Difluoroboron Dibenzoylmethane Research Articles

Substituent Effect on Difluoroboron β-diketonate Complexes: Synthesis, Photophysical and Electrochemical Properties, and Application as Nitro-Explosive Chemosensors

In this study, three difluoroboron dibenzoylmethane compounds that have substituents at the peripheral phenyl groups varying from electron-withdrawing to electron-donating, BF 2 dbm-F, BF 2 dbm-H, and BF 2 dbm-OMe, were prepared. The photophysical and electrochemical properties of these compounds, along with density functional theory and time-dependent density functional theory calculations, were systematically investigated to study the structure-property relationships of these compounds. The energy band gaps were systematically controlled, and the emission colors were tuned by the choice of substituent. In addition, the excited state behaviors of these compounds were significantly different, which resulted in variations in the fluorescence quantum yield and radiative/non-radiative decay rate constants. The BF2dbm compounds were employed as selective chemosensors for the detection of nitro explosives by fluorescence quenching, and BF 2 dbm-OMe showed the most efficient sensing ability for ortho-nitroaniline.

Boosting the triplet activity of heavy-atom-free difluoroboron dibenzoylmethane via sp3 oxygen-bridged electron donors.

Purely organic phosphors have important applications in imaging, sensing, informatics and illumination. Methoxy-substituted difluoroboron dibenzoylmethane (BF2dbm) complexes exhibit intense fluorescence with an almost unity quantum yield. Here we show that by simply introducing an sp3 oxygen-bridged methoxylphenyl group as a pendant to BF2dbm, the boron complex exhibits a triplet quantum yield of 0.16, a more than 100-fold increase compared to that of BF2dbm.

Meta‐Dimethoxy‐Substituted Difluoroboron Dibenzoylmethane Poly(Lactic Acid) Nanoparticles for Luminescence Anisotropy

AbstractDifluoroboron β‐diketonates derivatives are dyes with tunable fluorescence and room temperature phosphorescence when embedded in a rigid matrix such as poly(lactic acid) (PLA). Both fluorescence and phosphorescence are present in solid‐state PLA, enabling a variety of applications such as bio‐imaging and oxygen sensing. Here, a meta‐dimethoxy‐substituted difluoroboron dibenzoylmethane [BF2dbm(m‐OMe)2OH] is prepared, and two PLA polymers [BF2dbm(m‐OMe)2PLA] with different dye loadings are produced. Optical properties are studied in solution, and the emissions are environment sensitive. This is supported by density functional theory (DFT) calculations where intramolecular charge transfer is present and related to solvatochromism. Nanoparticles are fabricated with solvents of varied polarities via nanoprecipitation. Dynamic light scattering indicates dimethylformamide generates the smallest nanoparticles and tetrahydrofuran the largest. Luminescence polarization establishes that the absorbing and emitting dipoles are single axis and collinear. Förster resonance energy transfer within the nanoparticles is important and depends strongly on dye loadings.

Highly Efficient Room-Temperature Phosphorescence from Halogen-Bonding-Assisted Doped Organic Crystals.

The development of metal-free organic room temperature phosphorescence (RTP) materials has attracted increasing attention because of their applications in sensors, biolabeling (imaging) agents and anticounterfeiting technology, but remains extremely challenging owing to the restricted spin-flip intersystem crossing (ISC) followed by low-yield phosphorescence that cannot compete with nonradiative relaxation processes. Here, we report a facile strategy to realize highly efficient RTP by doping iodo difluoroboron dibenzoylmethane (I-BF2dbm-R) derivatives into a rigid crystalline 4-iodobenzonitrile (Iph-C≡N) matrix. We found that halogen bonding between cyano group of Iph-C≡N matrix and iodine atom of I-BF2dbm-R dopant is formed in doped crystals, i.e., Iph-C≡N···I-BF2dbm-R, which not only suppresses nonradiative relaxation of triplets but also promotes the spin-orbit coupling (SOC). As a result, the doped crystals show intense RTP with an efficiency up to 62.3%. By varying the substituent group R in I-BF2dbm-R from electron donating -OCH3 to electron accepting -F, -CN groups, the ratio between phosphorescence and fluorescence intensities has been systematically increased from 3.8, 15, to 50.

