Organic Luminescent Materials Research Articles

A cascade X-ray energy converting approach toward radio-afterglow cancer theranostics.

Leveraging X-rays to initiate prolonged luminescence (radio-afterglow) and stimulate radiodynamic 1O2 production from optical agents provides opportunities for diagnosis and therapy at tissue depths inaccessible to light. However, X-ray-responsive organic luminescent materials are rare due to their intrinsic low X-ray conversion efficiency. Here we report a cascade X-ray energy converting approach to develop organic radio-afterglow nanoprobes (RANPs) for cancer theranostics. RANPs comprise a radiowave absorber that down-converts X-ray energy to emit radioluminescence, which is transferred to a radiosensitizer to produce singlet oxygen (1O2). 1O2 then reacts with a radio-afterglow substrate to generate an active intermediate that simultaneously decomposes to emit radio-afterglow. Through finetuning such a cascade, intraparticle radioluminescence energy transfer and the 1O2 transfer process, RANPs possess tunable wavelengths and long half-lives, and generate radio-afterglow and 1O2 at tissue depths of up to 15 cm. Moreover, we developed a biomarker-activatable nanoprobe (tRANP) that produces a tumour-specific radio-afterglow signal, leading to ultrasensitive detection and the possibility of surgical removal of diminutive tumours (1 mm3) under an X-ray dosage 20 times lower than inorganic materials. The efficient radiodynamic 1O2 generation of tRANP permits complete tumour eradication at an X-ray dosage lower than clinical radiotherapy and a drug dosage one to two orders of magnitude lower than most existing inorganic agents, leading to prolonged survival rates with minimized radiation-related adverse effects. Thus, our work reveals a generic approach to address the lack of organic radiotheranostic materials and provides molecular design towards precision cancer radiotherapy.

Recent Advances of Boron‐Containing Chiral Luminescent Materials†

Comprehensive SummaryAs a class of organic dyes, boron‐containing compounds play an important role in organic luminescent materials. They have attracted considerable attention due to their unique photophysical properties. Chiral luminescent systems have a wide range of practical applications in biological imaging, optoelectronic devices, information storage and 3D display. Boron‐containing chiral luminescent materials can not only effectively improve the luminescent properties of CPL materials, but also bring unique properties to the system, which enables them to be used as favorable CPL emitting materials for an expanded range of applications. Here, we review the research progress of boron‐containing chiral luminescent materials by the detailed discuss according to different chiral skeletons, such as point chirality, 1,1’‐binaphthyl, [n]helicenes, [2,2]paracyclophane and pillar[5]arenes. We believe that this review is of significance for the development of boron‐containing compounds and CPL materials. Key ScientistsThe studies of circularly polarized luminescence (CPL) based on small organic molecules have advanced significantly. However, boron‐containing chiral luminescent materials have gained attention only in recent years. In 2019, Zhao's group prepared a binaphthalene derivative modified with triarylborane, representing the organic small molecule luminescent material to exhibit CPL characteristics responsive to both solvent and fluoride ions. In 2020, the Chen's group used the unique luminescence properties and steric effects of triarylborane and triphenylamine to prepare CPL materials based on the planar chiral pillar[5]arenes. In 2021, Wang's group developed a new class of B,N‐embedded double hetero[7]helicenes molecules that exhibit strong chiroptical responses in the UV‐visible region. In the same year, He's group used asymmetric reactions to synthesize boron‐based point‐chirality compounds with high efficiency and enantioselectivity. In 2023, Ravat synthesized 1,4‐B,N‐embedded helicenes exhibiting narrow‐band fluorescence and CPL. During this period, Matthias Wagner et al obtained (BO)2‐doped tetrathia[7]helicene via an efficient four‐step synthesis, and Zheng reported the nearly pure green circularly polarized electroluminescent device (CP‐OLED). In 2024, Chen's group prepared B,N‐embedded hetero‐[9]helicenes offering a pathway towards significantly enhanced efficiency in helicene‐based CPEL.

The Molecular Design and Electroluminescent Performance of Near-Infrared (NIR) Iridium(III) Complexes Bearing Isoquinoline-, Phthalazine- and Phenazine-Based Ligands.

