New BODIPY-triazine based tripod fluorescent systems

A new tripod fluorescent system was developed, which bears a triazine core for combining three different functional groups, such as fluorophore (BODIPY), ligand, and auxiliary group. This concept was confirmed by photophysical properties due to the different auxiliary subunits.     

Study on the BODIPY-triazine-based tripod fluorescent systems: various structures from similar procedure

We report a small library of fluorophore-triazine tripod fluorescent system that can accommodate a combination of three different functional groups, such as fluorophore (BODIPY), ligand (or ligands) and auxiliary group. Syntheses, photophysical properties as well as binding properties towards metal ions of these BODIPY-triazine derivatives are described.     

Tuning the Photophysical Properties of BODIPY Molecules by π‐Conjugation with Fischer Carbene Complexes

The synthesis, structure, and photophysical properties of novel BODIPY–Fischer alkoxy‐, thio‐, and aminocarbene dyads are reported. The BODIPY chromophore is directly attached to the carbene ligand by an ethylenic spacer, thus forming donor–bridge–acceptor π‐extended systems. The extension of the π‐conjugation is decisive in the equilibrium geometries of the dyads and is clearly reflected in the corresponding absorption and emission spectra. Whereas the BODIPY fragment is mainly isolated in aminocarbene complexes, it is fully conjugated in alkoxycarbene derivatives. The former thus exhibit the characteristic photophysical properties of BODIPY units, whereas complete suppression of the BODIPY fluorescence emission is observed in the latter, as a direct consequence of the strong electron‐accepting character of the (CO)₅M?C moiety. As the π‐acceptor character of the metal–carbene group can be modified, the electronic properties of the conjugated BODIPY can be tuned. Density functional calculations have been carried out to gain insight into the photophysical properties.     

Efficient Intramolecular Energy Transfer between Two Fluorophores in a Bis‐Branched [3]Rotaxane

A bis‐branched [3]rotaxane, with two [2]rotaxane arms separated by an oligo(para‐phenylenevinylene) (OPV) fluorophore, was designed and investigated. Each [2]rotaxane arm employed a difluoroboradiaza‐s‐indacene (BODIPY) dye‐functionalized dibenzo[24]crown‐8 macrocycle interlocked onto a dibenzylammonium in the rod part. The chemical structure of the [3]rotaxane was confirmed and characterized by ¹H and ¹³C NMR spectroscopy and high‐resolution ESI mass spectrometry. The photophysical properties of [3]rotaxane and its reference systems were investigated through UV/Vis absorption, fluorescence, and time‐resolved fluorescence spectroscopy. An efficient energy‐transfer process in [3]rotaxane occurred from the OPV donor to the BODIPY acceptor because of the large overlap between the absorption spectrum of the BODIPY moiety and the emission spectrum of the OPV fluorophore; this shows the important potential of this system for designing functional molecular systems.     

A series of polyamide receptor based PET fluorescent sensor molecules: positively cooperative Hg2+ ion binding with high sensitivity

[structure: see text] A series of PET fluorescent sensor molecules were designed and synthesized based on BODIPY fluorophore and polyamide receptors. Comparison of the photophysical properties of these sensor molecules, equipped with di-, tri-, and tetraamide receptor, provided a deep insight into the polyamide-Hg2+ interactions, and an unusual positively cooperative tetraamide-Hg2+ complexation was disclosed. In addition, sensor S3 displayed several favorable sensing properties.     

α-Acrylaldehyde 3-Pyrrolyl BODIPY as a Specific Optical Sensor for Cysteine and Homocysteine

A new fluorophore, α-acrylaldehyde 3-pyrrolyl BODIPY was synthesized by treating 3-pyrrolyl BODIPY with a mixture of 3-(dimethylamino) acrolein and POCl₃ under Vilsmeier–Haack reaction conditions. The X-ray structure revealed that the fluorophore was almost planar, and the appended pyrrole was in the same plane with a small deviation from the mean plane. We investigated the potential use of α-acrylaldehyde 3-pyrrolyl BODIPY for sensing thiol containing amino acids such as cysteine/homocysteine (Cys/Hcy). Our studies showed that the α-acrylaldehyde- 3-pyrrolyl BODIPY was found to be useful for exclusive sensing of Cys/Hcy and to exhibit different optical signaling responses to Cys and Hcy at physiological pH in aq. CH₃CN (1 : 1 v/v, PBS) medium. The enhancement in optical properties for Cys and quenching in same properties for Hcy was attributed to different binding modes of Cys/Hcy with α-acrylaldehyde 3-pyrrolyl BODIPY.     

