Stepwise taming of triplet excitons via multiple confinements in intrinsic polymers for long-lived room-temperature phosphorescence

Engineering Organic Photochromism with Photoactivated Phosphorescence: Multifunctional Smart Devices and Enhanced Four-Channel Data Storage

The development of organic photoresponsive materials with multiple responses is essential for advancing multichannel data storage systems. In this study, interactions between photochromic and phosphorescent components are engineered by covalently linking them to obtain NMC (the compound containing naphthalimide and merocyanine units), which converted into NSP (the compound containing naphthalimide and spiropyran units) upon blue light irradiation, resulting in a maximum decrease in absorption of more than 90%, a blueshift of the fluorescent emission peaks from 605 to 490 nm, and an 84 fold enhancement in phosphorescence emission intensity. These significant optical changes across the three modes upon exposure to blue light are unprecedented. The conversion of optical signals to electrical signals enables the successful implementation of devices for remote monitoring of acid gas and blue light, as well as automatic control of blue light exposure. Furthermore, the data storage capacity of the device is significantly enhanced, increasing from 1 bit to log2(4n) bits per point in a four-channel data storage system. The design and synthesis of this compound present a promising approach for the development of sustainable, efficient, and flexible smart optoelectronic devices.

Manipulating room-temperature phosphorescence by electron-phonon coupling

Designing and optimizing efficient organic room-temperature phosphorescent (RTP) materials remains a captivating yet challenging endeavour due to the inherent difficulties in generating and stabilizing triplet excitons. Here, we report a suite of highly efficient phosphors characterized by near-unity intersystem crossing (ISC) yields. Surprisingly, upon doping these dyes into a polyvinyl alcohol matrix, their phosphorescence quantum yields (Φ P) spanned a wide range from 2.7% to 69.6%, governed by the position of the methyl substituent. Theoretical calculations and experimental results indicate that the variation in phosphorescence efficiency is primarily due to the strong electron-phonon coupling caused by the positional variation of the methyl substituents, rather than common factors such as ISC or energy levels. These findings provide a new insight into the design of high-performance organic RTP dyes.

Enhanced Room-Temperature Phosphorescence in Delignified Wood Through Combination with Pyrene-Based Materials

Organic room-temperature phosphorescent (RTP) materials, featured by their large Stokes shifts and long lifetimes, have garnered significant attention due to their promising applications in biophotonics and optoelectronics. However, the instability of their triplet states and their proneness to quenching in aerobic, room-temperature environments pose significant challenges. Herein, delignified wood (DW) is used as a porous substrate and applied heat to drive dehydration condensation between cellulose/hemicellulose hydroxyls and the phosphorescent chromophore 1-pyrenylboronic acid (Py-BOH). This reaction forms B─O bonds, anchoring Py-BOH in a rigid microenvironment created by hydrogenbonding in the DW pores, which restricts molecular thermal motion and facilitates the RTP emission, resulting in a lifetime of 340 ms for the target RTP-DW film. Furthermore, due to the susceptibility of the cellulose hydrogen-bond network to disruption by water molecules, the RTP-DW film is sensitive to water and exhibits repeatable stimulus-responsive behavior under water/thermal stimulation. This material can be processed into various luminous objects by directly cutting the wood film into different shapes or grinding it into powder and compounding it with polymers, thereby holding potential applications in luminous indication and anti-counterfeiting. The successful preparation of this (room-temperature phosphorescent-delignified wood)RTP-DW film will provide an effective pathway for achieving high-value utilization of wood resources.

Bright and Ultralong Organic Phosphorescence via Sulfonic Acid Functionalization for High-Contrast Real-Time Light-Writing Display

It is challenging to achieve room-temperature phosphorescence (RTP) in pure organics with both high efficiency and long lifetime. While much effort has been placed on discovering efficient phosphor skeletons, the importance of phosphor functionalization in enhancing the RTP performance has not received adequate attention. Herein, we demonstrate that functionalization of phosphors with sulfonic acid can ensure both bright and ultralong RTP, outperforming other substituents. The unique trigonal pyramidal structure of sulfonic acid group allows for more effective (n, π*) transitions to enhance intersystem crossing efficiency. Its highly polarized S-O bonds render strengthened hydrogen bonding interactions and a narrower confinement within the poly(vinyl alcohol) (PVA) matrix, to minimize the nonradiative dissipation. Furthermore, its excellent water solubility contributes to the outstanding transparency of PVA film (over 97%), yielding high-quality optical imaging with a high contrast ratio of 48.0 and a low blurriness of 0.24. Moreover, full-color phosphorescence with exceptional performance (ΦP, max = 37.2%, τP, max = 2.09 s) is achieved from different sulfonic acids, validating the effectiveness and universality of this strategy. By leveraging these advantages, real-time light-writing displays with sharp imaging, high sensitivity, and exceptional rewritability are demonstrated. This work not only contributes to the substituent engineering in the molecular design of phosphors but also opens new opportunities for RTP materials in the next-generation intelligent optoelectronic materials.

