Organic Room Temperature Phosphorescence Materials Research Articles

Photo-Responsive Dynamic Organic Room-Temperature Phosphorescence Materials Based on a Functional Unit Combination Strategy.

A rational molecular design strategy facilitates the development of a purely organic room-temperature phosphorescence (RTP) material system with precisely regulated luminescence properties, which surely promotes its functional integration and intelligent application. Here, a functional unit combination strategy is proposed to design novel RTP molecules combining a folding unit with diverse luminescent cores. The different luminescent cores are mainly responsible for tunable RTP properties, while the folding unit contributes to the spin-orbit coupling (SOC) enhancement, which makes the RTP material design as workable as the building block principle. By this strategy, a series of color/lifetime-tunable RTP materials is achieved with unique photo-responsive RTP enhancement when subjected to UV irradiation, which expands their application scenarios in reusable privacy tags, advanced "4D" encryption, and phase separation analysis of blended polymers. This work suggests a simple and effective strategy to design purely organic RTP materials with tunable color and lifetime, and also provides new application options for photo-responsive dynamic RTP materials.

Naphthyl Substituted Impurities Induce Efficient Room Temperature Phosphorescence

AbstractAccidentally, it was found that triphenylamine (TPA) from commercial sources shows ultralong yellow‐green room temperature phosphorescence (RTP) like commercial carbazole, which however disappears for lab‐synthesized TPA with high purity. Herein, we for the first time identify the impurity types that cause RTP of commercial TPA, which are two N, N‐diphenyl‐naphthylamine isomers. Due to similar molecular polarity and very trace amount (≈0.8 ‰, molar ratio), these naphthyl substituted impurities can be easily overlooked. We further show that even at an extremely low amount (1000000 : 1, mass ratio) of impurities, RTP emission is still generated, attributed to the triplet‐to‐triplet energy transfer mechanism. Notably, this doping strategy is also applicable to the triphenylphosphine and benzophenone host systems, of which strong RTP emission can be activated by simply doping the corresponding naphthyl substituted analogues into them. This work therefore provides a general and efficient host/guest strategy toward high performance and diverse organic RTP materials.

Naphthyl Substituted Impurities Induce Efficient Room Temperature Phosphorescence.

Accidentally, it was found that triphenylamine (TPA) from commercial sources shows ultralong yellow-green room temperature phosphorescence (RTP) like commercial carbazole, which however disappears for lab-synthesized TPA with high purity. Herein, we for the first time identify the impurity types that cause RTP of commercial TPA, which are two N, N-diphenyl-naphthylamine isomers. Due to similar molecular polarity and very trace amount (≈0.8 ‰, molar ratio), these naphthyl substituted impurities can be easily overlooked. We further show that even at an extremely low amount (1000000 : 1, mass ratio) of impurities, RTP emission is still generated, attributed to the triplet-to-triplet energy transfer mechanism. Notably, this doping strategy is also applicable to the triphenylphosphine and benzophenone host systems, of which strong RTP emission can be activated by simply doping the corresponding naphthyl substituted analogues into them. This work therefore provides a general and efficient host/guest strategy toward high performance and diverse organic RTP materials.

Multi‐Color Pure Organic Room Temperature Phosphorescent Materials with Long Lifetime and High Efficiency

AbstractOrganic room temperature phosphorescent (ORTP) materials have garnered significant interest in the fields of anti‐counterfeiting, optical display, and bio‐imaging owing to their distinctive optical properties. However, a major drawback of most existing ORTP materials is their short phosphorescence lifetime and low quantum yields (QYs), which greatly limit their applicability across multiple fields. In this paper, a covalently assisted host‐guest doping strategy that involves embedding three aminobenzoic acids with different carboxylate substitution positions into a cyanuric acid (CA) matrix through covalent bonding using microwave heating is proposed. All three prepared ORTP materials exhibit long phosphorescence lifetime exceeding 600 ms and high phosphorescence quantum yields (PhQYs) surpassing 20%. Among them, the composite of 2‐aminoterephthalic acid (2‐A) anuric acid stands out with its unique blue phosphorescence, boasting an exceptional absolute photoluminescence quantum yield (PLQY) of 98.95% and remarkable phosphorescence quantum yield (PhQY) of 76.42%, along with a long lifetime of 800 ms. Importantly, these high‐performance ORTP materials have been successfully utilized in anti‐counterfeiting and display applications.

