BODIPY Unit Research Articles

Efficient synthesis of α/β-isomeric oxadiazolyl and triazolopyridyl BODIPYs for sensing of Hg2+ ions and pH sensors

A simple sequential one-pot protocol has been developed to prepare oxadiazolyl and triazolopyridyl-BODIPY derivatives 4–6 by employing iodine (III)-promoted oxidative cyclization of BODIPY hydrazide-hydrazones which are readily accessible from the reaction of formyl BODIPYs with arylhydrazides. Photophysical studies of the prepared compounds 4–6 showed a significant red shift in absorption and emission maxima when compared to that of the parent BODIPY. Presence of triazolopyridyl substituent in 6a has affected its binding ability with metal ions and has rendered unique photophysical response by 6a selectively in presence of Hg2+ ions. Compound 6a showed high affinity towards Hg2+ (Ka = 1.8 × 104 M−1) with 2.1 μM limit of detection. The binding stoichiometry between 6a and Hg2+ was determined to be 2:1 by Job's plot analysis. Under acidic conditions, compounds 4c, 5c, 6a and 6b bearing dimethylamino- and triazolopyridyl moieties at α/β-positions of BODIPY unit exhibit blue shifted absorption (10–15 nm) and emission spectra (7–34 nm). Photophysical response of the compounds 4c, 5c, 6a and 6b on changing pH was validated by DFT calculations.

Synthesis and studies of m/p-phenylene bridged bis(3-Pyrrolyl BODIPY)s

The first examples of m-/p-phenylene bridged bis(3-pyrrolyl BODIPY)s were synthesized by oxidizing the readily available m-/p-phenylene bridged bis(dipyrromethane) with DDQ in CH3CN followed by treatment with excess pyrrole and complexation with BF3⸱OEt2 in the presence of triethylamine. To the best of our knowledge, no straightforward synthetic method is available to prepare m-/p-phenylene bridged bis(3-pyrrolyl BODIPY)s. The bis(3-pyrrolyl BODIPY)s can be used as novel ligands for metal coordination chemistry by demasking BF2 units from bis(3-pyrrolyl BODIPY)s in the presence of Lewis acids. The bis(3-pyrrolyl BODIPY)s absorb at ∼585 nm with enhanced molar absorptivity compared to the monomer, 3-pyrrolyl BODIPY. The m-phenylene bridged bis(3-pyrrolyl BODIPY) emits strongly at ∼600 nm with a quantum yield of 0.34 whereas p-phenylene bridged bis(3-pyrrolyl BODIPY) emits relatively weakly in the same region with a quantum yield of 0.21. The electrochemical studies revealed that the two 3-pyrrolyl BODIPY units in bis(3-pyrrolyl BODIPY) dyads did not interact with each other. DFT/TD-DFT studies were used to understand the structure and electronic properties of bis(3-pyrrolyl BODIPY)s.

Engineering giant excitonic coupling in bioinspired, covalently bridged BODIPY dyads.

Strong excitonic coupling in photosynthetic systems is believed to enable efficient light absorption and quantitative charge separation, motivating the development of artificial multi-chromophore arrays with equally strong or even stronger excitonic coupling. However, large excitonic coupling strengths have typically been accompanied by fast non-radiative recombination, limiting the potential of the arrays for solar energy conversion as well as other applications such as fluorescent labeling. Here, we report giant excitonic coupling leading to broad optical absorption in bioinspired BODIPY dyads that have high photostability, excited-state lifetimes at the nanosecond scale, and fluorescence quantum yields of nearly 50%. Through the synthesis, spectroscopic characterization, and computational modeling of a series of dyads with different linking moieties, we show that the strongest coupling is obtained with diethynylmaleimide linkers, for which the coupling occurs through space between BODIPY units with small separations and slipped co-facial orientations. Other linkers allow for broad tuning of both the relative through-bond and through-space coupling contributions and the overall strength of interpigment coupling, with a tradeoff observed in general between the strength of the two coupling mechanisms. These findings open the door to the synthesis of molecular systems that function effectively as light-harvesting antennas and as electron donors or acceptors for solar energy conversion.