Large-Area, Ultra-thin Organic Films with Both Photochromic and Phosphorescence Properties

Polyethylene terephthalate (PET), polystyrene (PS), and polyvinyl chloride (PVC) are the most commonly used polymers in plastic products. Therefore, endowing these polymers with unique optical properties would significantly enhance their overall technological value. Herein, we synthesized a phosphorescent molecule, 2,2'-diphenyl-3,3'-bibenzofuran (DBF), with notable reversible photochromic properties (switching between colorless and deep red) as the guest and constructed a doped system with the above polymers as the hosts. All doped materials exhibited both room-temperature phosphorescence and reversible photochromic properties. The guest molecule exhibited strong reversible cyclization activity and small conformational changes during the reaction process, as well as moderate rigidity of the host matrix, which enabled the uncommon coexistence of these two properties in the doped system. Finally, DBF/PET was successfully formed into a transparent and uniform film with a length of 200 m, a width of 20 cm, a thickness of only 60-70 μm. This film exhibited excellent thermal-stability, sensitivity, and resistance to photo-fatigue, indicating its applicability in industrial production.

Coordination Self-Assembly Induced Hot Exciton Fluorescence and Multi-Source Excitation Long Afterglow

Metal-organic complexes with long afterglow luminescence have attracted extensive attention due to potential applications in display, sensing and information security. However, most of the metal-organic complex long afterglow materials reported so far are limited to the use of UV light as the excitation source, and the ambiguity of the structure-activity relationship makes the development of metal-organic complexes extremely limited. Herein, a series of metal-organic complexes with ultralong emission lifetime is constructed by coordination assembly of Zn(II) with three isomers. These complexes can emit afterglow when excited by UV light, blue LED, cell phone flashlight or even near-infrared light (800 nm) under ambient conditions, and the afterglow is also observed at 360 K. More interestingly, the inactivation pathway of the triplet exciton was altered by the strategy of supramolecular self-assembly, which leads to these complexes having hot exciton fluorescence (HEF) emission that is not present in the ligand. The relationship between structure and optical properties is investigated in detail by experiments and theoretical calculations. This work provides guidance for studying the modulation of optical properties by coordination interactions.

Lone Pairs-Mediated Multiple Through-Space Interactions for Efficient Room-Temperature Phosphorescence

The simultaneous generation and stabilization of triplet excitons are the key to realizing efficient organic room temperature phosphorescence (RTP), which is challenging owing to the obscure mechanism and structure-property relationships. Herein, a strategy of lone-pair-mediated multiple through-space interactions (TSIs) is proposed to availably induce RTP. By incorporating heteroatoms to facilitate through-space n-n and n-π interactions, the lone pairs are delocalized throughout the structure, resulting in the dense splitting of the excited-state energy levels. Thus, more matched energy levels with a small energy gap between singlet and triplet states (ΔEST) emerge, resulting in multiple intersystem crossing (ISC) transition channels that assist triplet excitons generation. The strong TSIs also effectively rigidify the molecular structures and thus stabilize triplet excitons for radiation. Furthermore, the manipulation of TSI intensity allows efficiency enhancement, persistent time prolongation, and tolerance to high temperatures of RTP. This work not only explores the fundamental principle of the RTP mechanism from a new view but also provides a universal strategy for ISC promotion and triple excitons stabilization.

Adjusting TADF and Phosphorescence for Tailored Dynamic Time-Dependent Afterglow Colored Carbon Dots spanning Full Visible Region

Time-dependent afterglow colored (TDAC) behavior differs from static afterglow by involving wavelength changes, enabling low-cost, high-level encryption and anti-counterfeiting. However, the existing carbon dot (CD)-based TDAC materials lack a clear mechanistic explanation and controllable wavelength changes, significantly hindering the progress of practical applications in this field. In this study, we synthesized CDs composites with customizable tunable TDAC wavelengths across the visible region. Furthermore, we elucidated the underlying mechanism of TDAC that exhibits sequential weakening and relative strengthening of long- and short-wavelength afterglow centers. This phenomenon arises due to strong emission with a short lifetime originating from long-wavelength thermally activated delayed fluorescence (TADF), along with weak emission having a longer lifetime originating from short-wavelength phosphorescence. The presence of surface-rich carboxyl groups on CDs determines the short-wavelength afterglow in their dispersed state while their high conjugation degree governs the long-wavelength afterglow in their aggregated state. Additionally, appropriate doping levels of CDs enhance color change phenomena during afterglow. Finally, by embedding CDs into different rigid matrix, the range of afterglow changes can be tailored arbitrarily within the visible light region. Leveraging these exceptional TDAC characteristics has allowed us to successfully develop advanced 4D coding technologies that facilitate multi-mode anti-counterfeiting and dynamic information encryption.