Near-infrared (NIR) light has characteristics of invisibility to human eyes, less background interference, low light scattering, and strong cell penetration. Therefore, NIR luminescent materials have significant applications in imaging, sensing, energy, information storage and display. The development of NIR luminescent materials thus has emerged as a highly dynamic area of research in the realm of contemporary materials. To date, NIR luminescent materials are roughly divided into inorganic materials and organic materials. Compared with inorganic materials, organic NIR luminescent materials have become a hot research topic in recent years due to their rich sources, easy control of structure, simple preparation process, low cost, and good film-forming properties. Among them, iridium(III) [Ir(III)] complexes exhibit excellent properties such as thermal stability, simple synthesis, easy color modulation, short excited state lifetimes, and high brightness, thus becoming one of the ideal luminescent material systems for preparing high-quality organic light-emitting diodes. Therefore, how to obtain Ir(III) complexes with NIR emission and high efficiency through molecular design is a necessary and promising research topic. This work reviews the research progress of representative NIR Ir(III) complexes bearing isoquinoline-, phenazine-, and phthalazine-based ligands reported in recent years and introduces the design strategies and electroluminescent performances of NIR Ir(III) complexes.

Copper‐Mediated C–H Cyclization of Heterocycles: Facile Access to Multiple Resonance Thermally Activated Delayed Fluorescence Materials

AbstractReported herein is the first example of a copper‐mediated C─H cyclization of heterocycles to construct structurally diverse carbonyl‐bridged triphenylamine compounds with multiple resonance thermally activated delayed fluorescence (TADF) characteristics. The one‐pot synthesis method exhibits a broad substrate scope and opens a new avenue for rapidly screening high‐performance organic TADF luminescent materials. Novel organic TADF single‐molecule white‐light material 5g with anti‐Kasha dual‐emission character is the first time developed herein and shows a Commission Internationale de l’Eclairage (CIE) coordinate of (0.33, 0.35) in the thin film, and can be used to fabricate robust and low cost organic white light‐emitting diodes (LED). Furthermore, the anti‐Kasha dual‐emission material 5g is fabricated as water‐dispersed nanoparticles (NPs)NPs, which can be efficiently endocytosed into the HeLa cells and dual emission imaging in living cells, and be used in two‐channel emission intensity ratio imaging to observe the intercellular structure.

Pyrene‐Modified Blue Emitters for OLED Applications: Efficiency and Stability Advancements

AbstractBlue light materials have always posed a challenge in the OLED industry due to their high energy, which negatively impacts the stability of organic luminescent materials. Consequently, there is a significant disparity in efficiency and lifespan compared to red and green materials. In this study, we successfully synthesized three blue fluorescent luminescent materials with high fluorescence quantum efficiency by utilizing pyrene as the core. The 1,6‐positions of pyrene were substituted with diphenylamine and further modified with methoxy, isopropyl, and dibenzofuran. These modifications were introduced to enhance efficiency, increase spatial site resistance, and improve structural rigidity. Each structure exhibits a maximum current efficiency of over 8.2 cd/A and a maximum external quantum efficiency (EQE) of more than 5.8%. Notably, the compound N1,N6‐bis(4‐isopropylphenyl)‐N1,N6‐bis(2‐methoxyphenyl)pyrene‐1,6‐diamine (BD1), with methoxy modification, achieves a maximum current efficiency of 9.3 cd/A. Additionally, the compound N1,N6‐bis(dibenzo[b,d]furan‐4‐yl)‐N1,N6‐di‐o‐tolylpyrene‐1,6‐diamine (BD2) exhibits significantly less EQE roll‐off. This article provides valuable insights into the substitution‐based modification strategy for optimizing blue light performance in OLED applications.

Study on the Influence of Host-Guest Structure and Polymer Introduction on the Afterglow Properties of Doped Crystals.

