Long-wavelength Emission Research Articles

Carbon Dots with Charge Storage Ability Promote the Red Emission of TFB via Carrier Secondary Injection.

Dual-emission light-emitting diodes (DEDs) have great promising applications in medical imaging, optical communication, data storage, and three-dimensional display. The precise material design and advanced packaging technology for the construction of DEDs are still key challenges for practical application. We demonstrate a straightforward strategy to construct DEDs that deviates from traditional approaches, utilizing commercially available luminescent material of poly(9,9-dioctylfluorene-co-N-(4-(3-methylpropyl))diphenylamine) (TFB) and carbon dots (CDs). In the DEDs, the mixture of CDs and TFB was used as the luminescent layer, which exhibits dual-wavelength emission located at 436 and 632 nm, respectively. Notably, the CDs, with charge storage ability, can store the interfacial charges, reinject the carriers into TFB, and then facilitate the long-wavelength (632 nm) emission from TFB. This work provides a new way for the design and construction of fresh DEDs through the CD-based interfacial charge transport process.

Fabrication of Yellow-Emitting Chiral Silicon Nanoparticles and Fluorescence/Colorimetric Dual-Mode Recognition of Lysine Enantiomers together with Nanobioimaging.

Long-wavelength emission fluorescent chiral silicon nanoparticles (c-SiNPs) hold significant potential for biological imaging and complex sample analysis due to their superior optical properties. However, the synthesis of these materials remains a considerable challenge. The activity of lysine is intrinsically linked to its configuration, making it crucial to develop a rapid, sensitive, and selective method for differentiating lysine enantiomers in biochemical and biomedical fields. In this study, N-[3-(trimethoxysilyl)propyl]ethylenediamine and chlorogenic acid were innovatively employed as precursors, and the yellow-emitting c-SiNPs with an emission wavelength of 572 nm were synthesized at room temperature for the first time by adjusting experimental parameters. The obtained c-SiNPs exhibited excellent optical properties, stability, and cell compatibility. Furthermore, the c-SiNPs demonstrated outstanding fluorescence and colorimetric recognition capabilities for lysine enantiomers. Consequently, fluorescence/colorimetric dual-mode sensing methods with high selectivity and sensitivity for the recognition of lysine enantiomers were established, and the linear ranges of these methods for d-lysine were 0.050-20 and 0.10-30 mM, with detection limits of 7.5 and 17 μM, respectively. Additionally, the c-SiNPs demonstrated an ability to bioimaging d-lysine within HeLa cells. Using density functional theory to calculate the recognition mechanism and correlating this with fluorescence and ultraviolet-visible (UV-vis) absorption spectra data, it was confirmed that the recognition mechanism was associated with the Gibbs free energy, binding energy, and hydrogen bond number difference between the c-SiNPs and lysine enantiomers. The method developed in this study for preparing c-SiNPs provided a reference for synthesizing fluorescent c-SiNPs with longer emission wavelengths. Moreover, the established method for identifying lysine enantiomers holds significant guiding implications for the use of high-purity lysine.

Green synthesis of red-emitting carbon dots for bioimaging, sensing, and antibacterial applications

It is a highly desirable and formidable challenge to synthesize carbon dots with long-wavelength emission using green synthesis. In this work, we explored red-emitting carbon dots (rCDs) via a hydrothermal strategy and their multifunctional application for bioimaging in vivo/vitro, curcumin sensing, and antibacterial materials. As-prepared rCDs were water-soluble and monodispersed with an average diameter of 2.34 nm. Significantly, these rCDs exhibited low toxicity and outstanding biocompatibility, which was consistent with the excellent bioimaging performance in living cells, zebrafish, and nude mice, providing them a promising prospect for clinical applications. Meanwhile, the obtained rCDs were also used as a fluorescent probe for sensitive detection of curcumin in a wide linear range of 0.03–135.73 μM with a limit of detection of 29.37 nM. Furthermore, quaternized rCDs were designed and used as antibacterial material with minimum inhibitory concentrations against Staphylococcus aureus and Escherichia coli of 0.15 mg/mL and 0.5 mg/mL, respectively, which advanced the development of novel antibacterial agents and broadened the applications of red-emitting CDs. Therefore, this work provided multifunctional CDs with red emission for use in the fields of biological imaging, fluorescence sensing, and antibacterial materials.

