BODIPY-based probes for the fluorescence imaging of biomolecules in living cells

BODIPY-based small molecular probes for fluorescence and photoacoustic dual-modality imaging of superoxide anion in vivo

Superoxide anion contributes significantly in the pathological process of acute liver injury. Therefore, real-time in vivo imaging of superoxide anion is of great significance for understanding the pathogenesis. Nevertheless, developing superoxide anion probes that possess high sensitivity and resolution continues to be a challenge. Herein, we report the design of BODIPY-based molecule probes (BDPOS1-2) for fluorescence and photoacoustic dual-modality imaging of superoxide anion. The probes exhibited exceptional selectivity and specificity towards superoxide anion, with a "turn-on" photoacoustic and "turn-off" fluorescence response. They maintained good stability and demonstrated the response behavior to superoxide anion within the pH range of 5-10. BDPOS1-2 can be used for fluorescence imaging endogenous and exogenous superoxide anion in HepG2 cells with detection in the 670-750 nm channel. Notably, galactose-modified BDPOS2 demonstrated selective hepatocyte-targeting capability and achieved dual-modality imaging of superoxide anions during acute liver injury in live mice via capturing photoacoustic signals at 715 nm and fluorescence signals in the 650-690 nm channel. Our findings offer a powerful approach for high-sensitivity and high-resolution in vivo imaging, with considerable potential for early and precise diagnosis of liver injury.

NIR-II Photosensitizer-Based Nanoparticles Defunctionalizing Mitochondria to Overcome Tumor Self-Defense by Promoting Heat Shock Protein 40

Inherent self-defense pathways within malignant tumors include the action of heat shock proteins (HSPs) and often impede photothermal therapy efficacy. Interestingly, HSP40 inhibits glycolysis and disrupts mitochondrial function to overcome tumor self-defense mechanisms and exhibits a tumor-suppressive effect. Reactive oxygen species (ROS), especially hydroxyl radicals, generated by type-I photodynamic therapy inhibit adenosine triphosphate (ATP) production and lead to ATP-independent HSP40 overexpression during heat stress. However, the regulatory mechanisms linking heat and hydroxyl radicals to induce HSP40 expression remain unclear. Therefore, it is imperative to elucidate the underlying mechanism governing the induction of HSP40 expression during heat stress and explore its potential as a promising therapeutic strategy against tumor development. By strategically modifying the aza-BODIPY structure to precisely distribute the excited-state energy, we have demonstrated that HSP40 specific expression is correlated with the proportion of heat to hydroxyl radicals rather than their individual levels. This orchestrated NIR-II photosensitizer-based nanoparticles reduced tumor glycolysis and disrupted ATP production, driving cell apoptosis and amplifying the efficacy of photothermal therapy. Silencing and compensation of HSPs under heat and ROS stress represent a promising and effective strategy for overcoming tumor self-defense mechanisms in cancer therapy.

Effects of Nitro-Substitution on the Spectroscopic and Self-Assembly Properties of BODIPY Dyes

A series of boron dipyrromethene (BODIPY) dyes were nitrated in high yields using nitronium tetrafluoroborate at positions 2, 3, and 2,6 of the BODIPY core. This method allows for the regioselective nitration of the pyrrolic positions under milder conditions than previously reported methods. The photophysical properties and electronic transitions of these BODIPYs were investigated by using UV-vis spectroscopy, fluorescence spectroscopy, and density-functional theory (DFT) calculations. The introduction of one nitro group dramatically increases the dipole moment of the molecule, induces marked blue shifts in the absorption and emission bands, decreases the molar absorptivity, and increases the Stokes shifts of the BODIPYs. When a second nitro group is symmetrically introduced, the calculated dipole moments of the BODIPYs decrease in both the ground and excited states. Our studies show that the spectroscopic and self-assembly properties of nitro-substituted BODIPYs are highly dependent on solvent polarity and polarizability. In a polar organic solvent, nitro-substitution tends to quench the characteristic fluorescence of BODIPYs, while in a nonpolar solvent, significantly higher absolute fluorescence quantum yields are observed. On the other hand, aggregates are formed in aqueous solution, as observed by atomic force microscopy (AFM). Our results suggest a potential application of nitro-BODIPYs as polarity sensors.

Naphthalimide and Carbazole Based Mechanochromic Molecular Dyads and Triads for Selective Lysosome Imaging

In this study, we report the design and development of a stable fluorescent probe that is selectively localized in the cytosol of Hela cells. We designed two probes, 1 and 2, with D-π-A (carbazole (Cbz)-vinyl-naphthalimide (NPI)) and A-π-D-π-A (NPI-vinyl-Cbz-vinyl-NPI) architecture, respectively. Probes 1 and 2 exhibit broad photoluminescence (PL) spectra ranging from green (550 nm) to far-red (800 nm) in solutions and aggregated states. In the solid-state, the PL of these probes shows a bathochromic shift, which can be attributed to intermolecular interactions. In a water-rich medium, Probe 1, with a single NPI moiety, shows aggregation-caused quenching (ACQ) but retains a moderate quantum yield of 13.7 % (Φsoln=61.4 %). On the other hand, probe 2, with two NPI units, showed aggregation-induced enhanced emission AIEE, where the PLQY is increased nearly 4 times (Φsoln=3.5 %, Φagg=12.8 %). In-vitro cell studies revealed that these probes are non-toxic and effectively stain cells in green and red channels. Notably, Probe 1 demonstrated excellent cellular uptake and selectivity for lysosome, with a Pearson overlap coefficient of 0.91.

Advances in mercury ion sensing using BODIPY-based compounds: a sexennial update

Pollution from mercury ions (Hg2+) continues to pose a significant threat to the environment and public health because of its extreme toxicity and bioaccumulative nature. BODIPY-based compounds are emerging as strong candidates for creating selective and sensitive chemosensors for mercury ion detection. Their structural tunability facilitates the introduction of various functional groups, improving their binding affinity and specificity toward mercury ions. This review elucidates various sensing mechanisms and provides comprehensive insights into the performance of these sensors, particularly with regard to selectivity, sensitivity, and detection limits. The synthetic routes for synthesizing the chemosensors are mentioned in detail. Given their reliability and flexibility, BODIPY-based sensors are poised to make significant contributions in the fields of both sensors and analytical chemistry.

