a silica scaffold and obtain a colourtuned germanium silicon oxide with ultra-long phosphorescence and delayed fluorescence across a broad temperature range.

Accessing Excitation- and Time-Responsive Afterglows from Aqueous Processable Amorphous Polymer Films through Doping and Energy Transfer

Smart afterglow materials in response to excitation and delay time, including crystals, polymeric films, and carbon dots, have attracted considerable attention on account of their fundamental value in photophysics and promising applications in optoelectronics. However, the fabrication of amorphous and flexible polymer films with fine control remains underexplored. Herein, new doped polymer films based on sodium alginate and aromatic carboxylates are developed, which demonstrate following advantages: (i) easy and fast fabrication through the aqueous solution process, (ii) flexible, transparent, and re-dissolvable characteristics, (iii) multi-tunable afterglow colors from blue to red and even white with fine control. Specifically, even better controllability can be achieved through co-doping and triplet-to-singlet Förster resonance energy transfer (TS-FRET). Multimode advanced anti-counterfeiting of these materials is demonstrated using their excitation- and time-dependent as well as TS-FRET-mediated afterglow colors.

Molecular Thermal Motion Modulated Room-Temperature Phosphorescence for Multilevel Encryption

The stimulus-responsive room-temperature phosphorescence (RTP) materials have become an increasingly significant topic in the fields of bioimaging, sensing, and anticounterfeiting. However, this kind of materials is scarce to date, especially for the ones with delicate stimulus-responsive behavior. Herein, a universal strategy for multilevel thermal erasure of RTP via chromatographic separation of host-guest doping RTP systems is proposed. The tunable host-guest systems, matrix materials, heating temperature, and time are demonstrated to allow precise six-level data encryption, QR code encryption, and thermochromic phosphorescence encryption. Mechanistic study reveals that the thermal-responsive property might be attributed to molecular thermal motion and the separation effect of the silica gel, which provides expanded applications of host-guest RTP materials such as cold chain break detection. This work offers a simple yet universal way to construct advanced responsive RTP materials.

Hyperbranched Polyborate: A Non-conjugated Fluorescent Polymer with Unanticipated High Quantum Yield and Multicolor Emission

Non-conjugated fluorescent polymers have attracted great attention due to their excellent biocompatibility and environmental friendliness. However, it remains a huge challenge to obtain a polymer with high fluorescence quantum yield (QY) and multicolor emission simultaneously. Herein, we reported three kinds of nonaromatic hyperbranched polyborates (P1-P3) with multicolor emission, surprisingly, P2 also exhibits an unanticipated high QY (54.1 %). The natural bond orbital (NBO) analysis and density functional theory (DFT) calculation results revealed that the synergistic effect of rigid BO₃ planar and flexible carbon chain, as well as the through-space dative bond in supramolecular aggregate, were the key factors contributing to the ultrahigh QY of P2. Moreover, the applications of P2 in Fe³⁺ ions detection and cell imaging were also investigated. This work provides a new perspective for designing non-conjugated fluorescent polymers with both high QY and multicolor emission.

Quadruple Anticounterfeiting Encryption: Anion-Modulated Forward and Reverse Excitation-Dependent Multicolor Afterglow in Two-Component Ionic Crystals

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.

Mobile Phone Flashlight-Excited Red Afterglow Bioimaging

Organic room temperature phosphorescence (RTP) materials with ultralong lifetime possess the remarkable advantage in bioimaging for elimination of background noise by characteristic time scale. However, most of RTP luminogens need to be excited by the harmful ultraviolet (UV) lamp, and exhibit green or yellow emission with shallow tissue penetration, constraining the in vivo bioimaging for further application in clinical diagnosis and pathological study. In this text, the much safer excitation process by sunlight and mobile phone flashlight is realized by organic luminogens with various electronic pull-push systems. Moreover, the bright red RTP emission with lifetime up to 344 ms is achieved by optimizing molecular geometry and electronic property. Especially, the mobile phone flashlight-excited red afterglow imaging of lymph nodes in living mice has been realized for the first time, affording a safe and conventional approach to achieve the afterglow imaging of living mice with deep issue penetration and high signal-to-noise ratios.

