J-aggregates of strong electron-donating groups linked Aza-BODIPY adjusting by polypeptide for NIR-II phototheranostics

The commonly employed strategies for engineering second near-infrared (NIR-II) organic phototheranostic agents are based on expanding conjugated backbone length, strengthening donor (D)-acceptor (A) effect, or forming J-aggregates. We constructed the D-A-D' structure by incorporating strong electron-donating methoxy and tetraphenylethene (TPE) moieties on the electron-deficient Aza-BODIPY core, and simultaneously expanded the π-conjugation effect by introducing thiophene groups, to obtain a dye BDP-TPE. Next, the nanoparticles P-TPE were prepared via the assembly of BDP-TPE with amphiphilic polypeptides (mPEG2000-P(Asp)10), and successfully constructed the J-aggregates. The obtained P-TPE exhibited strong absorption and fluorescence with maxima at 808 and 1018 nm, respectively, with a conspicuous absolute quantum yield of 0.241 %. Moreover, P-TPE also showed excellent biocompatibility, and high photothermal conversion efficiency of 61.15 %, and excellent resistance to pH, long-term storage, and photobleaching. In vitro and in vivo experiments revealed that P-TPE exhibited good biocompatibility and effectively achieved NIR-II fluorescence imaging-guided PTT with complete tumor ablation under 808 nm laser irradiation. These results provided good evidence for the use of P-TPE as a NIR-II fluorescence imaging-guided PTT therapeutic agent in vivo.

Conceptually innovative fluorophores for functional bioimaging

Fluorophore chemistry is at the forefront of bioimaging, revolutionizing the visualization of biological processes with unparalleled precision. From the serendipitous discovery of mauveine in 1856 to cutting-edge fluorophore engineering, this field has undergone transformative evolution. Today, the synergy of chemistry, biology, and imaging technologies has produced diverse, specialized fluorophores that enhance brightness, photostability, and targeting capabilities. This review delves into the history and innovation of fluorescent probes, showcasing their pivotal role in advancing our understanding of cellular dynamics and disease mechanisms. We highlight groundbreaking molecules and their applications, envisioning future breakthroughs that promise to redefine biomedical research and diagnostics.

Janus Reactivity of Crownphyrinoids: Alkali- vs. Transition Metal-Mediated Transformations of Crown Ether-Porphyrin Hybrids

Crownphyrinogens and crownphyrins constitute a group of macrocycles that combine the structural facets of porphyrinoids and crown ethers. The dual-nature cavity embedded in their molecules enables reactivity involving two structurally distinct parts of the macrocyclic ligand. Upon Ni(II) and Pd(II) insertion, coordination compounds are produced wherein the metal is incorporated into the porphyrinoid-like pocket, resulting in monomeric or accordion-like dimeric products, depending on the oxidation level of the macrocycle and metal cation. The reactions with Na(I) and K(I) resulted in the formation of complexes where only the crown ether segment of the molecule is involved in metal binding, yielding remarkable dimeric species. The exploitation of a crownphyrin large enough to accommodate two metal cations allowed the synthesis of an alkali/transition metal binuclear complexes wherein the macrocycle demonstrated the Janus reactivity with one cavity acting as a porphyrinoid and the other mimicking the crown ether.

Benzo-Fused BOPAM Fluorophores: Synthesis, Post-functionalization, Photophysical Properties and Acid sensing Applications

A novel category of asymmetric boron chromophores with the attachment of two BF2 moieties denoted as BOPAM has been successfully synthesized via a one-pot three-step reaction starting from N-phenylbenzothioamide. This synthetic route results in the production of [a] and [b]benzo-fused BOPAMs along with post-functionalization of the [a]benzo-fused BOPAMs. The photophysical properties of these compounds have been systematically investigated through steady-state absorption and fluorescence emission measurements in solvents at both ambient and cryogenic temperatures, as well as in the solid state. Computational methods have been employed to elucidate the emissive characteristics of the benzo-fused BOPAMs, revealing distinctive photophysical attributes, including solvent-dependent fluorescence intensity. Remarkably, certain BOPAM derivatives exhibit noteworthy photophysical phenomena, such as the induction of off-on fluorescence emission under specific solvent conditions and the manifestation of intermolecular charge transfer states in solid-state matrices. Through post-functionalization strategies involving the introduction of electron-donating groups onto the [a]benzo-fused BOPAM scaffold, an intramolecular charge transfer (ICT) pathway is activated, leading to substantial fluorescence quenching via non-radiative decay processes. Notably, one [a]benzo-fused BOPAM variant exhibits a pronounced fluorescence enhancement upon exposure to acidic conditions, thereby underscoring its potential utility in pH-sensing applications.

BODIPY dyes for optical limiting applications on the nanosecond timescale

Since 2017, the Institute for Nanotechnology Innovation at Rhodes University has studied the optical limiting properties of boron dipyrromethene (BODIPY) dyes with respect to high-intensity nanosecond timescale laser pulses. Concerns over the irresponsible use of laser pointers in the context of aviation safety have provided a need for materials that can readily transmit light under ambient conditions while rapidly attenuating intense incident laser pulses. The structural flexibility of the BODIPY chromophore facilitates the red shift of the main BODIPY spectral band that typically lies at ca. 500 nm to the red end of the visible and the near-infrared through the introduction of vinylene groups at the 3,5-positions or an aza-nitrogen atom. Research carried out in this context is described, and possible future directions are discussed.

