A large stokes shift fluorescent probe for sensing of thiophenols based on imidazo[1,5-α]pyridine in both aqueous medium and living cells

Differential evaluation of sulfur oxides in the natural lake water samples by carbazole-furan fluorescent probe

Water bodies are frequently polluted, with sulfur oxides being the most common form of water pollution. Therefore, developing a detection mechanism for sulfur oxides in water bodies is particularly urgent. A new fluorescent probe YX-KZBD was designed and developed. This probe releases fluorescent signals with its own sulfurous acid recognition site, detects sulfurous acid based on the Michael addition reaction, and evaluates the pollution degree of sulfur oxides in the water environment through the transformation mode of the sulfur cycle. This probe has high energy transfer efficiency in aqueous solutions. In addition, the fluorescence data obtained by analyzing the water samples were linearly fitted with the gene abundance values of the functional genes of sulfur-producing bacteria, and a significant correlation was obtained. The Kriging interpolation model was used to evaluate the sulfate content distribution at each sampling point to understand the distribution of sulfur oxides in natural water intuitively. The fluorescence signal excited by the probe was also combined with a real-time quantitative polymerase chain reaction (qPCR), and sulfate-reducing and sulfur-oxidizing bacteria were introduced in the sulfur cycle, providing a new method to assess the extent of water pollution effectively.

A novel 2-(2-aminophenyl) imidazo [1,5-a] pyridine-based fluorescent probe for rapid detection of phosgene

Phosgene is a highly concealed and highly toxic gas that seriously threatens human health and public security. Therefore, the detection of phosgene is of great significance to world security. Herein, a new type of fluorescent probe based on 2-(2-aminophenyl) imidazo [1,5-a] pyridine is reported for the rapid detection of phosgene. The probe itself only emits a faint green fluorescence, while phosgene allows it to produce a strong blue fluorescence. During the recognition process, phosgene interacts simultaneously with both amino site and imidazole moiety in the probe molecule, resulting in a four-ring-fused rigid structure with high fluorescence quantum yield. The probe not only has the characteristics of high efficiency, high sensitivity (detection limit 2.68 nM), and high selectivity, but also has remarkable spectral changes. Finally, a portable test strip is used to detect phosgene in the gas phase, and the fluorescent color change of the test strip can be easily observed. The most exciting thing is that the portable test strip with the probe PMPY-NH2 can produce a strong fluorescence response to 1 ppm of phosgene, which is far lower than the level of phosgene that seriously threatens to human health.

Applications of Pyrrole and Pyridine-based Heterocycles in Cancer Diagnosis and Treatment

BACKGROUND

The escalation of cancer worldwide is one of the major causes of economy burden and loss of human resources. According to the American Cancer Society, there will be 1,958,310 new cancer cases and 609,820 projected cancer deaths in 2023 in the United States. It is projected that by 2040, the burden of global cancer is expected to rise to 29.5 million per year, causing a death toll of 16.4 million. The hemostasis regulation by cellular protein synthesis and their targeted degradation is required for normal cell growth. The imbalance in hemostasis causes unbridled growth in cells and results in cancer. The DNA of cells needs to be targeted by chemotherapeutic agents for cancer treatment, but at the same time, their efficacy and toxicity also need to be considered for successful treatment.

OBJECTIVE

The objective of this study is to review the published work on pyrrole and pyridine, which have been prominent in the diagnosis and possess anticancer activity, to obtain some novel lead molecules of improved cancer therapeutic.

METHODS

A literature search was carried out using different search engines, like Sci-finder, Elsevier, ScienceDirect, RSC etc., for small molecules based on pyrrole and pyridine helpful in diagnosis and inducing apoptosis in cancer cells. The research findings on the application of these compounds from 2018-2023 were reviewed on a variety of cell lines, such as breast cancer, liver cancer, epithelial cancer, etc. Results: In this review, the published small molecules, pyrrole and pyridine and their derivatives, which have roles in the diagnosis and treatment of cancers, were discussed to provide some insight into the structural features responsible for diagnosis and treatment. The analogues with the chromeno-furo-pyridine skeleton showed the highest anticancer activity against breast cancer. The compound 5-amino-N-(1-(pyridin-4- yl)ethylidene)-1H-pyrazole-4-carbohydrazides was highly potent against HEPG2 cancer cell. Redaporfin is used for the treatment of cholangiocarcinoma, biliary tract cancer, cisplatin-resistant head and neck squamous cell carcinoma, and pigmentation melanoma, and it is in clinical trials for phase II. These structural features present a high potential for designing novel anticancer agents for diagnosis and drug development.

