Nonsymmetric Benzo[a]fused and Thiophene/Thieno[3,2-b]thiophene[b]fused BODIPYs: Synthesis and Photophysical Properties

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

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

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.

Novel organoboron complexes with robust core: Synthesis, functionalization, and subcellular targeting

The construction of novel organoboron complexes with facile synthesis and unique advantages for biological imaging remains a challenge and thus has garnered considerable attention. Herein, we developed a new molecular platform, boron indolin-3-one-pyrrol (BOIN3OPY) via a two-step sequential reaction. The molecular core is robust enough to allow for post-functionalization to produce versatile dyes. When compared to the standard BODIPY, these dyes feature an N,O-bidentate seven-membered ring center, significantly redshifted absorption, and a larger Stokes shift. This study establishes a new molecular platform that provides more flexibility for the functional regulation of dyes.

Synthesis of N,O-bidentate organic difluoroboron complexes and their photophysical studies

We disclose a novel boron trifluoride induced C-H activation and difluoroboronation at room temperature, thus providing a straightforward gateway to a series of N,O-bidentate organic BF₂ complexes. The scope of the method is demonstrated with 24 examples. All the synthesized compounds exhibit fluorescence and some of them have large Stokes shifts.

Synthesis and Spectroscopic Properties of Selenophene[3, 2-b]-Fused BODIPYs

Fusion selenophene endows the chromophore with more intrinsic and special functions. Herein, nonsymmetric selenophene-fused BODIPYs were designed and synthesized starting from the selenophene unit. The fused ring of selenophene not only maintains the rigid structure of BODIPY but also further modulates its spectral properties. The newly prepared dyes possessed many promising properties including large molar extinction coefficients, low fluorescence quantum yields, and moderate singlet oxygen generation. Quantum calculations affirmed that the smaller singlet-triplet energy gap and larger spin-orbit coupling cause efficient intersystem crossing, thus enhancing the singlet oxygen generation yield. Furthermore, selenophene-fused BODIPY exhibited significant phototoxicity with negligible dark cytotoxicity, based on the fluorescence imaging of the reactive oxygen species detection experiment.

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.

A Colormetric and Fluorescence Probe for Highly Specific Cu2+ and its Application in Live Cell Imaging

Fluorescent probes are intriguing material for ion detection. In this study, 4,4-difluoro-4-bora3a,4a-diaza-s-indacene (BODIPY) containing a dipicolylethylenediamine unit was developed as a colorimetric and fluorescence "turn-off" probe for Cu²⁺. The probe exhibited higher selectivity for Cu²⁺ than other common metal ions with a detection limit of 8.49 μM. With increasing Cu²⁺ concentration, the probe showed a red-shift in the absorption spectrum as well as fluorescence quenching, possibly due to the intramolecular charge transfer effect of the probe-Cu(II) complex. Furthermore, the probe was used for imaging Cu²⁺ in living cells based on confocal fluorescence imaging. The results show that the probe is an effective tool for detection copper ions.

N,O-Chelated Organoboron Complexes with Seven-Membered Rings

Organoboron complexes have gained considerable attention owing to their versatile chemical structures and excellent optical properties. Nevertheless, stable seven-membered organoboron complexes have rarely been reported because of their challenging synthesis. Herein, seven-membered N,O-boron-chelated dyes, whose photophysical properties have been thoroughly studied via spectroscopic tests and theoretical calculations, were synthesized from commercially available materials via a facile method. Single-crystal X-ray diffraction studies provided evidence of their seven-membered ring N,O-boron-chelated skeleton. These complexes produced singlet oxygen species under laser irradiation, endowing them with potential application as a photosensitizer to treat superficial tumors (B16 cells). Our study provided a new skeleton to construct versatile organoboron compounds and offered a strategy to design heavy-atom-free photosensitizers.

Recent advances in zig-zag-fused BODIPYs

Recent progress in the synthesis of zig-zag-fused BODIPY, structure–property relationships, as well as their applications are summarized.

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.