Development of Mono- and Di-AcO Substituted BODIPYs on the Boron Center

Benzo-Crown-Ether Functionalized O-BODIPY Probes for Cations - A Selective Fluorescent Probe for Ba2

Herein, we report the synthesis and sensing characteristics of 4,4'-methoxy-substituted BODIPY fluorescent probes (O-BODIPYs) 3, 4 and 5 equipped with differently sized benzo-crown ethers (cf. Scheme 1, 3 (benzo-15-crown-5), 4 (benzo-18-crown-6) and 5 (benzo-21-crown7)). O-BODIPYs 3, 4 and 5 exhibited in comparison to their known F-BODIPY analogues 3a, 4a and 5a (cf. Scheme 1) an improved solubility in aqueous medium and higher fluorescence quantum yields. Fluorometric study in aqueous solutions of 3, 4 and 5 in the presence of different cations show cation induced fluorescence enhancements (FE). Compared to the benzo-crown ether substituted F-BODIPY analogues 3a, 4a and 5a, we found for the free O-BODIPYs 3, 4 and 5 higher fluorescence quantum yields (φf) but lower cation induced FEs. We show that in aqueous medium the fluorescence quenching process (OFF switching), a photoinduced electron transfer, in O-BODIPYs 3, 4 and 5 is less effective and consequently sensitive and selective ON switching of the fluorescence by cations, too. Albeit these observations the novel benzo-21-crown-7 equipped fluorescent probe 5 exhibits a good fluorometric Ba2+ selectivity and Ba2+ sensitivity in conjunction to their aqueous solubility.

Substitution at boron in BODIPYs

Recent synthetic achievements have led to 4,4-disubstituted-4-bora-3a,4a-diaza-s-indacenes (BODIPYs) with varying substituents at the meso, pyrrolic and/or boron sites, with each influencing photophysical properties and utility. This Feature article gives an overview of chemistry at the boron atom in BODIPYs, highlighting our contributions that evolved from synthetic curiosities and now offer this dipyrrolic skeleton potential across a wider range of applications. We first summarise preparative routes to BODIPYs through complexation of boron with the dipyrrinato ligand. The role of boron in protecting dipyrrins is then discussed, followed by strategies by which to achieve facile substitution at the boron atom.

Near-infared upper phenyl-fused BODIPY as photosensitizer for photothermal-photodynamic therapy

BODIPY scaffolds by introducing ring-fused segment promoted bathochromic-shift spectrum and enhanced intersystem crossing capability by a twisted structure. In this work, we designed the upper phenyl-fused BODIPY with 4-dimethylaminostyryl groups...

BCl3-Activated Synthesis of COO-BODIPY Laser Dyes: General Scope and High Yields under Mild Conditions

A general and straightforward method for the synthesis of COO-BODIPYs from F-BODIPYs and carboxylic acids is established. The method is based on the use of boron trichloride to activate the involved substitution of fluorine, which leads to high yields through rapid reactions under soft conditions. This mild method opens the way to unprecedented laser dyes with outstanding efficiencies and photostabilities, which are difficult to obtain by the current methods.

BODIPY-Based Fluorescent Probes for Biothiols

Fluorescent probes for biothiols have aroused increasing interest owing to their potential to enable better understanding of the diverse physiological and pathological processes related to the biothiol species. BODIPY fluorophores exhibit excellent optical properties, which can be readily tailored by introducing diverse functional units at various positions of the BODIPY core. In the present review, the development of fluorescent probes based on BODIPYs for the detection of biothiols are systematically summarized, with emphasis on the preferable detection of individual biothiols, as well as simultaneous discrimination among cysteine (Cys), homocysteine (Hcy), reduced glutathione (GSH). In addition, organelle-targeting probes for biothiols are also highlighted. The general design principles, various recognition mechanisms, and biological applications are elaboratively discussed, which could provide a useful reference to researchers worldwide interested in this area.

