Ultralong Organic Phosphorescence Research Articles

Photoactivated ultralong room‐temperature phosphorescence from epoxy polymer films doped with carbazole derivatives for erasable light printing

AbstractThe development of polymer‐based luminescent materials with efficient and switchable ultralong organic phosphorescence (UOP) under ambient conditions is of great importance but remains challenging. In this work, three new organic luminogens have been developed by attaching the ethyl benzoate to the nitrogen atoms of carbazole, 7H‐benzo[c]carbazole, and 7H‐dibenzo[c,g]carbazole via the Buchwald‐Hartwig coupling reaction, respectively. Subsequently, they are embedded into epoxy polymers through doping into the mixtures of bisphenol A diglycidyl ether and 1,3‐propylenediamine, followed by a thermal curing reaction. It is found that the resulting polymer films EB‐BCz@EP and EB‐2BCz@EP show unique photoactivated UOP properties. After UV light irradiation, their phosphorescence quantum yields are up to 7.6%, and the lifetimes reach 1.84 and 1.18 s, respectively. These observations suggest that it is possible to elevate the UOP lifetime without reducing the phosphorescence quantum yield by tuning the molecular structure of the guest luminogen. Upon thermal annealing, the photoactivated polymer films can recover to the pristine state, demonstrating switchable UOP characteristics of the polymer films in the air. Inspired by these exciting results, the EB‐2BCz@EP has been successfully explored as a transparent polymer film for erasable light printing.

Finely manipulating room temperature phosphorescence by dynamic lanthanide coordination toward multi-level information security

Room temperature phosphorescence materials have garnered significant attention due to their unique optical properties and promising applications. However, it remains a great challenge to finely manipulate phosphorescent properties to achieve desirable phosphorescent performance on demand. Here, we show a feasible strategy to finely manipulate organic phosphorescent performance by introducing dynamic lanthanide coordination. The organic phosphors of terpyridine phenylboronic acids possessing excellent coordination ability are covalently embedded into a polyvinyl alcohol matrix, leading to ultralong organic room temperature phosphorescence with a lifetime of up to 0.629 s. Notably, such phosphorescent performance, including intensity and lifetime, can be well controlled by varying the lanthanide dopant. Relying on the excellent modulable performance of these lanthanide-manipulated phosphorescence films, multi-level information encryption including attacker-misleading and spatial-time-resolved applications is successfully demonstrated with greatly improved security level. This work opens an avenue for finely manipulating phosphorescent properties to meet versatile uses in optical applications.

Highly stable ultralong organic phosphorescence from a 3D organic supramolecule constructed by halogen bonding and π–π interactions

Ultralong organic phosphorescence (UOP) materials have offered new exciting possibilities in the fields of photoelectric device, scintillators, anti-counterfeiting and bioprobe. However, pure organic phosphorescent materials inevitably suffer from rapid nonradiative transitions under oxygen, humidity, and high temperature, rending their phosphorescence is significantly quenched. Herein, a three-dimensional (3D) organic supramolecule (named SFIz) featuring UOP property was constructed successfully. Impressively, benefiting from the unique halogen bonding and π–π interactions, dual phosphorescent emission route of high energy state T1 (Br···O interaction predominates) and low energy state T1* (π–π interaction predominates) was simultaneously realized. Furthermore, owing to the robust supramolecular structural characteristic, SFIz shows highly stable UOP property with remarkably thermal, force stimulus and water-resistant stabilities that can be applied directly in extreme environments such as high temperatures 453 K (180 °C), high pressure and humidity. This work not only provides a much needed solution for achieving highly stable UOP materials and promoting their applications in extreme environments, but also gives in-depth understanding of both UOP and dual phosphorescent emission mechanisms in a non-metallic organic molecule.