Iron ore pellets based-Ag2O nanoparticles as efficient Bi-functional heterogeneous catalyst for the synthesis tetrahydrobenzo[α]xanthens in green media

Through the use of a microwave, iron ore pellets (IOP)-based Ag2O nanoparticles were successfully synthesized. They were then characterized by means of a vibrating sample magnetometer (VSM), Brunauer-Emmett-Teller (BET) surface area analysis, energy-dispersive X-ray (EDX) analysis, powder X-ray diffraction (XRD) analysis, EDX elemental mapping, and field emission scanning electron microscopy (FESEM). High quantities of tetrahydrobenzo[a]xanthen derivatives were obtained in a brief amount of time by the newly prepared nanocomposite, known as Ag2O NP@IOP, in a one-pot, three-component reaction involving different aryl aldehydes, naphthol, and dimedone. There is no appreciable loss of catalytic activity when the catalyst is recycled and utilized several times, and it can be easily retrieved using an external magnet. The reason for functionality of designed hybrid catalyst can be related to textural properties such as desirable specific surface area and significant porosity as well as the structural nature of the Ag2O NP@IOP catalyst.

Design strategies for tetrazine fluorogenic probes for bioorthogonal imaging

Tetrazine fluorogenic probes play a critical role in bioorthogonal chemistry, selectively activating fluorescence upon reaction to enhance precision in imaging and sensing within complex biological environments. Recent structural innovations-such as varied fluorophore choices, spacer optimization, and direct tetrazine integration within a fluorophore's π-conjugated system-have expanded their spectral range from visible to NIR, enhancing adaptability across various applications. This review examines advancements in the rational design and synthesis of these probes. We examine key fluorogenic mechanisms, such as energy transfer, internal conversion, and electron/charge transfer, that significantly influence fluorescence activation. We also highlight representative applications in live-cell imaging, super-resolution microscopy, and therapeutic monitoring, underscoring the expanding role of tetrazine probes in biomedical research and diagnostics. Collectively, these insights provide a strategic foundation for developing next-generation tetrazine probes with tailored properties to address evolving diagnostic and therapeutic challenges.

Indole-Boron-Difluoride Complexes with Anticancer and Fluorescence Properties

Eight indole-boron-difluoride complexes were synthesized from 2,3-arylpyridylindole derivatives via Sonogashira coupling and Larock heteroannulation. These complexes exhibited distinct photophysical properties. Solvent polarity influenced their spectral behavior showing hypsochromic absorption, bathochromic emission shifts, and aggregation-induced emission (AIE) in mixed solvents. The ¹⁹F NMR shifts and photophysical properties, including excitation, emission maxima, and Stokes shift, correlated with Hammett substituent constants highlighting electronic effects on molecular properties. The synthesized complexes exhibited a range of intramolecular charge transfer (ICT) behaviors, as evidenced by their Lippert-Mataga parameters. TD-DFT calculations aligned with experimental data, offering insight into spectroscopic behavior. Notably, the indole-boron-difluoride complex bearing a methyl ester group exhibited significant anticancer activity against HeLa cells and potential for fluorescence imaging, indicating its promise for biomedical applications in cell imaging and therapy.

AIEgen-biomacromolecule conjugates: Visualized delivery and light-controlled theranostic platforms

Biomacromolecules play a critical role in advancing disease diagnosis and treatment. Traditional carriers often lack real-time tracking capabilities, controlled drug release, and may induce adverse effects for delivering biomacromolecules. Aggregation-induced emission luminogens (AIEgens) provide significant advantages in biomacromolecule delivery, enabling real-time fluorescence imaging and reactive oxygen species generation for photodynamic therapy (PDT). This dual functionality allows for the visualization of the biomacromolecule delivery process, providing valuable insights into biodistribution, cellular uptake, and drug-cell interactions. Additionally, the light-responsive nature of AIEgens enables precise spatial-temporal control over cargo release and imaging-guided PDT with minimal side effects. In this perspective, we summarize recent advancements in the use of AIEgens for visualized delivery and light-controlled theranostic applications of biomacromolecules, highlighting their potential to overcome challenges in targeted imaging and precision treatments. Key topics covered include covalent linkage strategies and the biomedical applications of AIEgen-functionalized biomacromolecules, including nucleic acids, proteins, polysaccharides, and lipids. We further highlight AIEgen-functionalized gene therapy and PDT for cancer, peptide transport for disease diagnosis, as well as polysaccharides and lipids delivery in antimicrobial treatments. This perspective concludes by addressing future challenges and opportunities, emphasizing the potential of AIEgen-functionalized biomacromolecules to advance precision theranostics.

Image-Based Phenotypic Profiling Enables Rapid and Accurate Assessment of EGFR-Activating Mutations in Tissues from Lung Cancer Patients

Determining mutations in the kinase domain of the epidermal growth factor receptor (EGFR) is critical for the effectiveness of EGFR tyrosine kinase inhibitors (TKIs) in lung cancer. Yet, DNA-based sequencing analysis of tumor samples is time-consuming and only provides gene mutation information on EGFR, making it challenging to design effective EGFR-TKI therapeutic strategies. Here, we present a new image-based method involving the rational design of a quenched probe based on EGFR-TKI to identify mutant proteins, which permits specific and "no-wash" real-time imaging of EGFR in living cells only upon covalent targeting of the EGFR kinase. We also show that the probe enables distinguishing EGFR mutant tumor-bearing mice from wild-type tumor-bearing mice via fluorescence-intensity-based imaging with high signal contrast. More interestingly, the image-based phenotypic approach can be used to predict EGFR mutations in tumors from lung cancer patients with an accuracy of 94%. Notably, when immunohistochemistry analysis is integrated, an improved accuracy of 98% is achieved. These data delineate a drug-based phenotypic imaging approach for in-biopsy visualization and define functional groups of EGFR mutants that can effectively guide EGFR-TKI therapeutic decision-making besides gene mutation analysis.

Synthesis, Spectral, and Computational Investigation of a New Red-Emissive BOIMPY

The search for fluorophores with intense absorption and emission in the red region of the spectrum is an important task, as such compounds can be used in fluorescence imaging, providing high image resolution due to the deep penetration of low energy photons into tissues. In this paper, we present the results of the synthesis and photophysical characterization of a novel ms-benzimidazole-4,4',5,5'-tetramethyldipyrromethene bis(difluoroborate) (BOIMPY) compound, which exhibits intensive absorption and emission in the long-wavelength region while maintaining high fluorescence quantum yields (up to 60%). Using DFT analysis, we investigated the geometry of BOIMPY in both ground and excited states and described the influence of the molecular structure on its practically relevant photophysical properties.

