Fluorescent indicators based on BODIPY

BODIPY based Metal-Organic Macrocycles and Frameworks: Recent Therapeutic Developments

Boron dipyrromethene, commonly known as BODIPY, based metal-organic macrocycles (MOCs) and metal-organic frameworks (MOFs) represent an interesting part of materials due to their versatile tunability of structure and functionality as well as significant physicochemical properties, thus broadening their applications in various scientific domains, especially in biomedical sciences. With increasing concern over the efficacy of cancer drugs versus quality of patient's life dilemma, scientists have been trying to fabricate novel comprehensive therapeutic strategies along with the discovery of novel safer drugs where research with BODIPY metal complexes has shown vital advancements. In this review, we have exclusively examined the articles involving studies related to light harvesting and photophysical properties of BODIPY based MOCs and MOFs, synthesized through self-assembly process, with a special focus on biomolecular interaction and its importance in anti-cancer drug research. In the end, we also emphasized the possible practical challenges involved during the synthetic process, based on our experience on dealing with BODIPY molecules and steps to overcome them along with their future potentials. This review will significantly help our fellow research groups, especially the budding researchers, to quickly and comprehensively get the near to wholesome picture of BODIPY based MOCs and MOFs and their present status in anti-cancer drug discovery.

Recent advances in fluorescent probes for lipid droplets

Lipid droplets (LDs) have been known as a non-negligible cellular organelle for lipid storage and metabolism. Fluorescent probes for imaging LDs would be paramount for depicting their functions in cells. Although commercially available Nile Red and BODIPY^tm 493/503 have been widely used for labelling LDs, they exhibit unsatisfactory specificity and spectroscopic properties. This feature article reviews the recent advances in organic fluorescent probes for imaging LDs. We first introduce the key points for probe design, including regulating hydrophobicity and enhancing fluorescence quantum yield in LDs. Then, we summarize the structural features and biological applications of some representative LD probes classified by their frameworks. In addition, the current challenges and future research trends for the fluorescent probes of LDs are discussed as well.

New BODIPY Dyes Based on Benzoxazole as Photosensitizers in Radical Polymerization of Acrylate Monomers

A series of 2-phenacylbenzoxazole difluoroboranes named BODIPY dyes (1-8) was designed and applied as photosensitizers (PS) for radical photopolymerization of acrylate monomer. The light absorption within the ultraviolet-visible (UV-Vis) range (λ_max = 350-410 nm; ε_max = 23,000-42,500 M^-1cm^-1), that is strongly influenced by the substituents on the C3 and C4 atoms of phenyl ring, matched the emission of the Omnicure S2000 light within 320-500 nm. The photosensitizer possess fluorescence quantum yield from about 0.005 to 0.99. The 2-phenacylbenzoxazole difluoroboranes, together with borate salt (Bor), iodonium salt (Iod) or pyridinium salt (Pyr) acting as co-initiators, can generate active radicals upon the irradiation with a High Pressure Mercury Lamp which initiates a high-performance UV-Vis light-induced radical polymerization at 320-500 nm. The polymers obtained are characterized by strong photoluminescence. It was found that the type of radical generator (co-initiator) has a significant effect on the kinetic of radical polymerization of acrylate monomer. Moreover, the chemical structure of the BODIPY dyes does not influence the photoinitiating ability of the photoinitiator. The concentration of the photoinitiating system affects the photoinitiating performance. These 2-phenacylbenzoxazole difluoroborane-based photoinitiating systems have promising applications in UV-Vis-light induced polymerization.

