Tailoring the Properties of Boron−Dipyrromethene Dyes with Acetylenic Functions at the 2,6,8 and 4-B Substitution Positions

Electrochemical Diselenation of BODIPY Fluorophores for Bioimaging Applications and Sensitization of 1 O2

We report a rapid, efficient, and scope-extensive approach for the late-stage electrochemical diselenation of BODIPYs. Photophysical analyses reveal red-shifted absorption - corroborated by TD-DFT and DLPNO-STEOM-CCSD computations - and color-tunable emission with large Stokes shifts in the selenium-containing derivatives compared to their precursors. In addition, due to the presence of the heavy Se atoms, competitive ISC generates triplet states which sensitize 1 O2 and display phosphorescence in PMMA films at RT and in a frozen glass matrix at 77 K. Importantly, the selenium-containing BODIPYs demonstrate the ability to selectively stain lipid droplets, exhibiting distinct fluorescence in both green and red channels. This work highlights the potential of electrochemistry as an efficient method for synthesizing unique emission-tunable fluorophores with broad-ranging applications in bioimaging and related fields.

From photosensitizers to light harvesters adapting the molecular structure in all-BODIPY assemblies

Herein we detail a protocol to design dyads and triads based solely on BODIPY dyes as halogen-free singlet oxygen photosensitizers or energy transfer molecular cassettes. The conducted photonic characterization reveals the key role of the BODIPY-BODIPY linkage to finely modulate the balance between the triplet state population and fluorescence decay.

Dual Emission of meso-Phenyleneethynylene-BODIPY Oligomers: Synthesis, Photophysics, and Theoretical Optoelectronic Study

Two series of 2,5-di(butoxy)phenyleneethynylenes, one halogenated (nPEC4-X; n=2, 3, or 4) and the other boron-dipyrromethene (BODIPY) terminated (nPEC4-By; n=3, 4, or 5; By=BODIPY), were synthesized monodirectionally by the step-by-step approach and the molecular structure was corroborated by NMR spectroscopy (¹ H, ¹³ C-DEPTQ-135, COSY, HSQC, HMBC, ¹¹ B, ¹⁹ F) and MALDI-TOF mass spectrometry. The multiplicity and J-coupling constants of ¹ H, ¹¹ B, and ¹⁹ F/¹¹ B NMR signals revealed, in the nPEC4-By series, that the phenyl in the meso position of BODIPY becomes electronically part of the conjugation of the phenyleneethynylene chain, whereas BODIPY is electronically isolated. The photophysical, electrochemical, and theoretical studies confirm this finding because the properties of nPEC4-By are comparable to those of the nPEC4-X oligomers and BODIPY, indicating negligible electron communication between BODIPY and the nPEC4 moieties. Nevertheless, energy transfer (ET) from nPEC4 to BODIPY was rationalized by spectroscopy and theoretical calculations. Its yield decreases with the nPEC4 conjugation length, according to the increase in distance between the two chromophores, resulting in dual emission for the longest oligomer in which ET is quenched.

New luminescent tetracoordinate boron complexes: an in-depth experimental and theoretical characterisation and their application in OLEDs

New luminescent 2-iminopyrrolyl boron complexes with different BX2 moieties are extensively studied via complementary experimental and theoretical methodologies, including application in OLEDs.

Mechanoresponsive Behavior of a Polymer-Embedded Red-Light Emitting Rotaxane Mechanophore