A water-soluble BODIPY-based fluorescent probe for rapid and selective detection of hypochlorous acid in living cells

We designed and synthesized 4,4-di-(4'-methylmercaptophenoxy)-8-(N-methylpyridinium-2-yl)-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene (probe 1) as a water-soluble BODIPY derivative for rapid and selective detection of hypochlorous acid. The pyridinium-2-yl linked at the meso position of BODIPY core was used to maintain highly fluorescent nature and to increase water solubility. Methylmercaptophenoxy was selected as responsive site installed on the boron atom (to replace the fluorine atom) and induced the photoinduced electron-transfer (PeT) effect to quench the fluorescence of BODIPY. The probe exhibited 83.9 μg mL^-1 solubility in PBS (10 mM, pH 7.4), and possessed very low fluorescence (Φ_f = 0.0013). Upon addition of HClO, the probe could display a distinct response in 1 min and generate marked fluorescence enhancement by 100-fold due to the oxidation of thioether into sulfoxide to terminate PeT process. A limit of detection of 53 nM was calculated for HClO in the linear response range from 0 μM to 10 μM, and the probe was successfully applied to image HClO in living cells.

Photophysical properties and application in live cell imaging of B,B-fluoro-perfluoroalkyl BODIPYs

The photophysical properties of newly identified B,B-fluoro-perfluoroalkyl BODIPYs (2 and 3), which possess a fluoro group and a trifluoromethyl or pentafluoroethyl group at the boron center, were investigated. B,B-Fluoro-perfluoroalkyl BODIPYs 2 and 3 exhibited better photophysical/chemical properties than B,B-difluoro-BODIPY 1, as follows: (1) higher photostability both in methanol solvent and in a live cell environment, (2) higher stability against acid degradation, and (3) improved fluorescence signal-to-noise ratios in a cell system. These favorable properties of B,B-fluoro-perfluoroalkyl BODIPYs are likely due to the highly electron-withdrawing nature of the perfluoroalkyl groups on the boron atom, which reduces the reactivity to 1O2 and strengthens the complexation of the dipyrromethene ligands to the boron atom. Thus, B,B-fluoro perfluoroalkyl BODIPYs may be useful functional molecules for various applications.

Novel π-extended hybrid xanthene dyes with two spirolactone rings for optoelectronic and biological applications

Two hybrid xanthene dyes that can operate as half-subtractors in methanol and can target mitochondria have been developed.

Modulation of ICT probability in bi(polyarene)-based O-BODIPYs: towards the development of low-cost bright arene-BODIPY dyads

Bi(polyarene)-based O-BODIPYs, a valuable and tunable scaffold for photonics.

A mitochondria-targeted turn-on fluorescent probe for the detection of glutathione in living cells

A novel turn-on red fluorescent BODIPY-based probe (Probe 1) for the detection of glutathione was developed. Such a probe carries a para-dinitrophenoxy benzyl pyridinium moiety at the meso position of a BODIPY dye as self-immolative linker. Probe 1 responds selectively to glutathione with the detection limit of 109nM over other amino acids, common metal ions, reactive oxygen species, reactive nitrogen species, and reactive sulfur species. A novel electrostatic interaction to modulate the SNAr attack of glutathione was believed to play significant role for the observed selective response to glutathione. The cleavage of dinitrophenyl ether by glutathione leads to the production of para-hydroxybenzyl moiety which is able to self-immolate through an intramolecular 1,4-elimination reaction to release the fluorescent BODIPY dye. The low toxic probe has been successfully used to detect mitochondrial glutathione in living cells.

Dual emission channels for sensitive discrimination of Cys/Hcy and GSH in plasma and cells

A new selective fluorescent and colorimetric chemosensor for the detection of GSH was developed. The discrimination of GSH from Cys and Hcy is achieved through two emission channel detection. The detection limit of probe 1 for GSH reached 10 nM (3 ppb). The excellent sensitivity and selectivity of probe 1 allow the selective detection of GSH over Cys and Hcy, which can be visualized colorimetrically and/or fluorescently. The sensitive detection of GSH allowed for convenient measurement of the GSH content in human plasma. The presence of GSH in cells was demonstrated through cell imaging.

Efficient deprotection of F-BODIPY derivatives: removal of BF2 using Brønsted acids

The effective and efficient removal of the BF2 moiety from F-BODIPY derivatives has been achieved using two common Brønsted acids; treatment with trifluoroacetic acid (TFA) or methanolic hydrogen chloride (HCl) followed by work-up with Ambersep(®) 900 resin (hydroxide form) effects this conversion in near-quantitative yields. Compared to existing methods, these conditions are relatively mild and operationally simple, requiring only reaction at room temperature for six hours (TFA) or overnight (HCl).

