Showing papers on "Stokes shift published in 2022"

Near-Infrared Fluorescent Probe with Large Stokes Shift for Imaging of Hydrogen Sulfide in Tumor-Bearing Mice.

Abstract: Hydrogen sulfide (H2S) is an important endogenous gas signal molecule in living system, which participates in a variety of physiological processes. Very recent evidence has accumulated to show that endogenous H2S is closely associated with various cancers and can be regarded as a biomarker of cancer. Herein, we have constructed a new near-infrared fluorescent probe (DCP-H2S) based on isophorone-xanthene dye for sensing hydrogen sulfide (H2S). The probe shows remarkable NIR turn-on signal at 770 nm with a large Stokes shift of 200 nm, together with high sensitivity (15-fold) and rapid detection ability for H2S (4 min). The probe also possesses excellent selectivity for H2S over various other analytes including biothiols containing sulfhydryl (-SH). Moreover, DCP-H2S has been successfully applied to visualize endogenous and exogenous H2S in living cells (293T, Caco-2 and CT-26 cells). In particular, the excellent ability of DCP-H2S to distinguish normal mice and tumor mice is shown, and it is expected to be a powerful tool for detection of H2S in cancer diagnosis.

Near-Infrared Fluorescent Probe with a Large Stokes Shift for Detection of Hydrogen Sulfide in Food Spoilage, Living Cells, and Zebrafish.

Abstract: Hydrogen sulfide (H2S) is a significant component of various physiological processes, and it can also cause a negative effect on foodstuffs. In this work, we designed and synthesized an NIR fluorescent turn-on responding probe (DDM-H2S) with a large Stokes shift (190 nm) for the detection of H2S. DDM-H2S exhibited high selectivity and sensitivity, obvious color changes, and a fast response time for tracing H2S. When DDM-H2S reacted with H2S, the PET process was eliminated, and the recovered ICT process and NIR fluorescence were observed. Moreover, DDM-H2S could image endogenous and exogenous H2S in living HeLa cells and zebrafish. What is more, the probe DDM-H2S could be deposited easily to test paper strips, which were able to detect the H2S gas produced during food spoilage (such as eggs, raw meat, and fishes) by the color of test paper strips changing from pink to purple. Therefore, this work provides a promising approach for monitoring H2S in complicated biological systems and practical food samples.

Photophysics in Zero‐Dimensional Potassium‐Doped Cesium Copper Chloride Cs3Cu2Cl5 Nanosheets and Its Application for High‐Performance Flexible X‐Ray Detection

Abstract: Zero‐dimensional Cs3Cu2Cl5 exhibits intriguing optical properties, which can meet the basic requirements of ideal scintillator application. Here, green emitter Cs3Cu2Cl5 nanosheets are successfully synthesized, and by doping with 2% potassium (K+), their photoluminescence quantum yield (70.23% to 81.39%), radioluminescence intensity, and stability are improved. Further experimental and theoretical studies point out that: (1) K+ brings the neighboring [Cu2Cl5]3− dimers groups closer, leading to lattice shrinkage and lower lattice constants; (2) such compact crystal structure results in stronger exciton–photon coupling and reduced phonon–electron coupling strength, which is beneficial to form self‐trapped excitons and enhanced luminescence; (3) lower lattice constants also induce decreased bandgap (2.58 to 2.51 eV) and increased Stokes shift (217 to 223 nm), for less self‐absorption and higher quantum efficiency. Finally, area‐controllable uniform flexible Cs3Cu2Cl5:2%K+–polystyrene film is successfully achieved with excellent X‐ray sensibility. Such flexible film shows low cost (2.8223 $/g), broadband response (20–160 keV), and high spatial resolution (5 lp mm−1) that is comparable to commercial CsI:Tl wafer. Moreover, it fits well with nonplanar surfaces for high‐quality medical and industrial flexible images applications. It is believed that this work can provide a viable tactic to enhance X‐ray detection in metal halide scintillators.

A synergistic strategy to develop photostable and bright dyes with long Stokes shift for nanoscopy

Abstract: The quality and application of super-resolution fluorescence imaging greatly lie in the dyes' properties, including photostability, brightness, and Stokes shift. Here we report a synergistic strategy to simultaneously improve such properties of regular fluorophores. Introduction of quinoxaline motif with fine-tuned electron density to conventional rhodamines generates new dyes with vibration structure and inhibited twisted-intramolecular-charge-transfer (TICT) formation synchronously, thus increasing the brightness and photostability while enlarging Stokes shift. The new fluorophore YL578 exhibits around twofold greater brightness and Stokes shift than its parental fluorophore, Rhodamine B. Importantly, in Stimulated Emission Depletion (STED) microscopy, YL578 derived probe possesses a superior photostability and thus renders threefold more frames than carbopyronine based probes (CPY-Halo and 580CP-Halo), known as photostable fluorophores for STED imaging. Furthermore, the strategy is well generalized to offer a new class of bright and photostable fluorescent probes with long Stokes shift (up to 136 nm) for bioimaging and biosensing.

Supramolecular assembly confined purely organic room temperature phosphorescence and its biological imaging

Abstract: Purely organic room temperature phosphorescence, especially in aqueous solution, is attracting increasing attention owing to its large Stokes shift, long lifetime, low preparation cost, low toxicity, good processing performance advantages, and broad application value. This review mainly focuses on macrocyclic (cyclodextrin and cucurbituril) hosts, nanoassembly, and macromolecule (polyether) confinement-driven RTP. As an optical probe, the assembly and the two-stage assembly strategy can realize the confined purely organic RTP and achieve energy transfer and light-harvesting from fluorescence to delayed fluorescence or phosphorescence. This supramolecular assembly is widely applied for luminescent materials, cell imaging, and other fields because it effectively avoids oxygen quenching. In addition, the near-infrared excitation, near-infrared emission, and in situ imaging of purely organic room temperature phosphorescence in assembled confinement materials are also prospected.

