Rational design of pyrrole derivatives with aggregation-induced phosphorescence characteristics for time-resolved and two-photon luminescence imaging

Aggregation-Assisted Three-Photon Fluorescence Resonance Energy Transfer Boosts Phosphorescence for Deep-Tissue Time-Resolved Intravital Brain Imaging

Three-photon phosphorescence microscopic bioimaging holds promise for deep-tissue time-resolved brain imaging with high spatial resolution and contrast. However, developing probes with bright phosphorescence and strong second near-infrared (NIR-II) three-photon absorption suitable for biological applications remains a formidable challenge. Herein, a kind of fluorescence resonance energy transfer (FRET)-based nanoparticles (NPFA-PorPt NPs) is proposed by co-encapsulation of a three-photon absorbing aggregation-induced emission luminogen (NPFA), and a phosphorescent platinum octaethylporphyrin (PorPt) using 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-2000] as the encapsulation matrix. NPFA is well designed to display superior three-photon absorption properties in the NIR-II region and its emission overlaps well with the absorption of PorPt, allowing efficient energy transfer to PorPt in nanoparticles. The phosphorescence of PorPt in the optimal NPFA-2%PorPt NPs is boosted by 350-fold as compared to that of pure PorPt aggregates upon the same excitation. The strong three-photon excited phosphorescence enables NPFA-2%PorPt NPs to be successfully applied for in vivo time-resolved brain and muscle vascular imaging with deep penetration, high spatial resolution, and contrast, and even the small capillaries in the deep tissue can be recognized. This study paves the way for the development of highly efficient multiphoton-absorbing phosphorescent probes for biomedical applications.

White light-excited organic room-temperature phosphorescence for improved in vivo bioimaging

Organic phosphorescence materials offer significant advantages for bioimaging applications. However, most of these materials are excited exclusively by ultraviolet (UV) light, which poses risks to living organisms. Herein, six donor-acceptor-type compounds incorporating triazine groups are designed as guests within doped systems. White-light excitable phosphorescent guests enable doped materials to show efficient afterglow under white-light excitation. By leveraging the ability of white-light to penetrate biological tissues, a bioimaging mode in which the materials are first concentrated within the organism and then excited was developed, yielding superior imaging effects compared with the traditional method in which materials are first excited and then concentrated. Furthermore, these materials are applied in imaging diagnosis of atherosclerosis plaques (male Apoe-/- mice) and intestinal diseases (female BALB/c-nude mice), as well as in navigation for in situ liver tumor surgery (female BALB/c-nude mice), achieving excellent imaging outcomes. This work addresses the limitations of phosphorescent materials that rely on UV-light, significantly enhancing their potential for practical applications in clinical imaging.

Dipyrroethene-Based Red-Light Emissive AIEgens

Aggregation-induced emission (AIE) molecules find myriads of applications in various fields ranging from biomedical probes and chemical sensors to optoelectronics. In this domain, tetraphenylethene (TPE) and its derivatives have long been a benchmark due to their unique luminescent properties in aggregated states. However, the limited tunability through further functionalization and the absorption and emission spectrum in higher-energy regions constrain their applications from multiple domains. To address these limitations, we have designed a new class of highly symmetric red-light emissive AIE-active molecules by structurally engineering the E-dipyrroethene (DPE) skeleton. This design enables pre- and postsynthetic modification opportunities through the two pyrrole rings and multiple heteroatoms, facilitating tunable photophysical properties. In this context, DPE-based AIEgens Tz and BTz were synthesized through the selective α,α-diformylation of DPE followed by condensation with 2-aminothiazole and 2-aminobenzothiazole, respectively. The π-extended conjugation systems in Tz and BTz containing multiple heteroatoms tune the excitation spectra in visible wavelength and emission spectra above 600 nm with a large Stokes shift in the range of 3632-5058 cm-1. Moreover, this modification provides a great platform for numerous noncovalent interactions, which significantly enhance aggregation- and solid-state fluorescence properties. Furthermore, various experimental, spectroscopic, and theoretical studies and X-ray crystallography measurements elucidate the structure-property relationships of these molecules, which pave the way for the development of novel materials with various applications in sensing and bioimaging. As a proof of concept, the potential of these molecules has been successfully demonstrated for the development of vapor- and solution-phase dynamic acid-base stimuli-responsive smart sensors, as well as the application of the BTz molecule in live-cell imaging.

Lone Pairs-Mediated Multiple Through-Space Interactions for Efficient Room-Temperature Phosphorescence

The simultaneous generation and stabilization of triplet excitons are the key to realizing efficient organic room temperature phosphorescence (RTP), which is challenging owing to the obscure mechanism and structure-property relationships. Herein, a strategy of lone-pair-mediated multiple through-space interactions (TSIs) is proposed to availably induce RTP. By incorporating heteroatoms to facilitate through-space n-n and n-π interactions, the lone pairs are delocalized throughout the structure, resulting in the dense splitting of the excited-state energy levels. Thus, more matched energy levels with a small energy gap between singlet and triplet states (ΔEST) emerge, resulting in multiple intersystem crossing (ISC) transition channels that assist triplet excitons generation. The strong TSIs also effectively rigidify the molecular structures and thus stabilize triplet excitons for radiation. Furthermore, the manipulation of TSI intensity allows efficiency enhancement, persistent time prolongation, and tolerance to high temperatures of RTP. This work not only explores the fundamental principle of the RTP mechanism from a new view but also provides a universal strategy for ISC promotion and triple excitons stabilization.

Multiscale and stimuli-responsive biosensing in biomedical applications: Emerging biomaterials based on aggregation-induced emission luminogens

Biosensors play a critical role in the diagnosis, treatment, and prognosis of diseases, with diverse applications ranging from molecular diagnostics to in vivo imaging. Conventional fluorescence-based biosensors, however, often suffer from aggregation-caused emission quenching (ACQ), limiting their effectiveness in high concentrations and complex environments. In contrast, the phenomenon of aggregation-induced emission (AIE) has emerged as a promising alternative, where luminescent materials exhibit strong emission in the aggregated state with good photostability, biocompatibility, large Stokes shift, high quantum yield, and tunable emission. This review article discusses the development of AIEgen-based biosensors for multiscale biosensing in biomedical applications. The integration of AIEgens with nanomaterials, such as graphene oxide and stimuli-responsive nanomaterials, can further improve the selectivity and multifunctionality of biomolecule detection. By careful molecular design, the affinity between AIEgens and specific biomolecules can be tuned, enabling the selective detection of targets like DNA, RNA, and proteins ex vivo, in vitro and in vivo, which can be applied across multiple scales, from detecting biomolecules and cellular structures to analyzing tissues and organs, underscoring their growing importance in disease diagnosis. Furthermore, we explore the potential integration of AIEgen-based biosensors with artificial intelligence (AI) technologies, offering promising avenues for future advancements in this field.