CONCLUSION

Therefore, the N- and C-substituted pyrrole and pyridine-based novel privileged small Nheterocyclic scaffolds are potential molecules used in the diagnosis and treatment of cancer. This review discusses the reports on the synthesis of such molecules during 2018-2023. The review mainly discusses various diagnostic techniques for cancer, which employ pyrrole and pyridine heterocyclic scaffolds. Furthermore, the anticancer activity of N- and C-substituted pyrrole and pyridine-based scaffolds has been described, which works against different cancer cell lines, such as MCF-7, A549, A2780, HepG2, MDA-MB-231, K562, HT- 29, Caco-2 cells, Hela, Huh-7, WSU-DLCL2, HCT-116, HBL-100, H23, HCC827, SKOV3, etc. This review will help the researchers to obtain a critical insight into the structural aspects of pyrrole and pyridine-based scaffolds useful in cancer diagnosis as well as treatment and design pathways to develop novel drugs in the future.

ESIPT-based fluorescent enhanced probes prompted by methylated β-cyclodextrin for the detection of thiophenols

Thiophenol and its derivatives are compounds with high toxicity to organisms and environmental pollution, so it is necessary to detect the level of thiophenols in the environment and biological samples. The probes 1a-b were obtained by introducing the 2,4-dinitrophenyl ether group into diethylcoumarin-salicylaldehyde based compounds. And they can form host-guest compounds with methylated β-cyclodextrin (M-β-CD), the association constants of inclusion complexes are 49.2 M-1, 125 M-1 respectively. The fluorescence intensities of probes 1a-b at 600 nm (1a) and 670 nm (1b) increased significantly in thiophenols detection. Meanwhile, with the addition of M-β-CD, the hydrophobic cavity of M-β-CD significantly increased the fluorescence intensity of probes 1a-b, thus the detection limits of probes 1a-b to thiophenols were reduced from 410 nM, 365 nM to 62 nM, 33 nM respectively. Whereas, the good selectivity and short response time of probes 1a-b towards thiophenols was not affected in the presence of M-β-CD. Moreover, probes 1a-b were used for further water sample detection and HeLa cell imaging experiments due to their good response to thiophenols and the results suggested that probes 1a-b had the potential to detect the content of thiophenols in water samples and living cells.

An imidazo[1,5-α]pyridines-based ratiometric fluorescent probe for sensing sulfur dioxide derivatives in real samples based on a FRET mechanism

A novel fluorescence resonance energy transfer (FRET)-based ratiometric emission fluorescent probe AT was designed and developed in which the imidazo[1,5-α]pyridine was served as a FRET donor and tricyanofuran (TCF) as the FRET acceptor to detect SO₃^2-/HSO₃^- based on the Michael addition reaction. Probe AT had a high energy transfer efficiency (95%) and a large pseudo-Stokes shift (259 nm) in EtOH/PBS buffer (5/5, v/v). It also possessed good selectivity and quick response to SO₃^2-/HSO₃^-. There was good linearity between the ratio of fluorescence intensity (F₄₉₉/F₆₄₅) and the concentrations of SO₃^2-/HSO₃^- in the ranges of 1.5-7.5 μM and 9-20 μM, with calculated detection limits (LOD) of 55 nM. In addition, the probe could also detect the concentrations of SO₃^2-/HSO₃^- in real samples such as environmental water and sugar, allowing the probe to be used in a variety of applications.