Meta-Alkoxy-Substituted Difluoroboron Dibenzoylmethane Complexes as Environment-Sensitive Materials.

The optical properties of meta-alkoxy-substituted difluoroboron dibenzoylmethane dyes were investigated in solution and in the solid state. Meta-alkoxy substitution induced strong intramolecular charge transfer (ICT) from the oxygen-donating substituent to the halide and boron acceptors in the excited state, as compared to the π-π* transition that is observed with para-alkoxy substitution. The optical properties of para- and meta-substituted alkoxy boron dyes were evaluated by calculations, in dilute solution, and in solid-state films. When embedded in amorphous matrixes (e.g., PLA, PMMA, PS, cholesterol), all dyes showed fluorescence (F) and phosphorescence (P) emission. In this report, we show that meta-substitution resulted in enhanced solvatochromism and an increased phosphorescence-to-fluorescence ratio in solid-state films compared to analogous para-substituted samples. With enhanced phosphorescence intensity via the heavy-atom effect, iodo-substituted dyes were further studied in PLA-PEG nanoparticles. Oxygen calibrations revealed stronger phosphorescence and a greater oxygen-sensing range for the meta- versus para-alkoxy-substituted dyes, features that are important for oxygen-sensing materials design.

Bright blue fluorescent nanoparticles for live cell imaging by fluorescence microscopy

Abstract Fluorescence imaging of labeled cells is an important method to monitor long-term cell behaviors. Long-lasting green stains such as CFSE (carboxyfluorescein succinimidyl ester) and its derivatives are routinely utilized for cell migration studies, but currently there are no commercially available long-lasting (days), non-cytotoxic blue cell stains compatible with a standard DAPI filter that is brighter than the autofluorescence of tissue. Here, we fabricated two bright blue emitting boron dye-polymer nanoparticles (BNPs) (e = 32100 M−1cm −1) from difluoroboron dibenzoylmethane conjugated to poly(lactic acid) (BF2dbmPLA) or poly(e-caprolactone) (BF2dbmPCL). Particles were < 100 nm diameter, and their excitation and emission wavelengths (lex = 381 nm; lem = 439 nm) corresponded to the DAPI filter. When incubated with mouse splenocytes, the blue emitting nanoparticles were taken up by the cells and readily detected by fluorescence microscopy (EVOS microscope) or a plate reader. Viability of the stained cells was assessed by calcein/propidium iodide staining. These data showed that BNPs have the capability to stain cells brightly without significantly diminishing viability and therefore show promise as a new tool for live cell tracking in the blue fluorescence channel. We are currently measuring cell fluorescence and viability over time, determining which types of cells take up the particles, and comparing the staining capabilities of the nanoparticles to commercial blue dyes.

Triphenylamine-modified difluoroboron dibenzoylmethane derivatives: Synthesis, photophysical and electrochemical properties

Two new triphenylamine functionalized difluoroboron (BF2) β-diketonate complexes, one asymmetrical 2 and the other symmetrical 3, were synthesized and fully characterized. The effects of the triphenylamine substituent on the photoluminescence, redox properties and photostability of these BF2 complexes were investigated. These new compounds exhibit long-wavelength absorption and strong intramolecular charge transfer emission and reversible oxidation and reduction waves in cyclic voltammetry experiments. It was found that they were highly fluorescent in toluene with large Stokes shifts, and demonstrated excellent photostability comparable to their parent BF2 nucleus. Meanwhile, these new complexes are highly sensitive to the solvent polarity, which indicates that they could be used as highly sensitive polar probes besides excellent emitting materials.

Modulating Mechanochromic Luminescence Quenching of Alkylated Iodo Difluoroboron Dibenzoylmethane Materials

Difluoroboron β-diketonate compounds exhibit solid-state luminescence phenomena. Among these are reversible mechanochromic luminescence (ML), aggregation induced emission (AIE), and mechanochromic luminescence quenching (MLQ). These properties can be tuned by alterations to the molecular structure. Dyes with varying halide substituents exhibit tunable ML, MLQ, and solid-state emission with high quantum yields. A series of difluoroboron dibenzoylmethane (BF2dbm) dyes with iodide and alkoxyl substituents (BF2dbm(I)OR) were synthesized where R = CH3 (C1), C5H11 (C5), C6H13 (C6), C12H25 (C12), and C18H37 (C18)). The 4-iodo parent compound BF2dbm(I) (H) was made for comparison. By keeping the heavy atom static, the dependence of ML properties on alkyl chain length was probed. The hydrogen derivative is only weakly emissive as a solid and exhibited minimal mechanoresponsive behavior. In contrast, alkoxy dyes exhibited tunable ML and MLQ properties depending on the length of the alkyl chain. Longer chain dyes co...

