NIR-absorbing and emitting α,α-nitrogen-bridged BODIPY dimers with strong excitonic coupling

Three new distinct NIR α,α-NH-bridged BODIPY dimers were prepared by a direct nucleophilic substitution reaction. The synergistic effects of the nitrogen bridges and strong excitonic coupling between each BODIPY unit play major roles in enhancing the delocalization of an electron spin over the entire BODIPY dimers. The in situ formed aminyl radical dimer showed an absorption maximum at 1040 nm.

Nucleophilic Aromatic Substitution (SNAr) as an Approach to Challenging Nitrogen-Bridged BODIPY Oligomers

A series of nitrogen-bridged BODIPY oligomers were synthesized via nucleophilic aromatic substitution (SNAr) as a convenient approach. Further transformations achieved novel α,α-aryl BODIPY dimers as well as a BODIPY hexamer efficiently. These BODIPY oligomers showed good photophysical properties, such as apparent absorption and emission both in visible and near-infrared regions. Interestingly, the high air and photothermal stability, strong NIR absorption, and high photothermal conversion rates of hexamer B6 suggest potential applications in photothermal therapy.

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.

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.

Tuning Shortwave-Infrared J-aggregates of Aromatic Ring-Fused Aza-BODIPYs by Peripheral Substituents for Combined Photothermal and Photodynamic Therapies at Ultralow Laser Power

Achieving photothermal therapy (PTT) at ultralow laser power density is crucial for minimizing photo-damage and allowing for higher maximum permissible skin exposure. However, this requires photothermal agents to possess not just superior photothermal conversion efficiency (PCE), but also exceptional near-infrared (NIR) absorptivity. J-aggregates, exhibit a significant redshift and narrower absorption peak with a higher extinction coefficient. Nevertheless, achieving predictable J-aggregates through molecular design remains a challenge. In this study, we successfully induced desirable J-aggregation (λabs max : 968 nm, ϵ: 2.96×105  M-1  cm-1 , λem max : 972 nm, ΦFL : 6.2 %) by tuning electrostatic interactions between π-conjugated molecular planes through manipulating molecular surface electrostatic potential of aromatic ring-fused aza-BODIPY dyes. Notably, by controlling the preparation method for encapsulating dyes into F-127 polymer, we were able to selectively generate H-/J-aggregates, respectively. Furthermore, the J-aggregates exhibited two controllable morphologies: nanospheres and nanowires. Importantly, the shortwave-infrared J-aggregated nanoparticles with impressive PCE of 72.9 % effectively destroyed cancer cells and mice-tumors at an ultralow power density of 0.27 W cm-2 (915 nm). This phototherapeutic nano-platform, which generates predictable J-aggregation behavior, and can controllably form J-/H-aggregates and selectable J-aggregate morphology, is a valuable paradigm for developing photothermal agents for tumor-treatment at ultralow laser power density.

Strategic Construction of meso-Aryl-Substituted N,N-Carbonyl-Bridged Dipyrrinones as Small, Bright, and Tunable Fluorophores

A series of novel N,N-carbonyl-bridged dipyrrinone fluorophores have been directly constructed from α-halogenated dipyrrinones, which are conveniently obtained from the acid-catalyzed hydrolysis of readily available α,α'-dihalodipyrrins. This novel methodology affords efficient modulation of the functional groups at both the meso- and α-positions of this fluorophore. These resultant dyes show tunable absorption and emission wavelengths, good molar absorption coefficients, relatively large Stokes shifts, and excellent fluorescence quantum yields up to 0.99, and have been successfully applied in both one- and two-photon fluorescence microscopy imaging in living cells.

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.

Rhodium-Catalyzed Two-Fold, Regioselective and Enantioselective C-H Activation: an Efficient Strategy to Chiral Single-Benzene-Based Fluorophores

A Rh-catalyzed two-fold, regioselective and enantioselective C-H activation via chiral transient directing group strategy has been demonstrated in moderate to good yields with commendable enantioselectivities. The newly synthesized chiral fluorophores exhibit favorable photophysical properties, including large Stokes shifts, good fluorescence quantum yields, aggregation-induced emission in aqueous solution, and intense emission and circularly polarized luminescence in the solid state, indicating great potential applications as chiral fluorescent probes or optoelectronic materials.