Thermal‐Annealing Enhanced Room‐Temperature Phosphorescence of Polymer‐Based Organic Materials

AbstractPolymer‐based organic room‐temperature phosphorescent (RTP) materials have recently attracted significant attention. In most of the previous works, ‘chemical approaches’ were applied to improve the performance of RTP materials, such as designing certain phosphors or selecting specific polymeric matrixes. However, enhancing triplet emission through facile ‘physical approaches’ is rarely reported. In this study, enhanced RTP emissions of phosphor‐doped polymers are reported by thermal annealing. By doping a difluoroboron β‐diketonate derivative into poly(diacetone acrylamide) (PDAAM), green RTP emissions can be obtained. After thermal annealing at 125 °C for 5 min, the afterglow duration of RTP increases from 2.6 to 5.3 s and also the brightness of RTP emission exhibits a threefold increase. Such post‐treatment is applicable for various polymeric matrixes. The mechanism underlying thermal‐annealing enhanced RTP is investigated. Moreover, it demonstrates that controlled RTP by thermal annealing can be used in information encryption and anti‐counterfeiting. This work provides new insight into the development of organic RTP materials with tunable emissions.

Recent Advances in Organic Molecular-to-Supramolecular Self-Assembled Room-Temperature Phosphorescent Materials for Biomedical Applications.

This minireview focuses on recent advancements in organic molecular-to-supramolecular self-assembled room-temperature phosphorescent (RTP) materials and their prospective biomedical applications. RTP materials, having their unique capacity to emit long-lasting phosphorescence at ambient temperature, have piqued researchers' interest in various biological applications, including biosensing, bioimaging, drug delivery, and photodynamic therapy (PDT). These materials have several benefits, including high sensitivity, remarkable photostability, and low cytotoxicity. RTP materials' self-assembly into supramolecular structures improves their performance and broadens their uses. Researchers have built organic RTP systems with long-lasting phosphorescence by leveraging weak noncovalent interactions in aquatic conditions. These materials have demonstrated incredible promise as biosensors that enable sensitive analyte detection and as photosensitizers in PDT that target and sensitize specific cell types. The review also outlines future directions and challenges in developing and utilizing pure organic RTP materials for biological imaging purposes, providing valuable guidelines for their future design and application.

Photoirradiation‐Gated Excitation‐Dependent Room‐Temperature Phosphorescence in Through‐Space Charge Transfer Molecules

AbstractOrganic materials showing reversible changes in persistent room‐temperature phosphorescence (RTP) upon exposure to external stimuli have attracted considerable attention in recent years. One potentially groundbreaking development in this area is the introduction of the gating concept for organic persistent RTP materials. This refers to a material where a desired responsive ability only occurs when it is triggered by a specific stimulus, but it remains a formidable challenge. In this study, photoirradiation‐gated excitation‐dependent (Ex‐De) persistent RTP is achieved. A series of molecules, triphenylphosphine and carbazole derivatives connected through flexible carbon chains, are designed and prepared. Upon removal of ultraviolet (UV) irradiation, all these compounds doped polyvinyl alcohol (PVA) films exhibit obvious blue or green afterglow RTP. Among them, (2‐(9H‐[3,9′‐bicarbazol]−9‐yl)ethyl)triphenylphosphonium bromide (TPP‐2C‐Cz) doped PVA film initially exhibits blue persistent RTP after removal of 300 nm excitation but no RTP upon ceasing 365 nm irradiation. Interestingly, upon UV irradiation with a power density of 0.05 W cm−2 (UVA) for 50 min, the Ex‐De RTP behavior of TPP‐2C‐Cz doped PVA film is activated. Eventually, photoirradiation‐gated Ex‐De afterglow emission will be used for a wide range of applications, including the quantitative determination of UV irradiation dose and the permanent record of UV irradiation history, and read on‐demand.

Electronic Modulation Induced Luminescence from Triphenylamine Derivative and Temperature Sensor Application

AbstractIn recent years, numerous long‐lived organic room temperature phosphorescence (RTP) systems have been well explored. However, the RTP emission mechanism of organic compounds is still not very clear. The structures of terphenyl amines (TPAs) are simple and their chromophores are definite, which makes them suitable for exploring the emission mechanism of organic RTP materials. A series of TPA derivatives are synthesized in this contribution. Excitingly, benefiting from a facile electronic characteristic modulation strategy, RTP emissions generated from TPAs are achieved successfully. The theoretical calculation and crystallographic analysis reveal that introducing electron‐donating substitutes is beneficial for the formation of a clear charge separation state and promoting triplet state energy transfer. This is the primary reason for the promotion effects of the electron‐donating substitutes on RTP emission. By varying the substituents and their substitution sites, the afterglow colors as well as the lifetime and efficiency of the resultant TPAs can be facilely tuned. Interestingly, o‐TPA‐OMe shows a temperature‐dependent fluorescence emission. Benefiting from these inspiring photoluminescence performances, these TPA derivatives can be applied in information encryption and temperature sensors.