Altering central atoms and bromination sites of phosphorescence units to control ultralong organic room temperature phosphorescence

We report two strategies to expand the library of Phosphorescence Units, including altering the central atom and bromination. Directed by these two strategies, numerous new Phosphorescence Units can be designed. Due to the limitation of organic synthesis and commercial availability, eight organic units (BCz, NBF, BNT, BrBCz-1, BrBCz-2, BrBCz-3, BrBCz-4 and BrBNT) were obtained to verify our proposed methods and study the impact of central atoms and bromination sites on organic room temperature phosphorescence. Considering BCz, NBF and BNT (Group Ⅰ) together, when the central atom is N or S, the room temperature phosphorescence is on as BCz and BNT have higher ISC (Intersystem Crossing) efficiency than NBF; from N to S, phosphorescence wavelength red shifts because the T1 energy level is closely related to the central atom and the lifetime shortens due to different ISC efficiency. Considering BCz, BrBCz-1, BrBCz-2 and BrBCz-3 (Group Ⅱ), bromination and different bromination sites on the benzene ring matters much to ISC efficiency but little to the intrinsic T1 energy level, leading to dramatical increase of phosphorescence intensity, sharp drop of phosphorescence lifetime and subtle change of phosphorescence wavelength (color). Considering BrBCz-4 and BrBNT (Group Ⅲ), bromination on the naphthalene moiety greatly affects both ISC efficiency and the intrinsic T1 energy level, resulting in dramatical increase of phosphorescence intensity, sharp drop of phosphorescence lifetime and significant red shift of phosphorescence color. Therefore, BNT, BrBCz-1, BrBCz-2, BrBCz-3, BrBCz-4 and BrBNT can be regarded as new Phosphorescence Units while NBF cannot be. To our best knowledge, this work for the first time gives design suggestions of organic room temperature materials from the atomic level. This work may give a deep insight into organic phosphorescence from the perspective of Phosphorescence Units and lay foundation for their future applications.

Color-tunable fluorescence and ultralong organic room temperature phosphorescence from multicomponent copolymers

Materials with color-tunable photoluminescence (PL) have attracted dramatically increasing interest in recent years, especially the tuning of both fluorescence (FL) and ultra-long organic room temperature phosphorescence (UOP). Herein, a series of polymer films are successfully fabricated by in situ copolymerization of carbazole derivatives, lanthanide complex, and acrylamide (AM). With a long lifetime of 2.82 s and a high quantum yield of 21.40%, these copolymers exhibit not only color-tunable FL from violet-red to blue, but also multicolor UOP scope from blue to chartreuse when the excitation wavelength is changed. Moreover, a nearly-white phosphorescence can also be observed by adjusting the excitation wavelength. Multiple information patterns with color-tunable FL and UOP emissions are captured, exhibiting promising potential in the information encryption and anti-counterfeiting fields.

Elucidating the Crystallization‐Caused Phosphorescence Quenching Mechanism to Achieve Efficient Photoactivated Persistent Luminescence for High‐Quality Light Printing

AbstractThe development of polymer‐based luminescent materials with efficient photoactivated ultralong organic phosphorescence (UOP) is of great importance but very challenging. Herein, a new class of organic phosphorescent luminogens is constructed by attaching phenyl rings and/or ethyl benzoates to the nitrogen atoms of a planar aromatic heterocycle pyrrolodiindole (PDI). The compounds show a significant elevation in phosphorescence emission capability after incorporating the ester group(s). However, they cannot produce room‐temperature phosphorescence in the crystalline state. These observations are identified to be associated with the formation of dimers and excimers and the motions of substituents within the molecules. In this context, the PDI derivatives are doped into epoxy polymers with compact and permanent 3D covalent networks. The resulting polymer films show reversible photoactivated UOP under ambient conditions, with quantum yields and lifetimes of up to 24.4% and 2.03 s, respectively, thereby enabling high‐quality and erasable light printing and multi‐level anti‐counterfeiting applications. In addition, they also exhibit excellent water and chemical resistance. This work is conducive to understanding the generation and decay mechanisms of the triplet excitons of organic luminophores with planar aromatic heterocycles in the crystalline state and provides a direction for the development of high‐performance photoactivated UOP materials.