Dynamically stable co-assembled supramolecular BOPPY systems with chiral amplification

New and dynamical chiral co-assembled systems bearing BOPPY were successfully developed with amplified CPL signals. Remarkably, these stable chiral co-assemblies prepared at high concentrations retain uniform microrods and exceptional chiroptical performance (glum = 0.028, ΦF = 14%) after 48 h.

Tuning of Redox Potentials and LUMO Levels of BODIPYs via Site-Selective Direct Cyanation

Through a strong oxidant Pb(OAc)4 promoted oxidative nucleophilic hydrogen substitution, site-selective direct and stepwise cyanation of BODIPYs using tetrabutylammonium cyanide was developed to give α-cyanated BODIPY derivatives. Characterization of optical and electrochemical properties of these dyes provides substantial enhancement of the electron affinity, with a reduction potential and LUMO level as low as -0.04 V and -4.43 eV, respectively. Radical anions of these electron-deficient 3,5-dicyanated BODIPYs were characterized by absorption and EPR spectroscopy.

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.

Synthesis, Properties, and Semiconducting Characteristics of Bisbenzothieno[b]-Fused BODIPYs

A novel family of bisbenzothieno[b]-fused BODIPYs containing seven fused aromatic rings has been developed from readily available benzothieo[3,2-b]pyrroles through an efficient two-step synthetic route, exhibiting planar skeletons with excellent photostabilities, deep-red absorptions, and near-infrared emissions (up to 753 nm). Importantly, the thin-film transistors based on BTB with a meso-dimethylamino-phenyl group exhibit unipolar n-type charge transporting characteristics with a high electron mobility of 0.013 cm2 V-1 s-1.

Pictet-Spengler synthesis of twisted quinoline-fused BODIPYs as heavy-atom-free photosensitizers

Singly and doubly quinoline-fused BODIPYs were effectively synthesized through a reaction sequence consisting of the reduction of nitrophenyl-substituted BODIPYs and subsequent Pictet-Spengler cyclization. The combination of the BODIPY core and fused quinoline rings imposed significantly twisted conformations in the quinoline-fused BODIPYs (around 20.0° deviation from coplanarity obtained from X-ray crystal structure analysis). These twisted BODIPYs showed significantly reduced LUMO, redshifted absorption/emission bands, high molar extinction coefficients and satisfactory reactive oxygen species generation efficiency up to 0.56, indicating potential use as heavy-atom-free photosensitizers.

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.

Direct Access to Pyrrolyltripyrrins and Calixsmaragdyrin from SNAr Reactions on α,α'-Dibromotripyrrins with Pyrroles or Indoles

Linear π-conjugated oligopyrroles are attractive precursors for the synthesis of expanded porphyrinoids, chemosensors, and supramolecular motifs. We demonstrate a new method for the synthesis of a set of linear pyrrolyltripyrrins and dipyrrolyltripyrrins through a regioselective S_NAr reaction on α,α'-dibromotripyrrins using various pyrroles or indoles. A representative calixsmaragdyrin was prepared via the 2-fold S_NAr reaction between α,α'-dibromotripyrrin and dipyrromethene through a convergent [3 + 2] strategy. These oligopyrroles showed intense deep red absorptions with an interesting pH response.

Palladium Catalyzed, Annulative Multiple C-H Bond Activations of BODIPYs to Access π-Extended Polycyclic Heteroaromatic Molecules with Deep Red Emissions and self-aggregation Behaviors

Aromatic ring fusion on BODIPY core can effectively tune its electronic property, and red-shift the absorption and emission wavelength. In this work, we report that a one-pot Pd(II) catalyzed multiple C-H activation to access acenaphtho[b]-fused BODIPYs though the reaction of α,β-unsubstituted-BODIPYs and 1,8-dibromonaphthalenes. These newly synthesized acenaphtho[b]-fused BODIPYs revealed intensified deep red absorptions (639 - 669 nm) and emissions (643 - 683 nm), with high fluorescence quantum yields (0.53 - 0.84) in dichloromethane. Notably, these acenaphtho[b]-fused BODIPYs exhibited well-defined self-aggregation behavior in water/THF mixture, and for instance, the absorption of 3a was red-shifted by 53 to 693 nm after forming aggregates.