High-Security Plastic with Integrated Holographic and Phosphorescent Images

Organic room temperature phosphorescence (ORTP) polymer materials have sparked considerable research interests in recent years, but their optical function is still limited for multi-mode optical imaging. Herein, a feasible and universal approach is proposed to endow ORTP polymer materials with periodic refractive index modulation functions by holographic patterning. The key to this approach is to design a two-stage stepwise crosslinking. Stage-1, with low crosslinking density (≤0.75 mol L-1), is phosphorescence-silent but can provide greater free volume for monomer diffusion and thus facilitate the patterning of refractive index modulated holograms via photopolymerization-induced phase separation. The dense crosslinking at stage-2 can turn on phosphorescence with the intensity rising by 144% when the crosslinking density increases from 3.77 to 4.12 mol L-1. The enhanced phosphorescence is primarily ascribed to the increase of conformational distortion and spin-orbit coupling of organic phosphors based on theoretical calculations. Eventually, the first example is demonstrated of holographic plastic with the unique capability of independently displaying holographic andphosphorescent images. This work not only provides a novel paradigm to impart added optical functions to ORTP polymer materials but also paves the way for the development of high-security optical materials to combat counterfeiting.

Regulating Room-Temperature Phosphorescence of Organic Luminophores Through Stepwise Stabilization by Coordination and In-Situ Precipitation Reaction

Developing efficiency and long-lived room-temperature phosphorescence (RTP) materials through straightforward methods is highly desired. In this work, a stepwise stabilization strategy was proposed by the coordination and in-situ precipitation reactions among organic precursors, inorganic cation and anions, producing room-temperature phosphorescence materials with high emission efficiency (phosphorescence quantum yield of 45 %). Structural and photophysical characterizations revealed the coordination reaction reduced the energy gaps between singlet and triplet states and stabilized the excited states of the guest molecules. The in-situ precipitation reaction produced a solid matrix, which provided isolated environments for protecting the excitons from quenching. The applications of RTP materials in information encryption were demonstrated. The presented results provided a new clue for producing RTP materials, and extended their applications in wide fields.

Promoting WLED-Excited High Temperature Long Afterglow by Orthogonally Anchoring Chromophores into 0D Metal-Organic Cages

Afterglow materials have garnered significant interest due to distinct photophysical characteristics. However, it is still difficult to achieve long afterglow phosphorescence from organic molecules due to aggregation-caused quenching (ACQ) and energy dissipation. In addition, most materials reported so far have long afterglow emission only at room or even low temperatures, and mainly use UV light as an excitation source. In this work, we report a strategy to achieve high temperature long afterglow emission through the assembly of isolated 0D metal-organic cages (MOCs). In which, both ACQ and phosphorescence quenching effects are effectively mitigated by altering the stacking mode of organic chromophores through orthogonally anchoring into the edges of cubic MOCs. Furthermore, improvement in molecular rigidity, promotion of spin-orbit coupling and broadening of the absorption range are achieved through the MOC-engineering strategy. As a result, we successfully synthesized MOCs that can produce afterglow emission even after excitation by WLEDs at high temperatures (380 K). Moreover, the MOCs are capable of generating afterglow emissions when excited by mobile phone flashlight at room temperature. Given these features, the potential applications of MOCs in the visual identification of explosives, information encryption and multicolor display are explored.

Cycloolefin Copolymers With a Multiply Rigid Structure for Protecting Triplet Exciton From Thermo- and Moisture-Quenching

Polymeric room temperature phosphorescence (RTP) materials have been well developed and utilized in various fields. However, their fast thermo- and moisture-quenching behavior highly limit their applications in certain harsh environments. Therefore, the preparation of materials with thermo- and moisture-resistant phosphorescence is greatly attractive. Compared with common water-soluble polymers, cycloolefin copolymers (COC) show outstanding hydrophobicity and higher rigidity, even at elevated temperatures, being as a promising candidate to prepare phosphorescence materials with suppressed thermo- and moisture-quenching behavior. Herein, a type of COC bearing hydroxyl, ester, and adamantanyl side groups is synthesized. After dispersing various phosphors into this matrix, the resultant composites exhibit full-color RTP with lifetimes of 249-590 ms. Their luminescence does not show obvious quenching in water, acid, alkalinous, reductive, and oxidative environments. In the presence of both rigid COC matrix and rigid phosphors, the corresponding composite displays high-temperature phosphorescence performance. Even at 378 K, the composite can emit phosphorescence with a lifetime of 40-98 ms. The applications of these COC-based composites for imaging, information encryption, and anti-counterfeiting are thus explored.

