Aggregation-induced emission luminogen for in vivo three-photon fuorescence lifetime microscopic imaging

Compared with visible light,near infrared(NIR)light has deeper penetration in biological tisues.Three-photon fuorescence microscopy(3PFM)can effectively utilize the NIR excitation to obtain high-contrast images in the deep tisue.However,the weak three photon fluorescence signals may be not well presented in the traditional fuorescence intensity imaging mode.Fluorescence lifetime of certain probes is insensitive to the intensity of the excitation laser.Moreover,fluorescence lifetimne imaging microscopy(FLIM)can detect weak signals by utilizing time correlated single photon counting(TCSPC)technique.Thus,it would be an improved strategy to combine the 3PFM imaging with the FLIM together.Herein,DCDPP-2TPA,a novel agegation-induced emission luminogen(AIEgen),was adopted as the fluorescent probes.The three-photon absorption cros-section of the AlEgen,which has a deep-red fluorescence emission,was proved to be large.DCDPP-2TPA nanoparticles were synthesized,and the three photon fluorescence lifetime of which was measured in water.Moreover,in vrivo thre-photon fuorescence lifetime microscopic imaging of a craniotomy mouse was conducted via a home made optical system.High contrast cerebrovascular images of different vertical depths were obtained and the maximun depth was about 600 pumn.Even reaching the depth of 600 pum,tiny capillary vessels as small as 1.9 pum could still be distinguished.The three photon fuorescence lifetimes of the capillaries in some representative images were in accord with that of DCDPP-2TPA nanoparticles in water.A vivid 3D reconstruction was further organized to present a wealth of lifetime information.In the future,the combination strategy of 3PFM and FLIM could be further applied in the brain functional imaging.

A ggregation-induced emission nanoparticles for in vivo three-photon fuorescence microscopic rat brain angiography

Rodents are popular biological models for physiological and behavioral research in neuroscience and rats are better models than mice due to their higher genome similarity to human and more accessible surgical procedures.However,rat brain is larger than mice brain and it needs powerful imaging tools to implement better penetration against the scattering of the thicker brain tissue.Three-photon fluorescence microscopy(3PFM)combined with near-infrared(NIR)excitation has great potentials for brain circuits imaging beause of its abilities of anti scattering,deep-tissue imaging,and high signal-to-noise ratio(SNR).In this work,a type of AIE lumninogen with red fuorescence was synthesized and encapsulated with Pluronic F-127 to make up form nano-particles(NPs).Bright DCDPP-2TPA NPs were employed for in trino three-photon fuorescent laser scanning microscopy of blood vessels in rats brain under 1550 nm femtosecond laser exci-tation.A fine three-dimensional(3D)reconstruction up to the deepness of 600 pm was achieved and the blood flow velocity of a selected vessel was measured in vrito as well.Our 3PFM deep brain imaging method simultaneously recorded the morphology and function of the brain blood vessels in vivo in the rat model.Using this angiography combined with the arsenal of rodent's brain disease,models can accelerate the neuroscience research and clinical diagnosis of brain disease in the future.

Lipid droplets imaging with three-photon microscopy

Lipid droplets(LDs)participate in many physiological processes,the abnormality of which will cause chronic diseases and pathologies such as diabetes and obesity.It is crucial to monitor the distribution of LDs at high spatial resolution and large depth.Herein,we carried three-photon imaging of LDs in fat liver.Owing to the large three-photon absorption cross-section of the luminogen named NAP-CF_(3)(1:67×10^(-79) cm^(6) s^(2)),three-photon fluorescence fat liver imaging reached the largest depth of 80μm.Fat liver diagnosis was successfully carried out with excellent performance,providing great potential for LDs-associated pathologies research.

Smart aggregation-induced emission polymers:Preparation,properties and bio-applications

Owing to the outstanding photophysical properties,organic luminescent materials featuring aggregation-induced emission(AIE)characteristics have attracted wide attention in various fields.Numerous researches focused on low-mass AIE luminogens,and relatively less attention has been paid on AIE polymers and the related applications,in spite of the fact that AIE polymers exhibit excellent advantages of processability,multifunctional integration and synergistic effects.In this review,we briefly summarize and discuss the superiorities of AIE polymers in preparation,properties and bio-applications,and the considerable progress in these aspects are introduced as well.Finally,the structure-property relationship,challenges and opportunities are also discussed.Hopefully,this review will be a trigger for smart AIE polymer research and further broaden their applications.