Multiphoton Excited Fluorescence Imaging over Metal-Organic Frameworks

Multiphoton excited fluorescence (MPEF) imaging has emerged as a powerful tool for visualizing biological processes with high spatial and temporal resolution. Metal-organic frameworks (MOFs), a class of porous materials composed of metal ions or clusters coordinated with organic ligands, have recently gained attention for their unique optical properties and potential applications in MPEF imaging. This review provides a comprehensive overview of the design, synthesis, and applications of multiphoton excited fluorescence imaging using MOFs. We discuss the principles behind the fluorescence behavior of MOFs, explore strategies to enhance their photophysical properties, and showcase their applications in bioimaging. Additionally, we address the current challenges and future prospects in this rapidly evolving field, highlighting the potential of multiphoton excited fluorescence imaging by MOFs for advancing our understanding of complex biological processes.

Tröger's Base as a Potential Bridge to Type-I Photosensitizers: Mechanism and Antitumor Applications

In contrast to Type-II photodynamic therapy (PDT), Type-I PDT with less oxygen consumption has shown great potential against tumor hypoxia. However, there are limited strategies available for designing Type-I photosensitizers (PSs). Herein, we present a promising strategy for synthesizing Type-I PSs (TBC-1-TBC-4) using Tröger's base (TB) framework. The TB framework can promote intersystem crossing efficiency and create an electron-rich environment, making it the most likely site for electron transfer to O2 to generate Type-I ROS. As anticipated, TBC-1-TBC-4 demonstrates Type-I ROS generation capability and their impressive visible light-harvesting ability significantly enhances this capability. Among them, TBC-1 demonstrates outstanding biocompatibility and PDT efficiency in vitro under both normoxia and hypoxia. Furthermore, TBC-1 effectively inhibits tumor growth in vivo, with negligible side effects. This is attributed to TBC-1's efficient generation of Type-I ROS and endoplasmic reticulum targeting ability. This study thus offers useful insights into developing Type-I PSs.

Bright "D-A-D" semiconducting small molecule aggregates for NIR-II fluorescence bioimaging guiding photothermal therapy

Donor-acceptor-donor (D-A-D) semiconducting small molecule nanoparticles have emerged as high-performance NIR-II fluorophores for real-time bioimaging. However, due to their intrinsic defects in aggregation-caused quenching (ACQ) and "energy gap law", D-A-D semiconducting small molecule nanoparticles typically exhibit low NIR-II fluorescence quantum yields (QYs). Herein, both the strategies of aggregation induced emission (AIE) and intermolecular charge transfer (CT) have been incorporated into the design of new D-A-D semiconducting small molecules. AIE enhances the NIR-II fluorescence intensity of NIR-II fluorophore aggregates in nanoparticles, while intermolecular CT increases both NIR absorption and NIR-II emission, thereby further improving their NIR-II fluorescence QYs. Four D-A-D semiconducting small molecules (TD, TT, TC, and TCD) were designed. Due to the combination of intermolecular CT and AIE of TCD aggregates, the NIR absorption and NIR-II fluorescence signals of TCD NPs were stronger than those of TD NPs and TT NPs with a single AIE property or TC NPs with strong intermolecular CT. Furthermore, TCD NPs demonstrated excellent performance in in vivo NIR-II fluorescence bioimaging guiding photothermal therapy.

Synthesis, structure, and reactivity of fully aryl-substituted pyrroles: toward the synthesis of nitrogen-doped buckybowls

This study describes the synthesis and potential applications of pentaaryl-substituted pyrroles. We report a Pd-catalyzed approach for their preparation from 4,5-diyne-9-fluorenone (1,7-diyne) and aromatic amines. The target nitrogen-doped corannulenes (CO-hub-Ncor) were investigated computationally to understand their electronic properties. While the conversion of pyrroles to CO-hub-Ncor is underway, the pyrroles themselves hold promise as valuable building blocks for N-doped buckybowls. Additionally, the synthesized pyrrole derivatives exhibit interesting reactivity, including pyrrole oxidation, leading to a ring-opening product, specifically a dicarbonyl compound.

Organic Materials with Ultrabright Phosphorescence at Room Temperature under Physiological Conditions for Bioimaging

In contrast to the high efficiency of room temperature phosphorescence in crystal states, the generally utilized nanoparticles of organic materials in bioimaging demonstrated sharply decreased performance by orders of magnitude under physiological conditions, badly limiting the realization of their unique advantages. This case, especially for organic red/near-infrared (NIR) phosphorescence materials, is not only the challenge present in reality but more importantly, for the theoretical problem of deeply understanding and avoiding the quenching effect by oxygen and water toward excited triplet states. Herein, thanks to the intelligent molecular design by the introduction of abundant hydrophobic chains and highly-branched structures, bright and persistent red/NIR phosphorescence under physiological conditions has been realized, which demonstrated the shielding effect towards oxygen, and the strengthened intermolecular interactions to suppress the non-radiative transitions. Accordingly, the record phosphorescence intensity of nanoparticles in bioimage, up to 8.21±0.36×108 p s-1 cm-2 sr-1, was achieved, to realize the clear phosphorescence imaging of liver and tumors in living mice, even lymph nodes in rabbit models with high SBRs. This work afforded an efficient way to achieve the bright red/NIR phosphorescence nanoparticles, guiding their further applications in biology and medicine.

Aggregation-Induced Emission Luminogens Realizing High-Contrast Bioimaging

A revolutionary transformation in biomedical imaging is unfolding with the advent of aggregation-induced emission luminogens (AIEgens). These cutting-edge molecules not only overcome the limitations of traditional fluorescent probes but also improve the boundaries of high-contrast imaging. Unlike conventional fluorophores suffering from aggregation-caused quenching, AIEgens exhibit enhanced luminescence when aggregated, enabling superior imaging performance. This review delves into the molecular mechanisms of aggregation-induced emission (AIE), demonstrating how strategic molecular design unlocks exceptional luminescence and superior imaging contrast, which is crucial for distinguishing healthy and diseased tissues. This review also highlights key applications of AIEgens, such as time-resolved imaging, second near-infrared window (NIR-II), and the advancement of AIEgens in sensitivity to physical and biochemical cue-responsive imaging. The development of AIE technology promises to transform healthcare from early disease detection to targeted therapies, potentially reshaping personalized medicine. This paradigm shift in biophotonics offers efficient tools to decode the complexities of biological systems at the molecular level, bringing us closer to a future where the invisible becomes visible and the incurable becomes treatable.

Aggregate Science: from Molecules, beyond Molecules

Over the past centuries, molecular science has played a dominant role in the advancement of physical science by exploring the structure-property relationships at a single molecular level. However, when molecules form aggregates, a dilemma arises as the structures and properties often differ significantly from those of molecular constituents. To address this, the concept of aggregate science emphasizes a holistic approach to understanding the structures-properties relationship of substances. Despite the recognition of holism in aggregate research, there are still challenges in investigating the complex operations and interplays, particularly in understanding the newly emergent structures and properties in the macroscopic world. Therefore, there is a need to further advance the concept and methodology. In this regard, this perspective highlights three types of influences that aggregation exerts on substance properties: activation, transformation, and emergence. Furthermore, examples from aggregation-induced emission research and related fields are provided to illustrate how aggregate science can be studied. This perspective emphasizes that the molecule is of significance and the structures and properties are also dramatically influenced by aggregation. Additionally, potential research methodologies, such as focusing on intra- and intermolecular interactions, adjusting aggregates morphology, and regulating the constituents, along with directions, and implications are offered for future studies.

