BODIPY Moiety Research Articles

I2BODIPY as a new photoswitchable spin label for light-induced pulsed EPR dipolar spectroscopy exploiting magnetophotoselection.

Electron paramagnetic resonance (EPR) pulsed dipolar spectroscopy (PDS) using triplet states of organic molecules is a growing area of research due to the favourable properties that these transient states may afford over stable spin centers, such as switchability, increased signal intensity when the triplet is formed in a non-Boltzmann distribution and the triplet signal is used for detection, and high orientation selection, when the triplet signal is probed by microwave pulses. This arises due to the large spectral width at low fields, a result of the large zero field splitting, and limited bandwidth of microwave pulses used. Here we propose the triplet state of a substituted BODIPY moiety as a spin label in light induced PDS, coupled to a nitroxide, in a model peptide with a rigid structure. Orientation selection allows information on the relative position of the centres of the two labels to be obtained with respect to the nitroxide reference frame. Additionally, magnetophotoselection effects are employed to introduce optical selection and additional constraints for the determination of the relative orientation of the spin labels considering the reference frame of the triplet state.

Synthesis of BODIPY-pyrrolo[3,4-b]pyridin-5-ones via Ugi-Zhu/cascade reactions and studies of fluorescence response toward viscosity.

A series of seven new meso-phenyl BODIPY-pyrrolo[3,4-b]pyridin-5-one conjugates were synthesized in one experimental step by using a Sc(III)-catalyzed Ugi-Zhu three-component reaction coupled to a cascade sequence (aza Diels-Alder/N-acylation/aromatization) as post-MCR functionalization process. Further experimental studies were performed behind understanding the fluorescence response toward viscosity. All compounds exhibited a linear response between increasing viscosity (DMSO and glycerol mixtures) and fluorescence intensity. The different substituents also influenced the photophysical properties. Furthermore, in DMSO all compounds exhibited dual emission. Each band is attributed to the pyrrolo[3,4-b]pyridin-5-one and BODIPY moieties, respectively. The electronic structure of all compounds was computed by DFT and TD-DFT calculations, allowing to determine the molecular orbitals involved in the electronic transitions.

Multicomponent synthesis and photophysical properties of meso-thienyl BODIPY-pyrrolo[3,4-b]pyridin-5-ones. An experimental and theoretical study

Seven new pyrrolo[3,4-b]pyridin-5-ones linked to a meso-thienyl BODIPY moiety by an ethynylbenzene π-conjugated system were synthesized in one-pot manner via an Ugi-Zhu reaction coupled to a cascade process [aza Diels-Alder cycloaddition/N-acylation/decarboxylation/dehydration]. The photophysical properties of the polyheterocyclic compounds were evaluated by UV–Vis and fluorescence spectroscopy in five solvents of different polarities. All synthesized products showed two distinct absorption/emission bands, corresponding to both fluorophores separately. The fluorescence intensity of the pyrrolo[3,4-b]pyridin-5-one was the highest in toluene, and it decreased with increasing solvent polarity. On the other hand, the fluorescence intensity of the meso-thienyl BODIPY fragment was insensitive to solvent polarity. The effect of different substituents bonded to the pyrrole ring was evaluated, finding that strong electron-donating groups influence the fluorescence intensity and decay rate of the compounds, even with the presence of a methylene spacer. Moreover, the electronic structure was assessed by DFT and TD-DFT calculations, which reproduced the experimental results reasonably well, showing that the HOMO is located on the pyrrolo[3,4-b]pyridin-5-one core, while the LUMO is on the BODIPY fragment.

Cyclotriphosphazene‐Based Photocatalysts containing Orthogonal BODIPY Moieties for Chemical Transformations

AbstractMolecular organic photocatalysts developed for use in chemical transformation reactions have gained momentum in recent years. In this study, six new triplet photosensitizers were prepared to determine their photocatalyst capabilities and chemical transformation abilities. The chemical structures of the synthesized orthogonal BODIPYs and their cyclotriphosphazene derivatives were analyzed and then their photophysical characteristics including the UV‐Vis absorption spectra, fluorescence emission spectra, fluorescence quantum yields, were investigated. The quantitative singlet oxygen formation was determined by chemical trapping using DPBF (diphenylisobenzofuran). In particular, cyclotriphosphazene derivative 12 having three BODIPY moieties showed efficient singlet oxygen production with high photostability and good molar extinction coefficient. The photo‐oxidation ratio constant of 1,5‐dihydroxynaphthalene (DHN) was calculated as 28.7×10−3 min−1 for compound 12 and at the end of 22.5 min., DHN converted to juglone with 100 % efficiency. In addition, the ability of the compounds to convert 1,3‐cyclohexadiene into peroxides in the presence of molecular oxygen and light was investigated and the conversion efficiency was determined by NMR technique. All compounds have been presented as photocatalysts for use in different synthetic photochemistry applications.