Mitochondria-targeted and FRET-based fluorescent probe for the imaging of endogenous SO2 in living cells

Sulfur dioxide (SO₂) is an important signal molecule in living systems, and plays a wide range of physiological functions. Real-time and in situ detection of the dynamic balance of SO₂ in mitochondria is of great significance to in-depth study its biological roles. Herein, we have developed a mitochondria-targeted fluorescent probe Nap-L based on the FRET mechanism to detect SO₂ in living cells. The probe Nap-L employed naphthalimide and positively charged benzopyridine as the donor and acceptor in the FRET system, and emitted green and red fluorescence under excitation. In respond to SO₂, the nucleophilic addition of bisulfite to benzopyridine and then interrupted the FRET process from naphthalimide to benzopyridine fluorophore, thereby triggering an obvious change in the fluorescence ratio. The probe Nap-L showed high selectivity to SO₂ over the biothiols (Hcy, GSH, Cys) and other biologically related species. Biological experiments suggested that the probe Nap-L mainly distributed in mitochondria, and can be successfully used to detect mitochondrial endogenous SO₂ in living cells.

Photoactivatable Fluorescent Tags for Dual-Modality Positron Emission Tomography Optical Imaging

Fluorescent protein conjugates are vital tools in a wide range of scientific disciplines from basic biochemical research to applications in clinical pathology and intraoperative surgery. We report the synthesis and characterization of photoactivatable fluorophores (PhotoTags) based on the functionalization of coumarin, fluorescein, BODIPY, rhodamine B, and cyanine dyes with a photochemically active aryl azide group. Photochemical labeling experiments using human serum albumin produced fluorescent proteins in high yields under irradiation with ultraviolet light for <15 min. We also synthesized DFO-RhodB-PEG₃-ArN₃─a photoactivatable compound that can be radiolabeled with ⁸⁹Zr for applications in optical imaging and positron emission tomography. One-pot ⁸⁹Zr-radiolabeling and light-induced protein conjugation produced [⁸⁹Zr]ZrDFO-RhodB-PEG₃-azepin-trastuzumab. Proof-of-concept studies in vitro and in vivo confirmed that [⁸⁹Zr]ZrDFO-RhodB-PEG₃-azepin-trastuzumab is a potential dual-modality agent for detecting human epidermal growth factor receptor 2 (HER2/neu) expression. Overall, the PhotoTag technology represents a rapid, synthetically versatile, and user-friendly approach for generating novel protein conjugates.

Red-Shift (2-Hydroxyphenyl)-Benzothiazole Emission by Mimicking the Excited-State Intramolecular Proton Transfer Effect

Novel strategies to optimize the photophysical properties of organic fluorophores are of great significance to the design of imaging probes to interrogate biology. While the 2-(2-hydroxyphenyl)-benzothiazole (HBT) fluorophore has attracted considerable attention in the field of fluorescence imaging, its short emission in the blue region and low quantum yield restrict its wide application. Herein, by mimicking the excited-state intramolecular proton transfer (ESIPT) effect, we designed a series of 2-(2-hydroxyphenyl)-benzothiazole (HBT) derivatives by complexing the heteroatoms therein with a boron atom to enhance the chance of the tautomerized keto-like resonance form. This strategy significantly red-shifted the emission wavelengths of HBT, greatly enhanced its quantum yields, and caused little effect on molecular size. Typically, compounds 12B and 13B were observed to emit in the near-infrared region, making them among the smallest organic structures with emission above 650 nm.

Applications of triarylborane materials in cell imaging and sensing of bio-relevant molecules such as DNA, RNA, and proteins

Triarylboranes have been known for more than 100 years and have found potential applications in various fields such as anion sensors and optoelectronics, for example in organic light emitting diodes (OLEDs), field effect transistors (OFETs), and organic photovoltaic devices. However, biological applications, such as bioimaging agents and biomolecule sensors have evolved much more recently. This review summarises progress in this relatively young field and highlights the potential of triarylboranes in biological applications.

Near-infared upper phenyl-fused BODIPY as photosensitizer for photothermal-photodynamic therapy

BODIPY scaffolds by introducing ring-fused segment promoted bathochromic-shift spectrum and enhanced intersystem crossing capability by a twisted structure. In this work, we designed the upper phenyl-fused BODIPY with 4-dimethylaminostyryl groups...