新型含双酚衍生物三枝氟硼二吡咯染料的合成及其光物理性能

以三聚氯氰为原料合成含醛基的二酚氧基取代中间体（1）; 1分别与酚衍生物（2a~2e）经取代反应制得三酚氧基中间体（3a~3e）; 3a~3e经缩合、氧化和配位等反应合成了5个新型的含双酚衍生物三枝氟硼二吡咯（BODIPY）荧光染料（4a~4e）,其结构经¹H NMR, ¹³C NMR和HR-MS(ESI)表征。4a~4e的最大吸收波长和发射波长分别位于499 nm和508 nm,荧光量子产率为0.41~0.55,显示出BODIPY荧光核典型的光物理性能。     

Photophysical and Laser Properties of Cassettes based on a BODIPY and Rhodamine Pair

This work deals with the synthesis and the photophysical and laser properties of new BODIPY‐rhodamine cassettes. These dyads differ in their rigid and conjugated spacer group (phenyl or acetylenephenyl) and in their linking positions (meta or para). The photophysical properties of these cassettes are controlled by the formation/opening of the spirolactone ring, which, in turn, switches off/on an energy‐transfer process between the chromophores. Herein, we thoroughly describe the influence of the attached spacer group, as well as the distance and orientation between the donor–acceptor pair, on the excitation energy transfer. The observed fast dynamics and efficiency suggest that the process mainly takes place “through‐bond”, although the “through‐space” mechanism also contributes to the whole process. As a result, efficient laser emission from the rhodamine is achieved upon excitation of the BODIPY, in particular for the cassette that contains an acetylenephenyl spacer group in a para disposition.     

Fluorine-18 Radiolabelling and Photophysical Characteristics of Multimodal PET–Fluorescence Molecular Probes

Positron emission tomography (PET)–fluorescence imaging is an emerging field of multimodality imaging seeking to attain synergy between the two techniques. The probes employed in PET–fluorescence imaging incorporate both a fluorophore and radioisotope which enable complementary information to be obtained from both imaging techniques via the administration of a single agent. Fluorine-18 is the most commonly used radioisotope in PET imaging and consequently many novel attempts to radiofluorinate various fluorophores have transpired over the past decade. In this Minireview, the most relevant fluorine-18 labelled PET–fluorescence probes have been classified into four groups as per the implemented fluorophore: 1) boron-dipyrromethene (BODIPY) dyes, 2) cyanine dyes, 3) alternative organic fluorophores and 4) organometallics, such as quantum dots (QDs) and rhenium complexes. The biological, radiochemical and photophysical properties of each probe have been systematically compared to aid future endeavours in PET–fluorescence chemistry.     

meso-Dithiole and tetrathiafulvalene dipyrromethanes a route to metal dithiole-dipyrrin complexes and to fluorescent tetrathiafulvalene-BODIPY

A series of meso-dithiole and tetrathiafulvalene (TTF) dipyrromethanes have been prepared via the reaction of the appropriate aldehyde with either pyrrole or 3-ethyl-2,4-dimethyl-pyrrole under acid catalysis. Oxidation to the corresponding meso-dithiole dipyrrins is reported together with the formation of the metal chelate complexes (M=Zn, Cu, Ni) as well as the meso-dithiole boron-dipyrromethene (BODIPY). The molecular structures of these metal (Cu, Ni) and boron complexes are presented and discussed. According to a similar strategy the meso-TTF BODIPY is prepared and its photophysical properties are presented and compared with those of the meso-dithiole BODIPY.     

Fluorescent In Situ Targeting Probes for Rapid Imaging of Ovarian‐Cancer‐Specific γ‐Glutamyltranspeptidase

γ‐Glutamyltranspeptidase (GGT) is a tumor biomarker that selectively catalyzes the cleavage of glutamate overexpressed on the plasma membrane of tumor cells. Here, we developed two novel fluorescent in situ targeting (FIST) probes that specifically target GGT in tumor cells, which comprise 1) a GGT‐specific substrate unit (GSH), and 2) a boron–dipyrromethene (BODIPY) moiety for fluorescent signalling. In the presence of GGT, sulfur‐substituted BODIPY was converted to amino‐substituted BODIPY, resulting in dramatic fluorescence variations. By exploiting this enzyme‐triggered photophysical property, we employed these FIST probes to monitor the GGT activity in living cells, which showed remarkable differentiation between ovarian cancer cells and normal cells. These probes represent two first‐generation chemodosimeters featuring enzyme‐mediated rapid, irreversible aromatic hydrocarbon transfer between the sulfur and nitrogen atoms accompanied by switching of photophysical properties.     