A co-doping strategy to fabricate ultralong organic room temperature phosphorescence (ORTP) materials: Designing, preparation and advanced applications

Isophthalic acid (IPA) is a star phosphorescence molecule, which is a commercially available raw material with simple chemical structure, but is of good phosphorescence performance. However, the great research vacancy is still maintained because of its limited applications. Absolutely, polymer-matrix strategy is a common method to produce phosphorescence amorphous material by dispersing IPA into matrix such as polyvinyl alcohol (PVA). But how to further optimize the phosphorescence property of the resulted doping material (PVA-IPA)? Up to now, this question is new and very little attention has been paid. In this work, a co-doping strategy was explored, that is, charging the second dopant of ClCH2COOH into PVA-IPA was verified as a promising method to further enhance the phosphorescence property of PVA-IPA, leading to the co-doping material PVA-IPA-ClCH2COOH with ultralong phosphorescence lifetime as 500 ms and high phosphorescence quantum yield (ΦP) as 23.7%. Depending on these promising phosphorescence behaviors, PVA-IPA-ClCH2COOH was successfully applied in the fields of information anti-counterfeiting and artificial light harvest.

Manipulation of Photo‐Active Ultralong Organic Phosphorescence in Host‐Guest System

AbstractThe photo‐active ultralong organic phosphorescence (UOP) materials can only emit UOP gradually under consistent UV irradiation, which is primarily attributed to internal quenching of triplet oxygen, yet manipulating the rate of the photo‐activating process is seldom reported. In addition, amorphous small‐molecule doping UOP material is rarely reported either. In this study, a series of host and guest materials are synthesized and doped into amorphous UOP doping systems. These doping systems demonstrated a tunable photo‐activating rate (4–6 seconds to reach a saturated state), and the amorphous structure realized the sensitive detection of oxygen. The results affirm that triplet oxygen plays a pivotal role in determining whether UOP can be emitted, and importantly, it is established that a crystalline structure in small‐molecular doping systems is not a necessary condition. Furthermore, polymer‐based UOP materials, manufactured through co‐doping with both host and guest, exhibited tunable photo‐activating rates (4–16 s) and lifetimes (226.38–462.78 ms). To expand the application, the UV‐curing resin‐based UOP materials are prepared via 3D‐printing technology. This innovative work introduces a new approach for applying UOP materials in the field of amorphous doping system, providing a guiding strategy for widespread applications in oxygen detecting, time‐resolved information display and dynamic multi‐dimensional anti‐counterfeiting.

Crystalline nanoxylan from hot water extracted wood xylan at multi-length scale: Molecular assembly from nanocluster hydrocolloids to submicron spheroids

As a contribution to expand accessibility in the territory of bio-based nanomaterials, we demonstrate a novel material strategy to convert amorphous xylan preserved in wood biomass to hierarchical assemblies of crystalline nanoxylan on a multi-length scale. By reducing the end group in pressurized hot water extracted (PHWE) xylan to primary alcohol as a xylitol form with borohydride reduction, the endwise-peeling depolymerization is effectively impeded in the alkali-catalyzed hydrolytic cleavage of side substitutions in xylan. Nanoprecipitation by a gradual pH decrease resulted in a stable hydrocolloid dispersion in the form of worm-like nanoclusters assembled with primary crystallites, owing to the self-assembly of debranched xylan driven by strong intra- and inter-chain H-bonds. With evaporation-induced self-assembly, we can further construct the hydrocolloids as dry submicron spheroids of crystalline nanoxylan (CNX) with a high average elastic modulus of 47–83 GPa. Taking the advantage that the chain length and homogeneity of PHWE-xylan can be tailored, a structure-performance correlation was established between the structural order in CNX and the phosphorescent emission of this crystalline biopolymer. Rigid clusterization and high crystallinity that are constructed by strong intra- and inter-molecule interactions within the nanoxylan effectively restrict the molecular motion, thereby promoting the emission of ultralong organic phosphorescence.

Photo- and Oxygen- Synergistically Controlled Selective Expression of Organic Phosphorescence Units.

