Fluorescence Emission Mediated by Metal-Dielectric-Metal Fishnet Metasurface: Spatially Selective Excitation and Double Enhancement

Enhancement of uorescent radiation is of great importance for applications including biological imaging,high-sensitivity detectors,and integrated light sources.Strong electromagnetic elds can be created around metallic nanoparticles or in gap of nanostructures,where the local state density of radiating mode is then dramatically enhanced.While enhanced uorescent emission has been demonstrated in many metallic nanoparticles and nanoparticle pairs,simultaneous mediation of absorption and emission processes of uorescent emitters remains challenging in metallic nanostructures.Here,we investigate uorescent emission mediated by metal-dielectric-metal fishnet metasurface,in which localized surface plasmon(LSP)and magnetic plasmon polaritons(MPPs)modes are coupled with absorption and emission processes,respectively.For absorption process,coupling of the LSP mode enables spatially-selective excitation of the uorescent emitters by rotating the polarization of the pump laser beam.In addition,the polarization-dependent MPP mode enables manipulation of both polarization and wavelength of the uorescent emission by introducing a rectangular fishnet structure.All the experimental observations are further corroborated by nite-difference time-domain simulations.The structure reported here has great potential for application to color light-emitting devices and nanoscale integrated light sources.

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.

Aggregation-Induced Emission with Large Redshift in 2,7-Diphenylfluorenone:Reality or Artifact?

The luminescence property of 2,7-diphenyl-fluorenone(DPFO)was previously reported to be very unusual with a large aggregationinduced effect associated with a fluorescence redshift of 150 nm.The phenomenon is reexamined in this work.It is found that the abnormal observations are caused by the presence of a trace amount of impurity 2,7-diphenyl-fluorene(DPF)in the as-synthesized DPFO.The pure DPFO molecule does have an intense fluorescence(FL)in solid(528 nm),about 4−5 times larger than in its dilute dichloromethane solutions(542 nm),but with a blueshifted rather than redshifted FL wavelength in solid.The enormous FL enhancement and redshifted FL wavelength of the as-synthesized DPFO solid are due to the presence of impurity DPF.The FL of DPF is much stronger than that of DPFO in dilute solutions and it also has shorter FL wavelengths.In a dilute solution of DPFO with a trace amount of DPF(∼1%),the dominant FL peaks are from DPF.Because the electronic absorption peaks of DPF overlaps with DPFO,the electronic energy of DPF can transfer to DPFO.The energy transfer is faster with the increase of concentration because DPF and surrounding DPFO molecules become closer,which quenches the FL of DPF(356 and 372 nm)and enhances the FL of DPFO(542 nm in solution and 528 nm in solid).Therefore,at high concentrations or in solids,only peak at about 542 or 528 nm shows up,and peaks at 356 and 372 nm disappear.

Gold Nanostars-AIE Theranostic Nanodots with Enhanced Fluorescence and Photosensitization Towards Effective Image-Guided Photodynamic Therapy

Dual-functional aggregation-induced photosensitizers(AIE-PSs)with singlet oxygen generation(SOG)ability and bright fluorescence in aggregated state have received much attention in image-guided photodynamic therapy(PDT).However,designing an AIE-PS with both high SOG and intense fluorescence via molecular design is still challenging.In this work,we report a new nanohybrid consisting of gold nanostar(AuNS)and AIE-PS dots with enhanced fluorescence and photosensitization for theranostic applications.The spectral overlap between the extinction of AuNS and fluorescence emission of AIE-PS dots(665 nm)is carefully selected using five different AuNSs with distinct localized surface plasmon(LSPR)peaks.Results show that all the AuNS s can enhance the 1 O2 production of AIE-PS dots,among which the AuNS with LSPR peak at 585 nm exhibited the highest 1 O2 enhancement factor of15-fold with increased fluorescence brightness.To the best of our knowledge,this is the highest enhancement factor reported for the metalenhanced singlet oxygen generation systems.The Au585@AIE-PS nanodots were applied for simultaneous fluorescence imaging and photodynamic ablation of HeLa cancer cells with strongly enhanced PDT efficiency in vitro.This study provides a better understanding of the metal-enhanced AIE-PS nanohybrid systems,opening up new avenue towards advanced image-guided PDT with greatly improved efficacy.