Investigation and Development of the BODIPY-Embedded Isotopic Signature for Chemoproteomics Labeling and Targeted Profiling

A common goal in mass spectrometry-based chemoproteomics is to directly measure the site of conjugation between the target protein and the small molecule ligand. However, these experiments are inherently challenging due to the low abundance of labeled proteins and the difficulty in identifying modification sites using standard proteomics software. Reporter tags that either generate signature fragment ions or isotopically encode target peptides can be used for the preemptive discovery of labeled peptides even in the absence of identification. We investigated the potential of BODIPY FL azide as a click chemistry enabled chemoproteomics reagent due to the presence of boron and the unique 1:4 natural abundance ratio of 10B:11B. The isotopes of boron encode BODIPY-labeled peptides with a predictable pattern between the monoisotopic (M) and M+1 peaks. BODIPY-labeled peptides were identified in MS1 spectra using an R script that filters for the signature 10B:11B intensity ratio and mass defect. Application of the boron detection script resulted in three times the labeled peptide coverage achieved for a BODIPY-conjugated BSA sample compared with untargeted data-dependent acquisition sequencing. Furthermore, we used the inherent HF neutral loss signature from BODIPY to assist with BODIPY-modified peptide identification. Finally, we demonstrate the application of this approach using the BODIPY-conjugated BSA sample spiked into a complex E. coli. digest. In summary, our results show that the commercially available BODIPY FL azide clicked to alkyne-labeled peptides provides a unique isotopic signature for pinpointing the site(s) of modification with the added potential for on- or off-line UV or fluorescence detection.

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.

Sequential nucleophilic aromatic substitutions on cyanuric chloride: synthesis of BODIPY derivatives and mechanistic insights

Herein we report a study on the sequential substitution of different nucleophiles on cyanuric chloride to obtain potential candidates for metal sensors (5a-c). The set of nucleophiles on the 1,3,5-triazine ring includes a phenolic BODIPY, an aminoalkyl pyridine and aminoalkyl phosphoramidates, each one designed to play a specific role in the final fluoroionophore. Three new triazine triads were synthesized in similar yields: 5a (45%), 5b (43%) and 5c (52%) after a methodical sequential combination of the nucleophiles via thermodependent nucleophilic aromatic substitution of the three chlorine atoms of cyanuric chloride. To ratify the synthetic results we simulated the reaction mechanisms for the different nucleophiles, aiming to address the distinctive orthogonality and temperature control inherent in this process, identifying and providing a sound rationale for any preferential sequence of nucleophiles inserted into the triazine core. According to our experimental and computational analysis (thermo- and kinetic preferences), we have identified the following preferential order for the sequential substitution: p-hydroxybenzaldehyde > 2-(pyridin-2-yl)ethanamine > aminoalkyl phosphoramidate, indicating that all steps follow a single-step process (concerted) in two stages, where nucleophilic addition precedes leaving group dissociation. The Meisenheimer σ-complex was identified as a transition state structure, with insufficient stability to exist as an intermediate. We observed a consistent and progressive increase in barrier height: 2-8 kcal mol-1 for the first step, 9-15 kcal mol-1 for the second step, and >15 kcal mol-1 for the third substitution. These findings align with the experimental observation of thermodependency in the sequential substitution.

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.

Supramolecular dye nanoassemblies for advanced diagnostics and therapies

Dyes have conventionally been used in medicine for staining cells, tissues, and organelles. Since these compounds are also known as photosensitizers (PSs) which exhibit photoresponsivity upon photon illumination, there is a high desire towards formulating these molecules into nanoparticles (NPs) to achieve improved delivery efficiency and enhanced stability for novel imaging and therapeutic applications. Furthermore, it has been shown that some of the photophysical properties of these molecules can be altered upon NP formation thereby playing a major role in the outcome of their application. In this review, we primarily focus on introducing dye categories, their formulation strategies and how these strategies affect their photophysical properties in the context of photothermal and non-photothermal applications. More specifically, the most recent progress showing the potential of dye supramolecular assemblies in modalities such as photoacoustic and fluorescence imaging, photothermal and photodynamic therapies as well as their employment in photoablation as a novel modality will be outlined. Aside from their photophysical activity, we delve shortly into the emerging application of dyes as drug stabilizing agents where these molecules are used together with aggregator molecules to form stable nanoparticles.