Multi-Mode and Dynamic Persistent Luminescence from Metal Cytosine Halides through Balancing Excited-State Proton Transfer

Persistent luminescence has attracted great attention due to the unique applications in molecular imaging, photodynamic therapy, and information storage, among many others. However, tuning the dynamic persistent luminescence through molecular design and materials engineering remains a challenge. In this work, the first example of excitation-dependent persistent luminescence in a reverse mode for smart optical materials through tailoring the excited-state proton transfer process of metal cytosine halide hybrids is reported. This approach enables ultralong phosphorescence and thermally activated delayed fluorescence emission colors highly tuned by modulation of excitation wavelength, time evolution, and temperature, which realize multi-mode dynamic color adjustment from green to blue or cyan to yellow-green. At the single crystal level, the 2D excitation/space/time-resolved optical waveguides with triple color conversion have been constructed on the organic-metal halide microsheets, which represent a new strategy for multi-dimensional information encryption and optical logic gate applications.

On-demand modulating afterglow color of water-soluble polymers through phosphorescence FRET for multicolor security printing

Developing full-color organic ultralong room temperature phosphorescence (OURTP) materials with continuously variable afterglow emission is of considerable practical importance in diverse optoelectronic applications but remains a formidable challenge. Here, we present an effective strategy for on-demand engineering of afterglow color in water-soluble polymeric systems via efficient phosphorescence Förster resonance energy transfer. Using a blue afterglow emitting water-soluble polymer as host and a series of fluorescent emitters with varied emissive colors as guests, afterglow emission is rationally modulated, conferring the full-color afterglow emission ranging from blue to red and even white with ultralong lifetimes up to 4.2 s and photoluminescence quantum yields of 36%.These water-soluble multicolor-emitting polymeric afterglow systems can function as OURTP security inks, and multilevel information encryption was successfully established by RGB-based multicolor security printing. These results present important guidance in developing high-performance afterglow polymers with on-demand color tuning ability for remarkable optoelectronic applications.

Irreversible Humidity-Responsive Phosphorescence Materials from Cellulose for Advanced Anti-Counterfeiting and Environmental Monitoring

Organic phosphorescence materials have many unique advantages, such as a large Stokes shift, high signal-to-noise ratio, and no interference from background fluorescence and scattered light. But, they generally lack responsiveness. Herein, we developed a new type of biopolymer-based phosphorescence materials with excellent processability and irreversible humidity-responsiveness, via introducing the imidazolium cation to cellulose chain. In the resultant cellulose derivatives, the imidazolium cation promotes the intersystem crossing, meanwhile the cation, chloride anion, and hydroxyl group form multiple hydrogen bonding interactions and electrostatic attraction interactions, which successfully inhibit the nonradiative transitions. As a result, the ionic cellulose derivatives exhibit green phosphorescence at room temperature and can be processed into phosphorescent films, coatings, and patterns. More interestingly, their phosphorescence emission changes when the different processing solvents are used. The ionic cellulose derivatives processed with acetone have a negligible phosphorescence, while they give an irreversible humidity-responsive phosphorescence, which means that the ionic cellulose derivatives processed with acetone exhibit significantly enhanced phosphorescence once they meet water vapor. Such novel irreversible responsive phosphorescence materials have huge potential in advanced anticounterfeiting, information encryption, molecular logic gates, smart tags, and process monitoring.

Long-Lived Room Temperature Phosphorescence Crystals with Green Light Excitation

Long-lived room temperature phosphorescence (RTP) materials are promising for applications in various fields including security information, medical diagnostics, and molecular imaging because of their unique optical properties. Previous RTP materials are mainly excited by ultraviolet light, while synthesizing long-lived RTP materials with visible-light-excitation remains a challenge. In particular, long-lived RTP materials that can be excited by green light are rare. Herein, a feasible and concise chemical strategy for constructing hydrogen-bonded frameworks in an aqueous environment is developed to fabricate large-size, green-light-excited, and excitation-dependent long-lived RTP carbon dot crystals (m,p/CDs-ME). The RTP performance of the crystals exhibits strong excitation wavelength dependence, leading to a full range of visible-light tuning from blue to red. Importantly, the maximum excitation wavelength of the RTP crystals is around 500 nm, thus successfully realizing green light excitation. m,p/CDs-ME presents long-lived phosphorescence (130 ms) under 500 nm excitation in aqueous solution, making it highly suitable for dopamine detection. This work not only provides a general guideline for the development of large size long-lived RTP crystals but also extends the operation scope of long-lived RTP materials in the detection of biomarkers by visible light excitation.