Synthesis of BODIPYs using organoindium reagents and survey of their cytotoxicity and cell uptake on nervous system cells

In this study, a series of BODIPY dyes were synthesized, containing various substituents at meso position. Further functionalization of the BODIPY framework at C2 and C2-C6 position(s) by palladium-catalysed cross-coupling reactions using organoindium reagents (R3In) was efficiently assessed, starting from C2(6)-halogenated BODIPYs, and their optical properties were measured. The cytotoxicity of BODIPY dyes on SH-SY5Y neuronal cells by MTT assay showed that those compounds bearing thien-2-yl and benzonitrile moieties at meso position, exhibited great efficiency in maintaining cell viability under all tested conditions (up to 50 µM for 24 h and 48 h). Furthermore, nanoliposomal encapsulation of a hydrophobic BODIPY, incorporating bis(trifluoromethyl)phenyl substituents at C2 and C6 positions, through the lipid-extrusion method was addressed. The liposomes exhibited spherical shape as observed in cryo-TEM image, with average particle size of 120 nm (average PdI 0.05) and Zeta potential 54.69 mV by DLS measurements. Simple incubation of gliobastoma U-87 cells with prepared liposomes led to efficient internalization, and visualization of brightness BODIPY in cytoplasm using fluorescence confocal microscopy, demonstrating encapsulation enhance biocompatibility of the hydrophobic BODIPY as preliminary approximation for further biomedical applications.

Recent advances in the development of enantiopure BODIPYs and some related enantiomeric compounds

During the process of developing smart chiroptical luminophores, small chiral organic dyes have emerged as candidates of utmost importance. In this regard, the chiral variants of boron dipyrromethene (BODIPY) serve as suitable molecules owing to their excellent photophysical properties such as high fluorescence quantum yields, narrow emission bandwidths with high peak intensities, high photo and chemical stability, and higher molar extinction coefficients. Thus, the last decade observed an influx of research from various research groups for the induction of chirality in originally achiral BODIPY. Among these, the generation of chiral centers at various positions in BODIPY favored the synthetic accessibility towards this particular chiral pool, which in turn is found to be applicable in various areas like photodynamic therapy, bio-imaging, dye-sensitized solar cells, optoelectronics, fluorescent indicators, dye lasers, and chiral sensing. This review summarizes these various aspects of creating stereogenic centers at various positions, like α, β, meso, or at boron, in BODIPYs.

BF3·Et2O controlled selective synthesis of α-substituted propargylamides and β-(N-acylamino) ketones: application to carbon and sulphur nucleophiles

This study presents a metal-free and selective synthesis of α-substituted propargylamides and β-(N-acylamino) ketones utilizing nitriles, aldehydes, and terminal alkynes, mediated by BF3·Et2O. The unique reactivity of BF3·Et2O, a potent Lewis acid, facilitates precise control over product formation. By adjusting the concentration of BF3·Et2O, we can effectively manipulate reaction pathways and selectivity, ensuring the desired products are achieved with enhanced specificity. Notably, this method demonstrates remarkable tolerance to other nucleophiles, such as β-naphthol, indole, arenes and thiol, thereby enabling the synthesis of a diverse array of functionally significant compounds. This approach offers a valuable tool for advancing synthetic methodologies in organic chemistry.

Emissive triphenylamine functionalised 1,8-naphthalimide and naphthalene diimide fluorophores: aggregation, computation and biological studies

Four new aromatic imides bearing triphenylamino (TPA) moieties are reported each of which differ by the number and/or positional arrangements of the TPA units. Compounds 1-3 are 1,8-naphthalimides (naps) that contain N,N'-diphenyl-[1,1'-biphenyl]-4-amino (TPA-Ph) groups appended to the N-termini of the respective imides. Each differs by their functionalisation of the 4-position of the nap: nitro (1), amino (2), or an additional TPA group (3). By contrast, compound 4 is a naphthalene diimide (NDI) functionalised with TPA-Ph moieties on each N-terminus. These simple modifications produce molecules with vastly different optoelectronic and aggregation properties. This article studies these characteristics with particular focus directed toward the contrast in aggregation-caused quenching (ACQ) properties of 2 compared with the aggregation-induced emission (AIE) properties of 3. The distinct aggregation and photophysical properties of 2 and 3 are delicately exploited using self-assembly with an amphiphilic poloxamer to generate nanoparticles capable of delivering 2 and 3 into cells for biological imaging.

A novel BODIPY-based fluorescent probe for naked-eye detection of the highly alkaline pH

A novel alkaline pH-responsive probe based on an asymmetric aza-BODIPY was synthesized in a one-pot Schiff base formation reaction. This pH-sensitive probe comprises an asymmetric aza-BODIPY as the luminescent core, with a benzothiazole moiety connected via an imine bond serving as the recognition site. The probe exhibits a turn-off fluorescence response upon exposure to alkaline pH (9.6-12.4), while a bathochromic band in the absorption emerges due to its extended π-conjugation system, accompanied by a visible colorimetric change from yellow to orange to red. Furthermore, the probe responds linearly in the highly alkaline region, with a pKa of 11.65. The recognition mechanism of the probe towards alkaline pH relies on the deprotonation of the imine group on the aza-BODIPY core, leading to an enhanced degree of π-electron conjugation. The quenched fluorescence intensity is attributed to the increased non-radiative decay of the deprotonated form of the probe. The probe demonstrates high reliability for practical applications due to its photostability and reversibility. This study provides new insights into the design of probes for detecting high alkaline pH levels.

Recent advances in glutathione fluorescent probes based on small organic molecules and their bioimaging

Glutathione (GSH), as one of the most important biological mercaptans, is involved in a variety of biological processes and is considered an important biomarker in early diagnosis, treatment and disease stage monitoring. Rapid and accurate detection of GSH in complex biological systems is of great significance for pathological analysis. Fluorescence imaging technology is widely used because of its advantages of high sensitivity, high resolution and non-destructiveness. In this paper, the latest research progress on GSH-responsive organic small molecule fluorescence probes in the last five years is summarized, and their response mechanisms are classified and discussed. In addition, the probe design strategy, sensing mechanism and biological application are discussed in this review. Finally, the challenges and future research directions of developing new GSH probes are presented.

Catalytic asymmetric C-N cross-coupling towards boron-stereogenic 3-amino-BODIPYs

3-Amino boron dipyrromethenes (BODIPYs) are a versatile class of fluorophores widely utilized in live cell imaging, photodynamic therapy, and fluorescent materials science. Despite the growing demand for optically active BODIPYs, the synthesis of chiral 3-amino-BODIPYs, particularly the catalytic asymmetric version, remains a challenge. Herein, we report the synthesis of boron-stereogenic 3-amino-BODIPYs via a palladium-catalyzed desymmetric C-N cross-coupling of prochiral 3,5-dihalogen-BODIPYs. This approach features a broad substrate scope, excellent functional group tolerance, high efficiency, and remarkable enantioselectivities, under mild reaction conditions. Further stereospecific formation of chiral 3,5-diamino-BODIPYs, along with an investigation into the photophysical properties of the resulting optical BODIPYs are also explored. This asymmetric protocol not only enriches the chemical space of chiroptical BODIPY dyes but also contributes to the realm of chiral boron chemistry.