Programmable Persistent Room Temperature Phosphorescence Switches through Wavelength-Selective Photoactivation

Controlling multicolor persistent room-temperature phosphorescence (RTP) through photoirradiation holds fundamental significance but remains a significant challenge. In this study, we engineered a wavelength-selective photoresponsive system utilizing the Förster resonance energy transfer strategy. This system integrates a photoactivated long-lived luminescent material as the energy donor with a fluorescent photoswitch as the energy acceptor, facilitating programmable persistent luminescence switches. Distinct afterglow color states, such as initial nonemissive, green, yellow, and orange, were achieved through irradiation at 400 nm, 365 nm, and 254 nm, respectively. Based on this capability, we established an interacting network for multistate afterglow color switching among these four emissive states. In addition, we demonstrate the potential of this wavelength-selective photoresponsive system in the photo-controlled rewritable printing of multicolor afterglow images on a single thin film. This work represents a substantial step towards the fabrication of sophisticated wavelength-selective photoresponsive systems, potentially revolutionizing applications in optical data storage, security labeling, and smart displays by enabling precise control over photoresponsive behaviors under various photoirradiation wavelengths.

Highly Efficient Red/Near-Infrared Phosphorescence from Doped Crystals

Organic red/near-infrared (NIR) room temperature phosphorescence (RTP) materials with low toxicity and facile synthesis are highly sought after, particularly for applications in biotechnology and encryption. However, achieving efficient red/NIR RTP emitters has been challenging due to the weak spin-orbit coupling of organics and the rapid nonradiative decay imposed by the energy gap law. Here we demonstrate highly efficient red/NIR RTP with boosted quantum yields (Φps) of up to 32.96 % through doping the thionated derivatives of phthalimide (PAI) (MTPAI and DTPAI) into PAI crystals. The red-shifted photoluminescence (PL) stems from a combination of the external heavy atom effect and the formation of emissive clusters centered around electron-rich sulfur atoms. Furthermore, the dopants enhance exciton generation efficiency and facilitate energy transfer from smaller PAI units to larger aggregates, leading to dramatically increased Φp. This strategy proves universal, opening possibilities for acquiring long-wavelength RTP with tunable photophysical properties. The doped crystals exhibit promising applications in optical waveguides and encryption paper/ink. This research provides a practical approach to obtaining long-wavelength RTP materials and offers valuable insights into the mechanisms governing host-guest systems.

Tunable Nano-Supramolecules Based on Cucurbiturils for Near-Infrared Phosphorescence Imaging

Nano-supramolecules based on artificial macrocycles can not only regulate assembly morphology but also boost phosphorescence resonance energy transfer (PRET). Herein, a water-soluble phosphorescence supramolecule was constructed from the hyaluronic acid-modified bromophenylpyridinium (HAPY), cucurbit[n]uril (CB[n], n = 7/8), and energy acceptor phenyl-bridged phenothiazine derivatives, displaying efficient PRET and achieving near-infrared (NIR) phosphorescence by macrocyclic CB[n] and the assembly confinements. As compared with weak phosphorescent nanofibers of HAPY/CB[7], the spherical nanoparticles of HAPY/CB[8] not only gave strong green phosphorescence with extended lifetime to 1.27 ms but also could act as the energy donor and confine cationic phenothiazine in the secondary assemblies, leading to highly efficient PRET efficiency (87.27%) from the phosphors to triplet acceptors, realizing phosphorescence emission at 750 nm and an ultralarge Stokes shift of 440 nm. Ultimately, the nanoassembly achieved by the multiscale confinements boosting PRET was successfully applied in targeted cancer cell imaging, providing new insight for fabricating NIR phosphorescence materials.

Visible-light-excited organic room temperature phosphorescence

Purely organic room temperature phosphorescence (RTP) materials have evoked considerable attention owing to their fantastic optical properties and broad application prospects. However, most of the reported organic RTP materials can be only excited by UV light, leading to accelerated photoaging of organic phosphors and severe lesions of organisms under excitation. In contrast to UV light, visible light (380-780 nm) has much lower phototoxicity, deeper penetrability and easier accessibility, which make visible-light-excited RTP materials more favorable for practical uses, especially for life-related applications. Although it remains greatly challenging to construct visible-light-excited RTP materials, impressive progress has been made with the rapid development of this field. Herein, we systematically outline the significant progress achieved in visible-light-excited RTP materials, including the design and construction strategies, unique properties, underlying mechanisms and their vital applications. In the final section, we highlight the current challenges and research perspectives for suggesting future studies of visible-light-excited RTP materials.