A Practical and Modular Method for Direct C-H Functionalization of the BODIPY Core via Thianthrenium Salts

Direct structural modification of small-molecule fluorophores represents a straightforward and appealing strategy for accessing new fluorescent dyes with desired functionalities. We report herein a general and efficient visible-light-mediated method for the direct C-H functionalization of BODIPY, an important fluorescent chromophore, using readily accessible and bench-stable aryl and alkenylthianthrenium salts. This practical approach operates at room temperature with extraordinary site-selectivity, providing a step-economical means to construct various valuable aryl- and alkenyl-substituted BODIPY dyes. Remarkably, this protocol encompasses a broad substrate scope and excellent functional-group tolerance, and allows for the modular synthesis of sophisticated symmetrical and asymmetrical disubstituted BODIPYs by simply employing different combinations of thianthrenium salts. Moreover, the late-stage BODIPY modification of complex drug molecules further highlights the potential of this novel methodology in the synthesis of fluorophore-drug conjugates.

One- and two-photon absorption spectra of organoboron complexes: vibronic and environmental effects

We synthesized a series of four parent aza-β-ketoiminate organoboron complexes and performed spectroscopic studies using both experimental and computational techniques. We studied how benzannulation influences the vibronic structure of the UV/Vis absorption bands with a focus on the bright lowest-energy π → π* electronic excitation. Theoretical simulations, accounting for inhomogeneous broadening effects using different embedding schemes, allowed gaining in-depth insights into the observed differences in band shapes induced by structural modifications. We observed huge variations in the distributions of vibronic transitions depending on the position of benzannulation. By and large, the harmonic approximation combined with the adiabatic hessian model delivers qualitatively correct band shapes for the one-photon absorption spectra, except in one case. We also assessed the importance of non-Condon effects (accounted for by the linear term in Herzberg-Teller expansion of the dipole moment) for S0 → S1 band shapes. It turned out that non-Condon contributions have no effect on the band shape in one-photon absorption spectra. In contrast, these effects significantly change the Franck-Condon band shapes of the two-photon absorption spectra. For one of the studied organoboron complexes we also performed a preliminary exploration of mechanical anharmonicity, resulting in an increase of the intensity of the 0-0 transition, which improves the agreement with the experimental data compared to the harmonic model.

Designing Antitrypanosomal and Antileishmanial BODIPY Derivatives: A Computational and In Vitro Assessment

Leishmaniasis and Human African trypanosomiasis pose significant public health threats in resource-limited regions, accentuated by the drawbacks of the current antiprotozoal treatments and the lack of approved vaccines. Considering the demand for novel therapeutic drugs, a series of BODIPY derivatives with several functionalizations at the meso, 2 and/or 6 positions of the core were synthesized and characterized. The in vitro activity against Trypanosoma brucei and Leishmania major parasites was carried out alongside a human healthy cell line (MRC-5) to establish selectivity indices (SIs). Notably, the meso-substituted BODIPY, with 1-dimethylaminonaphthalene (1b) and anthracene moiety (1c), were the most active against L. major, displaying IC50 = 4.84 and 5.41 μM, with a 16 and 18-fold selectivity over MRC-5 cells, respectively. In contrast, the mono-formylated analogues 2b and 2c exhibited the highest toxicity (IC50 = 2.84 and 6.17 μM, respectively) and selectivity (SI = 24 and 11, respectively) against T. brucei. Further insights on the activity of these compounds were gathered from molecular docking studies. The results suggest that these BODIPYs act as competitive inhibitors targeting the NADPH/NADP+ linkage site of the pteridine reductase (PR) enzyme. Additionally, these findings unveil a range of quasi-degenerate binding complexes formed between the PRs and the investigated BODIPY derivatives. These results suggest a potential correlation between the anti-parasitic activity and the presence of multiple configurations that block the same site of the enzyme.

Mitochondria-targeted BODIPY dyes for small molecule recognition, bio-imaging and photodynamic therapy

Mitochondria are essential for a diverse array of biological functions. There is increasing research focus on developing efficient tools for mitochondria-targeted detection and treatment. BODIPY dyes, known for their structural versatility and excellent spectroscopic properties, are being actively explored in this context. Numerous studies have focused on developing innovative BODIPYs that utilize optical signals for imaging mitochondria. This review presents a comprehensive overview of the progress made in this field, aiming to investigate mitochondria-related biological events. It covers key factors such as design strategies, spectroscopic properties, and cytotoxicity, as well as mechanism to facilitate their future application in organelle imaging and targeted therapy. This work is anticipated to provide valuable insights for guiding future development and facilitating further investigation into mitochondria-related biological sensing and phototherapy.

Linear Amine-Linked Oligo-BODIPYs: Convergent Access via Buchwald-Hartwig Coupling

A convergent route toward nitrogen-bridged BODIPY oligomers has been developed. The synthetic key step is a Buchwald-Hartwig cross-coupling reaction of an α-amino-BODIPY and the respective halide. Not only does the selective synthesis provide control of the oligomer size, but the facile preparative procedure also enables easy access to these types of dyes. Furthermore, functionalized examples were accessible via brominated derivatives.

The Advent of Bodipy-based Chemosensors for Sensing Fluoride Ions: A Literature Review

The detection of fluoride ions in water and other sources is crucial because they can harm human health if they exceed the safe limit of 1-1.5 ppm. BODIPY (boron dipyrromethene) dyes are promising fluorophores for chemosensors, and their design and modification have attracted a lot of attention. Their advantages include visible light excitation and emission, high molar absorption coefficients (ε) and fluorescence quantum yields [ϕ (λ)], and flexible scaffold manipulation for various applications. In this article, we review the progress of BODIPY-based sensors for fluoride ions from the early 2000s to the present. We focus on the different scaffold modifications of the sensors and their corresponding responses, as well as the underlying photophysical mechanisms and potential uses of each sensor.