Synthesis and optical properties of tyramine-functionalized boron dipyrromethene dyes for cell bioimaging

Tyramine signaling amplification (TSA) technology is generally applied in immunofluorescence, enzyme-linked immunoassays, in situ hybridization techniques, etc. Successful amplification of fluoresence signals cannot be achieved without excellent fluorescent dyes. BODIPY fluorophore is an ideal probe for cell fluorescence imaging, but pristine BODIPY cannot be direct used in the TSA system. In the paper, the new red-shifted tyramide-conjugated BODIPY (BDP-B/C/D) was synthesized via the Knoevenagel condensation reaction, which based on the tyramide-conjugated BODIPY (BDP-A). The synthesized dyes were combined with tyramine to obtain which could be used as a fluorescent substrate for enzymatic reaction of TSA. By using the selected substrate (BDP-C) in TSA, we found it to be more sensitive than the commercial dye 594 styramide for the detection of low-abundance antigen proteins.

Theoretical Study on Spectrum and Luminescence Mechanism of Cy5.5 and Cy7.5 Dye Based on Density Functional Theory (DFT)

Cy5.5 and 7.5 are the most commonly used NIR 2-region fluoresceins, which have good luminescence properties and important biomedical tracer applications. In this paper, their molecular non-covalent interactions, UV-Vis absorption spectra, main bond lengths, electrostatic potential distributions, frontier molecular orbitals (HOMO and LUMO) and energy gaps were calculated by density functional theory (DFT). We found that the differences in the luminescence properties and energy gaps of Cy5.5 and Cy7.5 molecules may be caused by the length of the conjugated chains between the two aromatic rings in the molecule. By calculating the relevant molecular characteristics, this paper can provide ideas and theoretical basis for the relevant modification and application, as well as the development of new fluorescent dyes.

Recent advances of lipid droplet-targeted AIE-active materials for imaging, diagnosis and therapy

Lipid droplets (LDs) are cellular organelles specialized in the storage and regulating the release of lipids critical for energy metabolism. As investigation on LDs deepens, the complex biological functions of LDs are revealed and their relationships with various diseases such as atherosclerosis, fatty liver, obesity, and cancer are uncovered. Fluorescence-based techniques with simple operations, visible results and high non-invasiveness are ideal tools for investigating LD-related biological processes and diseases. Materials with aggregation-induced emission (AIE) characteristics have emerged as promising candidates for investigating LDs due to their high signal-to-noise ratio (S/N), strong photostability, and large Stokes shift. This review discusses the principles and advantages of LD-targeting AIE probes for imaging LDs, diagnosis of LD-associated diseases including atherosclerotic plaques, liver diseases, acute kidney diseases and cancer, therapies with LD-targeting AIE-active photosensitizers and other relevant fields in the past five years. Through typical examples, we illustrate the status of investigating LD-related imaging, diagnosis of diseases and therapy with AIE materials. This review is expected to attract attentions from scientists with different research backgrounds and contribute to the further development of LD-targeting AIE materials.

Development and characterization of fluorescent cholesteryl probes with enhanced solvatochromic and pH-sensitive properties for live-cell imaging

We present novel fluorescent cholesteryl probes (CNDs) with a modular design based on the solvatochromic 1,8-phthalimide scaffold. We have explored how different modules-linkers and head groups-affect the ability of these probes to integrate into lipid membranes and how they distribute intracellularly in mouse astrocytes and fibroblasts targeting lysosomes and lipid droplets. Each compound was assessed for its solvatochromic behavior in organic solvents and model membranes. Molecular dynamics simulations and lipid partitioning using giant unilamellar vesicles showed how these analogs behave in model membranes compared to cholesterol. Live-cell imaging demonstrated distinct staining patterns and cellular uptake behaviors, further validating the utility of these probes in biological systems. We compared the empirical results with those of BODIPY-cholesterol, a well-regarded fluorescent cholesterol analog. The internalization efficiency of fluorescent CND probes varies in different cell types and is affected mainly by the head groups. Our results demonstrate that the modular design significantly simplifies the creation of fluorescent cholesteryl probes bearing distinct spectral, biophysical, and cellular targeting features. It is a valuable toolkit for imaging in live cells, measuring cellular membrane dynamics, and studying cholesterol-related processes.

Targeted Photoactivatable Green-Emitting BODIPY Based on Directed Photooxidation-Induced Activation and its Application to Live Dynamic Super-Resolution Microscopy

Photoactivatable fluorescent probes are valuable tools in bioimaging for tracking cells down to single molecules and for single molecule localization microscopy. For the latter application, green emitting dyes are in demand. We herein developed an efficient green-emitting photoactivatable furanyl-BODIPY (PFB) and we established a new mechanism of photoactivation called Directed Photooxidation Induced Activation (DPIA) where the furan is photo-oxidized in a directed manner by the singlet oxygen produced by the probe. The efficient photoconverter (93-fold fluorescence enhancement at 510 nm, 49 % yield conversion) is functionalizable and allowed targeting of several subcellular structures and organelles, which were photoactivated in live cells. Finally, we demonstrated the potential of PFB in super-resolution imaging by performing PhotoActivated Localization Microscopy (PALM) in live cells.

Enhancing Phototoxicity in BODIPY-Perylene Charge Transfer Dyads by Combined Iodination and Mesylation

The uptake and phototoxicity of a family of BODIPY-perylene charge transfer dyads are compared in live cancer and non-cancer cell lines to evaluate their performance in imaging and photodynamic therapy (PDT). The impact of iodination and mesylation of the meso position of the compounds on their optical properties, cell uptake and toxicity are compared. Notably, across all derivatives the probes were minimally dark toxic up to 50 μM, (the maximum concentration tested), but exhibited outstanding phototoxicity with nanomolar IC50 values and impressive phototoxic indices (PI, ratio of dark IC50 to light IC50), with best performance for the mesylated iodinated derivative MB2PI, which had a PI of >218 and >8.9 in MCF-7 cells and tumour spheroids respectively. This is significantly higher than non-iodinated analogue MB2P in MCF-7 cells with an observed PI of >109 and slightly higher than MB2PI in spheroids with a PI of >8. This compound also showed interesting emission spectral variation with localisation that responded to stimulation of inflammation. Additional studies confirmed efficient singlet oxygen generation by the BODIPYs, suggesting a Type II mechanism of phototoxicity. Overall, the data indicates that combining charge transfer and iodination is an effective strategy for enhancing phototherapeutic capacity of BODIPY PS.

