Synthesis of BODIPY dyes through postfunctionalization of the boron dipyrromethene core

Structural tuning of tetrazole-BODIPY Ag(i) coordination compounds via co-ligand addition and counterion variation

The coordination properties of a previously described fluorescence active ligand (L), consisting of a coordinating unit (1H-tetrazol-1-yl) and a fluorophore (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) derivative) towards Ag(i) were investigated. Additionally, the influence of different anions (BF4 -, PF6 -, PF2O2 -, ClO4 -, ReO4 - and NO3 -) and a co-ligand (CH3CN) on the crystal structure formation and intramolecular interactions of the Ag(i) coordination compounds was studied. Beside structural investigations via single crystal X-ray diffraction, bulk characterization of the coordination compounds was conducted in both solution and solid-state, including NMR (1H, 11B, 19F, 31P and 13C), ATR-IR, UV-vis and photoluminescence spectroscopy as well as PXRD. Eleven distinct coordination compounds are reported, each falling into one of four classes: the first group (I) comprises of a mononuclear complex, whereas group (II) consists of dinuclear complexes with ligand bridged metal centers (Ag(i)) and weak intermetallic interactions (∼4 Å). Group (III) likewise includes dinuclear complexes, but the bridging mode was prevented and the Ag-Ag distance was reduced (∼3.2 Å) upon the addition of a co-ligand. Group (IV), a structurally diverse category consists of coordination polymers, which in some cases show even shorter intermetallic contacts (<3.1 Å). All investigated coordination compounds exhibit photoluminescence in the solid state, with structurally dependent emission maxima distinct from those of the ligand.

Green Light Activated Dual-Action Pt(IV) Prodrug with Enhanced PDT Activity

Light induced release of cisplatin from Pt(IV) prodrugs is a promising tool for precise spatiotemporal control over the antiproliferative activity of Pt-based chemotherapeutic drugs. A combination of light-controlled chemotherapy (PACT) and photodynamic therapy (PDT) in one molecule has the potential to overcome crucial drawbacks of both Pt-based chemotherapy and PDT via a synergetic effect. Herein we report green-light-activated Pt(IV) prodrug GreenPt with BODIPY-based photosentitizer in the axial position with an incredible high light response and singlet oxygen generation ability. GreenPt demonstrated the ability to release cisplatin under low-dose green light irradiation up to 1 J/cm2. The investigation of the photoreduction mechanism of GreenPt prodrug using DFT modeling and ΔG0 PET estimation revealed that the anion-radical formation and substituent photoinduced electron transfer from the triplet excited state of the BODIPY axial ligand to the Pt(IV) center is the key step in the light-induced release of cisplatin. Green-light-activated BODIPY-based photosentitizers 5 and 8 demonstrated outstanding photosensitizing properties with an extraordinary phototoxicity index (PI)>1300. GreenPt prodrug demonstrated gradual intracellular accumulation and light-induced phototoxicity with PI>100, thus demonstrating dual action through light-controlled release of both cisplatin and a potent BODIPY-based photosensitizer.

A Bright Future for Photopharmaceuticals Addressing Central Nervous System Disorders: State of the Art and Challenges Toward Clinical Translation

Photopharmacology is an innovative approach that uses light to activate drugs. This method offers the potential for highly localized and precise drug activation, making it particularly promising for the treatment of neurological disorders. Despite the enticing prospects of photopharmacology, its application to treat human central nervous system (CNS) diseases remains to be demonstrated. In this review, we provide an overview of prominent strategies for the design and activation of photopharmaceutical agents in the field of neuroscience. Photocaged and photoswitchable drugs and bioactive molecules are discussed, and an instructive list of examples is provided to highlight compound design strategies. Special emphasis is placed on photoactivatable compounds for the modulation of glutamatergic, GABAergic, dopaminergic, and serotonergic neurotransmission for the treatment of neurological conditions, as well as various photoresponsive molecules with potential for improved pain management. Compounds holding promise for clinical translation are discussed in-depth and their potential for future applications is assessed. Neurophotopharmaceuticals have yet to achieve breakthrough in the clinic, as both light delivery and drug design have not reached full maturity. However, by describing the current state of the art and providing illustrative case studies, we offer a perspective on future opportunities in the field of neurophotopharmacology focused on addressing CNS disorders.

Advancing diagnostics with BODIPY-bismuthene DNA biosensors

In this work, an electrochemical biosensor is prepared based on few-layer bismuthene hexagons (FLBHs) and a water-soluble BODIPY (BDP) derivative (BDP-NaSO3) for early infection diagnosis. In particular, the detection in advance of a virus sequence in nasopharyngeal swab samples was developed. The combination of the FLBHs and BDP-NaSO3 facilitates the direct, sensitive, and specific detection of gene viruses without the need for any prior amplification step. This work demonstrates that the FLBHs provide an improved electrochemical platform for immobilizing thiolated DNA capture probes that increase the sensitivity of the biosensor, while BDP-NaSO3 serves as a newly powerful electrochemical indicator of the hybridization event. As a proof of concept, SARS-CoV-2 was selected as the model virus. The developed biosensor demonstrated selective, rapid, and straightforward detection of the specific sequence RNA-dependent RNA-polymerase (RdRp) of SARS-CoV-2 with a detection limit of 4.97 fM and a linear range from 16.6 fM to 100 fM. Furthermore, this platform successfully detects the virus directly in nasopharyngeal swab samples with a viral load of at least 19 Cts without being subjected to any prior amplification stage. Finally, the high stability of the biosensor response, which has been working under ambient conditions for over one month, the selectivity and rapidity for specific virus detection, and the requirement of low-volume samples for the determination are remarkable characteristics that make it ideal for its potential application in clinical diagnosis in point-of-care settings.