Dynamic control of ultralong organic room-temperature phosphorescence (UORTP) is a charming target. Herein, we report a stimuli-responsive phosphorescence unit 7H-indolo[2,3-c]quinoline (NBCz) and its derivatives (PCBNBCz, FSO2NBCz, and N2BCzSO2NBCz) that show photo- and oxygen- synergistically induced afterglow activation and afterglow color change in the PMMA film. PCBNBCz and FSO2NBCz feature a donor-acceptor (D-A) structure, and N2BCzSO2NBCz features acceptor-bridged two different phosphorescence units (NBCz and N2BCz). The photoactivated UORTP of PCBNBCz and FSO2NBCz arises from the photoinduced consumption of oxygen in the PMMA film. It is clear that the phosphorescence unit NBCz contributes to subsequent photoinduced UORTP color change because the NBCz-doped PMMA film shows the same UORTP color change process. ESR and HRMS measurements confirmed that oxidation of NBCz occurs at the nitrogen atom of the quinoline ring via photogenerated superoxide radicals, which results in the UORTP color change. TDDFT calculations proved that after oxidation of NBCz, the T1 energy level declines significantly. Furthermore, photocontrolled selective expression of phosphorescence units is achieved in the case of N2BCzSO2NBCz. After further UV irradiation, oxidation of NBCz happened, and the oxidized form N2BCzSO2NBCz-O emitted the intrinsic orange UORTP of NBCz-O selectively and screened the intrinsic yellowish-green UORTP of N2BCz. Finally, multilevel photolithography can be demonstrated based on the photoactivated UORTP and the photoinduced UORTP color change. This work may give a deep insight into organic phosphorescence and pave a simple way for the development of stimulus-responsive smart UORTP materials.

Afterglow Nanoprobe-Enabled Quantitative Lateral Flow Immunoassay by a Palm-Size Device for Household Healthcare.

Lateral flow immunoassay (LFIA), a classical point-of-care testing (POCT) technique, plays an important role in disease screening and healthcare monitoring. However, traditional LFIA is either designed for qualitative analysis or requires expensive equipment for quantification, limiting its use in household diagnosis. In this study, we proposed a new generation of LFIA for household health monitoring by using ultralong organic phosphorescence (UOP) nanomaterials as afterglow nanoprobes with a self-developed palm-size sensing device. The UOP nanoprobes exhibit a phosphorescence signal with a second-level lifetime, which completely avoids the interference from excitation light and biological background fluorescence. Therefore, an ultraminiaturized and low-cost UOP nanosensor was successfully designed by eliminating the complex optical path and filtering systems. We chose an inflammatory factor, C-reactive protein (CRP), for household POCT validation. The whole analysis was completed within 9 min. A limit of detection (LOD) of 0.54 ng/mL of CRP antigen was achieved with high stability and good specificity, which is comparable to laboratory instruments and fully satisfying the clinical diagnosis requirement.

Twofold rigidity activates ultralong organic high-temperature phosphorescence

A strategy is pioneered for achieving high-temperature phosphorescence using planar rigid molecules as guests and rigid polymers as host matrix. The planar rigid configuration can resist the thermal vibration of the guest at high temperatures, and the rigidity of the matrix further enhances the high-temperature resistance of the guest. The doped materials exhibit an afterglow of 40 s at 293 K, 20 s at 373 K, 6 s at 413 K, and a 1 s afterglow at 433 K. The experimental results indicate that as the rotational ability of the groups connected to the guests gradually increases, the high-temperature phosphorescence performance of the doped materials gradually decreases. In addition, utilizing the property of doped materials that can emit phosphorescence at high temperatures and in high smoke, the attempt is made to use organic phosphorescence materials to identify rescue workers and trapped personnel in fires.

Ultralong organic room-temperature phosphorescence modulated by balancing intramolecular charge transfer and localized excitation character of excited states

Long emission lifetime is the defining character of organic room-temperature phosphorescence (RTP) and afterglow materials. In the absence of heavy atom effect, organic localized excitation (LE) systems show small phosphorescence rates and exhibit potential to form long-lived phosphorescence materials. However, such LE systems usually have limited population of T1 states because of large singlet-triplet splitting energy (ΔEST, around 1 eV). Here we report ultralong RTP by balancing intramolecular charge transfer and localized excitation character of excited states. Aromatic functional groups of moderate electron-donating strength are selected to build difluoroboron β-diketonate (BF2bdk) systems with moderate intramolecular charge transfer (ICT) character in their S1 states. Such molecular design gives rise to ΔEST around 0.5 eV and is enough to populate BF2bdk's T1 states. Significantly, the resultant BF2bdk's T1 states exhibit 85–90% 3LE character and display long phosphorescence lifetimes up to 1.38 s upon doping under ambient conditions. This study shows that simple design of organic system can also lead to high-performance RTP materials and provide an insight into the fundamental photophysics of organic triplet system.

