Tunable Aggregation-Induced Emission Nanoparticles by Varying Isolation Groups in Perylene Diimide Derivatives and Application in Three-Photon Fluorescence Bioimaging

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.

A Long-Retention Cell Membrane-Targeting AIEgen for Boosting Tumor Theranostics

Designing and developing photosensitizers with cell membrane specificity is crucial for achieving effective multimodal therapy of tumors compared to other organelles. Here, we designed and screened a photosensitizer CM34 through donor/receptor regulation strategies, and it is able to achieve long-retention cell membrane targeting. It is not only an extremely excellent cell membrane targeted tumor theranostic agent, but also found to be a promising potential immune activator. Specifically, CM34 with a larger intramolecular twist angle is more likely to form larger aggregates in aqueous solutions, and the introduction of cyanide group also enhances its interaction with cell membranes, which were key factors hindering molecular penetration of the cell membrane and prolonging its residence time on the cell membrane, providing conditions for further membrane targeted photodynamic therapy. Furthermore, the efflux of contents caused by cell necrosis directly activates the immune response. In summary, this study realizes to clarify and refine all potential mechanisms of action through density functional theory calculations, photophysical property measurements, and cellular level mechanism exploration, providing a new direction for the clinical development of cell membrane targeted anti-tumor immune activators.

Synthesis of chitosan-based perylene dye material for photovoltaic solar-cell application

Renewable energy, such as solar energy, is infinite, readily available, and has extensive applications. Dye-sensitized solar cells (DSSCs) have been well developed; thus, they can be developed with low production costs, high efficiency, and facile manufacturing techniques. This study proposes a novel chitosan biopolymer-based perylene dye; the dye is modified by chitosan with perylene-3,4,9,10-tetracarboxylic anhydride using a one-pot acylation of nitrogen nucleophiles for DSSCs. The chitosan biopolymer-based perylene dyes were characterized using attenuated total reflection infrared spectroscopy, solid-state 13C CP-TOSS nuclear magnetic resonance spectroscopy, X-ray powder diffraction analysis, thermogravimetric analysis, X-ray photoelectron spectrometry, and high-resolution field-emission scanning electron microscopy. The ultraviolet-visible and fluorescence spectroscopy of chitosan biopolymer-based perylene dye exhibited a red-shift compared with perylene-3,4,9,10-tetracarboxylic anhydride and chitosan. The DSSC properties of chitosan biopolymer-based perylene dye were investigated, and it exhibited a 2.022 % power-conversion efficiency. Thus, this promising chitosan biopolymer-based perylene dye may have potential applications in solar-cell technology.

PDI-Based Organic Small Molecule Regulated by Inter/Intramolecular Interactions for Efficient Solar Vapor Generation

Organic small molecules with processing feasibility, structural diversity, and fine-tuned properties have the potential applications in solar vapor generation. However, the common defects of narrow solar absorption, low photothermal conversion efficiency, and photobleaching result in limited materials available and unsatisfactory evaporation performance. Herein, the perylene diimide (PDI) derivatives are exploited as stable sunlight absorbers for solar vapor generation. Particularly, the N,N'-bis(3,4,5-trimethoxyphenyl)-3,4,9,10-perylenetetracarboxylic diimide (PDI-DTMA) is well-designed with donor-acceptor-donor configuration based on plane rigid PDI core. The efficient photothermal conversion is enabled through strong intermolecular π-π stacking and intramolecular charge transfer, as revealed by experimental demonstration and theoretical calculation. The PDI-DTMA with a narrow band gap of 1.17 eV exhibits expanded absorption spectrum and enhanced nonradiative transition capability. The 3D hybrid hydrogels (PPHs) combining PDI-DTMA and polyvinyl alcohol are constructed. With the synergistic effect of solar-to-heat conversion, thermal localization management, water activation, and unobstructed water transmission of PPHs, the high water evaporation rates can reach 3.61-10.07 kg m-2 h-1 under one sun. The hydrogels also possess great potential in seawater desalination and sewage treatment. Overall, this work provides valuable insights into the design of photothermal organic small molecules and demonstrates their potentials in solar water evaporation.

Amphiphilic perylene diimide-based fluorescent hemispherical aggregates as probes for metal ions

The self-assembly behaviour of a newly synthesized amphiphilic core-positioned thioester appended with carboxylic acid functionalized perylene diimide derivative is studied in different organic solvents. Fluorescent J-type hemispherical aggregates are formed in THF solution. The effect of added metal ions on these fluorescent aggregates is evaluated using spectroscopic techniques, where we found these probes bind selectively to Fe³⁺ and Ba²⁺ ions. Two equivalents of Fe³⁺ ions bind cooperatively to one equivalent of perylene diimide derivative in the hemispherical aggregates with a binding constant of 1.4×10⁷ M^-1 and the limit of detection (LOD) was calculated to be 8.66×10^-6 M. The positive cooperative binding effect of Fe³⁺ ions towards hemispherical aggregates equipped with perylene diimide derivatives leads to supramolecular polymerization. Ba²⁺ ions showed selectivity and sensitivity towards the fluorescent aggregates in THF by quenching the fluorescence intensity completely. The linear Stern-Volmer plot with a Stern-Volmer constant value of 502.6 M^-1 signifies the heavy atom effect of Ba²⁺ ions, leading to fluorescence quenching. The morphological transformation of the fluorescent J-type hemispherical aggregates in the presence of Fe³⁺ and Ba²⁺ was studied in detail using electron microscopy.