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

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

Hierarchical Dual-Mode Efficient Tunable Afterglow via J-Aggregates in Single-Phosphor-Doped Polymer

The development of polymer-based persistent luminescence materials with color-tunable organic afterglow and multiple responses is highly desirable for applications in anti-counterfeiting, flexible displays, and data-storage. However, achieving efficient persistent luminescence from a single-phosphor system with multiple responses remains a challenging task. Herein, by doping 9H-pyrido[3,4-b]indole (PI2) into an amorphous polyacrylamide matrix, a hierarchical dual-mode emission system is developed, which exhibits color-tunable afterglow due to excitation-, temperature-, and humidity-dependence. Notably, the coexistence of the isolated state and J-aggregate state of the guest molecule not only provides an excitation-dependent afterglow color, but also leads to a hierarchical temperature-dependent afterglow color resulting from different thermally activated delayed fluorescence (TADF) and ultralong organic phosphorescence (UOP) behaviors of the isolated and aggregated states. The complex responsiveness based on the hierarchical dual-mode emission can serve for security features through inkjet printing and ink-writing. These findings may provide further insight into the regulated persistent luminescence by isolated and aggregated phosphors in doped polymer systems and expand the scope of stimuli-responsive organic afterglow materials for broader applications.

Accumulated in-situ spectral information analysis of room-temperature phosphorescence with time-gated bioimaging

This study introduces the time-gated analysis of room-temperature phosphorescence (RTP) for the in-situ analysis of the visible and spectral information of photons. Time-gated analysis is performed using a microscopic system consisting of a spectrometer, which is advantageous for in-situ analysis since it facilitates the real-time measurement of luminescence signal changes. An RTP material hybridized with a DNA aptamer that targets a specific protein enhances the intensity and lifetime of phosphorescence after selective recognition with the target protein. In addition, time-gated analysis allows for the millisecond-scale imaging of phosphorescence signals, excluding autofluorescence, and improves the signal-to-background ratio (SBR) through the accumulation of signals. While collecting the time-gated images and spectra of RTP and autofluorescent materials simultaneously, we develop a method for obtaining phosphorescence signals by means of selective exclusion of autofluorescence signals in simulated or real cell conditions. It is confirmed that the accumulated time-gated analysis can provide ample information about luminescence signals for bioimaging and biosensing applications.

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

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

Matrix-induced defects and molecular doping in the afterglow of SiO2 microparticles

A deep understanding of how the host matrix influences the afterglow properties of molecule dopants is crucial for designing advanced afterglow materials. Despite its appeal, the impact of defects on the afterglow performance in molecule-doped SiO2 matrices has remained largely unexplored. Herein, we detail the synthesis of monodisperse SiO2 microparticles by hydrothermally doping molecules, such as 4-phenylpyridine, 4,4'-bipyridine, and 1,4-bis(pyrid-4-yl)benzene. Our results demonstrate that hydrothermal reactions induce not only the formation of emissive defects in the SiO2 matrix but also enable molecule doping through SiO2 pseudomorphic transformation. Optical analyses reveal a remarkable afterglow activation of doped molecules, driven by a synergistic interplay of hydrogen bonding and physical fixation. Specifically, 4-phenylpyridine doping leads to an impressive 227- and 271-fold enhancement in fluorescence and afterglow, respectively, and an extraordinary 3711-fold enhancement in the afterglow lifetime of the resulting SiO2 MPs. We also document hybrid states involving molecule dopants and SiO2 defects, explaining energy transfer from molecule dopants to defects in both singlet and triplet states. The robust achievement of molecule doping provides flexibility to tailor excitation-dependent afterglow attributes while preserving angle-dependent structural colors, facilitating the creation of diverse building blocks for multiscale optical platforms for afterglow modulation and information encoding.

Theoretical Study on the Thermal Decomposition Mechanism of Fe(EDTA)- and Fe(EDTMP). Molecules 2024;29:4362. [PMID: 39339357 PMCID: PMC11433812 DOI: 10.3390/molecules29184362] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

The decomposition mechanisms of Fe(EDTA)- and Fe(EDTMP)- complexes, widely used in various industrial applications, were investigated through a theoretical approach. Despite their structural similarities, the phosphonic acid and carboxylic acid groups in these complexes lead to vastly different decomposition behaviors. Fe(EDTA)-, stabilized by delocalized π bonds in carboxylic acid groups, exhibited higher stability than that of Fe(EDTMP)-, which has only σ bonds in phosphonic acid groups. Interaction Region Indicator (IRI) analysis revealed that the steric hindrance of Fe(EDTMP)- was stronger than that of Fe(EDTA)-. Ab initio molecular dynamics simulations revealed that Fe(EDTMP)- undergoes rapid decomposition due to the ease of breaking P-C bonds and the repulsion between phosphonic acid groups. In contrast, Fe(EDTA)- decomposes more slowly. These findings suggest the incorporation of phosphonic acid groups for easier degradation pathways when designing organic acid molecules. Understanding these mechanisms provides a basis for developing strategies for wastewater treatment in industrial settings.