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.

Recent Advances of Highly Fluorescent Hydrazine Inserted Pyrrole-based Bisboron-anchoring Fluorophores: Synthesis and Properties

Hydrazine inserted pyrrole-based bisboron fluorophores showcasing strong fluorescence in either solution or solid state have attracted wide applications in biomedicine and optoelectronic materials science. The growing demand calls for multiple strategies for generating novel fluorophores to solve the problems of small Stokes shifts and poor solid fluorescence. By changing the frameworks, BOPHY, BOPPY, BOPYPY, BOPAHY and BOAPY has recently been developed as increasingly valuable classes of bisboron fluorophores owing to its tunable structures and promising spectroscopic properties, high photostability and low LUMO energy level and the electron-deficient bisBF2 groups. This review mainly highlights the key synthetic strategies of these hydrazine inserted pyrrole-based bisboron fluorophores BOPHY, BOPPY and BOAPY in our group and their superior properties. Moreover, significant photophysical data of these fluorophores in solution and solid states are also inside the scope of this review. The facile functionalization of these fluorophores’ platforms allows a practically structural modification and generate novel versatile dyes with excellent chemical and photophysical properties. We believe that these fluorophores will hold promise to make an important contribution to various applications.

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.

Hybridization of triphenylamine to BODIPY dyes at the 3,5,8-positions: A facile strategy to construct near infra-red aggregation-induced emission luminogens with intramolecular charge transfer for cellular imaging

A series of five BODIPY derivatives with triarylamine (TPA) moieties on their 3-, 5-, or 8-positions were reported, which showed wide-range fluorescence emissions across red and near infrared regions in their aggregation states. The influences of numbers and substituted positions of TPA groups on the optical and aggregation-induced emission (AIE) properties of these BODIPYs as well as organelle-specific imaging in live cells were investigated. The TPA groups installed at 3-/5-positions of BODIPY could effectively enlarge the conjugated system and red-shift the absorption and emission bands (λ_em^max up to 815 nm). In contrast, the TPA group linked to 8-position of BODIPY core has little contribution to decrease the HOMO-LUMO energy gap. Importantly, regardless the substitution positions of TPA groups, all these TPA-substituted BODIPYs (BTs) showed remarkable AIE performance and possessed high molar extinction absorption (up to ∼ 63000 M^-1 cm^-1), two-photon absorption (up to 171 GM at 870 nm), and large Stokes shifts. The BODIPY with one TPA group (BT1 and FBT1) showed lipid droplets-specific localization while BODIPY with two and three TPA groups (BT2, BT3 and FBT2) preferred to enrich in lysosomes. These BODIPYs all have been successfully used in tracking the dynamic behaviors of lipid droplets or lysosomes in living cells. Furthermore, BT1 and FBT1 can quantitatively detect the overexpression of lipid droplets, and BT3 has been successfully used to observe lysosomes behaviors of lipophagy process in living cells. This work systematically studied the influence of the number and position of TPA units on the optical properties and AIE-activities of BODIPYs, which not only enriched the BODIPY-based AIE NIR probes for organelle-specific imaging in live cells, but also provided a practical strategy for the effective construction of organic dyes with NIR AIE activity.

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.

Aromatic-Ring-Fused BOPPY Fluorophores: Synthesis, Spectral, Redox Properties, and Bioimaging Application

Tetracoordinated organoboron dyes exhibiting strong fluorescence in either solution or the solid state are currently receiving much attraction in view of their photovoltaic, optoelectronic, and biological applications. Herein, a series of aromatic-ring-fused BOPPY dyes have been developed by one-pot condensation of formylated isoindoles or indoles and pyridinylhydrazine followed by subsequent borylation coordination. The facile synthesis provides excellent diversity of these unsymmetrical α-benzo- and β-benzothiophene-fused BOPPY dyes with intriguing photophysical properties owing to their rigid and planar structure and extended π-conjugation while containing a reactive site. They display intense green to orange fluorescence in solution and red-to-near-infrared emission in the solid state, with high fluorescence quantum yields up to 92 and 21%, respectively, relatively large Stokes shifts, and excellent photostability. Furthermore, two representative benzo-fused BOPPY probes with morpholine or benzenesulfonamide groups were developed and used to selectively "light up" the subcellular organelles such as lysosomes and endoplasmic reticulum under ultralow concentration, respectively.