Dangling Water Molecules Bridge for ESIPT in Aggregated TMP: A Theoretical Study

We present a theoretical study on the occurrence of excited-state proton transfer in an aggregated structure of 2-(benzo[d]thiazol-2-yl)-6-methoxyphenol (TMP) exclusively in water among polar solvents, as reported in a recent experiment (Bhattacharyya, A. New J. Chem. 2019, 43, 15087). Our extensive investigation of the TMP monomer and dimer implementing density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods, in three different solvents, namely, water, methanol, and dimethyl sulfoxide (DMSO), with explicit inclusion of solvent molecules demonstrated the existence of both enol and keto forms of the TMP dimer in the excited state, but only in water; this confirmed the experimental emission spectra completely and simultaneously validated the aggregation-induced emission phenomenon. Further analysis of various parameters such as potential energy scan (PES) of the hydroxyl (O-H) bond involved in hydrogen bonding, frontier molecular orbitals (FMOs), molecular electrostatic potential (MEP), and infrared (IR) stretching frequencies of both the monomer and dimer forms of TMP in different solvents clearly indicated the geometry of the dimer, with the arrangement of the solvent molecules to be the sole reason for the excited-state charge transfer. The bridging alignment of water molecules in between the stacked units of the TMP dimer results in intermolecular interactions, ultimately leading to intermolecular proton transfer in the excited state.

Perylene diimide-based sensors for multiple analyte sensing (Fe2+/H2S/ dopamine and Hg2+/Fe2+): cell imaging and INH, XOR, and encoder logic

In this report, we present our results on the recognition of multiple analytes using trisubstituted PDI-based chemosensors DNP and DNB in 50% HEPES buffered-CH₃CN solution. Upon the addition of Hg²⁺, DNB showed a decrease and increase in absorbance intensity at 560 and 590 nm, respectively, with a detection limit of 7.17 μM and bleaching of the violet color (de-butynoxy). Similarly, the addition of Fe²⁺ or H₂S to the solution of DNP or DNB resulted in ratiometric changes (A_688nm/A_560nm) with respective detection limits of 185 nM and 27.6 nM for Fe²⁺, respectively, and a color change from violet to green. However, the addition of >37 μM H₂S caused a decrease in absorbance at 688 nm with a concomitant blue shift to 634 nm. Upon the addition of dopamine, the DNP + Fe²⁺ assay showed ratiometric (A_560nm/A_688nm) changes within 10 s along with a color change from green to violet. Moreover, DNP has been successfully used for the exogenous detection of Fe²⁺ in A549 cells. Further, the multiple outputs observed with DNP in the presence of H₂S have been used to construct NOR, XOR, INH and 4-to-2 encoder logic gates and circuits.

Molecular and Aggregate Synergistic Engineering of Aggregation-Induced Emission Luminogens to Manipulate Optical/Electronic Properties for Efficient and Diversified Functions

The optical/electronic properties of organic luminescent materials can be regulated by molecular structure modification, which not only requires sophisticated and time-consuming synthesis but also is unable to accurately afford the optical properties of materials in the aggregate state. Herein, a facile strategy of molecular and aggregate synergistic engineering is proposed to manipulate the optical/electronic properties of a luminogen, ACIK, in the solid state for efficient and diversified functions. ACIK is facilely synthesized and exhibits three polymorphic states (ACIK-Y, ACIK-R, and ACIK-N) with a large emission difference of 102 nm from yellow to near-infrared (NIR). Their structure-property relationships were investigated by crystallographic analyses and computational studies. ACIK-Y, with the most twisted structure, exhibits an intriguing color-tuned fluorescence between yellow and NIR in the solid state in response to multiple stimuli. Shuttle-like ACIK-R microcrystals exhibit an optical waveguide property with a low optical loss coefficient of 19 dB mm^-1. ACIK dots display bright NIR-I emission, large Stokes shift, and strong NIR-II two-photon absorption. ACIK dots show specific lipid droplets-targeting capability and can be successfully applied for two-photon fluorescence imaging of mouse brain vasculature with deep penetration and high spatial resolution. This study will inspire more insights in developing advanced optical/electronic materials based on a single chromophore for practical applications.