Ratiometric detection and bioimaging of endogenous alkaline phosphatase by a NIR fluorescence probe

Abstract: A novel near-infrared (NIR) fluorescent probe (SWJT-3) was designed based on phosphate protection of the electron donating group of the hemicyanine for the ratiometric determination of ALP at 590 and 670 nm. Notably, SWJT-3 could be used in the endogenous detection of ALP in vitro and vivo. Moreover, it was the first NIR and ratiometric fluorescent probe for the imaging of ALP in mice. It has large Stokes shift (185 nm), and also showed high selectivity, low detection limit (0.87 U/L). Meanwhile, SWJT-3 exhibited obvious color change in aqueous solution which could be observed by naked-eyes. In addition, the probe displayed low lifetime (0.74 ns), high substrate affinity (Km = 8.89 µM) and excellent fluorescence characterization under various polarity and viscosity conditions.

Highly luminescent scintillating hetero-ligand MOF nanocrystals with engineered Stokes shift for photonic applications

Abstract: Large Stokes shift fast emitters show a negligible reabsorption of their luminescence, a feature highly desirable for several applications such as fluorescence imaging, solar-light managing, and fabricating sensitive scintillating detectors for medical imaging and high-rate high-energy physics experiments. Here we obtain high efficiency luminescence with significant Stokes shift by exploiting fluorescent conjugated acene building blocks arranged in nanocrystals. Two ligands of equal molecular length and connectivity, yet complementary electronic properties, are co-assembled by zirconium oxy-hydroxy clusters, generating crystalline hetero-ligand metal-organic framework (MOF) nanocrystals. The diffusion of singlet excitons within the MOF and the matching of ligands absorption and emission properties enables an ultrafast activation of the low energy emission in the 100 ps time scale. The hybrid nanocrystals show a fluorescence quantum efficiency of ~60% and a Stokes shift as large as 750 meV (~6000 cm-1), which suppresses the emission reabsorption also in bulk devices. The fabricated prototypal nanocomposite fast scintillator shows benchmark performances which compete with those of some inorganic and organic commercial systems.

Efficient Yellow Self-Trapped Exciton Emission in Sb3+-Doped RbCdCl3 Metal Halides.

Abstract: Metal halide perovskites have flexible crystal and electronic structures and adjustable emission characteristics, which have very broad applications in the optoelectronic field. Among them, all-inorganic perovskites have attracted more attention than others in recent years because of their characteristics of large diffusion length, high luminescence efficiency, and good stability. In this work, Sb3+-doped RbCdCl3 crystalline powder was synthesized by a simple hydrothermal method, and its luminescence properties were studied, which showed a broad emission band with a large Stokes shift and efficient yellow light emission at about 596 nm at room temperature with a photoluminescence quantum yield of 91.7%. The emission came from the transition of the self-trapped exciton 1 (STE1) out of 3Pn (n = 0, 1, and 2) to S0 due to strong electron-phonon coupling, which scaled with increasing temperature. Moreover, its emission color became white at low temperatures due to the occurrence of transition of other self-trapped exciton 0 (STE0) state emission out of the 1S states of Sb ions to S0 in the lattice. These emission color changes may be used for temperature sensing, and this Sb3+-doped RbCdCl3 material expands the knowledge of the efficient luminescent inorganic material family for further applications of all-inorganic perovskites.

An Integration Strategy to Develop Dual-State Luminophores with Tunable Spectra, Large Stokes Shift, and Activatable Fluorescence for High-Contrast Imaging