Room temperature tunable multicolor phosphorescent polymers for humidity detection and information encryption

Amorphous polymer-based room temperature phosphorescence (RTP) materials exhibiting tunable emission colors have received tremendous attention and are extremely challenging to prepare. Herein, polyacrylamide-based RTP materials with tunable multicolor emission were prepared via copolymerizing phosphor with concentration dependent luminescence colors and acrylamide with different molar ratios. The hydrogen bonding interactions and chemically crosslinked structures in these polymers effectively restrict the mobility of phosphors and activate efficient RTP emission. The molar ratio of phosphor and acrylamide has a significant influence on the photophysical properties of these polymers, which can be used to fabricate multicolor materials. In addition, the RTP intensity decreases with increasing humidity due to the disassociation of hydrogen bonding by adsorption of water, manifesting as a humidity sensor. Benefiting from the distinguishable RTP lifetimes and the responsiveness to humidity, triple encoding for information encryption is successfully realized.

Unveiling the crucial contributions of electrostatic and dispersion interactions to the ultralong room-temperature phosphorescence of H-bond crosslinked poly(vinyl alcohol) films

Organic phosphors exhibiting room-temperature phosphorescence (RTP) in the amorphous phase are promising candidates for optoelectronic and biomedical applications. In particular, noncovalently embedding organic phosphors into a poly(vinyl alcohol) (PVA) matrix has emerged as the most commonly used yet effective approach to obtain amorphous organic RTP materials. While the role of intermolecular hydrogen-bonding interactions in determining the RTP properties of doping PVA systems has been well documented, we show that electrostatic and dispersion interactions contribute crucially to the ultralong RTP properties of doping PVA films. This impressive outcome reveals the nature of non-covalent interactions existing in doping PVA systems for the first time. We demonstrate this through detailed experimental and computational studies for a series of hydrogen-bond crosslinked PVA films where star-shaped organic phosphors containing active groups of carboxy, hydroxy, and amino act as multisite crosslinkers for the construction of extensive hydrogen-bonding networks. More importantly, we successfully obtain an ultralong RTP lifetime of up to 1.74 s by tuning the electrostatic and dispersion interactions between organic phosphors and the PVA matrix through simply modifying active groups of organic phosphors. This instructive work will provide new guiding principles for the exploration of amorphous organic RTP systems.

Ultralong phosphorescence cellulose with excellent anti-bacterial, water-resistant and ease-to-process performance

Herein, we present a phosphorescent cationized cellulose derivative by simply introducing ionic structures, including cyanomethylimidazolium cations and chloride anions, into cellulose chains. The imidazolium cations with the cyano group and nitrogen element promote intersystem crossing. The cyano-containing cations, chloride anions and hydroxyl groups of cellulose form multiple hydrogen bonding interactions and electrostatic attraction interactions, effectively inhibiting the non-radiative transitions. The resultant cellulose-based RTP material is easily processed into phosphorescent films, fibers, coatings and patterns by using eco-friendly aqueous solution processing strategies. Furthermore, after we construct a cross-linking structure by adding a small amount of glutaraldehyde as the cross-linking agent, the as-fabricated phosphorescent patterns exhibit excellent antibacterial properties and water resistance. Therefore, considering the outstanding biodegradability and sustainability of cellulose materials, cellulose-based easy-to-process RTP materials can act as antibacterial, water-resistant, and eco-friendly phosphorescent patterns, coatings and bulk materials, which have enormous potential in advanced anti-counterfeiting, information encryption, disposable smart labels, etc.

Stimulus-responsive room temperature phosphorescence materials with full-color tunability from pure organic amorphous polymers

Achieving stimulus-responsive ultralong room temperature phosphorescence (RTP) in organic materials especially with full-color tunable emissions is attractive and important but rarely reported. Here, a strategy was reported to realize stimulus-responsive RTP effect with color-tunable emissions by using water as solvent in the preparation process without any organic solvent through covalent linkage of arylboronic acids with different π conjugations and polymer matrix of polyvinyl alcohol. The yielded polymer films exhibit outstanding RTP performance (2.43 s). Furthermore, an excitation-dependent RTP film was obtained, and the afterglow color changes from blue to green, then to red as the excitation wavelength increases. The RTP property of all the above materials is sensitive to water and heat stimuli, because the rigidity of the system could be broken by water. Last, they were successfully applied in a multilevel information encryption and multicolor paper and ink.

