Boron Dipyrrin Research Articles

Excited state energy transfer from terminal β-diketonate ligands to a central boron dipyrrin (Bodipy), mediated by lanthanide (III) metals

A new boron-dipyrromethene (Bodipy) dye with phenanthro-fused groups at the β-pyrrole positions is described. The π-extended pyrrole units result in intense red-shifted absorption and emission in the visible region of the spectrum. The phenathroline groups are incorporated to allow for coordination of Ln(III) β-diketonates giving the first examples of bis-Ln(III)-Bodipy complexes (where Ln = Eu and Tb). Electronic spectroscopy of the disubstituted Ln(III)-Bodipy complexes reveal β-diketonate charge transfer in the ultraviolet region of the spectrum and π π * transitions associated with the Bodipy core. Upon excitation of the terminal antenna β-diketonate ligands, within the ultraviolet region, emission of the Bodipy core is observed with no evidence of Ln(III) emission; suggesting energy transfer from the antenna ligands to the lanthanide ion to the Bodipy core (An → Ln(III) → Bodipy).

Influence of structure and solvatation on photophysical characteristics of meso-substituted boron dipyrrins in solution and bulk hybrid materials

Here we report recent studies of pH and polarity fluorescent molecular sensorics involving range of 4-bora-3a,4a-diaza-s-indacene (BODIPY) derivatives. Photophysical characteristics of the dyes were investigated in liquid solutions and in bulk materials, doped to sol-gel silicon dioxide (pure and with surface modifiers), polymethylmethacrylate (PMMA), polysulfone (PSU) and polyvinyl chloride (PVC) matrices. Investigated compounds were shown to be effective fluorescent probes for precise evaluation of H+ concentration in a broad range of input values (pH 2–12). Factors affecting accuracy of the measurements in solvents and matrices of a different nature are discussed. Finally, Catalan linear regression is introduced as a potential approach for discrimination of solvent polarity effects from acidity.

Synthesis and Spectral Characteristics of BODIPY Dyes with Two or Three Dipyrrin Domains.

Several boron-dipyrrin (BODIPY) based fluorophores with two and three dipyrrin cores were synthesized and investigated in solvents under the concentration variation. Comparative analysis of spectral and photophysical changes under increasing the number of the cores in the dye molecule was made. Mutual influence of dipyrrin cores was detected leading to the increasing of the compounds rigidity and, thus, the absence of fluorescent molecular rotor effects under the viscosity variation. Aggregation induced quenching, which was observed for many mono-domain BODIPY dyes is reduced in case of investigated poly-domain compounds.

Synthesis and Unique Optical Properties of Selenophenyl BODIPYs and Their Linear Oligomers.

A series of selenophene-substituted boron-dipyrrin (BODIPY) monomers and selenophene-linked BODIPY oligomers was synthesized. The synthesized BODIPYs show good absorption/emission properties in the red to near-infrared region. Furthermore, some of the selenophenyl BODIPYs are not only useful fluorophores but also good photosensitizers to produce singlet oxygen.

Mono and di-substituted BODIPY with electron donating carbazole, thiophene, and 3,4-ethylenedioxythiophene units

In an effort to extend the conjugation system of boron-dipyrrin (BODIPY), the dye was coupled with polymerisable units of carbazole, alkylthiophene, and 3,4-ethylenedioxythiophene (EDOT). Due to electron donating character of the units connected to the strong electron accepting segment of tri-coordinated boron, the optical and electrochemical properties of the dye changed, and followed the strength of the electron donating substituent. All studied compounds exhibited electroactivity in both anodic and cathodic potential ranges, however, electropolymerisation was only observed for BODIPY modified with EDOT, leading to trimeric and tetrameric substituents. Potential controlled optical changes (spectroelectrochemistry) and in situ spin density distribution measurements, supported by quantum chemical calculations using density functional theory, were undertaken in order to understand the reversibility of the electrochemical processes. Hyperfine split ESR spectra of the radical anion species were successfully modelled revealing intriguing, hyperconjugation type unpaired spin delocalisation patterns.

Switch‐ON Near IR Fluorescent Dye Upon Protonation: Helically Twisted Bis(Boron Difluoride) Complex of π‐Extended Corrorin

A novel helically twisted π-extended corrorin derivative having two boron dipyrrin (BODIPY) moieties at the periphery, a BODIPY DYEmer (6-BF2 ) cross-bridged with π-conjugated dipyrrinylidene unit, was synthesized and characterized. The neutral 6-BF2 is nonfluorescent due to the internal photoinduced charge transfer (CT) character in the excited state as inferred from the femtosecond transient absorption spectroscopy. However, upon protonation, the CT process is suppressed and the species H6-BF2+ becomes near infrared (IR) emissive. With the aid of rigid helical conformations in 6-BF2 , the helical isomers (P- and M-forms) were resolved and their chiroptical property was investigated. The distinct circular dichroism (CD) spectral changes of the enantiomers were observed in the presence of acids, which demonstrates that 6-BF2 can be utilized for potential acid-responsive chiroptical materials.