Abstract: Open AccessCCS ChemistryRESEARCH ARTICLE6 Jun 2022An Integration Strategy to Develop Dual-State Luminophores with Tunable Spectra, Large Stokes Shift, and Activatable Fluorescence for High-Contrast Imaging Yongchao Liu, Lili Teng, Chengyan Xu, Tian-Bing Ren, Shuai Xu, Xiaofeng Lou, Lin Yuan and Xiao-Bing Zhang Yongchao Liu State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Collaborative Innovation Center for Chemistry and Molecular Medicine, Hunan University, Changsha 410082 Google Scholar More articles by this author , Lili Teng State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Collaborative Innovation Center for Chemistry and Molecular Medicine, Hunan University, Changsha 410082 Google Scholar More articles by this author , Chengyan Xu State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Collaborative Innovation Center for Chemistry and Molecular Medicine, Hunan University, Changsha 410082 Google Scholar More articles by this author , Tian-Bing Ren State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Collaborative Innovation Center for Chemistry and Molecular Medicine, Hunan University, Changsha 410082 Google Scholar More articles by this author , Shuai Xu State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Collaborative Innovation Center for Chemistry and Molecular Medicine, Hunan University, Changsha 410082 Google Scholar More articles by this author , Xiaofeng Lou State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Collaborative Innovation Center for Chemistry and Molecular Medicine, Hunan University, Changsha 410082 Google Scholar More articles by this author , Lin Yuan State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Collaborative Innovation Center for Chemistry and Molecular Medicine, Hunan University, Changsha 410082 Google Scholar More articles by this author and Xiao-Bing Zhang *Corresponding author: E-mail Address: [email protected] State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Collaborative Innovation Center for Chemistry and Molecular Medicine, Hunan University, Changsha 410082 Google Scholar More articles by this author https://doi.org/10.31635/ccschem.021.202100935 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Developing dual-state luminophores (DSLs) with strong fluorescence in both the monomer and aggregate states is urgently needed but remains a huge challenge because most current luminophores are either aggregation-induced emission or aggregation-caused quenching molecules. Moreover, limited by the structural conservation of the few existing DSLs, there are not enough response sites that can be used to customize various activatable fluorescent probes for specific molecular imaging. Herein, we engineered a general integration strategy for the fabrication of such DSLs with excellent photophysical properties. The DSLs, with their tunable spectra, a large Stokes shift (>170 nm), and achievable near-infrared (NIR) emission, show great potential for high-contrast imaging. Importantly, DSLs can be used as a universal platform for probe customization due to their activatable fluorescence through protection–deprotection of the phenolic hydroxyl group. Based on this, an NIR fluorescent probe DSL-Gal was developed for sensing of β-galactosidase in solutions, senescent cells, and liver metastases with high contrast, further confirming the superiority and universal feasibility of DSLs in probe design. The integration strategy may provide a novel approach for the generation of other DSLs and have great potential applications in bioimaging. Download figure Download PowerPoint Introduction Fluorescence imaging is a useful tool to illuminate biological information in complex systems and visualize the physiological process and other targets at the molecular level due to its high sensitivity and high spatial resolution.1–3 In recent decades, organic luminophores with excellent biocompatibility and easy modification appear to be a more promising choice for sensing and imaging of molecular targets in living systems.4–7 Such luminophores, however, easily suffer from the aggregation-caused quenching (ACQ) effect, of which the luminophores show strong fluorescence only in the monomer state but remain non- or less fluorescent in the aggregate state (Figure 1a).8 This is because these molecules in the aggregate state may experience strong π–π stacking interactions that lead to ACQ, which may lead to unreliable fluorescence sensing signals due to the generation of nonemissive aggregates.9 To eliminate the ACQ effect in the aggregate state, aggregation-induced emission (AIE) phenomenon, as a noncanonical emission mechanism, was first reported by Tang and co-workers,10–13 in which its applications were greatly extended. The AIE luminophores can be highly emissive in the aggregate state, but their monomeric emission in dilute aqueous solution is often weak (Figure 1b).14 This may lead to compromised fluorescence signals in the monomer state due to the generation of nonemissive monomer and place higher requirements on their application scenarios. Due to the complexity and diversity of the detection microenvironment, luminophores based on ACQ or AIE are still not adequate to meet the growing needs in the field of accurate imaging of biological targets because they can only exhibit bright fluorescence in a single monomer or aggregate state.13 To fill in the gap between AIE and ACQ, there is a growing interest in developing dual-state luminophores (DSLs) (Figure 1c), which intensely show fluorescence in both the monomer and aggregate states. Figure 1 | Strategies and characteristic analysis of the emission luminophores. Emission behavior of (a) ACQ luminophore with monomer-dependent emission, (b) AIE luminophore with aggregate-dependent emission, and (c) DSL with dual-state emission. Download figure Download PowerPoint In recent decades, only very few luminophores with dual-state properties have been reported.15,16 For instance, Zhao’s group15 developed several D–A–π–A–D molecules with high emission efficiency both in solution and in the solid state; Qian’s group16 reported a new class of dual-state emitters with apparent solvatochromism by constructing a donor–acceptor pattern and introducing a twisted triphenylamine moiety. Despite their unique emission properties, these DSLs lack appropriate fluorescence regulatory sites, which makes it difficult to customize activatable fluorescent probes to indicate the level of molecular targets via putting out a turn-on or ratiometric fluorescent signal. In addition, these DSLs also showed short emission wavelength (<600 nm), which greatly limits them for low background imaging and in vivo sensing. And it is hard to adjust their emission wavelengths and further derivatize such luminophores. So far, a universal strategy to produce DSLs with desirable photophysical properties is not available. In