BODIPY-based near-infrared semiconducting polymer dot for selective yellow laser-excited cell imaging.

Semiconducting polymer dots (Pdots) with both narrow-band absorption and emission are desirable for multiplexed bioassay applications, but such Pdots with absorption peaks beyond 400 nm are difficult to achieve. Here we describe a donor-energy transfer unit-acceptor (D-ETU-A) design strategy to produce a BODIPY-based Pdot that exhibits simultaneously narrow absorption and emission bands. A green BODIPY (GBDP) unit was employed as the main building block of the polymer backbone, conferring a strong, narrow-band absorption around 551 nm. An NIR720 acceptor provides narrow-band NIR emission. The small Stokes shift of the GBDP donor allows introduction of a benzofurazan-based ETU, resulting in a ternary Pdot with a fluorescence quantum yield of 23.2%, the most efficient yellow-laser excitable Pdot. Due to the strong absorbance band centered at 551 nm and weak absorbance at 405 nm and 488 nm, the Pdot showed high single-particle brightness when excited by a 561 nm (yellow) laser, and selective yellow laser excitation when used to label MCF cells, with much greater brightness when excited at 561 nm than at 405 nm or 488 nm.

A white light emitting single halochromic hydrazine bridged bis(3-pyrrolyl BODIPY) fluorophore.

In search of white light emitting fluorophores, a hydrazine bridged Schiff base compound, bis(3-pyrrolyl BODIPY), was synthesized by condensing readily available α-formyl 3-pyrrolyl BODIPY with hydrazine hydrate in CH3OH under reflux for 5 h followed by recrystallization. Bis(3-pyrrolyl BODIPY) was thoroughly characterized by HR-MS, 1D and 2D NMR, and X-ray crystallography. The X-ray structure revealed that the 3-pyrrolyl BODIPY units in the dyad were arranged trans to each other with respect to the hydrazine moiety. Bis(3-pyrrolyl BODIPY) showed absorption bands in the region of 390-705 nm and exhibited multiple fluorescence bands in the region of 395-720 nm at different excitation wavelengths. The protonated derivative of bis(3-pyrrolyl BODIPY) generated by the addition of TFA to its CH2Cl2 solution showed significant changes in the optical properties and generated white fluorescence under UV light with specific emission bands observed in blue, green, and red regions, indicating that bis(3-pyrrolyl)BODIPY is a single white light emitting halochromic fluorophore under acidic conditions. DFT and TD-DFT studies justify the structural and electronic properties of the protonated derivative of bis(3-pyrrolyl BODIPY) exhibiting white light emission.

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.

Erlotinib-Modified BODIPY Photosensitizers for Targeted Photodynamic Therapy.

Photodynamic therapy (PDT) is an innovative, non-invasive and highly selective therapeutic modality for tumours and non-malignant diseases. BODIPY based molecules can function as new generation photosensitizers (PSs) in various PDT applications. Despite numerous conjugated PS systems are available, BODIPYs containing erlotinib lagged behind other photosensitizer units. In this study, smart photosensitizers containing BODIPY, erlotinib and hydrophilic units were prepared for the first time, their physicochemical properties and PDT effects were investigated. Compared with non-halogenated compound, halogenated derivatives possessed much lower fluorescence profile as well as the good ROS generation ability under red light. In vitro PDT studies were performed on both healthy (PNT1a) and prostate cancerous cells (PC3) to determine the selectivity of the compounds on cancerous cells and their effects under light. The halogenated conjugates, exposed to low dose of light illumination exhibited potent activity on cancer cell viability and the calculated IC50 values proved the high phototoxicity of the photosensitizers. It was also determined that the PSs have very low dark toxicity and that the light illumination and ROS formation are required for the initiation of the cell death mechanism. As a result, erlotinib modified BODIPYs could serve as promising agents in anticancer photodynamic therapy.