Design and synthesis of stable four-coordinated benzotriazole-borane with tunable fluorescence emission

A new class of stable four-coordinated benzotriazole-borane compounds was developed via gold-catalyzed alkyne hydroboration. The application of polymeric (BH₂CN)_n reagent gave the formation of cyano-amine-boranes (CAB) complexes with less basic N-heterocyclic amines and anilines. Various new CABs were investigated in catalytic hydroboration to synthesize N–B cycles. The 1,2,3-benzotriazoles were identified as the only feasible N-source, giving the four coordinated borane N–B cycles (BTAB) in excellent yields (up to 90%) with good functional group tolerability. This new class of polycyclic N–B compounds showed excellent stability toward acid, base, high temperature, and photo-irradiation. The facile synthesis, excellent stability, strong and tunable fluorescence emission make BTAB interesting new fluorescent probes for future chemical and biological applications.

A new class of benzotriazole-boranes was developed via gold-catalyzed alkyne hydroboration. The facile synthesis, excellent stability, strong and tunable fluorescence emission make BTAB new fluorescent probes for chemical and biological applications.

Synthesis and photophysical properties of novel oxadiazole substituted BODIPY fluorophores

Using 3-phenyl-5-(5-phenyl-1H-pyrrol-3-yl)-1,2,4-oxadiazole, BODIPYs with the oxadiazole groups at the 1,7-positions were prepared and their photophysical properties were characterized.

Recent advances in zig-zag-fused BODIPYs

Recent progress in the synthesis of zig-zag-fused BODIPY, structure–property relationships, as well as their applications are summarized.

A Boron Dipyrromethene Chiral-at-Boron and Carbon with a Bent Geometry: Synthesis, Resolution and Chiroptical Properties

We report a boron dipyrromethene chiral-at-boron and carbon (B*C*-BODIPY) accessible through a two-pot, one-step synthesis—an interrupted Knoevenagel condensation. The ECD spectra of chiral HPLC resolved enantiomers show clear Cotton effects...

Tracking Labile Copper Fluctuation In Vivo/Ex Vivo: Design and Application of a Ratiometric Near-Infrared Fluorophore Derived from 4-Aminostyrene-Conjugated Boron Dipyrromethene

Specimen differences, tissue-dependent background fluorescence and scattering, and deviated specimen position and sensor concentration make optical imaging for labile copper fluctuation in animals questionable, and a signal comparison between specimens is infeasible. We proposed ratiometric optical imaging as an alternative to overcome these disadvantages, and a near-infrared (NIR) ratiometric sensor, BDPS1, was devised therefore by conjugating boron dipyrromethene (BODIPY) with 4-aminostyrene and modifying the 4-amino group as a Cu+ chelator. BDPS1 possessed an excitation ratiometric copper-sensing ability to show the ratio of NIR emission (710 nm) upon excitation at 600 nm to that at 660 nm, Fex600/Fex660, increasing from 2.8 to 10.7. This sensor displayed still the opposite copper response of its internal charge transfer (ICT; 670 nm) and local (581 nm) emission bands. Ratiometric imaging with this sensor disclosed a higher labile copper region near the nucleus apparatus, and HEK-293T cells were more sensitive to copper incubation than MCF-7 cells. Dual excitation ratiometric imaging with this sensor realized tracking of labile copper fluctuation in mice, and the whole-body imaging found that tail intravenous injection of CUTX-101, a therapeutical agent for Menkes disease, led to a distinct labile copper increase in the upper belly. The ex vivo imaging of the resected viscera of mice revealed that CUTX-101 injection enhanced the labile copper level in the liver, intestine, lung, and gall bladder in sequence, yet the kidney, heart, and spleen showed almost no response. This study indicated that modifying BODIPY as an extended ICT fluorophore, with its electron-donating group being derived as a metal chelator, is an effective design rationale of NIR ratiometric sensors for copper tracking in vivo/ex vivo.