Surface Filtration in Mesoporous Au Films Decorated by Ag Nanoparticles for Solving SERS Sensing Small Molecules in Living Cells

For surface-enhanced Raman spectroscopy (SERS) sensing of small molecules in the presence of living cells, biofouling and blocking of plasmonic centers are key challenges. Here, we have developed a mesoporous Au (AuM) film coated with a Ag nanoparticles (NPs) as a plasmonic sensor (AuM@Ag) to analyze aromatic thiols, which is an example of a small molecule, in the presence of a living cell strain (e.g., MDA-MB-231) as a model living system. The resulting AuM@Ag provides 0.1 nM sensitivity and high reproducibility for thiols sensing. Simultaneously, the AuM@Ag film filters large biomolecules, preventing Raman signals from overlapping produced by large biomolecules. After analysis, the AuM@Ag film undergoes recycling by the full dissolution of the Ag-thiol layer and removal of thiols from AuM. Furthermore, fresh AgNPs are formed for further SERS analysis, which circumvents the Ag oxidation issue. The ease of the AgNPs deposition allows up to 12 cycles of on-demand recycling and sensing even after utilization as a sensor in multicomponent media without enhancement and sensitivity loss. The reported mesoporous film with surface filtering ability and prominent recycling procedure promises to offer a new strategy for the detection of various small molecules in the presence of living cells.

A novel dibenzo[a,c]phenazine-based fluorescent probe for fast and selective detection of thiophenols in environmental water

A new dibenzo[a,c]phenazine-based fluorescent probe exhibits high selectivity and sensitivity towards thiophenols in environmental water.

Rational design of a new near-infrared fluorophore and apply to the detection and imaging study of cysteine and thiophenol

The development of a near-infrared fluorophore with excellent fluorescence performance, a large Stokes shift, and good biocompatibility has become a focus in the field of fluorescence imaging in recent years. Based on quantum chemistry calculations and reasonable molecular design strategies, a new NIR fluorophore was developed and characterized by simple synthesis, easy structural modification, and a large Stokes shift (105 nm). Furthermore, two new "activatable" fluorescent probes QN-Cys and QN-DNP were synthesized using a simple structural modification. The probe QN-Cys can recognize Cys with high sensitivity (LOD = 128 nM) and high selectivity, and its fluorescence intensity has a good linear relationship with the Cys concentration in the range of 5-35 μM. Furthermore, probe QN-Cys can effectively distinguish Cys from Hcy and GSH, and was successfully applied to the detection and imaging of Cys in human serum, cells, and zebrafish. The probe QN-DNP showed a good specific and sensitive (LOD = 78 nM) fluorescence response to thiophenol, and its fluorescence intensity has a good linear relationship with the thiophenol concentration in the range of 5-30 μM. Furthermore, it was successfully applied to detect thiophenol in real water samples with good recoveries (97-102%), and image thiophenol in living cells, zebrafish and mice. Notebly, the QN-DNP probe could be applied to visualize the distribution of thiophenol in the mice.

Nanomolar determination of nitrofurans in water via excited-state inter-ligand proton transfer

Qualification and quantification of trace organic contaminants necessitates development of highly efficient sensing system, where excited-state inter-ligand proton transfer (ESILPT) provides a feasible pathway to construct efficient chemo-sensors. Herein, a strategically synthesized lanthanide complex, Eu(DBM)₃(MeOH)₃ (briefly as Eu-DBM-MeOH; DBM = dibenzoylmethane), features two-step ESILPT processes, along with modification on molecular structure and energy band. As a result, Eu-DBM-MeOH exhibits excellent photophysical properties with characteristic luminescence of Eu³⁺ ion. Benefiting from these merits, the Eu-DBM-MeOH complex acts as ultra-sensitive chemo-sensor toward nanomolar-level nitrofuran antibiotics (nitrofurazone and nitrofurantoin) in water, by disrupting ESILPT processes. Combining the advantages on photophysical property and luminescent sensitivity, ESILPT-active compounds are expected to widen and deepen the research on complex-based luminophores, being potentially useful in trace detection and biological imaging.

Driving the Emission Towards Blue by Controlling the HOMO-LUMO Energy Gap in BF2 -Functionalized 2-(Imidazo[1,5-a]pyridin-3-yl)phenols

Several boron compounds with 2-(imidazo[1,5-a]pyridin-3-yl)phenols, differentiated by the nature of the substituent (R) in the para position of the hydroxy group, have been synthesized and thoroughly characterized both in solution (1 H, 13 C, 11 B, 19 F NMR) and in the solid state (X-ray). All derivatives displayed attractive photophysical properties like very high Stokes shift, high fluorescence quantum yields and a good photostability in solution. Time-Dependent Density Functional Theory (TD-DFT) calculations allowed to define the main electronic transitions as intra ligand transitions (1 ILT), which was corroborated by the Natural Transition Orbitals (NTOs) shapes. The HOMO-LUMO energy gap was correlated to the electronic properties of the substituent R on the phenolic ring, as quantified by its σp Hammett constant.