Supramolecular Assembly of Hydrogen-Bonded Organic Frameworks with Carbon Dots: Realizing Ultralong Aqueous Room-Temperature Phosphorescence for Anticounterfeiting

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.

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

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

Color-Tunable Room-Temperature Phosphorescence from Non-Aromatic-Polymer-Involved Charge Transfer

Polymeric room-temperature phosphorescence (RTP) materials especially multicolor RTP systems hold great promise in concrete applications. A key feature in these applications is a triplet charge transfer transition. Aromatic electron donors and electron acceptors are often essential to ensure persistent RTP. There is much interest in fabricating non-aromatic charge-transfer-mediated RTP materials and it still remains a formidable challenge to achieve color-tunable RTP via charge transfer. Herein, a charge-transfer-mediated RTP material by embedding quinoline derivatives within a non-aromatic polymer matrix such as polyacrylamide (PAM) or polyvinyl alcohol (PVA) is developed. Through-space charge transfer (TSCT) is achieved upon alkali- or heat treatment to realize a long phosphorescence lifetime of up to 629.90 ms, high phosphorescence quantum yield of up to 20.51%, and a green-to-blue afterglow for more than 20 s at room temperature. This color-tunable RTP emerges from a nonaromatic polymer to single phosphor charge transfer that has rarely been reported before. This finding suggests that an effective and simple approach can deliver new color-tunable RTP materials for applications including multicolor display, information encryption, and gas detection.

3D Printed Room Temperature Phosphorescence Materials Enabled by Edible Natural Konjac Glucomannan

Shaping room temperature phosphorescence (RTP) materials into 3D bodies is important for stereoscopic optoelectronic displays but remains challenging due to their poor processability and mechanical properties. Here, konjac glucomannan (KGM) is employed to anchor arylboronic acids with various π conjugations via a facile B─O covalent reaction to afford printable inks, using which full-color high-fidelity 3D RTP objects with high mechanical strength can be obtained via direct ink writing-based 3D printing and freeze-drying. The doubly rigid structure supplied by the synergy of hydrogen bonding and B─O covalent bonding can protect the triplet excitons; thus, the prepared 3D RTP object shows a striking lifetime of 2.14 s. The printed counterparts are successfully used for 3D anti-counterfeiting and can be recycled and reprinted nondestructively by dissolving in water. This success expands the scope of printable 3D luminescent materials, providing an eco-friendly platform for the additive manufacturing of sophisticated 3D RTP architectures.

Recent Progress in Nonconventional Luminescent Macromolecules and their Applications

Traditional π-conjugated luminescent macromolecules typically suffer from aggregation-caused quenching (ACQ) and high cytotoxicity, and they require complex synthetic processes. In contrast, nonconventional luminescent macromolecules (NCLMs) with nonconjugated structures possess excellent biocompatibility, ease of preparation, unique luminescence behavior, and emerging applications in optoelectronics, biology, and medicine. NCLMs are currently believed to produce inherent luminescence due to through-space conjugation of overlapping electron orbitals in solid/aggregate states. However, as experimental facts continue to exceed expectations or even overturn some previous assumptions, there is still controversy about the detailed luminous mechanism of NCLMs, and extensive studies are needed to further explore the mechanism. This Perspective highlights recent progress in NCLMs and classifies and summarizes these advances from the viewpoint of molecular design, mechanism exploration, applications, and challenges and prospects. The aim is to provide guidance and inspiration for the huge fundamental and practical potential of NCLMs.

Photophysical properties of DAPI in PVA films. Possibility of room temperature phosphorescence

We studied the spectral properties of 4'-6-diamidino-2-phenylindole (DAPI) in poly (vinyl alcohol) (PVA) films. Absorption and fluorescence spectra, emission and excitation spectra, quantum yield, and fluorescence lifetime have been characterized. An efficient room temperature phosphorescence (RTP) of DAPI has been observed with UV and blue light excitations. A few hundred millisecond phosphorescence lifetime enables a gated detection with sufficient background reduction. We found the phosphorescent Quantum Yield of DAPI in PVA Film to be 0.0009.

