8 research outputs found
Transforming Dyes into Fluorophores:Exciton-Induced Emission with Chain-like Oligo-BODIPY Superstructures
Herein we present a systematic study demonstrating to which extent exciton formation can amplify fluorescence based on a series of ethylene-bridged oligo-BODIPYs. A set of non- and weakly fluorescent BODIPY motifs was selected and transformed into discrete, chain-like oligomers by linkage via a flexible ethylene tether. The prepared superstructures constitute excitonically active entities with non-conjugated, Coulomb-coupled oscillators. The non-radiative deactivation channels of Internal Conversion (IC), also combined with an upstream reductive Photoelectron Transfer (rPET) and Intersystem Crossing (ISC) were addressed at the monomeric state and the evolution of fluorescence and (non-)radiative decay rates studied along the oligomeric series. We demonstrate that a âmaskedâ fluorescence can be fully reactivated irrespective of the imposed conformational rigidity. This work challenges the paradigm that a collective fluorescence enhancement is limited to sterically induced motional restrictions
Photoactivatable Fluorophore for Stimulated Emission Depletion (STED) Microscopy and Bioconjugation Technique for Hydrophobic Labels
The use of photoactivatable dyes in STED microscopy has so far been limited by twoâphoton activation through the STED beam and by the fact that photoactivatable dyes are poorly solvable in water. Here we report ONBâ2SiR, a fluorophore that can be both photoactivated in the UV and specifically deâexcited by STED at 775 nm. Likewise, we introduce a conjugation and purification protocol to effectively label primary and secondary antibodies with moderately waterâsoluble dyes. Greatly reducing dye aggregation, our technique provides a defined and tunable degree of labeling, and improves the imaging performance of dye conjugates in general
Benzothiadiazole oligoene fatty acids: fluorescent dyes with large Stokes shifts
Herein, we report on the synthesis and characterization of novel fluorescent fatty acids with large Stokes shifts. Three examples consisting of the same number of carbon atoms and thus of similar chain length are presented differing in their degree of unsaturation. As major fluorogenic contributor at the terminus benzo[c][1,2,5]thiadiazole was used. Respective syntheses based on Wittig reactions followed by iodine-mediated isomerization are presented. The absorption properties are modulated by the number of conjugated C=C double bonds of the oligoene chain ranging from one to three. Large Stokes shifts of about 4900â5700 cmâ1 and fluorescence quantum yields of up to 0.44 were observed
Fluorescent Penta- and Hexaene Fatty Acids by a WittigâHorner/Elimination Strategy
Molecular fluorescent probes have revolutionized biochemical
and
biophysical studies in the last decades, but with regard to lipids
there has been a lack of combining the slim shape of saturated acyl
chains with fluorescent properties. Our strategy to pentaene and hexaene
fatty acids builds upon commercially available 4-(<i>E</i>)-decenal, which is subjected to a WittigâHorner reaction
after chlorination in α-position. DBU-mediated ÎČ-elimination
of HCl proceeding the olefination establishes a highly conjugated
system to which a salt-free Wittig reaction adds a final double bond
leading to a good (<i>Z</i>)-selectivity of 83â86%.
The double bond geometry can be optionally isomerized with I<sub>2</sub> to furnish the all-(<i>E</i>)-species. The five conjugated
alkene moieties result in a longest-wavelength absorption maximum
of about 350 nm. A red-shift to 380 nm was realized by addition of
another double bond employing a common WittigâHorner prolongation
sequence. Stokes shifts of about 7300 and 7800 cm<sup>â1</sup>, respectively, were observed
Linear Amine-Linked Oligo-BODIPYs: Convergent Access via Buchwald-Hartwig Coupling
A convergent route towards nitrogen-bridged BODIPY oligomers has been developed. The synthetic key step is a Buchwald-Hartwig cross-coupling reaction of an alpha-amino-BODIPY and the respective halide. Not only does the selective synthesis provide control of the oligomer size, but the facile preparative procedure also enables easy access to this type of dyes. Furthermore, functionalized examples were accessible via brominated derivatives
Ethylene-Bridged Oligo-BODIPYs: Access to Intramolecular JâAggregates and Superfluorophores
A versatile
and rapid access to various chain lengths of ethylene-bridged
BODIPY motifs was discovered. Corresponding oligomers comprising up
to eight monomeric units were studied with respect to their microstructures
by photophysical, X-ray crystallographic, and computational means.
The investigation of three different dipyrrin cores revealed a crucial
dependence on the substitution pattern of the core, whereas the nature
of the <i>meso</i>-periphery is less critical. The impact
of substituent effects on the conformational space was investigated
by Monte Carlo simulations and a set of DFT methods (B3LYP, PBEh-3c,
TPSS/PWPB95), including dispersion effects. Cryptopyrrole-derived
oligo-BODIPYs are characterized by a tight intramolecular arrangement
triggering a dominant J-type excitonic coupling with red-shifts up
to 45 nm, exceptionally small line widths of the absorption and emission
event (up to 286 cm<sup>â1</sup>), outstandingly high attenuation
coefficients (up to 1âŻ042âŻ000 M<sup>â1</sup> cm<sup>â1</sup>), and quantum yields of up to unity
Novel Dyes Based on Extended Fulvene Motifs: Synthesis via Redox Reactions of Naphthoquinones with DonorâAcceptor Cyclopropanes and Their Spectroelectrochemical Behavior
Novel dyes based on extended fulvene motifs are reported. The carbon skeleton was generated by a catalyzed addition of donor-acceptor cyclopropanes to naphthoquinone. The hydroxy group at the central ring of the tricyclic fulvene motif was converted into the triflate, which reacted efficiently with a wide range of nucleophiles, resulting in substitution and thereby providing new derivatives. The synthetic versatility allowed us to investigate the absorption, electrochemical, and UV/Vis-NIR spectroelectrochemical properties of these dyes as a function of the substituents. The dyes were shown to participate in reductive electrochemistry, the reversibility of which can be improved by appropriate selection of the substituents. Additionally, first signs of NIR electrochromism are presented, opening new avenues for the future investigations of such dyes
Triple-photoinduced electron transfer (tri-PET) catalysis for activation of super strong bonds
Single electron redox processes allow the formation of highly reactive radicals â valuable intermediates that enable unique transformations in organic chemistry (1,2). An established concept to create radical intermediates is photoexcitation of a catalyst to a higher energy intermediate, subsequently leading to a photoinduced electron transfer (PET) with a reaction partner (3â7). The known concept of consecutive photoinduced electron transfer (con PET) leads to catalytically active species even higher in energy by the uptake of two photons (8). This process has already been used widely for catalytic reductions; however, limitations towards strong bonds and electron rich substrates remain (9,10). Generally speaking, increased photon uptake leads to a more potent reductant. Here, we introduce triple-photoinduced electron transfer catalysis, termed tri-PET, enabled by the three-photon uptake of a dye molecule leading to an excited dianionic super-reductant which is more potent than Li metal (11) â one of the strongest chemical reductants known. Irradiation of the metal-free catalyst by violet light enables the cleavage of strong carbon-fluoride bonds and reduction of other halides even in very electron-rich substrates. The resulting radicals are quenched by hydrogen atoms or engaged in carbon-carbon and carbon-phosphorus bond formations, highlighting the utility of tri-PET for organic chemistry. Thorough spectroscopic, chemical and computational investigations are presented to understand this novel mode of photoredox catalysis. The existence of the dianion which takes up a third photon when irradiated was proven by X-ray diffraction analysis