Manipulation of the through-space interactions in diphenylmethane

Through-space interaction(TSI)has been proven to play an important role in the newly emerging clusteroluminescence(CL)phenomenon.However,it is still a big challenge to manipulate the TSI at the molecular level due to the unclear relationship between the non-conjugated structure and TSI properties.Herein,the TSI in diphenylmethane is manipulated by breaking its symmetric structures and changing the isolated subunits.Finally,the CL wavelength and efficiency of diphenylmethane are successfully regulated at the aggregate state.

Positive/Negative Phototropism:Controllable Molecular Actuators with Different Bending Behavior

Herein,a series of molecular actuators based on the crystals of(E)-2-(4-fluorostyryl)benzo[d]oxazole(BOAF4),(E)-2-(2,4-difluorostyryl)benzo[d]oxazole(BOAF24),(E)-2-(4-fluorostyryl)benzo[d]thiazole(BTAF4),and(E)-2-(2,4-difluorostyryl)benzo[d]thiazole(BTAF24)showed unique bending behavior under UV irradiation.The one-dimensional(1D)crystals of BOAF4 and BTAF4 bent toward light,whereas those of BOAF24 and BTAF24 bent away from light.Although the chemical structures of these compounds are similar,the authors found that F···H–C interaction played a key role in the different molecular packing in structures crystals,which led to the positive/negative phototropism of the actuators.Moreover,theoretical calculations were carried out to reveal the mechanical properties of the crystals.Taking advantage of these photomechanical properties,the authors achieved the potential application in pushing objects,as well as enriching and removing pollutants.Hence,the molecular actuators with different bending behavior could be fabricated by introducing different number of F atom,which may open a novel gate for crystal engineering.

Deciphering Benzene-Heterocycle Stacking Interaction Impact on the Electronic Structures and Photophysical Properties of Tetraphenylethene-Cored Foldamers

Conjugation,as an essential chemical term used to describe electron delocalization,can be roughly grouped into two categories,through-bond conjugation(TBC)and through-space conjugation(TSC).A hybrid conjugation system integrating both TBC and TSC is rarely studied and utilized,for lack of a well-established model and difficulty of structure modification and property tuning,despite its theoretical significance and potential applications.Herein,various foldamers with a tetraphenylethene(TPE)core are employed as hybrid conjugation models to investigate structure–property correlation by introducing heterocycles of furan/thiophene into theπ-stacking TSC component.For comparison,two kinds of TPE-cored foldamers with different stacking models,a benzene–heterocycle stacking model and a benzene–benzene stacking model,are designed.Combining experimental measurements and theoretical calculations,the impact of benzene–heterocycle interaction on the hybrid conjugation natures and photophysical properties has been studied systematically.The results reveal that the benzene–heterocycle stacking model can fabricate a hybrid conjugation nature with an improved TSC component to make a more dominant contribution to the electronic transition natures than the benzene–benzene stacking model,leading to the distinguishing photophysical behavior.This work provides valuable guidance for the design of new functional materials with hybrid conjugation systems.

Enzyme-free photothermally amplified fluorescent immunosorbent assay(PAFISA)for sensitive cytokine quantification

Cytokine monitoring has attracted great attention due to its significance in the diagnosis and treatment of many diseases,such as tumors,microbial infections,and immunological diseases.Enzyme-linked immunosorbent assay(ELISA)is one of the most popular methods in cytokine detection,ascribing to the lavish signal amplification methods in the ELISA platform.In addition to classical enzymes,other signal amplifiers such as fluorescent probes,artificial nano-enzymes,and photothermal reagents have been applied to reduce the detection limit and produce more sensitive ELISA kits.Due to the accumulative effect of heat,photothermal reagents are promising materials in the signal amplification of ELISA.However,the lack of efficient photothermal generation material at an aggregate scale may delay the further development of this area.In this contribution,based on an efficient organic photothermal aggregate material,an enzyme-free photothermally amplified fluorescent immunosorbent assay system consisting of an assay microfluidic chip and detecting platform was developed.The photothermal nanoparticles with highly efficient photothermal conversion by harvesting energy via excited-state intramolecular motions and enlarging molar absorptivity were successfully prepared.The detection concentration at 50 pg/mL of interleukin-2 was achieved,realizing a signal improvement of detection limits by 20-fold compared to that of previously reported photothermal ELISA.The microscopic imaging integrated with plane sweeping technology provided high spatial resolution and precision,indicating the potential of achieving high throughput profiling at the microscale.Moreover,as an alternative excitation source,light-emitting diode not only provided a more affordable and miniaturized detection system but also revealed the great feasibility of intramolecular motion-induced photothermy nanoparticles for biological analyses.

