Difluoroboron Complexes Research Articles

Nontraditional π Gelators Based on β-Iminoenolate and Their Difluoroboron Complexes: Effect of Halogens on Gelation and Their Fluorescent Sensory Properties Towards Acids.

We have synthesized a series of new β-iminoenolates and their corresponding difluoroboron complexes without any traditional gelation moieties, and some of them were able to gelatinize organic solvents. It was found that the presence of halogen atoms as substituents had a significant effect on gelation ability. In particular, bromo-containing compounds 4 A and 4 B exhibited excellent gelation abilities compared with other halogen-substituted gelators. By analyses of the single-crystal structure, the PXRD pattern of the xerogel, and electronic spectral changes during gelation, we deemed that π-π, C-H⋅⋅⋅F, and C-H⋅⋅⋅Br interactions were the driving forces for the gelation of 4 B. Interestingly, (Z)-1-(4-bromophenyl)-2-(3-methylpyrazin-2-yl)ethen-1-ol (8 A), prepared in this work, is the lowest-molecular-weight organogelator to have been reported. It should be noted that although β-iminoenolates 3 A-5 A are nonemissive in solution, they emit strong yellow light in organogels, which suggests aggregation-induced emissive activity, whereas the difluoroboron complexes 3 B-5 B show strong fluorescence in solutions, organogels, and xerogel-based films. Moreover, we found that the emission of 4 B in a nanofiber-based film could be quenched significantly upon exposure to gaseous trifluoroacetic acid and that the decay time and detection limit were 0.5 s and 0.17 ppm, respectively. Thus, through this work we have provided a new strategy for the design of nontraditional π gelators by introducing halogen atoms into π-conjugated systems with moderate polarities.

Multi-stimuli responsive luminescent azepane-substituted β-diketones and difluoroboron complexes.

Difluoroboron β-diketonate (BF2bdk) compounds show environment-sensitive optical properties in solution, aggregation-induced emission (AIE) and multi-stimuli responsive fluorescence switching in the solid state. Here, a series of 4-azepane-substituted β-diketone (bdk) ligands (L-H, L-OMe, L-Br) and their corresponding difluoroboron dyes (D-H, D-OMe, D-Br) were synthesized, and various responsive fluorescence properties of the compounds were studied, including solvatochromism, viscochromism, AIE, mechanochromic luminescence (ML) and halochromism. Compared to the β-diketones, the boron complexes exhibited higher extinction coefficients but lower quantum yields, and red-shifted absorption and emission in CH2Cl2. Computational studies showed that intramolecular charge transfer (ICT) dominated rather than π-π* transitions in all the compounds regardless of boron coordination. In solution, all the bdk ligands and boron dyes showed red-shifted emission in more polar solvents and increased fluorescence intensity in more viscous media. Upon aggregation, the emission of the β-diketones was quenched, however, the boronated dyes showed increased emission, indicative of AIE. Solid-state emission properties, ML and halochromism, were investigated on spin cast films. For ML, smearing caused a bathochromic emission shift for L-Br, and powder X-ray diffraction (XRD) patterns showed that the "as spun" and thermally annealed states were more crystalline and the smeared state was amorphous. No obvious ML emission shift was observed for L-H or L-OMe, and the boronated dyes were not mechano-active. Trifluoroacetic acid (TFA) and triethylamine (TEA) vapors were used to study halochromism. Large hypsochromic emission shifts were observed for all the compounds after TFA vapor was applied, and reversible fluorescence switching was achieved using the acid/base pair.

Carbazole modified salicylaldimines and their difluoroboron complexes: effect of the tert-butyl and trifluoromethyl terminal groups on organogelation and piezofluorochromism

Luminescent nanofibers were generated from nontraditional π-gelators based on salicylaldimines and their difluoroboron complex bearing tert-butyl carbazole and trifluoromethylbenzene.

An expeditious method to synthesize difluoroboron complexes of β-keto amides from β-keto nitriles and BF3·OEt2.