Tuning the reversible mechanochromic luminescence of triphenylethylenes by rational introduction of functionalized thiophenes substituents

Four triphenylethylene derivatives have been designed and synthesized in this work. Compared to traditional tetraphenylethene (TPE) compounds, it was found that the obtained compounds could exhibit potential isomerism in chemical and spatial structures due to their unique asymmetry, which revealed that the subtle structural changes directly influence the packing modes of the compounds in aggregated state, tuning their mechanochromic luminescence properties. Moreover, the emission wavelength of mono-substituted triphenylethylene derivatives showed a blue-shift trend when stimulated by external mechanical forces. After fuming or recrystallization, they can recover to long-wavelength emission. Among them, compound TTC-2 exhibited the most significant color changes and the largest wavelength variation.

Benzo[c,d]Indole-Quinoline-Based Deep-Red Emissive Probes for Live-Cell Imaging of Nucleolar RNA.

Small molecular weight fluorescent probes capable of binding to RNAs have been powerful tools for understanding the intracellular behaviors of RNAs. In this chapter, we describe the fluorescence imaging of nucleolar RNA in living cells using deep-red emissive probes with benzo[c,d]indole-quinoline (BIQ) monomethine cyanine scaffolds. These probes feature a significant fluorescence "off-on" ability upon binding to RNAs (>100-fold) in the deep-red spectral region (λem>650nm). In addition, they have many advantages for fluorescence sensing of RNAs and nucleolar RNA imaging, such as longer emission wavelength, higher photostability, and better counterstaining compatibility for live cell imaging, compared to a commercially available RNA-binding probe, SYTO RNA select.

Cocrystallization-Induced Red Ultralong Organic Phosphorescence.

Organic cocrystals formed through multicomponent self-assembly have attracted significant interest owing to their clear structure and tunable optical properties. However, most cocrystal systems suffer from inefficient long-wavelength emission and low phosphorescence efficiency due to strong non-radiative processes governed by the energy gap law. Herein, an efficient long-lived red afterglow is achieved using a pyrene (Py) cocrystal system incorporating a second component (NPYC4) with thermally activated delayed fluorescence (TADF) and ultralong organic phosphorescence (UOP) properties. The cocrystal (NPYC4-Py) not only inherits the excellent luminescence of its monomeric counterparts, but also exhibits unique dual-mode characteristics, including persistent TADF and UOP emission with a high quantum yield of 58 % and a lifetime of 362 ms. The precise cocrystal stacking distinctly reveals that intermolecular interactions lock the cocrystal formation and weaken the intermolecular π-π interactions between NPYC4 and Py, thereby stabilizing the excited triplet excitons. Furthermore, the favorable energy level of NPYC4 acts as a bridge, reducing the energy gap between the S1 and T1 states for Py, therefore activating its red phosphorescence from Py. This research provides direct insights into achieving efficient red UOP through co-crystallization.

Multicolor emissive hyperbranched polysiloxanes from enhanced spatial electronic communication for security encryption and bacteria imaging

Unconventional fluorescent polymers with long-wavelength emission have attracted considerable attention due to their facile preparation, good biocompatibility, and excellent processability. However, their emission at long-wavelength is relative low. Herein, a series of aromatic amino acids functionalized hyperbranched polysiloxanes with deep red to cyan fluorescence were prepared. Experimental and theoretical calculation results show that the long-wavelength emission comes from the spatial electronic delocalization among conjugated π bonds and electron-rich functional groups. The balance between rigidity and flexibility is favorable for the strong long-wavelength emission. Moreover, the polymers’ fluorescence is sensitive to Fe3+ and OH– ions; and these polymers show potential applications in security encryption, fluorescent stamp inks and bacteria multicolor fluorescence imaging. This work provides an efficient method for the development of long-wavelength emissive unconventional fluorescence polymers

Cr3+-doped Na2CaSn2Ge3O12 garnet showing broadband near-infrared emission at 820 nm with zero thermal quenching and near-unity quantum yield