Tailoring Oxygen Sensitivity with Halide Substitution in Difluoroboron Dibenzoylmethane Polylactide Materials.

The dual-emissive properties of solid-state difluoroboron β-diketonate-poly(lactic acid) (BF2bdkPLA) materials have been utilized for biological oxygen sensing. In this work, BF2dbm(X)PLA materials were synthesized, where X = H, F, Cl, Br, and I. The effects of changing the halide substituent and PLA polymer chain length on the optical properties in dilute CH2Cl2 solutions and solid-state polymer films were studied. These luminescent materials show fluorescence, phosphorescence, and lifetime tunability on the basis of molecular weight, as well as lifetime modulation via the halide substituent. Short BF2dbm(Br)PLA (6.0 kDa) and both short and long BF2dbm(I)PLA polymers (6.0 or 20.3 kDa) have fluorescence and intense phosphorescence ideal for ratiometric oxygen sensing. The lighter halide-dye polymers with hydrogen, fluorine, and chlorine substitution have longer phosphorescence lifetimes and can be utilized as ultrasensitive oxygen sensors. Photostability was also analyzed for the polymer films.

Efficient and tunable fluorescence energy transfer via long-lived polymer excitons

A highly fluorescent polymer consisting of repeating pendant dye molecules, difluoroboron dibenzoylmethane (BF2dbm), and an end-capped Rhodamine B (RhB) exhibits efficient energy transfer (EnT) owing to long-lived polymer excitons.

A simple approach to aggregation-induced emission in difluoroboron dibenzoylmethane derivatives

The first example of an AIE active BF2dbm derivative with a single dimethylamino group connecting to the phenyl ring was revealed. It also showed capability of sensing HCl gas both in solution and in the solid state.

A mechanistic investigation of mechanochromic luminescent organoboron materials

Mechanochromic luminescence (ML) refers to the luminescence color and/or intensity change of solid-state materials induced by mechanical perturbations. For organic molecular solids, this phenomenon is related to the specific packing modes and orientations of individual fluorophores, which could give rise to different excited-state interactions. The molecular solids of difluoroboron dibenzoylmethane (BF2dbm) derivatives were previously found to exhibit reversible ML at room temperature and are promising as self-healing optical materials. In this report, we aim to shed some light on the mechanism of BF2dbm ML by trying to understand the excited-state interactions among solid-state BF2dbm molecules and elucidate how these interactions change upon mechanical stimulation. We first investigated the optical properties of monomeric, dimeric, and polymeric BF2dbm derivatives in optically dilute solutions and demonstrated unambiguously that BF2dbm moieties have a propensity to form H-aggregates. Next, we studied the physical properties of these boron complexes in the solid state including their crystal structures, fluorescence emissions, and mechanochromic luminescence. By correlating solution data with the solid-state characterization results, it was concluded that two coupled processes, force-induced emissive H-aggregate formation and energy transfer to the emissive H-aggregates, are responsible for the observed BF2dbm ML in the solid state.

Intracellular Uptake and Trafficking of Difluoroboron Dibenzoylmethane−Polylactide Nanoparticles in HeLa Cells