Syntheses and Investigations of Conformationally Restricted, Linker-Free α-Amino Acid-BODIPYs via Boron Functionalization

A series of α-amino acid-BODIPY derivatives were synthesized using commercially available N-Boc-l-amino acids, via boron functionalization under mild conditions. The mono-linear, mono-spiro, and di-amino acid-BODIPY derivatives were obtained using an excess of basic (histidine, lysine, and arginine), acidic (aspartic acid), polar (tyrosine, serine), and nonpolar (methionine) amino acid residues, in yields that ranged from 37 to 66%. The conformationally restricted mono-spiro- and di-amino acid-BODIPYs display strong absorptions in the visible spectral region with high molar extinction coefficients and significantly enhanced fluorescence quantum yields compared with the parent BF₂-BODIPY. Cellular uptake and cytotoxicity studies using the human HEp2 cell line show that both the presence of an N,O-bidentate spiro-ring and basic amino acids (His and Arg) increase cytotoxicity and enhance cellular uptake. Among the series of BODIPYs tested, the spiro-Arg- and spiro-His-BODIPYs were found to be the most cytotoxic (IC₅₀ ∼ 22 μM), while the spiro-His-BODIPY was the most efficiently internalized, localizing preferentially in the cell lysosomes, ER, and mitochondria.

Comparison Between Binuclear and Mononuclear Ru(II) Complexes: Synthesis, Structure, Photophysics, and Oxygen Sensing Performance

Owing to their attractive potential in optoelectronic application, luminescent Ru(II) complexes with diamine ligands are harvesting more and more research efforts. These literature efforts, however, are mostly mononuclear ones, with no detailed discussion on the performance comparison between mononuclear and multinuclear Ru(II) complexes. This work synthesized three diamine ligands having two or multiple chelating sites in each ligand, as well as their Ru(II) complexes. The single-crystal structure, electronic structure, and photophysical parameters of these Ru(II) complexes were analyzed and compared. It was found that multinuclear Ru(II) complexes had a pure MLCT (metal-to-ligand charge transfer)–based emissive center, showing longer emission lifetime and higher emission quantum yield, which were desired for oxygen sensing. Then, the oxygen sensing performance of these mononuclear and multinuclear Ru(II) complexes was systematically compared by doping them into polymer fibers via electrospinning method. Improved oxygen sensing performance was observed from binuclear Ru(II)-doped nanofibrous samples, compared with the sensing performance of mononuclear ones, including higher sensitivity, shorter response/recovery time, and better photostability. The causation was attributed to the fact that the emissive state of multinuclear Ru(II) complexes was MLCT-based ones and thus more sensitive to O₂ quenching than monocular Ru(II) complexes whose emissive state was a mixture of MLCT and LLCT (ligand-to-ligand charge transfer). In addition, a multinuclear Ru(II) complex had multiple emissive/sensing components, so that its sensing collision probability with O₂ was increased, showing better photostability and shorter response/recovery time. The novelty of this work was the linear oxygen sensing curve, which was rarely reported in the previous work.

Identification of diverse lipid-binding modes in the groove of zinc α2 glycoprotein reveals its functional versatility