Room Temperature Phosphorescent (RTP) Thermoplastic Elastomers with Dual and Variable RTP Emission, Photo-Patterning Memory Effect, and Dynamic Deformation RTP Response

Room temperature phosphorescent (RTP) polymers have advantages of strength, toughness, and processing and application flexibility over organic small molecular crystals, but the current RTP polymers are all from rigid plastics and involve chemical linkage and hydrogen and ionic bonds, and thermoplastic RTP elastomer has not been attempted and realized. Moreover, solution-processed films by simply mixing polymers and organic RTP materials can only show weak and single blue RTP. Here it is presented that such elastomer films, once thermomechanically plasticized, can emit bright and long-lived dual RTP. Moreover, they exhibit photo-activation memory effect, variable RTP colors and dynamic deformation RTP response. These results reveal that thermoplasticizing has altered the dispersion states and micro-environment of RTP molecules in matrix, and the cohesion of elastic polymer itself can also greatly restrict non-radiative relaxations to boost both blue mono-molecular and yellow micro-crystalline RTP. This work provides an effective and versatile processing strategy for tuning and enhancing the RTP properties of doped RTP polymers.

White Emissions Containing Room Temperature Phosphorescence from Different Excited States of a D-π-A Molecule Depending on the Aggregate States

Development of pure organic molecular materials with room temperature phosphorescence (RTP) and their applications for white emitters have received significant attentions recently. Herein, a D-π-A molecule (DMACPPY) which can realize white emitting under ambient conditions both in the crystal state and the doped-film state by combining RTP with two fluorescent emissions is reported. The white emission from the crystalline sample of DMACPPY consists fluorescence from S2 (the second excited singlet state) and S1 (the first excited singlet state) along with RTP from T1 (the first excited triplet state), namely, SST-type white light. While, the white emission from the poly methyl methacrylate (PMMA) film doped with DMACPPY contains fluorescences from S2 and S1 , and RTP from T2 (the second excited triplet state) rather than T1 (STS type). DMACPPY cannot exhibit white spectrum within alternative crystalline state since inferior RTP intensity despite similar ternary emissions. The results demonstrate that the emissive properties for excited states of DMACPPY can be tuned by changing the aggregate state from crystalline to dispersion state in PMMA film. This new RTP emitter fulfills the talent for white emitting and achieves dual-mode white emissions, invisibly, expands the application range for pure organic and heavy atom-free RTP materials.

Single-component color-tunable circularly polarized organic afterglow through chiral clusterization

Circularly polarized organic afterglow (CPOA) with both long-lived room-temperature phosphorescence (RTP) and circularly polarized luminescence (CPL) is currently attracting great interest, but the development of multicolor-tunable CPOA in a single-component material remains a formidable challenge. Here, we report an efficient strategy to achieve multicolor CPOA molecules through chiral clusterization by implanting chirality center into non-conjugated organic cluster. Owing to excitation-dependent emission of clusters, highly efficient and significantly tuned CPOA emissions from blue to yellowish-green with dissymmetry factor over 2.3 × 10-3 and lifetime up to 587 ms are observed under different excitation wavelengths. With the distinguished color-tunable CPOA, the multicolor CPL displays and visual RTP detection of ultraviolent light wavelength are successfully constructed. These results not only provide a new paradigm for realization of multicolor-tunable CPOA materials in single-component molecular systems, but also offer new opportunities for expanding the applicability of CPL and RTP materials for diversified applications.

Guest-host doped strategy for constructing ultralong-lifetime near-infrared organic phosphorescence materials for bioimaging

Organic near-infrared room temperature phosphorescence materials have unparalleled advantages in bioimaging due to their excellent penetrability. However, limited by the energy gap law, the near-infrared phosphorescence materials (>650 nm) are very rare, moreover, the phosphorescence lifetimes of these materials are very short. In this work, we have obtained organic room temperature phosphorescence materials with long wavelengths (600/657–681/732 nm) and long lifetimes (102–324 ms) for the first time through the guest-host doped strategy. The guest molecule has sufficient conjugation to reduce the lowest triplet energy level and the host assists the guest in exciton transfer and inhibits the non-radiative transition of guest excitons. These materials exhibit good tissue penetration in bioimaging. Thanks to the characteristic of long lifetime and long wavelength emissive phosphorescence materials, the tumor imaging in living mice with a signal to background ratio value as high as 43 is successfully realized. This work provides a practical solution for the construction of organic phosphorescence materials with both long wavelengths and long lifetimes.

