Room Temperature Phosphorescence Emission Research Articles

Regulation of Thermally Activated Delayed Fluorescence to Room‐Temperature Phosphorescent Emission Channels by Controlling the Excited‐States Dynamics via J‐ and H‐Aggregation

AbstractControl of excited‐state dynamics is key in tuning room‐temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF) emissions but is challenging for organic luminescent materials (OLMs). We show the regulation of TADF and RTP emissions of a boron difluoride β‐acetylnaphthalene chelate (βCBF2) by controlling the excited‐state dynamics via its J‐ and H‐aggregation states. Two crystalline polymorphs emitting green and red light have been controllably obtained. Although both monoclinic, the green and red crystals are dominated by J‐ and H‐aggregation, respectively, owing to different molecular packing arrangements. J‐aggregation significantly reduces the energy gap between the lowest singlet and triplet excited states for ultra‐fast reverse intersystem crossing (RISC) and enhances the radiative singlet decay, together leading to TADF. The H‐aggregation accelerates the ISC and suppresses the radiative singlet decay, helping to stabilize the triplet exciton for RTP.

Matrix‐free room‐temperature phosphorescence graphitic carbon nitride quantum dots based on halogen bond interactions for security applications

AbstractHerein, we first designed a one‐step strategy to achieve matrix‐free room temperature phosphorescence (RTP) materials by low temperature solid phase synthesis, using sodium citrate as carbon source and urea as nitrogen source. The NaF, NaCl, NaBr, and NaI were chosen as the inducer source of halogens to effective trigger the RTP emission from graphitic carbon nitride quantum dots (CNQDs) denoted F‐CNQDs, Cl‐CNQDs, Br‐CNQDs and I‐CNQDs. All the doped‐CNQDs emitted bright fluorescence upon 365 nm irradiation. After the 365 nm UV lamp is off, only the Br‐CNQDs showed green phosphorescence which can be observed by naked eye. The phosphorescence emission of Br‐CNQDs is excitation‐dependent from 510 to 610 nm with the average RTP lifetime of 70 milliseconds, which indicated Br‐CNQDs could exhibit color‐tunable phosphorescence. When 365 nm UV is off, Br‐CNQDs emitted green afterglow for about 3 seconds observed naked eye, while the Br‐CNQDs presented visible yellow afterglow for about 3 seconds with ceasing off 395 nm irradiation. The absolute phosphorescence quantum yield (PQY) of the Br‐CNQDs powder reaches up to 3.64%. Thus, the color change and long lifetime of phosphorescence from the excitation‐dependent feature could provide a security application for counterfeiting and information protection systems.

Room-Temperature Phosphorescence Emitters Exhibiting Red to Near-Infrared Emission Derived from Intermolecular Charge-Transfer Triplet States of Naphthalenediimide-Halobenzoate Triad Molecules.

Invited for the cover of this issue is Toshikazu Ono, Yoshio Hisaeda and co-workers at Kyushu University and their collaborators at Ochanomizu University, Chuo University, and Institute for Molecular Science. The image depicts a molecular assembly structure shining like a jewel, glowing in the red-to-near infrared region. Read the full text of the article at 10.1002/chem.202100906.

Hydrothermal Synthesis of Zinc-Doped Silica Nanospheres Simultaneously Featuring Stable Fluorescence and Long-Lived Room-Temperature Phosphorescence.

Fluorescence and phosphorescence are known as two kinds of fundamental optical signals, which have been used for myriad applications. To date, simultaneous activation of stable fluorescence and long-lived room-temperature phosphorescence (RTP) emission in the aqueous phase remains a big challenge. We prepare zinc-doped silica nanospheres (Zn@SiNSs) with fluorescence and RTP properties using a facile hydrothermal synthetic strategy. For the as-prepared Zn@SiNSs, the recombination of electrons and holes in defects and defect-stabilized excitons derived from oxygen vacancy/C=N bonds lead to the production of stable fluorescence and long-lived RTP (emission lasting for ≈9 s, quantum yield (QY): ≈33.6 %, RTP lifetime: ≈236 ms). The internal Si-O bonded networks and hydrophilic surface in Zn@SiNSs can reduce nonradiative decay to form self-protective RTP, and also provide high water solubility, excellent pH- and photostability.