A cascade strategy for vinyl chloride-substituted BODIPYs with tunable photophysical properties

An efficient and transition-metal-free method for the synthesis of unprecedented vinyl chloride-substituted BODIPYs has been developed through tandem Friedel-Crafts, enolization and chlorination reactions. This transformation offers high regioselectivity and stereoselectivity, enabling the synthesis of a variety of β-vinyl chloride-β'-acyl- and β,β'-divinyl chloride-substituted BODIPYs in a one-pot reaction at room temperature. Further functionalization gave a β,β'-divinyl chloride-substituted BODIPY with triphenyl phosphonium moieties, which showed favorable two-photon mitochondrion-targeting imaging capacity in living cells with intense deep-red fluorescence.

Phase-transfer-catalyst enabled enantioselective C-N coupling to access chiral boron-stereogenic BODIPYs

Tetracoordinate boron-based fluorescent materials have shown extensively applications in chemistry, biology and materials science owing to their unique optoelectronic properties. However, constructing chiral boron-stereogenic fluorophores through practical and universal strategies remains rare and challenging. Herein, as a proof of concept, we report an enantioselective postfunctionalization of boron dipyrromethene dyes (BODIPYs), to acess boron-stereogenic BODIPYs in moderate to good yields with commendable enantioselectivity. Chiral BODIPYs have attracted increasing attention owing to not only their distinctively photophysical properties and applications in circularly polarized luminescence (CPL) materials, but also diversely structural modification. In this·work, we present a phase-transfer-catalyst enabled enantioselective C-N coupling reaction of BODIPYs with diverse nucleophiles. This method serves as a practical SNAr (nucleophilic aromatic substitution reaction) route to achieve a series of boron-stereogenic amido/amino BODIPYs as well as demonstrates their promising CD and·CPL·activities, excellent biocompatibility, and high specificities, showing potential applications as chiral fluorescent imaging agents.

Ring-fused BODlPY derived heavy-atom-free triplet photosensitizers

Triplet photosensitizers are compounds that demonstrate strong absorption of the excitation light, high intersystem crossing (ISC) efficiency for efficient triplet state generation, and long triplet lifetimes to facilitate subsequent photochemical reactions. Among these, heavy-atom-free triplet photosensitizers have attracted particular attention due to their advantages of long-lived triplet states and low dark toxicity in comparison with heavy-atom-containing photosensitizers. Owing to the superior photophysical and chemical characteristics, boron dipyrromethene (BODIPY) dyes have been developed as promising heavy-atom-free triplet photosensitizers through specific molecular design strategies. However, many heavy-atom-free BODIPY-based photosensitizers exhibit relatively short excitation wavelengths in the visible-light region, and their ISC efficiencies dropped significantly with the extension of π-conjugation via the Knoevenagel condensation reaction. Recently, the ring-fused BODIPY skeleton has provided a feasible approach for the design of long-wavelength NIR photosensitizers. This review provides a comprehensive summary of the strategies utilized for the construction of ring-fused BODIPY-based photosensitizers including the installation of a twisted π-conjugation framework, the fusion of thiophene moieties and the formulation of an aggregation-induced ISC process. Meanwhile, some important spectroscopic and photophysical properties of these photosensitizers, along with their related applications, are also described.

Near-Infrared Twisted Polycyclic Arene-Fused BisBODIPYs through a Tandem Inter- and Intramolecular Scholl Reaction

Five novel polyaromatic-ring-fused bisBODIPYs have been synthesized from corresponding readily available α-arylBODIPYs through a FeCl3-mediated tandem inter- and intramolecular oxidative aromatic coupling reaction. These resultant bisBODIPYs show twisted planar conformations, strong absorptions (ε up to 1.8 × 105 M-1 cm-1), and good fluorescence emissions in the near-infrared region (NIR, 660-734 nm) and good intersystem crossing efficiencies (ΦΔ = 18.9% for dimer 2d in toluene), demonstrating their promising potential applications as heavy-atom-free photosensitizers.

Catalytic Enantioselective Synthesis of Boron-Stereogenic and Axially Chiral BODIPYs via Rhodium(II)-Catalyzed C-H (Hetero) Arylation with Diazonaphthoquinones and Diazoindenines

The molecular engineering of boron dipyrromethenes (BODIPYs) has garnered widespread attention due to their structural diversity enabling tailored physicochemical properties for optimal applications. However, catalytic enantioselective synthesis of structurally diverse boron-stereogenic BODIPYs through intermolecular desymmetrization and BODIPYs with atroposelectivity remains elusive. Here, we showcase rhodium(II)-catalyzed site-specific C-H (hetero)arylations of prochiral BODIPYs and polysubstituted BODIPYs with diazonaphthoquinonesand diazoindenines, providing efficient pathways for the rapid assembly of versatile (hetero)arylated boron-stereogenic and axially chiral BODIPYs through long-range desymmetrization and axial rotational restriction modes. The synthetic application of the procedures has been emphasized by the efficient synthesis of BODIPY derivatives with various functions. Photophysical properties, bioimaging, and lipid droplet-specific targeting capability of tailored BODIPYs are also demonstrated, indicating their promising applications in biomedical research, medicinal chemistry, and material science.

Twisted-Planar Molecular Engineering with Sonication-Induced J-Aggregation To Design Near-Infrared J-Aggregates for Enhanced Phototherapy

J-aggregates show great promise in phototherapy, but are limited to specific molecular skeletons and poor molecular self-assembly controllability. Herein, we report a twisted-planar molecular strategy with sonication-induced J-aggregation to develop donor-acceptor (D-A) type J-aggregates for phototherapy. With propeller aggregation-induced emission (AIE) moieties as the twisted subunits and thiophene as the planar π-bridge, the optimal twisted-planar π-interaction in MTSIC induces appropriate slip angle and J-aggregates formation, redshifting the absorption from 624 nm to 790 nm. In contrast, shorter π-planarity results in amorphous aggregates, and elongation promotes charge transfer (CT) coupled J-aggregates. Sonication was demonstrated to be effective in controlling self-assembly behaviors of MTSIC, which enables the transformation from amorphous aggregates to H-intermediates, and finally to stable J-aggregates. After encapsulation with lipid-PEG, the resultant J-dots show enhanced phototherapeutic effects over amorphous dots, including brightness, reactive oxygen species (ROS) generation, and photothermal conversion, delivering superior cancer phototherapy performance. This work not only advances D-A type J-aggregates design but also provides a promising strategy for supramolecular assembly development.

