Practice of green chemistry strategies in synthetic organic chemistry: a glimpse of our sincere efforts in green chemistry research

This feature article summarises our recent contributions (2019-2023) in designing and developing a handful of promising organic transformations for accessing several diversely functionalised biologically relevant organic scaffolds, following the green chemistry principles, particularly focusing on the application of low-energy visible light, electrochemistry, ball-milling, ultrasound, and catalyst- and additive-free synthetic strategies.

Xanthene, cyanine, oxazine and BODIPY: the four pillars of the fluorophore empire for super-resolution bioimaging

In the realm of biological research, the invention of super-resolution microscopy (SRM) has enabled the visualization of ultrafine sub-cellular structures and their functions in live cells at the nano-scale level, beyond the diffraction limit, which has opened up a new window for advanced biomedical studies to unravel the complex unknown details of physiological disorders at the sub-cellular level with unprecedented resolution and clarity. However, most of the SRM techniques are highly reliant on the personalized special photophysical features of the fluorophores. In recent times, there has been an unprecedented surge in the development of robust new fluorophore systems with personalized features for various super-resolution imaging techniques. To date, xanthene, cyanine, oxazine and BODIPY cores have been authoritatively utilized as the basic fluorophore units in most of the small-molecule-based organic fluorescent probe designing strategies for SRM owing to their excellent photophysical characteristics and easy synthetic acquiescence. Since the future of next-generation SRM studies will be decided by the availability of advanced fluorescent probes and these four fluorescent building blocks will play an important role in progressive new fluorophore design, there is an urgent need to review the recent advancements in designing fluorophores for different SRM methods based on these fluorescent dye cores. This review article not only includes a comprehensive discussion about the recent developments in designing fluorescent probes for various SRM techniques based on these four important fluorophore building blocks with special emphasis on their effective integration into live cell super-resolution bio-imaging applications but also critically evaluates the background of each of the fluorescent dye cores to highlight their merits and demerits towards developing newer fluorescent probes for SRM.

Optical substrates for drug-metabolizing enzymes: Recent advances and future perspectives

Drug-metabolizing enzymes (DMEs), a diverse group of enzymes responsible for the metabolic elimination of drugs and other xenobiotics, have been recognized as the critical determinants to drug safety and efficacy. Deciphering and understanding the key roles of individual DMEs in drug metabolism and toxicity, as well as characterizing the interactions of central DMEs with xenobiotics require reliable, practical and highly specific tools for sensing the activities of these enzymes in biological systems. In the last few decades, the scientists have developed a variety of optical substrates for sensing human DMEs, parts of them have been successfully used for studying target enzyme(s) in tissue preparations and living systems. Herein, molecular design principals and recent advances in the development and applications of optical substrates for human DMEs have been reviewed systematically. Furthermore, the challenges and future perspectives in this field are also highlighted. The presented information offers a group of practical approaches and imaging tools for sensing DMEs activities in complex biological systems, which strongly facilitates high-throughput screening the modulators of target DMEs and studies on drug/herb‒drug interactions, as well as promotes the fundamental researches for exploring the relevance of DMEs to human diseases and drug treatment outcomes.

Mild and Expeditious Synthesis of Sulfenyl Enaminones of l-α-Amino Esters and Aryl/Alkyl Amines through NCS-Mediated Sulfenylation

Sulfenylation or selenylation of enaminones of l-α-amino esters requires mild reaction conditions due to the presence of a racemization-prone chiral center and reactive side chains. An N-chlorosuccinimide (NCS)-mediated methodology has been developed for rapid sulfenylation of enaminones of l-α-amino esters and aryl/alkyl amines at room temperature in open air under metal-free conditions. Enaminones of l-α-amino esters bearing aliphatic, aromatic, and heterocyclic side chains react efficiently with diverse aryl/alkyl/heteroaryl thiols (R1SH) in the presence of NCS to afford a library of biologically important sulfenyl enaminones in good-to-excellent yields (71-90%). Under similar reaction conditions, the enaminones also react with benzeneselenol to produce selenyl enaminones in good yield (73-83%). The NCS-mediated pathway generates sulfenyl chloride (R1SCl) as an intermediate which leads to rapid sulfenylation of enaminones through cross-dehydrogenative coupling (CDC) under mild reaction conditions.