A dual-emission fluorescent probe with independent polarity and viscosity responses: The synthesis, spectroscopy and bio-imaging applications

Viscosity and polarity are essential parameters that play critical roles in various physiological processes. Thus, dual-emission fluorescent probes that respond to both polarity and viscosity are highly sought-after tools for studying these processes. In addressing this need, a novel fluorescent probe (L), with dual emissions centered at 460 nm and 780 nm, which can sensitively respond to polarity and viscosity respectively, has been developed. Probe (L) is constructed through rational molecular design, utilizing two conjugated synthons connected by a π-bond to form a D-π-A system. The twisted intramolecular charge transfer (TICT) state is dominant in low-viscosity environments, resulting in weak near-infrared (NIR) fluorescence. Conversely, the intramolecular charge transfer (ICT) state is expected to prevail in high-viscosity environments, leading to strong NIR fluorescence. The polarity-sensitive fluorescence centered at 460 nm can be attributed to the emission of the coumarin unit. Moreover, probe (L) exhibits low cytotoxicity and primarily targets mitochondria. By leveraging the dual-emission properties of probe (L), real-time imaging of polarity and viscosity fluctuations within cells has been achieved. Additionally, probe (L) can be used for in situ and in vivo imaging of rheumatoid arthritis (RA) with good imaging resolution.

AIE-active large Stokes-shift BODIPY Functionalized with Carbazolyl for Lysosome-Targeted Imaging in Living Cells

A large number of studies have shown that lysosomal microcircumstances changes can affect many physiological and pathological processes at the cellular level. However, the visual detection of lysosomal microcircumstances is relatively difficult due to low pH (4.5-6.0) value in lysosomal that require the probe not only stable under acidic condition but also has a good localization effect to lysosomal. Obviously, novel fluorescent which possessed both acidic stability and lysosomal-target property together with lysosomal viscosity active is highly demanded. Herein, a novel BODIPY molecular CarBDP based on carbazole group was rationally designed and synthesized for the lysosomal imaging. CarBDP exhibited AIE feature with a large Stokes shift of up to 157 nm. More importantly, co-localization assay of the CarBDP-treated MCF-7 cells indicated that CarBDP has a good localization effect on lysosomal (Rr = 0.7109) due to the carbazole group while the normal BODIPY that without carbazole group (PhBDP) shows poor localization performance, this was the first time that a small molecule can locate lysosomes only based on carbazole group. CarBDP exhibits strong solid emission with long fluorescence decay lifetime (τ = 44.54 ns) and was stable under acid condition.The probe CarBDP assembled with carbazole group was successfully utilized for lysosomal localization and mapping lysosomal viscosity in live cells, which provides a novel candidate tool for the determination of lysosomal microcircumstances.

Two-Dimensional Self-Assembly of BODIPY Derivatives with Different Functional Groups at the Liquid-Solid Interface

The 4,4-difluoro-boradiazaindacene (BODIPY) unit possesses a rigid aromatic backbone, which facilitates the formation of self-assemblies and aggregates. However, most current studies on the self-assemblies of BODIPY derivatives have relied on spectroscopic methods to indirectly gather information about the self-assembled structures. In this study, we presented three BODIPY derivatives (B-3OC12, B-3OC12-2I, and B-DOB-2OC12) that shared the same core but were decorated with different functional groups. The self-assembled structures were revealed using scanning tunneling microscopy (STM) in combination with density functional theory (DFT). The results showed that all the molecules self-assembled into lamellar structures. When modified with three dodecyloxy chains or with the introduction of additional halogen atoms, the B-3OC12 and B-3OC12-2I molecules tended to distribute in a staggered form to build a tetramer or dimer. In contrast, the B-DOB-2OC12 molecule, which contains a dioxaborole group, self-assembled in a head-to-tail manner. These results demonstrated that BODIPY derivatives self-assembled into different structures, depending on their distinct patterns of intermolecular interactions influenced by functional groups.

How to nurture natural products to create new therapeutics: Strategic innovations and molecule-to-medicinal insights into therapeutic advancements

Natural products (NPs) are privileged structures interacting with biomacromolecular targets and exhibiting biological effects important for human health. In this review, we have presented NP-inspired strategic innovations that are promising for addressing preclinical and clinical challenges. An analysis of 'molecule-to-medicinal' properties for improvement of P3 and absorption, distribution, metabolism, excretion, and toxicity (ADMET) profiles has been illustrated. The strategies include chemical evolution through knowledge of structure-medicinal properties, truncation of NPs to avoid molecular obesity, pseudo-NPs, selection of common structural features of NPs, medicinophore installation, scaffold hopping, and induced proximity. Molecule-to-medicinal property analysis can guide the development of 'nature-to-new' chemical therapeutics. Coupled with scientific advances and innovations in instrumentation, these strategies hold great potential for enhancing drug design and discovery.

Computational investigation of the effect of BODIPY labelling on peptide-membrane interaction

Optical monitoring of peptide binding to live cells is hampered by the abundance of naturally occurring fluorophores such as tryptophan. Unnatural amino acids incorporating synthetic fluorophores such as BODIPY overcome these optical limitations. A drawback to using fluorophores in lipid binding peptide design is their propensity to override other interactions, potentially causing the peptides to lose their binding selectivity. Here, the binding strength of a selection of peptides incorporating a variety of BODIPY derivatized amino acids has been studied via molecular dynamics simulations to quantify the impact of BODIPY incorporation on peptide-membrane binding behaviour.

Sterically Tuned Ortho-Phenylene-Linked Donor-Acceptor Benzothiazole-Based Boron Difluoride Complexes as Thermally-Activated Delayed Fluorescence Emitters for Organic Light-Emitting Diodes

Two donor-acceptor dyes with an ortho-phenylene-linked carbazole electron donor and a benzothiazole-fused boron heterocyclic acceptor were designed, synthesized, and spectroscopically investigated. Due to the steric effects of boron heterocyclic units, the dyes demonstrate different conformations in the crystalline state. The presence of numerous hydrogen-bonding intermolecular interactions and the very weak π-π stacking in the molecular packing results in intense solid-state emission with photoluminescence quantum yields of 40 and 18% for crystals and 50 and 42% for host-based light-emitting layers. The compounds show aggregation-induced emission and thermally activated delayed fluorescence (TADF). The received ionization potential and electron affinity values suggested good charge-injecting ability and bipolar charge-transporting properties of the developed dyes. Transport of holes and electrons was detected in layers of one dye by the time-of-flight measurements. The benzothiazole-based boron difluoride complexes showed high electron mobility of 1.5 × 10-4 and 0.7 × 10-4 cm2 V-1 s-1 at an electric field of 1.35 × 106 V cm-1. Therefore, these dyes were successfully applied as emitters in organic light-emitting diodes with external quantum efficiencies of 15 and 13%, respectively. Our study marks a critical advancement in the area of solid-state emissive boron difluoride dyes, which can be applied as TADF emitters into organic light-emitting diodes. The obtained results reveal that the orientation of the acceptor unit in the ortho-phenylene-linked donor-acceptor dyes makes a significant impact on the TADF activity.

