Long-lived Emission Research Articles

Unravelling Immune-Inflammatory Responses and Lysosomal Adaptation: Insights from Two-Photon Excited Delayed Fluorescence Imaging.

Two-photon excitation (TPE) microscopy with near-infrared (NIR) emission has emerged as a promising technique for deep-tissue optical imaging. Recent developments in fluorescence lifetime imaging with long-lived emission probes have further enhanced the spatial resolution and precision of fluorescence imaging, especially in complex systems with short-lived background signals. In this study, two innovative lysosome-targeting probes, Cz-NA and tCz-NA, are introduced. These probes offer a combination of advantages, including TPE (λex = 880nm), NIR emission (λem = 650nm), and thermally activated delayed fluorescence (TADF) with long-lived lifetimes (1.05 and 1.71 µs, respectively). These characteristics significantly improve the resolution and signal-to-noise ratio in deep-tissue imaging. By integrating an acousto-optic modulator (AOM) device with TPE microscopy, the authors successfully applied Cz-NA in two-photon excited delayed fluorescence (TPEDF) imaging to track lysosomal adaptation and immune responses to inflammation in mice. This study sheds light on the relationship between lysosome tubulation, innate immune responses, and inflammation in vivo, providing valuable insights for the development of autofluorescence-free molecular probes in the future.

Current Development of Lanthanide Complexes for Biomedical Applications.

Luminescent molecule-based bioimaging system is widely used for precise localization and distinction of cancer/tumor cells. Luminescent lanthanide (Ln(III)) complexes offer long-lived (sub-millisecond time scale) and sharp (FWHM <10 nm) emission, arising from the forbidden 4f-4f electronic transitions. Luminescent Ln(III) complex-based bioimaging has emerged as a promising option for both in vitro and in vivo visualizations. In this mini-review, the historical development and recent significant progress of luminescent Ln(III) probes for bioapplications are introduced. The recent studies are mainly focused on three points: (i) the structural modifications of Ln(III) complexes in both macrocyclic and small ligands, (ii) the acquirement of high resolution luminescence images of cancer/tumor cells and (iii) the constructions of ratiometric biosensors. Furthermore, our recent study is explained as a new Cancer GPS (cancer grade probing for determining tumor grade through photophysical property analyses of intracellular Eu(III) complex.

Organic-Inorganic Hybrid Ferroelectric and Antiferroelectric with Afterglow Emission.

Luminescent ferroelectrics are holding exciting prospect for integrated photoelectronic devices due to potential light-polarization interactions at electron scale. Integrating ferroelectricity and long-lived afterglow emission in a single material would offer new possibilities for fundamental research and applications, however, related reports have been a blank to date. For the first time, we here achieved the combination of notable ferroelectricity and afterglow emission in an organic-inorganic hybrid material. Remarkably, the presented (4-methylpiperidium)CdCl3 also shows noticeable antiferroelectric behavior. The implementation of cationic customization and halogen engineering not only enables a dramatic enhancement of Curie temperature of 114.4 K but also brings a record longest emission lifetime up to 117.11 ms under ambient conditions, realizing a leapfrog improvement of at least two orders of magnitude compared to reported hybrid ferroelectrics so far. This finding would herald the emergence of novel application potential, such as multi-level density data storage or multifunctional sensors, towards the future integrated optoelectronic devices with multitasking capabilities.

Oxygen-Tolerant Near-Infrared Organic Long-Persistent Luminescent Copolymers.

Organic materials exhibiting long-lasting emission in the near infrared are expected to have applications in bio-imaging and other areas. Although room temperature phosphorescence and thermally activated delayed fluorescence display long-lived emission of approximately one minute, organic long-persistent luminescence (OLPL) systems with a similar emission mechanism to inorganic persistent emitters can emit for several hours at room temperature. In particular OLPL with a hole-diffusion mechanism can function even in the presence of oxygen. However, ionic materials lack long-term stability in neutral organic host owing to aggregation and phase separation. In this study, we synthesized polymers with stable near-infrared persistent luminescence at room temperature via the copolymerization of electron donors and acceptors. The copolymers exhibit long-persistent luminescence (LPL) at temperatures below the glass transition temperature and can be excited by approximately the entire range of visible light. LPL properties and spectra can be controlled by the dopant.