Access to diverse organosulfur compounds via arynes: a comprehensive review on Kobayashi's aryne precursor

Arynes are highly reactive transient intermediates having enormous applications in organic synthesis. In the last three decades aryne chemistry has shown incredible developments in carbon-carbon and carbon-heteroatom bond formation reactions. After the discovery of Kobayashi's protocol for the generation of aryne intermediates in a mild way, this field of chemistry witnessed rapid growth in synthetic organic chemistry. One aspect of development in this field involves C-S bond formation under mild conditions which has a tremendous scope for the synthesis of various important organosulfur building blocks.

Iridium(III) complexes with 1-phenylisoquinoline-4-carbonitrile units for efficient NIR organic light-emitting diodes

Achieving the high external quantum efficiency (EQE) of near-infrared (NIR) emission in iridium(III) complexes still remains a challenge owing to their unsteady excited states which easily decay to the ground states through the nonradiative pathways. Herein, three Ir(III) phosphors in which the cyclometalated ligand 1-phenylisoquinoline-4-carbonitrile (piq-CN) is functionalized with the cyano, tert-butyl, and dimethyl groups are developed (CN-CNIr, Bu-CNIr, and DM-CNIr, respectively). Three simple synthetic steps can afford this class of deep red to NIR Ir(III) emitters. The organic light-emitting diodes (OLEDs) based on Bu-CNIr and DM-CNIr attain the maximum EQEs of 7.1% and 7.2% with the emission peaks at 695 and 714 nm, respectively. This strategy using substituted piq-CN derivatives as the cyclometalated ligands can offer an effective approach to promote the radiative rate of NIR-emitting Ir(III) materials. An insight into how the electron-withdrawing and electron-donating substituents on ligands influence the optoelectronic properties of their Ir(III) complexes is also provided.

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Efficient NIR-emitting Ir(III) phosphors are attained via three synthetic steps

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Cyano and alkyl groups exert different effects on the properties of complexes

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NIR OLEDs exhibit a maximum EQE of 7.2% with an emission peak at 714 nm

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High current densities are recorded as peak EQEs are dropped to their half values

Visible Light-Driven and Singlet Oxygen-Mediated Photochemical Cross-Dehydrogenative C3-H Sulfenylation of 4-Hydroxycoumarins with Thiols Using Rose Bengal as a Photosensitizer

A visible light (white light-emitting diode/direct sunlight)-driven photochemical synthesis of a new series of biologically interesting 3-(alkyl/benzylthio)-4-hydroxy-2H-chromen-2-ones has been achieved through a cross-dehydrogenative C₃-H sulfenylation of 4-hydroxycoumarins with thiols at ambient temperature in the presence of rose bengal in acetonitrile under an oxygen atmosphere. The notable features of this newly developed method are mild reaction conditions, energy efficiency, metal-free synthesis, good to excellent yields, use of low-cost materials, and eco-friendliness.

Explorations into the Effect of meso-Substituents in Tricarbocyanine Dyes: A Path to Diverse Biomolecular Probes and Materials

Polymethine cyanine dyes have been widely recognized as promising chemical tools for a range of life science and biomedical applications, such as fluorescent staining of DNA and proteins in gel electrophoresis, fluorescence guided surgery, or as ratiometric probes for probing biochemical pathways. The photophysical properties of such dyes can be tuned through the synthetic modification of the conjugated backbone, for example, by altering aromatic cores or by varying the length of the conjugated polymethine chain. Alternative routes to shaping the absorption, emission, and photostability of dyes of this family are centered around the chemical modifications on the polymethine chain. This Minireview aims to discuss strategies for the introduction of substituents in the meso-position, their effect on the photophysical properties of these dyes and some structure-activity correlations which could help overcome common limitations in the state of the art in the synthesis.

Synthesis of a New Amino-Furopyridine-Based Compound as a Novel Fluorescent pH Sensor in Aqueous Solution

Development of new fluorescent molecules, especially pH-sensitive fluorescent dyes, is always in high demand due to their wide applications in various fields and the limited number of common chromophores. In this work, a family of 3-amino-N-phenylfuro[2,3-b]pyridine-2-carboxamides (AFP) was synthesized as novel fluorescent compounds. Besides fluorescence in an organic solvent, AFP 1 and AFP 2 exhibit good fluorescence properties in both acidic and basic aqueous solution, which could be explained by protonation or different conformations formed in solution. Density functional theory (DFT) calculations on the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) of various conformations were performed for further support.