Due to their low cost, good biocompatibility, and ease of structural modification, organic long-persistent luminescence (LPL) materials have garnered significant attention in organic light-emitting diodes, biological imaging, information encryption, and chemical sensing. Efficient charge separation and carrier migration by the host-guest structure or using polymers and crystal to build rigid environments are effective ways of preparing high-performance materials with long-lasting afterglow. In this study, four types of crystalline materials (MODPA: DDF-O, MODPA: DDF-CHO, MODPA: DDF-Br, and MODPA: DDF-TRC) were prepared by a convenient host-guest doping method at room temperature under ambient conditions, i.e., in the presence of oxygen. The first three types exhibited long-lived charge-separated (CS) states and achieved visible LPL emissions with durations over 7, 4, and 2 s, respectively. More surprisingly, for the DDF-O material prepared with PMMA as the polymer substrate, the afterglow time of DDF-O: PMMA was longer than 10 s. The persistent room-temperature phosphorescence effect caused by different CS state generation efficiencies and rigid environment were the main reason for the difference in LPL duration. The fourth crystalline material was without charge separation and exhibited no LPL because it was not a D-A system. The research results indicate that the CS state generation efficiency and a rigid environment are the key factors affecting the LPL properties. This work provides new understandings in designing organic LPL materials.

Organic long-persistent luminescence materials with stretchability enabled by SEBS

Polymer-based organic long-persistent luminescence materials (OLPLMs) with good stretchability have attracted considerable attention due to their effective response to environmental stimuli and wide selection of application scenarios. However, the lack of a suitable stretchable polymer matrix has been a major limitation in the development of strongly stretchable OLPLMs. Here, we present a straightforward and universal method to fabricate a stretchable afterglow effect under ultraviolet or visible light by blending the flexible polymer styrene-ethylene-butylene-styrene (SEBS) with various phosphors that display superior stretchability compared to the reported OLPLMs. To further highlight the outstanding benefits of such stretchable OLPLMs in the field of security applications, we show their practical cases in safety warning, identity recognition and oxygen detection scenarios. This universal material preparation strategy will simplify the production of stretchable OLPLMs and broaden the application range of phosphors or luminescent dyes.

Synthesis, nonlinear optical activity, solvents effect, β-cyclodextrin effect, and cytotoxic activity on skin fibroblast and breast cancer cell lines of a new chalcone derivative of nabumetone

The use of small organic molecules, such as chalcones, for efficient applications as organic luminescent materials has attracted increasing attention owing to their interesting optical, photophysical, and biological properties. In this study, a new chalcone, 1-(4-isopropylphenyl)-5-(6-methoxynaphthalen-2-yl)pent-1-en-3-one (INM), was synthesized via base condensation between nabumetone and cuminaldehyde. INM was subsequently identified and characterized by FT-IR, NMR spectroscopy (1H and 13C), mass spectrometry, elemental analysis, X-ray diffraction, thermogravimetric analysis, and FESEM studies. Investigation of the solvent effect revealed that the π → π* transition involved a bathochromic shift from hexane to water and a large Stokes-shifted, twisted intramolecular charge-transfer emission in water. Diffuse reflectance spectral studies confirmed the formation of transparent INM chalcones with excellent crystallinity, and photoluminescence studies substantiated the low recombination rate of electrons and holes. Tauc plot analysis with the Kubelka–Munk algorithm revealed higher direct (3.57 eV) and indirect (3.41 eV) bandgap energies of INM. Density functional theory calculations at B3LYP/6-31G(d,p) revealed that INM had promising nonlinear optical activity (β ≈ 30.504 × 10−30 compared to a reference material, urea. Cell biocompatibility was evaluated after culturing skin fibroblasts and breast cancer cells with INM using the MTT assay and fluorescence microscopy of the live/dead cell assay. It was observed that INM exhibited good NIH/3T3 cell adhesion and proliferation and the weak inhibiting ability of MDA-MB231.

Highly crosslinked polymeric matrix for efficient ultralong dual-mode afterglow with multiple responses

Organic persistent luminescence (OPL) materials have enjoyed a long term research interest for promising applications in optical encryption, bio-imaging and optoelectronic devices. However, to achieve further promotion in afterglow efficiency and stability for responsive OPL systems are still challenging. Herein, an efficient responsive OPL system is prepared by doping an acridine derivative in a highly crosslinked poly(N-methylol acrylamide) matrix. The resulted doped polymeric system exhibits persistent phosphorescence and thermally activated delayed fluorescence with a high afterglow quantum yield up to 82.8% under ambient conditions without photoactivation for oxygen consuming. Benefitted from the dense structure brought by the chemical crosslinking with rich hydrogen bonding, the system exhibits good resistance to different organic solvents and shows response to water without complete afterglow quenching. Moreover, the dual-mode delayed emission consisting of persistent delayed fluorescence and phosphorescence provides time- and temperature-dependent OPL color. Benefitted from the stable feature, high afterglow efficiency and multiple stimuli-responses, the system can serve as OPL inkjet printing, providing potential applications in anti-counterfeiting and data-storage.