Remarkable mechanochromism and force-induced thermally activated delayed fluorescence enhancement from white-light-emitting organic luminogens with aggregation-induced emission

The development of organic materials with white-light emission and thermally activated delayed fluorescence(TADF)properties in the solid state remain a challenge.Herein,a series of white-light-emitting organic luminogens have been developed and are found to show aggregation-induced delayed fluorescence(AIDF)characteristics.The AIDF emitters present dual-emission consisted of prompt fluorescence and TADF in the crystalline state.Their white-light emissions can be easily tuned by altering the chemical structure and connecting position of the heterocyclic aromatic substituent.Under the stimuli of mechanical force and solvent vapor,the compounds exhibit remarkable and reversible mechanochromism,in which their emission colors are switchable between white and yellow.Upon grinding,they also display linearly tunable luminescence colors,as well as force-induced TADF enhancement,which may be associated with the more compact molecular packing and the restriction of intramolecular motions.The results from time-resolved emission scanning and theoretical calculation suggest that the dual-emission of the AIDF luminogens likely results from the twisted intramolecular charge transfer transitions of the molecules,and the reversible mechanochromism properties probably stem from the interconversion of the quasi-axial and the quasi-equatorial conformations.

Confinement fluorescence effect of an aggregation-induced emission luminogen in crystalline polymer

Despite the impressive progress of stimuli-responsive fluorescent materials,little is known about the influence of confinement created by crystalline polymer over the fluorescence properties of fluorescent molecules.The effects of confinement on the fluorescence of an aggregation-induced emission luminogen(AIEgen)are investigated using computational simulations,which reveal that the confined space induces the AIEgens to take a more planar conformation,resulting in a red-shifted emission spectrum.With this property,the study is extended to explore the confinement generated by various polymer crystalline forms,and it is shown that different fluorescence colors are activated.This confinement fluorescence effect is attributed to the different spatial dimensions of the polymer amorphous layer between lamellar crystals where the AIEgens are located.These results indicate the immediate association between crystalline structure and fluorescence signals,activating unprecedented photophysical properties of luminescent materials,and also providing the possibility for crystalline structure visualization,it is important for the many polymer crystallization processes occurring in the materials processing.

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.

Fluorogenic sensing of amorphous aggregates,amyloid fibers,and chaperone activity via a near-infrared aggregation-induced emission-active probe

The presence of protein aggregates in numerous human diseases underscores the significance of detecting these aggregates to comprehend disease mechanisms and develop novel therapeutic approaches for combating these disorders.Despite the development of various biosensors and fluorescent probes that selectively target amyloid fibers or amorphous aggregates,there is still a lack of tools capable of simultaneously detecting both types of aggregates.Herein,we demonstrate the quantitative discernment of amorphous aggregates by QM-FN-SO3,an aggregationinduced emission(AIE)probe initially designed for detecting amyloid fibers.This probe easily penetrates the membranes of the widely-used prokaryotic model organism Escherichia coli,enabling the visualization of both amorphous aggregates and amyloid fibers through near-infrared fluorescence.Notably,the probe exhibits sensitivity in distinguishing the varying aggregation propensities of proteins,regardless of whether they form amorphous aggregates or amyloid fibers in vivo.These properties contribute to the successful application of the QM-FN-SO3 probe in the subsequent investigation of the antiaggregation activities of two outer membrane protein(OMP)chaperones,both in vitro and in their physiological environment.Overall,our work introduces a near-infrared fluorescent chemical probe that can quantitatively detect amyloid fibers and amorphous aggregates with high sensitivity in vitro and in vivo.Furthermore,it demonstrates the applicability of the probe in chaperone biology and its potential as a high-throughput screening tool for protein aggregation inhibitors and folding factors.