Cluster-induced aggregation in polyurethane derivatives with multicolour emission and ultra-long organic room temperature phosphorescence

Cluster-induced aggregation, multicolour luminescence and ultra-long phosphorescence (0.45 s) in NCLPs based on polyurethane derivatives have been achieved by simply adjusting reaction temperature and reaction time; this is the longest reported phosphorescence lifetime for pure NCLPs.

Modulating the crystal packing to achieve efficient ultralong organic phosphorescence by simple methylation engineering

Simple methylation engineering strategy used to adjust the packing and UOP behavior is demonstrated. The intrinsic relationship between structure and UOP properties are investigated by combining the experimental and theoretical results.

Precisely Coordination‐Modulated Ultralong Organic Phosphorescence Enables Biomimetic Fluorescence‐Afterglow Dual‐Modal Information Encryption

AbstractInformation leakage and counterfeiting are serious worldwide issues that tremendously impact legitimate businesses and human life. Inspired by the Noctiluca scintillans, a new fluorescence‐afterglow dual‐modal information encryption enabled by precisely coordination‐modulated ultralong organic phosphorescence (UOP) is presented. Strikingly, the optical properties including fluorescence, lifetime and intensity of UOP can be precisely modulated on‐demand through energy transfer by lanthanide (LnIII) coordination, which enables information camouflage by similar LnIII luminescence to provide misleading information along with data decryption in the form of mutual afterglow. Moreover, the important data can be encrypted in a spatial‐time‐resolved way by programmatically coding information with afterglow gradients, yielding greatly improved security for verifying the authenticity. This study provides a new avenue to precisely modulate the optical properties of UOP materials and broadens the scope of optical materials for innovative information encryption and anticounterfeiting applications.

Regulating isolated-molecular and aggregated state phosphorescence for multi-color afterglow by photo-activation.

Ultralong organic phosphorescence (UOP) materials have attracted considerable attention in recent years. Herein, a new type of flexible films was fabricated by doping amphipathic pyrene tetra sulfonic acid sodium salts into amorphous poly(vinyl alcohol) matrix, which enabled the realization of color-tunable UOP spanning from orange-red to green after excitation light switched off. Interestingly, we demonstrated precise control of the proportion of isolated-molecular and aggregated state phosphorescence for colorful afterglow using photo-activation. A 2.19-fold increase in the dynamic phosphorescence lifetime of isolated molecules was observedfrom 752.94 to 1650.46 ms following an 8-minute irradiation under ambient conditions. This flexible and processable film exhibited versatile applications in multi-color afterglow displays, ultraviolet detection, multilevel information encryption, etc. Our study not only provides a strategy for the rational regulation of UOP colors but also expands the application potential of color-tunable UOP materials. This article is protected by copyright. All rights reserved.

Polymeric ultralong organic phosphorescence with excellent humidity and temperature resistance via hydrophobic effect

AbstractPolymeric ultralong organic phosphorescence (UOP) with persistent emission is of great importance in practical applications. However, achieving good water‐resistance for long‐term environmental stability is a formidable challenge. In this contribution, through tailoring the alkyl‐chain length of the hardeners and emitters, polymeric UOPs with varying crosslinking density and hydrophobic effect were obtained. Notably, all the polymers show no obvious decrease in UOP emission after high temperature‐humidity test (85°C/85% relative humidity for 7 days). Detailed investigations demonstrate that the rigid covalent crosslinking networks suppress the quenching of triplet excitons while the hydrophobic microenvironment affords good water/moisture‐resistance ability. Moreover, the polymers with superior processability are successfully applied as optical coatings, prepreg, and afterglow displays. With this work, we provide a new strategy to promote the long‐term stability of polymeric UOP materials in high‐temperature‐humidity conditions.

Axially chiral materials exhibiting blue-emissive ultralong organic phosphorescence and intense circularly polarized luminescence

Axially chiral materials exhibiting blue-emissive ultralong organic phosphorescence and intense circularly polarized luminescence

Achieving Stable and Switchable Ultralong Room-Temperature Phosphorescence from Polymer-Based Luminescent Materials with Three-Dimensional Covalent Networks for Light-Manipulated Anticounterfeiting.

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