Synthesis of mono-(p-dimethylamino)styryl-containing BOPHY dye for a turn-on pH sensor

Mono-substitutional BOPHY 3a with a (p-dimethylamino)styryl group in the α-position was confirmed to be synthesized by the Knoevenagel-type condensation. Dimethylamino-containing BOPHY 3a can be used as a pH probe.

Monoalkoxy BODIPYs--a fluorophore class for bioimaging

Small molecule fluorophores are indispensable tools for modern biomedical imaging techniques. In this report, we present the development of a new class of BODIPY dyes based on an alkoxy-fluoro-boron-dipyrromethene core. These novel fluorescent dyes, which we term MayaFluors, are characterized by good aqueous solubility and favorable in vitro physicochemical properties. MayaFluors are readily accessible in good yields in a one-pot, two-step approach starting from well-established BODIPY dyes, and allow for facile modification with functional groups of relevance to bioconjugate chemistry and bioorthogonal labeling. Biological profiling in living cells demonstrates excellent membrane permeability, low nonspecific binding, and lack of cytotoxicity.

Design, synthesis and photophysical studies of dipyrromethene-based materials: insights into their applications in organic photovoltaic devices

This review article presents the most recent developments in the use of materials based on dipyrromethene (DPM) and azadipyrromethenes (ADPM) for organic photovoltaic (OPV) applications. These chromophores and their corresponding BF2-chelated derivatives BODIPY and aza-BODIPY, respectively, are well known for fluorescence-based applications but are relatively new in the field of photovoltaic research. This review examines the variety of relevant designs, synthetic methodologies and photophysical studies related to materials that incorporate these porphyrinoid-related dyes in their architecture. The main idea is to inspire readers to explore new avenues in the design of next generation small-molecule and bulk-heterojunction solar cell (BHJSC) OPV materials based on DPM chromophores. The main concepts are briefly explained, along with the main challenges that are to be resolved in order to take full advantage of solar energy.

A styryl-containing aza-BODIPY as a near-infrared dye

A novel styryl-containing pyrrole was developed by the reaction of E-4-phenylbut-3-en-2-one with 3-phenyl-2H-azirine in the presence of LDA. Utilizing this pyrrole, asymmetric styryl-containing aza-BODIPYs have been prepared in the NIR region as a result of the extension of conjugation.

Structural modification strategies for the rational design of red/NIR region BODIPYs

The structure–property relationships of red/NIR region BODIPY dyes is analyzed, so that trends in their photophysical properties can be readily compared.

Energy-funneling-based broadband visible-light-absorbing bodipy-C60 triads and tetrads as dual functional heavy-atom-free organic triplet photosensitizers for photocatalytic organic reactions

C60-bodipy triads and tetrads based on the energy-funneling effect that show broadband absorption in the visible region have been prepared as novel triplet photosensitizers. The new photosensitizers contain two or three different light-harvesting antennae associated with different absorption wavelengths, resulting in a broad absorption band (450-650 nm). The panchromatic excitation energy harvested by the bodipy moieties is funneled into a spin converter (C60), thus ensuring intersystem crossing and population of the triplet state. Nanosecond time-resolved transient absorption and spin density analysis indicated that the T1 state is localized on either C60 or the antennae, depending on the T1 energy levels of the two entities. The antenna-localized T1 state shows a longer lifetime (τ(T)=132.9 μs) than the C60-localized T1 state (ca. 27.4 μs). We found that the C60 triads and tetrads can be used as dual functional photocatalysts, that is, singlet oxygen ((1)O2) and superoxide radical anion (O2(.-)) photosensitizers. In the photooxidation of naphthol to juglone, the (1)O2 photosensitizing ability of the C60 triad is a factor of 8.9 greater than the conventional triplet photosensitizers tetraphenylporphyrin and methylene blue. The C60 dyads and triads were also used as photocatalysts for O2(.-)-mediated aerobic oxidation of aromatic boronic acids to produce phenols. The reaction times were greatly reduced compared with when [Ru(bpy)3Cl2] was used as photocatalyst. Our study of triplet photosensitizers has shown that broadband absorption in the visible spectral region and long-lived triplet excited states can be useful for the design of new heavy-atom-free organic triplet photosensitizers and for the application of these triplet photosensitizers in photo-organocatalysis.