this study, we reported a general strategy to construct DSLs based on the integrated emission mechanism of excited state intramolecular proton transfer (ESIPT) and intramolecular charge transfer (ICT), wherein the protection–deprotection of the phenolic hydroxyl switch can finely regulate their fluorescence emission. By introducing ESIPT-generating groups into the classic ICT luminophore structure, a series of DSLs were fabricated, which not only retained the aggregate-state emissive characteristics of ESIPT luminophores, but also significantly enhanced the fluorescence of ICT luminophores in the monomer state through hydrogen-bond interaction. Consequently, these DSLs show dual-state emission, that is, they can emit fluorescence both in the monomer and aggregate states, as well as exhibit some excellent photophysical properties, including tunable fluorescence spectra, high fluorescence quantum yield (QY) and a large Stokes shift (>170 nm). Most importantly, by introducing functional groups on the phenolic hydroxyl group, the DSLs can perform OFF–ON fluorescence switching by protection–deprotection of the phenolic hydroxyl, indicating that DSLs could serve as a universal platform for customization of activatable fluorescent probes. As a proof of concept, an near-infrared (NIR) fluorescent probe DSL-Gal was developed for β-galactosidase sensing in solutions, senescent cells, and liver metastases with high contrast that further confirmed the improved superiority and feasibility of DSLs in molecular sensing. This unique emission behavior of DSLs would greatly facilitate the advancement of high-contrast bioimaging. Experimental Methods Reagents and apparatus All chemicals were purchased from commercial suppliers and used without further purification. β-gal was purchased from Sigma-Aldrich (Shanghai, China). The mice were purchased from Hunan Slake Jingda Laboratory Animal Co., Ltd. (Changsha, Hunan, China). Water was purified and doubly distilled by a Milli-Q system (Millipore, USA). The UV–vis absorption spectra were acquired via a Shimadzu UV-2600 spectrophotometer (Japan). Fluorescence spectra were recorded on a HITACHI F-4600 fluorescence spectrophotometer (Japan) with a 1 cm standard quartz cell. Mass spectra were performed using a Finnigan LCQ Advantage ion trap mass spectrometer (Thermo Fisher Scientific, USA). NMR spectra were recorded on a Bruker DRX400 spectrometer (Switzerland) using tetramethylsilane (TMS) as an internal standard. Thin-layer chromatography (TLC) was conducted using silica gel 60 F254, and column chromatography was carried out over silica gel (200–300 mesh), both of which were obtained from Qingdao Ocean Chemicals (Qingdao, China). Fluorescence images of cells were obtained using an Olympus FV1000-MPE laser scanning confocal-microscope (Japan). Spectral measurements The fluorescence measurement experiments of DSL-Gal (10 μM) were performed in phosphate-buffered saline (PBS) (10 mM) with dimethyl sulfoxide (DMSO) as cosolvent solution (PBS/DMSO = 9∶1, v/v, 10 mM, pH 7.4). The reaction solution was transferred into a quartz cell to measure the absorbance or fluorescence spectra, with both excitation and emission slits set at 5 nm. The fluorescence spectra were measured with the excitation wavelength at 450 nm. The solutions of various testing species were prepared from (1) Blank, (2) Na+ (10 mM), (3) K+ (10 mM), (4) Ca2+ (10 mM), (5) Fe2+ (1 mM), (6) H2O2 (250 μM), (7) HClO (50 μM), (8) ONOO− (50 μM), (9) O2− (100 μM), (10) t-BuOOH (100 μM), (11) ꞏ OH (100 μM), (12) Cys (500 μM), (13) reduced glutathione (GSH; 1 mM), (14) H2S (100 μM), (15) SO32− (50 μM), (16) β-gal (50 U/L) in twice-distilled water. Calculation of fluorescence QY Fluorescence QY was determined using optically matching solutions of rhodamine 6G (Φf = 0.95 in EtOH solution) and cresol purple as reference (φ = 0.58 in EtOH solution) as the standarde QY was calculated using the following equation: Φ s = Φ r ( A r F s / A s F r ) ( n s 2 / n r 2 ) where, s and r denote sample and reference, respectively. A is the absorbance, F is the relative integrated fluorescence intensity, and n is the refractive index of the solvent. The QYs of DSL2 and DSL4 were determined in tetrahydrofuran (THF)/H2O = 1/1 (v/v) solution by using rhodamine 6G as the reference. The QYs of DSL1 and DSL3 were determined in THF/H2O = 1/1 (v/v) solution by using cresol purple as reference. Cell culture HeLa or OVCAR3 cells were maintained in RPMI-1640 medium with 10% fetal bovine serum (FBS; GIBCO, USA) and 1% penicillin–streptomycin at 37 °C in a humidified atmosphere containing 20% O2 and 5% CO2 as the normoxic condition. Cells were seeded in a 20 mm glass-bottom dish plated and grown to around 80% confluency for 24 h before the experiment. Confocal imaging and in vivo imaging In fluorescence cell imaging, 10 μM of DSLs and ICTs were incubated with the cells for 30 min before conducting the confocal experiments. The fluorescence signal of cells incubated with DSL-Gal (10 μM) was collected in the channel (600–700 nm) by using a semiconductor laser at 488 nm as the excitation source. For (E)-4-(4-hydroxystyryl)-5,5-dimethyl-2-oxo-2,5-dihydrofuran-3-carbonitrile (ICT1), DSL1,3, λex = 488 nm, λem = 600–700 nm, for 2-(3,5,5-trimethylcyclohex-2-en-1-ylidene)-malononitrile (ICT2), DSL2,4, TPE1 and TPE2, λex = 405 nm, λem = 500–600 nm. The fluorescent images of mice were obtained via an IVIS Lumina XR Imaging System (Caliper Life Sciences, USA) equipped with a cooled charge-coupled device (CCD) camera with the collected channel (λex = 430 nm, λem = 600–700 nm). Circular Region of interests (ROIs) were drawn over the areas and quantified by Lumina XR Living Image software (USA), version 4.3. Tumor models of peritoneal metastases and subcutaneous tumor All animal procedures were performed in accordance with the Guidelines for Care and Use of Lboratory Animals of Hunan University, and experiments were approved by the Animal Ethics Committee of the College of Biology (Hunan University). To develop the peritoneal metastases model, 1 × 106 OVCAR3 cells suspended in 300 μL of PBS (pH 7.4) were intraperitoneally injected into female nude mice (BALB/c, 7–8 weeks old) for 36 days. To develop the sc tumor model, 1 × 106 OVCAR3 cells suspended in 25 μL of PBS were subcutaneously injected into the underarm of each female nude mouse (BALB/c, 7–8 weeks old). Tumors with diameters of around 10 mm were formed after 16 days. Fluorescence imaging of DSL1 and ICT1 in liver tissue Liver tissue slices were prepared from freezing microtome. Then these tissues were incubated with DSL1 (50 μM) and ICT1 (50 μM) at 37 °C for 30 min, followed by washing them three times with PBS solution. Under the confocal fluorescence microscope with a 60× objective lens, the probe was excited at 488 nm, and fluorescence emissions in the 600–700 nm channel were gathered, respectively. In