Synthesis and Properties of Bright Red-to-NIR BODIPY Dyes for Targeting Fluorescence Imaging and Near-Infrared Photothermal Conversion

An efficient synthesis of 3-pyrrolylBODIPY dyes has been developed from a rational mixture of various aromatic aldehydes and pyrrole in a straightforward condensation reaction, followed by in situ successively oxidative nucleophilic substitution using a one-pot strategy. These resultant 3-pyrrolylBODIPYs without blocking substituents not only exhibit the finely tunable photophysical properties induced by the flexible meso-aryl substituents but also serve as a valuable synthetic framework for further selective functionalization. As a proof of such potential, one 3-pyrrolylBODIPY dye (581/603 nm) through the installation of the morpholine group is applicable for lysosome-targeting imaging. Furthermore, an ethene-bridged 3,3'-dipyrrolylBODIPY dimer was constructed, which displayed a near-infrared (NIR) emission extended to 1200 nm with a large fluorescence brightness (2840 M-1 cm-1). The corresponding dimer nanoparticles (NPs) afforded a high photothermal conversion efficiency (PCE) value of 72.5%, eventually resulting in favorable photocytotoxicity (IC50 = 9.4 μM) and efficient in vitro eradication of HeLa cells under 808 nm laser irradiation, highlighting their potential application for photothermal therapy in the NIR window.

An easy tool to monitor the elemental steps of in vitro translation via gel electrophoresis of fluorescently labeled small peptides

Several methods are available to visualize and assess the kinetics and efficiency of elemental steps of protein biosynthesis. However, each of these methods has its own limitations. Here, we present a novel, simple and convenient tool for monitoring stepwise in vitro translation initiated by BODIPY-Met-tRNA. Synthesis and release of very short, 1-7 amino acids, BODIPY-labeled peptides, can be monitored using urea-polyacrylamide gel electrophoresis. Very short BODIPY-labeled oligopeptides might be resolved this way, in contrast to widely used Tris-tricine gel electrophoresis, which is suitable to separate peptides larger than 1 kDa. The method described in this manuscript allows one to monitor the steps of translation initiation, peptide transfer, translocation, and termination as well as their inhibition at an unprecedented single amino acid resolution.

Easy access to strongly fluorescent higher homologues of BODIPY

We present the easy and high yield synthesis of several group 13 MesDPM compounds (Al-In) with alkyl substituents at the metal atom. All these compounds were fully characterized using techniques including X-ray diffraction analysis and photoluminescence measurements. It shows that for aluminium and gallium pronounced green fluorescence is observed, which is absent for indium. DFT calculations confirm that the first electronic transition corresponds to a ligand-based π-π* transition.

Carbonylation as a Key Step in New Tandem Reactions - A Route to BODIPYs

Herein, a highly efficient five-step reaction sequence to BODIPYs is presented. The key step is the combination of transition metal-catalyzed in-situ generation of aldehydes and their subsequent organocatalytic activation to yield dipyrromethanes, which are further converted to the corresponding BODIPY. Classic syntheses towards BODIPYs have relied on aldehydes or acid chlorides, which are often not commercially available and rather sensitive to handle. The presented approach starts from readily available and stable alkenes or aryl-bromides, which allows to extend the range of readily available BODIPYs that can be tailored for their specific use. The synthesis of 55 derivatives with overall yields of up to 78 % demonstrates the wide applicability and advantages of the presented method.

Electropolymerization on ITO-Coated Glass Slides of a Series of π-Extended BODIPY Dyes with Redox-Active Meso-Substituents

A series of meso-carbazole and meso-pyrene boron dipyrromethene(BDP) dyes have been synthesized using a two-step method. This simplified synthetic method did not require catalysts or oxidizing agents. Solution spectroscopic and electrochemical studies indicate that the HOMO and LUMO energies are dependent on the extent of π-conjugation associated with the pyrroles. Solution electrochemistry of the dyes in chloroform reveal film formation onto glassy carbon electrodes. Electrolysis of chloroform solutions of the dyes using indium tin oxide (ITO) glass slides as the working electrode show, using UV/vis spectroscopy, the formation of films. For two of the dyes, the BODIPY structure stays in tact upon electrolysis, exhibiting sharp absorption peaks on the ITO slides similar to that observed for the same dyes in solution.

Design and synthesis of a BOAHY-derived tracker for fluorescent labeling of mitochondria

Fluorescence microscopy has proven to be a crucial powerful tool to specifically visualize cellular organelles. In-depth visualization of the structure of mitochondria in living cells is of great value to better understand their function. Herein, based on our experience in construction of fluorescent difluoroboronate anchored acylhydrazones (BOAHY) chromophores, we rationally designed a novel monoboron complex with a connected triphenylphosphonium moiety, and evaluated its spectroscopic properties, cytotoxicity and intracellular localization. Owing to the positive charge on our fluorescent dye, the molecule had an excellent mitochondria-targeting ability (Pearson's correlation is 0.86).To the best of our knowledge, this is the first example of a BOAHY dye which has been applied as an efficient tracker to target mitochondria in living cells.