Synthesis and Photophysical Properties of a Series of Cyclopenta[b]naphthalene Solvatochromic Fluorophores

The synthesis and photophysical properties of a series of naphthalene-containing solvatochromic fluorophores are described within. These novel fluorophores are prepared using a microwave-assisted dehydrogenative Diels-Alder reaction of styrene, followed by a palladium-catalyzed cross coupling reaction to install an electron donating amine group. The new fluorophores are structurally related to Prodan. Photophysical properties of the new fluorophores were studied and intriguing solvatochromic behavior was observed. For most of these fluorophores, high quantum yields (60-99%) were observed in methylene chloride in addition to large Stokes shifts (95-226 nm) in this same solvent. As the solvent polarity increased, so did the observed Stokes shift with one derivative displaying a Stokes shift of ～300 nm in ethanol. All fluorophore emission maxima, and nearly all absorption maxima were significantly red-shifted when compared to Prodan. Shifting the absorption and emission maxima of a fluorophore into the visible region increases its utility in biological applications. Moreover, the cyclopentane portion of the fluorophore structure provides an attachment point for biomolecules that will minimize disruptions of the photophysical properties.     

Substituents modification of meso-aryl BODIPYs for tuning photophysical properties

We successfully synthesized eight meso-aryl BODIPYs with 2,6-diethyl- or 1,2,6,7-tetraethyl substituents and characterized their photophysical properties. The steric hindrance resulting from the phenolic group in the meso-aryl moiety and the ethyl groups on the BODIPY core affected the synthesis of dipyrromethanes as an intermediate as well as the UV–Vis absorption and fluorescence emission of the BODIPYs due to the constrained rotation of the aryl ring. The potential use of the meso-hydroxyphenyl BODIPY as a pH sensor was also shown by the pH-dependent fluorescence emissions.     

Neurotransmitter amino acid—oxobenzo[f]benzopyran conjugates: synthesis and photorelease studies

A series of fluorescent conjugates of neurotransmitter amino acids, such as β-alanine, tyrosine, 3,4-dihydroxyphenylalanine (DOPA) and glutamic acid, were prepared by reaction with a suitable fluorophore, namely 1-chloromethyl-9-methoxy-3-oxo-3H-benzo[f]benzopyran. The photophysical properties of the resulting ester bioconjugates were evaluated as well as the stability to photolysis at different wavelengths of irradiation (250, 300, 350 and 419 nm).     

Exploring the Relationship between BODIPY Structure and Spectroscopic Properties to Design Fluorophores for Bioimaging

Designing chromophores for biological applications requires a fundamental understanding of how the chemical structure of a chromophore influences its photophysical properties. We here describe the synthesis of a library of BODIPY dyes, exploring diversity at various positions around the BODIPY core. The results show that the nature and position of substituents have a dramatic effect on the spectroscopic properties. Substituting in a heavy atom or adjusting the size and orientation of a conjugated system provides a means of altering the spectroscopic profiles with high precision. The insight from the structure–activity relationship was applied to devise a new BODIPY dye with rationally designed photochemical properties including absorption towards the near-infrared region. The dye also exhibited switch-on fluorescence to enable visualisation of cells with high signal-to-noise ratio without washing-out of unbound dye. The BODIPY-based probe is non-cytotoxic and compatible with staining procedures including cell fixation and immunofluorescence microscopy.     

Dipyrrin-based Complexes for Solution-processed Organic Solar Cells

Three dipyrrin-containing metal complexes and a boron dipyrromethene(BODIPY)-containing complex were designed and synthesized. The photophysical properties, electrochemical behaviours and photovoltaic performance were extensively investigated. Density functional theory calculations were also performed on those complexes. These complexes, together with electron-acceptor [6,6]-phenyl-C71-butyric acid methyl ester, were utilized for the fabrication of solution-processed bulk heterojunction solar cells as the electron-donor materials. The more efficient electron acceptor BODIPY segment renders a lower energy gap and a relatively better photovoltaic conversion efficiency of 0.58%. These results prove that BODIPY segment has a great potential for constructing efficient organic solar cell materials.     