tissue depth imaging, the three-dimensional (3D) images were constructed along the z-axis direction. Visualization of β-gal activity in peritoneal metastases tissue and in tumor After 32 days of intraperitoneal injection of OVCAR3 cells, the mice were sacrificed and dissected, and then the peritoneal metastases were collected. Tumor tissue slices were prepared from freezing microtome. Next, these tissues were incubated with DSL-Gal (50 μM) at 37 °C for 1 h, followed by washing them three times with PBS solution. Under the confocal fluorescence microscope with a 60× objective lens, the probe was excited at 488 nm, and fluorescence emission at the 600–700 nm channel was gathered. In tissue depth imaging, the 3D images were constructed along the z-axis direction. For the sc tumor model, DSL-Gal (50 μM) was intratumorally injected at different times. Subsequently, the mice were immediately imaged via an IVIS Lumina XR Imaging System. Circular ROIs were drawn over each well, and fluorescent intensity was quantified by Living Image software. Results and Discussion Revealing the design and luminous mechanism of DSLs Our group has been engaged in a long-term research project investigating the use of ESIPT-based solid-state luminophores, such as 2-(2’-hydroxyphenyl)-4(3H)-quinazolinone (HPQ) and 6-Chloro-2-(2-hydroxy-5-(1,2,2-triphenylvinyl)phenyl)quinazolin-4(3H)-one (HTPQ), aiming to expand the utility of such luminophores for in situ bioimaging.17–20 However, they have shown short excitation and emission wavelengths (<600 nm), and only emitted fluorescence in the solid state. Recently, we hoped to redshift the excitation and emission wavelengths of such solid-state luminophores by extending their conjugate structure (Figure 2a). We found a convenient approach to integrate HPQ together with the classic ICT dyes to build long-wavelength solid-state luminophores, including ICT1 and ICT2, which show weak solution fluorescence due to the presence of a phenolic hydroxyl group that is not easily ionized ( Supporting Information Figure S1).21,22 Interestingly, a luminophore termed as DSL1, which is fabricated by HPQ and ICT1, immediately grabbed our attention when we discovered its strong fluorescence in both the monomer and aggregate states. Upon excitation at 450 nm, DSL1 displayed similar fluorescence emission at 629 and 642 nm in the monomer and aggregate states, respectively (Figure 2b). In addition, similar fluorescence intensity of polymer-encapsulated DSL-NP and DSL1 in solution was observed ( Supporting Information Figure S2), suggesting that DSL1 can effectively avoid fluorescence quenching caused by molecular aggregation. Figure 2 | Revealing the design and luminous mechanism of DSL1. (a) Chemical structure of HPQ and DSL1. (b) Fluorescence spectra of DSL1 in monomer and aggregate states. (c) Optimized structure of DSL1 and ICT1. (d) DFT molecular orbital plots [lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO)] of DSL1-O−N+, DSL1-OH, ICT1-O−, and ICT1-OH. Oscillator strength and excitation wavelength of (e) DSL1-O−N+ and DSL1-OH, (f) ICT1-O− and ICT1-OH through DFT calculation. Exchange functional: B3LYP. Basis sets: 6-31G*. (g) Probable emissive mechanism of DSL1 and its responsive mechanism for customization activatable probes. Download figure Download PowerPoint To give a theoretical explanation of the emissive mechanism of DSL1, we carried out density functional theory (DFT) calculations (Figure 2c). We used DSL1-O−, DSL1-O−N+, and DSL1-OH to represent the ionized configuration, proton transferred configuration and unionized configuration of DSL1, respectively. Similarly, ICT1-O−, and ICT1-OH were used to represent the ionized configuration and unionized configuration of ICT1, respectively. Compared with DSL1-OH, DSL1-O−N+ showed an obviously increased electron distribution of orbital plots (Figure 2d), as well as increased oscillator strength ( Supporting Information Table S1). These results indicated that the occurrence of the proton transfer process will increase the electron donating ability of the donor of DSL1, which was consistent with the enhanced fluorescence intensity of DSL1 and redshifted wavelength in THF/H2O solutions ( Supporting Information Figure S3). Importantly, DSL1-O− (the ionized configuration of DSL1) and DSL1-O−N+ showed similar electron distribution of orbital plots ( Supporting Information Figure S4), suggesting that the proton transfer process can indeed increase the ICT effect of DSL1, which is near to the ICT effect in the DSL1-O− configuration. These results demonstrate that the quinazolinone moiety could effectively assist the ionization of phenolic hydroxyl through intramolecular hydrogen-bond interaction without the help of any external conditions. For ICT1, the reduced ICT effect was observed in the ICT-OH form from its electron distribution of orbital plots (Figure 2d), as well as decreased oscillator strength ( Supporting Information Table S1), which was consistent with the extremely low fluorescence intensity and the QY of ICT1 in the phenolic hydroxyl state in solution ( Supporting Information Table S2). The results showed that ICT1 can emit strong fluorescence only after the proton on the phenolic hydroxyl group is removed, which requires specific external conditions, such as alkalinity. In addition, compared with ICT1, DSL1 showed a reduced excitation-energy difference before and after the ionization of phenolic hydroxyl (from 81 to 44 nm) (Figures 2e and 2f and Supporting Information Table S1), which also suggests its improved ionization capacity of phenolic hydroxyl. Therefore, the introduction of quinazolinone moiety at the ortho position of the phenolic hydroxyl group of ICT1 can indeed enhance its luminous efficiency in solution by the intramolecular hydrogen bond. Through dynamic light scattering, transmission electron microscopy, and Tyndall effects results, we found that DSL1 was dissolved in 10% H2O/THF mixed solution, but showed in aggregate state in 98% and 60% H2O/THF mixed solution ( Supporting Information Figure S5), indicating their freely switchable molecular states. Moreover, the emission spectra of DSL1 in THF/H2O solution with different water fractions showed its monomer and aggregated state emissions, further confirming its dual-state emissive properties ( Supporting Information Figure S3). These results have also confirmed that the emissive mechanism of DSL1 is ESIPT and ICT (Figure 2g),7,23,24 which allows for customization of activatable probes by the protection–deprotection of the phenolic hydroxyl group. Engineering dual-state emissive luminophores Starting from this initial DSL1 molecule, a series of luminophores were developed based on simple structural modifications using the following general guidelines: (1) start with the quinazolinone and benzothiazole backbone as an ESIPT-generating unit; and (2) introduce an additional