BODIPY-Based Molecules for Biomedical Applications

BODIPY (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) derivatives have attracted attention as probes in applications like imaging and sensing due to their unique properties like (1) strong absorption and emission in the visible and near-infrared regions of the electromagnetic spectrum, (2) strong fluorescence and (3) supreme photostability. They have also been employed in areas like photodynamic therapy. Over the last decade, BODIPY-based molecules have even emerged as candidates for cancer treatments. Cancer remains a significant health issue world-wide, necessitating a continuing search for novel therapeutic options. BODIPY is a flexible fluorophore with distinct photophysical characteristics and is a fascinating drug development platform. This review provides a comprehensive overview of the most recent breakthroughs in BODIPY-based small molecules for cancer or disease detection and therapy, including their functional potential.

Access to isoindole-derived BODIPYs by an aminopalladation cascade

Here, we present a new route to dyes of the BODIPY family. We first built up a N-Boc-protected dipyrromethene scaffold via an aminopalladation cascade. Subsequentially, the pyrrole moiety was deprotected and the BF2 unit inserted. Depending on the terminating reaction, BODIPYs with either aryl or alkynyl moieties were accessible.

Antiproliferative activity of meso-substituted BODIPY photocages: Effect of electrophiles vs singlet oxygen

A series of BODIPY compounds with a methylphenol substituent at the meso-position and halogen atoms on the BODIPY core, or OCH3 or OAc substituents at the phenolic moiety was synthesized. Their spectral and photophysical properties and the photochemical reactivity upon irradiation in CH3OH were investigated. The molecules with the phenolic substituent at the meso-position undergo more efficient photo-methanolysis at the boron atom, while the introduction of the OCH3 group at the phenolic moiety changes the reaction selectivity towards the cleavage at the meso-position. The introduction of the halogen atoms into the BODIPY increases the photo-cleavage reaction efficiency, as well as the ability of the molecules to sensitize oxygen and form reactive oxygen species (ROS). The efficiency of the ROS formation was measured in comparison with that of tetraphenylporphyrin. The antiproliferative effect of BODIPY molecules was investigated against three human cancer cell lines MCF-7 (breast carcinoma), H460 (lung carcinoma), HCT116 (colon carcinoma), and two non-cancer cell lines, HEK293T (embryonic kindey) and HaCaT (keratinocytes), with the cells kept in the dark or irradiated with visible light. For most of the compounds a modest or no antiproliferative activity was observed for cells in the dark. However, when cells were irradiated, a dramatic increase in cytotoxicity was observed (more than 100-fold), with IC50 values in the submicromolar concentration range. The enhancement of the cytotoxic effect was explained by the formation of ROS, which was studied for cells in vitro. However, for some BODIPY compounds, the effects due to the formation of electrophilic species (carbocations and quinone methides, which react with biomolecules) cannot be disregarded. Confocal fluorescence microscopy images of H460 cells and HEK293T show that the compounds enter the cells and are retained in the cytoplasm and membranes of the various organelles. When the cells treated with the compounds are irradiated, photo-processes lead to cell death by apoptosis. The study performed is important because it provides bases for the development of novel photo-therapeutics capable of exerting photo-cytotoxic effects in both oxygenated and hypoxic cells.

One- and two-electron reductions of a bulky BODIPY compound

The redox reaction between a bulky BODIPY and a magnesium(I) reducing agent leads to the formal one-electron reduction of the BODIPY, initially generating a dipyrromethene-centred radical compound that dimerises via C-C bond formation. In contrast, reduction with magnesium anthracene leads to the formal two-electron reduction of the BODIPY, resulting in the formation of the corresponding anion.

Visible-Light-Induced Direct Photoamination of BODIPY Dyes with Aqueous Ammonia

By taking advantage of their strong absorption ability, visible-light-induced direct photoamination of BODIPY dyes with aqueous ammonia was developed to give structurally diverse α-amino BODIPYs. The excited state of BODIPYs possessed higher electron affinity than the ground state and thus showed largely enhanced reactivity toward weak nucleophile of ammonia. Those α-amino BODIPYs are valuable synthetic intermediates and have been successfully demonstrated in several post-transformation reactions. The work indicates that photoreaction is an excellent alternative to conventional functionalization of this popular fluorophore.