Chaperone Mimetic Strategy for Achieving Organic Room-Temperature Phosphorescence based on Confined Supramolecular Assembly.

The development of organic materials that deliver room-temperature phosphorescence (RTP) is highly interesting for potential applications such as anticounterfeiting, optoelectronic devices, and bioimaging. Herein, a molecular chaperone strategy for controlling isolated chromophores to achieve high-performance RTP is demonstrated. Systematic experiments coupled with theoretical evidence reveal that the host plays a similar role as a molecular chaperone that anchors the chromophores for limited nonradiative decay and directs the proper conformation of guests for enhanced intersystem crossing through noncovalent interactions. For deduction of structure-property relationships, various structure-related descriptors that correlate with the RTP performance are identified, thus offering the possibility to quantitatively design and predict the phosphorescent behaviors of these systems. Furthermore, application in thermal printing is well realized for these RTP materials. The present work discloses an effective strategy for efficient construction of organic RTP materials, delivering a modular model which is expected to help expand the diversity of desirable RTP systems.

Achieving TADF and RTP with Stimulus‐Responsiveness and Tunability from Phenothiazine‐Based Donor−Acceptor Molecules

AbstractResearch of thermally activated delayed fluorescence (TADF) and room‐temperature phosphorescence (RTP) materials is attractive owing to their extensive applications in various fields. However, achieving organic TADF and RTP materials, particularly those with stimulus‐responsiveness and tunability, is highly desirable but challenging and rarely reported. Herein, two easily synthesized organic molecules are reported with abnormal stimulus‐responsive switchable TADF and RTP effects, in which phenothiazine (PTZ) and benzo[b]phenothiazine (BPTZ) based donor−acceptor molecules PTZ‐DBQ and BPTZ‐DBQ show mechanical‐induced TADF in crystalline phase and photo‐responsive RTP in doping poly(methyl methacrylate) (PMMA) films. This is the first time tetracyclic BPTZ has been used as a donor in achieving TADF and RTP materials, and it is found that BPTZ‐DBQ exhibits remarkably better photophysical properties than PTZ‐DBQ. Systematic studies of experimental results and theoretical calculations indicate that the conformational heterogeneity plays an essential role in achieving mechanical‐induced TADF with mechanochromic luminescence (MCL) property. Embedding the organic phosphors into rigid polymer matrices effectively suppresses the molecular motion, thus turning on the RTP emission channel. The conversion of 3O2 to 1O2 under UV irradiation is mainly responsible for the photo‐induced process. These multifunctional luminescent materials have great potential applications in chemical sensors, information encryption, and anti‐counterfeiting.

Construction and Application of Large Stokes-Shift Organic Room Temperature Phosphorescence Materials by Intermolecular Charge Transfer.

Notably, the intermolecular charge transfer between pyrene (Py) and benzophonenes (BPs) can significantly enhance the quantum yield of the triplet state of Py, which will convert Py from a fluorescence molecule to a phosphorescence molecule. The intermolecular charge transfer is confirmed by steady-state and time-resolved spectroscopy and theoretical study. Based on these foundations, Py is doped into BPs systems and a large Stokes-shift organic room temperature phosphorescence (ORTP) is observed. By using different benzophenone derivatives, a series of host-guest ORTP materials with different luminescent properties adjusted by intermolecular charge transfer features are developed. Fortunately, these host-guest ORTP systems from benzophenone derivatives and pyrene are readily fabricated, and the red gradient color lasting as long as 3 s is observed after removing UV excitation. This host-guest charge transfer strategy plays an important role in the mechanism of the luminous type shift. Our strategy paves the way to design ORTP materials conveniently and apply these materials in encryption and temperature alarm device.