Designing Antitrypanosomal and Antileishmanial BODIPY Derivatives: A Computational and In Vitro Assessment.

Leishmaniasis and Human African trypanosomiasis pose significant public health threats in resource-limited regions, accentuated by the drawbacks of the current antiprotozoal treatments and the lack of approved vaccines. Considering the demand for novel therapeutic drugs, a series of BODIPY derivatives with several functionalizations at the meso, 2 and/or 6 positions of the core were synthesized and characterized. The in vitro activity against Trypanosoma brucei and Leishmania major parasites was carried out alongside a human healthy cell line (MRC-5) to establish selectivity indices (SIs). Notably, the meso-substituted BODIPY, with 1-dimethylaminonaphthalene (1b) and anthracene moiety (1c), were the most active against L. major, displaying IC50 = 4.84 and 5.41 μM, with a 16 and 18-fold selectivity over MRC-5 cells, respectively. In contrast, the mono-formylated analogues 2b and 2c exhibited the highest toxicity (IC50 = 2.84 and 6.17 μM, respectively) and selectivity (SI = 24 and 11, respectively) against T. brucei. Further insights on the activity of these compounds were gathered from molecular docking studies. The results suggest that these BODIPYs act as competitive inhibitors targeting the NADPH/NADP+ linkage site of the pteridine reductase (PR) enzyme. Additionally, these findings unveil a range of quasi-degenerate binding complexes formed between the PRs and the investigated BODIPY derivatives. These results suggest a potential correlation between the anti-parasitic activity and the presence of multiple configurations that block the same site of the enzyme.

Porous organic polymers incorporating BODIPY moieties for efficient removal of organic dyes from aqueous solutions

The incorporation of BODIPY units into porous frameworks enhances the materials’ ability to efficiently adsorb organic dyes from aqueous solutions.

Synthesis of chlorophyll-BODIPY conjugates and their intramolecular excitation energy transfer

Zinc 3-hydroxymethyl-pyropheophorbides-[Formula: see text] covalently linked with an 8-aryl-1,3,5,7-tetramethyl-BODIPY moiety in the 17-substituent were synthesized by chemically modifying naturally occurring chlorophyll(Chl)-[Formula: see text]. The synthetic Chl–BODIPY conjugates in tetrahydrofuran exhibited sharp visible absorption and weak circular dichroism spectra, indicating that their molecules were fully dispersed in the solution. In their ground states, no intramolecular interaction between the Chl and BODIPY parts was observed. By contrast, singlet excitation energy was efficiently transferred from the photoexcited BODIPY moiety to zinc chlorin moiety within their molecules. The intramolecular energy transfer efficiencies exceeded 90% and were independent of the linkages including ester and amide bonds as well as methylene and hexamethylene spacers.

Halogen Bonding in Brominated BODIPY Crystals: a Crystallographic and Computational Study.

The study of halogen bonds (XBs) has been a subject of great interest in recent years due to its clear application in catalysis, liquid crystals, and crystal engineering. In this study we analyzed the intermolecular interactions, in particular halogen bonds in BODIPYs with increasing number of bromine atoms. The computational study included analyses through three different methods: the first approach of close contacts provided by Mercury, then the expanded approach of the electron density partition of the molecules in the crystals provided by the analysis of Hirshfeld surfaces, and finally, the approach of the Quantum Theory of Atoms in Molecules (QT-AIM) to characterize the non-covalent interactions through finding electron density critical points between atoms and between neighboring molecules. The use of different computational methods allowed to gain insight on the interactions directing the crystal packing as the number of bromine atoms increase in the BODIPY moiety. Monocoordinated and bifurcated halogen bonds involving halide/halide were found. The penta-brominated BODIPY showed four-center cyclic nodes where each node is linked via XBs. This kind of motifs can be useful in supramolecular chemistry and self-assembly.