Iodine/DMSO-Promoted Selective Direct Arylthiation of Anilines with Thiols under Metal-Free Conditions

An iodine-promoted divergent thiolation of unprotected anilines with thiols for the synthesis of sulfide anilines has been described. The combinational use of I₂ and DMSO played an important role to realize this kind of transformation without the aid of a metal catalyst and strong oxidants. The reaction selectivity was well controlled to provide mono-, bis-, and trisubstituted diaryl sulfide derivatives. More importantly, iodination and sulfenylation can occur simultaneously to provide useful multifunctionalized iodoaniline products. This method afforded an efficient protocol for the construct C-S and C-I bonds from the C-H bond under mild reaction conditions.

Novel near-infrared fluorescent probe with a large Stokes shift for sensing hypochlorous acid in mitochondria

Hypochlorous acid (HOCl) plays a crucial role in various physiological and pathological processes. However, it is still a challenge to design a xanthene-based near-infrared (NIR) fluorescent probe with a large Stokes shift for sensing HOCl. In this work, a novel mitochondria-targeted fluorescent probe, MXS, with a large Stokes shift based on a xanthene-hemicyanine dyad structure, has been successfully designed and synthesized for the specific detection of HOCl. Gratifyingly, the peak-to-peak Stokes shift of MXS was found to be 130 nm, which was obviously larger than those of conventional rhodamine dyes and most reported xanthene-based hypochlorous acid probes. As expected, MXS exhibited high selectivity, high sensitivity, and fast response time (30 s) for the detection of HOCl via a specific HOCl-promoted intramolecular charge transfer process. The detection limit of MXS for HOCl is calculated to be as low as 72 nM, enabling its use within the physiological concentration range of HOCl (5-25 μM). Importantly, MXS is able to permeate cell membranes and accumulate in the mitochondria, which is convenient for monitoring the variation of hypochlorous acid concentration in the mitochondria of living cells.

Sulfenylation of Arenes with Ethyl Arylsulfinates in Water

A tetrabutylammonium iodide-mediated direct sulfenylation of arenes with ethyl arylsulfinates in water was developed. Various electron-rich arenes and ethyl arylsulfinates were investigated in the reaction, and a series of aryl sulfides were obtained in excellent yields. The advantages of this green protocol were simple reaction conditions (metal-free, water as the solvent, and under air), odorless and easily available sulfur reagent, broad substrate scope, and gram-scale synthesis. Moreover, the potential application of aryl sulfides was exemplified by further transformations.

A molecular-logic gate for COX-2 and NAT based on conformational and structural changes: visualizing the progression of liver disease

Lighting up the relevant lesion boundaries during operations is vital for guiding the effective resection of hepatopathic tissue.

Lighting up the relevant lesion boundaries during operations is vital for guiding the effective resection of hepatopathic tissue. We envisioned that molecular-logic gates, which are known for their excellent digital correlation between input and output signals, could be used to facilitate differential visualization of lesion boundaries. Herein, a series of flexible molecules, naphthalene imide-indole derivatives (IAN) were prepared and evaluated as molecular-logic gates. The input and output signals of the IAN derivatives were successfully used to highlight different hepatopathic regions in order to facilitate boundary differentiation. The IAN derivatives produce different signals due to collaborative changes in the conformation and structure. The hepatopathy-related enzymes (COX-2 and NAT) were used to induce conformational and structural changes in IAN derivatives. Based on these enzyme induced synergistic effects, IAN can sensitively emit different coloured signals such as green, cyan and blue (output signals) as a function of the different input signals, i.e. the different activity of COX-2 and NAT in solution and living cells. Significantly, the IAN derivatives were successfully used to distinguish the boundaries of hepatopathic lesions in tissues after spraying with IAN derivatives (mild cirrhosis, severe cirrhosis, in addition to early and late hepatocellular carcinoma) under a hand held lamp at 365 nm by naked eye.