A new aggregation-induced emission-based fluorescent probe for effective detection of Hg^(2+)and its multiple applications

Detection of mercury ions(Hg^(2+))in actual samples is of significant importance due to the toxicity of Hg^(2+)to human health.In this work,a simple tetraphenylethene(TPE)derived fluorescent probe TPE-Hg based on aggregation-induced emission(AIE)mechanism was synthesized.TPE-Hg can visually recognize Hg^(2+)in THF/HEPES(1:9,v/v,HEPES 20 mmol/L,pH 7.3)system with rapid response,strong anti-interference ability,large Stokes shift(203 nm),and low detection limit(7.548×10^(-7)mol/L).The results show that Hg^(2+)triggered elimination of TPE-Hg lead to releasing of an AIE-active compound 2 is responsible to the sensing mechanism.TPE-Hg is applicable to detect Hg^(2+)in actual water samples and image Hg^(2+)in living MCF-7 cells.In addition,TPE-Hg is suitable to assay the Hg^(2+)level in seafood and tea samples,and it is alsoapplicable intest strips.

A family of oligo(p-phenylenevinylene)derivative aggregation-induced emission probes:Ultrasensitive,rapid,and anti-interfering fluorescent sensing of perchlorate via precise alkyl chain length modulation

The precise regulation of interactions provided by aggregation-induced emission(AIE)probes is of considerable significance for improving the sensing performance in the field of on-site detection.Here,a highly sensitive perchlorate detection probe was designed by precisely modulating the van der Waals interactions by adjusting the length of the alkyl chain.The optimized AIE probe demonstrated superior perchlorate detection performance owing to its strong van der Waals interactions with perchlorate,including a low detection limit(53.81 nM),rapid response(<5 s),and excellent specificity even in the presence of 16 interfering anions.In addition,a hydrogel-based device loaded with the probe was constructed to achieve ultrasensitive recognition of perchlorate particles with a detection limit as low as 15 fg under a fluorescence microscope.Moreover,the practicality of the probe was further verified by employing a sensing chip in a portable detector,and thus the probe has been proven to be highly promising for trace perchlorate monitoring in real scenarios.We expect the present study to be of great value for the efficient design of high-performance fluorescent probes.

Biocompatible organic dots with aggregation-induced emission for in vitro and in vivo fluorescence imaging

Fluorescent probes play a key role in modern biomedical research. As compared to inorganic quantum dots (QDs) composed with heavy metal elements, organic dye-based fluorescent nanoparticles have higher biocompatibility and are richer in variety. However, traditional organic fluorophores tend to quench fluorescence upon aggregation, which is known as aggregation-caused quenching (ACQ) effect that hinders the fabrication of highly emissive fluorescent nanoparticles. In this work, we demonstrate the synthesis of organic fluorescent dots with aggregation-induced emission (AIE) in far-red/near-infrared (FA/NIR) region. A conventional ACQ-characteristic fluorescent dye, 3,4:9,10-tetracarboxylic perylene bisimide (PBI), is converted into an AIE fluorogen through attaching two tetraphenylethylene (TPE) moieties. The fluorescent dots with surface folic acid groups are fabricated from PBI derivative (DTPEPBI), showing specific targeting effect to folate receptor-overexpressed cancer cells. In vivo studies also suggest that the folic acid-functionalized AIE dots preferentially accumulate in the tumor site through enhanced permeability and retention (EPR) effect and folate receptor-mediated active targeting effect. The low cyto-toxicity, good FR/NIR contrast and excellent targeting ability in in vitro/in vivo imaging indicate that the AIE dots have great potentials in advanced bioimaging applications.

NIR-Ⅱ Excitation and NIR-I Emission Based Two-photon Fluorescence Lifetime Microscopic Imaging Using Aggregation-induced Emission Dots

Near-infrared(NIR)lights are powerful tools to conduct deep-tissue imaging since NIR-Ⅰ wavelengths hold less photon absorption and NIR-Ⅱ wavelengths serve low photon scattering in the biological tissues compared with visible lights.Two-photon fluorescence lifetime microscopy(2PFLM)can utilize NIR-Ⅱ excitation and NIR-Ⅰ emission at the same time with the assistance of a well-designed fluorescent agent.Aggregation induced emission(AIE)dyes are famous for unique optical properties and could serve a large two-photon absorption(2PA)cross-section as aggregated dots.Herein,we report two-photon fluorescence lifetime microscopic imaging with NIR-Ⅱ excitation and NIR-Ⅰ emission using a novel deep-red AIE dye.The AIE-gens held a 2PA cross-section as large as 1.61×10^(4)GM at 1040 nm.Prepared AIE dots had a two-photon fluorescence peak at 790 nm and a stable lifetime of 2.2 ns under the excitation of 1040 nm femtosecond laser.The brain vessels of a living mouse were vividly reconstructed with the two-photon fluorescence lifetime information obtained by our home-made 2PFLM system.Abundant vessels as small as 3.17µm were still observed with a nice signal-background ratio at the depth of 750µm.Our work will inspire more insight into the improvement of the working wavelength of fluorescent agents and traditional 2PFLM.