Synthesis and Optoelectronic Properties of Threaded BODIPYs

We report on the synthesis of two new threaded BODIPYs 5 and 6 in good yields using boron as a gathering atom and a macrocycle with a 2,2'-biphenol unit. In addition to usual techniques, they were characterized by X-ray crystallography. Their electrochemical and optical properties were investigated. In particular, both compounds are highly emissive with photoluminescence quantum yields of 54 and 81 % respectively. In addition, they both show a high photostability.

BODIPY Compounds Substituted on Boron

BODIPY compounds are important organic dyes with exceptional spectral and photophysical properties and numerous applications in different scientific fields. Their widespread applications have flourished due to their easy structural modifications, which enable the preparation of different molecular structures with tunable spectral and photophysical properties. To date, researchers have mostly devoted their efforts to modifying BODIPY meso-position or pyrrole rings, whereas the substitution of fluorine atoms remains largely unexplored. However, chemistry of the boron atom is possible, and it enables tuning of the photophysical properties of the dyes, without tackling their spectral properties. Furthermore, modifications of boron affect the solubility and aggregation propensity of the molecules. This review article highlights methods for the preparation of 4-substituted compounds and the most important reactions on the boron of the BODIPY dyes. They were divided into reactions promoted by Lewis acid (AlCl3 or BCl3), or bases such as alkoxides and organometallic reagents. By using these two methodologies, it is possible to cleave B-F bonds and substitute them with B-C, B-N, or B-O bonds from different nucleophiles. A special emphasis in this review is given to still underdeveloped photochemical reactions of the boron atom of BODIPY dyes. These reactions have the potential to be used in the development of a new line of BODIPY photo-cleavable protective groups (also known as photocages) with bio-medicinal and photo-pharmacological applications, such as drug delivery.

Novel carboranyl-BODIPY conjugates: design, synthesis and anti-cancer activity

A series of four carboranyl-BODIPY conjugates (o-CB-10, m-CB-15, Me-o-CB-28, and Me-o-CB-35) and one phenylene-BODIPY conjugate (PB-20) were synthesized. The carboranyl-BODIPY conjugates incorporate boron clusters, specifically ortho- and meta-carboranes, covalently linked to BODIPY fluorophores while the phenylene-BODIPY conjugate features a phenylene ring covalently linked to BODIPY fluorophore. The newly synthesized conjugates were characterized by 1H NMR, 13C NMR, 11B NMR, 19F NMR, FT-IR, and high-resolution mass spectral analysis. In vitro cytotoxicity of the synthesized conjugates has been evaluated against the HeLa cervical cancer cell line. The study reveals that o-CB-10 shows a maximum cell death potential at lower concentrations (12.03 μM) and inhibited cell proliferation and migration in cancer (HeLa) cells. Additionally, flow cytometry study reveals that o-CB-10 and Me-o-CB-28 arrest the cell cycle at the S phase. The results indicate that the carboranyl-BODIPY conjugates have the potential to be effective anticancer agents.

Investigation of excited states of BODIPY derivatives and non-orthogonal dimers from the perspective of singlet fission

We report state of the art electronic structure calculations RICC2 and XMCQDPT of BODIPY nonorthogonal dimers to understand the photophysical processes from the intramolecular singlet fission (iSF) perspective. We have calculated singlet, triplet and quintet states at the XMCQDPT(8,8)/cc-pVDZ level of theory and diabatic singlet states at the XMCQDPT(4,4)/cc-pVDZ level of theory. In all the systems studied, charge transfer states (1(CA) and 1(AC)) couple strongly with locally excited (1(S1S0)) and multiexcitonic (1(T1T1)) states. The rates of formation of the multiexcitonic state from the locally excited state are very low on account of large activation energy (E(1(T1T1)) - E(1(S1S0))). A relaxed scan along the torsional angle revealed contrasting results for axial and orthogonal conformers. We proposed a probable mechanism for contrasting photophysical properties of dimers B[3,3] and B[2,8]. We also found that substitution of CN, NH2 and BH2 at meso, β and α positions reduces the energy gap (ΔSF = 2E(T1) - E(S1)) significantly, making iSF a competing process in triplet state generation. Intrigued by the success of the CN group at the meso position in reducing the energy gap, we also studied the azaBODIPY monomer and its derivatives using the same methodology. The iSF is slightly endoergic with ΔSF ∼ 0.2 eV in these systems and iSF may play an important role in their photophysical responses.

Singlet and triplet excited states of a series of BODIPY dyes as calculated by TDDFT and DLPNO-STEOM-CCSD methods

The singlet and triplet excited states of three iodine substituted BODIPY dyes differing by their substituents (-phenyl, -phenylOH and -phenylNO2) at the meso position of the BODIPY core (BOD) are investigated using (TDA)-TDDFT and DLPNO-STEOM-CCSD calculations. An assessment of hybrid (B3LYP and MN15) and double hybrid (SOS-PBE-QIDH and SOS-ωPBEPP86) exchange-correlation functionals is performed with respect to the DLPNO-STEOM-CCSD method for four types of transitions, namely , , and . It is found that MN15 and SOS-PBE-QIDH provide a balanced description of the excited state energies when compared to the DLPNO-STEOM-CCSD results. An investigation of the effects of the solvent (dichloromethane), of the substituent and of geometrical relaxation in the excited states is then performed. In particular, the study discusses the possibility of populating charge transfer states ( and ) following photoexcitation in the first and second absorption bands in these systems.

Tetradentate carbene-anilido boron complexes: highly fluorescent dyes with larger Stokes shifts than BODIPY analogues

A new class of carbene-anilido boron complexes have been designed and synthesized. The complexes show intense fluorescence with large Stokes shift because of their charge-transfer excited states, different from typical BODIPY dyes. By using a chiral 1,1'-bi(2-naphthol) ligand, dyes exhibiting circularly polarized luminescence can also be facilely developed.