A Phenothiazine-HPQ Based Fluorescent Probe with a Large Stokes Shift for Sensing Biothiols in Living Systems

Due to the redox properties closely related to numerous physiological and pathological processes, biothiols, including cysteine (Cys), homocysteine (Hcy) and glutathione (GSH), have received considerable attention in biological science. On account of the important physiological roles of these biothiols, it is of profound significance to develop sensitive and selective detection of biothiols to understand their biological profiles. In this work, we reported an efficient fluorescent probe, PHPQ-SH, for detecting biothiols in vitro and vivo, based on the phenothiazine-HPQ skeleton, with DNBS (2,4-dinitrobenzenesulfonate) as the response unit. Probe PHPQ-SH exhibited brilliant sensing performances toward thiols, including a large Stokes shift (138 nm), excellent sensitivity (for GSH, LOD = 18.3 nM), remarkable fluorescence enhancement (163-fold), low cytotoxicity, rapid response (8 min), and extraordinary selectivity. Finally, the probe PHPQ-SH illustrated herein was capable of responding and visualizing biothiols in MCF-7 cells and zebrafish.

Fluorescent probes based on nucleophilic aromatic substitution reactions for reactive sulfur and selenium species: Recent progress, applications, and design strategies

Reactive sulfur species (RSS) and reactive selenium species (RSeS) are important substances for the maintenance of physiological balance. Imbalance of RSS and RSeS is closely related to a series of human diseases, so it is considered to be an important biomarker in early diagnosis, treatment, and stage monitoring. Fast and accurate quantitative analysis of different RSS and RSeS in complex biological systems may promote the development of personalized diagnosis and treatment in the future. One way to explore the physiological function of various types of RSS and RSeS in vivo is to detect them at the molecular level, and one of the most effective methods for this is to use fluorescent probes. Nucleophilic aromatic substitution (SNAr) reactions are commonly exploited as a detection mechanism for RSS and RSeS in fluorescent probes. In this review, we cover recent progress in fluorescent probes for RSS and RSeS based on SNAr reactions, and discuss their response mechanisms, properties, and applications. Benzenesulfonate, phenyl-O ether, phenyl-S ether, phenyl-Se ether, 7-nitro-2,1,3-benzoxadiazole (NBD), benzoate, and selenium-nitrogen bonds are all good detection groups. Moreover, based on an integration of different reports, we propose the design and synthesis of RSS- and RSeS-selective probes based on SNAr reactions, current challenges, and future research directions, considering the selection of active sites, the effect of substituents on the benzene ring, and the introduction of other functional groups.

A new long-wavelength emission fluorescent probe for imaging biothiols with remarkable Stokes shift

By using BPMOH as the fluorophore and 2, 4-dinitrobenzenesulfonate moiety as the recognition site for thiols, a new long-wavelength emission (645 nm) fluorescent probe BPMSH with large Stokes shift (133 nm) was designed and synthesized. Probe BPMSH exhibited almost no fluorescence emission because of the PET process. When adding thiols, BPMSH could be quickly converted into BPMOH emitting a significant red fluorescence at 645 nm. In addition, BPMSH displayed high selectivity toward thiols among various biologically related analytes. Probe BPMSH has been applied to exogenous and endogenous thiols detection and imaging in living MCF-7 cells and MGC-803 cells. Most importantly, this probe BPMSH was successfully utilized for imaging thiols in zebrafish.