Structural Engineering of Red Luminogens to Realize High Emission Efficiency through ACQ-to-AIE Transformation

Deep red/near-infrared (NIR, >650 nm) emissive organic luminophores with aggregation-induced emission (AIE) behaviours have emerged as promising candidates for applications in optoelectronic devices and biological fields. However, the molecular design philosophy for AIE luminogens (AIEgens) with narrow band gaps are rarely explored. Herein, we rationally designed two red organic luminophores, FITPA and FIMPA, by considering the enlargement of transition dipole moment in the charge-transfer state and the transformation from aggregation-caused quenching (ACQ) to AIE. The transition dipole moments were effectively enhanced with a "V-shaped" molecular configuration. Meanwhile, the ACQ-to-AIE transformation from FITPA to FIMPA was induced by a methoxy-substitution strategy. The experimental and theoretical results demonstrated that the ACQ-to-AIE transformation originated from a crystallization-induced emission (CIE) effect because of additional weak interactions in the aggregate state introduced by methoxy groups. Owing to the enhanced transition dipole moment and AIE behaviour, FIMPA presented intense luminescence covering the red-to-NIR region, with a photoluminescence quantum yield (PLQY) of up to 38 % in solid state. The promising cell-imaging performance further verified the great potential of FIMPA in biological applications. These results provide a guideline for the development of red and NIR AIEgens through comprehensive consideration of both the effect of molecular structure and molecular interactions in aggregate states.

Effects of Atypical Hydrogen Bonds and π-π Interactions on Nonlinear Optical Properties: Dimers of Triangular Structures Based on Perylene, Naphthalene, and Pyromellitic Diimides

Nonlinear optical (NLO) materials have become important materials in the field of high-speed optical devices due to the changes in light absorption and refraction caused by the photoelectric field. Compounds tend to exist as aggregates rather than single molecules, so intermolecular interactions are crucial to the nature of aggregates. Therefore, to study the effects of intermolecular interactions on nonlinear optical properties, we use a dimer simplified model and adopt the methods of controlling variables, which are the different intermolecular interactions resulting from the different stacking patterns of dimers based on the same monomer structures (2PMDI-1NDI and 2NDI-1PDI). It is found that compared with dimers involving π-π interactions, dimers involving C-H···O interactions have shorter intermolecular distances, larger intermolecular interaction energies, and smaller highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energy gaps. Moreover, the C-H···O interactions are more conducive to the intermolecular charge transfers and more beneficial for increasing the nonlinear optical response values of aggregates with respect to π-π interactions. This work provides an important basis for the influence of intermolecular interactions on nonlinear optical properties.

A Biomarker-Responsive Nanosystem with Colon-Targeted Delivery for Ulcerative Colitis's Detection and Treatment with Optoacoustic/NIR-II Fluorescence Imaging

Ulcerative colitis (UC) is a prevalent idiopathic inflammatory disease which causes such complications as intestinal perforation, obstruction, and bleeding, and thus deleteriously impacting people's normal work and quality of life. Hence, accurate diagnosis of UC is crucial in terms of planning optimal treatment plan. Herein, a pH/reactive oxygen species (ROS) dual-responsive nanosystem (BM@EP) is developed for UC's detection and therapy. BM@EP is composed of a chromophore-drug dyad and the enteric coating. The chromophore-drug dyad (BOD-XT-DHM) is synthesized by linking the chromophore (BOD-XT-BOH) and a flavonoid drug (dihydromyricetin DHM) through boronate ester bond. The enteric coating includes Eudragit S100 and poly(lactic-co-glycolic acid) (PLGA), the former is commonly employed as a pH-dependent polymer coating excipient so as to attain colon-targeted delivery, and the latter has been widely used as an excipient for the controlled-extended release. After oral administration, BM@EP delivers the dyad (BOD-XT-DHM) into the colon and releases the dyad molecules by being triggered by the alkaline pH in t colon, thereafter upon being stimulated by overexpressed H₂ O₂ in the inflamed colon, the boronate bond in the dyad is broken down and correspondingly the drug DHM is released for UC therapy, simultaneously the chromophore is released for near-infrared second window (NIR-II) fluorescence and optoacoustic imaging for UC diagnosis and recovery evaluation.

Large-depth three-photon fluorescence microscopy imaging of cortical microvasculature on nonhuman primates with bright AIE probe In vivo

Multiphoton microscopy has been a powerful tool in brain research, three-photon fluorescence microscopy is increasingly becoming an emerging technique for neurological research of the cortex in depth. Nonhuman primates play important roles in the study of brain science because of their neural and vascular similarity to humans. However, there are few research results of three-photon fluorescence microscopy on the brain of nonhuman primates due to the lack of optimized imaging systems and excellent fluorescent probes. Here we introduced a bright aggregation-induced emission (AIE) probe with excellent three-photon fluorescence efficiency as well as facile synthesis process and we validated its biocompatibility in the macaque monkey. We achieved a large-depth vascular imaging of approximately 1 mm in the cerebral cortex of macaque monkey with our lab-modified three-photon fluorescence microscopy system and the AIE probe. Functional measurement of blood velocity in deep cortex capillaries was also performed. Furthermore, the comparison of cortical deep vascular structure parameters across species was presented on the monkey and mouse cortex. This work is the first in vivo three-photon fluorescence microscopic imaging research on the macaque monkey cortex reaching the imaging depth of ∼1 mm with the bright AIE probe. The results demonstrate the potential of three-photon microscopy as primate-compatible method for imaging fine vascular networks and will advance our understanding of vascular function in normal and disease in humans.