Activatable Molecular Probes With Clinical Promise for NIR-II Fluorescent Imaging

The second near-infrared window (NIR-II) fluorescence imaging has been widely adopted in basic scientific research and preclinical applications due to its exceptional spatiotemporal resolution and deep tissue penetration. Among the various fluorescent agents, organic small-molecule fluorophores are considered the most promising candidates for clinical translation, owing to their well-defined chemical structures, tunable optical properties, and excellent biocompatibility. However, many currently available NIR-II fluorophores exhibit an "always-on" fluorescence signal, which leads to background noise and compromises diagnostic accuracy during disease detection. Developing NIR-II activatable organic small-molecule fluorescent probes (AOSFPs) for accurately reporting pathological changes is key to advancing NIR-II fluorescence imaging toward clinical application. This review summarizes the rational design strategies for NIR-II AOSFPs based on four core structures (cyanine, hemicyanine, xanthene, and BODIPY). These NIR-II AOSFPs hold substantial potential for clinical translation. Furthermore, the recent advances in NIR-II AOSFPs for NIR-II bioimaging are comprehensively reviewed, offering clear guidance and direction for their further development. Finally, the prospective efforts to advance NIR-II AOSFPs for clinical applications are outlined.

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.

Competing Photocleavage on Boron and at the meso-Position in BODIPY Photocages

BODIPY photocages (photocleavable protective groups) have stirred interest because they can release biologically active cargo upon visible light excitation. We conducted combined theoretical and experimental investigations on selected BODIPY photocages to elucidate the mechanism of the competing photocleavage at the boron and meso-position. Based on the computations, the former reaction involves elongation of the B-C bond, yielding a tight borenium cation and methyl anion. These ions are intercepted by CH3OH, enabling an efficient proton-coupled electron transfer (PCET) to produce the methane and isolated ether photoproducts. Singlet and triplet excited-state lifetimes were measured in CH3OH and CD3OD to probe the kinetic isotope effects (KIEs). The resulting KIEs are small, implying that the kinetic bottleneck is due to the C-B bond scission rather than the subsequent PCET. The introduction of a methoxy group in the meso-phenoxy substituent redirects the photosubstitution toward the meso-position. The corresponding regiochemistry was explained computationally. On elongating the C-O bonds in the S1 state, it is found that the unproductive conical intersection is encountered much earlier for the alkyl-O bond than for the phenyl-O bond. The current findings are valuable for the rational design of new BODIPY photocages with tailored biological applications.

Synthetic Approaches Toward Phosphorus-Containing BODIPY and Squaraine Dyes: Enhancing Versatility of Small-Molecule Fluorophores

Phosphorus-containing fluorophores provide a versatile framework for tailoring photophysical properties, enabling the design of advanced fluorogenic materials for various applications. Boron dipyrromethene (BODIPY) and squaraine dyes are of interest due to their multifaceted modularity and synthetic accessibility. Incorporating phosphorus-based functional groups into BODIPY or squaraine scaffolds has been achieved through a plethora of synthetic methods, including post-dye assembly functionalization. These modifications often influence key spectroscopic properties and molecular functionality by expanding their utility in bioimaging, sensing, photosensitization, and theranostic applications. By leveraging the tunable nature of phosphorus-containing moieties, these dyes hold immense promise for addressing current challenges in spectroscopy, imaging, and material designs while unlocking new opportunities for advanced functional systems in chemistry, biology, and medicine.

Circularly Polarized Luminescence Bioimaging Using Chiral BODIPYs: A Model Scaffold for Advancing Unprecedented CPL Microscopy Using Small Full-Organic Probes

Unprecedented circularly polarized luminescence bioimaging (CPL-bioimaging) of live cells using small full-organic probes is first reported. These highly biocompatible and adaptable probes are pivotal to advance emerging CPL Laser-Scanning Confocal Microscopy (CPL-LSCM) as an undeniable tool to distinguish, monitor, and understand the role of chirality in the biological processes. The development of these probes was challenging due to the poor dichroic character associated with the involved CPL emissions. However, the known capability of the BODIPY dyes to be tuned to act as efficient fluorescence bioprobes, together with the capability of the BINOL-O-BODIPY scaffold to enable CPL, allowed the successful design of the first examples of this kind of CPL probes. Interestingly, the developed CPL probes were also multiphoton (MP) active, paving the way for the envisioned MP-CPL-bioimaging. The described full-organic CPL-probe scaffold, based on an optically and biologically tunable BODIPY core, which is chirally perturbed by an enantiopure BINOL moiety, represents, therefore, a simple and readily accessible structural design for advancing efficient CPL probes for bioimaging by CPL-LSCM.

Diarenofuran[b]-fused BODIPYs: One-Pot SNAr-Suzuki Synthesis and Properties

We present a streamlined methodology that integrates regioselective tetrahalogen-BODIPY and o-hydroxyphenylboronic acid in a one-pot process, leveraging SNAr nucleophilic substitution in conjunction with Suzuki coupling to afford diarenofuran [b]-fused BODIPYs (DBFB1-9) with commendable yields (85-95%) and short reaction times (0.5-1.0 h). X-ray structure analyses of DBFB5,7-9 elucidate that these diarenofuran[b]-fused BODIPYs adopt a "butterfly" conformation, maintaining a highly rigid planarity. A comprehensive examination of the spectroscopic and electrochemical properties of these diarenofuran[b]-fused BODIPY derivatives, incorporating various substituents, reveals intriguing characteristics, including pronounced absorption and emission in the near-infrared region (NIR), elevated fluorescence quantum yields (ΦF = 75-89% in dichloromethane), and tunable HOMO-LUMO levels. Remarkably, compared to DBFB1-8, DBFB9 possesses a large extended π-conjugated system, resulting in significant red shifts in its absorption and emission maxima, reaching 623 and 635 nm, respectively, and a reduced HOMO-LUMO gap. Despite this substantial structural expansion, DBFB9 maintains a surprisingly high fluorescence quantum yield (ΦF = 80%), underscoring its exceptional photophysical performance and strong potential for applications requiring efficient NIR emission and robust fluorescence retention.