Confinement of the Triplet States in π-Conjugated BODIPY Dimers Linked with Ethynylene or Butadiynylene Bridges: A Different View on the Effect of Symmetry.

Understanding the impact of the excited state wavefunction confinement is crucial for the engineering of the photophysical properties and applications of organic chromophores. In the present contribution, the localization of the triplet state wavefunctions of some symmetric ethyne/butadiyne bridged BODIPY dimers and asymmetric BODIPY derivatives presenting extended π-conjugation frameworks is studied with time-resolved electron paramagnetic resonance spectroscopy and time-dependent density functional theory computations. Based on the Zero Field Splitting D parameters, we conclude that the triplet state wavefunctions are highly localized on one BODIPY unit in the symmetric dimers, which is consistent with the ab initio modelling that finds delocalized triplet state destabilized by 12-14 kcal mol-1 as compared to its localized counterpart. The result provides a new insight into the study of triplet excited state confinement and the design of molecular wires or photosensitizers for photovoltaics and photocatalysis.

Confinement of the Triplet States in π‐Conjugated BODIPY Dimers Linked with Ethynylene or Butadiynylene Bridges: A Different View on the Effect of Symmetry

AbstractUnderstanding the impact of the excited state wavefunction confinement is crucial for the engineering of the photophysical properties and applications of organic chromophores. In the present contribution, the localization of the triplet state wavefunctions of some symmetric ethyne/butadiyne bridged BODIPY dimers and asymmetric BODIPY derivatives presenting extended π‐conjugation frameworks is studied with time‐resolved electron paramagnetic resonance spectroscopy and time‐dependent density functional theory computations. Based on the Zero Field Splitting D parameters, we conclude that the triplet state wavefunctions are highly localized on one BODIPY unit in the symmetric dimers, which is consistent with the ab initio modelling that finds delocalized triplet state destabilized by 12–14 kcal mol−1 as compared to its localized counterpart. The result provides a new insight into the study of triplet excited state confinement and the design of molecular wires or photosensitizers for photovoltaics and photocatalysis.

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.

The control of chemical structures of dual-functioning photosensitizers as both therapeutic and imaging agents

A series of BODIPY dimer derivatives were selected to investigate their molecular geometric structures, the spectral properties, the molecular frontier orbitals, spin–orbit coupling (SOC) matrix between the first singlet excited state (S1 state) and the first triplet excited state (T1 state) and the decay rate constant of the S1 state. BOP-3-3-BOP showed long absorption and emission spectra, significant fluorescence quantum yields (Φf) and respectable singlet oxygen quantum yields (ΦΔ) in comparison with other BODIPY dimers BOP-2-8-BOP, BOP-8-8-BOP and BOP-2-2-BOP. The C–C bond between the two units of BOP-3-3-BOP decreased in length while the ground state (S0 state) moved to the first excited state (S1 state) by absorbing energy, which closes to conjugated double C = C bond and extends π-conjugation between the two BODIPY units. The more planar between the two BODIPY units in the first excited state facilitates emitting the red fluorescent of BOP-3-3-BOP. The smaller singlet–triplet adiabatic energy gap and larger SOC value promoted the intersystem crossing (ISC) process and produced singlet oxygen with high efficiency for BOP-3-3-BOP. Furthermore, BOP-3-3-BOP has significant kf (S1→S0) and respectable kisc (S1→T1), which is expected to be used as both therapeutic and imaging agent. Our results on effectively regulating photophysical properties, ISC rates and the molecular excited state radiation decay rates by tuning different linkage position between two BODIPY units will be useful for molecular design of BODIPY dimers for fluorescence imaging guided photodynamic therapy.