electron withdrawing unit at the para position of the phenolic hydroxyl group to form an ICT system (Figure 3a). To our delight, the DSLs all showed fluorescence both in the monomer and aggregate states (Figures 3b and 3c). The synthetic route for DSLs is outlined in Supporting Information Scheme S1, and all the new compound structures are confirmed by NMR ( Supporting Information). The photophysical properties of DSL1-4 were initially investigated in different solvents with a range of polarities ( Supporting Information Figure S6–S9). Relatively high absorbance and low fluorescence of ICT1 and ICT2 were observed, resulting in the extremely low fluorescence QY (<1%). On the contrary, DSL1-4 all showed improved fluorescence and QY in these solvents with different polarities ( Supporting Information Table S2), suggesting that the quinazolinone and benzothiazole groups might be helpful for fluorescence increase. Compared with ICT2, ICT1 had a larger conjugate system and stronger push–pull electron ability in the molecular skeleton. Hence the integrated DSL1,3 showed longer excitation and emission wavelengths than DSL2,4. The absorption and fluorescence spectra of DSL1-4 in the monomer and aggregate states are shown in Figures 3d and 3e, in which DSL2,4 exhibit yellow fluorescence and DSL1,3 exhibit deep-red fluorescence, corresponding to the colors obtained by color coordinates ( Supporting Information Figure S10). Moreover, the photophysical properties of DSLs exhibit less dependence on the solvent polarity ( Supporting Information Figure S11). The statistical results on the photophysical properties of DSL1-4 are summarized in Table 1, giving similar color of fluorescence in both solid and solution states, a large Stokes shift (>170 nm), and relatively high fluorescence QY. Figure 3 | A generalizable molecular engineering strategy for developing DSLs. (a) Illustration of the “integration” strategy for the design of novel DSLs. Fluorescent photographs of DSL1-4 in (b) THF solution and (c) solid state under 365 nm excitation. Normalized fluorescent spectra of DSL1-4 in (d) THF solution and (e) solid state. Download figure Download PowerPoint Table 1 | Photophysical Properties of DSLs Luminophores λabs (nm)a λem (nm)a Stokes Shifta QY (%)b λem (nm)c QY (%)c DSL1 413 629 216 18.6 642 11.8 DSL2 382 556 174 21.2 577 30.7 DSL3 416 649 233 15.3 644 3.5 DSL4 378 572 194 22.4 578 32.5 aThe data were determined in monomer state. bThe QYs of DSL2 and DSL4 were determined by using rhodamine 6G as reference (φ = 0.98 in EtOH solution). The QYs of DSL1 and DSL3 were determined by using cresol purple as reference (φ = 0.58 in EtOH solution). cThe data were determined in the aggregate state. Improved fluorescence and imaging effects of DSL4 Compared with the low fluorescence of ICT1 and ICT2, DSL1-4 all showed stronger fluorescence in both organic solvent and aqueous solutions (Figure 4a), indicating the improved fluorescence of DSLs after integration. Having demonstrated the huge potential of DSL1 as a probe precursor, we then attempted to explore its advantages in biological applications. First, we tested the cytotoxicity of DSLs (Figure 4b) and observed the negligible cell viability changes after treating cells with different concentrations of DSLs, indicating the good biocompatibility of DSLs. Since DSLs emitted stronger fluorescence than ICTs in both organic solvent and aqueous solutions, strong fluorescence in cell imaging was observed in DSL-incubated cells while weak fluorescence was observed in ICT-incubated cells (Figures 4c and 4d). Relative fluorescence intensity statistics show that DSL1 and DSL4 are 19.5 and 10.2 times stronger than ICT1 and ICT2, respectively (Figures 4e and 4f). Besides, in liver tissue imaging, DSL1 showed deeper tissue penetration under the same concentration and brighter fluorescence under the same penetration depth in imaging of liver tissue than ICT1 (Figure 4g). These results have confirmed the improved fluorescence of DSLs over ICTs in high-contrast cell imaging as a result of our integration strategy. Figure 4 | Improved fluorescence and imaging effects of DSLs over ICTs. (a) Normalized fluorescence intensity of ICT1, ICT2, and DSLs in different solvents under the maximum absorbance. (b) Cell viability of HeLa cells treated with different concentrations of DSLs. (c) Confocal fluorescent images of ICT1 and DSL1,3 in HeLa cells. (d) Confocal fluorescent images of ICT2 and DSL2,4 in living cells. For ICT1, DSL1,3, λex = 488 nm, λem = 600–700 nm, for ICT2, DSL2,4, λex = 405 nm, λem = 500–600 nm. Scale bar = 20 μm. (e and f) Normalized fluorescence intensity in (c) and (d), respectively. (g) Depth fluorescence images of DSL1 and ICT1 in liver tissues. λex = 488 nm, λem = 600–700 nm. Scale bar: 100 μm. Download figure Download PowerPoint Based on the excellent imaging properties and photostability of DSL1 ( Supporting Information Figure S12), we chose DSL1 as a representative luminophore to further clarify the advantages of DSLs in bioimaging, by comparing them with classic monomer-dependent emission luminophores (Rh 6G) and aggregate-dependent emission luminophores (TPE1 and TPE2).25–28 As shown in Supporting Information Figure S13, DSL1-loaded cells showed stronger fluorescence than TPE1 and TPE2-loaded cells under the same concentrations, suggesting its better imaging effects. In addition, with the increased incubation concentrations of these luminophores, the fluorescence in Rh 6G-incubated cells (or tissues) showed a tendency of first increasing and subsequently decreasing, and sharply increasing only in high concentrations of TPE1-incubated cells or tissues ( Supporting Information Figure S14). This phenomenon may be attributed to the fact that the compromised fluorescence of Rh 6G in the aggregate state and TPE1 in the monomer state, respectively. Surprisingly, the fluorescence of DSL1-incubated cells and tissues showed concentration-dependent enhancement, which mainly because the emission that DSL1 showed was not affected by the molecular states. All these results demonstrate that DSLs have great potential in high-contrast bioimaging. Customization of an activatable fluorescent probe DPL-Gal for sensing and imaging of β-gal Next, to further verify the feasibility of DSL1 for probe customization, we applied it to design and synthesize an activatable fluorescent probe for high-reliable imaging of β-gal ( Supporting Information Scheme S2), which has been demonstrated as an important biomarker for cell senescence and primary ovarian cancers.29–34 And to extend the emission wavelength of DSL1, we introduced a chlorine atom into the structure of DSL1, whose photophysical properties are shown in Supporting Information Figure S15 and Table S3, and then synthesized the probe DSL-Gal (Figure 5a). First, we confirmed the response ability of DSL-Gal to β-gal in buffer solutio