Elucidating charge-transfer mechanisms and their effect on the light-induced reactivity of metastable MIL-125(Ti)

Alcohol and water photooxidation reactions are employed in concert with optical spectroscopy analyses to demonstrate the occurrence of multiple and distinctive charge-transfer (CT) mechanisms in the environmental photocatalyst MIL-125(Ti). The contribution of ligand-to-metal CT (LMCT) mechanisms increases at wavelengths lower than 320 nm while that of node oxygen-to-metal CT (OMCT) mechanisms increases at longer wavelengths. The localization of photogenerated holes on different atoms leads to a selective reactivity of the framework depending on the mechanism and, during hydroxylation processes, to its spontaneous transition to the isostructural MIL-125-OH(Ti) and the development of an additional LMCT mechanism with a long-lived emission. Furthermore, a previously unidentified and extrinsic CT mechanism is spectroscopically related to the formation of terephthalate-based oligomers. The coexistence of distinctive CT mechanisms in MIL-125(Ti) implies their critical role in catalyst efficiency, and mastering them proves to be a powerful and simple strategy to produce the valuable MIL-125-OH(Ti).

Recent Advances in Long-Lived Emission in Coinage Metal Nanoclusters: Implications for Optoelectronic Applications

Recent Advances in Long-Lived Emission in Coinage Metal Nanoclusters: Implications for Optoelectronic Applications

(Invited) Emissive Transition-Metal Complexes and Their Applications for Optical Sensing and Bioimaging

Phosphorescent transition-metal complexes, such as the Pt(II) and Ir(III) complexes are attractive candidates for optical sensing (including biosensing) and bioimaging applications due to their long-lived emission that can avoid the interference from the autofluorescence of biosystems. By selecting appropriate ligands and incorporating different functional groups to the ligands, the emission color, intensity, and lifetime can be readily tuned. We have synthesized various red to near-IR emitting Pt(II) and Ir(III) complexes that can be potentially used as biosensing and bioimaging materials.

A Highly Bright Near-Infrared Afterglow Luminophore for Activatable Ultrasensitive In Vivo Imaging.

Afterglow luminescence imaging probes, with long-lived emission after cessation of light excitation, have drawn increasing attention in biomedical imaging field owing to their elimination of autofluorescence. However, current afterglow agents always suffer from an unsatisfactory signal intensity and complex systems consisting of multiple ingredients. To address these issues, this study reports a near-infrared (NIR) afterglow luminophore (TPP-DO) by chemical conjugation of an afterglow substrate and a photosensitizer acting as both an afterglow initiator and an energy relay unit into a single molecule, resulting in an intramolecular energy transfer process to improve the afterglow brightness. The constructed TPP-DO NPs emit a strong NIR afterglow luminescence with a signal intensity of up to 108 p/s/cm2 /sr at a low concentration of 10 μM and a low irradiation power density of 0.05 W/cm2 , which is almost two orders of magnitude higher than most existing organic afterglow probes. The highly bright NIR afterglow luminescence with minimized background from TPP-DO NPs allows a deep tissue penetration depth ability. Moreover, we develop a GSH-activatable afterglow probe (Q-TPP-DO NPs) for ultrasensitive detection of subcutaneous tumor with the smallest tumor volume of 0.048 mm3 , demonstrating the high potential for early diagnosis and imaging-guided surgical resection of tumors.

The Creation of Multimode Luminescent Phosphor through an Oxygen Vacancy Center for High-Level Anticounterfeiting.

Integrating multimode optical properties into a single material simultaneously is promising for improving the security level of fluorescent anticounterfeiting. However, there has been a lack of affirmative principles and unambiguous mechanisms that guide the design of such material. Herein, we achieve color-tunable photoluminescence, long-lived persistent emission, thermally stimulated luminescence, and reversible photochromism in a Tb3+-activated Mg4Ga8Ge2O20 phosphor by employing the F-like color center as an energy reservoir. It is experimentally revealed that the role of oxygen vacancies in the lattice of Mg4Ga8Ge2O20 is assumed as the main trap for the photogenerated electronic carriers, which is the origin of metastable F-like color centers. The formed color centers with the estimated depths of 0.48-0.95 eV could suppress the recombination of electron-hole pairs, thus giving rise to good photochromism and persistent emission properties, while under various modes of stimulation such as thermal attack or photo radiation, a quick recombination of electron holes happens, accounting for the bright thermally stimulated luminescence and the accompanied color bleaching. Finally, we fabricate a flexible phosphor/polymer composite by encapsulating the developed phosphor into a polydimethylsiloxane matrix, and conceptual demonstration of the composite for the high-security fluorescent anticounterfeiting technology, by virtue of multimode optical phenomena as authentication signals.