The continually advancing near-infrared (NIR) phosphor-converted light-emitting diode (pc-LED) hold pivotal significance in optical imaging and NIR spectroscopy. Cr3+-doped garnet broadband NIR phosphors have attracted considerable attention owing to their high optical performance enabled by the rigid structure. Nonetheless, the emission wavelength is severely restricted, and longer wavelength emissions usually result in inferior quantum efficiency and poor luminescence stability. In this work, the concurrent reconstruction of dodecahedral and octahedral sites by introducing [Na+-Sn4+]C unit in the framework of Na2CaSn2Ge3O12 garnet contributes to the Cr3+ broadband NIR emission spanning 700–1200 nm, with a peak at 820 nm. Utilizing a charge compensation strategy via Ta5+ codoping largely boosts the internal quantum efficiency (IQE) of Na2CaSn2Ge3O12:Cr3+ from 93.06 % up to 95.04 %. Trap-mediated energy compensation is proposed to achieve a record-breaking zero-thermal-quenching behavior (99.39 %@423 K) of Cr3+-doped garnet with such a longer wavelength emission. The encapsulated prototype broadband NIR pc–LED gives rise to an overwhelming NIR output power of 590.9 mW@1300 mA and a photoconversion efficiency (PCE) of 32.62 % at 30 mA, rendering exceptional performance in night vision, detection, and NIR imaging applications.

Red light-emitting diode with full InGaN structure on a ScAlMgO4 substrate

Abstract Here, we report the first demonstration of full InGaN-based red light-emitting diode (LED) grown on a c-plane ScAlMgO4 substrate. This work represents a potential approach for achieving red emissions from an InGaN quantum well grown on InGaN underlying layers. The LED device exhibits a peak wavelength of 617 nm at a current injection of 40 mA (10.5 A/cm2). The light output power and external quantum efficiency were 12.6 µW and 0.016% at 40 mA (10.5 A/cm2), respectively. These results are expected to contribute to the development of longer-wavelength emission LEDs and laser diodes.

Synthesis and application of optically stable red fluorescent carbon dots for sensitive and selective detection of ceftazidime

This study reports the successful synthesis of optically stable red-emitting carbon dots (R-CDs) through a solvothermal method, using glycine as the carbon source and o-phenylenediamine as the nitrogen-doping agent. The R-CDs exhibit long-wavelength emission characteristics with optimal excitation and emission wavelengths of 533 nm and 600 nm, respectively, and a quantum yield of 26.7 %. The results demonstrate that R-CDs possess excellent salt resistance and photostability. The R-CDs display bright fluorescence emission and show a sensitive response to ceftazidime (CF). Leveraging these properties, a fluorescent probe based on R-CDs was developed for the sensitive determination of CF. The fluorescence quenching intensity of this system exhibits a good linear relationship with CF concentration in the range of 0–0.7 mmol/L. The linear equation is (F0-F)/F0=0.9564CCF(mmol/L)+0.0089, with a linear correlation coefficient (R2) of 0.9945. The detection limit is 4.9 μmol/L, with recovery rates ranging from 94.2 % to 100.5 % and relative standard deviations between 2.2 % and 3.2 %. This work provides a theoretical basis for the detection of CF using red-emitting carbon dots and demonstrates promising potential for practical applications.

Dynamic exciton-to-dopant energy transfer tuning of Mn2+-Doped perovskite nanocrystals by PBG effect

Cesium lead halide perovskite nanocrystals (CsPbX3 NCs) doped with Mn2+ brings attractive long-wavelength emission and flexible color tunability. However, modulating the exciton-to-Mn2+ energy transfer efficiency poses a challenge, particularly when relying on traditional methods such as changing halogen composition or incorporating external cations, which often complicate the process. In this work, a simple photonic bandgap (PBG)-modulation strategy is applied to modulate the exciton-to-Mn2+ energy transfer by constructing a sandwich “PC-Perovskite-PC” structure with two photonic crystal (PC) films and Mn2+ doped CsPb(ClBr)3 NPs. When the PBG and the host emission band change from deviation to coincidence, the lifetime of Mn2+ decreases from 0.54 ms to 0.36 ms owing to the enhancing energy transfer efficiency by PBG effect. Meanwhile, the ratios of orange and blue emissions (O/B) increase from 1.36 to 1.6. In addition, the back energy transfer also can be modulated. When the PBG matches well with the Mn2+ emission band, the lifetime of the host emission exhibits the largest value (1.25 ns) owing to back energy transfer from Mn2+ the host. Meanwhile, the O/B value shows the smallest value (0.52) attributed to the decreased spontaneous radiation of Mn2+ and the enhanced host emission. When PBG deviates from the Mn2+ emission band, the lifetime of the host emission decreases but O/B value increases gradually. This work provides new strategy for the modulation of energy transfer in Mn2+ doped CsPb(ClBr)3 NPs.