Functional Diversity in Radiolabeled Nanoceramics and Related Biomaterials for the Multimodal Imaging of Tumors

Nanotechnology advances have the potential to assist toward the earlier detection of diseases, giving increased accuracy for diagnosis and helping to personalize treatments, especially in the case of noncommunicative diseases (NCDs) such as cancer. The main advantage of nanoparticles, the scaffolds underpinning nanomedicine, is their potential to present multifunctionality: synthetic nanoplatforms for nanomedicines can be tailored to support a range of biomedical imaging modalities of relevance for clinical practice, such as, for example, optical imaging, computed tomography (CT), magnetic resonance imaging (MRI), single photon emission computed tomography (SPECT), and positron emission tomography (PET). A single nanoparticle has the potential to incorporate myriads of contrast agent units or imaging tracers, encapsulate, and/or be conjugated to different combinations of imaging tags, thus providing the means for multimodality diagnostic methods. These arrangements have been shown to provide significant improvements to the signal-to-noise ratios that may be obtained by molecular imaging techniques, for example, in PET diagnostic imaging with nanomaterials versus the cases when molecular species are involved as radiotracers. We surveyed some of the main discoveries in the simultaneous incorporation of nanoparticulate materials and imaging agents within highly kinetically stable radio-nanomaterials as potential tracers with (pre)clinical potential. Diversity in function and new developments toward synthesis, radiolabeling, and microscopy investigations are explored, and preclinical applications in molecular imaging are highlighted. The emphasis is on the biocompatible materials at the forefront of the main preclinical developments, e.g., nanoceramics and liposome-based constructs, which have driven the evolution of diagnostic radio-nanomedicines over the past decade.

Recent Developments in the Design of New Water-Soluble Boron Dipyrromethenes and Their Applications: An Updated Review

Boron-dipyrromethene (BODIPY) and its derivatives play an important role in the area of organic fluorophore chemistry. Recently, the water-soluble boron-dipyrromethene dyes have increasingly received interest. The structural modification of the BODIPY core by incorporating different neutral and ionic hydrophilic groups makes it water-soluble. The important hydrophilic groups, such as quaternary ammonium, sulfonate, oligoethylene glycol, dicarboxylic acid, and sugar moieties significantly increase the solubility of these dyes in water while preserving their photophysical properties. As a result, these fluorescent dyes are utilized in aqueous systems for applications such as chemosensors, cell imaging, anticancer, biolabeling, biomedicine, metal ion detection, and photodynamic treatment. This review covers the most current developments in the design and synthesis of water-soluble BODIPY derivatives and their wide applications since 2014.

Regioselective Synthesis of Directly Connected BODIPY Dimers through Oxidative Coupling of α-Amino-Substituted BODIPYs

A family of directly β,β-linked BODIPY dimers with amino groups at α-positions were regioselectively prepared by the oxidative coupling reaction of α-amino-substituted BODIPYs. The structure of one representative dimer was elucidated by X-ray diffraction analysis, showing its twisted orientation of two BODIPY units with a dihedral angle of 49°. Comparing with the corresponding monomers, these dimers showed red-shifted absorptions and emissions along with efficient intersystem crossing, giving Φ_Δ of 43% for dimer 4b in toluene, indicating potential use as heavy-atom-free photosensitizers.

Interaction of Ions in Organic and Aqueous Media with an Ion-Pair Sensor Equipped with a BODIPY Reporter: An ON1-OFF-ON2-ON3 Fluorescent Assay

Here, we present a ditopic ion-pair sensor, B1, containing the BODIPY reporter unit in its structure, which is shown to be able-thanks to the presence of two heterogeneous binding domains-to interact with anions in an enhanced manner in the presence of cations. This enables it to interact with salts even in 99% aqueous solutions, making B1 a good candidate in terms of visual salt detection in the aquatic environment. Receptor B1's ability to extract and release salt was applied in the transport of potassium chloride through a bulk liquid membrane. Working with a concentration of B1 in the organic phase and with the presence of a specific salt in an aqueous solution, an inverted transport experiment was also demonstrated. By varying the type and the amount of the anions added to B1, we were able to develop diverse optical responses, including a unique four-step ON1-OFF-ON2-ON3 output.

BODIPY as a Multifunctional Theranostic Reagent in Biomedicine: Self-Assembly, Properties, and Applications

The use of boron dipyrromethene (BODIPY) in biomedicine is reviewed. To open, its synthesis and regulatory strategies are summarized, and inspiring cutting-edge work in post-functionalization strategies is highlighted. A brief overview of assembly model of BODIPY is then provided: BODIPY is introduced as a promising building block for the formation of single- and multicomponent self-assembled systems, including nanostructures suitable for aqueous environments, thereby showing the great development potential of supramolecular assembly in biomedicine applications. The frontier progress of BODIPY in biomedical application is thereafter described, supported by examples of the frontiers of biomedical applications of BODIPY-containing smart materials: it mainly involves the application of materials based on BODIPY building blocks and their assemblies in fluorescence bioimaging, photoacoustic imaging, disease treatment including photodynamic therapy, photothermal therapy, and immunotherapy. Lastly, not only the current status of the BODIPY family in the biomedical field but also the challenges worth considering are summarized. At the same time, insights into the future development prospects of biomedically applicable BODIPY are provided.

Synthesis, structural characterization, and chiroptical properties of planarly and axially chiral boranils

2-Amino[2.2]paracyclophane reacts with salicylaldehyde or 2-hydroxyacetophenone to yield imines that then give access to a new series of boranils (8b-d) upon complexation with BF₂ . These novel boron-containing compounds display both planar and axial chiralities and were examined experimentally and computationally. In particular, their photophysical and chiroptical properties were studied and compared to newly prepared, simpler boranils (9a-d) exhibiting axial chirality only. Less sophisticated chiral architectures were shown to demonstrate overall stronger circularly polarized luminescence (CPL) activity.