Aggregation Behavior of CHR-bis(BODIPY) Bichromophores in THF-water Mixtures: Effect of Linking Positions and Aryl-spacer Substituents

Aggregation-caused quenching effect (ACQ) greatly limits the practical use of many organic luminophores in biomedicine, optics and electronics. The comparative analysis of aggregation characteristics of CHR-bis(BODIPY) bichromophores 1-6 with R = H, Ph, MeOPh and various linking positions (α,α-; α,β-; β,β- and β',β'-) in THF-water mixtures with different water fractions or dye concentrations is first presented in this article. Both the linking style 1-4 and the arylation of the spacer with phenyl (Ph-) 5 or methoxyphenyl (MeOPh-) 6 substituents strongly affect the formation of luminophore aggregated forms in binary THF-water mixtures. The α,α-and β,β-isomers (1 and 3) form non-fluorescent H-type aggregates in THF-water mixtures with fw > 70%. The α,β-; β',β'-isomers (2, 4) and the MeOPh-substituted β,β-bichromophore 6 are characterized by predominant formation fluorescent aggregates. All bichromophores are characterized by the presence of residual amounts of non-aggregated forms in binary mixtures with maximum water content. The results are useful for controlling the aggregation behavior and spectral characteristics of CHR-bis(BODIPY) bichromophores in aqueous-organic media, which is important in the development of biomarkers and PDT agents.

Synthesis of New Bodipy Hydrazide Fluorescent Probes for the Detection of Carbonylated Proteins Generated by Oxidative Stress

Oxidative stress is a cellular disorder implicated in various severe diseases and redox biology and represents an important field of research for the last decades. One of the major consequences of oxidative stress is the carbonylation of proteins, which is also a reliable marker to assess protein oxidative modifications. Accumulation of carbonylated proteins has been associated with aging and age-related diseases and can ultimately causes cell death. Detection of these oxidative modifications is essential to understand and discover new treatments against oxidative stress. We describe the design and the synthetic pathway of new BODIPY fluorescent probes functionalized with hydrazide function for protein carbonyl labeling to improve existing methodologies such as 2D-Oxi electrophoresis. Hydrazide BODIPY analogues show very good fluorescent properties such as NIR emission up to 633 nm and quantum yield up to 0.88. These new probes were validated for the detection and quantification of carbonylated proteins with 2D-Oxi electrophoresis using mouse muscle protein extracts, as well as both flow cytometry and microscopy using oxidant stressed C2 C12 cells.

Modular enantioselective assembly of multi-substituted boron-stereogenic BODIPYs

Boron dipyrromethenes (BODIPYs) are some of the most popular and indispensable tetracoordinate boron compounds and have found widespread applications owing to their excellent spectroscopic and photophysical properties. BODIPYs possessing boron-stereogenic centres are scarce, and strategies for the synthesis of enantioenriched boron-stereogenic BODIPYs with structural diversity remain underdeveloped. In theory, the BODIPY core skeleton has several sites that could be decorated with different substituents. However, due to the lack of general and efficient asymmetric synthetic methods, this potential diversity of chiral BODIPYs has not been exploited. Here we demonstrate a modular enantioselective assembly of multi-substituted boron-stereogenic BODIPYs in high efficiency with excellent enantioselectivities. Key to the success is the Pd-catalysed desymmetric Suzuki cross-coupling, enabling the precise discrimination of the two α C-Cl bonds of the designed prochiral BODIPY scaffold, giving access to a wide range of highly functionalized boron-stereogenic BODIPYs. Derivatizations, photophysical properties and applications in chiral recognition of the obtained optical BODIPYs are further explored.

Fluorescent probes for neuroscience: imaging ex vivo brain tissue sections

Neurobiological research relies heavily on imaging techniques, such as fluorescence microscopy, to understand neurological function and disease processes. However, the number and variety of fluorescent probes available for ex vivo tissue section imaging limits the advance of research in the field. In this review, we outline the current range of fluorescent probes that are available to researchers for ex vivo brain section imaging, including their physical and chemical characteristics, staining targets, and examples of discoveries for which they have been used. This review is organised into sections based on the biological target of the probe, including subcellular organelles, chemical species (e.g., labile metal ions), and pathological phenomenon (e.g., degenerating cells, aggregated proteins). We hope to inspire further development in this field, given the considerable benefits to be gained by the greater availability of suitably sensitive probes that have specificity for important brain tissue targets.

Tripodal BODIPY-Tagged and Functional Molecular Probes: Synthesis, Computational Investigations and Explorations by Multiphoton Fluorescence Lifetime Imaging Microscopy

A range of novel BODIPY derivatives with a tripodal aromatic core was synthesized and characterized spectroscopically. These new fluorophores showed promising features as probes for in vitro assays in live cells and offer strategic routes for further functionalization towards hybrid nanomaterials. Incorporation of biotin tags facilitated proof-of-concept access to targeted bioconjugates as molecular probes. Computational explorations using DFT and TD-DFT calculations identified the most stable tripodal linker conformations and predicted their absorption and emission behavior. The uptake and speciation of these molecules in living prostate cancer cells was imaged by single- and two-photon excitation techniques coupled with two-photon fluorescence lifetime imaging (2P FLIM).

Development of BODIPY-based fluorescent probes for imaging Aβ aggregates and lipid droplet viscosity

Alzheimer's disease (AD), gradually recognized as an untreatable neurodegenerative disorder, has been considered to be closely associated with Aβ plaques, which consist of β-amyloid protein (Aβ) and is one of the crucial pathological features of AD. There are no obvious symptoms in the initial phase of AD, and thus the therapeutic interventions are important for early diagnosis of AD. Moreover, recent researches have indicated that lipid droplets might serve as a potential ancillary biomarker, and its viscosity changes are closely associated to the pathological process of AD. Herein, two newly fluorescent probes 5QSZ and BQSZ have been developed and synthesized for identifying Aβ aggregates and detecting the viscosity of lipid droplet. After selectively binding to Aβ aggregates, 5QSZ and BQSZ exhibited linear and obvious fluorescence enhancements (32.58 and 36.70 folds), moderate affinity (Kd = 268.0 and 148.6 nM) and low detection limits (30.11 and 65.37 nM) in aqueous solutions. Further fluorescence staining of 5QSZ on brain tissue sections of APP/PS1 transgenic mouse exhibited the higher selectivity of 5QSZ towards Aβ aggregates locating at the core of the plaques. Furthermore, 5QSZ and BQSZ displayed strong linear fluorescence emission enhancements towards viscosity changes and would be utilized to monitor variation in cellular viscosity induced by LPS or monensin. These two probes were non-cytotoxic and showed good localization in lipid droplets. Therefore, 5QSZ and BQSZ could serve as potential bi-functional fluorescent probes to image Aβ aggregates and monitor the viscosity of lipid droplets, which have significant implications for the early diagnosis and progression of AD.