A convenient and expeditious strategy to synthesize difluoroboron complexes of β-keto amides has been developed from β-keto nitriles and BF3·OEt2. BF3·OEt2 serves as both a BF2 source and a Lewis acid catalyst in the synthetic strategy. The formation mechanism of the difluoroboron complexes from β-keto nitriles and BF3·OEt2 was proposed. The difluoroboron complexes can be further converted into β-keto amides by treatment with sodium acetate. The strategy features advantages such as a wide substrate scope, non-metal catalysis, and easy operation. Some of the difluoroboron complexes display good fluorescence properties in the solid state and potential application in solid-state luminescent materials.

Mechanofluorochromic Behaviors of Salicylaldimine Difluoroboron Complexes

AbstractWe have synthesized a series of salicylaldimine difluoroboron complexes that contain carbazole moieties. Substituents on the carbazole and on the benzene rings of the salicylaldimine moiety influenced the intramolecular charge transfer (ICT) emissions of these complexes. Interestingly, the synthesized difluoroboron complexes emitted strong light in the solid state under UV irradiation and exhibited reversible mechanofluorochromism behavior. The emission of a pristine sample of 3‐[4‐(3,6‐di‐tert‐butyl‐9H‐carbazol‐9‐yl)phenyl]‐2,2‐difluoro‐2H‐2λ4,3λ4‐benzo[e][1,3,2]oxazaborinine (TCH) at 488 nm redshifted to 571 nm upon grinding, and the ground powder exhibited an orange emission. Fuming with dichloromethane (DCM) or heating at 200 °C for 2 min led to the recovery of the original solid state that emitted a bluish‐green light. XRD patterns illustrate that the mechanofluorochromism features are reasonable for the transformation between the crystalline and amorphous states.

ChemInform Abstract: Expeditious and Convenient Synthesis of Polycyclic Difluoroboron Complexes of 2‐Oxoindoline‐3‐carboxamides by Tandem Reaction.

AbstractThe boron trifluoride etherate serves as both a catalyst and reactant in the tandem reaction.

Red and near-infrared emitting bis-coumarin analogues based on curcumin framework-synthesis and photophysical studies

Abstract Four fluorescent bis-coumarin analogues were synthesized having donor-acceptor-donor (D-A-D) system based on curcumin framework, where the 7-(diethylamino)coumarin-3-carbaldehyde has been employed as donor while the central 1,3-diketo or 1,3-diketofluoroborate is the acceptor core. The structural modifications have been made by functionalizing acetylacetone or 2-acetyl cyclopentanone to study the effect of imparting rigidity on the photophysical properties of the bis-coumarin analogues. The difluoroboron complexes of bis-coumarin analogues were synthesized to study the effect of difluoroboron complexation on the photophysical properties. The mono-coumarin analogue is synthesized to understand the nature and the contribution of the donor groups in bis-coumarin of the curcumin framework. The photophysical properties are studied in detail using solvents of differing polarity. The photophysical properties of the newly synthesized bis-coumarin molecules were compared with the priviosly reported bis-coumarin analogues.

Expeditious and Convenient Synthesis of Polycyclic Difluoroboron Complexes of 2‐Oxoindoline‐3‐carboxamides by Tandem Reaction

AbstractN‐Aryl‐2‐cyanodiazoacetamides produce polycyclic difluoroboron 2‐oxoindoline‐3‐carboxamide complexes (up to pentacyclic conjugative and fused systems) directly and expeditiously in the presence of boron trifluoride etherate. The boron trifluoride serves as both a catalyst and reactant in the tandem reaction. The tandem reaction includes the carbene aromatic CH insertion, hydrolysis of the cyano group into an amide group, and boronation of the two amide carbonyl groups. The synthetic method features the advantages of wide substrate scope and excellent chemoselectivity.magnified image

Synthesis, characterization and properties of furan-containing difluoroboron complexes

New β-diketonate difluoroboron complexes (F1–F4) containing a furan ring have been developed, and their luminescence properties have been investigated systematically.