A red light-emitting photoluminescent supramolecular mechanophore based on an interlocked molecular motif is presented. The rotaxane-based mechanophore contains a cyclic compound featuring a π-extended 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) dye as a red emitter that was threaded onto a dumbbell-shaped molecule containing an electron-poor 1,4,5,8-naphthalenetetracarboxylic diimide quencher at its center. Through two aliphatic hydroxyl groups attached to the dumbbell and the cycle, the mechanophore was covalently embedded into the backbone of a thermoplastic polyurethane elastomer. The mechanophore is only weakly photoluminescent in solution, indicating that the BODIPY's emission is efficiently quenched. Solution-cast films of the rotaxane-containing polymer, by contrast, show an appreciable photoluminescence, which suggests that during film formation, some of the emitting cycles are trapped in positions away from the quencher. Interestingly, the emission intensity could be significantly reduced by swelling the films with an organic solvent and the emission increased again upon drying, suggesting that such solvent plasticization causes a reversible rearrangement. In both dry and solvent-swollen films, uniaxial deformation caused a significant, reversible increase of the emission intensity, on account of mechanically induced shuttling of the emitters away from and back to the quenchers. It is shown that the properties of the polymer can be tuned by the solvent, and that such plasticizing extends the small palette of approaches that allow modification of the activation stress of a given material system.

Dynamic exciton localisation in a pyrene-BODIPY-pyrene dye conjugate

The photophysics of a molecular triad consisting of a BODIPY dye and two pyrene chromophores attached in 2-position are investigated by steady state and fs-time resolved transient absorption spectroscopy as well as by field induced surface hopping (FISH) simulations. While the steady state measurements indicate moderate chromophore interactions within the triad, the time resolved measurements show upon pyrene excitation a delocalised excited state which localises onto the BODIPY chromophore with a time constant of 0.12 ps. This could either be interpreted as an internal conversion process within the excitonically coupled chromophores or as an energy transfer from the pyrenes to the BODIPY dye. The analysis of FISH-trajectories reveals an oscillatory behaviour where the excitation hops between the pyrene units and the BODIPY dye several times until finally they become localised on the BODIPY chromophore within 100 fs. This is accompanied by an ultrafast nonradiative relaxation within the excitonic manifold mediated by the nonadiabatic coupling. Averaging over an ensemble of trajectories allowed us to simulate the electronic state population dynamics and determine the time constants for the nonradiative transitions that mediate the ultrafast energy transfer and exciton localisation on BODIPY.

Tetrathienyl-functionalized red- and NIR-absorbing BODIPY dyes appending various peripheral substituents

A series of boron-dipyrromethene dyes (BODIPYs) 4a-g with different thienyl moieties at 2,3,5,6-positions of the BODIPY core were synthesized by the Stille cross-coupling reaction. The new compounds were characterized by ¹H NMR, ¹³C NMR, HRMS, and IR spectroscopy. The single crystal structure of compound 4e was obtained by X-ray crystallography. The optical and electrochemical properties of these dyes were studied by UV/Vis spectroscopy, fluorescence spectroscopy, and cyclic voltammetry. The DFT calculation of the frontier molecular orbitals of these dyes corroborates the observed effects of peripheral substituents on the optical and redox properties. These results reveal a good tunability of the optical and electronic properties of these BODIPYs by varying the peripheral groups at the α-positions of thienyl moieties, which leads to the absorption and emission reaching the NIR region.

Exploring the Application of the Negishi Reaction of HaloBODIPYs: Generality, Regioselectivity, and Synthetic Utility in the Development of BODIPY Laser Dyes

The generality of the palladium-catalyzed C-C coupling Negishi reaction when applied to haloBODIPYs is demonstrated on the basis of selected starting BODIPYs, including polyhalogenated and/or asymmetrical systems, and organozinc reagents. This reaction is an interesting synthetic tool in BODIPY chemistry, mainly because it allows a valuable regioselective postfunctionalization of BODIPY chromophores with different functional groups. In this way, functional patterns that are difficult to obtain by other procedures (e.g., asymmetrically functionalized BODIPYs involving halogenated positions) can now be made. The regioselectivity is achieved by controlling the reaction conditions and is based on almost-general reactivity preferences, and the nature of the involved halogens and their positions. This ability is exemplified by the preparation of a series of new BODIPY dyes with unprecedented substitution patterns allowing noticeable lasing properties.