Investigation of spectroscopic properties of mono and Di-styryl indole-containing BODIPYs

In the current study, two novel mono- and distyryl BODIPYs have been successfully synthesized employing the Knoevenagel type condensation reaction between 1,3,5,7‑tetramethyl BODIPY and 2,3-diphenyl-4,6-dimethoxyindole-7-carbaldehyde. This CC bond extension approach leads to change in hybridization of methyl carbon from sp3 to sp2 which play quite important role in the photophysical properties of BODIPYs by allowing extended conjugation. The absorption and fluorescence spectroscopy were used to determine the photophysical properties include molar extinction coefficient, fluorescence lifetime and fluorescence quantum yield. Moreover, the effect of solvent polarity on targeted BODIPY units were analysed with experimental investigations. The Density Functional Theory (DFT)-optimized structures were consisted with the experimental data obtained from the single-crystal X-ray structures.

Construction of an Artificial Light-Harvesting System with Efficient Photocatalytic Activity in an Aqueous Solution Based on a FRET-Featuring Metallacage.

Over the past few decades, the design and construction of high-efficiency artificial light-harvesting systems (LHSs) involving multistep fluorescence-resonance energy transfer (FRET) processes have gradually received considerable attention within wide fields ranging from supramolecular chemistry to chemical biology and even materials science. Herein, through coordination-driven self-assembly, a novel tetragonal prismatic metallacage featuring a FRET process using tetraphenylethene (TPE) units as donors and BODIPY units as acceptors has been conveniently synthesized. Subsequently, taking advantage of supramolecular hydrophobic interactions, a promising artificial LHS involving two-step FRET processes from TPE to BODIPY and then to Nile Red (NiR) has been successfully fabricated in an aqueous solution using the FRET-featuring metallacage, NiR, and an amphiphilic polymer (mPEG-DSPE). Notably, this obtained aqueous LHS exhibits highly efficient photocatalytic activity in the dehalogenation of a bromoacetophenone derivate. This study provides a unique strategy for fabricating artificial LHSs in aqueous solutions with multistep FRET processes and further promotes the future development of mimicking the photosynthesis process.

Expanded Azaporphyrins Consisting of Multiple BODIPY Units: Global Aromaticity and High Affinities Towards Alkali Metal Ions.

The one-pot self-coupling reaction of 3-amino-5-bromo-BODIPY 9 under Buchwald-Hartwig amination conditions gave nitrogen-bridged cyclic BODIPY tetramer 10, pentamer 11, and hexamer 12. Oxidation of 10, 11, and 12 in the presence of alkali metal ions provided 13, 15, and 16, respectively, as the first examples of expanded azaporphyrins possessing more than six pyrrole rings. Curiously, the oxidation even in the absence of alkali metal ions gave the same complexes as a result of spontaneous complexation. 10-12 showed large association constants (104 -106 M-1 ) with K+ and Na+ , but the spontaneous complexations were not observed, indicating the extremely high affinities of 13-16 toward alkali metal ions, which can be ascribed to the multiple and effective ion-dipole interaction of the alkali metal ion with the negatively polarized F atoms of the BF2 walls surrounding the cavity. Importantly, 13, 14, and 15 show diatropic ring currents as a result of global aromaticity.

Expanded Azaporphyrins Consisting of Multiple BODIPY Units: Global Aromaticity and High Affinities Towards Alkali Metal Ions

AbstractThe one‐pot self‐coupling reaction of 3‐amino‐5‐bromo‐BODIPY 9 under Buchwald–Hartwig amination conditions gave nitrogen‐bridged cyclic BODIPY tetramer 10, pentamer 11, and hexamer 12. Oxidation of 10, 11, and 12 in the presence of alkali metal ions provided 13, 15, and 16, respectively, as the first examples of expanded azaporphyrins possessing more than six pyrrole rings. Curiously, the oxidation even in the absence of alkali metal ions gave the same complexes as a result of spontaneous complexation. 10–12 showed large association constants (104–106 M−1) with K+ and Na+, but the spontaneous complexations were not observed, indicating the extremely high affinities of 13–16 toward alkali metal ions, which can be ascribed to the multiple and effective ion–dipole interaction of the alkali metal ion with the negatively polarized F atoms of the BF2 walls surrounding the cavity. Importantly, 13, 14, and 15 show diatropic ring currents as a result of global aromaticity.