Regulating Triplet Excitons of Organic Luminophores for Promoted Bioimaging

Afterglow materials with organic room temperature phosphorescence (RTP) or thermally activated delayed fluorescence (TADF) exhibit significant potential in biological imaging due to their long lifetime. By utilizing time-resolved technology, interference from biological tissue fluorescence can be mitigated, enabling high signal-tobackground ratio imaging. Despite the continued emergence of individual reports on RTP or TADF in recent years, comprehensive reviews addressing these two materials are rare. Therefore, this review aims to provide a comprehensive overview of several typical molecular designs for organic RTP and TADF materials. It also explores the primary methods through which triplet excitons resist quenching by water and oxygen. Furthermore, we analyze the principal challenges faced by afterglow materials and discuss key directions for future research with the hope of inspiring developments in afterglow imaging.

Exploring and Anticipating the Applications of Organic Room-Temperature Phosphorescent Materials in Biomedicine and Dentistry

As popular materials, organic room-temperature phosphorescent (RTP) materials have been studied and developed in many fields. RTP materials have the characteristics of a high signal-to-noise ratio (SNR) and high reactive oxygen species (ROS) quantum yield, which can achieve clear bioimaging and efficient ability of anti-tumor and antibacterial, and have received extensive attention from researchers for imaging, tumor therapy, and antibacterial treatment. Moreover, owing to their flexible molecular structures and various synthesis systems and methods, it may be possible to design and synthesize materials according to individual physiologic environments of patients in medical applications, making bioimaging more accurate and greatly improving tumor and bacterial killing rates. So they have great development potential in the medical field. On the basis of introducing the mechanism of RTP materials that emit phosphorescence and generate ROS, this review summarizes the medical applications of RTP materials from three aspects-bioimaging, tumor treatment and antibacterial treatment-to provide a basis for their application in the field of stomatology.

High-Performance Circularly Polarized Phosphorescence by Confining Isolated Chromophores with Chiral Counterions

Organic room-temperature phosphorescence (RTP) featuring circularly polarized luminescence (CPL) is highly valuable in chiroptoelectronics, but the trade-off issue between luminescence efficiency (Φ) and dissymmetry factor (glum) is still challenging to be solved. Here, chiroptical ionic crystals (R/S-DNP) are constructed through ionization-induced assembly, in which isolated chromophore of carboxylic anion is tightly confined by the surrounding chiral counterions. The long-range ordered and chiral counterions with asymmetric stacking are closely connected with isolated chromophores for molecular assembly via high-density electrostatic interactions, thus enabling the simultaneous realization of excellent single-molecule RTP emission and efficient chirality transfer. The synchronous enhancement of ΦP and glum is further achieved as 43.2% and 0.13, respectively. In view of the excellent CPL performances, the ionic materials hold the promising chiroptical encryption via programmable control in an electric-driven circularly polarized phosphorescent device. This result not only makes deeper insights into the relationship between the structure and chiral RTP property but also provides a guide to developing highly efficient chiroptical materials for potential applications.

Visible-light-excited organic room temperature phosphorescence

Purely organic room temperature phosphorescence (RTP) materials have evoked considerable attention owing to their fantastic optical properties and broad application prospects. However, most of the reported organic RTP materials can be only excited by UV light, leading to accelerated photoaging of organic phosphors and severe lesions of organisms under excitation. In contrast to UV light, visible light (380-780 nm) has much lower phototoxicity, deeper penetrability and easier accessibility, which make visible-light-excited RTP materials more favorable for practical uses, especially for life-related applications. Although it remains greatly challenging to construct visible-light-excited RTP materials, impressive progress has been made with the rapid development of this field. Herein, we systematically outline the significant progress achieved in visible-light-excited RTP materials, including the design and construction strategies, unique properties, underlying mechanisms and their vital applications. In the final section, we highlight the current challenges and research perspectives for suggesting future studies of visible-light-excited RTP materials.

Efficient and Stable NIR-II Phosphorescence of Metallophilic Molecular Oligomers for In Vivo Single-Cell Tracking and Time-Resolved Imaging

Molecular phosphorescence in the second near-infrared window (NIR-II, 1000-1700 nm) holds promise for deep-tissue optical imaging with high contrast by overcoming background fluorescence interference. However, achieving bright and stable NIR-II molecular phosphorescence suitable for biological applications remains a formidable challenge. Herein, we report a new series of symmetric isocyanorhodium(I) complexes that could form oligomers and exhibit bright, long-lived (7-8 μs) phosphorescence in aqueous solution via metallophilic interaction. Ligand substituents with enhanced dispersion attraction and electron-donating properties were explored to extend excitation/emission wavelengths and enhanced stability. Further binding the oligomers with fetal bovine serum (FBS) resulted in NIR-II molecular phosphorescence with high quantum yields (up to 3.93 %) and long-term stability in biological environments, enabling in vivo tracking of single-macrophage dynamics and high-contrast time-resolved imaging. These results pave the way for the development of highly-efficient NIR-II molecular phosphorescence for biomedical applications.

Simplifying complexity: integrating color science for predictable full-color and on-demand persistent luminescence using industrial disperse dyes

Developing color-tunable ultralong room temperature phosphorescence (RTP) materials with variable afterglow is essential for applications in displays, sensors, information encryption, and optoelectronic devices. However, designing full-color ultralong RTP for persistent luminescence remains a significant challenge. Here, we propose a straightforward strategy to achieve predictable full-color afterglow using readily available disperse dyes in polymeric systems, via the phosphorescence resonance energy transfer (PRET) process. We incorporated the unconventional luminophore tetraacetylethylenediamine (TAED) into polyurethane (PU) to create a polymer host with green afterglow. By adding three typical disperse dyes as guests, we achieved a modulated afterglow covering the full visible light spectrum. Leveraging PRET processes between TAED and the disperse dyes, we achieved a prediction accuracy of 88.89% for afterglow color, surpassing well-developed coloration dye systems. This work thus introduces a novel method to obtain easily predictable ultralong RTP emission and establishes an on-demand design strategy for constructing disperse dye-based full-color afterglow, effectively linking fundamental color science to practical customization.