A potent luminogen with NIR-IIb excitable AIE features for ultradeep brain vascular and hemodynamic three-photon imaging

Three-photon excited fluorescence microscopy (3PEFM) has emerged as a promising protocol for visualizing deep-brain vasculature and hemodynamics. However, the current situation is still far from satisfactory, due to small excitation action cross-section and short excitation wavelength of those previously reported 3PEFM luminogens. Herein, we manipulated molecular engineering by subtly regulating structural planarization/twisting to achieve ingenious integration of large three-photon absorption cross-section, high fluorescence quantum yield, ultralong near-infrared IIb excitation, and aggregation-induced emission features. The resulting molecule, namely DPCZ-BT, exhibited as high as 50.6% of fluorescence quantum yield and as large as 2.0 × 10-81 cm6s2/photon2 of three-photon absorption cross-section, which can be excited by 1665 nm fs laser and presents a recorded penetration depth of 1860 μm for deep-brain vascular structural imaging with high spatiotemporal resolution and signal-to-background ratio. Moreover, DPCZ-BT having good photostability and excellent biocompatibility is capable of impressively approaching 1600 μm depth in monitoring red blood cells flow velocity with extraordinary clarity for hemodynamics.

Förster Resonance Energy Transfer in Luminescent Solar Concentrators

Luminescent solar concentrators (LSCs) are an emerging technology to collect and channel light from a large absorption area into a smaller one. They are a complementary technology for traditional solar photovoltaics (PV), particularly suitable for application in urban or indoor environments where their custom colors and form factors, and performance under diffuse light conditions may be advantageous. Förster resonance energy transfer (FRET) has emerged as a valuable approach to overcome some of the intrinsic limitations of conventional single lumophore LSCs, such as reabsorption or reduced quantum efficiency. This review outlines the potential of FRET to boost LSC performance, using highlights from the literature to illustrate the key criteria that must be considered when designing an FRET-LSC, including both the photophysical requirements of the FRET lumophores and their interaction with the host material. Based on these criteria, a list of design guidelines intended to aid researchers when they approach the design of a new FRET-LSC system is presented. By highlighting the unanswered questions in this field, the authors aim to demonstrate the potential of FRET-LSCs for both conventional solar-harvesting and emerging LSC-inspired technologies and hope to encourage participation from a diverse researcher base to address this exciting challenge.

Optical molecular imaging and theranostics in neurological diseases based on aggregation-induced emission luminogens

Optical molecular imaging and image-guided theranostics benefit from special and specific imaging agents, for which aggregation-induced emission luminogens (AIEgens) have been regarded as good candidates in many biomedical applications. They display a large Stokes shift, high quantum yield, good biocompatibility, and resistance to photobleaching. Neurological diseases are becoming a substantial burden on individuals and society that affect over 50 million people worldwide. It is urgently needed to explore in more detail the brain structure and function, learn more about pathological processes of neurological diseases, and develop more efficient approaches for theranostics. Many AIEgens have been successfully designed, synthesized, and further applied for molecular imaging and image-guided theranostics in neurological diseases such as cerebrovascular disease, neurodegenerative disease, and brain tumor, which help us understand more about the pathophysiological state of brain through noninvasive optical imaging approaches. Herein, we focus on representative AIEgens investigated on brain vasculature imaging and theranostics in neurological diseases including cerebrovascular disease, neurodegenerative disease, and brain tumor. Considering different imaging modalities and various therapeutic functions, AIEgens have great potential to broaden neurological research and meet urgent needs in clinical practice. It will be inspiring to develop more practical and versatile AIEgens as molecular imaging agents for preclinical and clinical use on neurological diseases.

A cell membrane-targeting AIE photosensitizer as a necroptosis inducer for boosting cancer theranostics

The exploration of cellular organelle-specific anchoring photosensitizers with both prominent fluorescence imaging behavior and extraordinary reactive oxygen species (ROS) production capability is highly in demand but remains a severe challenge for effective cancer theranostics involving photodynamic therapy (PDT). In this contribution, we developed a cell membrane-targeting and NIR-emission photosensitizer having an aggregation-induced emission (AIE) tendency. The AIE photosensitizer, namely TBMPEI, is capable of lighting up and ablating cancer cells by means of a necroptosis procedure enabling cell membrane rupture and DNA degradation upon light irradiation, endowing TBMPEI with impressive performance for both in vitro and in vivo fluorescence imaging-guided PDT.