Facile Synthesis of Ln-Doped Hydrogen-Bonded Organic Frameworks with Rare-Earth-Characteristic Long Persistent Luminescence.

Tunable luminescence-assisted information storage and encryption holds increasing significance in today's society. A promising approach to incorporating the benefits of both organic long persistent luminescent (LPL) materials and rare-earth (RE) luminescence lies in utilizing organic host materials to sensitize RE luminescence, as well as hydrogen-bonded organic framework (HOF) phosphorescence Förster resonance energy transfer to RE compound luminescence. This work introduces a one-pot, in situ pyrolytic condensation method, achieved through high-temperature melting calcination, to synthesize lanthanide ion-doped HOF materials. This method circumvents the drawback of molecular triplet energy annihilation, enabling the creation of organic LPL materials with RE characteristics. The HOF material serves as the host, exhibiting blue phosphorescence and cyan LPL. By fine-tuning the doping amount, the composite material U-Tb-100 achieves green LPL with a luminescent quantum yield of 56.4%, and an LPL duration of approximately 2-3 s, demonstrating tunable persistence. Single-crystal X-ray diffraction, spectral analysis, and theoretical calculation unveil that U-Tb-100 exhibits exceptional quantum yield and long-lived luminescence primarily due to the efficient sensitization of U monomer to RE ions and the PRET process between U and RE complexes. This ingenious strategy not only expands the repertoire of HOF materials but also facilitates the design of multifunctional LPL materials.

Position-induced differential aggregation behavior with red-shifted emission: A case study of the promising copper ion sensor skeleton-based regio-isomers

AIE-ESIPT active Schiff base luminescent organic materials (LOM) have significant advantages and applications. Still, tuning their emission in the long-wavelength region (>600 nm) while maintaining low molecular mass remains challenging for the research community. Recently, researchers have found excellent capabilities like high CT nature, red-shifted emission, and large stokes shift in meta-fluorophores. However, such studies on the role of meta substitution, especially in the case of AIE-ESIPT active Schiff base LOM, have just been explored. Herein, we have presented a case study on the malonitrile-substituted regioisomers (p-BK and m-BK) based on the SDPA skeleton, a promising copper ion-sensing skeleton. It was found that the emission in m-BK is almost ∼ 50 nm red-shifted with approx. ∼ 200 nm stoke shift, compared to the p-BK. Although changing substituents from para to meta changes the aggregation behavior but, the selectivity remains identical towards copper ions. The practical sensing applicability of both isomers was analyzed in various environments, and bioimaging analysis in HeLa cells were performed to prove the promising nature of the SDPA skeleton. In sum, this case study highlighted the potential of unexplored meta-fluorophores, which can open up new avenues for researchers to create and design new AIE-active LOMs with desired emission wavelengths.

Organic Mechanochromic Luminescent Materials with Self-Recovering Characters.

Recently, applied research on stimuli-responsive materials with luminescence-switching characteristics has been conducted in various fields. A representative phenomenon of stimuli-responsive luminescent materials is mechanochromic luminescence (MCL), which exhibits luminescent color change induced by mechanical stimuli such as grinding. These materials are among the most prominent candidates for security and sensing applications. Interestingly, some mechanochromic luminescent materials have shown self-recovery character, in which their original luminescent color can be recovered by just standing under ambient conditions after grinding. Although there are more and more reports of such materials in recent years, the fundamental principles of molecular design still remain elusive. In this concept, we summarize distinctive advances in mechanochromic luminescent materials with self-recovery according to the core structures of luminescent molecules. Controlling amorphous state by introducing substituents such as alkyl or polar groups is effective method to provide self-recovering properties.