Piezoelectric-induced mechanoluminescence in centrosymmetric Lu3Al5O12: Properties of self-recoverable and tunable near-infrared luminescence

Mechanoluminescence (ML) materials with long-wavelength emission bands are essential for future in vivo bioimaging, non-destructive testing. However, most of the near-infrared (NIR) ML materials require pre-irradiation, which may limit their further applications. Generally, piezoelectric-induced ML materials were considered to be related to the piezoelectric effect from non-centrosymmetric structure. Innovatively in this work, a novel piezoelectric-induced near-infrared ML material Lu3Al5O12:Cr3+ with centrosymmetric structure is obtained. In Lu3Al5O12:Cr3+, piezoelectric effect is generated from the distortion of the centrosymmetric structure of the host due to the uneven electron distribution of Cr3+. Here, highly tunable ML FWHM from 7 nm to 118 nm is realized by introducing different content Ga3+ ions to Lu3Al5O12:Cr3+. The ML film fabricated by composite polydimethylsiloxane and Lu3Al2Ga3O12:Cr3+ can penetrate 20 mm pork tissue, which suggests the potential applications of the NIR ML material in the field of optical imaging of stress distribution in organisms. The discovery of distorted crystal structure to induce piezoelectric effect provides a new thinking for exploring ML in centrosymmetric materials. In addition, LuAl5-xGaxO:Cr3+ phosphors have broad prospects in self-powered sensing, temporomandibular disorders diagnosis, information security, and biomedical fields.

Carbon Dots and Their Films with Narrow Full Width at Half Maximum Orange Emission.

To obtain carbon dots (CDs) with narrow full width at half maximum (FWHM) and long-wavelength emission, carbon sources with high conjugate sizes and abundant functional groups can be employed to synthesize CDs. In this study, orange-emissive carbon dots (OCDs) were synthesized with phloroglucinol and rhodamine B as precursors. When the molar ratio of them was 30:1, and ethanol was served as the solvent, OCDs with optimized emission wavelength at approximately 580 nm, an FWHM of 30 nm, and a quantum yield (QY) of 27.31% were obtained. Subsequently, the OCDs were incorporated into polyvinyl alcohol (PVA) to fabricate solid-state OCD/PVA fluorescent films, which exhibited an FWHM of 47 nm. The PVA matrix facilitated the dispersion of OCDs, thereby suppressing non-radiative energy transfer among the OCDs and enhancing luminescence efficiency. Consequently, compared with OCDs, the OCD/PVA film exhibited significant luminescent enhancement, and the QY of the composite film was increased to 84.74%. Moreover, OCD/PVA film showed good transmittance and thermal stability. This research offers a solid theoretical and experimental foundation for the potential applications of CDs in the field of solid-state lighting.

Long-Wavelength Afterglow Emission with Nearly 100% Efficiency through Space-Confined Energy Transfer in Organic-Carbon Dot Hybrid.

Long-wavelength afterglow emitters are crucial for optoelectronics and information security; however, it remains a challenge in achieving high luminescence efficiency due to the lack of effective modulation in electronic coupling and nonradiative transitions of singlet/triplet excitons. Here, we demonstrate an organic-carbon-dot (CD) hybrid system that operates via a space-confined energy transfer strategy to obtain bright afterglow emission centered at 600 nm with near-unity luminescence efficiency. Photophysical characterization and theoretical calculation confirm efficient luminescence can be assigned to the synergistic effect of intermolecular energy transfer from triplet excitons of CDs to singlets of subluminophores and the intense restraint in nonradiative decay losses of singlet/triplet-state excitons via rationally space-confined rigidification and amination modification. By utilizing precursor engineering, yellow and near-infrared afterglow centered at 575 and 680 nm with luminescence efficiencies of 94.4% and 45.9% has been obtained. Lastly, these highly emissive powders enable superior performance in lighting and information security.