ZAG is a multifunctional glycoprotein with a class I MHC-like protein fold and an α1-α2 lipid-binding groove. The intrinsic ZAG ligand is unknown. Our previous studies showed that ZAG binds the dansylated C₁₁ fatty acid, DAUDA, differently to the boron dipyrromethane C₁₆ fatty acid, C₁₆ -BODIPY. Here, the molecular basis for this difference was elucidated. Multi-wavelength analytical ultracentrifugation confirmed that DAUDA and C₁₆ -BODIPY individually bind to ZAG and compete for the same binding site. Molecular docking of lipid-binding in the structurally related Cluster of differentiation 1 proteins predicted nine conserved ligand contact residues in ZAG. Twelve mutants were accordingly created by alanine scanning site directed mutagenesis for characterisation. Mutation of Y12 caused ZAG to misfold. Mutation of K147, R157 and A158 abrogated C₁₆ -BODIPY but not DAUDA binding. L69 and T169 increased the fluorescence emission intensity of C₁₆ -BODIPY but not of DAUDA compared to wild-type ZAG and showed that C₁₆ -BODIPY binds close to T169 and L69. Distance measurements of the crystal structure revealed K147 forms a salt bridge with D83. A range of bioactive bulky lipids including phospholipids and sphingolipids displaced DAUDA from the ZAG binding site but unexpectedly did not displace C₁₆ -BODIPY. We conclude that the ZAG α1-α2 groove contains separate but overlapping sites for DAUDA and C₁₆ -BODIPY and is involved in binding to a bulkier and wider repertoire of lipids than previously reported. This work suggested that the in vivo activity of ZAG may be dictated by its lipid ligand.

Orthogonally aligned cyclic BODIPY arrays with long-lived triplet excited states as efficient heavy-atom-free photosensitizers

In photosensitizers, long triplet excited state lifetimes are key to their efficient electron transfer or energy transfer processes. Herein, we report a novel class of cyclic trimeric BODIPY arrays which were efficiently generated from easily accessible meso-mesityldipyrrinone and arylboronic acids in one pot. Arylboronic acid, for the first time, was used to provide a boron source for BODIPY derivatives. Due to the well-defined and orthogonally aligned BODIPY cores as verified by X-ray crystallography, these BODIPY arrays show strong exciton coupling effects and efficient intersystem crossings, and are novel heavy-atom-free photosensitizers with a long-lived triplet excited state (lifetime up to 257.5 μs) and good reactive oxygen species generation efficiency (up to 0.72) contributed by both 1O2 and O2 -˙ under light irradiation.

On bio-MOF materials doped with phosphorescent iridium complexes for molecular oxygen determination: Synthesis, characterization and performance

In this paper, two phosphorescent Ir(III) complexes, Ir(ppy)₂(Ln), were synthesized using 2-phenyl pyridine (ppy) as the first (major) ligand and two phosphorous compounds (L1 and L2) as the auxiliary ligand. Their single crystal structure and electronic structure were discussed. Ir(ppy)₂(Ln) complexes were doped into a supporting matrix of bio-MOF-1 via cationic exchange to ensure their uniform distribution. Their successful doping was confirmed by SEM, fluorescence microscopy image, XRD, N₂ adsorption/desorption and ICP measurement. Their photophysical parameters, including absorption spectra, excitation spectra, emission spectra, emission lifetime and quantum yield, were discussed in detail. Their phosphorescent emission was confirmed by density functional theory and emission lifetime, making them applicable for oxygen sensing. Linear working curves were observed for both composite samples, showing sensitivity as high as 23.65 with response/recovery time of 9/22 s. Humidity effect on sensing performance was limited. These parameters were found superior to literature ones based on phosphorescent Cu(I), RE(III), Ru(II) and Re(I) complexes. The sensing mechanism was revealed as a dynamic collision between Ir(ppy)₂(Ln) and O₂ molecules. The novelty of this work was the combination of phosphorescent Ir(III) complexes with porous bio-MOF-1, resulting in greatly improved sensitivity and linear sensing with short response time.

A luminescent boron difluoride derivative of the YELLOW 101 dye

Inspired on the outstanding behavior of the BODIPY dye, a new fluorescent boron fluoride derivative of the classical 2,2'-dihydroxy-1,1'-naphtalazine or YELLOW 101 dye has been synthesized and investigated in this work. Analogously to YELLOW 101 (λ_emission = 510 nm), the new species, here denoted BYELLOW 101, exhibits strong fluorescence around 570 and 535 nm in the solid form and in organic solvents, respectively. The observed red shift of the luminescence emission can be explored in the superparamagnetic fluorescent materials employed in MPI (magnetic particle inspection) technology, decreasing the influence of the FRET mechanism, - a critical limitation in this type of system. BYELLOW 101 is stable in solid form, but in organic solvents, it hydrolyses very slowly regenerating the initial dye, keeping the fluorescence emission but exhibiting a small blue shift along the time.