Enhanced Singlet Oxygen Generation in Aggregates of Naphthalene-Fused BODIPY and Its Application in Photodynamic Therapy

Several reports are available on aggregation-induced emission and its applications in biomedical imaging and other material sciences. However, enhancement of singlet oxygen generation in nanoaggregates is rarely reported. Here, we report the synthesis of Naph-BODIPY Br2, which absorbs at 661 nm (monomer) with a high molar absorption coefficient. The presence of bromine promotes intersystem crossing, thereby enhancing the singlet oxygen quantum yield (ΦΔ ∼ 0.50 in methanol). In order to increase hydrophilicity, we developed Naph-BODIPY Br2 nanoaggregates (∼100 nm), which demonstrated aggregation-induced properties and exhibited a bathochromic shift with an absorption maximum at 757 nm. The bathochromic shift in the UV-vis spectra due to aggregation is corroborated by TD-DFT analysis. The computational data also confirm the presence of a low-lying triplet state, which enhances the generation of singlet oxygen, making it effective for photodynamic therapy. These aggregates showed excellent singlet oxygen generation in aqueous media, compared to their monomeric form and standard methylene blue. Their hydrophilic nature and high singlet oxygen generation enabled significant phototoxicity against human carcinoma cells with IC50 values of 4.06 ± 0.01 and 4.09 ± 0.1 μM, respectively, for MCF-7 and A549 cells upon 5 min exposure to light. Moreover, their phototoxicity further increases with an increasing exposure time of light for both cell lines. Notably, Naph-BODIPY Br2 nanoaggregates exhibited nearly zero dark cell toxicity and effectively induced apoptosis in cancer cells upon light activation, highlighting their potential as powerful photosensitizers for photodynamic cancer therapy.

Multicomponent Diversity-Oriented Access to Boronic-Acid-Derived Pyrrolide Salicyl-Hydrazone Fluorophores with Strong Solid-State Emission

Fluorescent molecular platforms are highly sought after for their applications in biology and optoelectronics but face challenges with solid-state emission quenching. To address this, bulky substituents or aggregation-induced emission luminogens to restrict intramolecular motion are used to enhance the brightness. Here, we have successfully engineered a novel class of boron complexed pyrrolide salicyl-hydrazone fluorophores named BPSHY. These dyes were synthesized through a diversity-oriented condensation of pyrrole and salicylaldehyde derivatives combined with various aromatic boronic acids. The resulting 3D structures, owing to bulky boron axially substituted aryl groups, impart excellent solubility in a variety of solvents. Significantly, the BPSHY dyes exhibit strong absorption in the visible region and remarkably large Stokes shifts. Crucially, they demonstrate intense emission in aqueous solutions due to aggregation-induced emission effects. In solid-states, these dyes achieve high quantum yields, reaching up to 58%. Further expanding their utility, we developed two new BPSHY probes: one incorporating morpholine and another containing triphenylphosphine salt. Both of them are found to specifically label subcellular organelles such as lysosomes and mitochondria within live cells. Notably, these probes demonstrate exceptional staining efficacy and two-photon fluorescence feature. This highlights the considerable promise of BPSHY fluorophores for monitoring and visualizing the dynamic transformations of organelles.

Engineered manganese-BODIPY coordinated nanoadjuvants for enhanced NIR-II photo-metalloimmunotherapy

Immunotherapy, a pivotal and promising approach for tumor treatment, has demonstrated prominent clinical efficacy. However, its effectiveness is often impeded by insufficient antitumor immune responses attributed to the immunosuppressive tumor microenvironment (TME). The combination of immune activation through the stimulator of interferon genes (STING) pathway and phototherapy holds great potential for surmounting this challenge in advanced tumor immunotherapy. Herein, a novel manganese-boosted NIR-II photo-metalloimmunotherapy is proposed to synergistically enhance antitumour efficacy by fabricating Mn2+-BODIPY-based coordinated photo-immune nanoadjuvants (BMR), modified with tumor-targeted peptide cRGD. The obtained BMR could effectively deliver Mn2+ to tumor sites, and immunogenic cell death (ICD) was evoked by localized photothermal ablation of tumors using NIR-II laser irradiation. Simultaneously, pH-responsive release of Mn2+ would trigger the activation of STING pathway to promote the production of type I interferons (I-IFNs), significantly facilitating the maturation of dendritic cells (DCs) and polarization of macrophages to M1 phenotypes. Furthermore, by synergistically initiating systematic and robust antitumour immune responses, the BMR-mediated NIR-II photo-metalloimmunotherapy achieved remarkable therapeutic efficacy against both primary and lung metastasis of B16F10 tumors. Overall, in light of the versatile functionalities and synthetic flexibility of coordinated nanoadjuvants, formulated with photofunctional ligands and diverse metal ions, this work provides new insights into the design of metal coordination nanomedicine for effective antitumor photo-metalloimmunotherapy.

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.

Versatile Metal-Free Arylation of BODIPY and Bis(BF2) Chromophores by Using Arylazosulfones in a Sunflow System

BODIPYs have a well-established role in biological sciences as chemosensors and versatile biological markers due to their chemical reactivity, which allows for fine-tuning of their photophysical characteristics. In this work, we combined the unique reactivity of arylazo sulfones with the advantages of a "sunflow" reactor to develop a fast, efficient, and versatile method for the photochemical arylation of BODIPYs and other chromophores. This approach resulted in red-shifted emitting fluorophores due to extended electronic delocalization at the 3- and 5-positions of the BODIPY core. This method represents an advantageous approach for BODIPY functionalization compared to existing strategies.