A BODIPY-Naphtholimine-BF2 Dyad for Precision Photodynamic Therapy, Targeting, and Dual Imaging of Endoplasmic Reticulum and Lipid Droplets in Cancer

Currently, effective therapeutic modalities for pancreatic ductal adenocarcinoma (PDAC) are quite limited, leading to gloomy prognosis and ∼6-months median patient survival. Recent advances showed the promise of photodynamic therapy (PDT) for PDAC patients. Next generation photosensitizers (PS) are based on "organelle-targeted-PDT" and provide new paradigm in the field of precision medicines to address the current challenge for treating PDAC. In this investigation, we have constructed a novel PS, named as N b B, for precise and simultaneous targeting of endoplasmic reticulum (ER) and lipid droplets (LDs) in PDAC, based on the fact that malignant PDAC cells are heavily relying on ER for hormone synthesis. Our live cell imaging and fluorescence recovery after photobleaching (FRAP) experiments revealed that N b B is quickly targeted to ER and subsequently to LDs and shows simultaneous dual fluorescence color due to polar and nonpolar milieu of ER and LDs. Interestingly, the same molecule generates triplet state and singlet oxygen efficiently and causes robust ER stress and cellular lipid peroxidation, leading to apoptosis in two different PDAC cells in the presence of light. Together, we present, for the first time, a potential next generation precision medicine for ER-LD organelle specific imaging and PDT of pancreatic cancer.

Correlative multimodal optical and X-ray fluorescence imaging of brominated fluorophores

Imaging with multiple modalities can maximise the information gained from the analysis of a single sample. probes for optical fluorescence and X-ray fluorescence microscopy based on brominated 4-amino-1,8-naphthalimide and BODIPY scaffolds have been successfully designed and synthesised. Herein we show that these prototype probes, based on each of these scaffolds, can be imaged in two different cancer cell lines, and that the respective optical fluorescence and X-ray fluorescence signals are well correlated in these images.

Protein aggregation monitoring in cells under oxidative stress: a novel fluorescent probe based on a 7-azaindole-BODIPY derivative

The development of new fluorescent probes as molecular sensors is a critical step for the understanding of molecular mechanisms. BODIPY-based probes offer versatility due to their high fluorescence quantum yields, photostability, and tunable absorption/emission wavelengths. Here, we report the synthesis and evaluation of a novel 7-azaindole-BODIPY derivative to probe hydrophobic proteins as well as protein misfolding and aggregation. In organic solvents, this compound shows two efficiently interconverting emissive excited states. In aqueous environments, it forms molecular aggregates with unique photophysical properties. The complex photophysics of the 7-azaindole-BODIPY derivative was explored for sensing applications. In the presence of albumin, the compound is stabilized in hydrophobic protein regions, significantly increasing its fluorescence emission intensity and lifetime. Similar effects occur in the presence of protein aggregates but not with other macromolecules like pepsin, DNA, Ficoll 40, and coconut oil. Fluorescence lifetime imaging microscopy (FLIM) and two-photon fluorescence microscopy on breast (MCF-7) and lung (A549) cancer cells incubated with this compound display longer fluorescence lifetimes and higher emission intensity under oxidative stress. Synchrotron FTIR micro spectroscopy confirmed that the photophysical changes observed were due to protein misfolding and aggregation caused by the oxidative stress. These findings demonstrate that this compound can serve as a fluorescent probe to monitor protein misfolding and aggregation triggered by oxidative stress.

Advancing cell biology with nanoscale fluorescence imaging: essential practical considerations

Recently, biologists have gained access to several far-field fluorescence nanoscopy (FN) technologies that allow the observation of cellular components with ~20 nm resolution. FN is revolutionizing cell biology by enabling the visualization of previously inaccessible subcellular details. While technological advances in microscopy are critical to the field, optimal sample preparation and labeling are equally important and often overlooked in FN experiments. In this review, we provide an overview of the methodological and experimental factors that must be considered when performing FN. We present key concepts related to the selection of affinity-based labels, dyes, multiplexing, live cell imaging approaches, and quantitative microscopy. Consideration of these factors greatly enhances the effectiveness of FN, making it an exquisite tool for numerous biological applications.

HFIP-Mediated Desulfinative Friedel-Crafts Cyclobutenylation Reaction

In 1,1,1,3,3,3-hexafluoroisopropyl alcohol (HFIP), gem-bis(triflyl)cyclobutenes, which can be prepared by the (2+2) cycloaddition reaction of Tf2C=CH2 with alkynes, underwent desulfination to generate the corresponding cyclobutenyl cation. This unique reactivity was successfully applied to the Friedel-Crafts type cyclobutenylation reaction of several (hetero)aromatic compounds.

Bora-Diaza-Indacene Based Fluorescent Probes for Simultaneous Visualisation of Lipid Droplets and Endoplasmic Reticulum

Organelle selective fluorescent probes, especially those capable of concurrent detection of specific organelles, are of benefit to the research community in delineating the interplay between various organelles and the impact of such interaction in maintaining cellular homeostasis and its disruption in the diseased state. Although very useful, such probes are synthetically challenging to design due to the stringent lipophilicity requirement posed by different organelles, and hence, the lack of such probes being reported so far. This work details the synthesis, photophysical properties, and cellular imaging studies of two bora-diaza-indacene based fluorescent probes that can specifically and simultaneously visualise lipid droplets and endoplasmic reticulum; two organelles suggested having close interactions and implicated in stress-induced cellular dysfunction and disease progression.

Pd and Pt Complexes of Benzo-Fused Dipyrrins: Synthesis, Structure, Electrochemical, and Optical Properties

Benzo-fused dipyrrins are π-extended analogs of conventional dipyrrins, which exhibit bathochromically shifted absorption and possess the synthetic capability to bind various metal ions. We aimed to investigate the synthetic potential of benzo-fused dipyrrins in the complexation with transition metals. Two new complexes with Pd2+ and Pt2+ were synthesized and characterized. X-ray crystallography reveals that both complexes exhibit a zigzag geometry with square planar coordination of the central metal. The Pd2+ complex possesses a very weak fluorescence at 665 nm, while the Pt2+ complex is completely nonemissive. Transient absorption spectroscopy confirmed triplet excited state formation for both complexes; however, they are short-lived and no phosphorescence was observed even at 77K. DFT calculations support the experimental observation, revealing the existence of the low-lying ligand-metal charge-transfer (LMCT) triplet state acting as an energy sink.