Introduction to aggregation induced emission (AIE) materials

Idea of introducing aggregation-induced emission (AIE) fundamentally altered the scientific community's perception of classical photophysical processes. Many exciting new possibilities have been coming into light due to the emergence of AIE, such as ability of rapid detection and in analyzing variety of bioactive substances required to monitor the complexed biological processes. This also became a handy tool in elucidating the essential physiological and pathological behaviors of organisms. AIE luminogens (AIEgens) are luminous substances that are either weakly or non-emissive in organic solvents or hydrophobic environment alone, but it gives strong emissive when aggregated along with transforming polarities upon aggregation. Owing to the their outstanding advantages such as rapid turn on/off of high brightness emission, big Stokes shift, excellent photostability, and strong biocompatibility AIEgens have become first choice among bio-inspired probes in biomedicine. In the view of providing basic information on AIE, this chapter give a brief overview of aggregation-caused quenching (ACQ) phenomenon, approaches to transform ACQ to AIE phenomenon, photo-physics of AIE phenomenon, followed by known and reportedly novel AIE active molecules and their biomedical applications.

Impact of the Arylation of Fused N-bridged BODIPY Dyes in Photophysical Properties

Functionalization of BODIPY dyes is commonly used to modulate photophysical properties. Among the chemical modification of these dyes, ring fusion indifferent faces of dipyrromethene cores is gaining attention in the literature, due to the modulation of emission/absorption properties and fluorophores with increased bright. N-bridged arylated BODIPYs were recently synthesized and shows intense bright and blu shifted emission. However, few examples of substituted compounds are described and none involving arylation with extention of the π-conjugation. In this manuscript, it is shown an optimized method for the synthesis of N-bridged arylated BODIPYs, including arylated derivatives, and the studies of molecular properties. It is also shown that fluorinated aryl substituted N-bridged arylated BODIPYs show high quantum yields and are red-shifted compared to unsubstituted examples. The work open opportunities for application of the new developed compounds as probes.

Double pH-sensitive nanotheranostics of polypeptide nanoparticle encapsulated BODIPY with both NIR activated fluorescence and enhanced photodynamic therapy

To achieve accurate fluorescence imaging-guided cancer therapy, intelligent systems with specific responsiveness to the tumor microenvironment need to be designed. Here, we have achieved both enhanced NIR fluorescence and photodynamic therapy by introducing a dimethylamino functional group in BODIPY dyes, which can be used as a pH sensor under acidic conditions by coordinating with the proton. At pH 7.4, the fluorescence is quenched due to the photo-induced electron transfer (PET) process. After the photosensitizer is protonated in tumor cell lysosomes (pH 4.0-5.5), the PET process is inhibited and the fluorophore emission capacity is restored (fluorescence enhancement up to 10-fold), resulting in near-infrared fluorescence with the OFF/ON transition inside the tumor and enhanced singlet oxygen production for lysosome targeting capability. Due to the substitution of heavy atom iodine, the compound has a high singlet oxygen quantum yield of 81.8% in dichloromethane. In addition, using a pH-sensitive amphiphilic polypeptide (POEGMA₂₃-PE₉) as a carrier to wrap the photosensitizer BDPI can release enough drug in the acidic environment (pH 5.5-6.5) of intracellular endosomes/lysosomes, which is conducive to more adequate interactions of the photosensitizer with H⁺ and more effective enhancement of fluorescence emission and ¹O₂ production, achieving precise fluorescence imaging capability and extremely low background toxicity.

