BODIPY Dimers Research Articles

A Diradical Approach towards BODIPY-Based Dyes with Intense Near-Infrared Absorption around λ=1100 nm.

A diradical approach to obtain stable organic dyes with intense absorption around λ=1100 nm is reported. The para- and meta-quinodimethane-bridged BODIPY dimers BD-1 and BD-2 were synthesized and were found to have a small amount of diradical character. These molecules exhibited very intense absorption at λ=1088 nm (ɛ=6.65×10(5) M(-1) cm(-1) ) and 1136 nm (ɛ=6.44×10(5) M(-1) cm(-1) ), respectively, together with large two-photon-absorption cross-sections. Structural isomerization induced little variation in their diradical character but distinctive differences in their physical properties. Moreover, the compounds showed a selective fluorescence turn-on response in the presence of the hydroxyl radical but not with other reactive oxygen species.

Synthesis and photophysical properties of meso-aryloxy linked BODIPY monomers, dimers, and trimer

A series of meso-aryloxy linked BODIPY monomers, dimers and trimer were synthesized by nucleophilic aromatic substitution (SNAr) reaction from phenols with meso-chloro BODIPY and their photophysical properties were systematically studied by UV-vis and fluorescence spectroscopy. The relationship between their photophysical properties and the spatial arrangement of meso-aryloxy linked BODIPYs has been discussed. The monomers exhibited different extent solvent-dependent fluorescence, and fluorescence quenching in polar solvents were found relative to the HOMO energies of the donor (meso-phenols), indicating possible PET effect from meso-phenols to the BODIPY fluorophore. Ortho-dimer showed unusual broad red-shifted emission bands centered at 550 nm with a larger Stokes shifts at the range of 2900–3400 cm[Formula: see text], and low fluorescence quantum yields, which was in sharp contrast to those of other dimers and trimer, indicating of possible excimeric species formation due to slipped cofacial arrangement ofortho-dimer.

Conformation-Restricted Partially and Fully Fused BODIPY Dimers as Highly Stable Near-Infrared Fluorescent Dyes.

A set of highly stable conformation-restricted partially and fully fused BODIPY dimers (α,β-cyclohexadiene-fused and α,β-benzene-fused dimers) were synthesized from a one-pot condensation of 2-formylpyrroles with α,β-cyclohexadiene-fused bipyrrole 3. Effective expansion of π-conjugation over these fused BODIPY dimers was observed by X-ray analysis, density functional theory (DFT) calculations, and electrochemical and optical measurements, as demonstrated by their strong absorption and emissions in the near-infrared (NIR) range (650 to 820 nm).

Masking and demasking strategies for the BF2-BODIPYs as a tool for BODIPY fluorophores.

An efficient and chemoselective route for transforming BF2-BODIPYs to Et2B-BODIPYs (masking) was developed using Et2AlCl. The Et groups can be easily replaced with F atoms using BF3·Et2O in moist CH2Cl2 to regenerate the BF2-BODIPYs (demasking). The masking-demasking strategy is very useful for synthesizing functionalized BODIPYs via nucleophilic and reductive reactions. The masking strategy was used to synthesize a BODIPY dimer by McMurry coupling of a formyl Et2B-BODIPY, while a new BODIPY with an asymmetrically substituted B-center was synthesized using the demasking strategy.

Axially chiral BODIPY DYEmers: an apparent exception to the exciton chirality rule.

The exciton chirality method (ECM) is commonly recognized as one of the best approaches to assign the absolute configuration of biaryls. This paper reports the first exception to this method for a simple biaryl system. ECD and VCD measurements in combination with DFT (B3LYP/6-311G*), TDDFT (CAM-B3LYP/6-311G*), and Coupled-Cluster (RI-SCS-CC2) calculations were used to determine the absolute configurations of axially chiral BODIPY DYEmers. The ECM fails to predict the sign of the intense CD couplet at 500 nm of the 1,1'-coupled dimer. The odd behavior was rationalized by considering the strong transition magnetic dipole associated with the 500 nm transition, which leads to an unexpected dominance of the μm coupling at the expense of the μμ one in these compounds. This is the first case in which a strong μm coupling hampers the use of the ECM, but this behavior should not be restricted to the BODIPY chromophore.