Employing racemization strategies to simultaneously enhance the quantum yield, lifetime, and water stability of room-temperature phosphorescent materials

Room temperature phosphorescence (RTP) materials are increasingly recognized for their superior luminescent properties, which are pivotal in applications such as anti-counterfeiting, information storage, and optoelectronics. Despite this, the sensitivity of most RTP systems to humidity presents a significant challenge in achieving durable RTP performance in aqueous environments. This study proposes a strategy to enhance organic room-temperature phosphorescence through racemization. By incorporating external racemates of various chiral phosphors-NDBD-Ph, NDBD-Ph-Ph, NDBD-CH3, and NDBD-O-CH3-into a polyacrylonitrile (PAN) matrix, we significantly enhance the RTP properties (quantum yield, lifetime, and afterglow-time) of the resultant films. This enhancement can be attributed to the increased density of racemic molecules in the matrix and the increased spin-orbit coupling (SOC), facilitating the development of a long-lasting polymer RTP system in water. Notably, the racemic rac-NDBD-Ph@PAN film exhibits a persistent bright turquoise afterglow, even after immersion in water for a month. Furthermore, for the first time, we achieved an enhanced green to cyan RTP response to pH variations under both acidic and alkaline conditions (pH = 2-12), with the maximum phosphorescence emission intensity increasing up to threefold. The remarkable water stability, reversible response characteristics, and enhanced phosphorescence properties of this system offer promising potential for dynamic information encryption in aqueous environments.

Urea-formaldehyde resin room temperature phosphorescent material with ultra-long afterglow and adjustable phosphorescence performance

Organic room-temperature phosphorescence materials have attracted extensive attention, but their development is limited by the stability and processibility. Herein, based on the on-line derivatization strategy, we report the urea-formaldehyde room-temperature phosphorescence materials which are constructed by polycondensation of aromatic diamines with urea and formaldehyde. Excitingly, urea-formaldehyde room-temperature phosphorescence materials achieve phosphor lifetime up to 3326 ms. There may be two ways to enhance phosphorescence performance, one is that the polycondensation of aromatic diamine with urea and formaldehyde promotes spin-orbit coupling, and another is that the imidazole derivatives derived from the condensation of aromatic o-diamine with formaldehyde maintains low levels of energy level difference and spin-orbit coupling, thus achieving ultra-long afterglow. Surprisingly, urea-formaldehyde room-temperature phosphorescence materials exhibit tunable phosphorescence emission in electrostatic field. Accordingly, 1,4-phenylenediamine, urea, and formaldehyde are copolymerized and self-assembled into phosphorescence microspheres with different electrostatic potential strengths. By mixing 1 wt% 1,4-phenylenediamine polycondensation microspheres with 1,4-phenylenediamine free microspheres, phosphor lifetime of the composite could be regulated from 27 ms to 123 ms. Moreover, vulcanization process enables precise shaping of urea-formaldehyde room-temperature phosphorescence materials. This work not only demonstrates that urea-formaldehyde room-temperature phosphorescence materials are promising candidates for organic phosphors, but also exhibits the phenomenon of electrostatically regulated phosphorescence.

Enhancing Purely Organic Room Temperature Phosphorescence via Supramolecular Self-Assembly

Long-lived and highly efficient room temperature phosphorescence (RTP) materials are in high demand for practical applications in lighting and display, security signboards, and anti-counterfeiting. Achieving RTP in aqueous solutions, near-infrared (NIR) phosphorescence emission, and NIR-excited RTP are crucial for applications in bio-imaging, but these goals pose significant challenges. Supramolecular self-assembly provides an effective strategy to address the above problems. This review focuses on the recent advances in the enhancement of RTP via supramolecular self-assembly, covering four key aspects: small molecular self-assembly, cocrystals, the self-assembly of macrocyclic hosts and guests, and multi-stage supramolecular self-assembly. This review not only highlights progress in these areas but also underscores the prominent challenges associated with developing supramolecular RTP materials. The resulting strategies for the development of high-performance supramolecular RTP materials are discussed, aiming to satisfy the practical applications of RTP materials in biomedical science.

Multi-Functional Integration of Phosphor, Initiator, and Crosslinker for the Photo-Polymerization of Flexible Phosphorescent Polymer Gels

A general approach to constructing room temperature phosphorescence (RTP) materials involves the incorporation of a phosphorescent emitter into a rigid host or polymers with high glass transition temperature. However, these materials often suffer from poor processability and suboptimal mechanical properties, limiting their practical applications. In this work, we developed benzothiadiazole-based dialkene (BTD-HEA), a multifunctional phosphorescent emitter with a remarkable yield of intersystem crossing (ΦISC, 99.83 %). Its high triplet exciton generation ability and dialkene structure enable BTD-HEA to act as a photoinitiator and crosslinker, efficiently initiating the polymerization of various monomers within 120 seconds. A range of flexible phosphorescence gels, including hydrogels, organogels, ionogels, and aerogels were fabricated, which exhibit outstanding stretchability and recoverability. Furthermore, the unique fluorescent-phosphorescent colorimetric properties of the gels provide a more sensitive method for the visual determination of the polymerization process. Notably, the phosphorescent emission intensity of the hydrogel can be increased by the formation of ice, allowing for the precise detection of hydrogel freezing. The versatility of this emitter paves the way for fabricating various flexible phosphorescence gels with diverse morphologies using microfluidics, film-shearing, roll coating process, and two/three-dimensional printing, showcasing its potential applications in the fields of bioimaging and bioengineering.