1,1’-Binaphthol annulated perylene diimides: Aggregation-induced emission enhancement and chirality inversion

Aggregation-induced emission enhancement and aggregation-induced chirality inversion are two individ-ual phenomena for the enantiomerically pure organic dyes in the aggregates.Herein we reported for the first time that these two interesting phenomena could be observed simultaneously in the aggregated states of enantiomerically pure S/R-1,1?-binaphthol annulated perylene diimides,in which two perylene diimides moieties were bridged by S/R-1,1?-binaphthol(BINOL)at the bay positions.Owing to the rotat-able C2 axes between two naphthol annulated perylene diimides moieties,both of them display intrinsic behaviors of aggregation-induced emission enhancements.At the same time,due to the steric hindrances in the imide and methoxy positions,the neighboring twoπ-systems of these two unique polycyclic aro-matic imides in poor solvents are preferable to adopt a cross-stacking mode and thus form helical X-aggregates of opposite chirality(M/P)with chirality inversion characteristics in their circular dichroism and circularly polarized luminescence spectroscopic studies.

Fabrication of high-performance non-doped OLEDs by combining aggregation-induced emission and thermally activated delayed fluorescence

Undoubtedly,the realization of"one stone and two birds"is ideal,which is also applicable to the molecular design in the pursuit of excellent performance.Recently,this standpoint has been confirmed again by an interesting story written from the lab of Zujin Zhao,Shi-Jian Su,and BenZhong Tang,at South China University of Technology and the Hong Kong University of Science and Technology,in the design of DBT-BZ-DMAC(Figure 1)[1].Despite its simple structure,DBT-BZ-DMAC exhibits wonderful characteristics,

Long-lasting chemiluminescence by aggregation-induced emission surfactant with ultralow critical micelle concentration

The development of green and simple chemiluminescence(CL)systems with intensive and long-lasting emission is highly desirable in lighting and extension of their applications.In this study,it is found that the involvement of aggregation-induced emission(AIE)surfactant could greatly enhance the CL of luminol–H2O2–Co2+system.The inserted hydrophobic tetraphenylethylene fluorophore in AIE is able to increase the hydrophobicity of alkyl chain and decrease the critical micelle concentration(CMC)of surfactant.The synergistic effect of micelle-improved enrichment and CL resonance energy transfer endows luminol–H2O2–Co2+system intensive and long-lasting emission under neutral pH conditions(pH 7.4).The visible emission is still observed even after 60 min.Our study has opened a new avenue for exploring green and simple effective CL systems through AIE surfactant with unltralow CMC toward various applications in lighting,optical sensing,and photocatalysis,etc.

Luminescent properties of thermally activated delayed fluorescence molecule with intramolecular π-π interaction between donor and acceptor

Influence of intramolecular π-π interaction on the luminescent properties of thermally activated delayed fluorescence（TADF） molecule（3, 5-bis（3,6-di-tert-butyl-9 H-carbazol-9-yl）-phenyl）（pyridin-4-yl） methanone（DTCBPY） is theoretically studied by using the density functional theory（DFT） and time-dependent density functional theory（TD-DFT）.Four conformations（named as A, B, C, and D） of the DTCBPY can be found by relax scanning, and the configuration C corresponds to the luminescent molecule detected experimentally. Besides, we calculate the proportion of each conformation by Boltzmann distribution, high configuration ratios（44% and 52%） can be found for C and D. Moreover, C and D are found to exist with an intramolecular π-π interaction between one donor and the acceptor; the intramolecular interaction brings a smaller Huang-Rhys factor and reduced reorganization energy. Our work presents a rational explanation for the experimental results and demonstrates the importance of the intramolecular π-π interaction to the photophysical properties of TADF molecules.