Developing an efficient garnet-type near-infrared phosphor Na1.5Gd1.5Sc2Ge3O12:Cr3+ with relatively long-wavelength emission.

Developing efficient near-infrared (NIR) phosphor with an emission peak wavelength over 850 nm is crucial to realize multi-functional spectroscopy applications, while this remains a significant challenge. Herein, a garnet-type Na1.5Gd1.5Sc2Ge3O12:Cr3+ phosphor with an emission peak located at 882 nm was created from NaδGdδCa3-2δSc2Ge3O12:Cr3+ (0 ≤ δ ≤ 1.5) solid solutions basing on the effect of cationic disorder. The maximum internal quantum efficiency (IQE) of Na1.5Gd1.5Sc2-xGe3O12:xCr3+ reached 84.6% when x = 0.01. The maximum external quantum efficiency (EQE) can be optimized to 20.6%. Using this material, a prototype NIR phosphor-converted light-emitting diodes (pc-LEDs) device was fabricated, which demonstrates an excellent prospect in spectroscopy applications.

Microenvironment-Activatable Probe for Precise NIR-II Monitoring and Synergistic Immunotherapy in Rheumatoid Arthritis.

Rheumatoid arthritis (RA) represents an insidious autoimmune inflammatory disorder that severely lowers the life quality by progressively destructing joint functions and eventually causing permanent disability, posing a serious public health problem. Here, an advanced theranostic probe is introduced that integrates activatable second near-infrared (NIR-II) fluorescence imaging for precise RA diagnosis with multi-pronged RA treatments. A novel molecular probe comprising a long-wavelength aggregation-induced emission unit and a manganese carbonyl cage motif is synthesized, which enables NIR-II fluorescence activation and concurrently releasing therapeutic carbon monoxide (CO) gas in inflamed joint microenvironment. This molecular probe self-assembles into a biocompatible nanoprobe, which is subsequently conjugated with anti-IL-6R antibody to afford active-targeting ability of RA. The nanoprobe exhibits significant turn-on NIR-II fluorescence signal at the RA lesion, enabling highly sensitive RA diagnosis and real-time therapeutic monitoring. The combination of ROS scavenging, on-demand CO gas release, and IL-6 signaling blockade results in potent therapeutic effect and synergistic immunomodulation impact, significantly alleviating the RA symptoms and preventing joint destruction. This research introduces a novel paradigm for the development of high-performance, activatable theranostic strategies to facilitate precise detection and enhanced treatment of RA-related diseases.

Crosslink-Enhanced Emission-Dominated Design Strategy for Constructing Self-Protective Carbonized Polymer Dots With Near-Infrared Room-Temperature Phosphorescence.

Self-protective carbonized polymer dots (CPDs) with advantageous crosslinked nano-structures have attracted considerable attention in metal-free room temperature phosphorescence (RTP) materials, whereas their RTP emissions are still limited to short wavelength. Expanding their RTP emissions to Near-Infrared (NIR) range is attractive but suffers from the difficulties in constructing narrow energy levels and inhibiting intense non-radiative decay. Herein, a crosslink-enhanced emission (CEE)-dominated construction strategy was proposed, achieving desired NIR RTP (710 nm) in self-protective CPDs for the first time. Structural factors, i.e., crosslinking (covalent-bond CEE), conjugation (conjugated amine with bridging N-H and C=C group), and steric hindrance (confined-domain CEE), were confirmed indispensable for triggering NIR RTP emission in CPDs. Contrast experiments and theoretical calculations further revealed the rationality of the design strategy originating from CEE in terms of promoting the narrow energy level emission of triplet excitons and inhibiting the non-radiative quenching. This work not only firstly achieves NIR RTP in self-protective CPDs but also helps understand the origin of NIR RTP to further guide the synthesis of diverse CPDs with efficient long-wavelength RTP emission.