Zig-zag-fused π-extended BODIPYs via gold-catalysed cycloisomerisation

π-Extension of the BODIPY core is an effective strategy to modulate the physical properties of BODIPYs. However, π-extension on the zig-zag edge of BODIPYs remains unexplored. Here, we disclose the synthesis of zig-zag-fused BODIPYs through gold-catalysed cycloisomerisation. The obtained BODIPYs show fascinating photophysical properties including near-infrared absorption and emission.

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.

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.

Enhancing Hybrid Photovoltaic-Thermal System Efficiency with Boron Dipyrromethene Dyes

A library of boron dipyrromethene (BODIPY) compounds was studied to assess their efficacy as components of a working liquid in hybrid photovoltaic-thermal (PVT) systems. Two series of BODIPY dyes were investigated: series I included alkylBODIPYs with varying substitution patterns, while series II included 1,3,5,7-tetramethyl-substituted BODIPYs featuring electron-rich aromatic groups in the meso position, such as naphthalene, anthracene, and carbazole. Series II dyes were designed to exhibit luminescence downshifting due to enhanced UV absorption (300-400 nm) and excited-state energy transfer, leading to visible-region fluorescence under UV excitation. Samples of PVT liquids based on decalin and containing each individual BODIPY dye were tested on a standard a-Si solar cell to evaluate their impact on solar energy conversion efficiency. The thermal behavior of the working liquid and the cell during the illumination cycle was monitored, alongside the cell's electrical characteristics. Energy conversion pathways and the overall effects of the dyes on the system performance were scrutinized. Results indicated that all BODIPY dyes enhanced both the electrical conversion efficiency (up to 2.41% increase) and thermal energy generation (up to 6.87%) compared to the solvent alone. These findings highlight the potential of BODIPY dyes to significantly improve the performance of PVT systems.

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.

Dithio-Fused Boron Dipyrromethenes: Synthesis and Impact of S-Heteroaromatic Annulation Mode

Three dithio-fused boron dipyrromethenes (BODIPYs), DTFB-1, DTFB-2, and DTFB-3, in which symmetrically S-heteroaromatic ring units fused at [a], zigzag, and [b] bonds of the parent BODIPY core, respectively, were prepared from the facile and efficient post-functionalization of tetra-halogenated BODIPYs through Pd-catalyzed cyclization. Dithio-fusion at various positions of BODIPY effectively tunes their photophysical properties and single-crystal structural packing arrangements. The single-crystalline microribbons of DTFB-2 exhibit commendable hole mobilities in air, reaching up to 0.03 cm2 V-1 s-1.

BODIPY-based photocages: rational design and their biomedical application

Photocages, also known as photoactivated protective groups (PPGs), have been utilized to achieve controlled release of target molecules in a non-invasive and spatiotemporal manner. In the past decade, BODIPY fluorophores, a well-established class of fluorescent dyes, have emerged as a novel type of photoactivated protective group capable of efficiently releasing cargo species upon irradiation. This is due to their exceptional properties, including high molar absorption coefficients, resistance to photochemical and thermal degradation, multiple modification sites, favorable uncaging quantum yields, and highly adjustable spectral properties. Compared to traditional photocages that mainly absorb UV light, BODIPY-based photocages that absorb visible/near-infrared (Vis/NIR) light offer advantages such as deeper tissue penetration and reduced bio-autofluorescence, making them highly suitable for various biomedical applications. Consequently, different types of photoactivated protective groups based on the BODIPY skeleton have been established. This highlight provides a comprehensive overview of the strategies employed to construct BODIPY photocages by substituting leaving groups at different positions within the BODIPY fluorophore, including the meso-methyl position, boron position, 2,6-position, and 3,5-position. Furthermore, the application of these BODIPY photocages in biomedical fields, such as fluorescence imaging and controlled release of active species, is discussed.

NIR-II Fluorescent Probes for Fluorescence-Imaging-Guided Tumor Surgery

Second near-infrared (NIR-II) fluorescence imaging is the most advanced imaging fidelity method with extraordinary penetration depth, signal-to-background ratio, biocompatibility, and targeting ability. It is currently booming in the medical realm to diagnose tumors and is being widely applied for fluorescence-imaging-guided tumor surgery. To efficiently execute this modern imaging modality, scientists have designed various probes capable of showing fluorescence in the NIR-II window. Here, we update the state-of-the-art NIR-II fluorescent probes in the most recent literature, including indocyanine green, NIR-II emissive cyanine dyes, BODIPY probes, aggregation-induced emission fluorophores, conjugated polymers, donor-acceptor-donor dyes, carbon nanotubes, and quantum dots for imaging-guided tumor surgery. Furthermore, we point out that the new materials with fluorescence in NIR-III and higher wavelength range to further optimize the imaging results in the medical realm are a new challenge for the scientific world. In general, we hope this review will serve as a handbook for researchers and students who have an interest in developing and applying fluorescent probes for NIR-II fluorescence-imaging-guided surgery and that it will expedite the clinical translation of the probes from bench to bedside.