A NIR-Light-Activated and Lysosomal-Targeted Pt(II) Metallacycle for Highly Potent Evoking of Immunogenic Cell Death that Potentiates Cancer Immunotherapy of Deep-Seated Tumors

Though platinum (Pt)-based complexes have been recently exploited as immunogenic cell death (ICD) inducers for activating immunotherapy, the effective activation of sufficient immune responses with minimal side effects in deep-seated tumors remains a formidable challenge. Herein, we propose the first example of a near-infrared (NIR) light-activated and lysosomal targeted Pt(II) metallacycle (1) as a supramolecular ICD inducer. 1 synergistically potentiates immunomodulatory response in deep-seated tumors via multiple-regulated approaches, involving NIR light excitation, boosted reactive oxygen species (ROS) generation, good selectivity between normal and tumor cells, and enhanced tumor penetration/retention capabilities. Specifically, 1 has excellent depth-activated ROS production (~7 mm), accompanied by strong anti-diffusion and anti-ROS quenching ability. In vitro experiments demonstrate that 1 exhibits significant cellular uptake and ROS generation in tumor cells as well as respective multicellular tumor spheroids. Based on these advantages, 1 induces a more efficient ICD in an ultralow dose (i.e., 5 μM) compared with the clinical ICD inducer-oxaliplatin (300 μM). In vivo, vaccination experiments further demonstrate that 1 serves as a potent ICD inducer through eliciting CD8+/CD4+ T cell response and Foxp3+ T cell depletion with negligible adverse effects. This study pioneers a promising avenue for safe and effective metal-based ICD agents in immunotherapy.

A perylene diimide probe for NIR-II fluorescence imaging guided photothermal and type I/type II photodynamic synergistic therapy

Phototherapy has garnered significant attention in the past decade. Photothermal and photodynamic synergistic therapy combined with NIR fluorescence imaging has been one of the most attractive treatment options because of the deep tissue penetration, high selectivity and excellent therapeutic effect. Benefiting from the superb photometrics and ease of modification, perylene diimide (PDI) and its derivatives have been employed as sensing probes and therapeutic agents in the biological and biomedical research fields, and exhibiting excellent potential. Herein, we reported the development of a novel organic small-molecule phototherapeutic agent, PDI-TN. The absorption of PDI-TN extends into the NIR region, which provides feasibility for NIR phototherapy. PDI-TN overcomes the traditional Aggregation-Caused Quenching (ACQ) effect and exhibits typical characteristics of Aggregation-Induced Emission (AIE). Subsequently, PDI-TN NPs were obtained by using an amphiphilic triblock copolymer F127 to encapsulate PDI-TN. Interestingly, the PDI-TN NPs not only exhibit satisfactory photothermal effects, but also can generate O2•- and 1O2 through type I and type II pathways, respectively. Additionally, the PDI-TN NPs emit strong fluorescence in the NIR-II region, and show outstanding therapeutic potential for in vivo NIR-II fluorescence imaging. To our knowledge, PDI-TN is the first PDI derivative used for NIR-II fluorescence imaging-guided photodynamic and photothermal synergistic therapy, which suggests excellent potential for future biological/biomedical applications.

Metastable Supramolecular Assembly of Simple Monomers Enabled by Confinement: Towards Aqueous Phase Room Temperature Phosphorescence

The application of supramolecular assembly (SA) with room temperature phosphorescence (RTP) in aqueous phase has the potential to revolutionize numerous fields. However, using simple molecules with crystalline RTP to construct SA with aqueous phase RTP is hardly possible from the standpoint of forces. The reason lies in that the transition from crystal to SA involves a structure transformation from highly stable to more dynamic state, leading to increased non-radiative deactivation pathways and silent RTP signal. Here, with the benefit of the confinement from the layered double hydroxide (LDH), various simple molecules (benzene derivatives) can successfully form metastable SA with aqueous phase RTP. The maximum of RTP lifetime and efficiency can reach 654.87 ms and 5.02 %, respectively. Mechanistic studies reveal the LDH energy trap can strengthen the intermolecular interaction, providing the prerequisite for the existence of metastable SA and appearance of aqueous phase RTP. The universality of this strategy will usher exploration into other multifunctional monomer, facilitating the development of SAs with aqueous phase RTP.

Preparation of AIEgen-based near-infrared afterglow luminescence nanoprobes for tumor imaging and image-guided tumor resection

Fluorescence imaging represents a vital tool in modern biology, oncology and biomedical applications. Afterglow luminescence (AGL), which circumvents the light scattering and tissue autofluorescence interference associated with real-time excitation source, shows remarkably increased imaging sensitivity and depth. Here we present a protocol for the design and synthesis of AGL nanoprobes with an aggregation-induced emission (AIE) effect to simultaneously red shift and amplify the afterglow signal for tumor imaging and image-guided tumor resection. The nanoprobe (AGL AIE dot) is composed of an enol ether format of Schaap's agent and a near-infrared AIE fluorogen (AIEgen) (tetraphenylethylene-phenyl-dicyanomethylene-4H-chromene, TPE-Ph-DCM) to suppress the nonradiative dissipation pathway. Pre-irradiating AGL AIE dots with white light could generate singlet oxygen to convert Schaap's agent to its 1,2-dioxetane format, thus initializing the AGL process. With the aid of AIEgen, the AGL shows simultaneously red shifted emission maximum (from ~540 nm to ~625 nm) and enhanced intensity (by 3.2-fold), facilitating better signal-to-background ratio, imaging sensitivity and depth. Intriguingly, the activated AGL can last for over 10 days. Compared with conventional approaches, our method provides a new solution to concurrently red shift and amplify afterglow signals for better in vivo imaging outcomes. The preparation of AGL AIE dots takes ~2 days, the in vitro characterization takes ~10 days (less than 1 day if not involving afterglow kinetic profile study) and the tumor imaging and image-guided tumor resection takes ~7 days. These procedures can be easily reproduced and amended after standard laboratory training in chemical synthesis and animal handling.

Synergistic meso-β regulation of porphyrins: squeezing the band gap into the near-infrared I/II region

The development of novel near-infrared (NIR) materials with extremely small energy gaps and high stability is highly desirable in bioimaging and phototherapy. Here we report an effective strategy for narrowing the energy gaps of porphyrins by synergistic regulation of meso/β substituents. The novel NIR absorbing/emitting meso-alkynyl naphthoporphyrins (Zn-TNP and Pt-TNP) are synthesized via the retro-Diels-Alder reaction. X-ray crystallography analysis confirms the highly distorted structures of the complexes. Both compounds exhibit intense Q bands around 800 nm, while Zn-TNP shows deep NIR fluorescence at 847 nm. Pt-TNP displays NIR-II room temperature phosphorescence peaking at 1106 nm with an extremely large Stokes shift of 314 nm, which are the longest wavelengths observed among the reported platinum porphyrinoids. Furthermore, Pt-TNP shows remarkable photostability and a notable capacity for synchronous singlet oxygen and heat generation under NIR light irradiation, demonstrating potential in combined photodynamic/photothermal therapy. A theoretical analysis reveals the progressive lifting of the HOMO by the β-fused benzene ring, the decrease of the LUMO upon meso-alkynyl substitution, and energy-releasing pathways varying with metal ions. This dual regulation approach demonstrates great promise in designing innovative multifunctional NIR porphyrin materials.

