BODIPY Monomers Research Articles

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.

Ultrabright Fluorescent Polymeric Nanoparticles Made from a New Family of BODIPY Monomers

Four novel BODIPY derivatives (π-) functionalized by different polymerizable groups, styrene (S), phenyl acrylate (PhA), ethyl methacrylate (EtMA) and ethyl acrylate (EtA) have been synthesized. Following a formerly established one-pot RAFT miniemulsion polymerization process (GrazonMacromol. Rapid Commun. 2011, 32, 699−705), the fluorophores were copolymerized in a controlled way at 2.6 mol % with styrene in water. On the basis of the polymerization-induced self-assembly (PISA) principle, the copolymers assembled during their formation into fluorescent nanoparticles. The distribution of the fluorescent monomers along the polymer backbone was monitored by kinetic studies of the copolymerization reaction. Fluorescent stationary and time-resolved spectroscopy was then performed on both the monomers and the nanoparticles (NPs) and the observed differences are discussed in view of the distribution of the fluorescent monomers in the polymer chain. With two of the novel fluorescent monomers (πS and πPhA), the b...

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.

Synthesis, Photophysics, Electrochemistry, and Electrogenerated Chemiluminescence of a Homologous Set of BODIPY-Appended Bipyridine Derivatives

Two new 2,2'-bipyridine (bpy) based ligands with ancillary BODIPY chromophores attached at the 4 and 4'-positions were prepared and characterized, which vary in the substitution pattern about the BODIPY periphery by either excluding (BB1) or including (BB2) a β-alkyl substituent. Both absorb strongly throughout the visible region and are strongly emissive. The basic photophysics and electrochemical properties of BB1 and BB2 are comparable to those of the BODIPY monomers on which they are based. The solid-state structures and electronic structure calculations both indicate that there is negligible electronic communication between the BODIPY moieties and the intervening bpy spacers. Electrogenerated chemiluminescence spectra of the two Bpy-BODIPY derivatives are similar to their recorded fluorescence profiles and are strongly influenced by substituents on the BODIPY chromophores. These 2,2'-bipyridine derivatives represent a new set of ligands that should find utility in applications including light-harvesting, photocatalysis, and molecular electronics.

Synthesis, Photophysical, Electrochemical, and Electrogenerated Chemiluminescence Studies. Multiple Sequential Electron Transfers in BODIPY Monomers, Dimers, Trimers, and Polymer

Synthesis of the C(8) BODIPY monomers, dimers, and trimers, a C(8) polymer, and N(8) aza-BODIPY monomer and dimer was carried out. Methyl and mesityl C(8)-substituted monomers, dimers, and trimers were used. Dimers, trimers, and polymer were formed chemically through the β-β (2/6) positions by oxidative coupling using FeCl(3). A red shift of the absorbance and fluorescence is observed with addition of monomer units from monomer to polymer for C(8) dyes. The aza-BODIPY dye shows red-shifted absorbance and fluorescence compared with the C(8) analogue. Cyclic voltammetry shows one, two, and three one-electron waves on both reduction and oxidation for the monomer, dimer, and trimer, respectively, for the C(8) BODIPYs. The separation for the reduction peaks for the C(8) dimers is 0.12 V compared with 0.22 V for the oxidation, while the trimers show separations of 0.09 V between reduction peaks and 0.13 V for oxidation peaks. The larger separations between the second and third peaks, 0.25 V for the oxidation and 0.2 V for the reduction, are consistent with a larger energy to remove or add a third electron compared with the second one. The BODIPY polymer shows the presence of many sequential one-electron waves with a small separation. These results provide evidence for significant electronic interactions between different monomer units. The aza-BODIPY dye shows a reduction peak 0.8 V more positive compared to the C(8) compound. Aza-BODIPY dimer shows the appearance of four waves in dichloromethane. The separation between two consecutive waves is around 0.12 V for reduction compared with 0.2 V for oxidation, which is comparable with the results for the C(8) dyes. Electrogenerated chemiluminescence (ECL) of the different species was obtained, including weak ECL of the polymer.

One‐Pot Synthesis of Pegylated Fluorescent Nanoparticles by RAFT Miniemulsion Polymerization Using a Phase Inversion Process

Water-soluble and fluorescent core-shell nanoparticles (FNP) are synthesized in a miniemulsion reversible addition-fragmentation transfer (RAFT) polymerization and are shown to respond to pH. The particles are obtained from a hydrophilic PEO-b-PAA macromolecular RAFT agent which is block-extended with styrene and a fluorescent BODIPY monomer. A miniemulsion is then formed with the residual hydrophobic monomers. After completion of the polymerization, FNP of ≈ 60 nm in diameter are obtained. The fluorescence of the BODIPY dye in the particles is found to remain (0.2 quantum yield). The particles can be precipitated in acidic pH and redispersed upon addition of base without loss of their integrity or noticeable rearrangement.