Meso-Aryloxy and meso-arylaza linked BODIPY dimers: synthesis, structures and properties

meso-Aryloxy and meso-arylaza linked BODIPY dimers have been designed and synthesized by the nucleophilic aromatic substitution (SNAr) type reactions of phenylenediamines (a, b, c) and phenylenediols (d, e, f) with 8-chloro BODIPY. The photophysical and electrochemical properties of the BODIPY dimers were found to be dependent on the nature of the heteroatom at the meso position on the BODIPY ligand and the substitution pattern of the BODIPYs on the phenyl ring (i.e. ortho, meta and para). The experimental observations were supported by theoretical calculations. The single crystal X-ray structures of 1, 2b, 2c and 3e are reported. The packing diagram of 1 reveals a herringbone like structural arrangement, whereas 2b, 2c and 3e show complex 3D structural motifs.

Synthesis of diazo-bridged BODIPY dimer and tetramer by oxidative coupling of β-amino-substituted BODIPYs.

A diazo-bridged BODIPY dimer and tetramer were prepared by the oxidative coupling reaction of β-amino-substituted BODIPYs. The structure of the dimer was elucidated by X-ray diffraction analysis, showing its coplanar orientation of two BODIPY units. Effective extension of π-conjugation was confirmed by optical and electrochemical investigations.

Atropisomeric Dyes: Axial Chirality in Orthogonal BODIPY Oligomers

A dissymmetrically substituted orthogonal BODIPY dimer and an orthogonal BODIPY trimer exist as two stable conformers, which are in fact atropisomeric enantiomers. The racemic mixture can be separated by HPLC using a chiral stationary phase. These enantiomeric derivatives hold great potential as chiral agents in asymmetric synthesis, fluorogenic/chromogenic sensing, and biological applications.

Unadulterated BODIPY-dimer nanoparticles with high stability and good biocompatibility for cellular imaging.

Purely organic nanoparticles based on a BODIPY dimer, BDY-NPs, have been prepared for the first time using a nanoprecipitation procedure. The fluorescent nanoparticles have high physical homogeneity, good stability in water, and low cytotoxicity, which are suitable for cell imaging.

Oxidation of 2-amino-substituted BODIPYs providing pyrazine-fused BODIPY trimers

Oxidation of 2-amino-substituted BODIPYs afforded BODIPY trimers in a one-step operation. The trimer consists of a pyrazine-fused BODIPY dimer to which one BODIPY unit is connected through an NH linkage. Effective expansion of π-conjugation over the fused dimer was observed in optical and electrochemical measurements.

Photosensitizer That Selectively Generates Singlet Oxygen in Nonpolar Environments: Photophysical Mechanism and Efficiency for a Covalent BODIPY Dimer

Photosensitizers that selectively generate singlet oxygen in non polar/polar microenvironments are highly desirable for photodynamic therapy of tumor but not yet reported. BODIPY (boron-dipyrromethene complexes) covalent dimer 1 is such a photosensitizer that forms singlet oxygen only in hexane, cyclohexane, and toluene significantly but not in polar solvents. Its corresponding monomer is not photoactive in any solvents for forming singlet oxygen. To reveal the mechanism, we measured the excited triplet-, singlet-, and ground-state properties as well as singlet oxygen generation capability with laser flash photolysis, fluorescence spectroscopy, time-correlated single photon counting, and absorption spectroscopy in various solvents. The striking difference is due to the fact that the excited dimer (excimer) undergoes very fast intramolecular charge transfer (ICT) that makes intersystem crossing noncompetitive in polar solvents, while ICT is negligible in nonpolar solvents.

Sulfur‐Bridged BODIPY DYEmers

Reactions of BODIPY monomers with sulfur nucleophiles and electrophiles result in the formation of new BODIPY dimers. Mono- and disulfur bridges are established, and the new dyestuff molecules were studied with respect to their structural, optical, and electrochemical properties. X-ray diffraction analyses reveal individual angulated orientations of the BODIPY subunits in all cases. DFT calculations provide solution conformers of the DYEmers which deviate in a specific manner from the crystallographic results. Clear exciton-like splittings are observed in the absorption spectra, with maxima at up to 628 nm, in combination with the expected weak fluorescence in polar solvents. A strong communication between the BODIPY subunits was detected by cyclic voltammetry, where two separated one-electron oxidation and reduction waves with peak-to-peak potential differences of 120-400 mV are observed. The qualitative applicability of the exciton model by Kasha for the interpretation of the absorption spectral shape with respect to the conformational state, subunit orientation and distance, and conjugation through the different sulfur bridges, is discussed in detail for the new BODIPY derivatives. This work is part of our concept of DYEmers, where the covalent oligomerisation of BODIPY-type dye molecules with close distances is leading to new functional dyes with predictable properties.