Single-Component Photochemical Afterglow Near-Infrared Luminescent Nano-Photosensitizers: Bioimaging and Photodynamic Therapy

Long afterglow luminescence-guided photodynamic therapy (PDT) performs advantages of noninvasiveness, spatiotemporal controllability, and higher signal to noise ratio. Photochemical afterglow (PCA) system emitting afterglow in an aqueous environment is highly suitable for biomedical applications, but still faces the challenges of poor tissue penetration depth and responsive sensitivity. In this work, two novel compounds, Iso-TPA and ABEI-TPA, are designed and synthesized to integrate the PCA system as a single component by coupling near-infrared (NIR) photosensitizers with singlet oxygen cache units, respectively. Both compounds emit NIR afterglow based on photochemical reaction. ABEI-TPA exhibits higher photoluminescence quantum efficiency with nonconjugated linkage, while Iso-TPA with conjugated linkage possesses better reactive oxygen species generation efficiency to achieve stronger PCA and effective PDT, which is ascribed to stronger intramolecular charge transfer effect of Iso-TPA. Iso-TPA nanoparticles can achieve effective long-lasting NIR afterglow in vivo bioimaging up to 120 s with higher imaging resolution and outstanding PDT efficacy of tumor, exhibiting promising potential on bioimaging and therapy.

Conformational Effect of Catechol-Terephthalonitrile Emitters Leading to Ambient Violet Phosphorescence

Organic ambient violet phosphorescent (AVP) materials are of great interest due to their involvement of high energy and longer-lived triplet excitons. Here, we show three fused ring functionalized donor-acceptor-donor (D-A-D/D-A-D') emitters (BPT1-BPT3), in which two catechol-based donors (3,4-dihydroxybenzophenone, catechol, or 3,5-ditert-butylcatechol) are covalently fused to the terephthalonitrile acceptor via four O-C single bonds. Spectroscopic analysis revealed that all the molecules show AVP (∼390-394 nm, τAVP = 73-101 μs) with phosphorescence quantum yields (ϕP) of 1.8-27.4% due to low singlet-triplet gaps (0.036-0.046 eV) and conformational effects. BPT3 with bulky tert-butyl groups increases AVP (ϕP = 27.4%). Quantum chemistry calculations reveal flat (F1) and twisted (F2) conformers (ground state) with a low energy difference (∼4-5 kcal/mol) for all molecules; the F1 conformer is responsible for efficient AVP, while weak blue thermally activated delayed fluorescence with longer-lived delayed components is realized from the F2 conformer. This approach may provide important clues for the design of high-energy organic phosphorescent materials.

Fused-Ring Pyrrole-Based Near-Infrared Emissive Organic RTP Material for Persistent Afterglow Bioimaging

Organic near-infrared room temperature phosphorescence (RTP) materials offer remarkable advantages in bioimaging due to their characteristic time scales and background noise elimination. However, developing near-infrared RTP materials for deep tissue imaging still faces challenges since the small band gap may increase the non-radiative decay, resulting in weak emission and short phosphorescence lifetime. In this study, fused-ring pyrrole-based structures were employed as the guest molecules for the construction of long wavelength emissive RTP materials. Compared to the decrease of the singlet energy level, the triplet energy level showed a more effectively decrease with the increase of the conjugation of the substituent groups. Moreover, the sufficient conjugation of fused ring structures in the guest molecule suppresses the non-radiative decay of triplet excitons. Therefore, a near-infrared RTP material (764 nm) was achieved for deep penetration bioimaging. Tumor cell membrane is used to coat RTP nanoparticles (NPs) to avoid decreasing the RTP performance compared to traditional coating by amphiphilic surfactants. RTP NPs with tumor-targeting properties show favorable phosphorescent properties, superior stability, and excellent biocompatibility. These NPs are applied for time-resolved luminescence imaging to eliminate background interference with excellent tissue penetration. This study provides a practical solution to prepare long-wavelength and long-lifetime organic RTP materials and their applications in bioimaging.

π-π Interaction-Induced Organic Long-wavelength Room-Temperature Phosphorescence for In Vivo Atherosclerotic Plaque Imaging

Room-temperature phosphorescent (RTP) materials have great potential for in vivo imaging because they can circumvent the autofluorescence of biological tissues. In this study, a class of organic-doped long-wavelength (≈600 nm) RTP materials with benzo[c][1,2,5] thiadiazole as a guest was constructed. Both host and guest molecules have simple structures and can be directly purchased commercially at a low cost. Owing to the long phosphorescence wavelength of the doping system, it exhibited good tissue penetration (10 mm). Notably, these RTP nanoparticles were successfully used to image atherosclerotic plaques, with a signal-to-background ratio (SBR) of 44.52. This study provides a new approach for constructing inexpensive red organic phosphorescent materials and a new method for imaging cardiovascular diseases using these materials.

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

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

Molecularly Engineered Room-Temperature Phosphorescence for Biomedical Application: From the Visible toward Second Near-Infrared Window

Phosphorescence, characterized by luminescent lifetimes significantly longer than that of biological autofluorescence under ambient environment, is of great value for biomedical applications. Academic evidence of fluorescence imaging indicates that virtually all imaging metrics (sensitivity, resolution, and penetration depths) are improved when progressing into longer wavelength regions, especially the recently reported second near-infrared (NIR-II, 1000-1700 nm) window. Although the emission wavelength of probes does matter, it is not clear whether the guideline of "the longer the wavelength, the better the imaging effect" is still suitable for developing phosphorescent probes. For tissue-specific bioimaging, long-lived probes, even if they emit visible phosphorescence, enable accurate visualization of large deep tissues. For studies dealing with bioimaging of tiny biological architectures or dynamic physiopathological activities, the prerequisite is rigorous planning of long-wavelength phosphorescence, being aware of the cooperative contribution of long wavelengths and long lifetimes for improving the spatiotemporal resolution, penetration depth, and sensitivity of bioimaging. In this Review, emerging molecular engineering methods of room-temperature phosphorescence are discussed through the lens of photophysical mechanisms. We highlight the roles of phosphorescence with emission from visible to NIR-II windows toward bioapplications. To appreciate such advances, challenges and prospects in rapidly growing studies of room-temperature phosphorescence are described.

Microwave-Responsive Flexible Room-Temperature Phosphorescence Materials Based on Poly(vinylidene fluoride) Polymer

The development of flexible, room-temperature phosphorescence (RTP) materials remains challenging owing to the quenching of their unstable triplet excitons via molecular motion. Therefore, a polymer matrix with Tg higher than room temperature is required to prevent polymer segment movement. In this study, a RTP material was developed by incorporating a 4-biphenylboronic acid (BPBA) phosphor into a poly(vinylidene fluoride) (PVDF) matrix (Tg =-27.1 °C), which exhibits a remarkable UV-light-dependent oxygen consumption phosphorescence with a lifetime of 1275.7 ms. The adjustable RTP performance is influenced by the crystallinity and polymorph (α, β, and γ phases) fraction of PVDF, therefore, the low Tg of the PVDF matrix enables the polymeric segmental motion upon microwave irradiation. Consequently, a reduction in the crystallinity and an increase in the α phase fraction in PVDF film induces RTP after 2.45 GHz microwave irradiation. These findings open up new avenues for constructing crystalline and phase-dependent RTP materials while demonstrating a promising approach toward microwave detection.