Narrowband clusteroluminescence with 100% quantum yield enabled by through-space conjugation of asymmetric conformation

Different from traditional organic luminescent materials based on covalent delocalization, clusteroluminescence from nonconjugated luminogens relies on noncovalent through-space conjugation of electrons. However, such spatial electron delocalization is usually weak, resulting in low luminescent efficiency and board emission peak due to multiple vibrational energy levels. Herein, several nonconjugated luminogens are constructed by employing biphenyl as the building unit to reveal the structure-property relationship and solve current challenges. The intramolecular through-space conjugation can be gradually strengthened by introducing building units and stabilized by rigid molecular skeleton and multiple intermolecular interactions. Surprisingly, narrowband clusteroluminescence with full width at half-maximum of 40 nm and 100% efficiency is successfully achieved via an asymmetric conformation, exhibiting comparable performance to the traditional conjugated luminogens. This work realizes highly efficient and narrowband clusteroluminescence from nonconjugated luminogens and highlights the essential role of structural conformation in manipulating the photophysical properties of unconventional luminescent materials.

Arylimidazole-terminated phenylene ethynylene molecules as organic luminescent materials

Three phenylene ethynylene derivatives substituted by arylimidazole groups (benzo[d]imidazole, phenanthro[9,10-d]imidazole and pyreno[4,5-d]imidazole) at both ends were successfully synthesized and characterized for organic electroluminescence devices. The photophysical, electrochemical, and thermal stability of the compounds were systematically investigated to reveal their structure-property relationships. All compounds presented a X-shaped structure, and exhibited excellent thermal stability and intense emission in solution and solid states. Furthermore, the solution-processed doped devices using the blend of tris(4-carbazoyl-9-ylphenyl)amine (TCTA) with the phenylene ethynylene derivatives as emitting layers emitted deep-blue emission with maximum external quantum efficiency (EQEmax) of 0.63 % for the benzo[d]imidazole-terminated derivative and blue emission with EQEmax of 1.93 % and 1.45 % for the phenanthro[9,10-d]imidazole- and pyreno[4,5-d]imidazole-terminated derivatives, respectively, suggesting that these compounds have a great potential as the organic emitters for deep-blue and blue devices.

White-light activatable organic NIR-II luminescence nanomaterials for imaging-guided surgery

While second near-infrared (NIR-II) fluorescence imaging is a promising tool for real-time surveillance of surgical operations, the previously reported organic NIR-II luminescent materials for in vivo imaging are predominantly activated by expensive lasers or X-ray with high power and poor illumination homogeneity, which significantly limits their clinical applications. Here we report a white-light activatable NIR-II organic imaging agent by taking advantages of the strong intramolecular/intermolecular D-A interactions of conjugated Y6CT molecules in nanoparticles (Y6CT-NPs), with the brightness of as high as 13315.1, which is over two times that of the brightest laser-activated NIR-II organic contrast agents reported thus far. Upon white-light activation, Y6CT-NPs can achieve not only in vivo imaging of hepatic ischemia reperfusion, but also real-time monitoring of kidney transplantation surgery. During the surgery, identification of the renal vasculature, post-reconstruction assessment of renal allograft vascular integrity, and blood supply analysis of the ureter can be vividly depicted by using Y6CT-NPs with high signal-to-noise ratios upon clinical laparoscopic LED white-light activation. Our work provides efficient molecular design guidelines towards white-light activatable imaging agent and highlights an opportunity for precision imaging theranostics.

Perfluoroaryl⋯aryl interaction: The most important subset of π -hole⋯ π bonding

The perfluoroaryl⋯aryl interaction, the most important subset of π-hole⋯π bonding, refers to the attractive stacking interaction between a perfluoroaryl group and an aryl group. In contrast to the aryl⋯aryl interaction with the same size, the much stronger perfluoroaryl⋯aryl interaction has its own characteristics and applications. A brief history of the development of the perfluoroaryl⋯aryl interaction was given first in this review, followed by an overview of the state-of-the-art of the nature of the perfluoroaryl⋯aryl interaction. Much attention was paid to the application of the perfluoroaryl⋯aryl interaction both in the traditional research fields such as crystal engineering and organic luminescent materials and in the hot research fields such as photovoltaics materials and biological engineering. It is believed that this timely and comprehensive review provides a foundation and guide for the future development and application of the perfluoroaryl⋯aryl interaction.