Preparation, characterization and spectroscopic properties of difluoroboron complexes with some fluoroquinolones

Abstract Six novel difluoroboron complexes with fluoroquinolones were prepared from fluoroquinolones via complexation with boron trifluoride etherate in DMF–CH2Cl2 solution. Their spectroscopic properties were investigated by UV–vis absorption, FTIR, 1H NMR and fluorescence spectroscopic techniques. The results showed that these difluoroboron complexes exhibited the intense fluorescence emission at 401–579 nm under UV visible illumination and possessed a relatively high quantum yield in DMSO solution and solid state. Especially, the difluoroboron complex of Levofloxacin displayed the strongest fluorescence and highest quantum yield (Φu = 0.63) in these difluoroboron complexes, due to its conjugated rigid plane system via four fused six-membered cyclic structures.

Difluoroboron complexes of functionalized dehydroacetic acid: electrochemical and luminescent properties

A series of dehydroacetic acid difluoroboron complexes functionalized by a phenyl ring or an electroactive core (tetrathiafulvalene or ferrocene) were synthesized and characterized. The redox properties of these derivatives have been analyzed by cyclic voltammetry and the molecular structures of some of the difluoroboron complexes are presented and discussed. The photophysical properties of selected difluoroboron complexes were determined in solution and in the solid state evidencing an AIEE (Aggregation Induced Enhancement Emission) phenomenon.

Triketonate difluoroboron complexes. Substitution-dependent liquid crystal and photophysical properties

Novel alkyloxyphenyl-substituted β,δ-triketonate difluoroboron complexes have been efficiently synthesised and thoroughly characterised. Significant features such as liquid crystal behaviour and solid and solution fluorescence are observed in all cases. The mesomorphism was determined by the presence of one, two or three alkyl chains in each substituent aromatic group of the triketonate ligand. So, smectic C mesophases were found for compounds carrying two lateral chains, each of them located at one of each phenyl substituent, while the presence of four or six chains at the whole molecule gave rise to smectic A or discotic lamellar and hexagonal columnar mesophases, respectively. Fluorescence in the solid state and in solution is again proved to be dependent on the ligand substitution as well as to be maintained in the mesophase. These multifunctional materials also present luminescent sensor activity towards Hg2+ and Cu2+.

Synthesis, characterization, and photoluminescence properties of difluoroboron complexes with bis-β-diketone ligands

Some novel difluoroboron bis-β-diketonates containing a pyridyl moiety were synthesized from diethyl 2,6-pyridinedicarboxylate via Claisen condensation with the corresponding aryl methyl ketones and followed by complexation with boron trifluoride etherate. Their spectroscopic behaviors were studied by FTIR, 1H NMR, UV–Vis, and fluorescence spectroscopic techniques. The results indicated that difluoroboron bis-β-diketonates exhibited violet or blue fluorescence emission at 428–454 nm under UV illumination in DMSO and possessed high extinction coefficients. It was found that the nature of the substituents at benzene ring in bis-β-diketone ligands had a significant impact on the photoluminescence behaviors of difluoroboron complexes. The complex 5b exhibited the strongest photoluminescence intensity and highest quantum yield (Φ u = 0.93), due to two strong electron-donating methoxyl moieties in molecule and the compound 4b displayed the lowest photoluminescence intensity and quantum yield, assigned to the heavy atom effect of the chlorine atom in its molecule. The photoluminescence intensity and quantum yield of these difluoroboron complexes decreased in the sequence, 5b > 2b > 1b > 3b > 4b.

ChemInform Abstract: Synthesis of Enaminones and Their Difluoroboron Complexes Through Domino Aryl Migration.

AbstractThis new domino strategy allows the selective synthesis of boron complexes.

Synthesis of enaminones and their difluoroboron complexes through domino aryl migration.