Deep-Brain Three-Photon Imaging Enabled by Aggregation-Induced Emission Luminogens with Near-Infrared-III Excitation

Understanding the morphology and hemodynamics of cerebral vasculature at large penetration depths and microscale resolution is fundamentally important to decipher brain diseases. Among the various imaging technologies, three-photon (3P) microscopy is of significance by virtue of its deep-penetrating capability and submicron resolution, which especially benefits in vivo vascular imaging. Aggregation-induced emission luminogens (AIEgens) have been recognized to be extraordinarily powerful as 3P probes. However, systematic studies on the structure-performance relationship of 3P AIEgens have been seldom reported. Herein, a series of AIEgens has been designed and synthesized. By intentionally introducing benzene rings onto electron donors (D) and acceptors (A), the molecular distortion, conjugation strength, and the D-A relationship can be facilely manipulated. Upon encapsulation with DSPE-PEG₂₀₀₀, the optimized AIEgens are successfully applied for 3P microscopy with emission in the far-red/near-infrared-I (NIR-I, 700-950 nm) region under the near-infrared-III (NIR-III, 1600-1870 nm) excitation. Impressively, using mice with an opened skull, vasculature within 1700 μm and a microvessel with a diameter of 2.2 μm in deep mouse brain were clearly visualized. In addition, the hemodynamics of blood vessels were well-characterized. Thus, this work not only proposes a molecular design strategy of 3P AIEgens but also promotes the performance of 3P imaging in cerebral vasculature.

Assembling of Perylene, Naphthalene, and Pyromellitic Diimide-Based Materials and Their Third-Order Nonlinear Optical Properties

π-conjugated aromatic diimides with chemical stability, heat resistance, and redox activity have attracted more attention due to their excellent fluorescence quantum yield in solution. The planar perylene diimide (PDI) derivatives generally have aggregation-induced emission quenching in the solid state, while the cyclic trimers based on pyromellitic diimides (PMDIs), naphthalene diimides (NDIs), and PDIs can increase the fluorescence quantum yield in the solid state and have large two-photon absorption cross section, which can be used as excellent nonlinear optical (NLO) materials. Therefore, this paper will study the effects of multiple assembly modes of the three monomers on the NLO responses of materials. It was found that the assembly modes of 2PMDI-1NDI and 2NDI-1PDI exhibit larger third-order NLO response (γ) values, which was due to the larger conjugate surface of PDI effectively reducing the energy gap between the HOMO and LUMO. Compared with other assembly methods, 2PMDI-1NDI and 2NDI-1PDI were conducive to causing redshifts (150 nm) in the absorption spectrum. Therefore, the larger conjugate surface of PDI and the assembly mode of the isosceles triangle were more favorable for intramolecular charge transfer, thus improving its NLO properties.

Progress and Perspective of Solid-State Organic Fluorophores for Biomedical Applications

Fluorescent organic dyes have been extensively used as raw materials for the development of versatile imaging tools in the field of biomedicine. Particularly, the development of solid-state organic fluorophores (SSOFs) in the past 20 years has exhibited an upward trend. In recent years, studies on SSOFs have focused on the development of advanced tools, such as optical contrast agents and phototherapy agents, for biomedical applications. However, the practical application of these tools has been hindered owing to several limitations. Thus, in this Perspective, we have provided insights that could aid researchers to further develop these tools and overcome the limitations such as limited aqueous dispersibility, low biocompatibility, and uncontrolled emission. First, we described the inherent photophysical properties and fluorescence mechanisms of conventional, aggregation-induced emissive, and precipitating SSOFs with respect to their biomedical applications. Subsequently, we highlighted the recent development of functionalized SSOFs for bioimaging, biosensing, and theranostics. Finally, we elucidated the potential prospects and limitations of current SSOF-based tools associated with biomedical applications.

An ambient complexation reaction of zinc acetate and ascorbic acid leads to a new form of nanoscale particles with emergent optical properties

We report the formation of nanoscale particles from the complexation reaction between zinc acetate and ascorbic acid under ambient conditions and in an aqueous medium. The reaction led to the formation of a molecular complex with the formula Zn _x (AA) _y (OAc) _z (x, y, and z = possible smallest positive integer) with AA meaning ascorbate, based on the mass spectrometry results. Following this, the formation of luminescent nanoscale particles - the size of which increased with time - was observed. During 24 h of observation, the sizes increased to about 50 nm in the presence of different sizes at all times. Transmission electron microscopy results also indicated the formation of polycrystalline as well as amorphous nanoparticles in the medium. Further, the appearance of a UV absorption peak at 380 nm and photoluminescence peak at 473 nm marked the formation of the nanoparticles. The luminescence was also observed to be wavelength tuneable. FTIR and NMR spectroscopy results also supported the formation of a molecular complex with the above formula. The present work highlights the importance of emergent properties of nanoscale molecular materials for crystallization. Also, the present discovery is expected to contribute to the development of safe nanomaterials.

Rh(iii)-Catalysed synthesis of cinnolinium and fluoranthenium salts using C-H activation/annulation reactions: organelle specific mitochondrial staining applications

The construction of a novel class of indazolo[2,1-a]cinnolin-7-ium and diazabenzofluoranthenium salts was developed by using Rh(iii)-catalyzed C-H activation/annulation reactions with 2-phenyl-2H-indazole, and internal alkynes, which resulted in structurally important polycyclic heteroaromatic compounds (PHAs). This reaction uses mild reaction conditions and has a high efficiency, low catalyst loading, and wide substrate scope. The overall catalytic process involves C-H activation followed by C-C/C-N bond formation. Furthermore, the synthesised cinnolinium/fluoranthenium salts exhibit potential fluorescence properties and 5i was targeted in particular for specific mitochondrial staining in order to investigate cancer cell lines.