Tetra-bodipy linked mono-spiro cyclotriphosphazene conjugates: Synthesis, characterization and photophysical properties

In this work, we report the design, synthesis, and characterization of two novel mono-spiro cyclotriphosphazene conjugates bearing four BODIPY units for the first time. The structures of new compounds were fully characterized by FT-IR, MALDI-TOF Mass analysis, 1H, and 31P NMR spectroscopies, and elemental analysis. On the other hand, precursor BODIPYs and mono-spiro compound were characterized by single-crystal X-ray diffraction technique. Photophysical properties including absorption and emission profiles and fluorescence lifetimes were investigated via UV–vis absorption and fluorescence emission spectroscopy techniques. The novel mono-spiro conjugates retain the unique photophysical properties of their precursor BODIPYs showing their promise as photosensitizers with remarkable ability like many other photosensitizers.

BODIPY-based fluorescent chemosensor for phosgene detection: confocal imaging of nasal mucosa and lung samples from mouse exposed to phosgene.

The improper use of phosgene, either as a chemical warfare agent or a leak during chemical production, causes significant risks to human life and property. Therefore, it is particularly important to develop a rapid and highly selective method for the detection of phosgene. In this article, a highly selective fluorescent sensor ONB with a BODIPY unit as a fluorophore and o-aminophenol as a reactive site was constructed for the selective and rapid detection of phosgene in solution. The ONB-containing nanofibers were sprayed onto a non-woven fabric by electrostatic spinning and cut into test films, which can be used well for the detection of gaseous phosgene. While, there were no reported bio-imaging applications for phosgene detection. In this work, nasal mucosa and lung samples from the mice exposed to gaseous phosgene after dropping the ONB solution through the nasal cavity achieved bio-imaging applications successfully.

Modulation of the photophysical properties of multi-BODIPY-siloxane conjugates by varying the number of fluorophores

A series of multifluorophore compounds with two, four, six and eight BODIPY residues linked to a siloxane core via a flexible spacer was synthesized. An increasing number of BODIPY units caused an enhanced propensity to chromophore aggregation with characteristic photophysical effects evoked by the aggregation. The increase in the number of fluorophores additionally resulted in considerable increase in molar extinction coefficient. Meanwhile, a slight drop of the extinction coefficient as calculated per a single chromophore was detected. Multifluorophore conjugates showed a significant broadening of fluorescence emission bands in polar solvents and a substantial decrease in the fluorescence quantum yield due to the aggregation-caused quenching. Time resolved fluorescence measurements of multifluorophore compounds in different solvents showed that the fluorescence decays have a multiexponential character and strongly depend on the number of fluorophores in the conjugate, polarity/viscosity of the solvent and the detection wavelength.

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.

A highly branched macrocycle-based dual-channel sensor: Bodipy and pillar[5]arene combination for detection of Sn (II) &Hg (II) and bioimaging in living cells

A highly branched pillar[5]arene-based sensor containing multiple BODIPY units has been designed and synthesized (B–P[5]arene). Systematical experiments on metal ion detection of B–P[5]arene in acetonitrile/water by emission and absorption spectra indicate that this macrocycle shows high sensitivity and selectivity to both Sn (II) and Hg(II) by dual-channels. Hg (II) ions quenched to the fluorescence intensity of B–P[5]arene, while Sn (II) caused a broader spectrum without any shifting in wavelength. The detection limits of B–P[5]arene for Hg (II) and Sn (II) were found to be 1.09 × 10−6 M and 3.18 × 10−7 M, respectively. For two complex interactions, the metal ion: ligand ratio was determined as 1:2. The complex interactions between the Hg (II)&Sn(II) metal ions and B–P[5]arene are generally stable in both basic and acidic media due to strong interaction.