1,4-Bisvinylbenzene-Bridged BODIPY Dimers for Fluorescence Imaging in the Second Near-Infrared Window

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.

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

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

Near-Infrared Absorbing BODIPY-Xanthene Hybrids for Multiplexed Photoacoustic Imaging

We report a series of ethenylene-bridged D-π-A BODIPY-xanthene hybrid dyes with precisely regulated absorption bands ranging from the far-red to the near-infrared region (NIR, 700-1000 nm) through rational molecular design. These dyes have excellent photoacoustic properties, and their biocompatibility can be significantly improved by facilely introducing water-soluble groups. In vivo two-channel multiplexed photoacoustic imaging demonstrated their high-resolution imaging capabilities, making them promising candidates for future NIR bioimaging applications.

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.

Dual-Responsive Near-Infrared BODIPY-Based Fluorescent Probe for the Detection of F- and HClO in Organisms

Fluoride anions (F-) play a crucial role in human physiological processes. However, excessive intake of F- would affect oxygen metabolism and promote the generation of oxygen-free radicals. Hence, it is essential to develop a precise and efficient fluorescent probe for visualizing F--induced oxidative stress. In this work, we developed the first bifunctional BODIPY-based fluorescent probe dfBDP with p-tert-butyldimethylsilanolate benzyl thioether as the sensing site for the detection of F- and HClO via two distinct reactions, the self-immolative removal and the thioether oxidation, which generate the sensing products with two nonoverlap fluorescence bands: 800-1200 and 500-750 nm, respectively. The probe dfBDP displays rapid response, high specificity, and sensitivity for the detection of F- (LOD, 316.2 nM) and HClO (LOD, 33.9 nM) in vitro. Cellular imaging reveals a correlation between F--induced oxidative stress and the upregulation of HClO. Finally, probe dfBDP was employed to detect F- and HClO in mice under the stimulation of F-. The experimental results display that the level of HClO elevates in the liver of mice.

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.

Natural Acceptor of Coumarin-Isomerized Red-Emissive BioAIEgen for Monitoring Cu2+ Concentration in Live Cells via FLIM

Artificial aggregation-induced emission luminogens (AIEgens) have flourished in bio-applications with the development of synthetic chemistry, which however are plagued by issues like singularity in structures and non-renewability. The unique structures and renewability of biomass moieties can compensate for these drawbacks, but their properties are hard to design and regulate due to their confined structures. Therefore, it appears to be a reasonable approach to derive AIEgens from abundant biomass (BioAIEgens), integrating the bilateral advantages of both synthetic and natural AIEgens. In this work, the blue-violet emissive coumarin with its lactone structure serving as a rare natural acceptor, is utilized to construct donor-π-acceptor typed BioAIE isomers incorporating the propeller-like and electron-donating triphenylamine (TPA) unit. The results show that Cm-p-TPA undergoes charge transfer with its keto form, emitting red light at 600 nm, which can be applied to monitor Cu2+ concentration during mitophagy using fluorescence lifetime imaging microscopy because of the excellent biocompatibility, photostability, and specific recognition to Cu2+ . This work not only demonstrates the feasibility of utilizing positional isomerization to modulate excited-state evolutions and resultant optical properties, but also provides evidence for the rationality of constructing biologically-active BioAIEgens via a biomass-derivatization concept.

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.

Access to isoindole-derived BODIPYs by an aminopalladation cascade

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

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.

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.

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.