A dicyanoisophorone-based highly sensitive and selective near-infrared fluorescent probe for sensing thiophenol in water samples and living cells

Thiophenol (PhSH) is an important sulfhydryl compound in organic synthesis, but it is also a volatile environmental pollutant with high toxicity to organisms. Herein, we reported a novel near-infrared (NIR) probe (1) for turn-on fluorescence detection of PhSH. The probe was prepared by coupling 2,4-dinitrophenyl (DNP) to a dicyanoisophorone-based fluorophore (2). PhSH can specifically perform a nucleophilic aromatic substitution on probe 1 and result in the release of fluorophore 2, thus achieving a turn-on fluorescence response (λ_em = 693 nm). A dramatic color change from red (λ_abs = 525 nm) to blue (λ_abs = 668 nm) was also observed. This fluorescent assay displayed a large Stokes shift (∼133 nm) and a high sensitivity for PhSH, as well as a low detection limit (34 nM). Moreover, probe 1 was successfully applied to monitor PhSH in real water samples and image PhSH in living cells.

Merocyanine-based turn-on fluorescent probe for the sensitive and selective determination of thiophenols via a pKa shift mechanism

The development of fluorescent probes for the sensitive and selective determination of highly toxic thiophenols is considerably important in the fields of biological and environmental sciences. Herein, a turn-on fluorescent probe for thiophenol, named MCSH, was constructed based on a pK_a shift mechanism, employing merocyanine dye as the fluorophore and 2,-4-dinitrobenzenesulfonamide (DNBS) group as the recognition unit. The imine nitrogen of MCSH has a pK_a value of 4.12, which renders its non-fluorescent Schiff base form exclusively under neutral conditions. However, after reacting with thiophenols, its DNBS group was removed to afford a merocyanine dye as the final product, whose pK_a value upshifts to 8.11, and was present mainly as the fluorescent protonated Schiff base form under neutral media. Such drastic change in pK_a values leads to a significant fluorescence enhancement and can be utilized for the detection of thiophenols. The fluorescence intensity at 627 nm increases linearly with thiophenol concentration in the range of 0.2-3 μM with a detection limit of 15 nM (S/N = 3). MCSH displays high selectivity for the detection of thiophenols over a wide range of other analytes, including aliphatic thiols. Furthermore, the preliminary applications of MCSH for monitoring thiophenols in living cells and environmental have been carried out.

Design of a facile fluorescent probe with a large Stokes shift for hydrogen peroxide imaging in vitro and in vivo

By modifying 4'‑hydroxybiphenyl‑4‑carbonitrile (BPN-OH) with 2‑(4‑(bromo‑methyl)phenyl)‑4,4,5,5‑tetramethyl‑1,3,2‑dioxaborolane group, a facile fluorescent probe, BPN-TOB, for sensitively tracing H₂O₂ was designed and synthesized. BPN-TOB displayed a low detection limit (67 nM), fast response time (10 min), low cytotoxicity, a mega Stokes shift (170 nm) and a remarkable fluorescence enhancement (72-fold) in the detection of H₂O₂. Additionally, probe BPN-TOB could monitor exogenous and endogenous H₂O₂ in living MGC-803 cells (human gastric cancer cells) and RAW264.7 cells (leukemia cellsin mouse macrophage). In particular, this probe BPN-TOB was successfully utilized for imaging H₂O₂ in zebrafish.

Simple NIR-Emitting ESIPT Fluorescent Probe for Thiophenol with a Remarkable Stokes Shift and Its Application

Thiophenol as a highly toxic compound can harm the environment and living organisms and thus demands effective detection. In this work, we presented a near-infrared fluorescent probe (DAPH-DNP) for detecting thiophenol according to the ESIPT mechanism using 2,4-dinitrophenyl group as a recognition unit. This probe displayed specificity toward thiophenol over other related analytes. Meanwhile, there was good linearity between the relative fluorescence intensity of DAPH-DNP and the concentration of thiophenol in the range of 0-80 μM. This probe also showed a low detection limit of 3.8 × 10^-8 and a marked Stokes shift (192 nm). Further, this probe could be used for monitoring thiophenol in environmental water samples and imaging thiophenol in living cells, which indicated that this probe had a real application in the environment and living organisms.