NIR Electrofluorochromic Properties of Aza-Boron-dipyrromethene Dyes

The photophysical properties of near-infrared (NIR) emissive aza-boron-dipyrromethene (aza-BDP) dyes incorporating nitrofluorene and alkoxy decorations were intensively investigated. Their highly reversible one-electron reduction process showed characteristic electrofluorochromic (EF) properties in the NIR range, depending on the substituents. The nitrofluorene ethynyl-substituted (Type I) dyes showed smaller EF effects than the alkoxy-containing (Type II) dyes because of the difference in their intrinsic fluorescence contrast between the neutral and reduced states (radical anion). In addition, the Type II chromophores showed a larger diffusion coefficient for ion transport, which enhanced the EF contrast and the response time for the fluorescence change at a given step potential. With an optimized condition, the NIR EF ON/OFF ratio reached a value of 6.1 and a long cyclability over 1000 EF cycles between −0.4 V and +0.4 V switching potentials, with approximately 20% loss of the initial ON/OFF switching ratio. The NIR EF switching was visually observed through a visible light cut-off filter, featuring high fluorescence contrast.

New 8-substituted BODIPY-based chromophores: synthesis, optical and electrochemical properties

BODIPY-based chromophores, in which an electron withdrawing difluoro-boraindacene fragment is connected via position 8 to different donor fragments, were synthesized. Their electrochemical and photophysical properties were studied. All compounds exhibit a quasi-reversible oxidation corresponding to the formation of a BODIPY π-radical cation at around 0.8 V vs. FeCp

Construction of the carbon–chalcogen (S, Se, Te) bond at the 2,6-positions of BODIPY via Stille cross-coupling reaction

Novel 2-chalcogen- or 2,6-dichalcogen-BODIPY derivatives were synthesized by a Pd-catalyzed C–heteroatom Stille cross-coupling reaction, overcoming the limitations of S_NAr.

Synthesis and properties of a series of carboranyl-BODIPYs

A series of four BODIPYs containing one or two ortho- or para-carborane clusters were synthesized using palladium(0)-catalyzed Suzuki cross-coupling or nucleophilic substitution reactions, at the 2,6- or the 8-positions of halogenated boron dipyrromethenes (BODIPYs). The spectroscopic, structural (including one X-ray) and in vitro BBB permeability of the BODIPYs using hCMEC/D3 brain endothelial cells were investigated.

Design, synthesis and photochemical properties of the first examples of iminosugar clusters based on fluorescent cores

The synthesis and photophysical properties of the first examples of iminosugar clusters based on a BODIPY or a pyrene core are reported. The tri- and tetravalent systems designed as molecular probes and synthesized by way of Cu(I)-catalysed azide-alkyne cycloadditions are fluorescent analogues of potent pharmacological chaperones/correctors recently reported in the field of Gaucher disease and cystic fibrosis, two rare genetic diseases caused by protein misfolding.

Unprecedented one-pot sequential thiolate substitutions under mild conditions leading to a red emissive BODIPY dye 3,5,8-tris(PhS)-BODIPY

Phenylthiol performs a thiol exchange with 8-MeS-BODIPY and activates/substitutes the 3,5 positions forming a tri-thiolated BODIPY.

Structural modification strategies for the rational design of red/NIR region BODIPYs

The structure–property relationships of red/NIR region BODIPY dyes is analyzed, so that trends in their photophysical properties can be readily compared.

BODIPY-tetrazine derivatives as superbright bioorthogonal turn-on probes

The fastest and the brightest: A new design that intimately connects tetrazine to a BODIPY fluorophore enables exceptionally efficient energy transfer and quenching. Upon reaction of the tetrazine, the brightness of the fluorophore increases more than a thousand-fold, a fluorogenic activation up to two orders of magnitude greater than previously described.

Synthesis of meso-halogenated BODIPYs and access to meso-substituted analogues

8-Halogenated boradiaza-s-indacenes can be efficiently prepared from dipyrrylketones. The new dyes react smoothly with nucleophiles to yield N-, O-, and S-substituted chromophores, as well as transition-metal-catalyzed cross-coupling reactions. The nature of the new substitutent has a strong influence on the spectral properties of the dyes.