Fluorophore position of headgroup-labeled Gb3 glycosphingolipids in lipid bilayers

Fluorescent lipid probes are an invaluable tool for investigating lipid membranes. In particular, localizing certain receptor lipids such as glycosphingolipids within phase-separated membranes is of pivotal interest to understanding the influence of protein-receptor lipid binding on membrane organization. However, fluorescent labeling can readily alter the phase behavior of a lipid membrane because of the interaction of the fluorescent moiety with the membrane interface. Here, we investigated Gb3 glycosphingolipids, serving as receptor lipids for the protein Shiga toxin, with a headgroup attached BODIPY fluorophore separated by a polyethylene glycol (PEG) spacer of different lengths. We found that the diffusion coefficients of the fluorescently labeled Gb3 species in 1,2-dioleoyl-sn-glycero-3-phosphocholine/Gb3 (98:2, n/n) supported lipid bilayers are unaltered by the PEG spacer length. However, quenching as well as graphene-induced energy transfer experiments indicated that the length of the PEG spacer (n = 3 and n = 13) alters the position of the BODIPY fluorophore. In particular, the graphene-induced energy transfer technique provided accurate end-to-end distances between the fluorophores in the two leaflets of the bilayer thus enabling us to quantify the distance between the membrane interface and the fluorophore with sub-nanometer resolution. The spacer with three oligo ethylene glycol groups positioned the BODIPY fluorophore directly at the membrane interface favoring its interaction with the bilayer and thus may disturb lipid packing. However, the longer PEG spacer (n = 13) separated the BODIPY moiety from the membrane surface by 1.5 nm.

Bodipy−corrole tetrads as heavy−atom−free triplet photosensitizers: Study of the energy transfer and application in triplet−triplet annihilation upconversion

Free base corrole can generate triplet state without invoking of heavy−atom effect, however, its weak and narrow absorption band in the visible spectral range make corrole not an ideal triplet photosensitizer. Herein, novel Bodipy−corrole tetrads were prepared by attaching visible light-harvesting antennae of Bodipy or electron spin converter with fullerene units (2B−Tur−Cor and B−C60−Tur−Cor) to solve the above problems, which show a stronger and broader absorption band in the visible region, and the maximum molar absorption coefficient is up to 2.58 × 105 M−1 cm−1 at 504 nm for 2B−Tur−Cor. By using of fluorescence spectroscopy, steady-state and time-resolved transient absorption spectroscopic methods, the singlet energy transfer progress from the Bodipy moiety to the corrole moiety was confirmed. Through fluorescence lifetimes and fluorescence excitation spectrum study, the rate constant of the singlet energy transfer was calculated as 9.58 × 107 s−1 for 2B−Tur−Cor and 2.45 × 108 s−1 for B−C60−Tur−Cor, respectively. The TD−DFT computation suggests that the first and second triplet state is localized in the corrole moiety and the Bodipy moiety for 2B−Tur−Cor, respectively, and the triplet state energy was calculated to be 1.37 eV and 1.61 eV, respectively. Nanosecond time−resolved transient difference absorption spectra show that the triplet excited states of these tetrads are localized on corrole unit, the lifetime of 2B−T−Cor is up to 143 μs, however, the lifetime of B−C60−Tur−Cor is only 3.3 μs. Long-lived triplet excited states play important role in applications of the triplet photosensitizers in photocatalysis or other photophysical processes concerning triplet–triplet−energy−transfer. As a proof of concept, these tetrads were used as heavy−atom−free organic triplet photosensitizers for triplet−triplet annihilation based upconversion. The upconversion quantum yield was up to 5.86% for 2B−Tur−Cor, however, it is only 0.52% for B−C60−Tur−Cor.