Photodynamic Therapy Directed by Three-Photon Active Rigid Plane Organic Photosensitizer

Multi-photon photosensitizers (PSs) could significantly improve the efficacy of photodynamic therapy due to the long-wavelength favorability for deeper tissue penetration and lower biological damage. However, most studies are limited to single-photon or two-photon PSs at a relatively short-wave excitation window. To overcome this barrier, we rationally design a series of rigid plane compounds with efficient reactive oxygen species (ROS) production in vitro under laser irradiation. Furthermore, the studies show that one of the compounds (U-TsO) could induce rapid multi-types of cell death under three-photon exposure, suggesting a promising clinical outcome in ex vivo 3D multicellular tumor spheroid. This work offers a novel strategy to construct functional materials with competitive multi-photon photodynamic therapy (PDT) outcome.

Swing Arm Location-Controllable DNA Walker for Electrochemiluminescence Biosensing

Here, we described a novel swing arm location-controllable DNA walker based on the DNA tetrahedral nanostructures (DTNs) for nucleic acid detection using the polycyclic aromatic hydrocarbon (PAH) microcrystals (TAPE-Pe MCs) consisting of the nonplanar molecular tetrakis(4-aminophenyl)ethene (TAPE) and planar molecular perylene (Pe) as electrochemiluminescence (ECL) luminophores. Specifically, the swing arm strands and track strands were fixed simultaneously on the DTNs to obtain the location-controllable DNA walker, which possessed an improved reaction efficiency compared to that of a fixed swing arm-based DNA walker due to the quantitative and orderly swing arm on the DTNs. On the other hand, the Pe microcrystals doped by TAPE molecules could decrease the π-π stacking of Pe molecules for the ECL efficiency enhancement, achieving a blue-shifted and intense ECL emission. Therefore, we defined this enhanced and blue-shifted ECL phenomenon as "inhibition of conjugation-driven ECL (IC-ECL)". To prove these principles, a location-controllable DNA walker-based ECL biosensor was developed with microRNA let-7a as target molecules. The ECL biosensor achieved a low detection limit of 4.92 fM within a wide linear range from 10 fM to 100 nM. This approach offers a new insight for ECL efficiency increase and location-controllable strategies with improved reaction efficiency, demonstrating potential in diagnostic analysis.

In Vivo Three-Photon Imaging of Lipids using Ultrabright Fluorogens with Aggregation-Induced Emission

Fluorescent probes capable of in vivo lipids labeling are highly desirable for studying lipid-accumulation-related metabolic diseases, such as nonalcoholic fatty liver disease, type-2 diabetes, and atherosclerosis. However, most of the current lipid-specific fluorophores cannot be used for in vivo labeling due to their strong hydrophobicity. Herein, organic dots from bright luminogens with aggregation-induced emission (AIEgen) are developed for in vivo labeling and three-photon fluorescence imaging of lipid-rich tissues, such as fatty liver, atherosclerotic plaques in brain vasculatures, and carotid arteries. The organic dots show excellent stability in an aqueous medium with high targeting specificity to lipids and strong three-photon fluorescence in the far-red/near-infrared (NIR) region under NIR-II laser excitation, which enables efficient in vivo labeling and imaging of lipids in deep tissues. The study will inspire the development of lipid-targeting fluorophores for in vivo applications.

Fabrication of claviform fluorescent polymeric nanomaterials containing disulfide bond through an efficient and facile four-component Ugi reaction

Multicomponent reactions (MCRs) have attracted broad interest for preparation of functional nanomaterials especially for the synthesis of functional polymers. Herein, we utilized an "old" MCR, the four-component Ugi reaction, to synthesize disulfide bond containing poly(PEG-TPE-DTDPA) amphiphilic copolymers with aggregation-induced emission (AIE) feature. This four-component Ugi reaction was carried out under rather mild reaction conditions, such as room temperature, no gas protection and absent of catalysts. The amphiphilic poly(PEG-TPE-DTDPA) copolymers with high number-average molecular weight (up to 86,440 Da) can self-assemble into claviform fluorescent polymeric nanoparticles (FPNs) in aqueous solution, and these water-dispersed nanoparticles exhibited strong emission, large Stokes shift (142 nm), low toxicity and remarkable ability in cellular imaging. Moreover, owing to the introduction of 3,3'-dithiodipropionic acid with disulfide bond, the resultant AIE-active poly(PEG-TPE-DTDPA) could display reduction-responsiveness and be utilized for synthesis of photothermal agents in-situ. Therefore, the AIE-active poly(PEG-TPE-DTDPA) could be promising for controlled intracellular delivery of biological activity molecules and fabrication of multifunctional AIE-active materials. Therefore, these novel AIE-active polymeric nanoparticles could be of great potential for various biomedical applications, such as biological imaging, stimuli-responsive drug delivery and theranostic applications.