3D/4D printed versatile fibre-based wearables for embroidery, AIE-chemosensing, and unidirectional draining

Fibre-based wearables for embroidery,chemosensing,and biofluid’s unidirectional draining with goodflexibility,tunability,and designability drive technological advance.However,synthetic polymerfibres are non-degradable,threatening the environment and human health.Herein,we have developed versatile microfibre-based wearables by combining many advantages in one platform of biodegradable polylactic acid(PLA)and melt electrowriting strategy.Diverse potential applications of PLA wearables are achieved byflexibly designing their printingfiles,components and structures.Three-dimensional printingfiles are generated from two-dimensional images to fabricate‘embroidery-like’patterns.PLA/aggregation-induced emissionfluorogens(AIE)chemosensors exhibit colorimetric andfluorescent colour changes upon exposure to amine vapours.Janus PLA-cotton textiles with a hydropho-bic/hydrophilic structure could facilitate unidirectional draining of sweats which is favourable for the management of temperature and humidity on the surface of skin.The proposed platform can not only broaden the design possibilities in 3D/4D printing but also offer wide potential applications for functional wearables.

D-type neuropeptide decorated AIEgen/RENP hybrid nanoprobes with light-driven ROS generation ability for NIR-Ⅱ fluorescence imaging-guided through-skull photodynamic therapy of gliomas

Glioma is one of the most common malignant tumors of the central nervous system,leading high mortality rates in human.Aggregation-induced emission(AIE)photosensitizers-based photodynamic therapy(PDT)has emerged as a promising therapeutic strategy for least-invasive treatment of glioma,which involves local irradiation of the tumor using an external near-infrared(NIR)laser.Unfortunately,most AIE photosensitizers suffered from poorly penetration of the visible light excitation,bad spatiotemporal resolution in deep tissues and low efficient blood-brain barrier(BBB)crossing ability,which greatly limited the clinical practice of AIE photosensitizers for especially deep-seated brain tumor treatment.In this work,we developed a multifunctional NIR-driven theranostic agent through hybrid of AIE photosensitizers TIND with rare-earth doping nanoparticles(RENPs)NaGdF4:Nd/Yb/Tm with up/down dual-mode conversion luminescence.The theranostic agent was further decorated with D-type neuropeptide DNPY for crossing BBB and targeting glioma.Under the 808-nm light irradiation,the down-conversion NIR-II luminescence could indicate the position glioma and the upconversion NIR-I luminescence could trigger the AIE photosensitizers producing reactive oxygen species to inhibit orthotopic glioma tumor growth in situ.These results demonstrate that the integration of Dtype neuropeptide,AIE photosensitizers and RENPs could be promising candidates for in vivo NIR-II fluorescence image-guided through-skull PDT treatments of brain tumors.

Multistimuli-Responsive Luminescent Porous Organic Polymers with Chiroptical Properties and Acid-Induced Degradation