Planar hexaphyrin-like macrocycles turning into bis-BODIPYs with box-shaped structures exhibiting excitonic coupling

Planar carbazole based hexaphyrin-like macrocycles with bis-coordinating cores and box-shaped cyclic BODIPYs were synthesized. Solution and solid-state structure analysis of the free macrocycles indicates an inversion of two pyrrole rings, resulting in a two-dipyrrin-like environment. The BF₂ complexes show large Stokes shifts and exhibit excitonic coupling, fine-tuned by the meso-substituents.

BODIPY derivatives as fluorescent reporters of molecular activities in living cells

Fluorescent compounds have become indispensable tools for imaging molecular activities in the living cell. 4,4-Difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) is currently one of the most popular fluorescent reporters due to its unique photophysical properties. This review provides a general survey and presents a summary of recent advances in the development of new BODIPY-based cellular biomarkers and biosensors. The review starts with the consideration of the properties of BODIPY derivatives required for their application as cellular reporters. Then review provides examples of the design of sensors for different biologically important molecules, ions, membrane potential, temperature and viscosity defining the live cell status. Special attention is payed to BODPY-based phototransformable reporters.

The bibliography includes 339 references.

Cytotoxicity of Amino-BODIPY Modulated via Conjugation with 2-Phenyl-3-Hydroxy-4(1H)-Quinolinones

The combination of cytotoxic amino-BODIPY dye and 2-phenyl-3-hydroxy-4(1H)-quinolinone (3-HQ) derivatives into one molecule gave rise to selective activity against lymphoblastic or myeloid leukemia and the simultaneous disappearance of the cytotoxicity against normal cells. Both species' conjugation can be realized via a disulfide linker cleavable in the presence of glutathione characteristic for cancer cells. The cleavage liberating the free amino-BODIPY dye and 3-HQ derivative can be monitored by ratiometric fluorescence or by the OFF-ON effect of the amino-BODIPY dye. A similar cytotoxic activity is observed when the amino-BODIPY dye and 3-HQ derivative are connected through a non-cleavable maleimide linker. The work reports the synthesis of several conjugates, the study of their cleavage inside cells, and cytotoxic screening.

Small molecule based fluorescent chemosensors for imaging the microenvironment within specific cellular regions

The microenvironment (local environment), including viscosity, temperature, polarity, hypoxia, and acidic-basic status (pH), plays indispensable roles in cellular processes. Significantly, organelles require an appropriate microenvironment to perform their specific physiological functions, and disruption of the microenvironmental homeostasis could lead to malfunctions of organelles, resulting in disorder and disease development. Consequently, monitoring the microenvironment within specific organelles is vital to understand organelle-related physiopathology. Over the past few years, many fluorescent probes have been developed to help reveal variations in the microenvironment within specific cellular regions. Given that a comprehensive understanding of the microenvironment in a particular cellular region is of great significance for further exploration of life events, a thorough summary of this topic is urgently required. However, there has not been a comprehensive and critical review published recently on small-molecule fluorescent chemosensors for the cellular microenvironment. With this review, we summarize the recent progress since 2015 towards small-molecule based fluorescent probes for imaging the microenvironment within specific cellular regions, including the mitochondria, lysosomes, lipid drops, endoplasmic reticulum, golgi, nucleus, cytoplasmic matrix and cell membrane. Further classifications at the suborganelle level, according to detection of microenvironmental factors by probes, including polarity, viscosity, temperature, pH and hypoxia, are presented. Notably, in each category, design principles, chemical synthesis, recognition mechanism, fluorescent signals, and bio-imaging applications are summarized and compared. In addition, the limitations of the current microenvironment-sensitive probes are analyzed and the prospects for future developments are outlined. In a nutshell, this review comprehensively summarizes and highlights recent progress towards small molecule based fluorescent probes for sensing and imaging the microenvironment within specific cellular regions since 2015. We anticipate that this summary will facilitate a deeper understanding of the topic and encourage research directed towards the development of probes for the detection of cellular microenvironments.