Aggregation-driven fluorescence quenching of imidazole-functionalized perylene diimide for urea sensing

Stimuli-responsive self-assembly of functional amphiphilic molecules by specific chemical stimulants is a promising strategy for sensor application. Herein, we demonstrate a fast optical detection of urea in human urine by exploiting bolaform perylene diimide functionalized with imidazoles (PDI-Hm), whose aggregation is induced by urea hydrolysis. The hydroxides produced from the enzymatic urea hydrolysis deprotonate the imidazoles to reduce electrostatic repulsion between PDI-Hm molecules in a HCl-methanol mixture, thereby leading to aggregation and consequent fluorescence quenching. The molecular interaction of PDI-Hm was further scrutinized to understand the aggregation behavior driven by the screening of electrical repulsion. As an optical sensing probe, PDI-Hm displays a prompt response (<1 min) to hydroxide and detection limit of 0.4 mM for urea. PDI-Hm incorporating urease offers considerable selectivity toward urea among various components in human urine. The urea sensing accuracy of this PDI-Hm fluorescence chemosensor is comparable to that of a clinical method, showing 93.4% consistency. Furthermore, the PDI-Hm was fabricated into a gel film allowed for the fast screening of excessive urea in urine.

Tuning molecular aggregation to achieve highly bright AIE dots for NIR-II fluorescence imaging and NIR-I photoacoustic imaging

Currently, bright aggregation-induced emission luminogens (AIEgens) with high photoluminescence quantum yields (PLQYs) in the NIR-II region are still limited, and thus an efficient strategy to enhance NIR-II fluorescence performance through tuning molecular aggregation is proposed here. The synthesized donor-acceptor tailored AIEgen (DTPA-TBZ) not only exhibits an excellent absorptivity in the NIR-I region, but also good fluorescence signals in the NIR-II region with an emission extending to 1200 nm. Benefiting from such improved intramolecular restriction and aggregation, a significant absolute PLQY value of 8.98% was obtained in solid DTPA-TBZ. Encouragingly, the resulting AIE dots also exhibit a high relative PLQY of up to 11.1% with IR 26 as the reference (PLQY = 0.5%). Finally, the AIE dots were applied in high performance NIR-II fluorescence imaging and NIR-I photoacoustic (PA) imaging: visualization of abdominal vessels, hind limb vasculature, and cerebral vessels with high signal to background ratios was performed via NIR-II imaging; Moreover, PA imaging has also been performed to clearly observe tumors in vivo. These results demonstrate that by finely tuning molecular aggregation in DTPA-TBZ, a good NIR-I absorptivity and a highly emissive fluorescence in the NIR-II region can be achieved simultaneously, finally resulting in a promising dual-modal imaging platform for real-world applications to achieve precise cancer diagnostics.

Deep-red fluorescence from isolated dimers: a highly bright excimer and imaging in vivo

Restricted by the energy-gap law, the development of bright near-infrared (near-IR) fluorescent luminophors in the solid state remains a challenge. Herein, we report a new design strategy for realizing high brightness and deep-red/near-IR-emissive organic molecules based on the incorporation of a hybridized local and charge-transfer (HLCT) state and separated dimeric stacks into one aggregate. Experimental and theoretical analyses show that this combination not only contributes to high photoluminescent quantum yields (PLQYs) but also significantly lessens the energy gap. The fluorophore BTA-TPA exhibits excellent fluorescence performance, achieving a PLQY of 54.8% for the fluorescence peak at 690 nm, which is among the highest reported for near-IR fluorescent excimers. In addition, because of its bioimaging performance, the designed luminophor has potential for use as a deep-red fluorescent probe for biomedical applications. This research opens the door for developing deep-red/near-IR emissive materials with high PLQYs.

A mass-amplifying electrochemiluminescence film (MAEF) for the visual detection of dopamine in aqueous media

A bright and metal-free mass-amplifying electrochemiluminescence film (MAEF) performing in aqueous media was reported for the first time. Systematic studies demonstrated that the film substrates have a remarkable influence on the electrochemiluminescence (ECL) performance. Gold substrates promote ECL reactions and the subsequent radiative decay process simultaneously, affording an unconventional 507-fold ECL enhancement. Such a gold-enhanced MAEF is opposite to ECL systems previously reported, in which the use of gold electrodes normally results in decreased ECL intensity due to passivation of the gold surface by oxide formation. More importantly, the ECL intensity of the MAEF is linearly amplified through facilely regulating luminogen loading. Morphological analysis reveals that the film consists of grass-like nanowires with a diameter of 57 nm, which facilitate electrical communication between the luminogen, electrode, and supporting electrolyte, giving rise to the mass-amplifying ECL. The bright ECL of the solid film in aqueous media can be readily observed by the naked eye, entirely different from visible ECL systems reported in which ruthenium complexes dissolved/dispersed in solution are used as the luminogens. The film is further utilized to detect dopamine (DA), an important biomolecule related to nervous diseases, in aqueous media, with a low detection limit of 3.3 × 10-16 M. Furthermore, a facile method based on grayscale analysis of ECL images (GAEI) of the film was developed for visual and ultrasensitive DA detection in aqueous media.

