Meso Alkynylated Tetraphenylethylene (TPE) and 2,3,3-Triphenylacrylonitrile (TPAN) Substituted BODIPYs

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.

Visible Light-Assisted Coordination of a Rh(III)-BODIPY Complex to Guanine

Most photodynamic therapeutics (PDTs) used in cancer treatment require oxygen to work efficiently to terminate cancer cells. These PDTs do not efficiently treat tumors in hypoxic conditions. Rh(III) polypyridyl complexes have been reported to have a photodynamic therapeutic effect in hypoxic conditions when exposed to UV light. UV light can damage tissue and cannot penetrate deep to reach cancer cells. This work proposes the coordination of a BODIPY fluorophore to a rhodium metal center to form a Rh(III)-BODIPY complex that enhances the reactivity of the rhodium under visible light. This complex formation is facilitated with the BODIPY as the highest occupied molecular orbital (HOMO), while the lowest unoccupied molecular orbital (LUMO) is localized on the Rh(III) metal center. Irradiation of the BODIPY transition at ∼524 nm can cause an indirect electron transfer from the orbital of the BODIPY-centered HOMO to the Rh(III)-centered LUMO, populating the dσ* orbital. In addition, photo binding of the Rh complex covalently coordinated to the N (7) position of guanine in an aqueous solution was also observed by mass spectrometry after chloride dissociation upon irradiation with green visible light (532 nm LED). Calculated thermochemistry values of the Rh complex reaction in methanol, acetonitrile, water, and guanine were determined using DFT calculations. All enthalpic reactions and Gibbs free energies were identified as endothermic and nonspontaneous, respectively. This observation supports the chloride dissociation using 532 nm light. This Rh(III)-BODIPY complex expands the class of visible light-activated Rh(III) photocisplatin analogs that may have potential photodynamic therapeutic activity for the treatment of cancers in hypoxic conditions.

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.

Precise Molecular Design of a Pair of New Regioisomerized Fluorophores With Opposite Fluorescent Properties

Aggregation-induced emission (AIE) has attracted much attention in the past 2 decades. To develop novel AIE-active materials, ACQ-to-AIE transformation via regioisomerization is one of the most straightforward method. However, most of the reported ACQ-to-AIE transformations are achieved by migrating bulky units. In this work, a facile conversion was realized by migrating a small pyrrolidinyl group from para- to ortho-position on the rofecoxib scaffold. As a result, a pair of new isomers named MOX2 and MOX4 exhibited AIE behavior and ACQ activity, respectively. Moreover, MOX2 also showed solvatochromic, mechanochromic, and acidochromic properties with reversible multi-stimulus behavior. Single crystal X-ray analysis of MOX2 revealed that the molecular conformation and its packing mode were responsible for the AIE emission behavior. Further investigation indicated that MOX2 showed high lipid droplets staining selectivity. Taken together, the current work not only provides a new design philosophy for achieving ACQ-to-AIE conversion by migrating a small pyrrolidinyl group but also presents a promising candidate MOX2 for potential applications such as in security ink, optical recording and biological applications.

Triphenylamine/4,4'-Dimethoxytriphenylamine-Functionalized Thieno[3,2-b]thiophene Fluorophores with a High Quantum Efficiency: Synthesis and Photophysical Properties

A wide series of 10 new triphenylamine (TPA)/4,4'-dimethoxytriphenylamine (TPA(OMe)₂)-functionalized thieno[3,2-b]thiophene (TT) fluorophores, 4a-e and 5a-e, bearing different electron-donating and electron-withdrawing substituents (-PhCN, -PhF, -PhOMe, -Ph, and -C₆H₁₃) at the terminal thienothiophene units were designed and synthesized by the Suzuki coupling reaction. Their optical and electrochemical properties were investigated by experimental and computational studies. Solid-state fluorescent quantum yields were recorded to be from 20 to 69%, and the maximum solution-state quantum efficiency reached 97%. Moreover, the photophysical characterization of the novel chromophores demonstrated a significant Stokes shift, reaching 179 nm with a bathochromic shift. They exhibited tuning color emission from orange to dark blue in solution and showed fluorescence lifetime reaching 4.70 ns. The relationship between triphenylamine (TPA)/4,4'-dimethoxytriphenylamine (TPA(OMe)₂)-derived triarylamines and different functional groups on thieno[3,2-b] thiophene units was discussed.