Designing a Red-Emitting Viscosity-Sensitive BODIPY Fluorophore for Intracellular Viscosity Imaging

Viscosity imaging at a microscopic scale can provide important information about biosystems, including the development of serious illnesses. Microviscosity imaging is achievable with viscosity-sensitive fluorophores, the most popular of which are based on the BODIPY group. However, most of the BODIPY probes fluoresce green light, whereas the red luminescence is desired for the imaging of biological samples. Designing a new viscosity probe with suitable spectroscopic properties is a challenging task because it is difficult to preserve viscosity sensitivity after modifying the molecular structure. Here we describe how we developed a new red-emitting, viscosity-sensitive, BODIPY fluorophore BP-PH-2M-NO₂ that is suitable for reliable intracellular viscosity imaging of lipid droplets in MCF-7 breast cancer cells. The design of BP-PH-2M-NO₂ was aided by DFT calculations that allowed a successful prediction of the viscosity sensitivity of fluorophores before synthesis. In summary, we report a new red viscosity probe possessing monoexponential fluorescence decay that makes it attractive for lifetime-based viscosity imaging.     

3-[2-(8-Quinolinyl)benzoxazol-5-yl]alanine derivative—a specific fluorophore for transition and rare-earth metal ion detection

A novel aromatic amino acid, 3-[2-(8-quinolinyl)benzoxazol-5-yl]alanine derivative was synthesized as a potential Zn(II) and rare-earth metal, Eu(III) and Tb(III), ion chemosensor. The fluorophore was obtained using lead tetraacetate in DMSO to oxidize the Schiff base obtained from N-Boc-3-amino-tyrosine methyl ester and quinoline-8-carboxaldehyde. Preliminary photophysical properties of this ligand show that it possesses the properties necessary to be an effective chemosensor for Zn²⁺, Tb³⁺ and Eu³⁺ ions.     

Synthesis of a Fluorescent‐Labeled Bisbenzamidine Containing the Central (6,7‐Dimethoxy‐4‐coumaryl)Alanine Building Block

The synthesis of an amino acid amide is reported, which contains two benzamidine cores, one placed in the amide part the other one within the sulfonyl N‐capping group. The amino acid side chain bears the 6,7‐dimethoxycoumarin fluorophore. The fluorescent amino acid was prepared by using the von‐Pechmann reaction. The two corresponding nitrile groups of a precursor molecule were simultaneously converted to the amidine moieties by the Pinner reaction. The fluorescent properties of the final compound were determined.     

New 2,6‐Distyryl‐Substituted BODIPY Isomers: Synthesis,Photophysical Properties,and Theoretical Calculations

A 2,6‐distyryl‐substituted boradiazaindacene (BODIPY) dye and a new series of 2,6‐p‐dimethylaminostyrene isomers containing both α‐ and β‐position styryl substituents were synthesized by reacting styrene and p‐dimethylaminostyrene with an electron‐rich diiodo‐BODIPY. The dyes were characterized by X‐ray crystallography and NMR spectroscopy and their photophysical properties were investigated and analyzed by carrying out a series of theoretical calculations. The absorption spectra contain markedly redshifted absorbance bands due to conjugation between the styryl moieties and the main BODIPY fluorophore. Very low fluorescence quantum yields and significant Stokes shifts are observed for 2,6‐distyryl‐substituted BODIPYs, relative to analogous 3,5‐distyryl‐ and 1,7‐distyryl‐substituted BODIPYs. Although the fluorescence of the compound with β‐position styryl substituents on both pyrrole moieties and one with both β‐ and α‐position substituents was completely quenched, the compound with only α‐position substituents exhibits weak emission in polar solvents, but moderately intense emission with a quantum yield of 0.49 in hexane. Protonation studies have demonstrated that these 2,6‐p‐dimethylaminostyrene isomers can be used as sensors for changes in pH. Theoretical calculations provide strong evidence that styryl rotation and the formation of non‐emissive charge‐separated S₁ states play a pivotal role in shaping the fluorescence properties of these dyes. Molecular orbital theory is used as a conceptual framework to describe the electronic structures of the BODIPY core and an analysis of the angular nodal patterns provides a reasonable explanation for why the introduction of substituents at different positions on the BODIPY core has markedly differing effects.