Engineering BODIPY-based near-infrared nanoparticles with large Stokes shifts and aggregation-induced emission characteristics for organelle specific bioimaging

Lipid droplets (LDs) and lysosomes, as two important subcellular organelles, play specific and indispensable roles in various cellular processes. The development of efficient LD- and lysosome-specific fluorescent bio-probes is of great importance. However, current commercial lipid droplet- (LD) and lysosome-specific fluorescent specific bio-probes often suffer from the aggregation-caused quenching (ACQ) effect, short absorption and emission wavelengths, poor photostability and low specificity. Herein, a typical ACQ luminogen BODIPY was directly conjugated to strong electron donating triarylamine units at its α-positions, giving near-infrared (NIR) fluorescent materials TPAB and 2TPAB with aggregation-induced emission (AIE). Both TPAB and 2TPAB nanoparticles were obtained by self-assembly, and showed NIR emissions, large Stokes shifts, good photostability and two-photon absorption. These nanoparticles presented remarkable bioimaging performances and were shown to specifically localize in LDs or lysosomes, respectively, depending on the number of triarylamine units attached. They have been successfully used to detect endogenous LD overproduction, and monitor abnormal activities of LDs/lysosomes, as well as real-time track the lipophagy process in cells. Their far NIR emission and two-photon excitation further supported their promising bioimaging application for lipid droplet tracking in liver tissue and live zebrafish larvae. Our work here enriches BODIPY based NIR AIE dyes and provides organelle specific bio-probes which are superior to currently used commercial ones.

Synthesis and Spectral Properties of Aggregation-Induced Emission-Active Push-Pull Chromophores Based On Isoindole Scaffolds

A new class of tailor-made push-pull isoindole fluorophores has been synthesized through the combination of Suzuki coupling and Knoevenagel reactions. The efficient synthetic strategy rendered the isoindole scaffold as the π-bridge and the isolation spacer and provided dyes bearing various types of electron donors and electron acceptors for manipulating their energy gaps and tuning their absorptions and emissions. Most of the N-alkylated isoindole dyes showed aggregation-induced emission behaviors suitable for bioimaging and nice solid-state emission with maxima up to 851 nm.

Silver-mediated, direct phosphorylation of BODIPY dyes at the 3- or 3,5-positions with H-phosphonates

A direct and regioselective C-H/P-H cross-coupling of dialkyl phosphites, and diphenylphosphine oxide to easily available BODIPYs through an Ag-mediated radical addition, resulted in a series of new α-phosphorylated BODIPY fluorophores under mild conditions. Hydrolysis of the phosphonate gave the corresponding BODIPY phosphoric acid, which is soluble and fluorescent in water with a high quantum yield of 0.83.

Boron-Templated Synthesis of B(III)-Submonoazaporphyrins: The Hybrids of B(III)-Subporphyrins and B(III)-Subporphyrazines

A new class of hybridized and core-contracted porphyrinoids, B(III)-submonoazaporphyrins, which may be viewed as the hybrids of B(III)-subporphyrins and B(III)-subporphyrazines, was reported. The versatile single-step synthesis was based on an efficient intramolecular nucleophilic substitution reaction on readily available α-amino-α'-bromotripyrromethenes, while boronic acids, trifluoroborate salts, or trimethoxyborate simultaneously acted as the template and provider of apical substituent. Those new hybrids, as robust and photostable compounds, were fully characterized by NMR, mass spectrometry, and X-ray crystallography. They showed intense absorption and emission in the visible region, and their electrochemical properties and computational calculation are also discussed.