Endowing imidazole derivatives with thermally activated delayed fluorescence and aggregation-induced emission properties for highly efficient non-doped organic light-emitting diodes

The development and enrichment of high-performance organic fluorophores that simultaneously possess thermally activated delayed fluorescence(TADF)and aggregation-induced emission(AIE)properties is going pursued but remains a great challenge due to severe exciton quenching.Herein,a systematical investigation on imidazole moiety has successfully given rise to a series of highly efficient imidazolebased TADF-AIE luminogens for the first time.The attachment of two cyano functionalities on imidazole moiety can significantly increase the electron-withdrawing ability,so as to realize TADF emissions with small singlet-triplet energy gaps(ΔEST)values.Meanwhile,the installation of a steric hindrance group at N1 position of imidazole moiety can twist the geometry between imidazole and phenyl bridge,thus transforming imidazole derivative from an aggregation-caused quenching emitter into an AIE luminogen.Consequently,the non-doped organic light-emitting diodes(OLEDs)utilizing these TADF-AIE luminogens as emitters exhibit outstanding skyblue and green emissions,with external quantum efficiency(EQE)as high as 20.0%and low efficiency roll-off(EQE at 1000 cd m−2,16.1%).These values represent the state-of-the-art performance for all imidazole-based OLED devices,which illustrates the significant potential of imidazole derivatives in assembling high-performance OLEDs.

Eu^(3+)Coordinated Hyperbranched Polysiloxane with Multicolor Emission and Long Fluorescence Lifetime

Comprehensive Summary,Hyperbranched polysiloxanes have attracted increasing interest due to their unique fluorescence properties.However,the relatively short emission wavelength and low fluorescence lifetime are still the main obstacles to their broader application.In this study,we first synthesized aβ-diketone contained hyperbranched polysiloxane with excitation-dependent multicolor emission.Further through the coordination of HBPSi-NMDEA with Eu^(3+)ion,a hybrid luminescent material was prepared.It exhibited not only aggregation-induced red emission at 613 nm,but also a long fluorescence lifetime of 681.45μs.Particularly,it showed highly sensitive reversible fluorescence response to temperature variation,thus displaying the potential to be used in fluorescence temperature detection.

Aggregation-induced emission biomaterials for anti-pathogen medical applications:detecting,imaging and killing

Microbial pathogens,including bacteria,fungi and viruses,greatly threaten the global public health.For pathogen infections,early diagnosis and precise treatment are essential to cut the mortality rate.The emergence of aggregation‐induced emission(AIE)biomaterials provides an effective and promising tool for the theranostics of pathogen infections.In this review,the recent advances about AIE biomaterials for anti-pathogen theranostics are summarized.With the excellent sensitivity and photostability,AIE biomaterials have been widely applied for precise diagnosis of pathogens.Besides,different types of anti-pathogen methods based on AIE biomaterials will be presented in detail,including chemotherapy and phototherapy.Finally,the existing deficiencies and future development of AIE biomaterials for anti-pathogen applications will be discussed.

Enantioselective recognition based on aggregation-induced emission

Chirality is one of the most important features of the nature.The recognition of enantiomers plays significant roles in the field of life science,pharmaceutical analysis and food chemistry.Among various recognition methods,fluorescence spectrometry has attracted much attention of researchers thanks to its high sensitivity and easy operation.Compared with traditional fluorescent probes,chiral molecules with aggregation-induced emission(AIE)have drawn increasing interests due to their huge potential in high-efficiency chemo/biosensors and solid emitters.Chiral AIE luminogens(AIEgens)can not only discriminate two enantiomers with excellent enantioselectivity,but also show general applicability for many chiral analytes,such as chiral acids,amino acids,amines,alcohols.In this review,we mainly summarized the recent development of chiral probes with AIE properties,including chiral tetraphenylethylene(TPE)derivatives,α-cyanostilbene derivatives,Schiff base derivatives and other AIEgens.Their synthetic routes,recognition capabilities and possible working mechanisms were well discussed.It is envisioned that the present review can give some significant guidance for design and synthesis of chiral AIEgens with good enantioselectivity and inspire more readers to join the research of chiral AIE.