Unique Visualization Growth Process of Long-Lived Room Temperature Phosphorescence in Polymer System.

Recently, embedding organic phosphors into the polyvinyl alcohol (PVA) matrix has emerged as a convenient strategy to obtain efficient long-lived room temperature phosphorescence (RTP) via forming strong intermolecular hydrogen bonds with organic phosphors to minimize nonradiative relaxations. Regrettably, it is discovered that PVA is unable to trigger RTP emission when a novel functional phosphor THBE containing six extended biphenyl formaldehyde arms is doped into PVA matrix. Surprisingly, the excellent long-lived RTP emission can be easily obtained by doping THBE into PVA analogs, poly(vinyl alcohol-co-ethylene) (PVA-co-PE). The unique visualization growth process (i.e., white streak generation) of long-lived RTP is observed by UV light-driven aggregation of functional molecules THBE in PVA-co-PE matrix. The phosphorescent intensity of the luminescent film is enhanced by 55 times, from 729 to 40,785 a.u., and its phosphorescence lifetime is increased by 38 times, from 37.08 to 1415.41ms. Due to the dynamically reversible RTP performance, as well as the permeability, flexibility, and wrinkle-free properties of the luminescent film, it can be utilized to create cutting-edge information storage devices.

Unveiling the Long-Lived Emission of Copper Nanoclusters Embedded in a Protein Scaffold.

Protein-conjugated coinage metal nanoclusters have become promising materials for optoelectronics and biomedical applications. However, the origin of the photoluminescence, especially the long-lived excited state emission in these metal nanoclusters, is still elusive. Here, we unveiled the underlying mechanism of long-lived emission in albumin protein-conjugated copper nanoclusters (Cu NCs) using steady state and time-resolved spectroscopic techniques. Our findings reveal room-temperature phosphorescence (RTP) in protein-conjugated Cu NCs. Time-resolved area-normalized spectra distinguished short- and long-lived components, where the former arises from the singlet state and the latter from the triplet state, thus resulting in RTP. The similarity of the emission spectra at room (298 K) and cryogenic (77 K) temperature ascertains the RTP phenomenon by harvesting the higher-lying triplet states. Time-gated bioimaging of A549 cells using the long-lived emission not only supports RTP emission in the cellular environment but also provides exciting avenues in long-term bioimaging using bovine serum albumin-conjugated Cu NCs.

Ultra-Small Air-Stable Triplet-Triplet Annihilation Upconversion Nanoparticles for Anti-Stokes Time-Resolved Imaging.

Image contrast is often limited by background autofluorescence in steady-state bioimaging microscopy. Upconversion bioimaging can overcome this by shifting the emission lifetime and wavelength beyond the autofluorescence window. Here we demonstrate the first example of triplet-triplet annihilation upconversion (TTA-UC) based lifetime imaging microscopy. A new class of ultra-small nanoparticle (NP) probes based on TTA-UC chromophores encapsulated in an organic-inorganic host has been synthesised. The NPs exhibit bright UC emission (400-500 nm) in aerated aqueous media with a UC lifetime of ≈1 μs, excellent colloidal stability and little cytotoxicity. Proof-of-concept demonstration of TTA-UC lifetime imaging using these NPs shows that the long-lived anti-Stokes emission is easily discriminable from typical autofluorescence. Moreover, fluctuations in the UC lifetime can be used to map local oxygen diffusion across the subcellular structure. Our TTA-UC NPs are highly promising stains for lifetime imaging microscopy, affording excellent image contrast and potential for oxygen mapping that is ripe for further exploitation.

Substrate-Responsive Pillar[5]arene-Based Organic Room-Temperature Phosphorescence

Room-temperature phosphorescence (RTP) is a photophysical phenomenon typically associated with a long-lived emission that can be detected by the unaided eye. Several natural proteins display RTP, as do certain artificial polymers. In both cases, the RTP is ascribed to effective intramolecular through-space electronic communication. However, small molecules with internal electronic communication that enable RTP are relatively rare. Herein, we describe an alkyl halide-responsive RTP system consisting of a meta-formylphenyl-bearing pillar[5]arene derivative that supports effective through-space charge transfer (TSCT) within the pillararene cavity. Treatment with bromoethane, a heavy atom-containing guest for the pillar[5]arene host, serves to enhance the emission. An isomeric para-formylphenyl-bearing pillar[5]arene system proved ineffective in producing an RTP effect. Quantum chemical calculations based on single-crystal X-ray diffraction analyses provided insights into the structural determinants governing TSCT between the 1,4-dimethoxybenzene donor units and the formylphenyl groups of the pillar[5]arene, as well as the associated energy gaps and intersystem crossing channels. We believe that the present system and the associated mechanistic analysis provide the foundation for design of new small molecule with tunable RTP features.