Boosting efficiency of luminescent solar concentrators using ultra-bright carbon dots with large Stokes shift.

Abstract: Luminescent solar concentrators (LSCs) are able to collect sunlight from a large-area to generate electric power with a low cost, showing great potential in building-integrated photovoltaics. However, the low efficiency of large-area LSCs caused by the reabsorption losses is a critical issue that hampers their practical applications. In this work, we synthesized novel yellow emissive carbon dots (CDs) with a large Stokes shift of 193 nm, which exhibit nearly zero reabsorption. The quantum yield (QY) of the yellow emitting CDs is up to 61%. The yellow emitting CDs can be employed to fabricate high-performance large-area LSCs due to successful suppression of the reabsorption losses. The as-prepared LSCs are able to absorb 14% of the sunlight as the absorption of the CDs matches well with the sun's spectrum. The large-area LSC (10 × 10 cm2) with a laminated structure based on the yellow emitting CDs achieves an optical conversion efficiency (ηopt) of 4.56% and power conversion efficiency (ηPCE) of 4.1% under natural sunlight (45 mW cm-2), which are significantly higher than other previously reported works with similar sizes. Furthermore, the prepared high-performance LSCs show good stability. This method of synthesizing novel CDs for high-efficiency LSCs provides a useful platform for future study and practical application of LSCs.