The Role of Locally Excited State and Charge Transfer State in Organic Room Temperature Phosphorescence and Corresponding Applications

AbstractDonor–acceptor (D–A) structure with charge transfer (CT) effect is widely utilized in the construction of organic luminescent materials. The adjustment of their CT effect and related luminescent property usually relies on the changes of molecular structure with different D or A moieties, which will lead to some uncertainties in structure‐property relationship. With the aim to explore the clear inherent luminescent mechanism for D–A molecule with CT effect, it is ideal that the regulation of intramolecular charge transfer in one same D–A molecule can be realized. Accordingly, three D–A type organic phosphorescence luminogens are designed and synthesized. Once being doped into different polymer matrixes, disparate charge transfer effects and related room temperature phosphorescence (RTP) properties can be achieved for a single molecule. Subsequent experiments confirm that different distributions of molecules with locally excited (LE) state and CT state are mainly responsible for their distinct RTP behaviors, exhibiting the well‐clarified structure‐property relationship of D–A type phosphorescence luminogens. Furthermore, the transition from CT to LE state can even be realized through chemical reaction, leading to the activated RTP effect for practical applications.

Recent progress on exciplex-based organic long-persistence luminescent materials

Recent progress on exciplex-based organic long-persistence luminescent materials

Neutral vs Charged Luminescent Radicals: Anti-Kasha Emission and the Impact of Molecular Surrounding.

Organic luminescent materials attract growing interest as an elegant solution for sustainable and inexpensive light-emitting devices. Most of them are neutral-emitting molecules with an implicit restriction of 25% internal quantum efficiency due to a spin-forbidden nature of the T1 → S0 transition. Utilizing organic radicals allows one to overcome such limits by theoretically boosting quantum yield up to 100%. Recently, different light-emitting radicals based on carbonyl- and carboxyl-substituted benzenes were synthesized and stabilized in different polymer matrices or ionic liquids. While some of them were proved to be suitable luminescent materials, the exact theoretical explanation of the nature of their emission is missing. There are two main hypotheses proposed in the literature. The first one suggests that the origin of luminescence is D2 → D0 anti-Kasha emission from anion radicals, while the second theory is based on D1 → D0 Kasha emission from neutral protonated radicals. In this work, we investigate both hypotheses and compare their derivatives with the available experimental data. We used density functional theory and complete-active space perturbation theory to investigate the absorption and emission properties in various aromatic carbonyl radicals. We found that both emission mechanisms can coexist simultaneously, with a dominant emission contribution made by anion radicals because of better agreement between oscillator strengths and radiative rate constants. Our numerical simulations agree with the experimental data and provide theoretical foundations for the fabrication of next-generation light-emitting devices based on luminescent radicals.

Construction of multi‐decay pathways and realizing polymer‐regulated organic smart luminescent materials

AbstractThe construction of multi‐decay pathways of smart organic light‐emitting materials has drawn intensive research enthusiasm owing to their substantial promise in diverse optoelectronic applications. Nowadays, numerous chemical substances have been refined to extend and enhance their intriguing luminescent properties. Nowadays, plenty of chemicals have been adapted to amplify more interesting luminescent properties. How to utilize an easy way to tune multi‐decay pathways resulting in various emissions is still challenging. Here, we present a triphenylamine derivative, TPA3BP, which exhibits a variety of multi‐decay pathways in different states and can exhibit thermally activated delayed fluorescence in both the polydimethylsiloxane and crystalline state, but also achieve room temperature phosphorescence by embedding it into the poly (methyl methacrylate) (PMMA) and polyvinyl pyrrolidone matrix. The multi‐decay luminescence can be attributed to the dual effect arising from the n‐π* transition of TPA3BP and the regulation of molecular transition pathways within the matrix environment. This intriguing phenomenon highlights the combined influence of TPA3BP's electronic transitions and the influence of the polarity and rigidity of the surrounding matrix on the observed characteristics. This advancement has widened the structural possibilities for multi‐decay luminescent materials, enabling their targeted synthesis for future applications, such as information encryption and smart anti‐counterfeiting.