In this study, nanoparticles based on difluoroboron dibenzoylmethane-poly(lactic acid) (BF(2)dbmPLA) are prepared. Polylactic acid or polylactide is a commonly used degradable polymer, while the boron dye possesses a large extinction coefficient, high emission quantum yield, two-photon absorption, and sensitivity to the surrounding environment. BF(2)dbmPLA exhibits molecular-weight-dependent emission properties and can be formulated as stable nanoparticles, suggesting that its unique optical properties may be useful in multiple contexts for probing intracellular environments. Here we show that BF(2)dbmPLA nanoparticles are internalized into cultured HeLa cells by endocytosis, and that within the cellular milieu, they retain their fluorescence properties. BF(2)dbmPLA nanoparticles are photostable, resisting laser-induced photobleaching under conditions that destroy the fluorescence of a common photostable probe, LysoTracker Blue. Their endocytosis is also lipid-raft-dependent, as evidenced by their significant colocalization with cholera toxin B subunit in membrane compartments after uptake and their sensitivity of uptake to methyl-beta-cyclodextrin. Additionally, BF(2)dbmPLA nanoparticle endocytosis utilizes microtubules and actin filaments. Internalized BF(2)dbmPLA nanoparticles do not accumulate in acidic late endosomes and lysosomes but within a perinuclear nonlysosomal compartment. These findings demonstrate the feasibility of using novel BF(2)dbmPLA nanoparticles exhibiting diverse emission properties for in situ, live cell imaging and suggest that their endogenous uptake occurs through a lipid-raft-dependent endocytosis mechanism.

Difluoroboron Dibenzoylmethane PCL-PLA Block Copolymers: Matrix Effects on Room Temperature Phosphorescence

Luminescent materials result when boron dyes are combined with polyester biomaterials. Previously, it was reported that difluoroboron dibenzoylmethane polylactide, BF2dbmPLA, exhibits intense fluorescence as well as unusual room temperature phosphorescence (RTP) in the solid state. To gain a better understanding of polymer effects on photophysical properties, a poly(ε-caprolactone) (PCL) analogue, BF2dbmPCL, was synthesized by tin catalyzed ring-opening polymerization and employed as a macroinitiator in combination with d,l- and l-lactide for the preparation of BF2dbmPCL-PLA and BF2dbmPCL-PLLA block copolymers, respectively. Reasonably well-defined materials with low polydispersity indices (PDIs) were obtained in good yield. 1H NMR and UV−vis spectroscopy and thermal analysis are reported. Luminescence spectra and lifetimes were measured for polymer solutions and films. All materials are intensely fluorescent with high quantum yields. Although no RTP is noted for BF2dbmPCL films, curiously, this property is restored for PCL-polylactide block copolymer analogues in the solid state.

Synthesis and Fluorescent Properties of Difluoroboron Dibenzoylmethane Polycaprolactone

Difluoroboron β-diketonate dyes are noted for their intense fluorescence, one- and two-photon absorption, solvatochromism, and good aqueous stability. Incorporation of these dyes into polymers leads to processable optical materials, which in some cases display additional emissive features. For example, previously we reported that difluoroboron dibenzoylmethane−polylactide (BF2dbmPLA) exhibits both fluorescence and room temperature phosphorescence (RTP). Typically RTP is ascribed to a matrix effect, where the rigid ordered medium restricts dye molecular motions, and excited-state decay via thermal pathways is hindered in favor of radiative decay. To test polymer effects on dye emissive properties, this study explores BF2dbmPCL (PCL = poly(e-caprolactone), a semicrystalline polymer) of different molecular weights ranging from ∼3 to 18 kDa. PCL materials exhibit the expected intense fluorescence and molecular weight dependent emission but, surprisingly, no RTP. Phosphorescence is evident at lower temperature...

Multi-Emissive Difluoroboron Dibenzoylmethane Polylactide Exhibiting Intense Fluorescence and Oxygen-Sensitive Room-Temperature Phosphorescence

Boron difluoride compounds are light emitting materials with impressive optical properties. Though their strong one- and two-photon absorption and intense fluorescence are well-known and exploited in molecular probes, lasers, and photosensitizers, phosphorescence, in contrast, is typically observed only at low temperatures. Here, we report that unusual room-temperature phosphorescence is achieved by combining a classic boron dye, difluoroboron dibenzoylmethane, BF2dbm, with poly(lactic acid) (PLA), a common biopolymer, resulting in a highly sensitive single-component oxygen sensor. Fluorescence quantum yields are enhanced, and temperature-sensitive delayed fluorescence is also observed. Multi-emissive BF2dbmPLA biomaterials show great promise as multifunctional molecular probes and sensors.