Near-Infrared Fluorescent and Photoacoustic Dual-Mode Probe for Highly Sensitive and Selective Imaging of Cysteine In Vivo.

Abstract: Cysteine (Cys) plays an important role in many physiological activities of human beings. Various diseases are always accompanied by abnormal levels of Cys. A series of Cys-responsive probes were recently developed. However, most fluorescent probes have many disadvantages and exhibit poor in vivo imaging. Therefore, a near-infrared fluorescence (NIRF)/photoacoustic (PA) dual-mode probe with high selectivity and sensitivity (limit of detection = 10.6 nM) toward Cys was developed in this study. The new Probe I interacted with Cys to activate NIRF/PA signals, detecting Cys in vitro with a large emission wavelength (851 nm) and Stokes shift (191 nm), monitoring the occurrence of liver cancer in vivo. This work not only presented an effective NIRF/PA dual-mode dicyanoisophorone probe for the first time in the imaging of Cys but also provided a comprehensive and accurate tool for detecting different analytes and tumors in deeper tissues, which could be conducive to the early diagnosis of diseases.

Precursor Tailoring Enables Alkylammonium Tin Halide Perovskite Phosphors for Solid‐State Lighting

Abstract: Broadband emission with a large Stokes shift is of interest for applications in solid‐state lighting. Such emission is often achieved with self‐trapped excitons; however, in reduced‐dimensional perovskites, high‐performance self‐trapped emission has, until now, been widely observed only in lead‐based materials. Here, the synthesis in an air ambient of reduced‐dimensional Sn‐based perovskite phosphors R2 + xSnI4 + x [R = octylammonium (OTA), hexylammonium (HA) or butylammonium (BA)] is reported, an advance achieved by tailoring the synthesis of the Ruddlesden‐Popper 2D perovskites R2SnI4. The lead‐free R2 + xSnI4 + x phosphors have broadband self‐trapped emission with over 80% photoluminescence quantum yield (PLQY) and more than a 150 nm Stokes shift. White‐light‐emitting diodes (WLEDs) based on OTA2 + xSnI4 + x phosphors exhibit warm‐white emission (correlated color temperature = 2654K) suited to home lighting, and a CRI of 92, among the best for Pb‐free perovskite WLEDs reported to date.

Bioimaging of hypochlorous acid using a near-infrared fluorescent probe derived from rhodamine dye with a large Stokes shift

Abstract: Hypochlorous acid (HClO) is a bioactive molecule that bears an important function in various physiological and pathological processes such as cell signal transduction, pathogen invasion, and redox balance regulation. The near-infrared (NIR) fluorescent probe with a large Stokes shift for bioimaging of HClO is envisioned to outperform other fluorescence probes with following advantages: greater penetration depth, smaller overlap between emission and absorption spectra, and greater reduction in false results caused by the excitation light and the scattered light, aiming to achieve selective and sensitive bioimaging of HClO in vivo. Herein, a NIR fluorescent probe, TJM, was synthesized by modifying the structure of rhodamine dye to make it water soluble and biocompatible for living cells. Under being excited at 585 nm, TJM exhibits an emission peak at 730 nm with a large Stokes shift of 145 nm. TJM also provides a fast NIR fluorescent response to HClO with excellent selectivity, high sensitivity, and low detection limit (0.11 μM). The fluorescence intensity of TJM is triggered by HClO based on HClO-induced oxidization of dibenzoyl hydrazine to dibenzoyl diimide, allowing imaging of HClO in living cells, zebrafish, and different disease mice models. TJM has been demonstrated a suitable NIR probe for imaging endogenous HClO in biological systems.

Tuning Intramolecular Stacking of Rigid Heteroaromatic Compounds for High-Efficiency Deep-blue Through-Space Charge-Transfer Emission.

Abstract: A series of ultrapure-blue thermally activated delayed fluorescence (TADF) emitters featuring through-space charge transfer (TSCT) were constructed via close stacking between donor and acceptor in rigid heteroaromatic compounds. The obviously accelerated radiative transition of singlet excitons, the diminished vibrionic relaxation of ground and excited states, consequently the reduced Stokes shift and the narrow emission can be found. The corresponding organic light-emitting diodes (OLEDs) based on AC-BO realize the best performance among all deep-blue TSCT-TADF emitters with an external quantum efficiency (EQE max ) of 19.3%. Meanwhile, the OLEDs based on QAC-BO display an EQE max of 15.8%, which achieve the first high-efficiency ultrapure-blue TSCT-TADF material with an excellent Commission Internationale de L'Eclairage coordinate (CIE) of (0.145, 0.076) which perfectly match the ultrapure-blue requirements of CIE (0.14, 0.08) defined by the National Television System Committee.

Structural Reconstruction in Lead-Free Two-Dimensional Tin Iodide Perovskites Leading to High Quantum Yield Emission

Abstract: : We report a structural reconstruction-induced high photoluminescence quantum yield of 25% in colloidal two-dimensional tin iodide nanosheets that are synthesized by a hot-injection method. The as-synthesized red-colored nanosheets of octylammonium tin iodide perovskites at room temperature transform to white hexagonal nanosheets upon washing or exposure to light. This structural change increases the bandgap from 2.0 eV to 3.0 eV, inducing a large Stokes shift and a broadband emission. Further, a long photoluminescence lifetime of about 1 µs is measured for the nanosheets. Such long-lived broad and intense photoluminescence with large Stokes shift is anticipated to originate from tin iodide clusters that are formed during the structural reconstruction. Stereoactive 5s 2 lone pair of tin (II) ions perturbs the excited state geometry of the white hexagonal nanosheets and facilitates the formation of self-trapped excitons. Such broadband and intensely emitting metal halide nanosheets are promising for white light-emitting diodes.

Development of a NIR fluorescent probe for detection of cysteine and its application in bioimaging

Abstract: In this work, A new near-infrared (NIR) fluorescent probe NIR-L based on dicyanoisophorone was rationally designed, synthesized and characterized for the detection of cysteine (Cys). This probe exhibited highly selective and sensitive response to Cys over other analytes including amino acids, cations and anions under physiological conditions, which can be identified by naked eyes. It was found that the probe showed NIR fluorescence turn-on response at 714 nm toward Cys with a large Stokes shift of 174 nm and a very low detection limit of 28.6 nM. The results of 1 H NMR and DFT calculation further confirmed that the addition of Cys triggered a reaction between Cys and NIR-L , leading to the release of a NIR fluorescent dye NIR-OH . Moreover, NIR-L was successfully used to realize the in vivo Cys bioimaging in HeLa cells and mice. Significantly, the sensing system was applied in imaging of Cys in B16-F10 tumor-bearing mice. A new dicyanoisophorone-based near-infrared-emission fluorescent probe for detecting cysteine has been realized when excited at 540 nm. • Rational design of a dicyanoisophorone-based near-infrared fluorescent dye by modification with 2-aminothiophenol. • The probe exhibits fluorescence turn-on response at 714 nm toward Cys. • The probe possesses a large Stokes shift of 174 nm and a very low detection limit of 28.6 nM. • Good performance of probe in bioimaging.