Porous organic polymers(POPs)have attracted great attention in past decades.Although diverse functional POPs have been developed,multistimuli-responsive POPs with excellent aggregate-state luminescence together with good chiroptical properties have rarely been reported.Herein,two pairs of Salen-type enantiomeric PoPs with multistimuli-responsive luminescence and chiral features were designed and synthesized by facile polycondensation reactions between polyfunctional aggregation-induced emission luminogen(AlEgen)-containing salicylaldehyde derivatives and chiral diamines.With Salen units in polymer backbones as tetradentate ligands,a series of POP-metal complexes were further prepared.The obtained POPs and metal complexes show good porosity,high thermal stability,and obvious circular dichroism signals.Moreover,benefiting from the coexistence of AlEgen and Salen units in polymer structures,these POPs exhibit excellent luminescence performance in aggregate states and tunable fluorescence behaviors in response to external stimuli of Zn^(2+)ion,mechanical forces,organic solvent,and acids.Due to the dynamic feature of Schiff base C=N bonds,the present POPs can efficiently undergo hydrolysis reactions under strong acidic conditions to reproduce the AlEgencontaining monomers,and such an acid-induced degradation process can be directly visualized and dynamically monitored via fluorescence variation.These properties collectively make the POPs candidate materials for applications in heterogeneous asymmetric catalysis,fluorescence sensing,biomedicine,etc.

Two-color emissive AIEgens with anti-Kasha property for dual-organelle imaging and phototherapy

Despite the rapid development of probes for targeting single organelle, the construction of robust dual-organelle targeting probes with multicolor emission was rarely reported. Herein, two dual-emissive aggregation-induced emission luminogens(AIEgens)with donor-π-acceptor structures were designed and synthesized, namely QT-1 and QF-2. Both two AIEgens exhibited excitation wavelength-dependence defying the Kasha's rule, and could stain lipid droplets(LDs) and mitochondria in blue and red fluorescence, respectively. Moreover, thanks to the near-infrared emission and abundant reactive oxygen species(ROS) generation efficiency of QT-1, it was chosen as a photodynamic therapy agent to selectively kill cancer cells from normal cells. Upon light irradiation, an obvious decrease of mitochondrial membrane potential(MMP) and serious change of mitochondrial shape in cells were observed, which corresponded to the efficient inhibition of tumor growth in vivo. This work afforded a promising strategy for the construction of multicolor emission by tuning anti-Kasha behaviors and expanding their application in dualorganelle targeting-based phototheranostics.

Light-driven sextuple theranostics:nanomedicine involving second near-infrared AIE-active Ir(Ⅲ)complex for prominent cancer treatment

Light-driven cancer theranostics has shown inexhaustible and vigorous vitality by virtue of its high efficacy,prominent controllability and noninvasiveness.Exploration of an all-round theranostic material simultaneously affording both multimodal diagnosis imaging and synergistic phototherapy would be an appealing yet significantly challenging task.Herein,a novel nanomedicine Ir@PPEG-MeEPO was ingeniously constructed by integrating beforehand1O2-charged amphiphilic polymer and well-tailored Ir(Ⅲ)complex IrDPTP,which was featured by second near-infrared(NIR-Ⅱ)aggregation-induced emission(AIE)tendency,efficient reactive oxygen species(ROS)generation,good photothermal conversion efficiency and high-performance hydrogen gas production.To the best of our knowledge,IrDPTP held the longest emission wavelength among all reported AIE Ir(Ⅲ)complexes.Moreover,Ir@PPEG-MeEPO was capable of controllably releasing ROS via triggered photothermal effect upon NIR irradiation,making it well-adapted to hypoxic environment of tumor.Those distinctive characteristics of Ir@PPEG-MeEPO endowed it with unprecedented performance on sextuple theranostics comprised of NIR-Ⅱfluorescence-photoacoustic-photothermal trimodal imaging and photodynamic-photothermal-hydrogen trimodal therapy,witnessed by the precise tumor diagnosis and complete tumor elimination.The study would open up new perspectives for the exploration of superior nanomedicine for practical cancer theranostics.

Acceptor-engineering tailored type-Ⅰ photosensitizer with aggregation-induced NIR-II emission for cancer multimodal phototheranostics