Recent advances in multicolor organic room-temperature phosphorescence

Multicolor organic room temperature phosphorescence (RTP) has garnered wide research attention due to the long luminescence lifetime and tunable excited state properties, which show great potential in displays, anticounterfeiting, data encryption, and sensing. However, because of the sensitivity of triplet excitons of organic materials, the triplet emitting level of organic compounds is hard to manipulate. Therefore, realizing multicolor RTP in organic materials is still a huge challenge. In this review, we summarize recent advances in multicolor organic RTP materials, including the underlying luminescence mechanisms, design principles of multicolor phosphorescence, detailed photophysical behaviors, and their potential applications. The last part presents existing challenges and future perspectives, such as expanding the color gamut, enriching stimuli-responsive properties, improving the phosphorescence performance, and exploring more advanced applications. This review will provide inspiration and guidelines for constructing multicolor RTP materials and expanding their potential applications in organic electronics, bioelectronics, flexible electronics, and so on.

Stimuli Responsive Features of Organic RTP Materials: An Intriguing Carbazole-Cyclic Triimidazole Derivative.

Stimuli responsive luminescent materials possessing room temperature phosphorescence (RTP) are extremely desirable for various applications. The here investigated derivative of cyclic triimidazole (TT) functionalized with carbazole (Cz), namely TT-Ph-Cz, belongs to this class. TT-Ph-Cz possesses high conformational freedom resulting in rigidochromic and multi-stimuli responsive emissive behavior. It has been isolated as MeOH-solvated and de-solvated forms characterized by distinctive emissive features. In particular, the solvated form, in which hydrogen bonds with MeOH inhibit competitive non-radiative deactivation channels, possesses a higher quantum yield associated with a strong phosphorescence contribution which is preserved in DMSO/water solutions.

An elastic organic crystal with multilevel stimuli-responsive room temperature phosphorescence

•Elastic organic RTP crystal with multilevel stimuli responsiveness was first reported •Highest RTP quantum yield of 25.1% was recorded in elastic organic RTP crystal •Modulation of RTP was realized via the transition of excited state conformation •RTP single to double emission under external stimuli in single-component system In this work, we report a series of single-component molecules crystals named dialkyl 4,4′-oxalyldibenzoate (n-BZ) with both efficient room temperature phosphorescence (RTP) emission, multilevel stimuli responsiveness, and elasticity or flexibility. The crystalline n-BZ will change from original RTP single emission to RTP dual emission after grinding or thermal annealing (TA). Interestingly, the emission wavelength difference between the RTP dual-emission peaks after grinding or TA reaches 82 nm with emission color changes from cyan blue to orange. In addition, to our knowledge, the largest RTP quantum yield of 25.1% (6-BZ) has been achieved as the highest recorded for organic RTP elastic crystals. Through a series of experiments and theoretical calculations, we demonstrate that the multilevel stimuli responsiveness of n-BZ originates from the transition of excited state conformation and its elasticity from many weak intermolecular interactions, which will provide a molecular design and construction strategy for organic stimuli-responsive RTP materials. In this work, we report a series of single-component molecules crystals named dialkyl 4,4′-oxalyldibenzoate (n-BZ) with both efficient room temperature phosphorescence (RTP) emission, multilevel stimuli responsiveness, and elasticity or flexibility. The crystalline n-BZ will change from original RTP single emission to RTP dual emission after grinding or thermal annealing (TA). Interestingly, the emission wavelength difference between the RTP dual-emission peaks after grinding or TA reaches 82 nm with emission color changes from cyan blue to orange. In addition, to our knowledge, the largest RTP quantum yield of 25.1% (6-BZ) has been achieved as the highest recorded for organic RTP elastic crystals. Through a series of experiments and theoretical calculations, we demonstrate that the multilevel stimuli responsiveness of n-BZ originates from the transition of excited state conformation and its elasticity from many weak intermolecular interactions, which will provide a molecular design and construction strategy for organic stimuli-responsive RTP materials.

Ultralong organic room-temperature phosphorescence, multiple stimulus responsiveness and high-level anti-counterfeiting based on multifunctional carbazolyl imidazolopyridine