Red-light excited efficient metal-free near-infrared room-temperature phosphorescent films.

A set of red-light-excited, metal-free room-temperature phosphorescence (RTP) systems was constructed with brominated phenolsulfonephthaleine derivatives. The best metal-free RTP system has the reddest near-infrared (NIR) RTP emission (λp = 819 nm) with the highest phosphorescence quantum yield (ΦRTP = 3.0%) so far identified. The RTP emission can be switched ON-OFF by adding acid and alkali alternately. A logic operation with half-subtractor function and dual-channel response (visible light emission/NIR RTP emission) was also constructed based on these properties.

Achieving Purely Organic Room-Temperature Phosphorescence Mediated by a Host-Guest Charge Transfer State.

Strategies for developing purely organic materials exhibiting both high efficiency and persistent room-temperature phosphorescence (RTP) have remained ambiguous and challenging. Herein, we propose that introducing an intermediate charge transfer (CT) state into the donor-acceptor binary molecular system holds promise for accomplishing this goal. Guest materials showing gradient ionization potentials were selected to fine-tune the intermolecularly formed CT state when doped into the same host material with a large electron affiliation potential. Such a CT intermediate state accelerates the population of the triplet exciton to benefit phosphorescent emission and decreases the phosphorescence lifetime via quenching the long-lived triplet excitons. As a result, a "trade-off" between a long phosphorescence lifetime (595 ms) and a high phosphorescent quantum yield (27.5%) can be obtained by tuning the host-guest energy gap offset. This finding highlights the key role of CT in RTP emission and provides new guidance for developing novel RTP systems.

Thermally Driven Amorphous‐Crystalline Phase Transition of Carbonized Polymer Dots for Multicolor Room‐Temperature Phosphorescence

AbstractMulticolor carbon dot (CD)‐based nanomaterials offer a variety of opportunities for potential applications in bioimaging, optoelectronic devices, and information security. However, it still remains a challenge to modulate the conjugated π‐structure of CDs to achieve multicolor room‐temperature phosphorescence (RTP). Herein, the authors present a strategy based on thermally driven amorphous−crystalline phase transition to achieve multicolor carbonized polymer dots (CPDs) with the emission color tunable from green to orange‐red. This is the first report on multicolor RTP emission from CDs by means of thermal stimulus. Further investigations reveal that the formation of self‐protective covalently crosslinked frameworks and codoping of multiple heteroatoms play a crucial role in the production of RTP. RTP color tunability can be attributed to different crystalline contents of the conjugated π‐domain within CPDs. Potential application of the developed CPDs as printable and writable security inks for advanced multilevel anti‐counterfeiting and encryption is demonstrated. This work paves a path for the development of multicolor RTP materials and suggests great potential of CDs in exploiting novel optical materials toward intriguing applications.

Blue-to-green manipulation of carbon dots from fluorescence to ultralong room-temperature phosphorescence for high-level anti-counterfeiting

Carbon dots (CDs) with fluorescence (FL) and room-temperature phosphorescence (RTP) optical properties have attracted dramatically growing interest in anti-counterfeiting application. Herein, color-tunable and stable FL and ultralong RTP (to naked eyes ~14 s) are successfully achieved in CDs system. Encoding information and patterns fabricated by directly screen-printing method are invisible to eyes under natural light. Interestingly, clear and multicolor patterns with tunable FL and RTP emissions are identified under the 365 nm, 395 nm and 465 nm excitation and removal of them, indicating potential application of carbon dots with different FL and RTP outputs in the high-level photonic anti-counterfeiting field.