Meso‐Alkynyl BODIPYs: Structure, Photoproperties, π‐Extension, and Manipulation of Frontier Orbitals

Bodipy building: meso-Alkynyl BODIPY monomers and dimers were synthesized and their crystal structures, photochemical properties, and electronic structures disclosed. The meso-arylethynyl group is coplanar with the BODIPY core. The resulting efficient π-conjugation red-shifts the intense absorption and bright fluorescence by about 40–70 nm. Cyclic voltammetry and DFT calculations revealed that the LUMO level is stabilized by meso-alkynylation, while the HOMO level remains constant.

Benzene-fused BODIPY and fully-fused BODIPY dimer: impacts of the ring-fusing at the b bond in the BODIPY skeleton

4,4-Difluoro-4-bora-3a,4a-diaza-s-indacenes (BODIPYs) are fascinating dyes with great potentials for various applications. To establish the design principle for the modification of the BODIPY skeleton, we now investigate the electronic impacts of the introduction of ring-fused structures. The DFT calculations revealed that while the benzene-fusing at the a bond in the BODIPY skeleton increases the HOMO level, the benzene-fusing at the b bond leads to a decreased LUMO level. Based on these results, a benzo[b]-fused BODIPY 1 and a fully-fused BODIPY dimer 2 were synthesized. X-ray crystal structure analysis demonstrated that the benzo[b]-fused structure significantly perturbs the π-conjugation with enhancement of an electron-accepting azafulvene character. In the ring-fused BODIPY dimer 2, the central benzene ring is largely deviated from the aromatic benzene geometry. As a consequence, 2 has a significantly low-lying LUMO delocalized along the periphery. In cyclic voltammograms, the benzene-fused BODIPY 1 and fully-fused dimer 2 indeed showed reversible reduction waves at much less negative potentials (E1/2 = −1.05 V vs. Fc/Fc+ for 1, −0.85 V for 2), relative to a non-fused BODIPY 3 (E1/2 = −1.40 V). In addition, the benzene-fused BODIPYs showed broad and intense absorption bands in the Vis-NIR region. In particular, the BODIPY dimer 2 showed an intense absorption at 629 nm with a broad shoulder band reaching 900 nm. Corresponding to the red-shifted absorption, compounds 1 and 2 showed weak fluorescence in the deep red region (λem = 690 nm, ΦF < 0.01) and in the near-infrared region (940 nm, ΦF < 0.01), respectively.

Hetero Bodipy-dimers as heavy atom-free triplet photosensitizers showing a long-lived triplet excited state for triplet–triplet annihilation upconversion

Bodipy dimers in which the two different sub-units take an orthogonal orientation were prepared, which show strong absorption of visible light, long-lived triplet excited states (140.9 μs) and high singlet oxygen ((1)O2) quantum yields (64%). The dimers were used for triplet-triplet annihilation upconversion (quantum yield is up to 3.7%).

Low PIP2 Molar Fractions Induce Nanometer Size Clustering in Giant Unilamellar Vesicles Containing POPC

Phosphatidylinositol (4,5) bisphosphate (PIP2) is a key lipid signaling molecule found on the inner leaflet of the cell membrane. Polyphosphoinositides signaling play an important role in regulation of many cell processes such as cell survival, proliferation, migration, and apoptosis. Phosphoinositides regulate signal transduction by providing binding or docking sites for intracellular proteins. In order to perform these functions, it has been suggested that PIP2 must be able to form localized clusters within the cell membrane. In this study, single point fluorescence correlation spectroscopy and brightness analysis of various BODIPY-labeled PIP2 was utilized to detect the presence of clusters in the membrane of giant unilamellar vesicles (GUVs) consisting of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC). The number of freely diffusing fluorescent BODIPY molecules in the membrane was calculated and we found that in GUVs containing various amounts of labeled PIP2 had significantly lower number of fluorescent molecules than in GUVs made with the control BODIPY labeled hexadecyl phosphatidylcholine (BODIPY-HPC). Also, an increase in brightness of the labeled PIP2 particles with increasing labeled PIP2 molar fraction was noted. These results show the existence of PIP2 enriched clusters in the liquid disordered phase of GUVs that are smaller than the resolution limit of the fluorescent microscope. Using LAURDAN generalized polarization function, we demonstrated that the formation of these clusters is not due to the presence of the BODIPY moiety on the lipids. In addition, we report for the first time the presence of a previously uncharacterized hypsochromic shift of the fluorescence for the BODIPY labeled lipids that we attributed to BODIPY dimers. Finally, by adding cholesterol to the GUVs, we showed that the BODIPY dimers tend to favor the liquid ordered phase.