A new domino strategy for selective synthesis of enaminones and their difluoroboron complexes through aryl migration has been developed. The reaction features low-cost and readily accessible starting materials, reliable scalability, and bond-forming efficiency as well as simple one-pot operation, which makes this strategy highly viable for future applications.

Luminescent organogels based on triphenylamine functionalized β-diketones and their difluoroboron complexes.

A series of new triphenylamine functionalized β-diketones 1–3 and their difluoroboron complexes 1B–3B were synthesized. They exhibited strong intramolecular charge transfer (ICT) emission. It was found that their self-assembling properties depended on the molecular structures. For example, compounds 1 and 1B, in which only one β-diketone or difluoroboron β-diketone unit was linked to triphenylamine, showed better gelation abilities directed by π–π interaction. Although bis-β-diketone substituted triphenylamine 2 could not form organogels, its difluoroboron complex 2B could gel DMSO due to the strong dipole–dipole interactions. Compound 3 could form gels in polar solvents, while 3B formed gels in nonpolar solvents. Notably, the asymmetric gelators 1, 1B and 2B exhibited AIEE behaviors during the gelation. Although the emission of the symmetric compounds 3 and 3B decreased to a certain degree upon gelation, the obtained gels still gave strong emission. The gels formed from 1 and 3 emitted strong green light and those based on 1B–3B emitted strong orange or red light. These highly luminescent materials might have potential applications in emitting devices and fluorescent sensors.

Salicylaldimine difluoroboron complexes containing tert-butyl groups: nontraditional π-gelator and piezofluorochromic compounds

tert-Butyl can lead to the loose packing of salicylaldehydehydrazone difluoroboron complexes in aggregated states to generate stimuli-responsive materials.

Synthesis of difluoroboron adamantyl-containing complexes and pyrazoles based thereon

One-stage synthesis has been developed for the preparation of adamantyl-containing difluoroboron complexes of 1,3-dicarbonyl compounds from 1-(1-adamantyl)ethanone, boron trifluoride etherate, and carboxylic acids anhydrides. The reaction of the complexes with hydrazine hydrate and its derivatives afforded the corresponding adamantyl-containing pyrazoles.

Trifluoromethyl-derived enaminones and their difluoroboron complexes: Synthesis, crystal structure and electrochemistry properties

Abstract Twelve trifluoromethylated enaminones including seven N,O-bidentate, three N,O,O- and one N,N,O-tridentate, and one N,N,O,O-tetradentate ligands that can include multiple coordination centers as well as redox-active and photosensitive units have been prepared. Seven new difluoroboron complexes 23–29 were prepared by the reaction of BF3·OEt2 in acetonitrile in the presence of Et3N with five bidentate ligands, one tridentate ligand and one tetradentate ligand. Their crystal structure, UV–vis absorption and redox properties have been studied. The role of the trifluoromethyl and difluoroboron moieties and their ability to form F H intra- and inter-complexes bonds leading to multidimensional networks have been also featured.

Synthesis and photoluminescence behavior of difluoroboron complexes with β-diketone ligands

Five new difluoroboron complexes with 4-pyridyl-β-diketones were synthesized and their structures were confirmed by elemental analysis, IR, 1H NMR, ESI-MS and UV–vis spectroscopy. Their photoluminescence behavior was studied in DMF solution and solid state. The quantum yields (Φu) of complexes 2a–2e in DMF solution were measured relative to quinine sulfate and their lifetime values (τ) were calculated according to the luminescence decay curves in the solid state. From these data, the difluoroboron complexes exhibited the excellent photoluminescence properties. Especially, the complexes 2d and 2e displayed the stronger photoluminescence intensity, much higher quantum yield and longer lifetime value as compared to complexes 2a, 2b and 2c. The results indicate that the substituents at the 4-position on benzene ring have a significant impacts on the photoluminescence properties of the difluoroboron complexes.