Photochromic and Room-Temperature Phosphorescent D–A Hybrid Crystals Induced by Anion−π Interactions

The donor–acceptor (D–A) hybrid crystals are an emerging class of crystalline hybrid complexes composed of semiconductive organic and inorganic components at the molecular level. These unique crystals not only possess intrinsic electron-transfer photochromic properties upon the high-energy irradiations but possibly exhibit unusual room-temperature phosphorescence (RTP) emissions when suitable charge-transfer states formed with the low-energy irradiations. Herein, we reported that an interesting class of D–A hybrid crystals indeed exhibited two such properties in which two D–A components, polyoxometalates (POMs) and naphthalene diimides (NDIs), are intercontacted through uncommon anion−π interactions. To go deep into their structure–property relationships, five D–A hybrid crystals with different POMs (PW12O403–, SiW12O404– or Mo6O192–) and protonated (or zinc-coordinated) pyrazolyl-substituted NDIs have been synthesized. Their light-induced color changes and RTP properties have been systematically investigated, which revealed that the matching electron energy levels of POMs and NDIs are the first factor to decide their RTP emissions while the heavy atoms in both POMs and coordination metal cations are mainly beneficial to their quantum yields. Notably, the RTP quantum yields for these interesting photochromic D–A hybrid crystals are up to 5.9%.

Arylene Diimide Phosphors: Aggregation Modulated Twin Room Temperature Phosphorescence from Pyromellitic Diimides

AbstractArylene diimide derived ambient organic phosphors are seldom reported despite their potential structural characteristics to facilitate the triplet harvesting. In this context, highly efficient room temperature phosphorescence (RTP) from simple, heavy‐atom substituted pyromellitic diimide derivatives in amorphous matrix and crystalline state is reported here. Multiple intermolecular halogen bonding interactions among these phosphors, such as halogen‐carbonyl and halogen‐π resulted in the modulation of phosphorescence, cyan emission from monomeric state and orange‐red emission from its aggregated state, to yield twin RTP emission. Remarkably, the air‐stable phosphorescence presented here own one of the highest quantum yield (≈48 %) among various organics in orange‐red emissive region.

Arylene Diimide Phosphors: Aggregation Modulated Twin Room Temperature Phosphorescence from Pyromellitic Diimides.

Arylene diimide derived ambient organic phosphors are seldom reported despite their potential structural characteristics to facilitate the triplet harvesting. In this context, highly efficient room temperature phosphorescence (RTP) from simple, heavy-atom substituted pyromellitic diimide derivatives in amorphous matrix and crystalline state is reported here. Multiple intermolecular halogen bonding interactions among these phosphors, such as halogen-carbonyl and halogen-π resulted in the modulation of phosphorescence, cyan emission from monomeric state and orange-red emission from its aggregated state, to yield twin RTP emission. Remarkably, the air-stable phosphorescence presented here own one of the highest quantum yield (≈48 %) among various organics in orange-red emissive region.

Recent Advances of Polymer-Based Pure Organic Room Temperature Phosphorescent Materials.

Room temperature phosphorescence (RTP) has attracted broad attention due to their long lifetimes, large Stokes shift, and widespread applications. Achieving RTP emission has long been a challenging task under common conditions, for the necessary requirements of promoting intersystem crossing processes and suppressing nonradiative transitions are always tough to meet. Over the past decade, RTP has been obtained through several specific strategies, among which an important method lies in immobilizing phosphors into polymer matrices. Via the effect of steric overcrowding exerted by the polymeric structures, the phosphorescence of the initial phosphors can be promoted significantly. Hence, polymer-based pure organic materials have proved to be one newly emerging subject in the field of RTP materials. In this review article, the progresses of polymer-based pure organic room temperature phosphorescent materials are elaborated from four main approaches, including doped polymer systems, copolymer systems, homopolymer systems, and host-guest complexation systems, whereby the design principles, synthesis methods, possible mechanisms, and applications are summarized and discussed in detail.