Ultralong organic room-temperature phosphorescence materials induced by host−guest doping and the underlying mechanism have become the current research focus. Furthermore, high-level anti-counterfeiting and information encryption require multifunctional luminescent materials. Here, CzIP and L-CzIP with push−pull electronic system are successfully constructed by imidazopyridine units and commercial/self-made carbazole. The comparison experiment results indicate that trace isomer doping not only shows slight influence on crystal stacking and molecular space conformation but also significantly changes fluorescence and phosphorescence spectra and phosphorescence lifetime by boosting intersystem spin–orbit coupling. Non-radiative relaxation of CzIP and L-CzIP can be effectively inhibited by polymethyl methacrylate (PMMA) doping but not for crystallize. PMMA doping further confirms intrinsic phosphorescent characteristic of L-CzIP, whose room-temperature phosphorescence lifetime (84.83 ms) is close to that of CzIP (100.14 ms). Concentration-dependent fluorescent and phosphorescent emission and dynamic phosphorescent emission are also observed for CzIP in PMMA film. More importantly, a new aminopyridine/CzIP-doped system gives room-temperature phosphorescence lifetimes of 657.56 ms and afterglow lifetimes of 4 s. Notably, CzIP also shows high-contrast mechanochromism, selective response and differentiation to HCl, CF3COOH, and CH3COOH, and excellent detection capability to picric acid in aqueous medium and solid state. Finally, various anti-counterfeiting and encryption patterns are successfully constructed based on multifunction of CzIP. This work not only provides a multifunctional luminous material but also more importantly provides a theoretical basis and experimental guidance for designing novel ultralong organic room-temperature phosphorescence materials and achieving high-level anti-counterfeiting and encryption.

Recent advances in room temperature phosphorescence of chiral organic materials.

Room temperature phosphorescence (RTP) in purely organic materials is an uncommon phenomenon of emission, which can be characterized by a long persistent luminescence after removal of the excitation source. In the recent years, RTP organic materials have received a considerable attention due to their high application potential in various advancing technologies, ranging from optoelectronic to biomedical applications. In parallel, many progresses have been achieved on the rationalization of this process and led to the emergence of innovative strategies aiming to achieve highest performances both in terms of phosphorescence efficiency and lifetime. While the topic is still on an ascendant development, the generation of circularly polarized phosphorescent (CPP) emission from purely organic molecules is by far much less explored and remains an impressive challenge. Still, the perspective of CPP materials appears as an interesting opportunity to answer several comprehensives issues existing in the field. In this article, we define, in a straightforward way, basic principles and key notions for the generation of RTP and CPluminescence (CPL) guiding the design toward CPP materials. After this brief insight, recent advances in the field of chiral organic RTP materials are discussed with an emphasis on their CP-RTP properties. Based on this development, the conclusion drawn allows establishing the next challenges and future opportunities standing in the field.

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.

Recent advances in room temperature phosphorescence materials: design strategies, internal mechanisms and intelligent optical applications.

Room temperature phosphorescence (RTP) materials comprising organic-inorganic hybrid, pure organic, and polymer RTP materials have been a research focus due to their tunable molecular structures, long emission lifetimes and extensive optical applications. Many design methods including halogen bonding interactions, heavy atom effect, metal-organic frameworks, polymerization, host-guest doping, and H-aggregation have been developed by RTP researchers. Narrowing the energy gap between the S1 and lowest Tn states, enhancing the intersystem crossing (ISC) rate, increasing the spin-orbit coupling (SOC) value and stabilizing triplet emission states are the core factors to promoting RTP performance. In this review, lots of cases of organic-inorganic hybrid, pure organic, and polymer RTP materials with advanced design strategies, excellent RTP properties and intelligent applications have been classified and sorted. Their molecule structural designability and stimulus responsiveness endow them with RTP adjustability, which makes them excellent phosphors for modern optical applications. This review provides a systematic case elaboration of typical RTP systems in recent years and identifies the future challenges to improving RTP performance and finding novel applications.

Recent advances in metal-free phosphorescent materials for organic light-emitting diodes

This review discusses organic room temperature phosphorescent materials for the emitting layer of OLEDs. The existing circumstances, potential and challenges of metal-free phosphorescent OLEDs are summarized.

Organic room-temperature phosphorescence materials for bioimaging.

Organic room-temperature phosphorescence (RTP) materials are currently the focus of research in the field of bioimaging. In comparison with the conventional imaging modalities based on organic fluorescent dyes, RTP materials with long lifetime enable time-resolved imaging to improve the imaging resolution by avoiding autofluorescence. In this review, we will start with summarizing strategies for achieving high performance RTP materials for bioimaging, including the development of RTP-compounds, host-guest doping materials, and supramolecular assemblies. We then discuss the optimization of nanonization processes to obtain RTP nanoparticles with controllable size, high dispersibility, and improved stability. The differences between top-down and bottom-up approaches are further described. Finally, we briefly introduce the emerging methods for preparing RTP materials for bioimaging.