Exploration of single molecular species synchronously featured by long excitation/emission wavelength, accurate diagnosis, and effective therapy, remains supremely appealing to implement high-performance cancer phototheranostics. However, those previously established phototheranostic agents are undiversified and stereotyped in terms of structural skeleton, and generally exhibit insufficient phototheranostic outcomes. Herein, we innovatively utilized indanone-condensed thiadiazolo[3,4-g]quinoxaline(ITQ) as electron acceptor to construct novel photosensitizer with second near-infrared(NIR-II) emission. Experimental study and theoretical calculation demonstrated that comparing with the counterparts constituting by widely employed NIR-II building block benzobisthiadiazole(BBTD) and 6,7-diphenylthiadiazoloquinoxaline(DPTQ), ITQ-based photosensitizer(TITQ) showed superior aggregation-induced emission(AIE) characteristics, much stronger type-I reactive oxygen species(ROS) production, and prominent photothermal conversion capacity. Furthermore, TITQ nanoparticles with excellent biocompatibility were capable of effectively accumulating in the tumor site and visualizing tumor through fluorescence-photoacoustic-photothermal trimodal imaging with highly spatiotemporal resolution, and completely eliminating tumor by type-I photodynamic-photothermal therapy.

Unrestricted molecular motions enable mild photothermy for recurrence-resistant FLASH antitumor radiotherapy

Ultrahigh dose-rate(FLASH)radiotherapy is an emerging technology with excellent therapeutic effects and low biological toxicity.However,tumor recurrence largely impede the effectiveness of FLASH therapy.Overcoming tumor recurrence is crucial for practical FLASH applications.Here,we prepared an agarose-based thermosensitive hydrogel containing a mild photothermal agent(TPE-BBT)and a glutaminase inhibitor(CB-839).Within nanoparticles,TPE-BBT exhibits aggregation-induced emission peaked at 900 nm,while the unrestricted molecular motions endow TPE-BBT with a mild photothermy generation ability.The balanced photothermal effect and photoluminescence are ideal for phototheranostics.Upon 660-nm laser irradiation,the temperature-rising effect softens and hydrolyzes the hydrogel to release TPE-BBT and CB-839 into the tumor site for concurrent mild photothermal therapy and chemotherapy,jointly inhibiting homologous recombination repair of DNA.The enhanced FLASH radiotherapy efficiently kills the tumor tissue without recurrence and obvious systematic toxicity.This work deciphers the unrestricted molecular motions in bright organic fluorophores as a source of photothermy,and provides novel recurrence-resistant radiotherapy without adverse side effects.

The superiority of nonconjugated structures in fluorescence:through-space vs.through-bond charge transfer

Constructing charge transfer(CT)state by introducing donor(D)and acceptor(A)is an efficient strategy to regulate the photophysical properties of luminescent materials.Traditional CT-type luminophores are built onπ-conjugated fused-ring structures,which always show hybrid CT/locally excited(LE)states and luminescence quenching effect in the aggregate state.In this work,eight conjugated biphenyl(BP)and nonconjugated diphenylmethane(DPM)derivatives with different donors and acceptors are synthesized to investigate the CT properties.Systematic photophysical characterization and theoretical calculation demonstrate that the through-space CT(TSCT)in nonconjugated DA-DPM exhibit superior photophysical performance than the conjugated DA-BP with through-bond CT(TBCT),the main manifestations are as follows:(1)TSCT luminophores produce longer maximum emission wavelength(λ_(em))than the corresponding TBCT ones.For example,the longest λ_(em)of DMA-CN-DPM(DMA,dimethylamino)is 621 nm but the corresponding λ_(em)of DMA-CN-BP is only 480 nm.(2)TSCT-based DA-DPM demonstrates more sensitive responsiveness to environmental stimuli such as temperature and polarity.(3)Complete separation of the the highest occupied molecular orbital(HOMO)and the lowest unoccupied molecular orbital(LUMO)distribution exists in all kinds of conformation of DA-DPM,which was hard to realize in conjugated DA-BP.

“Three birds with one stone”nanoplatform:Efficient near-infrared-triggered type-I AIE photosensitizer for mitochondria-targeted photodynamic therapy against hypoxic tumors

Currently three major problems seriously limit the practical application of can-cer photodynamic therapy(PDT):(i)the hypoxic tumor microenvironment(TME);(ii)low generation efficiency of toxic reactive oxygen species(ROS)in aggre-gates and(iii)shallow tissue penetration depth of excitation light.Very limited approaches are available for addressing all the above three problems with a single design.Herein,a rational“three birds with one stone”molecular and nanoengi-neering strategy is demonstrated:a photodynamic nanoplatform U-Ir@PAA-ABS based on the covalent combination of lanthanide-doped upconversion nanoparti-cles(UCNPs)and an AIE-active dinuclear Ir(III)complex provides a low oxygen concentration-dependent type-I photochemical process upon 980 nm irradiation by Föster resonance energy transfer(FRET).U-Ir@PAA-ABS targets mitochondria and has excellent phototoxicity even in severe hypoxia environments upon 980 nm irradiation,inducing a dual-mode cell death mechanism by apoptosis and ferropto-sis.Taken together,the in vitro and in vivo results demonstrate a successful strategy for improving the efficacy of PDT against hypoxic tumors.