Near-IR-Absorbing Bis-Donor Functionalized Aza-BODIPY Derivatives: Synthesis and Photophysical Study by Using Transient Optical Spectroscopy

A series of near-IR absorbing 2,6-diarylated BF2-chelated aza-boron-dipyrromethenes (aza-BDPs) derivatives bearing different electron donors (benzene, naphthalene, phenanthrene, phenothiazine and carbazole) were designed and synthesized. The effect of different electron donor substitutions on the photophysical properties was studied by steady-state UV-vis absorption and fluorescence spectra, electrochemical, time-resolved nanosecond transient absorption (ns-TA) spectroscopy and theoretical computations. The UV-vis absorption spectra of AzaBDP-PTZ and AzaBDP-CAR (λabs=710 nm in toluene) showed a bathochromic absorption profile compared with the reference AzaBDP-Ph (λabs=685 nm in toluene), indicating the non-negligible electronic interaction at the ground state between donor and acceptor moieties. Moreover, the fluorescence is almost completely quenched for AzaBDP-PTZ/AzaBDP-CAR (fluorescence quantum yield, ΦF=0.2-0.7 % in toluene) as compared with the AzaBDP-Ph (ΦF=27 % in toluene). However, the apparent intersystem crossing ability of these compounds is poor, based on the singlet oxygen quantum yield (ΦΔ=0.3-1.5 %). The ns-TA spectral study showed typical Bodipy localized triplet state transient features, short-lived excited triplet state for AzaBDP-Ph (τT=53.2 μs) versus significantly long-lived triplet state for AzaBDP-CAR (τT=114 μs) was observed under deaerated experimental conditions. These triplet state lifetimes are much longer than that obtained with diiodoAzaBDP (intramolecular heavy atom effect, τT=1.5~7.2 μs). These information are useful for molecular structure design of triplet photosensitizers, for which longer triplet state lifetimes are usually desired. Theoretical computations displayed that the triplet state is mainly localized on the AzaBDP core, moreover, it was found that the HOMO/LUMO energy gap decreased after introducing donor moieties to the skeleton as compared with the reference.

BODIPY(aryl)iodonium salts in the efficient synthesis of diversely functionalized BODIPYs and selective detection of serum albumin

BODIPY(aryl)iodonium salts were readily accessible from the high-yielding reaction of BODIPY with iodoarenes or hydroxyl(tosyloxy)iodoarenes in the presence of m-CPBA. The prepared BODIPY(aryl)iodonium salts bearing substituents of varied electronic nature were utilized for the direct syntheses of thiocyanate, azide, amine and acrylate functionalized BODIPYs and β,β'-bis-BODIPYs. The regioselective syntheses of α-piperidinyl and β-piperidinyl substituted BODIPYs were achieved through the reaction of BODIPY(aryl)iodonium salts with piperidine in the absence and presence of copper(I). Expeditious and high yielding (79-82%) synthesis of β,β'-bis-BODIPYs was also developed through the palladium-catalyzed reductive coupling of the easily accessible BODIPY(aryl)iodonium salts. Some of the indole-appended BODIPYs and bis-BODIPYs displayed strong absorption in the visible region (∼610 nm). The BODIPY(aryl)iodonium salts also showed significant binding with serum albumin and were observed to be selective serum protein sensors with estimated limits of detection as low as 7 μg mL-1 in some cases.

Rational design of CT-coupled J-aggregation platform based on Aza-BODIPY for highly efficient phototherapy

Supramolecular engineering is exceptionally appealing in the design of functional materials, and J-aggregates resulting from noncovalent interactions offer intriguing features. However, building J-aggregation platforms remains a significant challenge. Herein, we report 3,5-dithienyl Aza-BODIPYs with a donor-acceptor-donor (D-A-D) architecture as the first charge transfer (CT)-coupled J-aggregation BODIPY-type platform. The core acceptor moieties in one molecule interact with donor units in neighboring molecules to generate slip-stacked packing motifs, resulting in CT-coupled J-aggregation with a redshifted wavelength up to 886 nm and an absorption tail over 1100 nm. The J-aggregates show significant photoacoustic signals and high photothermal conversion efficiency of 66%. The results obtained in vivo show that the J-aggregates have the potential to be used for tumor photothermal ablation and photoacoustic imaging. This study not only demonstrates Aza-BODIPY with D-A-D as a novel CT-coupled J-aggregation platform for NIR phototherapy materials but also motivates further study on the design of J-aggregation.

Unsymmetrical Benzothieno-Fused BODIPYs as Efficient NIR Heavy-Atom-Free Photosensitizers

Heavy-atom-free photosensitizers are potentially suitable for use in photodynamic therapy (PDT). In this contribution, a new family of unsymmetrical benzothieno-fused BODIPYs with reactive oxygen efficiency up to 50% in air-saturated toluene was reported. Their efficient intersystem crossing (ISC) resulted in the generation of both 1O2 and O2-• under irradiation. More importantly, the PDT efficacy of a respective 4-methoxystyryl-modified benzothieno-fused BODIPY in living cells exhibited an extremely high phototoxicity with an ultralow IC50 value of 2.78 nM. The results revealed that the incorporation of an electron-donating group at the α-position of the unsymmetrical benzothieno-fused BODIPY platform might be an effective approach for developing long-wavelength absorbing heavy-atom-free photosensitizers for precision cancer therapy.

Synthesis and Photophysical Properties of β-Alkenyl-Substituted BODIPY Dyes by Indium(III)-Catalyzed Intermolecular Alkyne Hydroarylation

A new atom-economical synthesis of β-alkenyl-substituted BODIPYs via indium(III)-catalyzed intermolecular alkyne hydroarylation with meso-substituted BODIPYs is described. While catalysis with InI3 allows the double β-functionalization of BODIPY, resulting in regioselectively branched β,β'-disubstituted alkenyl BODIPYs, catalytic InCl3 enables the formation of linear β-substituted alkenyl BODIPYs. Subsequent In(III)-catalyzed intermolecular alkyne hydroarylation allows the synthesis of unsymmetrical push-pull BODIPY derivatives. Therefore, indium catalysis offers complementary regioselectivity in good chemical yields and functional group tolerance. The resulting BODIPY dyes displayed bathochromically shifted absorption and emission according to the electron-nature of the substituents in the alkenyl moiety with high molar extinction coefficients (ε up to 88,200 M-1 cm-1) and quantum yields (0.14-0.96).