Dual color carbon dots for simultaneous dynamic fluorescence tracking of mitochondria and lysosomes

The development of fluorescent probes to monitor mitochondria and lysosomes will be helpful not only to realize the status monitoring of the organelles, but also to gain insights into their functions in both healthy and diseased states. Carbon Dots (CDs), as a nanomaterial with excellent properties, have provided new tools and methods for research in organelle imaging in recent years. In this study, we synthesized green fluorescence-emitting carbon dots (G-CDs) with mitochondria-targeting ability and red fluorescence-emitting carbon dots (R-CDs) with lysosome-targeting ability by using the same precursors. G-CDs are brightly with a quantum yield of up to 51.8 % and R-CDs have a long-wavelength emission of 611 nm. Based on the unique properties of G-CDs and R-CDs, we observed the changes of mitochondria during apoptosis and mitochondrial autophagy in HeLa cells by using G-CDs. And the dynamics of lysosomes in the inhibition of cellular autophagy and cellular necrosis were observed by utilizing the R-CDs. Furthermore, we observed human intestinal organoids samples stained by G-CDs and R-CDs, extending the relevant applications of carbon dots imaging to the organoids field, which brings forth new possibilities for research and drug development of related diseases.

Photo-induced fluorescence discoloration and photo-responsive room temperature phosphorescence carbon dot-based composites with excellent reversibility and water resistance

Photo-stimulation responsive room temperature phosphorescence (RTP) carbon dots (CDs) have potential applications in advanced dynamic information encryption and anti-counterfeiting. However, the development of photo-responsive long-wavelength RTP CD materials with excellent reversibility and water resistance, as well as CD materials with both photo-induced fluorescence discoloration and photo-responsive reversible RTP properties, remains a challenge. Here, pyrene, which has a large conjugated structure, and 4-(1,2,2-triphenylvinyl)benzaldehyde, which has a tetraphenylethylene structure, were selected as the main raw materials to synthesize two CDs. Then, by introducing a PMMA matrix, reversible photo-responsive long-wavelength red RTP emission with a lifetime of 257 ms from a CD-based composite is realized for the first time, and the combination of photo-induced fluorescence discoloration and photo-responsive reversible yellow RTP with a lifetime of 287 ms is realized. Importantly, photo-responsive reversible RTP has excellent water resistance. The fluorescence discoloration was caused by photocyclization under long-term UV irradiation due to the presence of the tetraphenylethylene structure. The rigid environment provided by the PMMA matrix and the hydrogen bonds formed between the PMMA and CDs promote the generation of RTP. The photo-responsiveness of RTP is caused by the conversion of molecular oxygen (3O2) to singlet oxygen (1O2) under continuous UV irradiation. It is filled with 3O2 again after being placed in air to inactivate the RTP, thus achieving reversible RTP behavior. Owing to their excellent photo-responsive properties and water resistance, these materials have the potential to achieve repeatable dynamic information encryption and multilevel pattern anti-counterfeiting while also broadening the range of applications in water environments.

Exploration of red and deep red Thermally activated delayed fluorescence molecules constructed via intramolecular locking strategy

Red and deep red (DR) organic light-emitting diodes (OLEDs) have garnered increasing attention due to their widespread applications in display technology and lighting devices. However, most red OLEDs exhibit low luminescence efficiency, severely limiting their practical applications. To address this challenge, we theoretically design four novel TADF molecules with red and DR luminescence using intramolecular locking strategies building upon the experimental findings of DCN-DLB and DCN-DSP, and their crystal structures are predicted with the lower energy and higher packing density. The photophysical properties and luminescence mechanism of six molecules in toluene and crystal are clarified using the first principles calculation and thermal vibration correlation function (TVCF) method. The proposed design strategy is anticipated to offer several advantages: enhanced electron-donating capabilities, more rigid structures, longer emission wavelengths and higher luminescence efficiency. Specifically, we introduce oxygen atoms and nitrogen atoms as intramolecular locks, and the newly developed DCN-DBF and DCN-PHC have redshifted emission, narrow singlet–triplet energy gap (ΔEST), fast reverse intersystem crossing rate and enhanced photoluminescence quantum yield (PLQY). Notably, DCN-DBF achieves both long wavelength emission and high efficiency, with emission peaks at 598 nm and 587 nm corresponding to PLQY of 52.13 % and 43.42 % in toluene and crystal, respectively. Our work not only elucidates the relationship between molecular structures and photophysical properties, but also proposes feasible intramolecular locking design strategies and four promising red and DR TADF molecules, which could provide a valuable reference for the design of more efficient red and DR TADF emitters.