Recent progress on pure organic room temperature phosphorescent polymers

AbstractSo far, pure organic room temperature phosphorescence (RTP) materials are developing rapidly and have become a research hotspot in the scientific community. They are regarded as valuable resources with great potential for development in many fields, such as biomedicine, information multi‐level encryption, smart anti‐counterfeiting, and so on. Among them, a series of pure organic RTP polymer systems emerged at the right moment based on the excellent properties of polymers such as easy processing, low cost, and good biocompatibility. Furthermore, the huge molecular weight, long‐chain intertwined structure, and potential interactions with phosphors of polymers make them a focus for RTP emission. Herein, we describe the development history of this system in detail, explore the necessary factors for highly efficient emission from the phosphorescence emission process, and based on the dual effects of enhancing phosphorescence emission and shortening luminescence lifetime brought by heavy atoms, we summarize the internal mechanism and achievements of various researches from the perspective of heavy atom–containing and non‐heavy atom systems.

Carbon dots-based room-temperature phosphorescent test strip: Visual and convenient water detection in organic solvents

Room-temperature phosphorescence (RTP) has got more and more attentions in sensing due to its specific optical properties of longer lifetime and higher signal-to-noise ratio. However, developing low-cost RTP test strip (RTP-TS) for visual and convenient detection is still a challenging. Here, we reported the construction of new RTP-TS based on N-doped carbon dots (N-CDs), which was synthesized with a simple hydrothermal method using isophthalic acid (IPA) and ethylenediamine (EDA) as precursors. The constructed RTP-TS exhibited bright green RTP emission under UV excitation (365 nm) with a longer lifetime of 0.769 s. The mechanism studying indicates the efficient RTP emission of RTP-TS is from the N/O-rich CDs and the anchor effect of polyacrylic acid (PAA), which can restrict the varication/rotation of N-CDs by H-bonds, and suppress the nonirradiative quenching processes. Nevertheless, the presence of H2O can destroy these H-bonds and therefore effectively quench the RTP emission of RTP-TS, the changes of RTP intensity is inversely proportional to H2O concentration. Based on this, the RTP-TS has been successfully used for visual and convenient water detection in several common organic solvents (ethanol, acetone, acetonitrile, tetrahydrofuran) with high sensitivity, excellent stability, accuracy and reliability. This work will open a new approach to construct visual RTP-TS for practical use in sensing.

Self-assembly-induced luminescence of Eu3+-complexes and application in bioimaging.

Design and engineering of highly efficient emitting materials with assembly-induced luminescence, such as room-temperature phosphorescence (RTP) and aggregation-induced emission (AIE), have stimulated extensive efforts. Here, we propose a new strategy to obtain size-controlled Eu3+-complex nanoparticles (Eu-NPs) with self-assembly-induced luminescence (SAIL) characteristics without encapsulation or hybridization. Compared with previous RTP or AIE materials, the SAIL phenomena of increased luminescence intensity and lifetime in aqueous solution for the proposed Eu-NPs are due to the combined effect of self-assembly in confining the molecular motion and shielding the water quenching. As proof of concept, we also show that this system can be further applied in bioimaging, temperature measurement and HClO sensing. The SAIL activity of the rare-earth (RE) system proposed here offers a further step forward on the roadmap for the development of RE light conversion systems and their integration in bioimaging and therapy applications.

Tunable multicolor room-temperature phosphorescence including white-light emission from amorphous copolymers

Research on amorphous pure organic room-temperature phosphorescent (RTP) materials has been receiving great attentions in recent years, while smart materials with color-tunable RTP emission are still rare, especially those with white-light emission and white afterglow. A series of pure organic amorphous copolymers with dual-emissive RTP have been synthesized by copolymerizing benzoic acid, 4-bromo-1,8-naphthalic anhydride and acrylamide with different feeding ratios. The two phosphor moieties display different absorption spectra, different RTP emission spectra and lifetimes, which can induce tunable multicolor RTP with different feeding ratios and different excitation wavelengths, including white-light emission (CIE coordinates (0.32, 0.33)). Moreover, time-dependent multicolor afterglow can also be observed because of the different decay lifetimes of these two phosphors, including nearly white afterglow. Since the acrylamide polymers are water-soluble, their RTP emission can be quenched with the existence of water by breaking the rigid structure, which makes their emission color tunable under different humidity conditions.