Synthesis and Properties of BODIPY Appended Tetraphenylethylene Scaffolds as Photoactive Arrays

Tetraphenylethylene (TPE) and its derivatives exhibit excellent aggregation-induced emission (AIE) properties. The TPE unit is easily accessible, and many functional groups can be introduced in a facile manner to yield effective luminescent materials in both solution and the solid-state. It is because of this, several TPE-based compounds have been developed and applied in many areas, such as OLEDs and chemical sensors. Boron dipyrromethenes (BODIPYs) are a class of pyrrolic fluorophore of great interest with myriad application in both material science and biomedical applications. Through the combination of Pd-catalyzed cross-coupling reactions and traditional dipyrromethene chemistry, we present the syntheses of novel tetra-BODIPY-appended TPE derivatives with different distances between the TPE and BODIPY cores. The TPE-BODIPY arrays 6 and 9 show vastly differing AIE properties in THF/H2O systems, with 9 exhibiting dual-AIE, along with both conjugates being found to produce singlet oxygen (1O2). We presume the synthesized BODIPY-appended TPE scaffolds to be utilized for potential applications in the fields of light-emitting systems and theranostics.

Thioether linked meso functionalized BODIPY DYEmer

Thioether linked meso BODIPY DYEmer 3 was synthesized by two different routes. The reaction of dipyrrothioketone 1 and 8-chloro BODIPY 2 in the presence of triethylamine followed by complexation with BF[Formula: see text] resulted in thioether linked meso functionalized BODIPY DYEmer 3. Using another route, the reaction of 8-chloro BODIPY 2 with sodium hydrosulphide (NaSH) at room temperature resulted in the thioether linked meso BODIPY DYEmer 3. The DYEmer 3 was characterized by 1H, [Formula: see text]C, [Formula: see text]B, [Formula: see text]F NMR, HRMS, and single crystal X-ray crystallography. The properties of DYEmer 3 was compared with the previously reported thioether linked [Formula: see text] and [Formula: see text] BODIPY DYEmers 4 and 5. The structural parameters indicating the intramolecular arrangements of two BODIPY units of DYEmer were compared and corelated with the observed properties. The time-dependent DFT (TD-DFT) calculations suggested that the thioether group at meso position of BODIPY 3 stabilizes the LUMO energy than 8-chloro BODIPY 2. Compared to 8-chloro BODIPY 2 the HOMO-1 of DYEmer 3 is destabilized whereas the LUMO+1 is stabilized.

Configuration-controllable synthesis of Z/E isomers based on o-carborane-functionalized tetraphenylethene

Two Z/E isomers, namely, Z-TPE-2Car and E-TPE-2Car, with clear configuration were synthesized using an effective route and have high solid-state fluorescence quantum yields, reaching 99% and 90%, respectively.

BODIPY Dyes as Probes and Sensors to Study Amyloid-β-Related Processes

Amyloid formation plays a major role in a number of neurodegenerative diseases, including Alzheimer's disease. Amyloid-β peptides (Aβ) are one of the primary markers associated with this pathology. Aβ aggregates exhibit a diverse range of morphologies with distinct pathological activities. Recognition of the Aβ aggregates by using small molecule-based probes and sensors should not only enhance understanding of the underlying mechanisms of amyloid formation, but also facilitate the development of therapeutic strategies to interfere with amyloid neurotoxicity. BODIPY (boron dipyrrin) dyes are among the most versatile small molecule fluorophores. BODIPY scaffolds could be functionalized to tune their photophysical properties to the desired ranges as well as to adapt these dyes to various types of conditions and environments. Thus, BODIPY dyes could be viewed as unique platforms for the design of probes and sensors that are capable of detecting and tracking structural changes of various Aβ aggregates. This review summarizes currently available examples of BODIPY dyes that have been used to investigate conformational changes of Aβ peptides, self-assembly processes of Aβ, as well as Aβ interactions with various molecules.

BODIPY–ortho-carborane–tetraphenylethylene triad: synthesis, characterization, and properties

Two new compounds, BODIPY–tetraphenylethylene dyad and BODIPY–o-carborane–tetraphenylethylene triad, were designed and synthesized.

Exploration of Highly Efficient Blue-Violet Light Conversion Agents for an Agricultural Film Based on Structure Optimization of Triphenylacrylonitrile

To obtain highly efficient blue-violet light conversion agents used for an agricultural film, six triarylacrylonitrile derivatives and their doping films were prepared. Further, the luminogens have the ability to convert ultraviolet light into blue-violet light and exhibit aggregation-dependent fluorescence emission and high-contrast fluorescence quantum yields from 0.004 to 0.833. On the basis of X-ray single-crystal diffraction analysis and aggregation-induced emission activity tests, the variant fluorescence quantum yields are attributed to intermolecular π-π stacking and phase transition between the crystalline state and amorphous state. In a simulated greenhouse environment, the luminogens exhibit excellent photostability. However, their fluorescence intensity drops to 17-40% of the prime intensity after outdoor radiation for 1 month as a result of the ring-closing oxidation reaction (in the summer). By comprehensively considering the above photophysical properties and mechanical properties of the doping film, 2-([1,1'-biphenyl]-4-yl)-3,3-diphenylacrylonitrile is a potential light conversion agent for an agricultural film in the winter. More importantly, the results indicate that the properties of the light conversion films are expected to be further improved by molecular design, inhibiting the ring-closing oxidation reaction and dispersion of crystalline nanoparticles in the doping film.