Though room-temperature phosphorescence (RTP) in organics is advantageous for bioimaging, designing materials that meet lifetime and wavelength emission requirements is challenging. Here, the authors us a guest-host doped strategy to construct RTP materials with ultralong-lifetime, NIR emission.

Cucurbit[n]uril-based host-guest interaction enhancing organic room-temperature phosphorescence of phthalic anhydride derivatives in aqueous solution

A cyan RTP in aqueous solution was enhanced by supramolecular host–guest complexation of water-soluble halogen-substituted phthalic anhydride (PA) derivatives with cucurbit[n]urils (CB[n]s).

Cluster-luminescent polysiloxane nanomaterials: adjustable full-color ultralong room temperature phosphorescence and a highly sensitive response to silver ions

Non-conjugated polysiloxane nanomaterials with amino and urea groups show persistent cluster-induced phosphorescence regulated by doping different small molecules, and fluorescence/phosphorescence dual responses to Ag+ in aqueous solutions.

Stimuli-Responsive Polymers with Room-Temperature Phosphorescence

Taking advantages of the impressing behaviors of room-temperature phosphorescence (RTP), the explorations in RTP materials are not only limited to efficient emission and ultralong lifetime of phosphorescence. The discovery and creation of stimuli-responsive properties have become the major pursuit, which will lay a solid foundation for future applications in RTP materials. Based on this, a review centered on recent progress of stimuli-responsive RTP materials is summarized to show frontier development in polymer systems. Different kinds of stimuli-responsive factors including light, oxygen, temperature, mechanical force and pH regulations are investigated in this review. Many potential applications and promising strategies are deeply discussed with the hope to assist future studies in this area.

Tunable Second-Level Room-Temperature Phosphorescence of Solid Supramolecules between Acrylamide-Phenylpyridium Copolymers and Cucurbit[7]uril

A series of solid supramolecules based on acrylamide-phenylpyridium copolymers with various substituent groups (P-R: R=-CN, -CO₂ Et, -Me, -CF₃ ) and cucurbit[7]uril (CB[7]) are constructed to exhibit tunable second-level (from 0.9 s to 2.2 s) room-temperature phosphorescence (RTP) in the amorphous state. Compared with other solid supramolecules P-R/CB[7] (R=-CN, -CO₂ Et, -Me), P-CF₃ /CB[7] displays the longest lifetime (2.2 s), which is probably attributed to the fluorophilic interaction of cucurbiturils leading to a uncommon host-guest interaction between 4-phenylpyridium with -CF₃ and CB[7]. Furthermore, the RTP solid supramolecular assembly (donors) can further react with organic dyes Eosin Y or SR101 (acceptors) to form ternary supramolecular systems featuring ultralong phosphorescence energy transfer (PpET) and visible delayed fluorescence (yellow for EY at 568 nm and red for SR101 at 620 nm). Significantly, the ultralong multicolor PpET supramolecular assembly can be further applied in fields of anti-counterfeiting and information encryption and painting.

Core-Shell Fluorescent Polymeric Particles with Tunable White Light Emission Based on Aggregation Microenvironment Manipulation

White-light emitting polymers (WLEPs) based on aggregation microenvironment-sensitive aggregation-induced emission (AIE) and Förster resonance energy transfer (FRET) have aroused great interest in lighting and optoelectronic devices. Herein, we developed a novel strategy to construct WLEP particles via a stepwise self-stabilized precipitation polymerization of two emission-complementary AIEgens under core-shell engineering, where the AIE characteristics and FRET process of core-shell fluorescent polymeric particles (CS-FPPs) could be modulated by altering aggregation microenvironment under swelling and shrinking of polymers, facilitating the tunable white light emission of CS-FPPs. Furthermore, such tuning could be fast realized in the solid state, thus demonstrating the potential in anti-counterfeiting. This work proved the significance of aggregation microenvironment on emission of luminogens, guiding the development of high-efficiency emission-tunable materials.