Synthesis, Reactivity, and Properties of a Class of π-Extended BODIPY Derivatives

A new family of π-extended BODIPY derivatives were obtained through the condensation of aldehyde and pyrrole in aqueous solution in the presence of HCl. The new rigid π-framework extends beyond the dipyrromethene unit, which is significantly different from classical BODIPYs in the electronic configuration. Both π-extended BODIPYs displayed intense absorption and moderate emission with maxima around 565 and 620 nm, respectively, and showed interesting reactivity toward various nucleophiles. Moreover, these π-extended BODIPYs were developed as fluorescent probes for rapid and selective detection of GSH and were successfully applied for live-cell imaging.

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

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

One-Pot Access to Ethylene-Bridged BODIPY Dimers and Trimers through Single-Electron Transfer Chemistry

A Cu(I)-promoted oxidative dimerization of BODIPY dyes was developed to give a series of α,α- ethylene-bridged BODIPY dimers and trimers for the first time. This methodology does not need harsh conditions but relies on the singlet-electron-transfer process between alkylated BODIPYs and Cu(I) salt to generate BODIPY-based radical species, which undergo a selective radical homocoupling reaction. Moreover, these resultant dimers and trimers showed high attenuation coefficients, small line widths of the absorption and emission, and intense fluorescence.

Palladium(II)-Catalyzed Dehydrogenative Strategy for Direct and Regioselective Oligomerization of BODIPY Dyes

A family of directly β,γ-linked BODIPY oligomers up to pentamers were regioselectively prepared via Pd(II)-catalyzed oxidative C-H cross-coupling. The structural integrity of β,γ-linked dimers was unambiguously confirmed by X-ray crystallography. These structurally unprecedented oligomers showed red-shifted absorptions and near-infrared emissions along with efficient intersystem crossing, giving Φ_Δ in the range of 12-43%, for potential use as heavy-atom-free photosensitizers.

Thiophene-Fused BODIPY Dimers and Tetramers from Oxidative Aromatic Couplings as Near-Infrared Dyes

We describe a straightforward, postmodification synthesis for a family of thiophene-fused BODIPY dimers and tetramers through transforming flexible sulfur bridges into coplanar thiophene fusions. FeCl₃ was used as a bifunctional oxidant for both intramolecular and intermolecular oxidative aromatic coupling reactions. Oxidative fusion and dimerization gave strong red-shift absorptions from 509 nm for a BODIPY monomer to 830 nm for a tetramer.

FeCl3-promoted regioselective synthesis of BODIPY dimers through oxidative aromatic homocoupling reactions

The direct 3,3'-dimerization of BODIPYs lacking substituent groups in the 1,2,6, and 7 positions was developed by oxidative coupling with FeCl₃. This regioselective dimerization was achieved for BODIPYs substituted only in the 5-position with Cl or aryl groups. Further functionalization of the 5,5'-dichloride dimer gave the corresponding pyrrole or 4-(2-aminoethyl)morpholine disubstituted dimers 2f and 2g, respectively. While dimer 2f exhibited intense NIR absorption/emission maxima at 773/827 nm in toluene, dimer 2g showed favorable lysosome-targeting NIR fluorescence in living cells.

Strategic Construction of Sulfur-Bridged BODIPY Dimers and Oligomers as Heavy-Atom-Free Photosensitizers

An efficient strategy for building sulfur-bridged oligo-BODIPYs based on the S_NAr reaction is described. These oligo-BODIPYs showed broadband and strong visible-near-infrared (NIR) light absorption, strong intramolecular exciton coupling, and efficient intersystem crossing (ISC). Generation of ¹O₂ as well as O₂^•- under irradiation was found to give high reactive oxygen species generation efficiencies for those oligomers.