An imidazo[1,5-α]pyridine-derivated fluorescence sensor for rapid and selective detection of sulfite

Sulfur-containing species are essential in the composition and the metabolism of the organisms, thus developing a full set of implements to cover all of them is still a favorable choice. Herein, we chose imidazo [1,5-α]pyridine moiety as the basic fluorophore for the detection of sulfite, and preliminarily completed the toolset since biothiols (GSH, Cys, Hcy), H₂S, and PhSH could be detected by sensors based on the same backbone. The designed sensor, IPD-SFT, with structural novelty and large Stokes shift (130 nm), indicated the most attractive advantages of remarkably rapid response period (within 1 min) and high selectivity for sulfite from all the sulfur-containing species. Other practical properties included high sensitivity (LOD = 50 nM) and wide pH adaptability (5.0-11.0). Furthermore, IPD-SFT could monitor both exogenous and endogenous sulfite. It not only raised a potential tool for sulfite detection, but also preliminarily completed the toolset for all the sulfur-containing species. The development of such toolsets might reveal the sulfur-containing metabolism and corresponding physiology and pathological procedures.

Phenothiazine-based fluorescence probe for ratiometric imaging of hydrazine in living cells with remarkable Stokes shift

By modifying the 10-butyl-2-methoxy-10H-phenothiazine-3-carbaldehyde with malonontrile group, a new fluorescent sensor PBM for selective detection of hydrazine in ratiometric mode has been developed. Probe PBM owned the advantages of quick response (10 min), remarkable Stokes shift (168 nm for PBM, 161 nm for PBM-NH₂), excellent selectivity, high sensitivity (detection limit of 63.2 nM was obtained from in vitro experiment), profound ratiometric change (82-fold) and low cytotoxicity in response to hydrazine. Additionally, it could be utilized to monitor hydrazine in gas state with various concentrations through vivid color changes and imaged hydrazine in living MCF-7 cells with excellent performance.

Imidazo[1,5-α]pyridine-based fluorescent probe with a large Stokes shift for specific recognition of sulfite

By taking advantage of the intramolecular charge transfer (ICT) process, we presented a novel fluorescent probe IPY-SO₂ based on imidazo[1,5-α]pyridine derivative for detecting SO₃^2- with a low detection limit (70 nM). Combining its favorable turn-on fluorescence feature (75-fold), rapid response (5 min), high selectivity, large Stokes shift (174 nm) and low cytotoxicity, IPY-SO₂ was successfully applied to imaging SO₃² in living MCF-7 cells and zebrafish.

Recent Progress in the Development of Fluorescent Probes for Thiophenol

Thiophenol (PhSH) belongs to a class of highly reactive and toxic aromatic thiols with widespread applications in the chemical industry for preparing pesticides, polymers, and pharmaceuticals. In this review, we comprehensively summarize recent progress in the development of fluorescent probes for detecting and imaging PhSH. These probes are classified according to recognition moieties and are detailed on the basis of their structures and sensing performances. In addition, prospects for future research are also discussed.

Recognition of Thiols in Living Cells and Zebrafish Using an Imidazo[1,5-α]pyridine-Derivative Indicator

A new cyan fluorescent probe, MIPY-DNBS, using an imidazo[1,5-α]pyridine derivative as the fluorophore and 2,4-dinitrobenzensufonate as the recognition site for the selective detection of thiols (Cys, GSH, and Hcy), was designed and synthesized. Probe MIPY-DNBS exhibited a 172 nm Stokes shift, a fast response time (400 s), low cytotoxicity, low detection limits (12.7 nM for Cys), and excellent selectively in the detection of thiols. In addition, MIPY-DNBS was successfully applied to imaging thiols in living MCF-7 cells and zebrafish.

A new turn-on fluorescent probe with ultra-large fluorescence enhancement for detection of hydrogen polysulfides based on dual quenching strategy

Based on dual quenching strategy (ESIPT inhibited quenching and PET quenching), we have developed a new turn-on fluorescent probe 1. Combining 3-(benzo[d]thiazol-2-yl)-10-butyl-10H-phenothiazin-2-ol (dye 2) as the fluorophore and 2-fluoro-5-nitro-benzoic as the recognition moiety, probe 1 had feature of notable large Stokes shift, highly sensitivity and selective for monitoring H₂S_n with remarkable fluorescence enhancement (328-fold) response at 534 nm. Probe 1 exhibited excellent performance in the quantitative detection of H₂S_n with a 137 nm Stokes shift and a low detection limit of 26 nM in solution. Finally, probe 1 was successfully utilized to image H₂S_n in living A549 cells and zebrafish.