Aggregation-induced emission (AIE) luminescent materials boosting optical storage into the new era of petabit-level capacity

The recording of information stands as the most significant milestone in human civilization.Historically,the recording and storage of information have undergone a technological evolution from paintings to carvings,scribing,and digitization.The invention of optical compact discs(CDs)was one of the major landmarks in digital information technology.Over the past half-century,scientists have endeavored to enhance optical storage capacity by improving both optical systems and optical storage materials,as shown in Scheme 1.In terms of commercial products,the storage capacity has increased from 700 MB(CDs)to 27 GB(Blu-ray discs)by optimizing the optical system based on the same optical storage medium(polycarbonate).To surpass the conventional optical diffraction limit,the optical systems have evolved from traditional lasers to nonlinear two-photon absorption(TPA)and stimulated emission depletion(STED),which has minified the laser spot size from microns to approximately tens of nanometers,marking a remarkable achievement.

Exploring and leveraging aggregation effects on reactive oxygen species generation in photodynamic therapy

Aggregate-level photodynamic therapy(PDT)has attracted significant interest and driven substantial advances in multifunction phototheranostic platforms.As exem-plified by two typical instances of aggregation-caused quenching of reactive oxygen species(ROS)and aggregation-induced generation of ROS,the aggregation effect plays a significant role on the ROS generation of photosensitizers(PSs),which is worthy of in-depth exploration and full utilization.However,in contrast to the well-developed researches on the aggregation effect on luminescence,the studies concerning the aggregation effect on ROS generation are currently in a relatively nascent and disjointed stage,lacking guidance from afirmly established research paradigm.To advance this regard,this review aims at providing a consolidated overview of the fundamental principles and research status of aggregation effects on the ROS generation.Here,the research status can be organized into two main facets.One involves the comparison between isolated state and aggregated state,which is mainly conducted by two methods of changing solvent environments and adding adjuvants into a given solvent.The other underscores the distinctions between different aggregate states,consisting of three parts,namely comparison within the same or between different categories based on the classification of single-component and multicomponent aggregates.In this endeavor,we will present our views on cur-rent research methodologies that explore how aggregation affects ROS generation and highlight the design strategies to leverage the aggregation effect to optimize PS regiments.We aspire this review to propel the advancement of phototheranostic plat-forms and accelerate the clinical implementation of precision medicine,and inspire more contributions to aggregate-level photophysics and photochemistry,pushing the aggregate science and materials forward.

Fjord-Type AIEgens Based on Inherent Through-Space Conjugation

Through-space conjugation(TSC)is a noncovalently electronic interaction that is emerging as a potential complement to through-bond conjugation(TBC)-based strategies for constructing luminescent materials.However,the design of efficient luminogens based on TSC is currently challenging due to a lack of established structure-property understanding.This is particularly true in the case of luminogens displaying aggregation-induced emission(AIE)effects.In this work,three terphenyl derivatives were prepared,and their photophysical properties were systemically studied.It was found that relative to the corresponding m-and p-linked analogues,the electronic interaction of TBC is weakened while the strength of TSC is commensurately enhanced in the constitutional isomer containing an o-linked fjordtype subunit.Within this set of luminogens,the presence of a fjord-type arrangement promotes a transformation from aggregation-caused quenching to AIE.Further investigations involving congeneric quaterphenyl and pentphenyl isomers support the universality of the fjord-type unit as a framework for synthesizing AIE-active luminogens(AIEgens)with inherent TSC.This work not only provides a novel set of AIEgens but also establishes the utility of TSC in controlling the photophysical properties of nonconventional and twisted luminogens.