Facile Preparation of Full-Color Tunable Room Temperature Phosphorescence Cellulose via Click Chemistry

Sustainable long-lived room temperature phosphorescence (RTP) materials with color-tunable afterglows are attractive but rarely reported. Here, cellulose is reconstructed by directed redox to afford ample active hydroxyl groups and water-solubility; arylboronic acids with various π conjugations can be facilely anchored to reconstructed cellulose via click chemistry within 1 min in pure water, resulting in full-color tunable RTP cellulose. The rigid environment provided by the B─O covalent bonds and hydrogen bonds can stabilize the triplet excitons, thus the target cellulose displays outstanding RTP performances with the lifetime of 2.67 s, phosphorescence quantum yield of 9.37%, and absolute afterglow luminance of 348 mcd m-2 . Furthermore, due to the formation of various emissive species, the smart RTP cellulose shows excitation- and time-dependent afterglows. Taking advantages of sustainability, ultralong lifetime, and full-color tunable afterglows, et al, the environmentally friendly RTP cellulose is successfully used for nontoxic afterglow inks, delay lighting, and afterglow display.

Recent advances in the design of afterglow materials: mechanisms, structural regulation strategies and applications

Afterglow materials are attracting widespread attention owing to their distinctive and long-lived optical emission properties which create exciting opportunities in various fields. Recent research has led to the discovery of many new afterglow materials featuring high photoluminescence quantum yields (PLQY) and lifetimes of up to several hours under ambient conditions. Afterglow materials are typically categorized according to their luminescence mechanism, such as long-persistent luminescence (LPL), room temperature phosphorescence (RTP), or thermally activated delayed fluorescence (TADF). Through rational design and novel synthetic strategies to modulate spin-orbit coupling (SOC) and populate triplet exciton states (T1), luminophores with long lifetimes and bright afterglow characteristics can be realized. Initial research towards afterglow materials focused mainly on pure inorganic materials, many of which possessed inherent disadvantages such as metal toxicity or low energy emissions. In recent years, organic-inorganic hybrid afterglow materials (OIHAMs) have been developed with high PLQY and long lifetimes. These hybrid materials exploit the tunable structure and easy processing of organic molecules, as well as enhanced SOC and intersystem crossing (ISC) processes involving heavy atom dopants, to achieve excellent afterglow performance. In this review, we begin by briefly discussing the structure and composition of inorganic and organic-inorganic hybrid afterglow materials, including strategies for regulating their lifetime, PLQY and luminescence wavelength. The specific advantages of organic-inorganic hybrid afterglow materials, including low manufacturing costs, diverse molecular/electronic structures, tunable structures and optical properties, and compatibility with a variety of substrates, are emphasized. Subsequently, we discuss in detail the fundamental mechanisms used by afterglow materials, their classification, design principles, and end applications (including sensing, anticounterfeiting, and photoelectric devices, among others). Finally, existing challenges and promising future directions are discussed, laying a platform for the design of afterglow materials for specific applications.

The Bioimaging Story of AIEgens

Observations of the micro world, especially the structures of organelles, have been attractive topics since the 17th century. As a powerful detection tool, the fluorescence technique has played a significant role in bioimaging to provide more details and enhance the signal-to-noise ratio compared to that of traditional optical microscopes. The boom of aggregate-induced emission luminogens (AIEgens) in the last two decades has revolutionized the design strategy of luminescent materials for biological applications. This Review summarizes the advantages and recent progress of AIEgens in imaging and tracking. Different imaging strategies of AIEgens including turn-on imaging, stimuli-response sensing, and long-term tracking are presented. NIR AIEgens used for in-depth bioimaging via different methods are also discussed. Finally, we propose several potential development directions for AIEgens in bioimaging.

A functional unit combination strategy for enhancing red room-temperature phosphorescence

Red room-temperature phosphorescence (RTP) materials based on non-metallic organic compounds are less reported compared to the commonly found green RTP materials. Here, we propose a novel approach to obtain red RTP materials by integrating and combining two functional units, resembling a jigsaw puzzle. In this approach, benzo[c][2,1,3]thiadiazole (BZT) serves as the red RTP unit, while a folding unit containing sulphur/oxygen is responsible for enhancing spin-orbit coupling (SOC) to accelerate the intersystem crossing (ISC) process. Three new molecules (SS-BZT, SO-BZT, and OO-BZT) were designed and synthesized, among which SS-BZT and SO-BZT with folded geometries demonstrate enhanced red RTP in their monodisperse films compared to the parent BZT. Meanwhile, the SS-BZT film shows a dual emission consisting of blue fluorescence and red RTP, with a significant spectral separation of approximately 150 nm, which makes the SS-BZT film highly suitable for applications in optical oxygen sensing and ratiometric detection. Within the oxygen concentration range of 0-1.31%, the SS-BZT film demonstrates a quenching constant of 2.66 kPa-1 and a quenching efficiency of 94.24%, indicating that this probe has the potential to accurately detect oxygen in a hypoxic environment.

Durable organic nonlinear optical membranes for thermotolerant lightings and in vivo bioimaging

Organic nonlinear optical materials have potential in applications such as lightings and bioimaging, but tend to have low photoluminescent quantum yields and are prone to lose the nonlinear optical activity. Herein, we demonstrate to weave large-area, flexible organic nonlinear optical membranes composed of 4-N,N-dimethylamino-4'-N'-methyl-stilbazolium tosylate@cyclodextrin host-guest supramolecular complex. These membranes exhibited a record high photoluminescence quantum yield of 73.5%, and could continuously emit orange luminescence even being heated at 300 °C, thus enabling the fabrication of thermotolerant light-emitting diodes. The nonlinear optical property of these membranes can be well-preserved even in polar environment. The supramolecular assemblies with multiphoton absorption characteristics were used for in vivo real-time imaging of Escherichia coli at 1000 nm excitation. These findings demonstrate to achieve scalable fabrication of organic nonlinear optical materials with high photoluminescence quantum yields, and good stability against thermal stress and polar environment for high-performance, durable optoelectronic devices and humanized multiphoton bio-probes.

Lighting up metastasis process before formation of secondary tumor by phosphorescence imaging

Metastasis is the leading cause of cancer-related deaths; until now, the detection of tumor metastasis is mainly located at the period that secondary tumors have been formed, which usually results in poor prognosis. Thus, fast and precise positioning of organs, where tumor metastases are likely to occur at its earliest stages, is essential for improving patient outcomes. Here, we demonstrated a phosphorescence imaging method by organic nanoparticles to detect early tumor metastasis progress with microenvironmental changes, putting the detection period ahead to the formation of secondary tumors. In the orthotopic and simulated hematological tumor metastasis models, the microenvironmental changes could be recognized by phosphorescence imaging at day 3, after tumor implantation in liver or intravenous injection of cancer cells. It was far ahead those of other reported imaging methods with at least 7 days later, providing a sensitive and convenient method to monitor tumor metastases at the early stage.