A near-infrared fluorescent probe based on a novel rectilinearly π-extended rhodamine derivative and its applications

A novel NIR fluorescent probe RQNA based on a π-extended rhodamine derivative RQN for the specific detection of mitochondrial Cu²⁺ has been synthesized.

Novel rhodamine dye with large Stokes shifts by fusing the 1,4-diethylpiperazine moiety and its applications in fast detection of Cu2+

Rhodamine dyes were widely developed for designing probes due to their excellent photophysical properties and biocompatibility. However, traditional rhodamine dyes still bear major drawbacks of short emission wavelengths (<600 nm) and narrow Stokes shifts (<30 nm), which limit their biological imaging applications. Herein, we reported a novel mitochondria-targeted fluorescent dye JRQ with near-infrared (NIR) emission wavelength and improved Stokes shift (63 nm) by tuning the donor–acceptor–donor (D–A–D) character of the rhodamine skeleton. As expected, JRQ exhibited multiple excellent properties and could accumulate in mitochondria, and can therefore be used as a signal reporter for the design of fluorescent probes by taking advantage of the fluorescence controlled mechanism of the ring opening and closing chemical processes of the spirolactone platform. By using JRQ as a precursor, a highly sensitive fluorescent probe JRQN for the fast detection of mitochondrial Cu²⁺ ions was synthesized based on the Cu²⁺-triggered specific hydrolysis mechanism because mitochondria are an important reservoir of intracellular Cu²⁺. We expect that the Stokes shift increase of rhodamine dyes via tuning the donor–acceptor–donor (D–A–D) character of the rhodamine skeleton will provide a novel synthetic approach for the development of rhodamine dyes and expansion of their applications.

A novel NIR rhodamine dye JRQ with large Stokes shift (70 nm) by fusing the 1,4-diethylpiperazine moiety in rhodamine dyes has been synthesized and utilized to design a probe.

Fluorogenic probes for disease-relevant enzymes

Traditional biochemical methods for enzyme detection are mainly based on antibody-based immunoassays, which lack the ability to monitor the spatiotemporal distribution and, in particular, the in situ activity of enzymes in live cells and in vivo. In this review, we comprehensively summarize recent progress that has been made in the development of small-molecule as well as material-based fluorogenic probes for sensitive detection of the activities of enzymes that are related to a number of human diseases. The principles utilized to design these probes as well as their applications are reviewed. Specific attention is given to fluorogenic probes that have been developed for analysis of the activities of enzymes including oxidases and reductases, those that act on biomacromolecules including DNAs, proteins/peptides/amino acids, carbohydrates and lipids, and those that are responsible for translational modifications. We envision that this review will serve as an ideal reference for practitioners as well as beginners in relevant research fields.

Creation of thio and selenocyanate derivatives of 4-quinolone via regioselective C–H bond functionalization under ambient conditions

An operationally simple C–SCN and C–SeCN bond formation technique to generate different SCN/SeCN substituted 4-quinolone derivatives using NH₄SCN/KSeCN in excellent yields was developed.

A fluorescent probe based on tetrahydro[5]helicene for highly selective recognition of hydrogen sulfide

Endogenous hydrogen sulfide plays an important role in various physiological and pathological processes and the convenient and selective recognition of hydrogen sulfide has become a research hotspot. We designed and synthesized a tetrahydro[5]helicene and 2,4-dinitrobenzene conjugate (HD-DNP) as an effective fluorescent probe for selective detection of H₂S. The selective deprotection of 2,4-dinitrophenyl ether group of HD-DNP by H₂S led to a dramatic fluorescent enhancement (101-fold) at 500 nm and colorimetric change in DMSO-PBS solution. HD-DNP displays many advantages including low background without any self-fluorescence, as well as high selectivity towards common bio-thiols such as Cysteine, Homocysteine and Glutathione. The detection limit of this probe for H₂S was found to be about 2.4 μM with a wide linear range (10-70 μM). The response mechanism of the probe with HS^- is confirmed to be thiolysis of the dinitrophenyl ether induced by HS^- through ¹H NMR comparison investigations.