Solid-State Emissive meso-Aryl/Alkyl-Substituted and Heteroatom-Mixed BOPPY Dyes: Syntheses, Structures, Physicochemical, Redox Properties, and Computational Analysis

A series of solid-state emissive meso-aryl/alkyl-substituted and heteroatom-mixed bisBF2-anchoring fluorophore incorporating pyrrolyl-pyridylhydrazone (BOPPY) dyes have been developed by a one-pot condensation of ketonized or formylated pyrroles and 2-heterocyclohydrazine as well as the subsequent borylation coordination. Interestingly, the BOPPY dyes with meso-alkyl-substituted groups or oxygen-substituted pyridine moieties exhibit high fluorescence quantum yields (QYs) of up to 79%, the highest solid QY of 74%, and long lifetimes independent of polarity in the available BOPPYs. On the other hand, the BOPPYs with meso-aryl or N-substituted moieties display a high solution QY of up to 93% and slight emission wavelength maxima. However, the S-substituted BOPPY dye exhibited weak fluorescence in all studied solvents, which was attributed to the structural flexibility of the N-C-S bond and different from those BOPPYs with O or N substitution, indicated by quantum calculations. And the significant excited-state structural rearrangement in a polar solvent is further confirmed by femtosecond time-resolved transient absorption spectroscopy. More importantly, those novel and barely fluorescent BOPPYs in acetonitrile show advantageous aggregation-induced enhanced emission and viscosity-dependent activities. These advancements in the photophysical and electrochemical properties of BOPPY dyes offer valuable insights into their further development and potential applications.

Reversible Dual Fluorescence-Lifetime Imaging of Mitochondrial GSH and Microviscosity: Real-Time Evaluation of Ferroptosis Status

Ferroptosis, as a new form of regulated cell death, is implicated in various physiological and pathological processes. Developing a single probe for an independent analysis of multiple analytes related to ferroptosis can provide more accurate information and simplify the detection procedures, but it faces great challenges. In this work, we develop a fluorescent probe for the simultaneous detection of GSH through ratiometric fluorescence response and microviscosity via a fluorescence lifetime model. Based on the reversible Michael addition reaction between GSH and unsaturated C═C bond, the probe responds reversibly to GSH with a ratiometric fluorescence variation and a fast response time (t1/2 = 4.7 s). At the same time, the probe is sensitive to environmental viscosity by changing its fluorescence lifetimes. The probe was applied to monitor the drug-induced ferroptosis process through both the classical Xc-/GSH/GPX4- and DHODH-mediated defense mechanisms. We hope that the probe will provide a useful molecular tool for the real-time live-cell imaging of GSH dynamics, which is benefit to unveiling related physiological and pathological processes.

Design, Synthesis, and Characterization of Organometallic BODIPY-Ru(II) Dyads: Redox and Photophysical Properties with Singlet Oxygen Generation Capability†

A series of Ru(II)-acetylide complexes (Ru1, Ru2, and Ru1m) with alkynyl-functionalized borondipyrromethene (BODIPY) conjugates were designed by varying the position of the linker that connects the BODIPY unit to the Ru(II) metal center through acetylide linkage at either the 2-(Ru1) and 2,6-(Ru2) or the meso-phenyl (Ru1m) position of the BODIPY scaffold. The Ru(II) organometallic complexes were characterized by various spectroscopic methods, including nuclear magnetic resonance (NMR) spectroscopy, infrared (IR) spectroscopy, CHN, and high-resolution mass spectrometry (HRMS) analyses. The Ru(II)-BODIPY conjugates exhibit fascinating electrochemical and photophysical properties. All BODIPY-Ru(II) complexes exhibit strong absorption (εmax = 29,000-72,000 M-1 cm-1) in the visible region (λmax = 502-709 nm). Fluorescence is almost quenched for Ru1 and Ru2, whereas Ru1m shows the residual fluorescence of the corresponding BODIPY core at 517 nm. The application of the BODIPY-Ru(II) dyads as nonporphyrin-based triplet photosensitizers was explored by a method involving the singlet oxygen (1O2)-mediated photo-oxidation of diphenylisobenzofuran. Effective π-conjugation between the BODIPY chromophore and Ru(II) center in the case of Ru1 and Ru2 was found to be necessary to improve intersystem crossing (ISC) and hence the 1O2-sensitizing ability. In addition, electrochemical studies indicate electronic interplay between the metal center and the redox-active BODIPY in the BODIPY-Ru(II) dyads.

De Novo Access to BODIPY C-Glycosides as Linker-Free Nonsymmetrical BODIPY-Carbohydrate Conjugates

Recent years have witnessed an increasing interest in the synthesis and study of BODIPY-glycoconjugates. Most of the described synthetic methods toward these derivatives involve postfunctional modifications of the BODIPY core followed by the covalent attachment of the fluorophore and the carbohydrate through a "connector". Conversely, few de novo synthetic approaches to linker-free carbohydrate-BODIPY hybrids have been described. We have developed a reliable modular, de novo, synthetic strategy to linker-free BODIPY-sugar derivatives using the condensation of pyrrole C-glycosides with a pyrrole-carbaldehyde derivative mediated by POCl3. This methodology allows labeling of carbohydrate biomolecules with fluorescent-enough BODIPYs within the biological window, stable in aqueous media, and able to display singlet oxygen generation.

The Rise of Boron-Containing Compounds: Advancements in Synthesis, Medicinal Chemistry, and Emerging Pharmacology

Boron-containing compounds (BCC) have emerged as important pharmacophores. To date, five BCC drugs (including boronic acids and boroles) have been approved by the FDA for the treatment of cancer, infections, and atopic dermatitis, while some natural BCC are included in dietary supplements. Boron's Lewis acidity facilitates a mechanism of action via formation of reversible covalent bonds within the active site of target proteins. Boron has also been employed in the development of fluorophores, such as BODIPY for imaging, and in carboranes that are potential neutron capture therapy agents as well as novel agents in diagnostics and therapy. The utility of natural and synthetic BCC has become multifaceted, and the breadth of their applications continues to expand. This review covers the many uses and targets of boron in medicinal chemistry.