Spectral Properties and Possibilities of meso-Substituted BODIPY Usage in Sol-Gel Process and Materials.

Hybrid materials based on organically modified silica with immobilized boron-dipyrrins (BODIPY) dyes were obtained. Spectral characteristics of the dyes were measured during the matrix formation and in obtained materials. It was stated, that immobilization does not affect the character of the absorption and fluorescence spectra of the dye, but due to the effect of fluorescent molecular rotor observed for meso-substituted BODIPY, the fluorescent quantum yields were found to increase during the matrix sealing. Quantum yield increase is linear for all of the investigated matrices except phenyl-substituted one, where the π-π interactions of the dye molecule with matrix could be observed. This effect could be used for fine control of the matrix formation process and leads to increase of the dye emission in the final material for further practical applications. All obtained hybrid materials were found to be stable upon UV light irradiation, hence immobilization enhance the stability of the dye in comparison with the BODIPY in organic solvents.

Design and Evaluation of a Boron Dipyrrin Electrophore for Redox Flow Batteries.

A boron dipyrrin (BODIPY) dye was designed as a molecular single-component electrophore for redox flow batteries. All positions of the BODIPY core were assessed on the basis of literature data, in particular cyclic voltammetry and density functional calculations, and a minimum required substitution pattern was designed to provide solubility, aggregation, radical cation and anion stabilities, a large potential window, and synthetic accessibility. In-depth electrochemical and physical studies of this electrophore revealed suitable cathodic behavior and stability of the radical anion but rapid anodic decomposition of the radical cation. The three products that formed under the conditions of controlled oxidative electrolysis were isolated, and their structures were determined by spectroscopy and comparison with a synthetic model compound. From these structures, a benzylic radical reactivity, initiated by one-electron oxidation, was concluded to play the major role in this unexpected decomposition.

BODIPY dyes in bio environment: Spectral characteristics and possibilities for practical application

Abstract Boron dipyrrin (BODIPY) dyes serve as perspective fluorescent sensors and probes in a vast range of biochemical and medical applications. Thus, mechanisms of interaction with biomolecules and accompanying spectral behavior of BODIPY are of major interest for fundamental science and practical applications. 8-aryl BODIPY derivatives were found to have high fluorescent respond upon the protein addition. Investigation of the interaction between the series of BODIPY complexes and Bovine Serum Albumin (BSA) using ultraviolet-visible (UV-vis) absorption, fluorescence spectroscopy under simulated physiological conditions (pH 7.4) and molecular docking methods was performed. The results of fluorescence spectroscopy indicated that the fluorescence of hydrophobic BODIPY dyes substantially increases in the presence of BSA. The prospected reason is binding of the dye to the BSA hydrophobic cavities in the subdomain IIA. Aromatic moiety size increase causes shifting of the interaction driving force from mostly non-specific to the π-stacking. Among all probes, the 8-phenyl substituted dye showed the highest sensitivity and the quantitative fluorescent response for BSA in aqueous solution. BODIPY with 8-phenyl substituent or analogs therefore could be used as protein surface polarity sensors, at the same time all of the investigated dyes with bulky aromatic groups could be used as hydrophobic molecule tags and markers for bioimaging tasks.

Recent Advances of Individual BODIPY and BODIPY-Based Functional Materials in Medical Diagnostics and Treatment.

The group of fluorophores on boron dipyrrin platform (4,4- difluoro-4-bora3a,4a-diaza-s-indacene, also known as BODIPY) has attracted much attention in the field of molecular sensorics, including sensing of biomolecules and bioprocesses. Structural diversity of existing BODIPY with ample opportunities of directed modification of compounds makes this class of fluorophores attractive for medical and biological purposes. The recent progress in the design and functionalization of BODIPY allows using them for modification of drug micro- and nanocarriers in order to improve their therapeutic effect in cancer treatment. At the same time, integration of BODIPY into drug carriers provides the possibility of in vitro and in vivo real time imaging of used drug carriers. The high fluorescent intensity and low toxicity of BODIPY granted for conjugation with different biomolecules. The present review focuses on the recent advances for application of individual BODIPY in medical diagnostics, antimicrobial activity, as well as establishing the role of BODIPY in labeling of biomolecules (e.g. proteins, hormones and DNA). Also the review highlights the potential of BODIPY in functionalization of drug micro- and nanocarriers in order to achieve better therapeutic efficiency compared with non-modified materials. The advantages derived from the use of BODIPY for preparation and modification of drug carriers are critically evaluated and potential for future challenges, especially concerning the design of innovative multi-functional BODIPY-based nanocarriers, is discussed in detail using representative examples from literature. Our objective was to show that BODIPY are powerful tools for bioimaging, labeling of biomolecules and construction of new multifunctional drug carriers.