Cytotoxic and N-Acetyltransferase Inhibitory Meroterpenoids from Ganoderma cochlear

Seven compounds, including two pairs of new meroterpenoids, (+)- and (−)-gancochlearol C (1), (+)- and (−)-cochlearoid Q (3), and a new meroterpenoid gancochlearol D (2), together with four known meroterpenoids were isolated from the aqueous EtOH extract of the fruiting bodies of Ganoderma cochlear. Their structures were determined by spectroscopic data. The isolated compounds were evaluated for their cytotoxic activity against three human lung cancer cells (H1975, PC9, A549) and N-acetyltransferase inhibitory property. The results show that (+)-gancochlearol C could inhibit N-acetyltransferase with an IC₅₀ value of 5.29 μM. In addition, ganomycin F was found to show moderate activity against the H1975 human lung cancer cell line, with an IC₅₀ value of 19.47 μM.

Fine tuning the emission wavelengths of the 7-hydroxy-1-indanone based nano-structure dyes: Near-infrared (NIR) dual emission generation with large stokes shifts

Near-infrared (NIR) fluorescent dyes have recently gained special attention due to their applications to use as molecular probes for imaging of biological targets and sensitive determination. In this study, photophysical properties of the 7-hydroxy-1-indanone based fluorophors A1, A2, A3, B1, B2 and 3R-B2 (R=CF₃, NH₂, NO₂ and OMe) in the gas and three solution phases were probed using TD-DFT method at PBE0/6-311++G(d,p) and M06-2X/6-311++G(d,p) levels of theory. In addition to structural and photophysical properties as well as ESIPT mechanism of all mentioned molecules, the FC and relaxed potential energy surfaces of B2 and 3R-B2 (R=CF₃ and NH₂) molecules were explored in gas phase and acetonitrile, cyclohexane and water solvents. It is predicted that the A1, A3 and 3R-B2 chromophores afford normal (615-670nm) and NIR fluorescence emissions (770-940nm; biological window) with the large Stokes shifts of >160 and >300nm, respectively. A good aggrement was found between theoretical and experimental results. In sum, these new types of dyes may render the new approaches for the development of the most efficient NIR fluorescent probes for enhanced image contrast and optimal apparent brightness in biological applications.

Direct thiolation of aza-heteroaromatic N-oxides with disulfides via copper-catalyzed regioselective C–H bond activation

A novel and efficient thiolation reaction of aza-heteroaromatic N-oxides with disulfides via copper catalyzed C–H activation has been developed.

In vivo imaging of leucine aminopeptidase activity in drug-induced liver injury and liver cancer via a near-infrared fluorescent probe

The liver, a main detoxification organ, has evolved a complex enzymatic system to respond to multiple pathological conditions, in which leucine aminopeptidase (LAP) has been reported to participate in detoxifying cisplatin in hepatoma cells and contribute to the intrinsic drug resistance. In vivo imaging of LAP activity in liver disease models is thus helpful to further understand the function of LAP in detoxification and medicine, but such an imaging approach is still lacking. Herein, we develop a selective and sensitive near-infrared fluorescent probe (HCAL) for this purpose. Using the probe, combined with confocal fluorescence imaging, we disclose the upregulations of LAP in acetaminophen-induced liver injury and tumor-bearing mice models. Supplementary acetylcysteine can suppress this upregulation, revealing that the LAP increase may be connected with a deficiency in biothiols. Moreover, HCAL has been used to image LAP in hepatoma cells, tumor tissues and xenograft tumor mice models successfully. These results demonstrate that HCAL may be a promising tool for studying the function of LAP in LAP-associated liver diseases.

A unique rectilinearly π-extended rhodamine dye with large Stokes shift and near-infrared fluorescence for bioimaging

A NIR rhodamine fluorophore, TJ730, with a large Stokes shift over 110 nm has been developed. Using the dye as a platform, we have prepared two novel NIR probes for the detection of Cu²⁺ as well as for cytoplasmic and lysosomal Cu²⁺ imaging in living cells.

Deep-red to near-infrared fluorescent dyes: Synthesis, photophysical properties, and application in cell imaging

More and more attention has been paid to the design of new fluorescent imaging agents with good photostability and water solubility, especially those with emissions in the deep-red and near-infrared regions. In this work, we designed and synthesized four novel fluorescent dyes with deep-red or NIR fluorescence by hybridizing coumarin and pyronin moieties based on our previous work. Introduction of carboxylic acid in the dyes not only imparted the dyes with water solubility but also provided a versatile sensing platform for designing the fluorescent probes and sensors of biomolecules. The photophysical properties of these new dyes were investigated through absorption and fluorescence spectroscopy. Cell imaging experiments showed that esterification products could selectively stain lysosomes with good photostability, thereby indicating that they could be useful in the development of fluorescent probes for bioimaging.