Revisiting the BODIPY-borane dyad for the design of efficient aqueous phase molecular probes for anion recognition: A DFT/TD-DFT study

Fluoride (F−), cyanide (CN−) etc. ions have important roles in various chemical and biological applications. But their excessive use can lead to severe health issues like kidney, gastric etc. Generally analytical methods with costly instruments and laborious treatment are involved for the detection of such analytes. Density functional theory (DFT) and time dependent-density functional theory (TD-DFT) studies suggest that BODIPY-TAB dyad (where BODIPY implied boron dipyrrometehene and TAB is triarylborane) molecular receptor, 1 and the four newly designed receptors 2–5 have selective binding feasibility with CN−, F− and chloride (Cl−) among F−, CN−, Cl−, bromide (Br−), acetate (CH3COO−), nitrate (NO3−), sulphate (SO4−) and bisulphate (HSO4−) via computing thermodynamic energy viz free energy changes, ΔG and binding energies, ΔE. The NPA show the analyte binding at boron atoms of TAB moieties making them the electrophilic centers. The change in optical properties (fluorescence quenching) in the receptor-analyte complexes of CN−, F− and Cl− involve intramolecular charge transfer (ICT) between BODIPY and TAB moieties, associated configurational changes and internal conversion (while π-π* transitions in the receptors make them fluorescent). CAM-B3LYP/6-31G(d) model chemistry provides best results among all the twelve tested functionals. Keeping in view the practical importance, the designed receptors will be improved fluorescent probes for CN−, F− and Cl−. Due to the increased Stokes shifts in case of aqueous medium, 1–5 act as best receptors for CN−, F− and Cl− recognition in aqueous medium in comparison to tetrahydrofuran and dichloromethane.

Bis(naphthobipyrrolyl)methene-derived hexapyrrolic BODIPY as a single-molecule helicate with near-infrared emission.

Helically twisted bis(naphthobipyrrolyl)methene-derived open-chain hexapyrroles have been synthesized as HCl salts and the corresponding BODIPY. Their solid-state structures elucidated by single-crystal X-ray diffraction analysis clearly showed the presence of intramolecular hydrogen bonds, which were concluded to play a pivotal role in stabilizing the twisted conformation. Both molecules were observed to be NIR active, with the BODIPY moiety emission extending beyond 800 nm.

Cis-difunctionalized 21-telluraporphyrin building blocks and their use in the synthesis of (BODIPY)2-telluraporphyrin triad

A series of cis-difunctionalized 21-telluraporphyrins containing two functionalized meso-aryl groups such as [Formula: see text]-iodophenyl, [Formula: see text]-bromophenyl, [Formula: see text]-cyanophenyl, [Formula: see text]-nitrophenyl and [Formula: see text]-trimethylsilyl ethynylphenyl groups in cis-fashion were synthesized by condensing one equivalent of 16-telluratripyrrin with two equivalents of functionalized benzaldehyde and three equivalents of pyrrole in CH2Cl2 under acid catalyzed porphyrin forming conditions. The cis-difunctionalized 21-telluraporphyrins were thoroughly characterized by HR-MS, 1D and 2D NMR, and absorption spectroscopic techniques. To show the use of cis-difunctionalized 21-telluraporphyrin building blocks, the covalently linked (BODIPY)2-telluraporphyrin triad was synthesized by coupling cis-diiodophenyl 21-telluraporphyrin with meso-ethynylphenyl BODIPY under Pd(0) coupling conditions and afforded (BODIPY)2-telluraporphyrin triad in 24% yield. The NMR and absorption studies of the triad indicated that the telluraporphyrin and BODIPY moieties interact weakly in the (BODIPY)2-telluraporphyrin triad and retain their individual characteristic features. The steady-state fluorescence and DFT studies indicated a possibility of charge transfer between 21-telluraporphyrin and BODIPY units in the triad.

8-Hydroxyquinoline-BODIPY based dual mode pH probe: Intuits acidic and basic environments through two different mechanisms

A new BODIPY based optical pH probe that effectively distinguishes acidic and basic solutions through opposite fluorescence responses was designed and subsequently synthesized. The fluorescence response in basic medium was governed by photoinduced electron transfer (PeT). Effective PeT quenched the emission of the probe in basic pH while it was inhibited in acidic pH. The visible colour change on addition of acidic and basic solutions enabled naked eye detection of pH. Comparing the optical property of this probe with other analogous compounds it was realized that substituent at BODIPY has significant impact on possibility of PeT from excited BODIPY moiety. Electron donating substituent facilitates the d-PeT (donor) of excited BODIPY moiety and absence of which inhibits such transition. These experimental observations were validated with theoretical study. The mechanism of pH sensing was also investigated by 1H NMR titration experiment. Interestingly, probe was found to be responsive to pH change in the entire range of pH. Moreover, the probe can reversely detect the pH change through absorption which allows extension of pH sensing in real life samples.