Deep-Red Fluorescent Organic Nanoparticles with High Brightness and Photostability for Super-Resolution in Vitro and in Vivo Imaging Using STED Nanoscopy

To achieve super-resolution imaging in biological research using stimulated emission depletion (STED) nanoscopy, organic luminescent materials and their corresponding fluorescent nanoparticles with high brightness and photostability are of great significance. Herein, donor-acceptor-typed DBTBT-4C8 bearing flexible alkyl chains was developed, not only to afford deep-red emission from 600 to 800 nm but also to obtain high fluorescent brightness with the absolute photoluminescence quantum yields of 25%. After that, well-defined and monodispersed spherical nanoparticles using DBTBT-4C8 with bright emission, excellent biocompatibility, and photostability, which can easily mix with amphipathic block polymers, were then produced for super-resolution in vitro and in vivo imaging using STED nanoscopy. The observations showed that in contrast to confocal microscopy with a full width at half-maximum (FWHM) value of ≈400 nm, superior resolution with a significantly improved FWHM value of only 100 nm was achieved in biomedical cell imaging, which was also used to reconstruct three-dimensional images of stained HeLa cells at an ultrahigh resolution. More importantly, by using the prepared fluorescent organic nanoparticles (FONPs) in STED nanoscopy, in vivo imaging in glass catfish with largely enhanced resolution was also successfully achieved, demonstrating that these developed deep-red FONPs here are highly suitable for super-resolution in vitro and in vivo imaging using STED nanoscopy.

A novel water-soluble quinoline–indole derivative as a three-photon fluorescent probe for identifying nucleolus RNA and mitochondrial DNA

We present the design and synthesis of water-soluble quinoline–indole-based derivatives (IM-1, IM-2, and IM-3) with three-photon absorption activity.

Tetrakis(4-aminophenyl) ethene-doped perylene microcrystals with strong electrochemiluminescence for biosensing applications

A facile and economic method for the inhibition of ACQ effect was developed by doping of non-planar moleculars ETTA into Pe MCs, which exhibited almost 10 times stronger ECL signal in aqueous phase compared to that of pure Pe MCs.

Aggregation-Induced Nonlinear Optical Effects of AIEgen Nanocrystals for Ultradeep In Vivo Bioimaging

Nonlinear optical microscopy has become a powerful tool in bioimaging research due to its unique capabilities of deep optical sectioning, high-spatial-resolution imaging, and 3D reconstruction of biological specimens. Developing organic fluorescent probes with strong nonlinear optical effects, in particular third-harmonic generation (THG), is promising for exploiting nonlinear microscopic imaging for biomedical applications. Herein, a simple method for preparing organic nanocrystals based on an aggregation-induced emission (AIE) luminogen (DCCN) with bright near-infrared emission is successfully demonstrated. Aggregation-induced nonlinear optical effects, including two-photon fluorescence (2PF), three-photon fluorescence (3PF), and THG, of DCCN are observed in nanoparticles, especially for crystalline nanoparticles. The nanocrystals of DCCN are successfully applied for 2PF microscopy at 1040 nm NIR-II excitation and THG microscopy at 1560 nm NIR-II excitation, respectively, to reconstruct the 3D vasculature of the mouse cerebral vasculature. Impressively, the THG microscopy provides much higher spatial resolution and brightness than the 2PF microscopy and can visualize small vessels with diameters of ≈2.7 µm at the deepest depth of 800 µm in a mouse brain. Thus, this is expected to inspire new insights into the development of advanced AIE materials with multiple nonlinearity, in particular THG, for multimodal nonlinear optical microscopy.

Near-Infrared Microlasers from Self-Assembled Spiropyrane-Based Microsphercial Caps

Near-infrared (NIR) microlasers play a significant role in telecommunication and biomedical tissue imaging. However, it remains a big challenge to realize NIR microlasers because of the difficulty in preparing highly efficient NIR luminescent materials and perfect optical resonators. Here, we propose a molecular design strategy to creatively realize the first spiropyrane (SP)-based NIR microlasers with low threshold from self-assembled microsphercial caps. The tetraphenylethylene (TPE) moiety with a highly twisted conformation provides a large free volume to facilitate the photoisomerization process of SP and enhance NIR emission of merocyanine in the solid state. Moreover, self-assembled TPE-SP microsphercial caps simultaneously serve as gain media and resonant microcavities, providing optical gain and feedback for NIR laser oscillations with a low threshold (3.68 μJ/cm²). These results are beneficial for deeply understanding the SP microstructures-lasing emission characteristic relationship and provide a useful guideline for the rational molecular design of NIR microlasers with special functionalities.