Oxidization enhances type I ROS generation of AIE-active zwitterionic photosensitizers for photodynamic killing of drug-resistant bacteria

Type I photosensitizers (PSs) with an aggregation-induced emission (AIE) feature have received sustained attention for their excellent theranostic performance in the treatment of clinical diseases. However, the development of AIE-active type I PSs with strong reactive oxygen species (ROS) production capacity remains a challenge due to the lack of in-depth theoretical studies on the aggregate behavior of PSs and rational design strategies. Herein, we proposed a facile oxidization strategy to enhance the ROS generation efficiency of AIE-active type I PSs. Two AIE luminogens, MPD and its oxidized product MPD-O were synthesized. Compared with MPD, the zwitterionic MPD-O showed higher ROS generation efficiency. The introduction of electron-withdrawing oxygen atoms results in the formation of intermolecular hydrogen bonds in the molecular stacking of MPD-O, which endowed MPD-O with more tightly packed arrangement in the aggregate state. Theoretical calculations demonstrated that more accessible intersystem crossing (ISC) channels and larger spin-orbit coupling (SOC) constants provide further explanation for the superior ROS generation efficiency of MPD-O, which evidenced the effectiveness of enhancing the ROS production ability by the oxidization strategy. Moreover, DAPD-O, a cationic derivative of MPD-O, was further synthesized to improve the antibacterial activity of MPD-O, showing excellent photodynamic antibacterial performance against methicillin-resistant S. aureus both in vitro and in vivo. This work elucidates the mechanism of the oxidization strategy for enhancing the ROS production ability of PSs and offers a new guideline for the exploitation of AIE-active type I PSs.

Photoactivated organic phosphorescence by stereo-hindrance engineering for mimicking synaptic plasticity

Purely organic phosphorescent materials with dynamically tunable optical properties and persistent luminescent characteristics enable more novel applications in intelligent optoelectronics. Herein, we reported a concise and universal strategy to achieve photoactivated ultralong phosphorescence at room temperature through stereo-hindrance engineering. Such dynamically photoactivated phosphorescence behavior was ascribed to the suppression of non-radiative transitions and improvement of spin-orbit coupling (SOC) as the variation of the distorted molecular conformation by the synergistic effect of electrostatic repulsion and steric hindrance. This "trainable" phosphorescent behavior was first proposed to mimic biological synaptic plasticity, especially for unique experience-dependent plasticity, by the manipulation of pulse intensity and numbers. This study not only outlines a principle to design newly dynamic phosphorescent materials, but also broadens their utility in intelligent sensors and robotics.

Composite Mesoporous Silica Nanoparticles with Dual-color Afterglow for Cross-correlation-based Living Cell Imaging

Room temperature phosphorescence (RTP) materials are characterized with emission after removing the excitation source. Such long-lived emission feature possesses great potential in biological fluorescence imaging because it enables a way regarding temporal dimension for separating the interference of autofluorescence and common noises typically encountered in conventional fluorescence imaging. Herein, we constructed a new type of mesoporous silica nanoparticles (MSNs)-based composite nanoparticles (NPs) with dual-color long-lived emission, namely millisecond-level green phosphorescence and sub-millisecond-level delayed red fluorescence by encapsulating a typical RTP dye and Rhodamine dye in the cavities of the MSNs with the former acting as energy donor (D) while the latter as acceptor (A). Benefiting from the close D-A proximity, energy match between the donor and the acceptor and the optimized D/A ratio in the composite NPs, efficient triplet-to-singlet Förster resonance energy transfer (TS-FRET) in the NPs occurred upon exciting the donor, which enabled dual-color long-lived emission. The preliminary results of dual-color correlation imaging of live cells based on such emission feature unequivocally verified the unique ability of such NPs for distinguishing the false positive generated by common emitters with single-color emission feature.

Functional Roles of Polymers in Room-Temperature Phosphorescent Materials: Modulation of Intersystem Crossing, Air Sensitivity and Biological Activity

Organic room-temperature phosphorescent (RTP) materials routinely incorporate polymeric components, which usually act as non-functional or "inert" media to protect excited-state phosphors from thermal and collisional quenching, but are lesser explored for other influences. Here, we report some exemplary "active roles" of polymer matrices played in organic RTP materials, including: 1) color modulation of total delayed emissions via balancing the population ratio between thermally-activated delayed fluorescence (TADF) and RTP due to dielectric-dependent intersystem crossing; 2) altered air sensitivity of RTP materials by generating various surface morphologies such as nano-sized granules; 3) enhanced bacterial elimination for enhanced electrostatic interactions with negatively charged bio-membranes. These active roles demonstrated that the vast library of polymeric structures and functionalities can be married to organic phosphors to broaden new application horizons for RTP materials.

Stimulus-Responsive Organic Phosphorescence Materials Based on Small Molecular Host-Guest Doped Systems

Small molecular host-guest doped materials exhibit superiority toward high-efficiency room-temperature phosphorescence (RTP) materials due to their structural design diversity and ease of preparation. Dynamic RTP materials display excellent characteristics, such as good reversibility, quick response, and tunable luminescence ability, making them applicable to various cutting-edge technologies. Herein, we summarize the advances in host-guest doped dynamic RTP materials that respond to external and internal stimuli and present some insights into the molecular design strategies and underlying mechanisms. Subsequently, specific viewpoints are described regarding this promising field for the development of dynamic RTP materials. This Perspective is highly beneficial for future intelligent applications of dynamic RTP systems.

Room-Temperature Phosphorescence and Cellular Phototoxicity Activated by Triplet Dynamics in Aggregates of Push-Pull Phenothiazine-Based Isomers

In this study, we report a comprehensive time-resolved spectroscopic investigation of the excited-state deactivation mechanism in three push-pull isomers characterized by a phenothiazine electron donor, a benzothiazole electron acceptor, and a phenyl π-bridge where the connection is realized at the relative ortho, meta, and para positions. Spin-orbit charge-transfer-induced intersystem crossing takes place with high yield in these all-organic donor-acceptor compounds, leading also to efficient production of singlet oxygen. Our spectroscopic results give clear evidence of room-temperature phosphorescence not only in solid-state host-guest matrices but also in highly biocompatible aggregates of these isomers produced in water dispersions, as rarely reported in the literature. Moreover, aggregates of the isomers could be internalized by lung cancer and melanoma cells and display bright luminescence without any dark cytotoxic effect. On the other hand, the isomers showed significant cellular phototoxicity against the tumor cells due to light-induced reactive oxygen species generation. Our findings strongly suggest that nanoaggregates of the investigated isomers are promising candidates for imaging-guided photodynamic therapy.