A comparative study on photophysics of meso-substituted mono- and bis-BODIPY carbazoles

A comparative study of the photophysics of mono- and bis-BODIPY (BDP) substituted N-butylcarbazoles (CBZ): CBZ-BDP and CBZ-bisBDP has been carried out. The longest wavelength electronic absorption band at ∼495 nm corresponds to BODIPY moiety and does not exhibit solvatochromism. The absorbance value of CBZ-bisBDP is twice that of CBZ-BDP due to the presence of two BODIPY chromophores in the former. For both the molecules, fluorescence spectra show locally excited (LE) emission in non-polar solvents and red-shifted broad Intramolecular Charge Transfer (ICT) emission in polar solvents. CBZ-BDP shows a larger red-shift and more significant intensity reduction of the ICT band than the bis-conjugated molecule. Theoretical calculations reveal that the Highest Occupied Molecular Orbitals (HOMO) of the two molecules are localized primarily on the carbazole unit. In contrast, the Lowest Unoccupied Molecular Orbitals (LUMO) are mainly concentrated on BODIPY unit. This suggests that excited state charge transfer in both the fluorophores is from the carbazole unit to the BODIPY unit. The S1 states of both CBZ-BDP and CBZ-bisBDP are Twisted Intramolecular Charge Transfer (TICT) states. The temperature-dependent study in ethyl acetate has shown an increase in emission intensity with temperature accompanied by a blue shift of emission spectrum in CBZ-BDP. In contrast, CBZ-bisBDP displayed a decrease in intensity along with blue shift. Besides, CBZ-bisBDP showed an additional LE emission whose emission intensity gets enhanced with increasing temperature. The Critical Micelle Concentration (CMC) of sodium deoxycholate (NaDC) bile salt in aqueous medium was determined by using CBZ-BDP as a fluorescent probe. Three independent parameters: absorbance, fluorescence intensity and anisotropy of the molecule were employed to determine the CMC value. Cell imaging studies using confocal fluorescence microscopy showed that, unlike the mono-BODIPY, CBZ-bisBDP could penetrate the cells and reveal the cytoplasmic distribution in Hela cells. The IC50 values obtained via MTT assay indicate that the cytotoxicity against cancer cells is significant in CBZ-bisBDP compared to the mono-BODIPY.

Tuning the photophysical properties ofBODIPYdyes used inDSSCsas predicted by double‐hybridTD‐DFT: The role of the methyl substituents

AbstractA series of 16 BODIPY dye for DSSC applications are designed with the aim of obtaining a controlled red‐shift of their absorption band maxima. The design is based on changing the number and position of the substituted methyls at the BODIPY moiety. The excited‐state properties of the proposed molecular dyes were predicted with the TD‐B2PLYP/def2‐TZVP level. In going from the fully methyl substituted dye (D1357) to the unsubstituted one (D0) where all the methyls are replaced by hydrogens, a gradual red‐shift of the lowest and most intense electronic excitation was observed (reaching a max. of 0.8 eV ≈ 220 nm) which resulted from lower HOMO–LUMO gaps and higher conjugation. The tuning function of the methyls on the electronic spectra and other relevant properties of these chemical moieties is carefully analyzed. Replacing the methyls with hydrogens was also found to induce more significant charge‐transfer character, as indicated by natural transition orbital (NTO) and electronic structure analysis, enhanced excited‐state life‐times, and electron transport abilities, while slightly reduce the calculated light harvesting efficiency and the free‐energy of electron injection ΔGinj.