Adsorption of indole[3, 2-b]carbazole derivatives in the filter paper matrix to realize long-lived room temperature phosphorescence emission

Adsorption of indole[3, 2-b]carbazole derivatives in the filter paper matrix to realize long-lived room temperature phosphorescence emission

Long-lived NIR emission in sulfur-doped zeolites due to the presence of [S3]2- clusters

The exploration of novel long-lived near-infrared (NIR) luminescent materials has attracted significant attention due to their applications in optical communications, anticounterfeiting, and bioimaging. However, these materials usually present low photoluminescence quantum yields and low photo- and chemical stability. Novel emitters that overcome these limitations are in demand. In this study, NIR emission was achieved using widely available, sustainable, and non-toxic materials through the synthesis of sulfur-doped zeolites, with different S/Cl ratios. With a combination of computational calculations (TD-DFT) and spectroscopic data, this emission was assigned to the radiative decay of excited triplet states of [S3]2- clusters, which resulted in a remarkably high Stokes shift (1.97 eV, 440 nm) and an average decay time of 0.54 ms. These new materials present high stability, external quantum efficiency of up to 17%, and a long-lived NIR emission, placing these compounds in a unique position to be used in applications demanding NIR emitters.

Room Temperature Phosphorescence of 5,6-Benzoquinoline

Phosphorescence emission of 5,6-Benzoquinoline embedded in poly (vinyl alcohol) film has been studied at room temperature. A strong green long-lived emission was observed in films doped with 5,6-Benzoquinoline while illuminated on a UV plate. A broad phosphorescence emission spectrum is centered at about 500 nm. The phosphorescence excitation spectrum follows the absorption spectrum of 5,6-Benzoquinoline, except for a long-wavelength part, which is well beyond the absorption band. This long-wavelength part of the absorption spectrum is responsible for the forbidden S0—T1 transition. The excitation at 430 nm resulted in the long-lived emission with a spectrum similar to the phosphorescence spectrum obtained with UV excitation within the absorption of 5,6-Benzoquinoline. The phosphorescence anisotropy obtained with a direct S0—T1 excitation is positive, while the UV excitation is negative. In contrast to fluorescence, the phosphorescence intensity strongly depends on temperature. Phosphorescence lifetimes with UV and long-wavelength excitation are similar, with a mean value of about 0.5 s.

Rapid handheld time-resolved circularly polarised luminescence photography camera for life and material sciences

Circularly polarised luminescence (CPL) is gaining a rapidly increasing following and finding new applications in both life and material sciences. Spurred by recent instrumental advancements, the development of CPL active chiral emitters is going through a renaissance, especially the design and synthesis of CPL active luminescent lanthanide complexes owing to their unique and robust photophysical properties. They possess superior circularly polarised brightness (CPB) and can encode vital chiral molecular fingerprints in their long-lived emission spectrum. However, their application as embedded CPL emitters in intelligent security inks has not yet been fully exploited. This major bottleneck is purely hardware related: there is currently no suitable compact CPL instrumentation available, and handheld CPL photography remains an uncharted territory. Here we present a solution: an all solid-state small footprint CPL camera with no moving parts to facilitate ad hoc time-resolved enantioselective differential chiral contrast (EDCC) based one-shot CPL photography (CPLP).