A Green-emitting Fluorescent Probe Based on a Benzothiazole Derivative for Imaging Biothiols in Living Cells

A new green-emitting fluorescent probe 1 was developed for biothiol detection. The sensing mechanism was considered to be biothiol-induced cleavage of the 2,4-dinitrobenzene- sulfonate group in probe 1 and resulting inhibition of the probe’s photoinduced electron transfer (PET) process. Probe 1 exhibited favorable properties such as excellent selectivity, highly sensitive (0.12 µM), large Stokes shift (117 nm) and a remarkable turn-on fluorescence signal (148-fold). Furthermore, confocal fluorescence imaging indicated that probe 1 was membrane-permeable and suitable for visualization of biothiols in living A549 cells.

An AcOH-mediated metal free approach towards the synthesis of bis-carbolines and imidazopyridoindole derivatives and assessment of their photophysical properties

A concise, atom-economical and environmentally sustainable tandem strategy has been formulated to access highly fluorescent (Φ_F up to 40%) target molecules via the formation of three C–N bonds in a single operation.

The construction of an effective far-red fluorescent and colorimetric platform containing a merocyanine core for the specific and visual detection of thiophenol in both aqueous medium and living cells

Thiophenol is toxic to the environment and biological systems although it is an indispensable material for chemical products.

Highly sensitive fluorescent probe based on a novel phenothiazine dye for detection of thiophenols in real water samples and living cells

Based on an excited-state intramolecular proton transfer (ESIPT) fluorophore, a novel fluorescent off-on probe for detection of thiophenols was designed and synthesized. This probe (λ_ex = 401 nm, λ_em = 527 nm) displayed high specificity for sensing thiophenols over other biologically related species. Besides, this probe possessed capabilities of monitoring thiophenols with rapid response rate (3 min), a large Stokes shift (126 nm), and high sensitivity (2.7 nM). The sensing mechanism was considered to be that thiophenols triggered thiolysis of the probe and the ESIPT fluorophore was released, as confirmed by means of HPLC and HRMS. Most notably, this probe was successfully applied to monitor levels of thiophenols in realistic samples and MDA-MB-231 cells. Graphical abstract A novel phenothiazine-based fluorescent probe was developed for sensitively sensing thiophenols in both aqueous medium and living cells.

A rapid and selective fluorescent probe with a large Stokes shift for the detection of hydrogen sulfide

We have successfully developed a new green-emitting H₂S fluorescence probe employing a 2,4-dinitrophenyl ether moiety as the sensing group based on 3'-formyl-4'-hydroxybiphenyl-4-carbonitrile. This probe displayed a rapid (2 min), sensitive (the detection limit was 0.18 μM) and selective with a large Stokes shift (183 nm) in response to H₂S, which was beneficial for fluorescence sensing and cell imaging studies. Moreover, this probe can qualitatively and quantitatively detect H₂S with a good linearity (R² = 0.9991). Importantly, this probe had been used for the detection of H₂S in living MDA-MB-231 cells with good performance.

A highly sensitive fluorescent probe based on the Michael addition mechanism with a large Stokes shift for cellular thiols imaging

A novel fluorescent probe IPY-MAL for thiols was developed based on imidazo[1,5-α]pyridine derivative, which was decorated with a maleimide group. The probe IPY-MAL showed a rapid response (30 s), high sensitivity and selectivity for thiols with a large Stokes shift (140 nm), which was triggered by the Michael addition reaction of thiols toward the C=C double bond of the maleimide group. Moreover, this probe IPY-MAL could quantitatively detect the concentrations of thiols ranging from 0 to 50 μM, and the detection limit was found to be as low as 28 nM. Cell imaging results indicated that the probe IPY-MAL could detect and visualize thiols in the living cells. Graphical abstract A novel imidazo[1,5-α]pyridine-based fluorescent probe was developed for sensitively monitoring and imaging thiols in living A549 cells with a large Stokes shift.

Synthesis of imidazo[1,5-a]pyridines via I2-mediated sp3 C–H amination

A transition-metal-free sp³ C–H amination reaction has been developed employing molecular iodine for imidazo[1,5-a]pyridine synthesis.