Bis-BODIPY-based fluoride and cyanide sensor mediated by unconventional deprotonation of C−H proton

A novel bis-BODIPY-based colorimetric and fluorescent sensor (BODIPY-NN) for F− and CN− recognition with high selectivity and high sensitivity is reported. The designed sensor, BODIPY-NN, was synthesized by a one-step click reaction of azido-BODIPY with N,N′-dipropargylbenzene-1,2-diamine. The BODIPY-NN sensor displays a marked color change from pink to colorless and a remarkable turn-off fluorescence behavior exclusively toward F− and CN− ions. Analysis of 1H, 13C, 19F, 11B NMR and mass spectra, together with theoretical calculations, provides insight into the mechanism of anion binding to BODIPY-NN. The sensing mechanism was found to be unconventional deprotonation at pseudo-benzylic carbons attached to BODIPY cores in the presence of F− and CN− ions, to form the less highly conjugated BODIPY moieties, thereby displaying fluorescence quenching. Addition of water in the BODIPY-NN + F− system regenerates the sensor with restoration of its spectroscopic properties. In contrast, the CN− ions permanently disrupt the BODIPY moieties by nucleophilic displacement at the central boron atoms, which is irreversible upon addition of water. The detection limits for F− and CN− in THF are 83 and 72 nM, respectively. In particular, BODIPY-NN embedded in cetyltrimethylammonium micelles can be used as colorimetric detection of CN− ions in aqueous media.

Synthesis, spectroscopic characterization, one and two-photon absorption properties of β-β linked BODIPY dimers

Five β-β linked BODIPY dimers (d1-d5) with different electron-donating/withdrawing groups at the meso-position were synthesized through improved synthetic methods. All compounds were characterized by 1H and 13C NMR and HRMS. The single crystal X-ray analyses indicate that d4 and d5 display a linear coplanar conformation with two linked BODIPY moiety. Their photophysical and electrochemical properties have been investigated by UV–vis absorption spectroscopy, steady-state and time-resolved fluorescence spectroscopy, two-photon excited spectroscopy and cyclic voltammetry. The β-β linked BODIPY dimers exhibit a prominent red shift from the visible region to the red/near-infrared region of their absorption and emission spectra, large Stokes shifts and moderate two-photon absorption cross section σ2 with different groups at the meso-position.

Selective population of tripletexcited states in heavy-atom-free BODIPY-C60based molecular assemblies.

Photophysical studies on a BODIPY-fullerene-distyryl BODIPY triad (BDP-C60-DSBDP) and its reference dyads (BODIPY-fullerene; BDP-C60 and distyryl BODIPY-fullerene; DSBDP-C60) are presented herein. In the triad, the association of the two chromophore units linked by a fullerene moiety leads to strong near UV-Visible light absorption from 300 to 700nm. The triplet-excited state was observed upon visible excitation in all these assemblies, and shown to be localized on the C60 or BODIPY moieties. Using quantitative nanosecond transient absorption, we provide a complete investigation on the lifetime and formation quantum yield of the triplet-excited state. In the BDP-C60 dyad, the tripletexcited state of C60 (τ = 7 ± 1μs) was obtained with a quantum yield of 40 ± 8%. For the DSBDP-C60 dyad and BDP-C60-DSBDP triad, a longer-lived tripletexcited state with a lifetime of around 250 ± 20μs centered on the DSBDP moiety was formed, with respective quantum yields of 37 ± 8 and 20 ± 4%. Triplet-triplet annihilation up-conversion is characterized in the BDP-C60 dyad and the bichromophoric triad in the presence of perylene and DSBDP-monomer as respective annihilators. The photo-induced formation of a long-lived 3DSBDP* in the triad coupled with panchromatic light absorption offers potential applications as a heavy-atom-free organic triplet photosensitizer.

Synthesis and Characterization of Far-Red Emissive Boron-Based Triads Showing Large Stokes Shifts: Optical, TRANES, and Electrochemical Studies.

Herein, we report the design and synthesis of far-red emissive boryl-thiophene-BODIPY triads 1-3. The π-conjugation length and electronic communication between borane and BODIPY moieties are tuned by judiciously varying the size of the oligothiophene spacer in these triads (1, terthiophene; 2, quarterthiophene; and 3, pentathiophene). Conjugates 1-3 showed intriguing triple emissions in the blue to far-red regions. Detailed optical, time-resolved decay kinetics, time-resolved area-normalized emission spectra (TRANES), fluoride binding, and computational studies suggest that the multiple emissions in these triads are due to an inefficient transfer of energy from the boryl-oligothiophene to the BODIPY unit. In addition, all of the conjugates showed a ratiometric fluorescence response to fluoride ions.