Synthesis of pyrrolyl-BODIPY dyes through regioselective SN Ar reactions and application as a fluorescent sensor for fluoride anion

Two pyrrolyl-BODIPY dyes with 3,5-di-[Formula: see text]-butyl-4-hydroxyphenyl group were synthesized through stepwise S[Formula: see text]Ar reactions of 3,5-dibromoBODIPYs, which were used as a fluorescent sensor for basic anions. The intermediate pyrrolyl-BODIPYs 2a–2b were regioselectively synthesized through an efficient S[Formula: see text]Ar reaction between 3,5-dibromoBODIPY 1a and pyrroles. The target pyrrolyl-BODIPYs 3a–3b with a 3,5-di-[Formula: see text]-butyl-4-hydroxyphenyl group at 3-position and a pyrrole substituent at 5-position were obtained through a second S[Formula: see text]Ar reaction between pyrrolyl-BODIPYs 2a–2b and high steric hindrance 2,6-dibutylphenol in 90% and 88% yields, respectively. In contrast, the reaction between pyrrolyl-BODIPYs 2a–2b and phenol gave pyrrolyl-BODIPYs 3c–3d with phenoxy substituent at 3-position. These pyrrolyl-BODIPYs 3a–2d show strong, sharp absorptions (551–604 nm) and emissions (564–634 nm) with high fluorescence quantum yields up to 0.86 in dichloromethane. Importantly, the 3,5-di-[Formula: see text]-butyl-4-hydroxyphenyl group of pyrrolyl-BODIPY 3a showed a turn-off fluorescent response toward fluoride anion.

A Family of Highly Fluorescent and Membrane-Permeable Bis(BF2) Acyl-Pyridinylhydrazine Dyes with Strong Solid-State Emission and Large Stokes Shifts: The BOAPH Fluorophores

Organic small-molecule fluorescent chromophores have become essential to modern chemical, biological, and materials related investigations. Herein, a straightforward synthesis and subsequent borylation were presented to form a novel family of bisBF₂-anchoring acyl-pyridinylhydrazine, which we named BOAPH. The chromophore enjoys outstanding structural diversities owing to varied acyl chlorides and N-heteroarenylhydrazides. These resultant BOAPH dyes are confirmed by NMR, HRMS, and single-crystal X-ray structure analysis. Their spectroscopic properties were studied, and most of the strong absorbance and bright fluorescence with maximum wavelengths centered in the range of 400 and 650 nm. More importantly, they exhibit promising fluorescence quantum yields up to 0.79 in solution and solid states, good photostability, and large Stokes shifts. Furthermore, a respective BOAPH dye with a para-dimethylaminophenyl group exhibited the interesting ability of ultrafast staining and two-photon imaging, which can specifically label lipid droplets of living cells immediately without the need for incubation.

Aromatic [b]-fused BODIPY dyes as promising near-infrared dyes

Far-red and near-infrared (NIR) absorbing/emitting dyes have found diverse applications in biomedicine and material science. However, the absorption and emission of classical BODIPY chromophores at short wavelength hamper their applications. Several strategies have been adopted to modify the structure of the BODIPY core to design NIR dyes. Among these, the most efficient approach to expand the π-conjugation of the BODIPY core is via fusion of aromatic rings. So far, many novel BODIPY skeletons fused to aromatic hydrocarbons and heterocycles at the b bond have been reported. This review comprehensively describes the recent advances regarding the development of aromatic [b]-fused BODIPY dyes with the focus on the design and synthesis, the relationships between their photophysical/spectroscopic properties and molecular structures, and the potential applications in bioassays and optoelectronic devices.

Sterically Protected and Conformation-Restricted BOBHY Dyes with Bright Near-Infrared Fluorescence: N2O-type Expanded BOPHY Dyes Derived from Boronic Acids

A new family of N₂O-type hydrazine-containing bipyrrole boron complexes has been developed via a one-pot condensation of formylisoindole, hydrazine, and various organoboronic acids. Because of the conformation-restricted coplanar structure and the axial-substituted aryl groups, these novel dyes show deep-red absorption, bright near-infrared (NIR) fluorescence in both solution and solid states, and good solubility in organic solvents. The derivative with pyridinium ions also has been synthesized as an NIR mitochondrially targetable fluorescent probe.