Self-Assembled BODIPY Nanoparticles for Near-Infrared Fluorescence Bioimaging

In vivo optical imaging is an important application value in disease diagnosis. However, near-infrared nanoprobes with excellent luminescent properties are still scarce. Herein, two boron–dipyrromethene (BODIPY) molecules (BDP-A and BDP-B) were designed and synthesized. The BODIPY emission was tuned to the near-infrared (NIR) region by regulating the electron-donating ability of the substituents on its core structure. In addition, the introduction of polyethylene glycol (PEG) chains on BODIPY enabled the formation of self-assembled nanoparticles (NPs) to form optical nanoprobes. The self-assembled BODIPY NPs present several advantages, including NIR emission, large Stokes shifts, and high fluorescence quantum efficiency, which can increase water dispersibility and signal-to-noise ratio to decrease the interference by the biological background fluorescence. The in vitro studies revealed that these NPs can enter tumor cells and illuminate the cytoplasm through fluorescence imaging. Then, BDP-B NPs were selected for use in vivo imaging due to their unique NIR emission. BDP-B was enriched in the tumor and effectively illuminated it via an enhanced penetrability and retention effect (EPR) after being injected into the tail vein of mice. The organic nanoparticles were metabolized through the liver and kidney. Thus, the BODIPY-based nanomicelles with NIR fluorescence emission provide an effective research basis for the development of optical nanoprobes in vivo.

Anti-stokes luminescent organic nanoparticles for frequency upconversion biomedical imaging

Frequency upconversion optical imaging has attracted great attention due to its remarkable advantages over traditional down-conversion optical imaging. However, the development of frequency upconversion optical imaging is extremely limited. Herein, five derivatives with BODIPY structure (B1-B5) were developed to investigate its frequency upconversion luminescence (FUCL) performance by introducing electron-donating and electron-withdrawing groups. Except for the nitro group decorated derivative, the other derivatives have strong and stable FUCL around 520 nm under 635 nm light excitation. More importantly, B5 retains FUCL ability after self-assembly. When applied to FUCL imaging of cells, B5 nanoparticles can be enriched in the cytoplasm and show a good signal-to-noise ratio. Meanwhile, FUCL tumor imaging can be achieved after 1 h of injection. This study not only provides a potential agent for FUCL biomedical imaging but also develops a new strategy for designing FUCL agents that exhibit excellent performance.

Red-to-Near-Infrared Emitting PyrrolylBODIPY Dyes: Synthesis, Photophysical Properties and Bioimaging Application

Near-infrared (NIR) fluorophores with characteristics such as deep tissue penetration, minimal damage to the biological samples, and low background interference, are highly sought-after materials for in vivo and deep-tissue fluorescence imaging. Herein, series of 3-pyrrolylBODIPY derivatives and 3,5-dipyrrolylBODIPY derivatives have been prepared by a facile regioselective nucleophilic aromatic substitution reaction (S_N Ar) on 3,5-halogenated BODIPY derivatives (3,5-dibromo or 2,3,5,6-tetrachloroBODIPYs) with pyrroles. The installation of a pyrrolic unit onto the 3-position of the BODIPY chromophore leads to a dramatic red shift of both the absorption (up to 160 nm) and the emission (up to 260 nm) in these resultant 3-pyrrolylBODIPYs with respect to that of the BODIPY chromophore. Their further 5-positional functionalization provides a facile way to fine tune their photophysical properties, and these resulting dipyrrolylBODIPYs and functionalized pyrrolylBODIPYs show strong absorption in the deep red-to-NIR regions (595-684 nm) and intense NIR fluorescence emission (650-715 nm) in dichloromethane. To demonstrate the applicability of these functionalized pyrrolylBODIPYs as NIR fluorescent probes for cell imaging, pyrrolylBODIPY 6 a containing mitochondrion-targeting butyltriphenylphosphonium cationic species was also prepared. It selectively localized in mitochondria of HeLa cells, with low cytotoxicity and intense deep red fluorescence emission.

Aryl-Boron-Substituted BODIPYs: Direct Access via Aluminum-Chloride-Mediated Arylation from Arylstannanes and Tuning the Optoelectronic Properties

An efficient procedure is presented for functionalization of BODIPYs at boron with arylstannanes as weak nucleophiles in the presence of aluminum chloride, providing new aryl-boron-substituted BODIPY and aza-BODIPY derivatives of singular importance. Most of these aryl-boron-substituted BODIPYs showed bright emission in the aqueous solution with significant aggregation-induced emission enhancement and high solid-state emission as a result of the restricted rotation of the meso-phenyl group and boron-substituted aryl groups as well as the formation of J-type aggregates.