Synthesis and Characterization of Water-Soluble Conjugated Oligoelectrolytes for Near-Infrared Fluorescence Biological Imaging

Near-infrared (NIR) fluorophores attract increasing attention as a molecular marker (or probe) for in vivo and in vitro biological fluorescence imaging. Three types of new NIR fluorescent conjugated oligoelectrolytes (COEs: Q-FlTBTTFl, Q-FlBBTFl, and Q-FlTBBTTFl) are synthesized with quaternized ammonium ionic groups in their side-chains for water solubility. The emission wavelength is modulated in the range 600-1300 nm, by adjusting the intramolecular charge transfer in the molecular backbone based on the electron-rich fluorene (and/or thiophene) and electron-deficient benzo[2,1,3]thiadiazole (or benzo[1,2-c:4,5-c']bis[1,2,5]thiadiazole) moieties. The COEs show a remarkably larger Stokes shift (147-276 nm) compared to commercial rhodamine and cyanine dyes in water, avoiding self-quenching and interference from the excitation backscattered light. The photoluminescence (PL) quantum efficiency is improved substantially by up to 27.8% in water by fabricating a vesicular complex, COE/v, with a block ionomer, poly[(ethylene oxide)-block-(sodium 2-acrylamido-2-methyl-1-propanesulfonate)]. In vitro cellular uptake images with the COEs are obtained with good biocompatibility by confocal single-photon and two-photon microscopy. The ex vivo and in vivo images of a mouse xenograft model treated with the Q-FlBBTFl/v exhibit a substantially stronger fluorescence signal at the tumor site than at the other organs, highlighting the potential of the COE/v as an NIR fluorescent imaging agent for the diagnosis of cancer.

Single near-infrared fluorescent probe with high- and low-sensitivity sites for sensing different concentration ranges of biological thiols with distinct modes of fluorescence signals

We describe a unique approach for the development of an interesting type of the fluorescent probes, which can show different modes of fluorescence signals to distinct concentration ranges of a target of interest. The key points for the design of the new type of the fluorescent probes include the judicious selection of the dye platforms and the corresponding high- and low-sensitivity sites. It is known that the normal concentrations of biological thiols have significant biological functions. However, up- or down-regulated concentrations of thiols may induce several diseases. Therefore, it is highly important to monitor the changes of thiol concentrations in living systems. Based on the proposed strategy, we engineer the novel NIR fluorescent probe, CHMC-thiol, which remarkably can display a turn-on signal to the low concentration range of thiols and a ratiometric response to the high concentration range of thiols for the first time. We anticipate that the intriguing strategy formulated herein will be widely useful for the development of concentration range-dependent fluorescent probes.

A unique approach toward near-infrared fluorescent probes for bioimaging with remarkably enhanced contrast

Near-infrared (NIR) fluorescent probes are attractive molecular tools for bioimaging because of their low autofluorescence interference, deep tissue penetration, and minimal damage to sample. However, most previously reported NIR probes exhibit small Stokes shift, typically less than 30 nm, and low fluorescence quantum yield, strictly limited contrast and spatial resolution for bioimaging. Herein, by expanding the π-conjugated system of rhodamine B, while, at the same time, keeping its rigid and planar structure, we reported an efficient NIR dye, HN7, with large stokes shift of 73 nm and fluorescence quantum yield as high as 0.72 in ethanol, values superior to those of such traditional cyanine NIR dyes as Cy5. Using HN7, living cells, tissues and mice were imaged, and the results showed significantly enhanced contrast, improved spatial resolution, and satisfactory tissue imaging depth when compared to Cy5. Moreover, the nonfluorescent spirocyclic structure of rhodamine B is an inherent component of HN7; therefore, our strategy provided a universal platform for the design of efficient NIR turn-on bioimaging probes for various targets. As a proof-of-concept, two different NIR probes, HN7-N2 and HN7-S for NO and Hg²⁺, respectively, were designed, synthesized, and successfully applied for the imaging of NO and Hg²⁺ in living cells, tissues and mice, respectively, demonstrating the potential bioimaging applications of the new probes. In sum, this new type of dye may present new avenues for the development of efficient NIR fluorescent probes for contrast-enhanced imaging in biological applications.