Pure room temperature phosphorescence emission of an organic host–guest doped system with a quantum efficiency of 64%

A doped system with strong pure phosphorescent emission has been constructed, and the QY phos. can reach up to 64%. The ISC efficiency of excitons can be adjusted by changing the excitation wavelength, so the doped materials can selectively emit green phosphorescence or cyan fluorescence.

Unveiling the theoretical mechanism of purely organic room temperature phosphorescence emission and heteroatomic effects on singlet-triplet intersystem crossing for isopropylthioxanthone derivatives

In this work, the density functional theory (DFT) and time-dependent density functional theory (TDDFT) method were performed to investigate the mechanism of purely organic room temperature phosphorescence emission and heteroatomic effect on the electronic structures and photochemistry for the isopropylthioxanthone (ITX) and its derivatives. We designed a series of compounds by replacing sulfur atom on the heterocyclic ring and oxygen atom on the double bond of ITX by the atoms from the same group, which were named as O-, Se-HC-ITX, and S-, Se-DB-ITX. The result shows that both different heteroatoms and different positions of heteroatoms have a prominent impact on the photochemical properties of ITX derivatives. With the change of heteroatoms and their positions, the molecular structures are distorted causing the change of electron densities distribution and energy levels of the frontier molecular orbitals. The energy gaps between lowest unoccupied molecular orbitals (LUMOs) and the highest occupied molecular orbitals (HOMOs) are red-shifted from 6.83 to 5.28 eV with the heteroatom changed from O to Se, which is relative to the energy-level configuration. As a result, the maximum absorption wavelengths of the UV absorption spectra are red-shifted from 218 to 259 nm, and the fluorescence and phosphorescence emission spectra can be tuned from the ultraviolet region to the visible region even to the infrared region with the heteroatom on the double bond changed from O to Se. Moreover, the change of heteroatoms also introduces into the heavy-atom effect which enhances the spin-orbital coupling (SOC) between singlet and triplet excited states dramatically and increases the probability of singlet-triplet intersystem crossing (ISC) happening which lead to purely organic room temperature phosphorescence (RTP). Hence, this work demonstrates that the change-heteroatom strategy can make the tunable photochemical properties realizable, which provides a new strategy for researches to design molecular systems.

Tunable-Emission Amorphous Room-Temperature Phosphorescent Polymers Based on Thermoreversible Dynamic Covalent Bonds.

Pure organic room-temperature phosphorescence (RTP) materials are useful for photoelectric, biochemical devices, and bioimaging sensors. In the last few years, dynamic covalent chemistry has aroused substantial attention as it offers a way to create intelligent materials with feedback and response functions. Through a Diels-Alder reaction, a [4+2] cycloaddition reaction between dienes and dienophiles, three polymers were synthesized that can be reversibly transformed by thermally reversible dynamic covalent bonds. All polymers show decent RTP emission with different colors. For the poly-Br-An solid, the absolute phosphorescence quantum yield reaches up to 12 %. This study provides a new method for the rational design and synthesis of tunable-emission organic RTP materials via dynamic covalent bonds.

Tunable‐Emission Amorphous Room‐Temperature Phosphorescent Polymers Based on Thermoreversible Dynamic Covalent Bonds

AbstractPure organic room‐temperature phosphorescence (RTP) materials are useful for photoelectric, biochemical devices, and bioimaging sensors. In the last few years, dynamic covalent chemistry has aroused substantial attention as it offers a way to create intelligent materials with feedback and response functions. Through a Diels–Alder reaction, a [4+2] cycloaddition reaction between dienes and dienophiles, three polymers were synthesized that can be reversibly transformed by thermally reversible dynamic covalent bonds. All polymers show decent RTP emission with different colors. For the poly‐Br‐An solid, the absolute phosphorescence quantum yield reaches up to 12 %. This study provides a new method for the rational design and synthesis of tunable‐emission organic RTP materials via dynamic covalent bonds.