Novel Alkoxy-Substituted Dipyrrins and Near-IR BODIPY Dyes-Preparation and Photophysical Properties.

Starting from 3-alkoxy-2-aryl-substituted pyrroles and aromatic aldehydes, a collection of new dipyrrins was prepared. Under the standard conditions of Treibs, these were converted into the corresponding boron dipyrrins (BODIPYs). Compounds of this type with alkoxy groups at C-3 position of both pyrrole subunits are new and hence the photophysical properties of this collection of novel dipyrrins and BODIPY dyes were investigated. The dipyrrins show absorption maxima up to 596 nm and emissions of up to 677 nm. For the BODIPY series a remarkable effect of the alkoxy groups was identified, resulting in red shifts for absorptions and emissions. The compound substituted with two 2-thien-2-yl groups and a meso-C6 F5 substituent shows an absorption maximum at 725 nm and emits at 754 nm and thus is a new representative of a near-IR BODIPY dye related to certain aza-BODIPYs. Our results demonstrate the influence of the alkoxy groups on the spectroscopic data and reveal the potential of 3-alkoxy-2-aryl-substituted pyrroles for the design of new fluorophores.

Tripping the Light Fantastic: Organoboron Compounds

Small molecules containing boron can play all sorts of roles in chemistry, biology and materials science. Molecular boron compounds display a wide range of unusual and fascinating structures, and their chemical reactivity can be very different from that of boron's next-door neighbour carbon. Some of the reasons for this will be considered and illustrated through applications in energy, medicine and new materials. The boron dipyrrins, also known as BODIPYs, are a prime example. They are strongly fluorescent when excited by illumination and are widely used as fluorescent tags in biology and as biosensors. More recently, they have been studied for their energy transfer properties in light-harvesting applications.

Sequential Nucleophilic Substitution of the α‐Pyrrole and p‐Aryl Positions of meso‐Pentafluorophenyl‐Substituted BODIPYs

Boron–dipyrrins (BODIPYs) have found widespread application in bioimaging and materials science. These applications require the tuning of the chemical and photophysical properties of the fluorophore through the introduction of functional groups at the BODIPY core. In this context, an approach to difunctionalized BODIPYs was explored. Oxidative nucleophilic substitution of hydrogen (ONSH) in the 3‐(α‐)position of the BODIPYs was combined with nucleophilic substitution (SNAr) at the aryl unit of pentafluorophenyl‐substituted BODIPYs and their dipyrrane precursors. In an alternative approach, α‐alkoxy‐substituted BODIPYs were prepared starting from the corresponding dipyrrin. In this case, the α‐methoxy group of the BODIPY was susceptible to a hitherto unreported methoxy/amino exchange. The compounds were investigated with respect to their optical spectroscopic properties, revealing the influence of the different substitution patterns on their absorption and emission spectra.

Vibrational Optical Activity of BODIPY Dimers: The Role of Magnetic-Electric Coupling in Vibrational Excitons.

The vibrational exciton (VE) interpretation of intense bisignated couplets in vibrational circular dichroism (VCD) spectra of a pair of atropisomeric BODIPY (boron dipyrrin) dimers is discussed. The role of intrinsic magnetic moments is crucial to reproduce the different behaviors of quasi-isomeric BODIPY dimers with different aryl junction.

One‐Pot Preparation of Non‐Symmetric meso‐Aryl‐BODIPYs: Functional Derivatives with Unusual Reactivity

The formation of meso‐aryl‐BODIPYs (boron dipyrrins) through the acidic condensation of 3,4‐dialkylpyrroles with aromatic aldehydes, followed by 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) oxidation and BF2 complexation, has been reviewed. Surprisingly, it was found that the major products from these reactions were not the anticipated symmetric BODIPYs, but non‐symmetric derivatives carrying one benzyl substituent at the BODIPY α position. The best yields and simple purification conditions were be achieved if the oxidant was not employed in the one‐pot reaction sequence. Electron‐rich benzaldehydes provided the best results, whereas precursors with electron‐withdrawing substituents gave significant amounts of the symmetric BODIPYs as side‐products. This unexpected result can be rationalized mechanistically on the basis of two reaction pathways that diverge from a common intermediate at an early step in the condensation sequence. Preliminary reactivity investigations showed chlorination to give unexpected results, but a typical substitution and coupling chemistry.