Assembled structures of dipyrrins and their oligomers bridged by dioxy-boron moieties

A linear arrangement of BODIPY dimers and trimers was transformed into boron-bridged box, ladder and cage structures on treatment with spacer units possessing multiple diol moieties.

Revisiting the optical signatures of BODIPY with ab initio tools

BODIPY dyes constitute one of the most efficient class of fluorescent molecules, yet their absorption and emission signatures are hardly predictable with theoretical tools. Here, we use a robust Time-Dependent Density Functional Theory approach that simultaneously accounts for solvent and vibrational effects, in order to simulate the optical properties of a large panel of BODIPY derivatives. In particular, this contribution is focussed on the accurate determination of both the 0–0 energies and vibronic shapes, that allow meaningful comparisons between experimental measurements and theoretical simulations. It turns out that Truhlar's M06-2X functional is well suited for modelling the variations of the 0–0 energies induced by side groups, modifications of the skeleton, stiffening or extension of the π-path. Indeed, while the absolute mean deviation remains quite sizeable, the determination coefficient between experimental and theoretical energies is exceptionally large (R2 = 0.98), highlighting the robustness of the proposed approach. In addition, for most BODIPYs, theory is able to accurately reproduce vibrationally resolved bands. The developed protocol was successfully applied to provide insights for both pH and ion sensors. It also allowed the understanding of the optical behaviours of a series of BODIPY dimers and NIR dyes. This constitutes an unprecedented investigation of several BODIPY dyes both in terms of the number of treated molecules (more than sixty) and of the reliability of the predictions.

Synthesis and spectroscopic properties of bodipy dimers with effective solid-state emission

Boron-dipyrromethenes (BODIPYs) dimers with phenyl and bulky triphenylsilylphenyl substituents were synthesized through oxidative self-coupling of the 2-position with FeCl3. Spectroscopic properties of all the dyes in various solvents and on films have been investigated. In comparison with the corresponding monomers, the dimers exhibit higher molar absorption coefficients, relative moderate fluorescent quantum yields and redshifted wavelengths. The luminescence yields of the dimers are solvent polarity dependent and decrease dramatically in acetonitrile. More intensive solid-state emission of triphenylsilylphenyl substituted BODIPY dimer is observed with a quantum yield of 9.7% relative to the phenyl substituted dimer, which could be attributed to the introduction of the bulky group that inhibits aggregation.

π-Fused bis-BODIPY as a candidate for NIR dyes

Benzene-fused bis-(borondipyrromethene)s (bis-BODIPYs) were synthesized by retro-Diels-Alder reaction of the corresponding bicyclo[2.2.2]octadiene-fused (BCOD-fused) bis-BODIPYs, which were, in turn, prepared from 4,8-ethano-4,8-dihydropyrrolo[3,4-f]isoindole derivatives. The π-fused bis-BODIPY chromophores were designed to show intensive absorption and strong fluorescence in the near-infrared region and not to have any strong absorption in the visible region. A 6,10-dibora-5a,6a,9a,10a-tetraaza-s-indaceno[2,3-b:6,5-b']difluorene derivative (syn-bis-benzoBODIPY) obtained by a thermal retro-Diels-Alder reaction of the corresponding BCOD-fused BODIPY dimer has strong absorption and emission bands at 775 and 781 nm, respectively. The absolute quantum yield is 0.36. The absorption is more than 5.0 times stronger than other absorptions observed in the visible region. In the case of 6,15-dibora-5a,6a,14a,15a-tetraaza-s-indaceno[2,3-b:6,7-b']difluorene derivatives (anti-bis-benzoBODIPY), the absorption and emission maxima exceed 840 nm.