Highly selective, colorimetric probes for cyanide ion based on β-formylBODIPY dyes by an unprecedented nucleophilic addition reaction

Two β-formylBODIPYs with strong daylight excitable fluorescence and highly selective visual and colorimetric responses to cyanide anion (CN^-) have been prepared. NMR titration experiments have been performed to study the sensing mechanism for these two dyes. Surprisingly, cyanide anion is nucleophilic addition to the α-position of BODIPY core (the azafulvene framework) in aqueous system instead of the expected classical nucleophilic addition to the formyl moiety of the probes. This nucleophilic addition of cyanide anion to the azafulvene framework causes the interruption of the π-conjugation of the BODIPY system, which brings a significant blue-shift (up to 104 nm) of the absorption maxima. A broadened and decreased absorption as well as ratiometrical fluorescence response (with maxima shifts from 523 to 670 nm) were observed with the titration of cyanide anion to probe 1b.

Direct C–H alkoxylation of BODIPY dyes via cation radical accelerated oxidative nucleophilic hydrogen substitution: a new route to building blocks for functionalized BODIPYs

A convenient C–H alkoxylation reaction between BODIPY dyes and a variety of alcohols was developed via a cation radical accelerated oxidative nucleophilic hydrogen substitution.

Conjugated BODIPY Oligomers with Controllable Near-Infrared Absorptions as Promising Phototheranostic Agents through Excited-State Intramolecular Rotations

Conjugated molecules with coplanar strong donor and acceptor (D-A) units have been widely used in the design of near-infrared (NIR) photothermal agents to increase an absorption band through intramolecular charge transfer and to control intramolecular motions in aggregated states. However, such conjugated D-A systems have strong dipolar moments and intermolecular interactions, which may inhibit other channels of photothermal conversion and are often susceptible to nucleophiles, especially in the presence of light irradiation. Now, we report a molecular guideline to develop novel NIR organic photothermal nanoagents based on conjugated boron dipyrromethene (BODIPY) oligomers. This oligomerization is helpful not only for their tunable NIR absorptions in the ground state with distinctly redshifted absorption maxima up to 1002 nm and high extinction coefficients but also for their highly efficient photothermal conversion because of the possible motion of the BODIPY motifs around the ethene linked group in the excited state. These oligomers were fabricated as ultra-photostable nanoagents for multiple imaging-guided phototherapies, which efficiently accumulated in tumors, and gave complete tumor ablation with NIR laser irradiation. This strategy of "ground-state conjugation, excited-state rotation" provides a novel guideline to develop advanced theranostic molecules with NIR absorption.

Inhibiting Radiative Transition-Mediated Multifunctional Polymeric Nanoplatforms for Highly Efficient Tumor Phototherapeutics

It is highly desired to explore ideal phototherapeutic nanoplatforms, especially containing satisfactory phototherapeutic agents (PTAs), for potential cancer therapies. Herein, we proposed an effective strategy for designing a highly efficient PTA through inhibiting radiative transition (IRT). Specifically, we developed an ultralow radiative BODIPY derivative (TPA-IBDP) by simply conjugating two triphenylamine units to iodine-substituted BODIPY, which could simultaneously facilitate the nonradiative decay channels of singlet-to-triplet intersystem crossing and intramolecular charge transfer. In comparison to the normal BODIPY compound, TPA-IBDP exhibited an outstanding singlet oxygen yield (31.8-fold) and a higher photothermal conversion efficiency (PCE; over 3-fold), respectively, benefiting from the extended π-conjugated donor-to-accepter (D-A) structure and the heavy atom effect. For tumor phototherapy using TPA-IBDP, TPA-IBDP was conjugated with a H₂O₂-responsive amphiphilic copolymer POEGMA₁₀-b-[PBMA₅-co-(PS-N₃)₂] to construct a multifunctional phototherapeutic BODIPY-based nanoplatform (PB). PB produced abundant singlet oxygen (¹O₂) and heat along with negligible fluorescence emission under near-infrared laser irradiation. Additionally, PB could generate a GSH-depletion scavenger (quinone methide, QM) after reacting with the abundant intracellular H₂O₂ in tumor for the cooperative enhancement of IRT-mediated phototherapy. We envision that this highly efficient multifunctional phototherapeutic nanoplatform cooperated by GSH-depletion could be a valuable paradigm for tumor treatments.