BODIPY-peptide conjugate: Synthesis, photo-physical and cell viability studies

The synthesis and biological studies of BODIPY-GPR peptide conjugate (BD-2) are reported. As compared to the parent BODIPY (BD-1), the peptide linked BD-2showed blue shifted absorption and emission with excellent Stokes shift of 201 nm. Molecular docking studies on EGFR protein kinase indicated very efficient binding affinity of BD-2 as compared to the standard drug (Erlotinib). The cell viability experiments of BD-2on normal (HEK293T) and lung cancer (A549) cell lines indicated 85–95% viability. Bioimaging studies showed that, BD-2was able to penetrate the lung cancer cell line.

Halogen-Bonding Strapped Porphyrin BODIPY Rotaxanes for Dual Optical and Electrochemical Anion Sensing

Anion receptors employing two distinct sensory mechanisms are rare. Herein, we report the first examples of halogen-bonding porphyrin BODIPY [2]rotaxanes capable of both fluorescent and redox electrochemical sensing of anions. 1 H NMR, UV/visible and electrochemical studies revealed rotaxane axle triazole group coordination to the zinc(II) metalloporphyrin-containing macrocycle component, serves to preorganise the rotaxane binding cavity and dramatically enhances anion binding affinities. Mechanically bonded, integrated-axle BODIPY and macrocycle strapped metalloporphyrin motifs enable the anion recognition event to be sensed by the significant quenching of the BODIPY fluorophore and cathodic perturbations of the metalloporphyrin P/P+. redox couple.

Mechanochemical Synthesis of Organic Dyes and Fluorophores

The syntheses of dyes and fluorophores have significant commercial importance. In recent years, mechanochemistry has emerged as a green and sustainable alternative for the synthesis of conventional dyes, new fluorophores, and also synthetic modification of known dyes for their use as chemosensors. The dyestuffs based on BODIPYs, rhodamine, fluorescein, perylenedimides, coumarins, benzothiazoles, etc. were synthesized or derivatized by grinding or milling. The synopsis aims to pay key attention to their synthesis and the applications as chemosensors will be briefly covered.

Synthesis and Spectroscopic Properties of 1,2,3-Triazole BOPAHY Dyes and Their Water-Soluble Triazolium Salts

Water-soluble BOPAHY fluorophores have not yet been reported. The potential of 1,2,3-triazolium salts for the formation of water-soluble chromophores is explored. 1,2,3-Triazole-substituted pyrroles were synthesized in a metal-free pathway and alkylated to obtain water-soluble 1,2,3-triazolium BOPAHY dyes. High fluorescence quantum yields were observed for triazole-bridged BOPAHY dyes in DCM and moderate fluorescence quantum yields for 1,2,3-triazolium-bridged BOPAHY chromophores in DCM and water. The fluorescence of the freely rotatable 1,2,3-triazolium-linked BOPAHYs is partially quenched in water.

Supramolecular BODIPY based dimers: synthesis, computational and spectroscopic studies

The synthetic procedures for the preparation of supramolecular BODIPY dimers decorated with complementary patterns able to induce the formation of a triple hydrogen bond through mutual interactions are here reported. The BODIPY and styryl-equipped BODIPY species have been suitably functionalized in meso position with 2,6-diacetamido-4-pyridyl and 1-butyl-6-uracyl moieties. Dimers and monomers have been subjected to computational and photophysical investigations in solvent media. Various peculiarities concerning the effects of the interaction geometry on the stability of the H-bonded systems have also been investigated. The combination of modelling and experimental data provides a paradigm for improving and refining the BODIPY synthetic pathway to have chromophoric architectures with a programmable supramolecular identity. Furthermore, the possibility of assembling dimers of different dyes through H-bonds could be appealing for a systematic investigation of the principal factors affecting the dynamics of the energy migration and possibly driving coherent transfer mechanisms. Our work highlights how the chemical versatility of these dyes can be exploited to design new BODIPY-based supramolecular architectures.