Tryptophan-Doped Poly(vinyl alcohol) Films with Ultralong-Lifetime Room-Temperature Phosphorescence and Color-Tunable Afterglow Under Ambient Conditions

The development of a persistent luminescence system with long-lived phosphorescence and color-tunable afterglow at room temperature represents a challenge, largely due to the intensive non-radiative deactivation pathway. In this study, an ultralong-lived room temperature phosphorescence (RTP) system has been achieved using a hydrogen-bonding strategy where poly(vinyl alcohol) (PVA) matrices were doped with tryptophan (Trp) derivatives. The PVA film doped with N-α-(9-Fluorenylmethoxycarbonyl)-L-tryptophan (Fmoc-L-Trp) exhibited a long-lived phosphorescence emission of up to 3859.70 ms, and a blue afterglow for a duration greater than 34 s, under ambient conditions. The introduction of two other fluorescent dyes (i. e., Rhodamine B and Basicred14) to the PVA film facilitates adjustment to the color of the afterglow from blue to orange, and pink, by a triplet-to-singlet Förster-resonance energy transfer (TS-FRET) process. These films have been successfully applied in silk-screen printing and in multicolor afterglow light-emitting diode (LED) arrays.

Phosphorescent acyclic cucurbituril solid supramolecular multicolour delayed fluorescence behaviour

Organic photoluminescent macrocyclic hosts have been widely advanced in many fields. Phosphorescent hosts with the ability to bind organic guests have rarely been reported. Herein, acyclic cucurbituril modified with four carboxylic acids (ACB-COOH) is mined to present uncommon purely organic room-temperature phosphorescence (RTP) at 510 nm with a lifetime of 1.86 μs. Its RTP properties are significantly promoted with an extended lifetime up to 2.12 s and considerable quantum yield of 6.29% after assembly with a polyvinyl alcohol (PVA) matrix. By virtue of the intrinsic self-crimping configuration of ACB-COOH, organic guests, including fluorescence dyes (Rhodamine B (RhB) and Pyronin Y (PyY)) and a drug molecule (morphine (Mor)), could be fully encapsulated by ACB-COOH to attain energy transfer involving phosphorescent acyclic cucurbituril. Ultimately, as-prepared systems are successfully exploited to establish multicolor afterglow materials and visible sensing of morphine. As an expansion of phosphorescent acyclic cucurbituril, the host afterglow color can be readily regulated by attaching different aromatic sidewalls. This study develops the fabrication strategies and application scope of a supramolecular phosphorescent host and opens up a new direction for the manufacture of intelligent long-lived luminescent materials.

Double-Model Decay Strategy Integrating Persistent Photogenic Radicaloids with Dynamic Circularly Polarized Doublet Radiance and Triplet Afterglow

Organic phosphors integrating circularly polarized persistent luminescence (CPPL) across the visible range are widespread for applications in optical information encryption, bioimaging, and 3D display, but the pursuit of color-tunable CPPL in single-component organics remains a formidable task. Herein, via in situ photoimplanting radical ion pairing into axial chiral crystals, we present and elucidate an unprecedented double-module decay strategy to achieve a colorful CPPL through a combination of stable triplet emission from neutral diphosphine and doublet radiance from photogenic radicals in an exclusive crystalline framework. Owing to the photoactivation-dependent doublet radiance component and an inherent triplet phosphorescence in the asymmetric environment, the CPL vision can be regulated by altering the photoactivation and observation time window, allowing colorful glow tuning from blue and orange to delayed green emission. Mechanism studies clearly reveal that this asymmetric electron migration environment and hybrid n-π* and π-π* instincts are responsible for the afterglow and radical radiance at ambient conditions. Moreover, we demonstrate the applications of colorful CPPL for displays and encryption via manipulation of both excitation and observation times.

Macromolecular Engineered Multifunctional Room-Temperature Phosphorescent Polymers through Reversible Deactivation Radical Polymerization

Despite the intensive research in room-temperature phosphorescent (RTP) polymers, the synthesis of RTP polymers with well-defined macromolecular structures and multiple functions remains a challenge. Herein, reversible deactivation radical polymerization was demonstrated to offer a gradient copolymer (GCP) architecture with controlled heterogeneities, which combines hard segment and flexible segment. The GCPs would self-assemble into a multiphase nanostructure, featuring tunable stretchability, excellent RTP performance, and intrinsic healability without compromising light emission under stretching. The mechanical performance is tunable on demand with elongation at break ranging from 5.0% to 221.7% and Young's modulus ranging from 0.5 to 225.0 MPa.