Switchable and Highly Robust Ultralong Room-Temperature Phosphorescence from Polymer-Based Transparent Films with Three-Dimensional Covalent Networks for Erasable Light Printing

In this work, an efficient polymer-based organic afterglow system, which shows reversible photochromism, switchable ultralong organic phosphorescence (UOP), and prominent water and chemical resistance simultaneously, has been developed for the first time. By doping phenoxazine (PXZ) and 10-ethyl-10H-phenoxazine (PXZEt) into epoxy polymers, the resulting PXZ@EP-0.25 % and PXZEt@EP-0.25 % films show unique photoactivated UOP properties, with phosphorescence quantum yields and lifetimes up to 10.8 % and 845 ms, respectively. It is found that the steady-state luminescence and UOP of PXZ@EP-0.25 % are switchable by light irradiation and thermal annealing. Moreover, the doped films can still produce conspicuous UOP after soaking in water, strong acid and base, and organic solvents for more than two weeks, exhibiting outstanding water and chemical resistance. Inspired by these exciting results, the PXZ@EP-0.25 % has been successfully exploited as an erasable transparent film for light printing.

Aggregation Effect on Multiperformance Improvement in Aryl-Armed Phenazine-Based Emitters

The concept of aggregate science was proposed to explain changes in materials performance that accompany the generation of aggregates, but aggregation-triggered multifunction improvements in a class of materials have rarely been reported. Herein, we present the first report of a new class of multifunctional aggregation-induced emission (AIE) luminogens (AIEgens) based on 5,10-diarylphenazine (DPZ) derivates with full-wavelength emission. Intriguingly, multiple properties, such as fluorescence intensity and free radical and type I reactive oxygen species (ROS) efficiencies, could be simultaneously activated from the unimolecular level to the aggregate state. The mechanisms of this multiple performance improvement are discussed in detail based on sufficient performance characterization, and some of the newly prepared AIEgens exhibited toxicity to cancer cells during photodynamic therapy. This work systematically demonstrates the positive effect of aggregation on improving multiple functions of materials, which is expected to promote the development of aggregate science theory for the design of multifunctional materials.

One-Pot Three Carbon Dots with Various Lifetimes Rooted in Different Decarboxylation Degrees for Matrix-Free, Anti-Oxygen, and Time-Resolved Information Encryption and Cellular Imaging

Activating long-lived room temperature phosphorescence (RTP) in the aqueous environment and thus realizing matrix-free, anti-oxygen, and time-resolved information encryption and cellular imaging remain a great challenge. Here, we fabricated three types of carbon dots (C-dots), i.e., fluorescent C-dots (F-C-dots) and two types of phosphorescent C-dots denoted as Pw-C-dots and Py-C-dots by a one-pot strategy. Their formation was attributed to the difference in the decarboxylation degree at high temperatures using trimesic acid (TMA) as a sole precursor. Unexpectedly, the yield reached as high as ∼92%, and the proportions were ∼27% for F-C-dots, ∼17% for Pw-C-dots, and ∼56% for Py-C-dots. These nanomaterials could help implement carbon peaking and carbon neutrality. Both green RTP of the two C-dots resulted from the small energy gap (ΔEST). These two RTP C-dots had a long lifetime of over 270 ms with a relatively high quantum yield (4.5 and 6.2%). They exhibited excellent photostability and anti-photobleaching performances. The dry and wet powders of the RTP C-dots were applied to high-level information encryption. The lifelike patterns were greatly different from those of the original ones and could last for several seconds to the naked eye, demonstrating that the RTP C-dots could be potentially employed as anti-oxygen and time-resolved contrast reagents. Most significantly, the cellular imaging experiments showed that the biofriendly PVP-coated Py-C-dots could localize at lysosomes and sustain hundreds of milliseconds. This approach not only pioneers a time-resolved lysosome localization model but also opens up a promising door for anti-oxygen and time-resolved RTP cytoimaging.

The effect of substituents and molecular aggregation on the room temperature phosphorescence of a twisted π-system

Room temperature phosphorescence of an intrinsically apolar twisted π-system is modulated by polar substituents. Persistent phosphorescence is visible by eye in poder, induced by molecular aggregation.

Research and Design of Aggregation-Induced Phosphorescent Materials for Time-Resolved Two-Photon Excited Luminescence Imaging

Pure organic two-photon excited room temperature phosphorescent (RTP) materials have attracted great attention for time-resolved imaging due to their long emission lifetime and high resolution. The materials with an aromatic carbonyl group exhibit aggregation-induced emission (AIE) and RTP characteristics simultaneously. Here, we deeply explored the nature of aggregation-induced phosphorescence (AIP), especially the relationship between molecular configuration and optical properties. It was found that aggregation effect can suppress geometrical vibrations and regulate energy difference between S₁ and T₁. The aromatic carbonyl group plays significant roles in changing electronic configuration, resulting in large Stokes shift and spin-orbit coupling. It also leads to small transition dipole moment, decreasing two-photon absorption cross section and radiative decay rate. To improve two-photon absorption properties, we further designed a π-conjugated compound with large two-photon absorption cross section in the biological window (36.40 GM/656 nm) and AIP characteristics, which is a potential material in the application of time-resolved two-photon excited imaging.

Dynamic B/N Lewis Pairs: Insights into the Structural Variations and Photochromism via Light-Induced Fluorescence to Phosphorescence Switching

Ultralong afterglow emissions due to room-temperature phosphorescence (RTP) are of paramount importance in the advancement of smart sensors, bioimaging and light-emitting devices. We herein present an efficient approach to achieve rarely accessible phosphorescence of heavy atom-free organoboranes via photochemical switching of sterically tunable fluorescent Lewis pairs (LPs). LPs are widely applied in and well-known for their outstanding performance in catalysis and supramolecular soft materials but have not thus far been exploited to develop photo-responsive RTP materials. The intramolecular LP M1BNM not only shows a dynamic response to thermal treatment due to reversible N→B coordination but crystals of M1BNM also undergo rapid photochromic switching. As a result, unusual emission switching from short-lived fluorescence to long-lived phosphorescence (rad-M1BNM, τ_RTP =232 ms) is observed. The reported discoveries in the field of Lewis pairs chemistry offer important insights into their structural dynamics, while also pointing to new opportunities for photoactive materials with implications for fast responsive detectors.

Organic persistent luminescence imaging for biomedical applications

Persistent luminescence is a unique visual phenomenon that occurs after cessation of excitation light irradiation or following oxidization of luminescent molecules. The energy stored within the molecule is released in a delayed manner, resulting in luminescence that can be maintained for seconds, minutes, hours, or even days. Organic persistent luminescence materials (OPLMs) are highly robust and their facile modification and assembly into biocompatible nanostructures makes them attractive tools for in vivo bioimaging, whilst offering an alternative to conventional fluorescence imaging materials for biomedical applications. In this review, we give attention to the existing limitations of each class of OPLM-based molecular bioimaging probes based on their luminescence mechanisms, and how recent research progress has driven efforts to circumvent their shortcomings. We discuss the multifunctionality-focused design strategies, and the broad biological application prospects of these molecular probes. Furthermore, we provide insights into the next generation of OPLMs being developed for bioimaging techniques.