Dibenzodipyridophenazines with Dendritic Electron Donors Exhibiting Deep-Red Emission and Thermally Activated Delayed Fluorescence

The development of deep-red thermally activated delayed fluorescence (TADF) emitters is important for applications such as organic light-emitting diodes (OLEDs) and biological imaging. Design strategies for red-shifting emission include synthesizing rigid acceptor cores to limit nonradiative decay and employing strong electron-donating groups. In this work, three novel luminescent donor-acceptor compounds based on the dibenzo[a,c]dipyrido[3,2-h:20-30-j]-phenazine-12-yl (BPPZ) acceptor were prepared using dendritic carbazole-based donors 3,3″,6,6″-tetramethoxy-9'H-9,3':6',9″-tercarbazole (TMTC), N3,N3,N6,N6-tetra-p-tolyl-9H-carbazole-3,6-diamine (TTAC), and N3,N3,N6,N6-tetrakis(4-methoxyphenyl)-9H-carbazole-3,6-diamine (TMAC). Here, dimethoxycarbazole, ditolylamine, and bis(4-methoxyphenyl)amine were introduced at the 3,6-positions of carbazole to increase the strength of these donors and induce long-wavelength emission. Substituent effects were investigated with experiments and theoretical calculations. The emission maxima of these materials in toluene were found to be 562, 658, and 680 nm for BPPZ-2TMTC, BPPZ-2TTAC, and BPPZ-2TMAC, respectively, highlighting the exceptional strength of the TMAC donor, which pushes the emission into the deep-red region of the visible spectrum as well as into the biological transparency window (650-1350 nm). Long-lived emission lifetimes were observed in each emitter due to TADF in BPPZ-2TMC and BPPZ-2TTAC, as well as room-temperature phosphorescence in BPPZ-2TMAC. Overall, this work showcases deep-red emissive dendritic donor-acceptor materials which have potential as bioimaging agents with emission in the biological transparency window.

Biphenyl Au(III) Complexes with Phosphine Ancillary Ligands: Synthesis, Optical Properties, and Electroluminescence in Light-Emitting Electrochemical Cells.

A series of ten cationic complexes of the general formula [(C^C)Au(P^P)]X, where C^C = 4,4'-di-tert-butyl-1,1'-biphenyl, P^P is a diphosphine ligand, and X is a noncoordinating counteranion, have been synthesized and fully characterized by means of chemical and X-ray structural methods. All the complexes display a remarkable switch-on of the emission properties when going from a fluid solution to a solid state. In the latter, long-lived emission with lifetime τ = 1.8-83.0 μs and maximum in the green-yellow region is achieved with moderate to high photoluminescence quantum yield (PLQY). This emission is ascribed to an excited state with a mainly triplet ligand-centered (3LC) nature. This effect strongly indicates that rigidification of the environment helps to suppress nonradiative decay, which is mainly attributed to the large molecular distortion in the excited state, as supported by density functional theory (DFT) and time-dependent DFT (TD-DFT) computation. In addition, quenching intermolecular interactions of the emitter are avoided thanks to the steric hindrance of the substituents. Emissive properties are therefore restored efficiently. The influence of both diphosphine and anion has been investigated and rationalized as well. Using two complexes as examples and owing to their enhanced optical properties in the solid state, the first proof-of-concept of the use of gold(III) complexes as electroactive materials for the fabrication of light-emitting electrochemical cell (LEC) devices is herein demonstrated. The LECs achieve peak external quantum efficiency, current efficiency, and power efficiency up to ca. 1%, 2.6 cd A-1, and 1.1 lm W-1 for complex 1PF6 and 0.9%, 2.5 cd A-1, and 0.7 lm W-1 for complex 3, showing the potential use of these novel emitters as electroactive compounds in LEC devices.

Emergence of Structural Phosphorescence in Free-Standing, Laterally Organized Polymer Nanofiber Membranes

In the past decade, the phosphorescence of metal-free confined polymer structures has generated interest in optoelectronics due to their sustainability, low toxicity, and deployment in sensing applications. Herein, a free-standing array of laterally organized nanofibers was prepared via templated chemical vapor deposition polymerization into a liquid crystalline (LC) phase, and their optical properties were compared to compositionally identical films. The fibers converge into laterally aligned membranes that maintain a high internal order despite the surfaces of the membranes remaining uniform and closed. The membranes consisted of hourglass-shaped nanofibers with features in the micro- and nanometer regime. Free-standing nanofiber membranes differ from polymer films of equivalent chemical composition in several key features: (1) Anisotropic growth of polymer nanofibers with constraint and compliance to an LC template, (2) a high surface-to-volume ratio, and (3) the occurrence of a long-lived emission in the blue region, which persists for multiple seconds after excitation. This study constitutes the first report of long-lived emission from solid-state poly(p-xylylenes) nanofibers. Prospective applications of morphologically controlled polymer arrays with structural luminescence include organic sensors and optoelectronic devices.