Metal-Free and Versatile Synthetic Routes to Natural and Synthetic Prodiginines from Boron Dipyrrin.

Prodiginines, as a family of bacterial alkaloids, possess a number of interesting biological activities. New, concise synthetic routes for the facile preparation of both synthetic and natural prodiginines in good yields have been developed, which use BODIPY functionalization reactions, such as condensation, nucleophilic substitution, and BF2 deprotection. This new metal-free synthetic method opens the door toward a wide variety of C-ring functionalized prodiginines, including those that are not possible to obtain through current synthetic methods, for their advanced biological activities.

Fluorescent Properties of BODIPY Sensors Based on Photoinduced Electron Transfer.

Two boron-dipyrrin (BODIPY) based dyes with dimethylaminophenyl and carboxyphenyl substituents in 8-position of dipyrrin ligand have been synthesized and characterized. Photophysical and spectral properties of the obtained compounds have been investigated in water-ethanol mixture and water-cyclohexane system with variation of pH values. The equilibria constants of the compounds were identified by classical methods of acid-base titration. BODIPY bearing dimethylaminophenyl and carboxyphenyl subunits show deprotonation/protonation dependent fluorescence off/on-switching. The change of the emission could be mechanistically explained by a PET (photoinduced electron transfer) from the 8-substituent to the fluorophore. The present study demonstrates that BODIPY-based fluorescent sensors can be used to measure the pH in the range of 2-13 extending the scope of BODIPY dyes available as pH-indicators. Investigated compounds demonstrate weak dye-dye interaction allowing their cooperative usage as indicators.

Color-Tunable Resonant Photoluminescence and Cavity-Mediated Multistep Energy Transfer Cascade.

Color-tunable resonant photoluminescence (PL) was attained from polystyrene microspheres doped with a single polymorphic fluorescent dye, boron-dipyrrin (BODIPY) 1. The color of the resonant PL depends on the assembling morphology of 1 in the microspheres, which can be selectively controlled from green to red by the initial concentration of 1 in the preparation process of the microspheres. Studies on intersphere PL propagation with multicoupled microspheres, prepared by micromanipulation technique, revealed that multistep photon transfer takes place through the microspheres, accompanying energy transfer cascade with stepwise PL color change. The intersphere energy transfer cascade is direction selective, where energy donor-to-acceptor down conversion direction is only allowed. Such cavity-mediated long-distance and multistep energy transfer will be advantageous for polymer photonics device application.

Unidirectional Threading into a Bowl‐Shaped Macrocyclic Trimer of Boron–Dipyrrin Complexes through Multipoint Recognition

AbstractBowl‐shaped macrocycles have the distinctive feature that their two sides are differentiated, and thus can be developed into elaborate hosts that fix a target molecule in a controlled geometry through multipoint interactions. We now report the synthesis of a bowl‐shaped macrocyclic trimer of the boron–dipyrrin (BODIPY) complex and its unidirectional threading of guest molecules. Six polarized Bδ+−Fδ‐ bonds are directed towards the center of the macrocycle, which enables strong recognition of cationic guests. Specifically, the benzylbutylammonium ion is bound in a manner in which the benzyl group is located at the convex face of the bowl and the butyl group at its concave face. Furthermore, adrenaline was strongly captured on the convex side of the bowl by hydrogen bonding, Coulomb forces, and C−H⋅⋅⋅π interactions.

Unidirectional Threading into a Bowl‐Shaped Macrocyclic Trimer of Boron–Dipyrrin Complexes through Multipoint Recognition

Bowl-shaped macrocycles have the distinctive feature that their two sides are differentiated, and thus can be developed into elaborate hosts that fix a target molecule in a controlled geometry through multipoint interactions. We now report the synthesis of a bowl-shaped macrocyclic trimer of the boron-dipyrrin (BODIPY) complex and its unidirectional threading of guest molecules. Six polarized B(δ+) -F(δ-) bonds are directed towards the center of the macrocycle, which enables strong recognition of cationic guests. Specifically, the benzylbutylammonium ion is bound in a manner in which the benzyl group is located at the convex face of the bowl and the butyl group at its concave face. Furthermore, adrenaline was strongly captured on the convex side of the bowl by hydrogen bonding, Coulomb forces, and C-H⋅⋅⋅π interactions.