Phenyliodine(III) Bis(trifluoroacetate) (PIFA)-Promoted Synthesis of Bodipy Dimers Displaying Unusual Redox Properties

Phenyliodine(III) bis(trifluoroacetate) (PIFA) in conjunction with a Lewis acid promotes C-C coupling of Bodipy monomers leading to mixtures of various oligomers. When a single position is blocked with an iodo or phenyl group, formation of the dimer is favored. These dimers display two successive oxidation and two reduction waves separated on average by 260 and 130 mV, respectively, corresponding to each Bodipy subunit.

Aromatic Ring-Fused BODIPY-Based Conjugated Polymers Exhibiting Narrow Near-Infrared Emission Bands

Three conjugated copolymers, consisted of alternating p-phenylene-ethynylene and boron di(iso)indomethene units in the backbone, were synthesized via palladium-catalyzed Sonogashira coupling reaction of 1,4-diethynyl-2,5-dihexadecyloxybenzene and three diiodophenyl-fused BODIPY monomers. The structures and properties of the conjugated polymers were characterized by 1H NMR, 11B NMR, and Fourier transform infrared (FT-IR) spectroscopies, elemental analysis, size exclusion chromatography (SEC), UV−vis absorption spectroscopy, photoluminescence (PL) spectroscopy, and theoretical calculation using density-functional theory (DFT) method. The polymers obtained were fusible and soluble in common organic solvents including THF, benzene, toluene, CHCl3, and CH2Cl2, etc. The incorporation of the indomethene monomers into p-phenylene-ethynylene main chain led to red shifts in UV-absorption and PL spectra by extended π-conjugation of the copolymers in comparison with the monomers. Accordingly, the copolymers emitted i...

Deep‐red emissive conjugated poly(2,6‐BODIPY‐ethynylene)s bearing alkyl side chains

AbstractNovel deep‐red emissive poly(2,6‐BODIPY‐ethynylene)s bearing dodecyl side chains (polymers A, B, and C) have been prepared by palladium‐catalyzed Sonogashira polymerization of 2,6‐diiodo‐functionalized BODIPY monomers with 2,6‐diethynyl‐functionalized BODIPY monomers. These polymers emit in the deep‐red region with emission maxima at up to 690 nm, and exhibit significant red shifts (up to 166 and 179 nm) of both absorption and emission maxima compared with their parent BODIPY dyes due to significant extension of π‐conjugation. These polymers possess good thermal stability with decomposition temperature between 270 and 360 °C. The polymers exhibit a little larger Stokes shifts and shorter lifetime than their corresponding BODIPY dyes. The solid state thin films of polymers A, B, and C emit in near‐infrared region between 723 and 743 nm, and show significantly red shifts (up to 57 nm) in absorption and emission maxima relative to their polymer solution. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5354–5366, 2009

Poly(BODIPY)s: A New Class of Tunable Polymeric Dyes

We present a new class of polymeric dyes bearing the difluoroboraindacene (BODIPY) chromophore within the main chain. Starting from a diiodinated BODIPY monomer, homo- and copolymers with a fully c...

Synthesis and Optical Properties of Red and Deep-Red Emissive Polymeric and Copolymeric BODIPY Dyes

Deep-red emissive polymeric BODIPY dyes (polymers A and B), poly(2,6-BODIPY-ethynylene)s, were prepared by palladium-catalyzed Sonogashira polymerization of 2,6-diiodo-functionalized BODIPY monomers with 2,6-diethynyl-functionalized BODIPY monomers. Poly(2,6-BODIPY-ethynylene)s emit in the deep-red region with emission spectral maxima at around 680 nm and exhibit significant red shifts (up to 163 and 172 nm) of both absorption and emission maxima compared with their initial BODIPY dyes due to significant extension of π-conjugation. Red emissive copolymeric BODIPY dyes (polymers C, D, and E) were also prepared by palladium-catalyzed Sonogashira polymerization of a diethynyl-functionalized BODIPY monomer with 9,9-bis(6′-(hexylthio)hexyl)-2,7-diiodo-9H-fluorene, 1,4-diiodo-2,5-didecyloxybenzene, and 2,5-diiodo-3-decylthiophene, respectively. Incorporation of different band gap monomer units into poly(2,6-BODIPY-ethynylene)s resulted in copolymers with a range of emission wavelengths from 641 to 664 nm. The fluorescence lifetimes of these polymers (polymers A−D) are from 2.8 to 3.8 ns except the copolymer with thiophene moieties (polymer E), which displays a much shorter lifetime of 0.23 ns with low fluorescence quantum yield due to efficient intersystem crossing induced by the heavy atom effect of sulfur.

Color Tuning of Polyfluorene Emission with BODIPY Monomers

Three fluorescent conjugated copolymers, comprised of alternating fluorene and BODIPY units in the main chain, have been prepared by palladium-catalyzed Suzuki polymerization of 9,9-dihexylfluorene-2,7-diboronic acid with each of three different 2,6-diiodo-substituted BODIPY monomers. The copolymers were characterized using FT-IR spectroscopy, UV−vis spectroscopy, photoluminescence (PL), and molecular weight studies. Low-band gap BODIPY comonomers are effective in expanding the emission wavelength to the orange region because of significant extension of π-conjugation and have significantly enhanced fluorescent intensity with fluorescent quantum yield of up to 85% in methylene chloride solution. The copolymers show absorption maxima between 547 and 557 nm and emission maxima between 585 and 588 nm in methylene chloride solutions. The copolymers possess high molecular weight, good solubility and readily dissolve in common organic solvents such as THF, CH2Cl2, CHCl3, and toluene. The copolymers display sensitive fluorescent responses to fluoride and cyanide anions through their multivalent interactions while they do not respond to chloride, bromide, and iodide anions.