Electrochemical Diselenation of BODIPY Fluorophores for Bioimaging Applications and Sensitization of 1 O2

We report a rapid, efficient, and scope-extensive approach for the late-stage electrochemical diselenation of BODIPYs. Photophysical analyses reveal red-shifted absorption - corroborated by TD-DFT and DLPNO-STEOM-CCSD computations - and color-tunable emission with large Stokes shifts in the selenium-containing derivatives compared to their precursors. In addition, due to the presence of the heavy Se atoms, competitive ISC generates triplet states which sensitize 1 O2 and display phosphorescence in PMMA films at RT and in a frozen glass matrix at 77 K. Importantly, the selenium-containing BODIPYs demonstrate the ability to selectively stain lipid droplets, exhibiting distinct fluorescence in both green and red channels. This work highlights the potential of electrochemistry as an efficient method for synthesizing unique emission-tunable fluorophores with broad-ranging applications in bioimaging and related fields.

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.

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.

Synthesis and In Vitro Biocompatibility Studies of Novel Alkoxy 4,4-Difluoro-4-bora-3a,4a-diaza-s-indacenes

BODIPYs are bicyclic aromatic compounds with unique spectroscopic, photophysical, and chemical properties. This study aimed to find BODIPYs with characteristics biocompatible with human cell lines for possible use as imaging agents. Six BODIPY derivatives were synthesised with groups linked to boron, fluorine, phenol, or catechol, resulting in compounds with different physicochemical characteristics. NMR, absorption, and emission spectroscopy and mass spectrometry were subsequently used to characterise them. Afterwards, the biocompatibility of these compounds was evaluated using MTT, SRB, and cellular uptake assays in A549 and H1299 cell lines. Furthermore, a haemolysis assay was performed on human blood cells. To summarise the main results, BODIPYs 1 to 4 showed considerable fluorescence. In contrast, BODIPYs 5 and 6 showed very weak fluorescence, which could be related to the presence of the catechol group and its quenching properties. Regarding biocompatibility, all compounds had metabolic activity and viability above 80% and 70%, respectively. BODIPYs 3 and 6 presented the most consistent data, demonstrating good uptake and, in general, haemolytic activity below 25%. In conclusion, the cytotoxic effects of the compounds were not considerable, and the presence of cyclic alkoxides in BODIPYs 3 and 6 may introduce exciting features that should be highlighted for dual imaging for BODIPY 3 due to its fluorescence or for radioactive labelling in the case of both BODIPYs.

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.

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.

ROS generating BODIPY loaded nanoparticles for photodynamic eradication of biofilms

Bacterial biofilms can pose a serious health risk to humans and are less susceptible to antibiotics and disinfection than planktonic bacteria. Here, a novel method for biofilm eradication based on antimicrobial photodynamic therapy utilizing a nanoparticle in conjunction with a BODIPY derivative as photosensitizer was developed. Reactive oxygen species are generated upon illumination with visible light and lead to a strong, controllable and persistent eradication of both planktonic bacteria and biofilms. One of the biggest challenges in biofilm eradication is the penetration of the antimicrobial agent into the biofilm and its matrix. A biocompatible hydrophilic nanoparticle was utilized as a delivery system for the hydrophobic BODIPY dye and enabled its accumulation within the biofilm. This key feature of delivering the antimicrobial agent to the site of action where it is activated resulted in effective eradication of all tested biofilms. Here, 3 bacterial species that commonly form clinically relevant pathogenic biofilms were selected: Escherichia coli, Staphylococcus aureus and Streptococcus mutans. The development of this antimicrobial photodynamic therapy tool for biofilm eradication takes a promising step towards new methods for the much needed treatment of pathogenic biofilms.

Functionalization of BODIPY Dyes with Additional C-N Double Bonds and Their Applications

BODIPY (4-bora-3a,4a-diaza-s-indacene) dyes are regarded as highly useful compounds due to their rich photophysical properties, stability, and ease of functionalization. In recent years, hot topics studied with this class of compounds are targeted photodynamic therapy, photothermal therapy, fluorescent bioimaging agents, structural modification of the BODIPY core, synthesis of BODIPY analogs, and BODIPY-based supramolecular constructs. This review covers the advances in BODIPY structures substituted with additional carbon-nitrogen double bonds, namely imines, hydrazones, oximes, and related derivatives for various applications. Works based on fluorescent indicators of anions, cations, and neutral molecules are included in this review. In addition, the use of such structures for pharmaceutical applications, photodynamic therapy, fluorescent switches, and fluorescent building blocks are also investigated. In addition to covering the major literature within the mentioned subclass, design principles, working mechanisms, and outlooks are also provided to enlighten forthcoming promising efforts. With this work, we aim to provide insights about the synthesis, photophysical properties, contribution of C=N bonds to a class of dye, and possible areas of use and stimulate researchers to present new ideas and overcome the current problems using these derivatives.

Formylation as a Chemical Tool to Modulate the Performance of Photosensitizers Based on Boron Dipyrromethene Dimers

Heavy-atom-free photosensitizers are envisioned as the next generation of photoactive molecules for photo-theragnosis. In this approach, and after suitable irradiation, a single molecular scaffold is able to visualize and kill tumour cells by fluorescence signalling and photodynamic therapy (PDT), respectively, with minimal side effects. In this regard, BODIPY-based orthogonal dimers have irrupted as suitable candidates for this aim. Herein, we analyse the photophysical properties of a set of formyl-functionalized BODIPY dimers to ascertain their suitability as fluorescent photosensitizers. The conducted computationally aided spectroscopic study determined that the fluorescence/singlet oxygen generation dual performance of these valuable BODIPY dimers not only depends on the BODIPY-BODIPY linkage and the steric hindrance around it, but also can be modulated by proper formyl functionalization at specific chromophoric positions. Thus, we propose regioselective formylation as an effective tool to modulate such a delicate photonic balance in BODIPY-based dimeric photosensitizers. The taming of the excited-state dynamics, in particular intramolecular charge transfer as the key underlying process mediating fluorescence deactivation vs. intersystem crossing increasing, could serve to increase fluorescence for brighter bioimaging, enhance the generation of singlet oxygen for killing activity, or balance both for photo-theragnosis.