Nucleotides Bearing Red Viscosity-Sensitive Dimethoxy-Bodipy Fluorophore for Enzymatic Incorporation and DNA Labeling

Nucleosides and 2'-deoxyribonucleoside triphosphates (dNTPs) bearing 3,3'-dimethoxy-2,2'-diphenyl-6-(4-hydroxyphenyl)-bodipy fluorophore attached through a propargyl or propargyl-triethylene glycol linker to position 5 of 2'-deoxycytidine were designed and synthesized. They exerted bright red fluorescence and good sensitivity to viscosity changing their lifetime from 1.6 to 4.5 ns. The modifed dNTPs were substrates for DNA polymerases and were used in enzymatic synthesis of labeled DNA through primer extension. The modified DNA probes served as viscosity sensors responding to protein binding by changes of lifetime. The nucleotide with longer linker (dC^pegMOBTP) was transported to live cells and incorporated into the genomic DNA, which can be useful for staining of DNA and imaging of DNA synthesis.

Recent Advances in N-Heterocyclic Small Molecules for Synthesis and Application in Direct Fluorescence Cell Imaging

Nitrogen-containing heterocycles are ubiquitous in natural products and drugs. Various organic small molecules with nitrogen-containing heterocycles, such as nitrogen-containing boron compounds, cyanine, pyridine derivatives, indole derivatives, quinoline derivatives, maleimide derivatives, etc., have unique biological features, which could be applied in various biological fields, including biological imaging. Fluorescence cell imaging is a significant and effective imaging modality in biological imaging. This review focuses on the synthesis and applications in direct fluorescence cell imaging of N-heterocyclic organic small molecules in the last five years, to provide useful information and enlightenment for researchers in this field.

Unconventional OFF-ON Response of a Mono(calix[4]arene)-Substituted BODIPY Sensor for Hg2+ through Dimerization Reversion

A new selective fluorogenic chemosensor for Hg²⁺, which combines a calixarene derivative with a BODIPY core as a fluorescent reporter, is described. The remarkable change in its fluorogenic properties in DMSO and CHCl₃ has been analyzed. A study of its spectral properties on dilution, along with molecular modeling studies, allowed us to explain that this behavior involves the formation of a J-dimer, as well as how the sensing mechanism of Hg²⁺ proceeds.

Halogen-free photosensitizers based on meso-enamine-BODIPYs for bioimaging and photodynamic therapy

The search for efficient heavy atom free photosensitizers (PSs) for photodynamic therapy (PDT) is a very active field. We describe herein a simple and easily accessible molecular design based on the attachment of an enamine group as an electron-donor moiety at the meso position of the BODIPY core with different alkylation patterns. The effect of the alkylation degree and solvent polarity on the photophysical properties in terms of splitting absorption bands, fluorescence efficiencies and singlet oxygen production is analyzed in depth experimentally using spectroscopic techniques, including femtosecond and nanosecond transient absorption (fs- and ns-TA) and using computational simulations based on time-dependent density functional theory. The correlation between the theoretical/experimental results permits the rationalization of the observed photophysical behavior exhibited by meso-enamine-BODIPY compounds and the determination of mechanistic details, which rule the population of the triplet state manifold. The potential applicability as a theragnostic agent for the most promising compound is demonstrated through in vitro assays in HeLa cells by analyzing the internalization, localization and phototoxic action.

Long-Wavelength Photoconvertible Dimeric BODIPYs for Super-Resolution Single-Molecule Localization Imaging in Near-Infrared Emission

Sulfoxide-bridged dimeric BODIPYs were developed as a new class of long-wavelength photoconvertible fluorophores. Upon visible-light irradiation, a sulfoxide moiety was released to generate the corresponding α,α-directly linked dimeric BODIPYs. The extrusion of SO from sulfoxides was mainly through an intramolecular fashion involving reactive triplet states. By this photoconversion, not only were more than 100 nm red shifts of absorption and emission maxima (up to 648/714 nm) achieved but also stable products with bright fluorescence were produced with high efficiency. The combination of photoactivation and red-shifted excitation/emission offered optimal contrast and eliminated the interference from biological autofluorescence. More importantly, the in situ products of these visible-light-induced reactions demonstrated ideal single-molecule fluorescence properties in the near-infrared region. Therefore, this new photoconversion could be a powerful photoactivation method achieving super-resolution single-molecule localization imaging in a living cell without using UV illumination and cell-toxic additives.

Photophysical properties of furan-bridged dimeric boron-dipyrromethene derivatives (BODIPYs)

In order to investigate the changes in the spectroscopic properties of dimeric boron-dipyrromethenes (BODIPYs), four BODIPY derivatives are synthesized, including a monomer BODIPY in which a furyl group is substituted at the meso position and a dimer BODIPY with a furan group as a bridge. The four synthesized BODIPY derivatives are characterized through nuclear magnetic resonance and mass spectrometry. Photophysical properties such as ultraviolet–visible absorbance and the fluorescence emission of monomers (mT1 and mT2) and dimers (biT1 and biT2) are studied in eight different solvents. In addition, the relationship of their structural properties and optical properties are also considered through density functional theory calculations. The covalent link between the two BODIPY units using a furan group has a profound effect on the optical properties of the dimeric BODIPYs. We believe that an understanding of the synthesis and physical properties of dimeric BODIPYs will have a promising perspective in designing new BODIPY derivatives and predicting their spectroscopic characteristics in the future.