Near-infrared fluorescence of π-conjugation extended benzothiazole and its application for biothiol imaging in living cells

The fluorescence emission of benzothiazole derivatives (1–3) was efficiently tuned from green to red by elongation of π-conjugation, and a novel NIR fluorescent probe for biothiols was constructed which allows for imaging applications in living cells.

Long-wavelength analyte-sensitive luminescent probes and optical (bio)sensors

Long-wavelength luminescent probes and sensors become increasingly popular. They offer the advantage of lower levels of autofluorescence in most biological probes. Due to high penetration depth and low scattering of red and NIR light such probes potentially enable in vivo measurements in tissues and some of them have already reached a high level of reliability required for such applications. This review focuses on the recent progress in development and application of long-wavelength analyte-sensitive probes which can operate both reversibly and irreversibly. Photophysical properties, sensing mechanisms, advantages and limitations of individual probes are discussed.

Design strategy for photoinduced electron transfer-based small-molecule fluorescent probes of biomacromolecules

As the cardinal support of innumerable biological processes, biomacromolecules such as proteins, nucleic acids and polysaccharides are of importance to living systems. The key to understanding biological processes is to realize the role of these biomacromolecules in thte localization, distribution, conformation and interaction with other molecules. With the current development and adaptation of fluorescent technologies in biomedical and pharmaceutical fields, the fluorescence imaging (FLI) approach of using small-molecule fluorescent probes is becoming an up-to-the-minute method for the detection and monitoring of these imperative biomolecules in life sciences. However, conventional small-molecule fluorescent probes may provide undesirable results because of their intrinsic deficiencies such as low signal-to-noise ratio (SNR) and false-positive errors. Recently, small-molecule fluorescent probes with a photoinduced electron transfer (PET) "on/off" switch for biomacromolecules have been thoroughly considered. When recognized by the biomacromolecules, these probes turn on/off the PET switch and change the fluorescence intensity to present a high SNR result. It should be emphasized that these PET-based fluorescent probes could be advantageous for understanding the pathogenesis of various diseases caused by abnormal expression of biomacromolecules. The discussion of this successful strategy involved in this review will be a valuable guide for the further development of new PET-based small-molecule fluorescent probes for biomacromolecules.

A simple and effective "capping" approach to readily tune the fluorescence of near-infrared cyanines

A simple and effective capping approach was introduced to readily tune the fluorescence of NIR cyanines.

Heptamethine cyanines are favorable for fluorescence imaging applications in biological systems owing to their near-infrared (NIR) absorption and emission. However, it is very difficult to quench the fluorescence of NIR dyes by the classic photoinduced electron transfer mechanism due to their relatively high-lying occupied molecular orbital energy levels. Herein, we present a simple and effective “capping” approach to readily tune the fluorescence of NIR cyanines. The resulting new functional NIR CyBX (X = O, N, or S) dyes not only retain the intact tricarbocyanine scaffold, but also have a built-in switch to regulate the fluorescence by spiro-cyclization. When compared to traditional cyanines, novel CyBX dyes have a superior character in that their NIR optical properties can be readily tuned by the intrinsic spiro-cyclization mechanism. We expect that this “capping” strategy can be extended across not only the visual spectrum but also to structurally distinct fluorophores.

Facile synthesis of a class of aminochromene–aniliniumion conjugated far-red to near-infrared fluorescent dyes for bioimaging

An innovative class of aminochromene–aniliniumion conjugated far-red to near-infrared dyes, namely ACA, was developed.

A near-infrared chemodosimeter with Pi-selective colorimetric and fluorescent sensing and its application in vivo imaging

A near-infrared colorimetric and fluorescent chemosensor for detecting phosphate ion (Pi) has been developed. The practical utility of this chemosensor was demonstrated by employing it to detect Pi in Paramecium and C. elegans.

Generation of ArS-substituted flavone derivatives using aryl thiols as sulfenylating agents

The regioselective and metal-free sulfenylation of flavones was achieved under aerobic conditions with ammonium iodide as an inducer.