Bis(BF2)-2,2′-bidipyrrins, a class of BODIPY dyes with new spectroscopic and photophysical properties

The photophysical and spectroscopic characterization of four new dimeric bis(BF2)-2,2′-bidipyrrins (BisBODIPYs) recently synthesized and characterized (Chem. Eur. J., 2008, 14, 2976–2983) has been undertaken along with that of the component BODIPY monomers. The monomers display the typical photophysical properties of this family; (i) narrow and intense single absorption band in the visible range at 530 nm; (ii) intense, solvent independent emission (Φflca. 1); (iii) narrow emission band with a 200–400 cm−1 Stokes shifted emission, independent of solvent polarity; (iv) no absorption features for the singlet excited state; (v) very little triplet yield and no ability to sensitize singlet oxygen. The absorption spectra of the corresponding new dimers exhibit split band maxima in the visible range at about 490 and 560 nm, corresponding to an exciton splitting of ca. 2600 cm−1. The luminescence in toluene is strong (Φflca. 0.7, τ =3.4 ns), broad and Stokes shifted by ca. 2200 cm−1, but both luminescence yield and Stokes shift are solvent polarity dependent; Φfl < 0.1, τ < 1 ns and the Stokes shift is close to 2700 cm−1 in acetonitrile. Solvent viscosity does not appear to play an important role and freezing of the solvents to 77 K in a solid matrix cancels the differences in luminescence parameters. Singlet and triplet excited state absorbance was measured in toluene and acetonitrile and the ability of these new dyes to sensitize singlet oxygen was examined. The nature and dynamics of the excited state is discussed in comparison with the monomers properties and with some intra- or inter-molecular BODIPY dimers reported in the literature. Potential applications of these new dyes with respect to BODIPYs are pointed out on the basis of their spectroscopic and photophysical properties.

Bis(BF2)‐2,2′‐Bidipyrrins (BisBODIPYs): Highly Fluorescent BODIPY Dimers with Large Stokes Shifts

Four new dimeric bis(BF(2))-2,2'-bidipyrrins (bisBODIPYs), and their corresponding BODIPY monomers, have been prepared and studied with respect to their structural and photophysical properties. The solid-state molecular structure of the dimers and the relative orientation of the subunits have been revealed by an X-ray diffraction study, which showed that the molecules contain two directly linked BODIPY chromophores in a conformationally fixed, almost orthogonal arrangement. Two of the fluorine atoms are in close contact with each other and the (19)F NMR spectra show a characteristic through-space coupling in solution. The new chromophores all exhibit a clear exciton splitting in the absorption spectra with maxima at about 490 and 560 nm, and are highly luminescent with an intense emission band at around 640 nm. The Stokes shift, which is the difference between the maximum of the lowest-energy absorption band and the maximum of the emission band, has a typical value of 5 to 15 nm for simple BODIPYs, whereas this value increases to 80 nm or more for the dimers, along with a slight decrease in fluorescence quantum yields and lifetimes. These properties indicate potential uses of these new fluorophoric materials as functional dyes in biomedical and materials applications and also in model compounds for BODIPY aggregates.

Physical and Photophysical Characterization of a BODIPY Phosphatidylcholine as a Membrane Probe

Lipids containing the dimethyl BODIPY fluorophore are used in cell biology because their fluorescence properties change with fluorophore concentration (C.-S. Chen, O. C. Martin, and R. E. Pagano. 1997. Biophys J. 72:37–50). The miscibility and steady-state fluorescence behavior of one such lipid, 1-palmitoyl-2-(4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza- s-indacene-3-pentanoyl)- sn-glycero-3-phosphocholine (PBPC), have been characterized in mixtures with 1-stearoyl-2-oleoyl- sn-glycero-3-phosphocholine (SOPC). PBPC packs similarly to phosphatidylcholines having a cis-unsaturated acyl chain and mixes nearly ideally with SOPC, apparently without fluorophore–fluorophore aggregation. Increasing PBPC mole fraction from 0.0 to 1.0 in SOPC membranes changes the emission characteristics of the probe in a continuous manner. Analysis of these changes shows that emission from the excited dimethyl BODIPY monomer self quenches with a critical radius of 25.9 Å. Fluorophores sufficiently close (≤13.7 Å) at the time of excitation can form an excited dimer, emission from which depends strongly on total lipid packing density. Overall, the data show that PBPC is a reasonable physical substitute for other phosphatidylcholines in fluid membranes. Knowledge of PBPC fluorescence in lipid monolayers has been exploited to determine the two-dimensional concentration of SOPC in unilamellar, bilayer membranes.