Structure Based Modulation of Electron Dynamics in meso-(4-Pyridyl)-BODIPYs: A Computational and Synthetic Approach

The effects of structural modification on the electronic structure and electron dynamics of cationic meso-(4-pyridyl)-BODIPYs were investigated. A library of 2,6-difunctionalized meso-(4-pyridyl)-BODIPYs bearing various electron-withdrawing substituents was designed, and DFT calculations were used to model the redox properties, while TDDFT was used to determine the effects of functionalization on the excited states. Structural modification was able to restructure the low-lying molecular orbitals to effectively inhibit d-PeT. A new meso-(4-pyridyl)-BODIPY bearing 2,6-dichloro groups was synthesized and shown to exhibit enhanced charge recombination fluorescence. The fluorescence enhancement was determined to be the result of functionalization modulating the kinetics of the excited state dynamics.

Photophysical and optical limiting properties at 532 nm of BODIPY dyes with p-benzyloxystyryl groups at the 3,5-positions

The synthesis and characterization of a series of 3,5-di-[Formula: see text]-benzyloxystyrylBODIPY dyes with different substituents at the meso-aryl position is reported. The photophysical and nonlinear optical properties are described. BODIPYs of this type are found to be suitable for optical limiting at 532 nm on the nanosecond timescale. An enhancement of the population of the T[Formula: see text] state through the incorporation of bromine atoms at the 2,6-positions does not result in an enhancement of the optical limiting properties on a nanosecond timescale. This suggests that, in contrast with phthalocyanines, access to excited state absorption (ESA) from the T[Formula: see text] state through the introduction of a heavy atom effect does not provide a significantly improved reverse saturable absorbance response compared to ESA from the S[Formula: see text] state.

Regioselective and Stepwise Syntheses of Functionalized BODIPY Dyes through Palladium-Catalyzed Cross-Coupling Reactions and Direct C-H Arylations

Regioselective and stepwise syntheses of a series of functionalized BODIPY dyes through palladium-catalyzed cross-coupling reactions and direct C-H arylations have been developed. In particular, this method allows the straightforward synthesis of 2,6-dibromo-3,5-diarylBODIPYs and 2-bromo-3-arylBODIPYs from polybrominated BODIPYs. The X-ray structure of intermediates 5a-c indicated that the palladium was first inserted into the C-Br bonds at 3,5-positions of brominated BODIPYs. The resulting 2,6-dibromo-substituted BODIPYs are potential long wavelength photosensitizers which are not easily accessible using previous methods.

An experimental and theoretical study of dimethylaminostyryl BODIPY-perylenetetracarboxylic derivative dyads: synthesis, properties and DFT calculation

Three novel dyads composed of perylene tetracarboxylic unit and BODIPY moiety were synthesized and subjected to detailed spectroscopic examination and DFT calculations. Comparisons about the physical properties with changed acceptors were made.

Aggregation-induced emission enhancement and cell imaging of a novel (carbazol-N-yl)triphenylamine–BODIPY

The AIEE fluorogen BCPA–BODIPY emits strong red fluorescence and shows a good uptake by MCF-7 cells.

Tetracyanobutadiene functionalized ferrocenyl BODIPY dyes

Tetracyanobutadiene (TCBD) derivatives of ferrocenyl BODIPYs 2a-2c were designed and synthesized by [2 + 2] cycloaddition-retroelectrocyclization reaction of tetracyanoethylene (TCNE) with meso alkynylated ferrocenyl BODIPYs. The TCBD substituted ferrocenyl BODIPYs were designed in such a way that the distance between the ferrocenyl unit and the TCBD remains constant, whereas the distance between the BODIPY and the TCBD unit varies. The TCBD and BODIPY units were connected directly through a single bond (in 2a), through a phenylacetylene linkage (in 2b) and through a vinyl linkage (in 2c). The photonic and electrochemical properties of ferrocenyl BODIPYs were strongly perturbed by the incorporation of TCBD. The TCBD derivatives 2a-2c show red shifted absorption compared to their precursors 1a-1c. The single crystal structures of TCBD functionalized ferrocenyl BODIPYs 2a and 2c reveal extensive intermolecular hydrogen bonding but lack π-π stacking interactions.

Unusual spectroscopic and photophysical properties of meso-tert-butylBODIPY in comparison to related alkylated BODIPY dyes

meso-t-Bu-BODIPY produces unusual spectroscopic and photophysical characteristics in comparison to those of related alkylated BODIPY dyes.

Aggregation induced emission and mechanochromism in tetraphenylethene substituted pyrazabole

The strong aggregation induced emission (AIE) and reversible mechanochromic behavior for tetraphenylethene (TPE) substituted pyrazabole2was reported.